Hi Alessandro - I guessed you must have been away on holiday. As Dave says would be good to start another thread and hear more about it.

If you don't have a protruding keel usual practice is to have it inside the hull and slot the frames over it. But if you have come up with an alternative solution then great.

Have you decided on how you are going to skin your hull? Reason I ask is that hard chine hulls are usually fairly simple compared with round hulls, including war ships and yachts and you don't need many frames. Most of my builds only have between 5 and 7 frames as apart from the bow there is not a dramatic change in shape as you travel down the hull. All my hard chine hulls are ply skinned with in some cases balsa blocks to form the bow as ply doesn't like being bent in two directions.

But if your hull does have some curves in it then it will be better to plank it. As you know this normally requires many more frames closer together though if you diagonally plank using more stringers than just at the deck and chine then you can still only use a small number of frames. I did this with my Fisherman build though that is a round hull.

I've now got my Huntsman 31 ready for lake trials, including with the motor I recommended for you, so it will be interesting to see how it performs. Will be a few weeks away though as I will be away soon.

Chris

@AlessandroSPQR Your thread on the planing hull is interesting.
BUT, I'd love it if you would start another thread referencing your holiday at "Calabria on the Ionian Sea". Not knowing anything about the area, I just did a little quick search ... it sounds heavenly!
We will be back in (northern) Italy with my wife's choir next year. Maybe we should plan an extension on our own and visit this area as well?
Dave B

Hello everyone.
Hi Chris.

I'm back after a bit of inactivity; I was swimming in Calabria on the Ionian Sea.

After modifying the hull, I started drawing the first lines of the keel.

So far, I've designed hulls with the keel protruding beyond the hull. This required a method of inserting the frames onto the keel that I'd become accustomed to.
In this case, the keel isn't exposed, so I'll have to adopt another method.
I've already thought of a solution that I'll show you later.

I also drew two decks, but only in 3D. It's still premature to transfer them to 2D for cutting out, including all the joints on the keel and frames.

Once the hull was complete, I started making the frames.
As you can see from the images, this is my method: I create vertical surfaces parallel to the hull.
The intersection of these horizontal surfaces with the hull will give me the frames.
I imagined making them 4 mm thick, so the distance between the pairs of vertical surfaces is precisely 4 mm.

The next step will be the very difficult one of creating the intersections of the frames on the keel and with the two decks.

The ultimate goal is to transfer the keel, decks, and frames into 2D sheets so that anyone can cut them out and create the hull skeleton.

@ChrisF
What you say is so true. Damn laziness.

Thanks for the information, some of which I understand!
Most users of the different kinds of software only use a small percentage of the capabilities of software, even for their jobs. I did data management for a few years before retiring and used Microsoft Excel a lot and sometimes in depth but even so I only scraped the surface of it's capabilities.

Same with Microsoft Visio which I used for architectural work which it's not designed for! And same for my boat drawings. But I had years of experience on the drawing board and so just work in the same way, that is 2D, which suits me. The hull for my Fisherman stretched my capabilies though as you have to visualise the curves in 3D and draw in 2D!

Most of my drawings are for models with hard chine hulls though so pretty easy in Visio.

We all tend to just learn enough to do what we need to do. I certainly do with my photographic software and only find out about other things when we need to.

@ChrisF
Since my last message, I haven't drawn anymore; in fact, I haven't even opened the drawing program due to lack of time.

You wrote: "Surprised you can't just alter the stern from a saved copy?"

Excellent point.

Rhinoceros is different from 3D modeling programs.
But before I try to explain the differences, you should know that I know how to use 15% (and probably less) of this program's commands and features.
I only use a minimal part of the software's potential (and I have an English version, which certainly doesn't make learning easier).
This is why I'm forced to redo the hull drawing almost from scratch. There could probably be a simpler and faster way.

That said, you should know that (I did some research on this topic and watched some video tutorials on the subject):

3D programs are based, as far as I understand, on three main modalities: the use of NURBS (Non-Uniform Rational Basis Spline); polygon meshes; and parametric solid modeling.
Rhinoceros stands out primarily for its native use of NURBS geometry, which allows you to create mathematically perfect surfaces and smooth curves, unlike most other software based on polygon meshes or parametric solid modeling.
Software like Blender, Maya, or 3ds Max use meshes (networks of triangles or squares).
Rhino uses mathematical formulas (NURBS). Surfaces remain perfectly smooth even when zoomed in to infinity. Polygons reveal facets when magnified.
Rhino is millimetric and exchanges clean data with CNC machines and 3D printers. Polygon programs are ideal for visually organic shapes, but they lack engineering precision.
Rhino is used for product design, architecture, and jewelry. Blender and Maya are used for animation, video games, and visual effects (VFX).
Programs like SolidWorks, Fusion 360, and Inventor are based on a rigid construction history and dimensional constraints.
Rhino allows you to "draw in space" freely and sculpturally, without having to define rigid geometric constraints before starting.
In parametric CAD, you change a dimension and the entire model updates. In Rhino (without specific plugins), radical changes to an advanced model often require rebuilding parts of the surface.
Rhino vs. BIM Software (Revit, Archicad)
In architecture, Rhino is used very differently than BIM programs.
Revit thinks in terms of real architectural elements (walls, windows, floors). Rhino thinks in terms of pure geometry (points, lines, surfaces).
Rhino allows you to create fluid facades, parametric roofs, and organic shapes that are almost impossible to manage in Revit.

To build solids, I start from lines and surfaces, not directly from pieces that I then model, but maybe that's just my limitation. It's also worth considering that I don't have many very important plug-ins.

Basically, now I limit myself to this.
1. I set the starting lines.
2. I create the surfaces, such as the hull, which is the most difficult part of all. Obviously, the difficulty depends on the type of hull. In fact, if I have to make the hull of a Springer tug, which is essentially a raft, it takes me two minutes. All I have to do is draw the profile curve, then the surface from that, and finally extrude this surface to create the volume. The hull of a speedboat is much more difficult, the hull of a clipper ship is even more complicated (obviously, I'm referring to projects that start from a blank sheet of paper).
3. I cut the hull surfaces to create the keel and frames, then build the hull skeleton on which I'll apply the planking.
4. When do I need to create volume and surfaces aren't enough?
As you may have realized, with this method, I can create a model from scratch without necessarily creating volumes; I just need 3D surfaces.
I need volume (and therefore I need to close the surfaces) in two cases: when I want to know the volume value, for example, the immersed volume to determine the displacement (i.e., the total weight) in advance, or when I need to 3D print a part. This part must be a solid.

Hi Alessandro

Surprised you can't just alter the stern from a saved copy?

Keep thinking I must dust off my TurboCAD and have another go at learning it. Trouble is I keep leaving it for such a long time I have to start from scratch! Microsoft Visio is not the program really for producing this type of drawing but I've made it work and I know it well enough for my needs. Actually I need to learn CAD as I'm thinking of getting the deck planking laser etched on my Christina build!

The replacement motor arrived yesterday for my Huntsman 31 and whilst I'm keen to try it in the bath it's just too hot for fitting that, the prop shaft and rudder and RC gear etc.! 😎

Chris

Hi Chris, I was completing the outlines to draw the keel and then the frames.
Here are some photos.

I stopped because I rethought the stern; I want to modify it; I like it, but I'll make it with a less pronounced slope.
So, unfortunately, I'll start from scratch.

@ChrisF
Thanks Chris that's exactly what I wanted.

Can you please repeat the length of the axis and how many degrees is the angle in the drawing in the last message?

Not sure what you mean by this, but if it's about the prop shaft:

Angle 13 degrees - it could have easily been less than this but it's a slow speed craft so not really important - though with the motor it has in it and the hull being based on the Huntress hull it would plane easily - I have resisted so far!
Prop shaft (M4) - 290mm, Tube (8mm outside diameter) - 240mm.

This boat is smaller than yours at 584mm.

The angles I've given so far in all my comments are from my drawings. It would be interesting if I measured the actual angles on the models as I always allow myself some looseness with the hole through the keel so that I can align the prop shaft accurately with the motor. Once I have done this using a fixed/solid coupling I glue the prop tube in place. So the angle has more than likely changed a little.

@ChrisF

Hi Chris, I wanted to reassure you on a few things.
You wrote:""""""You also need to think about positioning of bulkheads/formers as Ideally you want to avoid the motor mount sitting on one as this can affect how low you can position the motor. """""
My method is this: Near the motor (once I've decided where it will be placed), I create special spaces in the bulkheads/formers. In practice, the engine doesn't rest on them but fits inside them.
A few images can help you better understand what I mean. The images are of a displacement hull, and the goal was to place it as low as possible and, at the same time, as far aft as possible.
That, however, was a different type of hull, and the electric engine wasn't tilted; now it will be a little more difficult.

You wrote: """""I know that you like short prop shafts, and that's a good idea, but don't worry too much about it. Some of mine are really long, longer than necessary, as in my early days I was nervous about cutting them down! You only have two bearings, whatever the length (though some folks introduce a middle bearing) and so the only thing affecting performance losses is the mass of the additional length of the inner shaft and an extra length of tube which is no problem for a brushless motor!"
This heartens me a lot because, from the tests I have done so far, I have seen that with very long shafts the resistance and Ampere absorption greatly increases. Here is another element in favor of choosing a brushless motor.
For information, I put three bearings (one also intermediate with internal spacers).



You wrote: """Have you allowed for the coupling in the prop shaft length you are working with? I can give you dimensions of the one I use in my planing models - keep away from those red plastic universal joint types! You can see I've used a UJ coupling in the River Cruiser but it's a better quality one and it's a slow boat. You need to allow for the amount of motor shaft and inner prop shaft going inside the coupling, which obviously affects the overall length of the motor and prop shaft."""""""
Thanks so much for the suggestion. I had foreseen and written it, but I suspected the translation wouldn't be very clear.
When I wrote: "The motor pinion should be added to the total length. It's a useful tool to keep aside," that's exactly what I meant.

I would prefer to use a fixed metal coupling.

I'm aiming to reduce the angle as much as possible because I know that various practical issues will increase it.

Can you please repeat the length of the axis and how many degrees is the angle in the drawing in the last message?

Good morning Alessandro and Harry (well good evening Harry!).

Like you I draw a composite of the whole prop shaft and motor set up to work out it's position and angle. Can't really tell from the drawings so far but are you leaving sufficient distance between the bottom of the motor and hull allowing for the practicalities of mounting the motor? This distance will depend, as I said before, on how you mount the motor and can soon add up when taking into consideration the motor mount and base it is fixed to.

I've attached a drawing of my River Cruiser. The keel is deeper than it needs to be, so yours can be less so, and it can be cut into at an angle for the mounting. As you can see I could have moved the motor further back as it is well above the keel anyway and plenty of prop shaft protruding through the keel for connecting the coupling. You also need to think about positioning of bulkheads/formers as Ideally you want to avoid the motor mount sitting on one as this can affect how low you can position the motor. With most of my builds I fixed the position of the formers first which explains why the motors are further forward. Actually whilst the drawing shows quite a distance to the prop tube the photographs show it isn't that great and I could only have shortened the shaft a bit. Differences are going to happen between the drawing and building - the drawing is only a good starting point to show that it's feasible!

I know that you like short prop shafts and that is a good idea but don't worry too much about it, some of mine are really long, longer than necessary as in my early days I was nervous of cutting them down! You only have two bearings, whatever the length (though some folks introduce a middle bearing) and so the only thing affecting performance losses is the mass of the additional length of the inner shaft and an extra length of tube which is no problem for a brushless motor!

Note that the keel design includes a raised piece for the rudder monting.

Have you allowed for the coupling in the prop shaft length you are working with? I can give you dimensions of the one I use in my planing models - keep away from those red plastic universal joint types! You can see I've used a UJ coupling in the River Cruiser but it's a better quality one and it's a slow boat. You need to allow for the amount of motor shaft and inner prop shaft going inside the coupling which obviously affects the overall length of the motor and prop shaft.

Chris

@canabus
Thank you very much Harry.

The standard pitch for props is 1.4 which the CNC props that are sold on Aliexpress.
These the dog drive setup.
They also have different complete drive line with or without plastic props.
The units have ball races both ends which maybe OK for fresh water but NOT for salt water.
I replace the lower bearing with tefron.
As for props 37 mm 3blade or 40/42 mm 2 blade.
I have used a 45 mm 2 blade but it's a bit power hungry.
Harry

@ChrisF

Hi Chris, I'm addressing you, but anyone (especially those with experience with planing models) can weigh in. So, when it's time to purchase electric motors, I'll ask you more questions and ask for more support. For now, I'll update you on the project's status.

I'm so glad I've rekindled your enthusiasm!



ELECTRIC MOTOR AND PROPELLER DIMENSIONS

As you can see in the first two images, I've briefly drawn the dimensions of the purple propeller, the green propeller shaft, and the brown motor.

The cylinder representing the motor dimensions has a diameter of 50 mm (I don't think I'll use a motor with a larger diameter), and the cylinder representing the propeller dimensions has a diameter of 45 mm (again, I've considered the maximum; I don't think I'll use a larger propeller, probably 35 to 40 mm).

I've tried different lengths for the propeller shaft. As you can see in the first two images, the lengths are 250 mm, 300 mm, 320 mm, 350 mm, and 400 mm.
The 250, 300, and 350 mm lengths are commercial lengths, meaning I can easily find them online if I want to purchase them, so I started with those.
If I want to make the shafts myself, I can easily make them any size.

The motor pinion should be added to the total length. It's a useful tool to keep aside.



ANGLING THE MOTOR-SHAFT-PROPELLER ASSEMBLY

I combined the motor, shaft, and propeller into a single solid so that they could be oriented at the desired angle.

Very small angles are not possible for this hull and the assumed dimensions of the engine and propeller. In the third and fourth images, you can see that, at a 5-degree angle, the propeller would hit the hull and the engine would protrude from the outline.

As you can see in the fifth image, with a 250 mm shaft, an angle of at least 12 degrees is needed (measured between the propeller shaft and the keel), which you think is acceptable, so that's fine.

The sixth and seventh images show the 10-degree angle solution with 300 and 320 mm shafts.

The eighth image shows the solution with a 350 mm shaft; in this case, the angle was reduced to 9 degrees.

In the ninth and tenth images, the shaft is 400 mm long (I don't think it's commercially available, at least not at a low cost); in this case, the angle was reduced to 8 degrees.

I would never have chosen such long shafts (25 cm is already too long for my taste) if I had had a choice.
To minimize engine performance losses, I keep the shaft as short as possible.
In this case, I couldn't, unless I used a flexible shaft (but that's not a solution I'm very fond of, even though I often see it used in scale speedboats).

However, given the current situation, I would discard the extreme solutions (25 cm 12 degrees and 40 cm 8 degrees) and focus on those ranging from 300 to 350 mm, with angles of 9 and 10 degrees.

The entire assembly (engine-shaft-propeller) of any of the above solutions can be moved a little forward or a little backward. This will be determined by the position of the rudder and servomechanism.



READING AND EXPLANATION OF THE CURRENT DRAWING

I didn't draw the actual thickness of the hull. What you see in the drawing (blue hull) is therefore the internal volume.
It's a bit difficult to make myself understood because of the translation, but I'll try.
The volume drawing will be used to draw the frames. To make them, I'll intersect several vertical surfaces orthogonal to the keel at predetermined distances. The result of these intersections will be the individual frames, which I'll plot on 2D sheets for cutting by hand or laser (later you'll see better what I mean and how I'll do it).
The strips will be glued onto these frames, once cut, so the volume will be greater, considering the additional thickness of at least 1.5 or 2 mm.
This will result in some changes, for example, the distance between the propeller rotation and the hull will decrease, while the immersed volume will increase.



Any suggestions or comments are welcome.

I see on the site they are giving 10% off until tomorrow, I guess for Fathers Day, and so I've ordered one of those motors I recommended for use in my Huntsman 31.

This thread has been good for me as although I still have a passion for my Fairey builds progress had slowed on the earlier ones I'd started, partly due to starting my Faun and Fisherman builds. My enthusiasm has been reawakened to get the Huntsman 31 and Swordsman on the water, even if not completely finished, to see how my choice of motors for them works out as regards performance. My other builds have performed as hoped but I'm particularly keen to see how the Swordsman performs as it's a bigger and much heavier boat than my others.

So thank you Alessandro!

@AlessandroSPQR That's strange.

Try putting Overlander Batteries UK into Google and see if it comes up.

They state that due to Brexit they can't export outside of the UK mainland. Wouldn't have thought that would stop access to their web-site though? Maybe it does?

Chris

@ChrisF
Hi Chris, unfortunately I can't reach the link you posted. I'm getting this page.

@AlessandroSPQR The lower the better to some extent, though if you go too low you have to deal with water ingress through the prop tube and may have difficulty in mounting the motor low enough, due partly to how you are going to mount the motor - you will of course deal with this when you are working on your drawings. Many of my Faireys (planing hulls) are 12 degrees which matches the full-size boats and the Swordsman for which I showed the drawing is 11 degrees - this uses a 42mm diameter motor but it is a bigger model than yours at 838mm and so I could use a longer prop shaft to keep the angle down. And lowering the motor then affects the position of the prop and it's clearance. It is all a bit of a balancing act and a compromise - will be interesting to see what you come up with.

As I said, 42mm diameter is bigger than you really need, but your choice obviously, and for that size and bigger the choice of motors becomes less and less and the kV also and so you need bigger (more volts) and more expensive batteries. Whereas the 35mm gives plenty of options. This leads me to believe it would be difficult to find a suitable brushless motor for a big planing model, say over 50"/1270mm, as motors sold for boats don't have a high enough kV to produce a higher enough rpm unless say a pully system is used. Maybe have to look outside of model boat motors?

Anyway, for your research purposes here is a link to Overlander Batteries showing what motors they have. They have a smaller range of outrunners than they used to have, though still suitable for my needs, and have added more inrunners.

https://overlander.co.uk/

Unless you have any specific questions I won't say anymore for now and leave you to get on with your designing!

@Ronald You certainly would be! There's enough variables as it is! Most of my models are scale/near scale and for the planing models I basically just choose what looks right! I use 3 bladed Standard Scale bronze from Prop Shop. If the optimum is say 35mm diameter I don't think it will make a great deal of difference to the performance if I went 5mm either way as I only want decent not crazy speed. Different for race boats of course as you want to maximise speed or use a big lake where you can use higher speeds.

https://www.prop-shop.co.uk/products.php?cat=standard-scale

For my slower, non-planing models I use the Raboesch 3 Blade Metric props.

https://raboeschmodels.com/product/162-3-blade-metric/

I know some folks experiment with different props; number of blades, diameter and pitch but that is often after they have chosen the motor.

@ChrisF
Hi Chris, I wanted to write this message after completing the motor-shaft-propeller position drawings, to show you what solutions I'd found to stay under a 10° angle (I know you said 12°).
However, while I was looking for electric motors with the right specifications (I agree with you that the best option is to oversize everything to avoid high temperatures rather than adopt cooling systems), I encountered some problems.
For example, on Aliexpress I find class 42 motors (so with a 42 mm case diameter) 4240, 4250, and 4260, but none with 1000 or 1200 KV; the 42s only reach 700 or 900 KV.
With the outrunner motors I found on Aliexpress, I can't reach the required RPM (with 3S/11.1 Volts I would reach the theoretical maximum of 8880 with 800 KV); And the idea was to power a 3S electric motor even though it supports 4S, so as not to overheat it.
As I said, I'm only looking at the maximum dimensions now, so I'm not researching the 35 class because if a 42 motor fits, I'll be able to fit even smaller ones, like the 35 class ones.
However, I've had trouble finding even 35 class motors with 12,000 KV.

I read the article you linked. It's well-written and very helpful. Many guides give the same advice, but the problem is that no one knows how much power should be required for a given model with certain weight and shape characteristics. If this data were known (which no one does, although someone has tried to draw up indicative tables), it would be easy to do all the subsequent calculations.

I'll continue drawing to show you the various solutions.
If I continue drawing, I can start building even before purchasing the individual components.

@canabus
Hi Harry, thanks so much for the information.
I didn't have any major problems with permanent magnet brushed motors, either in theory or in practice. We've actually discussed them extensively on several occasions.
Some time ago, I thought it was necessary to summarize some basic concepts for everyone's benefit in the link at the end of this text. Let me know what you think.
As for brushless motors, however, I only have theoretical knowledge.
It's obvious—and this has been reiterated many times—that brushless motors, given the same size and voltage, are much more powerful than brushed motors. I've always used brushed motors because they're much cheaper (in fact, I've gotten many for free), and I didn't need them to be lighter or have greater power.
Now I absolutely have to consider them because I'm building a planing hull.


https://model-boats.com/wiki/147457

Next is to post the best prop/pitch for each motor based upon type of boat being built.
Tugboat vs pleasure cruiser vs speedboat

Maybe I am opening up a can if worms !

Useful information there Harry. Good to see that 35mm motors of both types will fit the same mount. So, Alessandro, you can use the 500 - 600 right-angle motor mount as I do, the one Bob uses or some folks use their own design and/or mount in a similar way to aircraft i.e. on a bulkhead or former.

That information clearly shows the different power output for both types and confirms what I said that with brushless, it almost doesn't matter what power output you choose for a given diameter as even the lowest would be more than an equivalent brushed. More power is probably good as heat production goes though as the motor wouldn't be working hard. That's my philosophy; powerful (over-powered) motor, decent ESC and battery and everything stays cool and so no water-cooling. Racing speeds for lap after lap will be a different story though. Worth noting that quoted power outputs for brushless motors are if using the maximum voltage batteries allowed, so really only any good for comparative purposes.

Harry, do you have any planing boats using brushed motors?

Here is another useful article; see the table at the end for suggested brushed motor sizes for different models. I had an 850 and lead-acid battery in my 48 inch Fairey Huntsman 31 and the performance was adequate at best, no pretty poor really! Sold it to a club member who put a brushless motor in it and it performed as it should.

https://www.modelboats.co.uk/1112/but-i-dont-understand-electronics/

Hi All
The standard 540 brush motor weight is about 185 grams and 35mm in diameter.
Depending on the number of turns on the motor is the number of revs.
e.g. 13 turns 32,500 rpm on 7.2 volts (unloaded).
21 turns 20,000
35 turns 13,000
45 turns 9,500
55 turns 7,700
65 turns 7,000
80 turns 5,500
To convert to brushless motor divide the rpm by the voltage.
eg 45 turn brush motor would about a 1250kv brushless motor but the power difference about 90 Watts to 800Watts .
The brushless weight is less by about 50 grams.
The good news is the 35 mm motors both fit the same mount with the same size screw holes.
Battery weight eg a 2400mah 7.2 volt is about 300 grams and a 2S (7.2 volt) 30C is about 140 grams.
Battery size is about the same but the Lipo is a lot thinner.
Battery placement can change the balance point of the boat without trim tabs.
I am not a great fan of trim tabs !!!!!

I use full metal uni-joints between motor and shaft with a bit of grease.
Adding heat shrink tube over them to keep the grease in and cut down the noise.

Harry

Written some years ago, 2011 in fact (!) but a good article on brushless motors and still relevant in many ways. The power of brushless motors is often given nowadays, certainly as regards those from Overlander Batteries. Not sure how relevant knowing the power is unless you can do complex calculations to determine what a particular model needs. Though if I'm looking at two or more motors of a suitable, similar size I will look at the power output and usually go for the most powerful to be on the safe side as I don't build my models particularly light. But having said that, given the power of brushless motors I don't think you can go far wrong as long as you choose a suitable diameter motor and kV to achieve the rpm required. It doesn't cost much more to over power/err on the side of safety (within reason) a model compared with a full-size boat and that is what I tend to do. In that respect I can't wait to see how my Swordsman performs as that is getting to be a quite heavy boat!

Alessandro, maybe as part of your testing, it would be interesting to see how 35mm diameter motors with widely differing power outputs actually perform?

Actually, I'm going to do a bit of experimenting myself! I think the motor I recommended to you will be better than the one I've got for my Huntsman 31. This was bought some years ago not long after I joined the hobby and is an Overlander Tornado Thumper V3 3548/05 900KV which has a lower kV than I usually recommend and on 3S doesn't really provide enough rpm. I've tried the same in the Huntsman 28 though and that performs well, I rarely use full throttle though as our lake isn't that big but it's fast enough anyway. The motor is powerful at 710 watts and I'm guessing will lose less power than the theoretical 20% between loaded and unloaded that we work on?

https://www.modelboats.co.uk/935/going-brushless/

@ChrisF

Top.
Thank you so much for your long, clear, and thorough answers (just the way I like them).
I find this information incredibly useful.

My next step will be to conduct online market research on the brushed and brushless outrunner motors that emerged from my discussions with you.
From this research, I'll obtain dimensions and weights. With the dimensions of the possible motors, I'll design one or more solutions for the electric motor-shaft-propeller system.
It's possible (and I sincerely hope so) that the design for an electric motor setup will work for several different models. This would allow me to test more than one once the hull is completed.
I'll update you as soon as I have time to draw.

@canabus

Thanks for your reply and your opinion on Canabus.

As you say, you don't need to buy a motor just yet but it might be a good idea to decide on one as a starting point so that you can find out the length of the shaft. They probably don't vary that much but you need to check, as along with the coupling, it determines the position of the motor mount and the length of the prop shaft.

Haven't heard of GARTT but I'm pretty sure that Bob and Harry have used Surpass Hobby. I standardised on Overlander after my first one as I knew I was going to build a number of models and in some cases overlapping. They are also a UK supplier though and have detailed information on their site (so good for reference) but of course the motors are made in China!

Further off, but for ESCs I use HobbyWing Quicrun and Seaking with the Quicrun being used by Harry. Bob has/is using various but is going to try a Shark soon. They don't weigh that much anyway so differences will be pretty insignificant. The heaviest items, as you know being the motor (certainly the bigger diameters like 42mm which you don't really need), battery, prop shaft and servo. The rudder to some extent but still quite light.

Motors

As regards brushed motors I don't know that much about them and if I wanted to use one I'd have to research first. I came late to the hobby, around 9 years ago, by which time brushless had become well established and largely understood so I didn't see any need to consider brushed. I do have brushed in a couple of plastic ready-to-run boats and they perform well. As long as a motor is chosen that provides the required rpm (around 12k. unloaded) for the battery being used then they are fine. Problem with them years ago is that performance boats needed heavy lead-acid batteries and the performance was often poor. With NiMh and LiPo this isn't the case, certainly with mid-sized models.

Brushless - Yes, outrunners are the best choice for this type of model. Bob has tried an inrunner in one of his - I understand he's going to change it to an outrunner though if he hasn't already? Inrunners can be used with any type of prop but due to their lower torque and potential higher rpm they are more suited to high speed and race boats. The water-jet I bought for one of my future builds uses an inrunner with a water-jacket (as you mentioned) but I wouldn't use one in my type of sports cruiser builds.

I suggested that motor as it will give good performance on 3S/11.1 volts. 1250kV x 11.1v = 13875 rpm unloaded. Loaded = 13875 x 80% = 11100 rpm. This is slightly higher than needed (circa 10k. rpm) so yes, other options are perfectly fine - that's one reason I like brushless, the flexibility. Even higher kV if used on 2S/7.4 volts. Personally I don't like going above 3S (no scientific reason! Though cost comes into it) and that is my common size (apart from my smaller/slower builds) though I'm having to go 4S on Swordsman as the kV is only 800. It is a 42mm diameter motor as it is a heavy boat and I wanted plenty of torque. The kV tends to reduce for bigger diameter motors.

Water-cooling - if the motor and ESC isn't overworked by say using a prop that is too big then you shouldn't need it. I don't and as he says, Harry doesn't either. Bob does though in most of his models, partly because he has always done and also because, as I mentioned, he uses a motor mount with integral water-cooling along with water-cooled ESC's. So your choice on that - water-cooling does give you a water stream/outlet as per full-sized if you want it though!

Chris

Hi Alessandro

A lot to answer so I'll spread them out over a number of posts and in some cases make a short response followed by more detailed ones later as we go along in addition to posts by Harry and Bob who have more experience than me with different motors and props.

Prop Shaft, Prop and Motor Mounting

As I mentioned before ideally you want to aim around 12 degrees for the prop shaft. For that length of boat a 40mm prop is probably the maximum but it wouldn't hurt to allow for 45mm plus the required clearance to the hull. For mounting the motor I mainly use the right-angle alloy mounts (though unfortunately the supplier went out of business and no-one makes the exact same ones) or the nylon equivalents. Considering brushless for now, the mounts will take a number of different sized motors as long as the mounting hole centres are the same - if say you went for a smaller motor of say 28mm diameter you would need a smaller mount with holes closer together. I always make my mounts removeable and so if you did this you could change for different sized motors if required.

I've attached a drawing and photos from my Swordsman build so you can see what I'm talking about. I've used a 5mm prop shaft in that but for smaller builds like yours I use 4mm.

Bob is a big fan of using a different mount, which is water-cooled if needed, and allows him to change motors quickly and easily. But he does glue them in so they may not be suitable for some motors - Bob can provide more information on this.

When producing your drawing the motor position will be influenced by the type of coupling you intend to use. My drawing shows a short coupling though I have standardized on the longer ones with a rubber centre section and if using one of those you need to allow for it. You will note that my motor is quite a long way forward. It could be moved further back by shortening the prop shaft as long as you can accommodate the motor being lower - Bob tends to have his motors further back than me.

I do have one of the motor mounts that Bob uses, possibly for a future build, and I also used it to provide the drawings for Bob's Sprite build.

Chris

Hello
I am using 1250kv motors (only two) in my 40" PT 109 with 37 mm 3 blade props.
Running on 2S 4000 mah Lipo batteries with 80 Amp 2-4S car ESCs.
No water cooling used.
The boat is a bit over scale speed.
Canabus

Hi Chris, I'm starting with this last hull; if necessary, I'll make another one with a different shape and proportions.

I want to start studying the positions for the engine and the propeller shaft, as well as its inclination (for now, we're using a single-propeller solution).

I was thinking about installing a three-bladed propeller with a diameter of 42 or 40 mm.
Be careful, it's clear that if I set up the propeller shaft for a 40 mm propeller, I can experiment with smaller but certainly not larger diameter propellers. So for now, I'm considering the larger diameter. I wouldn't go beyond 42 mm. What do you think?

Returning to the motor, in a previous message, you recommended an Overlander Tornado Thumper V3 3542/05 1250 KV.

This is very important to me because I already have a starting point.

Keep in mind that the advice I'm asking you and other ship modelers for right now isn't aimed at immediately purchasing an electric motor, but at studying its size and weight to accommodate it in the project.

Ideally, I'd like to find a position for the propeller shaft and the hull mounting arrangements that allows me to easily try out different types of motors and experiment with them.


BRUSHED MOTORS (should we just eliminate them?)
I know you're not hesitant about choosing brushless motors over brushed ones, but I'm asking you to make an effort to answer this question.
Given that when it comes to fast boats, brushless motors are almost a must for many reasons (high power and RPM that brushed motors can't reach, and low weight despite high power and RPM), I'd like to know if it's still possible to use a brushed motor for a ship model with a planing hull with these characteristics.
The reason is essentially economic, as brushless motors and their ESCs are much more expensive.
I wanted to draw your attention to two types of motors in particular.
How would you evaluate the choice of a 775 class brushed motor at 12V-16.8V powered by 4S LiPo or 12V NiMH, combined with a 42-45mm two-blade plastic or brass propeller (fully submerged)?
To save money, instead of the Graupner, I would choose a lower-cost equivalent. Or I could opt for an even more powerful brushed motor such as an 800 (or 850) class motor, a Graupner Speed ​​800 12V, or a high-performance industrial equivalent, powered above 12 volts.

BRUSHLESS MOTORS
Speaking of brushless motors, I think the choice should fall on outrunners.
In short, if you agree, I would discard any research into inrunner motors.
The high RPM of these motors, I believe (but correct me if I'm wrong) is incompatible with the choice of a submerged propeller, as in my case. I would have to install a surface propeller, which isn't a solution to my liking and isn't suitable (at least I don't think so) for the hull I've designed.

Well, staying on the subject of outrunner motors, I wanted to ask you: besides the Overlander Tornado Thumper V3 3542/05 1250 KV motor, do you have any other options?
Specifically, how do you rate these outrunner motors?
Brushless Outrunner class 3542 or 4240 (approximately 1000 - 1200 KV)
On Aliexpress, I'm leaning toward a 1200KV 4240 outrunner motor (Surpass Hobby or GARTT).
In this case, is it better to power it with a 3S LiPo (11.1V) to achieve approximately 11,000 - 13,000 rpm?

WATER COOLING JACKET AND OTHER COOLING SYSTEMS
Having always worked on displacement boats (with low speeds), I've never needed any cooling system, also because I always used oversized motors that weren't at their maximum power.
In the case of the motor you recommended (Overlander Tornado Thumper V3 3542/05 1250 KV) and the motors I mentioned, do you think a cooling system is mandatory?
If so, which one? Should I use it, since we're talking about outrunner motors, not inrunners?
I don't think a cooling jacket can be used for an outrunner motor. What method do you use?


Sorry for the many questions, but I invite you to answer me slowly and calmly.
If you'd like, please send me the commercial links for your options directly.

Looking good Alessandro. I think the revised bow is more suitable for a naval craft. The bow will cut through waves at lower speeds until it gets on the plane and will look better with a naval superstructure.

The immersed volume is a good result.

Chris

Hi All
I found the best hull design for straight line and turning is the Spearfish hull.
Built in chine rails and two spray rails each side which finish short of the stern.
Also a curve up in the stern keel which I think helps with the turning.
We clocked my boat at 37KPH !!!
Harry

You may ask how you press the wrong button, easy if you have fat fingers on a smart phone, deadly combination

Good evening to all naval modelers, I've been able to draw very little since last time.

This is the new hull.
I'm a little more convinced than the others, but I don't know if it will be the final one to work on.

It has the following characteristics:
- The ratio between width and length is 1:3.48 (so we're back to the value of 3.5)
- The slope of the bow has been accentuated.
- The transom has a reverse slope (this means the total length is greater than the length at the waterline)
- The shape of the hull (at the waterline it has a wedge shape). That is, it widens towards the stern while the lines on the deck become narrower.

The keel is parallel to the waterline, while the gunwale is sloped and rises slightly towards the bow.

I temporarily imagined a scale of 1:32 for this model.
So the actual hull would have been about 24 meters long.

The proportions are as follows:

Height 120 mm
Length 756 mm
Width 217 mm
Maximum draft 50 mm
Minimum draft 40 mm

The deadrise angle is 21 degrees.

The maximum immersed volume (with 50 mm draft)
is just over 3 dm3.
This is a satisfactory value, considering Chris's valuable information.

The red hull represents the immersed volume.

Here are the first lines of the other prototype.

Hi Alessandro

It is difficult to see if the chine does rise upwards at the bow but I think I can make it out in Picture 4, so yes it is quite subtle. Are the chines rounded or as Bob said a soft chine?

The chines don't rise much on my Fairey Swordsman I suppose - see photo.

For interest also see the photos showing the comparison between my Swordsman 33 and Huntsman 31 hulls. The Swordsman is only 50mm longer but has a wider beam and almost parallel sides. The model is much bigger and heavier which is evident when just moving them around whilst I'm painting.

Chris

@ChrisF

Hi Chris

you wrote:
"""""""""""""Evening Alessandro - the drawing was primarily for interest and to show how twin prop shafts are often positioned rather than suggesting it was the best hull design for your needs.""""""""
Perfect, that's what I meant and thank you very much, you understood exactly what I needed.


you wrote:
""""""""""Whilst I have provided detailed information on some aspects, for example the vee hull and narrowing on plan as you move towards the stern I've been conscious of not trying to impose my own design preferences on you - not that, that would happen! Like me you ask for and research information and then make your own decisions based on what you want. Quite right!""""""""""""""
We're on the same page.



you wrote:
"""""""""""You don't need to worry about it planing. Anything from a flat bottom to a deep vee will do that, just that the deep vee will do it at a lower point below the water surface than a flatter hull.
I like this about your advice. The very direct approach based on experience. Clear and concise answers. Thank you so much. They are infinitely helpful. I'm taking advantage of your experience (I'm new to planing hulls). You can't understand how useful this simple statement of yours is for me to continue.

You wrote:
""""""""""I know that the drawing is to show the submerged volume, but don't forget that the chine and chine rail will curve upwards at the bow.""""""""""""
So I ask you: why does the drawing seem to you like there's no upward curvature? Is it too subtle?

Evening Alessandro - the drawing was primarily for interest and to show how twin prop shafts are often positioned rather than suggesting it was the best hull design for your needs.

Whilst I have provided detailed information on some aspects, for example the vee hull and narrowing on plan as you move towards the stern I've been conscious of not trying to impose my own design preferences on you - not that, that would happen! Like me you ask for and research information and then make your own decisions based on what you want. Quite right!

You don't need to worry about it planing. Anything from a flat bottom to a deep vee will do that, just that the deep vee will do it at a lower point below the water surface than a flatter hull.

I know that the drawing is to show the submerged volume but don't forget that the chine and chine rail will curve upwards at the bow.

Chris

Hello all the ship modelers, hello Chris and Bob.

Chris, I drew another hull as soon as I had time.
Of course, I'm not referring to the drawing you sent me, because I could faithfully trace it if I wanted, but I prefer to find a different shape. Your drawing was very helpful, however.

You can see the images of the new shape and the comparison with the other one (in blue).
Here's a summary of the changes:
I further reduced the length-to-width ratio, now the ratio is 3.2.
I redid the keel, which is now parallel to the waterline.
At the same time, the deck line rises toward the bow with a slight slope (less than one degree).
The bow has the same slope, but the waterline (the profile at the waterline) is less sharp and therefore has a larger surface area, resulting in more underwater volume.
I raised the freeboard.

The resulting hull is more likely than the other to plane, even at moderate speeds (at least I think so). It has a submerged volume exceeding 2 dm3 (2 kg of weight), but its shape is not very slender, a bit squat. I'm still not convinced by the result I have in mind.
I'll have to find a compromise between the hull with the aesthetic lines I like (very slender with an aggressive bow and a sharp profile, which, however, could be difficult to control when turning, could have difficulty planing immediately, or could lose control and capsize) and a hull with proportions more suited to motorized navigation at high scale speeds.
It's clear that the chosen prototype will then have to pass practical tests and still prove a failure.

I'll design other prototypes until I find the one I'm most satisfied with (and which will in any case be put to the test).
My next hull will have a steeper bow, a reverse-rake stern, and perhaps I'll return to the 3.5 length/beam ratio. To compensate for the inevitable reduction in submerged volume caused by these changes, I might increase the draft.
In the meantime, any comments or suggestions on the images I've attached are welcome.

I said previously that the weight of my Huntress 28 is 2.3kg. I've just calculated what the weight of my 1:12 model "should be" based on the weight of the full-sized boat and it works out to 2.15kg. So I'm pretty pleased with that especially as the weight of the full-sized one would increase once passengers, provisions and crates of champagne are taken into consideration.

Chris

Bob - it was the drawing but as we've said there shouldn't be much difference between builds from the drawing or kit. You know what, looking at the hull whilst painting it I wouldn't be surprised if it did need some ballast! Though it it only sits a bit high I won't bother. As we know for it's length of 33" (838mm) it has a wide beam of 11.4" (290mm) and a vee angle of 24 degrees - it gets away with this because it is so wide! This angle was often used in race boats. Will take me sometime to finish painting the hull as it's two-tone but I'm aiming to get it on the water soon - about 3 weeks I hope.

Alessandro - this actually is an interesting hull for you as it it very similar (though bigger) than your original design in that the beam doesn't narrow much as it approaches the stern and why it has a high submerged volume helped by the very deep vee hull. It has an S shaped bow as there is some flare which extends a small distance along the hull. I didn't really mention this one as I haven't even tried it in the bath yet so don't know how it sits.

Chris

@zooma
Thanks, Bob, but calculations are a big word, just a few measurements here and there.
I'm still deciding on the hull shape.

Hi Chris.

Don't worry about the provenance too much, I am sure that this advice (given at the time) would apply equally to either of the 33" versions of the Swordsman.

I think we need to get our own 33" replica's into the water this year and find out for ourselves..............

Bob.

Hi Bob - It's from the magazine article but can't remember if it related to the kit or drawing, I'll check tomorrow. But obviously the volume of each would be the same and the weight around the same even with the different constructions. I'm still amazed at the quoted ballast, it's not like it's a tug or something and you certainly don't want to be lugging that around!

It's inspiring me to get mine on the water to see how it sits and performs.

@ChrisF Thats an interesting artefact Chris.

Did that little gem come with the original Aerokits Swordsman kit (I don't remember it) or did it come in the Model Boats review of their same size plans that were printed in the 1960's ?

It does seem like a lot of dead weight to "heft" around, but we forget just how light our Classic Model Power Boats were with just a (typical) 10cc glow engine and a small fuel tank of fuel to carry in the hull.

Our current brushless motors and LiPo battery packs with suitable ESC probably weight quite a lot more and should make quite a dent in the suggested additional ballast weight suggested?

Bob

I am looking forward to seeing all of your calculations transformed into a working power boat hull that planes beautifully Alessandro.

Bob.

Just checked and my length/beam ratio, 654/217mm at the waterline, is actually just over 3.0 which does surprise me as the H28 doesn't look particularly short and fat! Out of interest I will have to look at the Huntress which is basically the same hull which was extended by 5 feet for the H28. I'll look at the Swordsman 33 as well as that does have a wide beam. All interesting stuff!

I know you like doing your calculations and nothing wrong with that but don't get hung up on them. Whatever you design, being a planing hull, can't differ that much from all the designs and kits that have already been designed over the years which don't have a problem with weight. It tends to be small displacement models like destroyers that you have to be careful with isn't it? As I've said from my own experience, planing hulls are very buoyant and I don't think that even doubling up on components will make much difference. In fact I read the story that came with the release of the 1:12 Swordsman 33 model drawings years ago and it states that 7.5 pounds (3.4kg) of ballast is needed to get it down to the waterline!!! See text. I find that very hard to believe and look forward to trying mine in the bath! I have a feeling it will be fine without any ballast!