Looks strong and smooth running. Great work.

Lew
Florida 😎🚤, USA

Well done Les. You will have learnt such a lot building this boat and should be very proud of the finished result. I hope it sails well.
If you need a double jointed coupling for your next project they are available in various disguises from Deans Marine. www.deansmarine.co.uk
Good luck. 😉

Well done Les, you got a great result.

Hello Les
Looks a really neat installation to me, well done and when you put the lid on the boat the moderate noise will lessen.
Regards ChrisG

Hello LesW
I'm glad we could help you. I am also very satisfied with the shaft connection. I got the tip myself from a very good friend who unfortunately has already passed away.👍

I said I would update on this problem and the motor mount is done. took me longer due to having to wait for the new coupling.
The mounting is a bit chunky in build as I used what I had in my workshop/garage. The alignment was made using a ridged substitute coupler I made. The new coupling follows forum member 'Wolle' and was bought from a CNC parts supplier I use (3d printers and similar). Its a very nice item with very good flexibility for about 5 deg each side of its axis and has 2x grub screws each side of the part for clamping, it cost £3.95. I could not find the dumas dog bone coupler in the UK. (USA has plenty) As for the sound deadening erasers, I have little room underneath the motor so had to pass on that this time and opted for a Hybrid Polymer Sealant Adhesive to provide a shallow bed of silicone under the motor mount plates. I have experience of using Hybrid Polymers on my Campervan build and they provide excellent bonding with a slightly flexible joint. So its in place and I think it is the best I can do on this build. If I build another boat next winter I will tackle the whole build differently as I have made plenty of mistakes on this first one. Thanks to all for their comments and advice and I will do the boating lake test probably next week if the weather improves. Video is shown at full motor speed and reverse.

Hello Alessandro
The connections I used are not completely rigid, they allow for a slight, non-optimal position and compensate for it.

Here is a link.


https://www.ebay.de/itm/332909225030?mkcid=16&mkevt=1&mkrid=707-127634-2357-0&ssspo=JKohSFcNRnK&sssrc=4429486&ssuid=G_z1PYR1SEG&var=&widget_ver=artemis&media=COPY

Hi LesW.

Very well, now you have a lot of information available and it seems to me that they are all quite in agreement or at least not in antithesis. You simply have more solutions available.

Let's recap to get things in order.

The noise is loud but not excessive, there is worse. But it's a symptom.
It is a symptom of vibrations.
Better to reduce them as much as possible. I agree with you on this.

You have narrowed down and identified the problem very well.
It is possible to act simultaneously on two directions of attack.
1. The axle and the joint.
2. The absorption on the motor block.
The potential problem with the motor brushes and any other internal problems within the motor itself, we have already ruled out.
It's excluded, the engine runs well.

1. For the axle and the joint you have two options for the solution.

1A. Finding the precise alignment (I would say perfect, even if perfection does not exist in this world) is the first choice in my opinion.
If you line everything up perfectly any joint should be fine.
But, as Wolle advised you, in a perfect alignment I would put a fixed joint and save the cardanic joint for other situations.
I like it as a solution because, generally speaking, I opt for misalignment only if I have this need.
If there are no other priorities, it is always better to align perfectly, but there are actually situations in which one is forced to make different choices.
It is the cheapest solution and you don't have to make many changes to the state of the work you are in now.

1B. As you already know, the cardan joint (in Italian we call it a "cardanic" joint or simply "cardan" after the Italian mathematician Gerolamo Cardano (1501-1576) even though it was already known to the ancient Greeks) creates vibrations at high speeds because it is not homokinetic.
At this point, if you maintain the misalignment (but I don't see the need or reason), to reduce vibrations you have two solutions to reduce vibrations:
1BA. Either you use a "homokinetic" joint (there should be "homokinetic" joints on the market also for modeling but I have never done specific research on this),
1BB. Or you use two cardan joints in series which, as they have already explained to you, create a cardan shaft that is very close to a "homokinetic" condition (instantaneous angular velocity of the driven shaft constant during a complete rotation), as long as they have the same angle of misalignment of the driven shaft axis with respect to the drive shaft axis.
To avoid confusion, I tell you that what I saw in your photo in Italian we call a "cardan" joint (it is not homokinetic). Instead, we call the double "cardanic" joint a "universal joint" (it is homokinetic).
Sorry but Google Translate is driving me crazy and always replaces words.

2. As I had already suggested to you in the twelfth message: "These supports must not "choke" the engine and it would be better to insert some rubbery material between the engine casings and the supports to dampen vibrations", it seems that this possibility is shared by many naval modelers who have adopted it successfully.
I am very pleased that it is such a shared solution even though I would have used materials other than erasers and I was sending you a hypothetical drawing of what the support with rubberized edges could look like.
However, I have a lot of respect for successful solutions dictated by experience so I won't add anything else.


For the other macro area, consisting of buoyancy in the water, we await your tests and further news.

Lew I also use dog bones in addition to using u-joints. The newest dog bones I have gotten have 4 nibs instead of 2. I don't remember were I got the new ones from. Len

I like the dog bones coupler as well, will also look at that

Let me stand corrected 😔. I said that I use "two u-joint couplings with a short shaft between them". Most of my boats in fact do use Dumans "Dog-Bones" (photo 1) which escentially functions the same but is much shorter. These couplings are surprisingly durable considering small diameter of the connector and the very small nibs on them 👍. My heaviest is my PT-61 (PT boat/Gunboat) at 1/20 scale and 47 inches long. With three shafts and the heavy weight of the boat I am amazed how well they have lasted 😊. (Photos 2 & 3.)

My experience with direct drive (ideal setup) is when I was given a Pro-Boat USCG 47 ft. MLB (a RTR model). One of the shafts was frozen☹️. Had to cut off one of the solid couplings (photo 4)🤞. I found it difficult to work in the small opening and was never able to get the motors aligned good enough with the shafts. Factory probably had the right tooling. So I made new motor mounts and added the Dog-bones (had to shift the motors forward a bit). They work fine 😎!

Lew
Florida ☀️ (record high temp today), USA

Lew is defiantly right about the need for 2 U-joints if there is a large amount of misalignment of the motor and prop shaft. Think of it like the drive shaft of the older rear drive cars. A single u-joint can tolerate only a small amount of misalignment. Len

Hello Les

I have attached a photo of my 500 motor installation which although not pretty is tank tested (well my bath) for quite some time tethered or should I say moored to the taps. It also runs more quietly than most of my other models and the hull is as yet without a lid, this thanks to 3 erasers.
Hope this might help ChrisG

Hi you can buy motor mounts from most model suppliers for only a few quid they allow a slight amount of flex in the motor good luck anyway
Phil👍

Some more good ideas with the Erasers / vibration mounts and the double UV joint. Thanks for those and will take all comments made into account. I have the outline of the new motor mount in my head and will make a start this weekend.
Thanks to all

Going on from this I have recently bought some erasers from stationary in Tesco and after cutting to size have made good vibration and sound deadeners for a 500 motor. A cost effective solution to my noise problem.
Hope you solve your problem regards ChrisG

Your noise is simply the joint, you would be better spending your time aligning the shaft and motor exactly and using a solid joint, use some hard rubber in your motor mount which will remove most of the noise transmitted though the solid mounting and the hull acting like an old horn gramophone.

Hello Lew
🤔I thought that too. But I didn't know if I was right.

One thing that I noticed with the U-joint is you have only one. All my boats have two U-joints with a short shaft between them. One U-joint is OK for angular connection but the shafts still need to be aligned with both the shaft and motor axis being in alignment. Two U-joints compensate for that mis-alignment. This could be your problem and is a very common error.

The other option is to use a different style joint that allows for mis-alignment.

Lew
Florida, USA

Well done Les. You're doing very well with the engine tests. You have ruled out possible causes and have most likely identified the problem.
From the noise I hear and comparing the two videos, I don't think it's an engine problem. The noise of the motor without coupling seems completely normal to me.
So I think working on proper alignment is the way to go (maybe you don't even have to replace the joint).
However, you could also reduce the noise of the engine (disconnected) a little by creating additional supports and blocking it better (not just on the front).
These supports must not "choke" the engine and it would be better to insert some rubbery material between the engine casings and the supports to dampen vibrations.
After all, sound waves are nothing more than mechanical waves generated by vibrations.

Yes, of course the hull is of the planing, non-displacement type. It is not related to the limiting speed of the length on the waterline.
It is a type of hull that allows you to have high speeds.
Excellent, we'll see the tests in the water.

Good fun.

Hello LesW
🤞I wish you much success and I'm looking forward to the result.

Well this has been an interesting morning.
1. The motor noise, please see the vids. I tried adding friction the the UV coupling (pressing finger against the side) no change to the noise. No vibration felt through the motor casing.
2. Motor runs well when disconnected and again tried adding friction to the shaft with the motor running well and no added 'noise' or vibration
3. Prop shaft runs smooth on the housing when not connected to the motor

So for the motor noise issue I will make a whole new motor mount with some adjustment means built in to line it up correctly and buy a better quality UV coupling and then try that. It will take me to mid next week to complete that and I post the outcome for interest.

For the water line / ballast question, thanks for that very good Info in your response and I have decided to go with the 446gm AFT ballast added and go try it at the boating lake and see how it runs. Then adjust from there. The Hull was described as a 'Deep V' by the seller and the boat is a planing hull? its going to be a cabin type cruiser when completed.

All this will happen after the motor fix and the weather improves, maybe end of the month all being well.
So thanks to all and I will update my post after the changes
Cheers
(Hope the media files work)

Of course Wolle, this is essential.
I agree with you. Sorry if I took it for granted.

Hey Alessandro and LesW
With the water line, I think it's important that the screw is completely under water, otherwise it will suck in air. At least that's what I've had with my ships.

Hi LesW.

First of all, precise alignment is very useful for reducing vibrations (and consequently some noises) regardless of the type of joint you are using.
Aligning the engine and axles well will still benefit you, as Wolle rightly said.
With fixed and non-universal joints you necessarily notice if you are not perfectly aligned, this is the advantage but, in my opinion, it is not necessary for you to replace them immediately. Let's wait for a full analysis first.
With correct alignment versus an offset alignment your engine will perform better. It's not just a matter of noise.

We await your evidence. In fact I suspect that by blocking the engine well many vibrations will stop.

If you have any suspicions about motor jerking caused by loose brushes, it's worth checking it out.
It's strange for this to happen on a new engine you just bought but you can try it without connecting it to the coupling.
If this is the problem you should hear the same noise even if the motor has its shaft free.
If the motor works well and does not make noise acting on its own (you can hold it in your hand to avoid any misunderstandings) logically that is not the cause of the noise.

Excellent photos.
I'll give you my opinion but listen carefully to others too, I may have misunderstood despite your very clear explanation.

I do it like this:
Before any test in the water you must have the waterline clearly in mind (drawing it on the hull) and then adapt the weights to it. You shouldn't do the opposite (even though I've seen many do this).
If you are the designer yourself you will have made some assessments on the correct position of the waterline, if you have a kit or drawings made by other people you must base yourself on those.
In any case, the waterline drawn on the hull (it is the lighthouse to follow) must be preparatory to any test with ballast.
The ballast must be positioned so that the drawn line and the water surface coincide (or the drawn waterline is slightly higher).
Never the opposite.
That is, you should never try to find the right waterline with subsequent additions or movements of weights.
Although this method can work and is adopted by many modelers, it is conceptually incorrect and can lead to many errors.

But what if you have no indication of where the waterline should be drawn?
In my opinion you should try to track it anyway. I won't dwell now on the method and criteria of how to trace it unless you ask me.

To narrow the discussion to your specific case (I hope I haven't gone too far off topic) and talk about weights, I'll tell you that this evidently appears to be a planing and not a displacement hull.
In fact it is most likely the hull of a motorboat. Correct me if I'm wrong.
It seems to me that in the fifth photo it is too heavy. If you have a theoretical waterline drawn there, then that's fine, otherwise I'd keep it higher.
Being a planing hull (which by definition has a stability of shape and not of weight) I would consider the weight of the mandatory elements (engine, etc. batteries, receiver, servomechanism for the rudder, etc. etc.) and add only the necessary ballast to counterbalance these weights to obtain a correct setup.

To answer your question, a middle ground between the first and third photos. At most a setup like the one in the third photo, no more.
Achieve correct buoyancy first (longitudinally and transversally) with minimal addition of ballast.
Then try it in the water. If you see that at high speeds it is too light, gradually add more weight.
I repeat: These last tips refer only to the case in which you do not have a waterline already drawn to respect.

Alessandro, sorry, I should have added both wts for the total ballast , so setup3 is 1011gm.
Must be an age thing I have

Alessandro, the noise, I will do some 'tests' today and make a reply on the forum. Another person advised that Brushed motors might not have the brush edges run in and could be causing a bump each revolution? The noise repeat increases with RPM.
For the Ballast, well these pics may add some amusement, this is the hull in my bath.
1. No ballast fitted - you can see it is very high AFT
2. 466gm AFT - fishing watch wts set on dowels
3. 545gm AFT and MID - I think this is looking too low in the water?

So my question is some advice of how this hull should sit in the water, 1 or 2 or 3 or some in between. I have several fishing wts of different sizes so easy to change. I still have the upper decks to make but I will test the hull at the boating lake first
Cheers

Wolle, thanks I like the look of flex coupling and will try that. I may also try and rework my motor position to correct the miss alignment

Hi LesW.

First of all I agree with Wolle. This is not a stupid question but an interesting problem to solve.

I'll try to give you some advice but it's not easy to identify the cause of the noise.
In fact, I believe that the first thing to do is to identify precisely where the noise is coming from.
From the photos I can see that the joint is not perfectly aligned (or so it seems to me). Since it is a cardan joint it works anyway but it could be the cause or contributory cause of the noise.
Still looking at the photos, it seems to me that the motor, even if fixed, could still be too free to vibrate and bang against something creating noise.
Before intervening on this aspect, I would advise you to do a test. As you test the motor at different speeds up to maximum speed, try to block it with one hand. If by blocking it the noise decreases then we have identified the cause or one of the causes.
I generally think that a machine gun noise is due to something banging rather than frictional rubbing.
But I should hear the noise. A very short video would help a lot in this regard.
Furthermore, the transmission shaft must be well made especially if it is too long. I use micro bearings, other systems can produce a huge clank as I have personally experienced.

Regarding ballast, I didn't quite understand what you mean by "going off a water line".
While waiting for your clarification, I tell you that, in general, the waterline can emerge a little from the surface of the water but it must never be lower.
But I don't want to give bad advice if I don't have a clear and complete picture.
In this regard, it would be better if you attached some photos relating to this specific aspect.

There are no stupid questions, only stupid answers. I didn't use a cardan shaft, these run very smoothly.