Hi Paul
Haven't got them yet, but as far as I know, you can leave them plugged in. if you can't, I will certainly go back to your link. Thanks.
Steve

Hi Steve, can you leave your alarm plugged into the balance lead as you run the boat, this is what you need, so you get an alarm when the boat is running signifying playtime is over😁

If its not, then consider for the money my link, or similar, I have a few, and use them on planes, helis, boats, it will pay for itself time and time over to stop you over discharging the lipo 👍

Thank you both. I have these on order - 1S-8S RC Lipo Battery Low Voltage Alarm Buzzer indicator Meter Tester Checker EH.
They seem similar to the ones you both suggest.
Steve

Hi Steve
Your link is personal to your ebay account so I can't view. I looked on ebay and found RC 2-8S LiPo LiFe Cell VOLTAGE CHECKER LOW VOLTAGE METER ALARM.
If this is similar to what you have bought and with an alarm then it should be OK
Dave

Mtroniks do have lipo friendly vipers, they are call "tio" I recall, if that is written on the cover you can set upo for lipo, if not then its imperative you have some sort of alarm as dave says, they plug into the balance lead on the lipo, and are current sensitive, so need to be the right way round to work. The ones I use are here, and also can be pre programmed to sound at a given low voltage. I use 3.7v on a boat, and 3.8v on a plane. Ant lower and they take longer to charge. if over discharged they are generally finished. There are ways to recover them, but its regarded as bad practise. Nims can be discharged fully, but are now really yesterdays technonlogy, heavier, and not any cheaper these days!
https://hobbyking.com/en_us/cell-checker-with-low-voltage-alarm-2s-8s.html
Paul

Hi Dave
I have one of these already on order https://vod.ebay.co.uk/vod/FetchOrderDetails?itemid=391742391266&transid=738429804026&ul_noapp=true

Should be ok?
Steve

Hi Steve
Try BRC Hobbies http://www.brchobbies.co.uk/ 1-8 Cell Lithium Battery Voltage Checker & Low Volt (LOUD) Alarm. Approx£4.
Cheap if it saves your battery
Dave

Hi Steve
You are limited to 12v with your ESC. I suspect the 2 cell 7.4 should fit the bill. I think the Viper does not have the cut off for Lixx batteries so you will need to source a separate warning device. I used to have one from my model aircraft days that sounded a buzzer and flashed lights but I don't know of a current supplier, sorry
Dave

Hi Dave
I am using Mtronics Viper Marine 20s- (I did order 15s but Howes sent these by mistake). I am using 3cell 30-40c 5000mah in the Perkasa - batteries are overkill I suspect?
A 7.4 2 cell lipo seems a good bet then?
Steve

Hi Steve
Yes I intended to use silicon to fix the motors on the Perkassa. Works well and acts as a damper to any noise.
The battery really depends on your speed controller as that may have a max voltage of say 12v. it's not a big model so I suspect a 3 cell 11.1v at 2200/3000 mA would suffice and provide plenty of power for the two motors. if you have a 7.2 NiMh available I suggest you try that and see if its fast enough. A 7.4 LiPo will give more endurance and speed so a 2 cell may suffice.
LiPos do need protecting from over discharge so make sure your ESC has such protection or buy an add on unit that warns you when the battery voltage is too low. The ESC version is better as it cuts or reduces the current before damage is done.
The Amp/Hr rating gets dearer the higher you go, so its down to you as to what you buy. Higher ratings will give you more speed but also longer running times.
Glad the coupling worked.
Dave

Hi Dave. Motors installed and running smoothly with double couplings as you suggested. Thank you.
Called in at Jotika for some bits and spoke to John about my fear of piercing the hull. He suggested I use silicone to fix the motors to the mounts as he uses it for things such as flexible drives on his big powerboats. That's what I've used and it seems to work.
I am using 4 -15v 540 brushed motors. Being sold on lipos, what batteries do you suggest I use? I'm not looking for high speed.
Steve

Thanks for that Dave. Good thing you had another look!

Steve
Just noticed you have used two coupling end pieces in the middle. You can get a double male insert to join the two red bits. Will save a bit on the length and cost!
Dave

Hi Steve
Yes that looks like it. You do need to fiddle around with the mounting to get a good smooth alignment. if you can align both couplings with a length of close fitting tubing or four strips of wood and two rubber bands this will give you a good starting point. I use a 1.5v battery to power the motor and adjust for best speed and lowest noise level. You can use an ammeter to monitor the current and adjust for the lowest level for best results.
Dave

Thanks Dave. Do you mean something like this?
I'm going to stick with the 540 motors as they should give me enough speed for this type of boat.
Steve

Hi Steve
I do believe the type of coupling you are using is able to be extended by using two in line with a brass joiner in the middle. I often use silicon exhaust tubing in place of the red bits - its a tight fit over the serrated brass bits and can be cut to any size. A solid piece of stainless rod inside the tube will help to stop any tendency to whip.
Another alternative would be to use some JP Power 480 motors (28mm dia - got mine from Cornwall MB) which are fast and would suit this type of speedboat and may fit in the original position. Simon (ex propshop http://www.prop-shop.co.uk/) supplies a really well matched prop - it's used for racing.
Good luck with the project
Dave

Can I extend the shafts without extending the tubes?

Ok, move the motor back a little, you don't have to follow the plans they are actually guide lines so you can change what you like to adapt to a situation. Make the shafts a little longer.

The piece of wood you are mounting the motor on looks a little thin to me. Try something a little thicker and bevel the bottom of one side to match the hull contour.