HI John
Just had a quick look at the Power Set Up section on this site to confirm what other are using. 50amp ESC are popular so yours should be OK.
With a 600 type motor 3 blade 40/45 mm props are popular.
For 540 motors 3 blade 35mm seem to work well.
Your 2" prop is 50mm so I suspect this may be your problem.
Your motors may well be suitable and the cheapest option would be to buy a selection of smaller props. Looking at Cornwall Model Boats site their plastic prop pitches vary with the size so you probably can't choose the pitch. Prices seem reasonable at about £2. if you are in a model boat club one of your fellow sailors may have a selection of props you can try.
At the end of the day the correct prop is the one that pushes your boat realistically round the lake and gets on the plane easily.
Ideally you model should start to go on the plane at half throttle and if this isn't the case you may need to add small amounts of lead to the stern or replace anything heavy from the bows. it really is a quite fine balance point you are seeking to achieve but a slight bow up attitude works best.
I'm sure you will achieve your aim in time. All part of the fun with model boats. 😀

HI Dave
Its the shorter of the Perkasa's at 36 inches, the battery is quite heavy being a lead acid and sits 6 inches from the stern and 24 inches from the bow so I think its well back.
The prop is a red plastic one with a diameter of 2 inches no idea of the pitch.
I don't have a selection of props to play with,
Advice/suggestions on motor and prop size/pitch would be appreciated.

HI John
From the info given it would appear the motor is struggling to cope. if you are only getting on the plane at full throttle this suggests your balance needs moving towards the stern.
Without motor specifications its difficult to generalise on prop size. There are many variants of the 550 motors and each will have different power ratings. is this the smaller version of the Perkassa?
Prop size is really what best suits your motor. if you have a selection of props I suggest you try different sizes and monitor the heat generated.
At the end of the day I suspect some form of water cooling will be your best bet.

HI Dave and thanks for your response.
I am perfectly happy with the way the Perkasa gets up on the plane on full throttle. I guess I have the balance correct to achieve this.
I am using 2 x UJ couplings even though the line of drive is quite straight. Of course if I were to fit a larger motor the drive would then end up slightly out, due to the motor output shaft being higher but no real way to remedy that without stripping out the propshaft.
My prop is a 3 blade plastic one no idea of the pitch. What size would you suggest for a 550 motor ?
You are of course correct in what you say about restricting the movement of the stick, but doing so with my setup would then prevent the boat getting up on the plane.
I guess I will have to limit the time I run at full stick and cool the motor and ESC

HI John
Just seem your reply to Nasraf.
You originally asked how to reduce the voltage to protect your ESC.
The ESC provides a variable voltage to the motor so by not pushing the throttle stick fully you will restrict the voltage to the engine. Many of my club members stick bits of plasticard in the throttle slot to restrict the movement.

HI John
I must admit I have bought motors designed for power tools but only used in Tugs and slow moving craft. They are quite torky but some are also rather heavy on current.
If you are getting heat problems it is because the motor is overloaded and not running at peak efficiency. Your ESC is getting hot because of the high current drawn.
Using lower voltage motors with a higher supply voltage is not advisable for any length of time and will more than likely burn out the brushes or even the motor coils. I know the racing fraternity favour high voltages but they water cool everything and use special motors.
With your Perkassa I assume you wish to sail with a nice plane and to achieve that will you need a good high rev motor.
The position of your battery and ballast will have a marked effect on the sailing performance - too far forward and you waste energy lifting the boat out of the water to achieve a plane.
The other Important bits are the shaft drive and prop. The shaft should turn freely with no high spots and be dead straight. Couplings and motor need to be correctly aligned so they are dead in line. Finally the prop must be of a suitable size and pitch for the motor. Adding a larger prop or increasing the pitch will increase the current drawn. A smaller lesser pitched prop will allow the motor to run faster (and cooler) and your model will also go faster.
I'm guessing you are using a racing type prop on your model and this may be the cause of your overheating. A good 3 blade brass prop will work much better but you still have to pick a size and pitch to suit the motor.
Hope this helps 😀

HI Nasraf
I don't doubt what you are saying and after all you have been in the hobby for a long time and I respect your experience.
But this is another thing I am failing to comprehend, I did take the time to check out the specifications and most of them are MabuchI 500/550's and the specs seem the same as for those supposedly sold as being specifically for model boats. Unless I made a error as usual, HaHa.
Even some I have carrying a Johnson sticker which I have often seen criticised are actually Mabuchi.
Anyway at the moment I have 25 of various voltages sitting on the shelf so replacements are no problem for a while.
The 550/12v set up gets the boat well up on the plane at full speed so I am OK with this, I guess I will just have to try and keep the motor/ESC cool.
But we have gone slightly on a side track as the original question was how to lower the voltage to the ESC by 3 volts, which in doing so should also underpower the motor just as we have been discussing.

HI John

Using motors out of power tools may be a bit risky as they may only be rated for short running periods and may be arranged with the field windings in series with the rotor to give max torque like a car starter motor. if they have permanent magnets for the field they will be ok as far as the winding arrangements are concerned, but may be short period rated as far as heating is concerned.
Series connected motors are not much good in model applications as it is very difficult to control the speed. Shunt wound I.e. with the field connected in parallel with the rotor or permanent magnet motors,due to the back emf they generate run at a speed proportional to the applied voltage with the current changing as the load varies.

If you do not mind replacing motors if they burn out or only run your boat for a short period the use of ex power tool shunt motor may be OK.

A good solution would be as you suggest is to run a motor rated at a higher voltage than the battery e.g.your 18 v motor/12 v battery combination thus derating the motor, but you will get considerably less power.
Unless you are running a very power hungry motor the battery should not heat very much and discharging at these high rates will not do much for the battery life.
Your battery has a capacity rating of 3.4 Ah, this means that in a fully charged state is should be capable of supplying 3.4 amps at 12 volts for 1 hour. At a rate 10 times that I.e. 34 amps, the time of discharge mathematically is 6 minutes, but due to the loss of efficiency in the chemical reaction in the battery the actual time of discharge will be considerably shorter, and heating in the battery may damage its construction.
I would have thought that with a 3.4 ah lead/acid battery it would be advisable not to exceed a max current of 15 amps and for normal running 10 amps.

nasraf

Many Thanks to Dave & Nasraf for your response,
The Perkasa motor is a single RS550/12v running of a 12v 3.4Ah battery,
I did have a problem with the motor & ESC getting hot and everything shutting down especially after a short burst high speed run.
I have fitted a small fan to the ESC to try and keep it cool but have yet to try it to see if the problem is solved. May water cool the motor as well.
I have a lot of motors of various voltages all removed from rechargeable power tools so would also ask if it is better to;
Run a 9v motor off 12v supply or run a 18 v motor of 12v.
Thinking logically about this I would have thought;
9v motor/12v supply = overheated motor,
18v motor/12v supply = overheated battery,
so either way one cant win. 😭
But then this would only apply when running at full speed which wouldn't be all the time so one of the answers must be a happy medium. 😊
Thoughts welcome

HI John

As usual Dave is correct in all his advice but what its worth I will add a bit more.

I learnt the hard way see my bit in previous forum subject " Fireboat c of g ".

You do not say what capacity your batteries have or your motor type so cannot estimate the sort of current your system will draw.

Basically a drive system using brushed motors is a series connected circuit I.e. batteries, wiring and speed controller/motor are all connected in a ring and consequently are subjected to the same current ( amps ) flowing through all of them. Dependent on the Impedance ( resistance ) of each item, some of the voltage available from the battery is dropped across each element including the battery, this has internal resistance of its own so as the current rises the battery terminal volts fall. in the motor, most, you hope, of the voltage drop is converted into mechanical power, however in all the rest of the components virtually all the drop is converted into heat.

My experience of the " Blue " esc is that they work but mine results in a very large voltage drop across it, that reduces the voltage at the motor and consequently the power available, it also means that the electronics gets very hot and can cause its death very easily, as many on this site can testify. So be very careful in how long you run your motor and check that the esc is not getting hot quickly, if you have a dc voltmeter measure the voltage drop across the motor leads of the esc.

In general I would not have thought that the motor control part of the esc would be that sensitive to the output available from a 6 cell I.e. 12 volt lead/acid battery, but if the controller has a bec output connector for the r/c system, this may be a bit more delicate. it may be sensible not to use this until you have some confidence in the rest of the system.

It would also be advisable to incorporate a fuse in the system to limit the current that the esc/motor can draw.

Another safety item worth considering is adding a dropping resistor in the circuit of about 0.1 ohms this at 10 amps will lower the voltage available to the rest of the circuit by 1 volt but will at this current result in 10 watts of heating. At other currents watts can calculated by the equation.

Watts =Ohms times Amps squared.

Once you have some confidence in the system this can be removed.

But in the final outcome, as Dave advises, it is your decision what to do but be careful and proceed slowly and if running with the prop connected make sure it is always clear of obstruction and stalling the motor.

nasraf

HI John
Good question.
A 12v SLA is fully charges when it reaches 14.4volts and most chargers then maintain the battery at 13.5 volts. This is the open circuit voltage and will drop to 12.5volts as soon as any substantial load is applied. if you have ever had a car battery tested this is exactly what is used in the form of a large resistor.
I have a similar blue ESC but have only used with NiMh batteries (