41″ Seaplane tender propulsion advice

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41″ Seaplane tender propulsion advice

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7 January 2023 at 18:55 #103489
Christopher Chapman
Participant
@christopherchapman42421
Hello everyone,

My question surrounds motor choice for a 41" 2.8kg (empty) RAF seaplane tender model I picked up second hand.

As I have spare brushless motors from my rc planes, I will fit one of them, but which one?! 😲

Anyhoo what do you use to power your 41" MTB hulls with?

This may seem lazy to just ask, but after reading many articles on the subject on rc boat power plants it brought back memories of naval architecture classes. To be honest it is very hard indeed to condense an entire subject into an article or forum response so no one should feel bad for not having a full understanding. Goodness knows I couldn't apply these principles to an rc boat (or a big one), so why reinvent the wheel.

Christopher
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7 January 2023 at 18:55 #5653
Christopher Chapman
Participant
@christopherchapman42421
What do you use to power 41″ MTB style vessels.
7 January 2023 at 19:08 #103491
Christopher Chapman
Participant
@christopherchapman42421
Here are some photos
8 January 2023 at 12:07 #103504
Richard Simpson
Participant
@richardsimpson88330
Hi Chris and welcome to the forum. Lovely looking hull, well worth making the most of. Just one question members will need to know, are you going to fit a separate motor to each shaft or a single motor and use gears or belts to drive both shafts?
8 January 2023 at 12:56 #103506
neil hp
Participant
@neilhp
I built some years ago the smaller ST 200 SEA PLANE tender at 36" long.

I put into my model 2 x 585 brushed motors and she performs well getting up on the plane easily………..but disregarding what motors are used, if i were you I would for good performance and low speed manouvrebility fit t with twin motors as she is already fitted with 2 shafts……..

my model will turn in her own length with one forrard and one astern motor ……but enjoy the build……nice boats to sail now and then and a change from slow chugging lifeboats, lol.

Edited By neil howard-pritchard on 08/01/2023 13:00:57
8 January 2023 at 13:14 #103507
Christopher Chapman
Participant
@christopherchapman42421
Thank you for the thoughts and pictures Neil, I am sorry about not saying earlier but originally I would guess that it had a single prop and was then modified to a twin screw set up, the shafts you see in the photos are not in good shape and will need to come out.

I like things simple, also I don't have many motor sets, so I am leaning towards a single brushless powered prop by reinstating the central shaft.

Edited By Christopher Chapman on 08/01/2023 13:19:45
8 January 2023 at 16:08 #103510
ashley needham
Participant
@ashleyneedham69188
Christopher. What size and Kv are your spare motors?

if I were buying a new motor then a 35mm outrunner say 1000Kv might fall in the bag, on 3s and an X40-50mm prop. This also depends what voltage battery you will use…Harry will comment soon from Taz, he is the man who knows.

There are right or wrong choices here, just that some are better than others.

Ashley
10 January 2023 at 21:53 #103542
Christopher Chapman
Participant
@christopherchapman42421
Thank you for your responses,

After abit of searching I have a 1100KV, 900KV a couple of 2300kvs but i will keep looking. As for batteries I have some 3A 3s and 1.8A 4s batteries. I am more inclined to the 3s for the capacity.

Christopher
11 January 2023 at 07:35 #103543
harry smith 1
Participant
@harrysmith1
Hi Chris

Harry from Tasmania !!!

I think Banggood Surpass C3542-1250(850Watts on 4S) Or the C3542-1450kv(1050 Watts on 4S).

A 80Amp car ESC which handles up tp 4S.

Both motors run fine on 3S.

So no watercooling required.

Battery about the 4000Mah.

With both the motors and a 3s and 4s battery you have a free rpm range between 13875 and 21480 .

Both motors are 35mm with the same bolt pattern and same 5mm shaft.

Prop range 35 to 40mm as per Sir Ashley.

Harry
11 January 2023 at 11:05 #103544
Dave Smith 17
Participant
@davesmith17
I have a Robbe police boat, a little smaller than your seaplane tender (35"x7&#39 and that goes very well on a pair of 2830 1000kv outrunners. It's not excessively fast, but looks right on the water, and I get an hour or more on a pair of 7.2v 5000mah NiMh packs.

I originally tried using 2836 1000kv motors but the boat was unstable at the speed they allowed (full throttle and a little rudder would make the boat roll through 360 degrees!) so I reduced the motor and prop size and it is a lovely boat to sail now.
16 January 2023 at 11:01 #103597
Christopher Chapman
Participant
@christopherchapman42421
Thank you for all your responses, I have been mulling them over and looking them up.

After measuring the one remaining prop on the bent shaft, it is 50mm with plenty of clearance. Considering Harry's motor suggestions would going to a 50mm prop put too much strain on the motors, if a suitable pitch was chosen?

Also the much higher capacity than required esc, this is due to heating within the confined space of a hull right?

I have also been looking at rudders, the one left on the hull appears massive. Would this be due to the inability to scale the waves and weather? Or a choice by the previous owner?

Lastly a single prop is definitely out of the question, this is to do with maneuverability right?

Christopher
16 January 2023 at 11:23 #103598
harry smith 1
Participant
@harrysmith1
Hi Chris

50mm prop would load the motor and ESC too much.

Standard prop pitch is 1.4 .

The car ESCs have a small electric fan on them which works well for cooling.

A program for the ESC makes for easier setting up.

As for the rudder a 55mm deep x 35mm works OK on my boats.

Harry
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