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Motor and Prop Survey 2020 Update

Article in forthcoming Special Issue oif Model Boats

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Robin Lee14/05/2011 10:58:26
129 forum posts
122 photos
Thanks Colin - usually I am very unlucky with prize draws. Hopefully my luck will hold out for today's Lotto draw!
Robin Lee
Gareth Jones30/07/2011 20:30:45
791 forum posts
1067 photos
I know time has moved on, the article has been published and most of you have lost interest but for the anoraks among you here is another variation on a theme of TIDs. My TID has had is Speed 900BB torque surgically removed and transplanted into Shemarah II. Its replacement motor is a Graupner Speed 720 BB torque, and here is the performance data.
Name TID13 (I know there never was a TID 13 in real life)
Type Tug
Scratch built, ply plank on frame hull
Length 900 mm
Breadth 230 mm
Draught 70 mm
Weight 6.4 kg
Propellers 1
Motor Graupner Speed 720BB torque (type number 6372)
Propeller type 4 blade Rivabo brass general purpose
Propeller diameter 55 mm
Direct drive, no gearing
Battery 12 volt 7 amp hour lead acid
Duration not known but well over an hour
The motor takes 4.7 amps at full power of 54 watts into the speed controller.
Battery voltage was 11.65 at this condition.
Prop speed was 2140 rpm which is about 52% of the free running speed of the motor.
The static thrust from the propeller was 720 gramms max.
The attached photos show the motor installation and the tug running at full power on the pond at Goole today. I have not tried towing anything yet but it looks quite good at full power, much more realistic than with the previous motor. Note the picture of the tug on page 1 of this thread is not at full power, its much less.

Mark Beard30/07/2011 21:30:38
164 forum posts
84 photos
Gareth, Much appreciated! Your friendly neighbourhood Anorak! Mark
Gareth Jones19/09/2011 09:31:04
791 forum posts
1067 photos
Hello Mark and the other anoraks, here is another interesting combination to add to the database and follows on nicely from the TID above because it details the performance of the Speed 900 transplanted into Shemarah 2 and can be compared with the same motor ungeared
Name Shemarah 2
Type Modern twin rig trawler
Scratch built, mainly ply, plank on frame hull and still a long way to go to completion
Length 1050 mm
Beam 350 mm
Draft 140 mm
Weight Ballasted to 25 kg (somewhere around the expected complete weight)
Propeller One
Motor Graupner Speed 900 BB torque (model number6373)
Propeller size 75 mm in a Kort nozzle (Prop-Shop matched pair)
Reduction gear 2.1:1 using MFA Como Drills belt drive
Battery 12 V 7ah lead acid (all the other batteries in the photo are temporary ballast)

Measured motor performance at full power static in the water was 10.85 Volts, 6.5 amps, 71 watts.
Propeller speed was 2080 rpm which is equivalent to a motor speed of 4368 or 67% of the motor free running speed which is a pretty good match.
The static thrust was measured at between 1800 and 2000 grams.
The photo below shows that perfomance on the water looks good with plenty of power in reserve and the ability to make some really big waves if you are in that sort of mood.


Edited By Gareth Jones on 19/09/2011 09:42:03

harry smith 121/07/2019 11:46:05
1040 forum posts
1215 photos

brush motor specs.jpgprop specs001.jpgprop specs002.jpgprop specs003.jpgprop specs004.jpgprop specs005.jpgprop specs006.jpgHi All

This is a very grey area for us model boaters, but in the planes with brushless motor you get all the data !!!

Prop size, pitch, thrust, Amps, voltage and required ESC.

I found a good start is with the Raboesch Prop Chart which gives you all the specs including vessel type and mainly the maximum RPM for each prop.

Brushless motors are easy to work out, divide maximum prop speed by the voltage (7.2volts(2S Lipo)11.1volts(3S Lipo)).

EG 11,000 rpm divide by 7.2 equals 1500kv and 11.1 is 1000kv.

A bit of rounding out to get to a motor kv which is available.

Motor size, the first two numbers are the diameter and the second two are the can length.

EG 3639-750KV is 36mm diameter(about the same as a 540 brush motor) and the second two 39mm is the can length, note the larger the length the more powerful the motor.

Onto 540 rock crawler brush motors which I was talk into buying for my Hellen Fishing Boat (all 14 pounds of it).

I found at least some info on these at 7.2 volts from websites.

Maximum rpm for a 20 Turn(18400), 27Turn(15,000), 35turn(12,500), 45Turn(9,500), 55Turn(7,700), 65Turn(7000), 80Turn(4450).

So using my brushless motor maths a 80Turn equals a 600kv brushless!!!


As for the other brush motor specs the best chart I found I added below.

Some of the other motor spec charts are a dog's breakfast and totally poor.

So checkout the pics below and post ideas !!!

Harry Smithprop specs007.jpg

Colin Bishop17/09/2020 12:47:01
4592 forum posts
6071 photos
400 articles

I'm sure many of you will recall this particular topic where the data gathered was used in an article about selecting motors and props for the Model Boats Special Isse published in 2011.

In the years since then the subject of matching the motor and prop to particular models has come up again and again and Editor Lindsey Amrani and I feel that it would be useful to update the article and feature it in the regular magazine which of course has a wider readership than did the Special Issue.

Looking at the original, most of the information is still quite valid but it was biased very much towards brushed motors and NiMH/SLA batteries whereas brushless motors are now much more common and are often the first choice, even for scale models. Likewise, the greater availability of LiPos and smart chargers has made this power source far more popular due to it's light weight/high power ratio.

I am therefore looking for examples of brushless motors being used in models using the same data that we used before together with photos of either the model or the interior layout. These are repeated below. If you scroll back through this topic, the previous examples can be seen.

I look forward to your contributions (including Ashley's innovative models).


The list of parameters that I have identified is as follows. We need all of them to do an effective job.

Boat Name
Type: ie. tug, destroyer, cabin cruiser etc.
If a Kit – which kit?
Length (mm)
Beam (mm)
Draught (mm)
Weight (Kg)
Number of propellers
Motor(s) used. (specific rather than generic i.e. Not just ‘540’ but ‘Dean’s Kondor’ for example so we know exactly which motor is being referred to.)
Propeller type and description: i.e. 2 blade/3 blade/4blade etc. conventional or racing
(precise prop details if available i.e. manufacturer and product ref
Propeller diameter.
If geared drive what is the reduction ratio and are gears or belts used?
Battery type and capacity.
Approximate average running time obtained.
Any special comments on the setup. (new item)

Please don’t use this topic to ask questions about which motors to use, it is intended for gathering information only! I have started a new topic for any discussions of a general nature that yield useful information for the article.


Edited By Colin Bishop on 18/09/2020 11:21:39

Colin Bishop18/09/2020 14:10:17
4592 forum posts
6071 photos
400 articles

As stated above, please only post data on this topic and use the following topic for discussions.


Many thanks,


Robin Lee19/09/2020 14:12:44
129 forum posts
122 photos

Hi Colin. Since my last contribution to this thread I have made several brushed motor models but I have two brushed motor models, one complete, one on the stocks (Model Slipways Vliestroom).

My contribution to the data base update -

Boat Name: USN PT212
Type: US PT Boat type Higgins 78 foot fast planing hull
If a Kit: Dumas PT212 Higgins 78 foot 30:1
Length: 762 mm
Beam: 203 mm
Draught: -
Weight: 2.3 Kg
Number of propellers: 2 (NB kit designed for 1, actual PT boat had 3)

Motor(s) used: 2 off Turnigy D2830-11, 1000kv 210 watts, 21 Amp max, 7.4-14.8 volts
Propeller type and description: 2 off Raboesch type RAB174-03/04, 4 blade, 35 mm dia, 35.9 mm pitch
Propeller diameter. : 35 mm
If geared drive what is the reduction ratio and are gears or belts used: n/a
Battery type and capacity: one off 9.6 volt NiMH 4300 mAh
Approximate average running time obtained: 30 minutes (not flat out say 50% cruising, 50% having fun!)

Comments: Uses two off HobbyKing Marine ESCs maximum 30 Amp. ESCs are not water cooled but temperature of the ESCs and motors is reasonable if boat is used sensibly. The kit in its 2 motor set up is a little heavy so a Lipo battery might have been a better choice but the boat with its NiMH battery floats only about 3 mm too deep and performs well. The drive train installed is a little too powerful for scale speed but I use a programmable transmitter permitting throttle stick maximum demand to be adjusted. I have found a setting of 70% limit gives a good approximation to a scale maximum speed for this 40 knot boat. 100% demand which would be the default for a non-programmable transmitter is a bit hairy for the model particularly on tight turns where a capsize looks possible!

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img_0844 (medium).jpg

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Edited By Robin Lee on 19/09/2020 14:14:51

Edited By Robin Lee on 19/09/2020 14:15:24

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We welcome well written contributions from Website members on almost any aspect of Model Boating with a particular emphasis on practical hints, tips, experience and builds.

In order to maintain a consistent standard and format, all suggestions should first be sent to me by Personal Message for approval in principle. Only a very limited amount of time is available for editing contributions into a suitable format for placing on the website so it is important that the material is well presented, lucid and free from obvious spelling errors. I think it goes without saying that contributions should be illustrated by appropriate photos. I shall be happy to give advice on this.

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