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Auxiliary Drive for Pride of Baltimore

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SloopJohnB25/06/2020 01:13:24
3 forum posts
6 photos

Hello guys.

I have been a RC sailor for 20 years racing IOM's, DF65 & 95's but decided to do a scratch build classic boat, the Pride of Baltimore II.

I am in the process of building a 1:24 scale boat, the hull is completed and turned over now working on the inside of the boat. I have 2 sets of drawings for reference, copies of the original Thomas C Gillmer drawings and the 1:64 Shipway drawings.

Boats details:


1157 mm LWL

310 mm BeamWL

120 mm Hull Draft

155 mm Keel Draft

1.39 kg Displacement

1.6 knts scale speed

I have started to build a test rig to sort out the sail sheeting and hoisting, I will be using RMG sail winches, which I have recovered from an earlier build (2003) F100 canting keel 1 meter yacht, 3 x 380HD and 1 x 280D winches and 2 Hitec HS-715BB Sail arm servos......plenty of pulling power.

The next thing is the auxiliary drive, the original boat has twin feathering propellers, so I would like to duplicate that setup, after searching the web I came across the Microcosom viable pitch propellers, I believe that the blades rotate thru 90 degrees (+45 to -45) with some re-engineering I could make them feathering by reattaching the blades at 90 degrees, which will cover forward and reverse if the ESC is unidirectional.

The big questions are, I am not great of electronics having spend my life as a mechanical designer, its great seeing product, water steam coming out the end of a pipe, but you can’t see volts, amps and watts out the end of a piece of wire.

Motors, brushless or brushed motors

What size motors

Single or twin motors, if single a dual output gearbox

Gearbox/belt drives, I have calculated about 2000 rpm propeller shaft speed.

Counter and clockwise propeller rotation

Single or 2 ESC, it looks like a single ESC can drive 2 brushed motors.

Do ESC have forward and reverse, some car units do.


Reading some of the topics on forum they are some great minds, so I am looking forward to the recommendations, Thanks a lot.


Regards SloopJohnB

Edited By John Beavis on 25/06/2020 01:16:12

SloopJohnB25/06/2020 01:54:34
3 forum posts
6 photos

Oops, I forgot to add the voltage for the winches is 7.2 volts so it would preferable to use the same battery for the motors.

harry smith 125/06/2020 05:43:53
1072 forum posts
1272 photos

Hi Sloop

Brush motors MFA 950D2.51 are 2329 rpm on 6volts or 3494 rpm on 9Volts with no load.

The props would load them down to about your requires on 7.2 volts.

ESC a single Hobbywing Quicrun 6o Amp on a 2S Lipo battery will handle the motors and it has a link setting for forward/ reverse only.

I use this ESC in all my tugs and fishing boats with 540 80 turn brush motors swinging 60 mm brass props.

The only mods to the ESC, I change the connectors to 4mm gold for the motor and XT60 connector for the battery.

No water cooling required on the motors or ESC.

Harry Smith

Malcolm Frary25/06/2020 08:50:33
995 forum posts

Possibly rather a lot of motor for an auxiliary on a 1.39Kg sail boat. A 385, possibly geared down, would probably be more appropriate. An ESC that can work a big motor can just as easily work a small one. When you buy a brushed motor, you have all that is needed, he ESC just controls speed. When you get a brushless motor, until you get its correct ESC and get them working together, you have a paperweight.

It sounds like an awful lot of big heavy servos/winches working the sails (not seen the sail plan, but there surely can't be a lot of sail area on a boat that light and shallow) Something a lot less bulky and heavy might be needed to ensure that the boat can have the weight where it is needed to ensure that it floats and sails upright.

Just found a reference to the variable pitch prop - with its 2" diameter prop, it will need to have a small motor geared down by about 6:1.  It is intended for use with a steam plant.

Edited By Malcolm Frary on 25/06/2020 08:56:23

Ray Wood 225/06/2020 09:44:18
2374 forum posts
831 photos

Hi All

The weight/displacement is not correct, maybe 13 kilos is nearer the mark for a hull over a metre long 😄

Regards Ray

SloopJohnB25/06/2020 10:20:31
3 forum posts
6 photos

Thanks for your replies, the displacement is a factor of 10 out its should be 13.9 kg.surprise

Dave Cooper 625/06/2020 10:47:22
287 forum posts
29 photos

I'm just wondering what, exactly, is the purpose of the auxiliary motor(s) ?

Is it just to get the boat back to 'base' if the wind dies, or, is there is a scale application here - ie does it need to supplement sail power in order to achieve scale speed ?

Context: I'm learning about scale sailing and have a need for something auxiliary on Yacht Ardent (mine may well be a little electric outboard hung off the stern though...)

I'll follow the thread with interest !


Malcolm Frary25/06/2020 22:32:11
995 forum posts

On a tops'l schooner I would expect that an auxiliary motor would be a good help tacking. A square sail does nothing helpful there, being a very effective air brake just when you don't want one,

From earlier reading elsewhere, the options were either to gybe round, to do a lot of very sharp work swinging the yards so that you got the wind on the right side at the right time, or to go into irons, fall backwards and hope that the rudder would do the job in reverse.

A fore and aft rig shouldn't need help tacking, having a prop hanging there might reduce performance enough so that it becomes needed, and learning to rely on auxiliary power on a boat that doesn't need it will not help learning.

Ray Wood 226/06/2020 05:39:48
2374 forum posts
831 photos

Hi All,

The original Baltimore Clippers didn't have engines and were able to sail & tack perfectly well, the 1976 new build replica has engines for convenience, I saw her in London's docklands in 1991 😀

Regards Ray

Edited By Ray Wood 2 on 26/06/2020 05:44:20

Ray Wood 226/06/2020 09:52:47
2374 forum posts
831 photos

Hello John,

Are you having a detachable fin keel ? It will have a large rig and the stability maybe an issue, I only mention this because we use them on our Thames Sailing barges of similar size 😀

Regards Ray

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