Dumas Trojan F-31

[Andy hopParticipant @andyhop65854]

single or double screws ?

[Andy hopParticipant @andyhop65854]

firstly happy new year all

I got a Dumas Trojan F-31 for my xmas just looking at the fittings kit haha £170 plus I no think so

looking for info on 1 brushless inrunner

or 2 double motor twin screws

would rather the first option …

cheers

[Chris FellowsParticipant @chrisfellows72943]

Why an inrunner? They are more suited to aircraft or racing boats where very high revs are required.

Motors as per your Vosper Fireboat thread would be more suitable.

[Andy hopParticipant @andyhop65854]

Hi chris

Inrunner just for watercooling thats all

[Colin BishopModerator @colinbishop34627]

It's a cabin cruiser design, not a racing boat so you shouldn't need water cooling if you get the right motor/battery combination. You want the power to go into moving the boat, not heating up the motor.

Colin

[Andy hopParticipant @andyhop65854]

Colin thumbs up ill try for 900kv motor with 3s lipo

Is it the lower kv better the motor ?

[Colin BishopModerator @colinbishop34627]

I'm not an expert on brushless I'm afraid but there are several members who should be able to advise you. There's bound to be a decent combination for the Trojan.

I agree with you that it would be simpler (and a lot cheaper!) to have a single motor.

Colin

[ashley needhamParticipant @ashleyneedham69188]

A quick search reveals that Dumas recommend 2x 2004 or 2x 2005 motors (Dumas`s own ones) for this model .

These rev to 5000 rpm no load and draw 2A with a 2 inch prop.

As a comparison, perhaps, my MFA Fantome (48 inches by 12) was fitted with a pair of MFA 800 motors, 5000rpm and about 5A with X50 props on 12v. This propelled the boat adequately, but not that brisk. The Dumas one is only 31 inches, but with motors as slow as this, performance will be in the Norfolk broads class.

Generally the lower Kv has more torque, so a 900 Kv motor would be ok on a 50mm prop, but not give that many revs for performance..

The question is how fast do you want to go??? A 35mm outrunner on a 40-50-ish 50mm prop with about 1300Kv and 100W or so would give a decent turn of speed, pending someone who has actually built your vessel.

Ashley

[Chris FellowsParticipant @chrisfellows72943]

Posted by Andy hop on 01/01/2020 17:08:17:

Colin thumbs up ill try for 900kv motor with 3s lipo

Is it the lower kv better the motor ?

Not better, just suited to different uses. For boats of the size, weight and type (planing hull) that you have you want a motor with good torque to move the boat along without too much effort and also give enough revs for good speed on the plane. Hence the recommendation for motors around 900 kv and upto around 1200kv. On 3s LiPo the motors in the range stated will rev from 9900 to 13320 which will give plenty of speed and you have the option of going to 4s if more is required.

Motors much below 900kv have more torque and are suited to slower craft e.g. displacement and won't give enough revs for a planing boat. Start going much over 1200kv and you will start getting too many revs and you start to run into prop shaft problems e.g. exceeding their designed rev limit. Yes, you can limit by the amount of throttle stick or using a 2s battery but the motor won't be operating in its designed i.e. higher rev range and it and the battery and ESC may run run hotter which will require cooling. Much better to use a beefier motor and battery to suit the application and run cooler. High kv motors, including inrunners are better suited to lighter, high speed/racing boats where you want high revs but maybe a smaller, lighter battery.

If you ever need to cool a brushless outrunner to can get water cooled motor mounts for a more elegant solution.

Chris

Edited By Chris Fellows on 01/01/2020 22:12:22

[Dave Cooper 6Participant @davecooper6]

Having recently read Dave Milbourne's introductory article for Model Boats magazine, he talks about this subject in depth.

There's a section on using twin motors /props with a 'mixer' ESC which can give advantages for manoeuvring in turns /harbours etc and at different speeds. I guess this is a throttle /rudder mix, but, I'm no expert…

Recommend you read this as it's packed with useful info'. I think Dave has put a link to it in one of the more recent "Beginners" threads.

Happy new year,

Dave

[Malcolm FraryParticipant @malcolmfrary95515]

If the right motor is chosen for a tug, no cooling is needed.

Having said that, cooling is much simpler on an outrunner. When motor cooling is mentioned, the first thought is a coil round the can, which is sensible on a brushed motor. But on a brushless motor, the thing that does the heating is the coil assembly, which is very firmly fixed to the motor mount. Hence, a water cooled mount.

An inrunner, will need the right geabox to increase the torque and reduce the revs from what the motor is naturally inclined to do down to what is sensible at the prop.

While there are certainly very good mixer/esc combined units, I haven't heard of one for a brushless setup, so that will probably mean separate ESCs and a mixer, or channel mixing at the transmitter.

[Dave MilbournParticipant @davemilbourn48782]

I don't know of any combined Mixer/ESC units for brushless motors, but the ACTion P40E can be used with brushless speed controllers P40E Marine Motor Mixer

Dave M

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