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RTTL help please

advice on motor selection

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Peter Mason 313/11/2017 15:15:46
4 forum posts

Hi all,

Sorry but Think I put this in the wrong place initially I'm returning to model boats after over Fifty years of aeromodelling. I have built a number of boats of various types in the past. Vic Smeeds 34'' RTTL is the boat chosen, however the plan shows a DC Rapier Diesel engine and I know that these are regarded as environmental poison. So my question is: what electric motor to use and what type, and what propellor.

John W E13/11/2017 17:47:33
276 forum posts
272 photos

004 [800x600].jpg005 [800x600].jpg

Hi there Peter - are you going to build the model as per Plan single prop? or twin prop or even triple prop as some of these boats were? If you do a search on Mayhem - I build this model using Vic Smeed's plans as a reference and also I used an awful lot of original material from Vosper. My model has twin props both rotating in the same direction as per original. Props are 32 mm diameter 3 bladers and Mtronik motors vision 600s.








Edited By bluebird on 13/11/2017 17:50:16

Peter Mason 314/11/2017 03:57:20
4 forum posts

Hi Bluebird, That is an impressive boat, diagonal planking as well. I am almost lost for words. Sorry I should made clear I'll only use a single motor, that will be enough to cope with. My last launch built over forty years ago was a Fairy Swordsman from a Model Maker drawing.

Dave Milbourn14/11/2017 08:37:25
4025 forum posts
282 photos


I think a brushless motor would be the answer. I would personally go for this one **LINK**

with a 60A marine speed controller like this one **LINK**

and a 1.5" {40mm} diameter 3-blade cast bronze scale prop from Protean Design. Run the motor on 11.1v i.e. a 3S LiPo battery. I doubt that you would need the water-cooling facility. Note that 35mm diameter motors fit a standard glass-nylon moulded 500/600 sized motor mount like this one **LINK**

You'll need to remove the aluminium prop adapter from the back of the motor and use the plain 4mm shaft at the front for coupling to the prop shaft.

Dave M

Ray Wood 214/11/2017 08:58:22
2505 forum posts
864 photos

Hi Peter

Vic's RTTL is such a super drawing which I've had for years, it's on the to-do list, keep us posted with photos of your build progress, I also spent 40 years Aeromodelling and realised having turned out over 100 aeroplanes I had nothing to show for my labours and even harder to sell than boats ! , except lots of flying time, and I still fly electric to keep my hand/eye in

Regards Ray

John W E14/11/2017 15:59:06
276 forum posts
272 photos

Hi ya there Peter

Simplicity is sometimes the best policy by keeping it single prop - although I am not a great lover of brushless motors - I prefer the old ones (plug in and play ) instead of having to programme but that just me ..

The motor Dave Milbourn has mentioned will no doubt do the job - the thing to remember is - when Vic Smeed originally drew the plans up for 99% of his plans it was to use with materials that were available at the time. When the RTTL plans were originally drawn in the 1950s there wasn't a great choice of materials to build the craft from or was there a very good choice of motors to power the craft - compared to what we have these days.

Taking that into consideration we can now build a model using lighter materials and therefore requiring much less power to propel the model in the motor apartment to achieve a greater speed and this is why when I built my RTTL I only used 4mm ply for the bulkheads and I removed the centres of all of them which, if you have a look at the plan which Vic has drawn. you can see he has left several bulkheads 'solid'. He also uses a very thick keel which I reduced down to 4mm in thickness.

Hope this has given you some food for thought. John

Edited By bluebird on 14/11/2017 16:00:50

Peter Mason 319/11/2017 13:34:22
4 forum posts

Hi all, Many thanks for all the advice, I don't suppose this will be my last plea for help though.wink

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