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Vosper MTB propulsion

Printed From: BMPT Forum
Category: General Discussion
Forum Name: Modelling
Forum Description: Discussion about Modelling
URL: http://www.bmpt.co.uk/forum_posts.asp?TID=226
Printed Date: 26 March 2026 at 5:17pm


Topic: Vosper MTB propulsion
Posted By: Adrian
Subject: Vosper MTB propulsion
Date Posted: 26 October 2006 at 12:09pm

Hi all,

Does anyone know which way the 3 shafts on the early Vospers (No 35 in particular) rotated?




Replies:
Posted By: Pioneer
Date Posted: 27 October 2006 at 3:22pm

Hello Adrian, I thought that maybe one of the technical body's may have answered you by now but here goes -most of the early Vosper boats especially those numbered in the 30+ series (inc 35) were constructed with the very heavy Hall scott 'Defender' supercharged Engines giving a max speed of around 29-30knts these being replaced by the Packard Units late in '42-43 giving an increase to 39-40 knts - but to answer you question - viewed from the Gearbox end the engines were right-handed ie 'clockwise' - the outer engines drove direct through theThrust Box's - so with both wing engines turning 'clockwise' this would be the rotation of the outer  Props. The center engine drove through a 'V' drive which would turn counter clockwise on the output shaft - so the center Prop would be anti-clockwise - with modelling how ever I found that this made my model difficult to maneovre (as was indeed the full size craft)- hope this helps

Regards



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Pioneer - Forum Moderator


Posted By: Adrian
Date Posted: 29 October 2006 at 12:10pm
Many thanks, No, no replies from anyone else - even the Imperial War Museum didn't know! You are right, with the two outer props turning one way and only the centre engine to counter the paddle wheel effect the boats must have been pigs to steer.  I will have to experiment with shaft rotations and 'handed' props to see which is best.


Posted By: Pioneer
Date Posted: 29 October 2006 at 12:48pm

Hello again Adrian,

According to several articles that I have read- in full size craft, including Destroyers and the like, a more efficent use of Props and to keep reasonable steering capabilities etc would be to have the Wing props turning 'outwards' ie when viewed from the Stern - Port side turning 'anticlockwise' while Stbd turning 'clockwise'. I found that when modelling the Gay class with 3 props - the above arrangement made the model behave quite reasonable - in my model the centre prop could be 'wired up' for either a left hand or right hand - depending what propeller was available - I did try the model with the correct - full size arrangement- of all props turning anticlockwise - but I was a danger on the lake

Please keep us informed of your model

Regards



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Pioneer - Forum Moderator


Posted By: E.S.ChildsDrum1
Date Posted: 12 November 2006 at 7:53pm

 

                    Hi. All.

On my Proud  Class the two wing props turn inwards looking at the Transom towards the bow, That is the port prop clockwise and the starb`d anti clockwist the centre as pioneer said can rotate depending on the prop you have. and my Gay will turn likewise.

             Ted Drum 1.



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E.S.Childs


Posted By: Christian
Date Posted: 12 November 2006 at 8:09pm

Hi Adrian and Teds

When I set up my Fairmile A I wanted to make it more manouverable so I fitted a mixer which controls the speed controllers according to rudder input, i.e. it slows down the inner motor in turns and with no throttle it reverses the inner motor on rudder input alone. I'd set the props as per most real boats, LH prop on port and RH prop on stbd. It proved impossible to get the mixer to accept this so I had to switch the props over and reverse polarity to the motors. So if you're using a mixer, use Ted's set-up with inboard turning props as outboard turning seems to confuse the electronics. I later noticed that the Robbe props are marked RH on the LH prop and vice-versa indicating that this is the norm in model boats, it does seem to give better turning ability without much affect to performance of the boat.

Rgds, Christian

p.s. see the pictures of Dave Abbott's MTB 74, even the proffessionals contra-rotate the outer props for the sake of manouverability over scale precision.



Posted By: E.S.ChildsDrum1
Date Posted: 13 November 2006 at 10:23am

             

           Hi. Christian.

          I have been using the JCC prop rudder control but without much success, i-e the boat started to behave erraticly, however over the weekend at the boat show I had words with JCC and he was a bit puzzled about this and he gave the newest up to date controller,to try, this contains up to date software and asked me to let him know if I encounter any problems.



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E.S.Childs



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