Dual prop question

[Neil Powell 1Participant @neilpowell1]

Hi quick question.

If i have 2 LH(at least i think they are LH) Props on a dual prop boat will the boat naturally steer in one direction? i know from flying dual prop RC planes that if the props aren't turning in opposite directions the plane can suffer from unwanted banking.

Thanks

Neil

[Neil Powell 1Participant @neilpowell1]

[ashley needhamParticipant @ashleyneedham69188]

Neil. Yes, basically.

BUT it may not be that noticeable and easily trimmed by a bit of rudder.

Ashley.

Edited By ashley needham on 21/08/2021 21:39:31

[Neil Powell 1Participant @neilpowell1]

So looking at the stern of the boat my props run counter clock wise. Will that make the boat go left or right?

[Richard SimpsonParticipant @richardsimpson88330]

Props tend to "walk" in the direction of rotation so, if they rotate anticlockwise it will have a tendency to move the stern towards port.  This can them make the boat steer slightly to starboard.

 

 

Edited By Richard Simpson on 22/08/2021 11:13:22

[Paul TParticipant @pault84577]

Hello Neil

I used to fit contra rotating props to my twin engined boats which, whilst correct, were expensive and ultimately a waste of money.

As Uncle Ashley points out a slight trim adjustment on the rudder control solves the problem of 'propwalk'

However if you wish to avoid the corrosive comments of the numerous rivet counters then you should either fit contra rotating props or ask them for the correct sequence of rotations on a triple engined boat.

Paul

[Charles OatesParticipant @charlesoates31738]

I totally agree with Paul, keep it simple. Once you're sailing the model you can't see any difference and no one could care less which way your props turn.

Chas

[redpmgParticipant @redpmg]

Been on a Natal Parks Board full size (18ft ) Boat – fitted with twin 75hp outboards – both same rotation – made no difference to performance.

Some big Shark Diving/ Excursion boats here in Gansbaai are fitted with four  300hp outboards – although they usually only run on two. A couple have counter rotating props – most have not………….

So totally agree with Paul & Charles – ignore the rivet counters and keep it simple – makes no difference when running.

Edited By redpmg on 23/08/2021 14:10:41

[Ray Wood 3Participant @raywood3]

Hi All,

Where has the term rivet counter come from with reference to Neil's bait boat ? not actually a model of a boat ?

I'm not aware the DeHavilland Mosquito had any banking issues with the Merlin's both rotating the same direction tricky to keep straight on the ground my father inlaw told me !

Regards Ray

[Paul TParticipant @pault84577]

Ray

The Lancaster was the same as all four props rotated in the same direction.

As for model aircraft I only fit contra rotating props on small electrics.

Paul

Edited By Paul T on 23/08/2021 17:22:47

[Colin BishopModerator @colinbishop34627]

I rather think that in the model boating world 'rivet counters' have faded away. There are relatively few people now building what might be regarded as traditional 'scratch built' models as there are virually no scale model boating competitions remaining. They have all gone over the last few years.

So people building what might now be termed 'scale replicas' are more than happy to use bought in components, especially those from 3D printing, if it enables them to construct the model they want. And what's not to like really if it enables you to finish your model to a higher standard and more quickly.

Why slave forever over making cowl vents if you can simply purchase the exact versions you want and get on with your model? With no competitions who is to judge what route you take to achieve the result that you want.

Times have changed.

Colin

[Richard SimpsonParticipant @richardsimpson88330]

Posted by Paul T on 23/08/2021 17:21:56:

Ray

The Lancaster was the same as all four props rotated in the same direction.

As for model aircraft I only fit contra rotating props on small electrics.

Paul

Edited By Paul T on 23/08/2021 17:22:47

 

Cheaper and easier to manufacture them all the same and increased interchangeability.

Edited By Richard Simpson on 23/08/2021 19:30:48

[Ray Wood 3Participant @raywood3]

Hi All,

I think Rolls Royce were the problem as Richard says they were so busy producing engines for single seat fighters they didn't want to make a special gearbox for the Mosquito as it was only a private venture

I'm glad DeHavilland made the wooden wonder the brilliant aeroplane that it was (no Rivets)

Regards Ray

[Dave Cooper 6Participant @davecooper6]

Speaking as a very inexperienced own-design /semi-scale builder there is a certain (perverse ?) pleasure in 'getting it right'. I'm sure the craftsmen of old – shipwrights /aircraft workers etc. all aimed high.

I think keeping it simple is a good road to this goal. The pilot cutter will have one motor, one rudder and one prop' to get me out of trouble when the sails fall limp…

I suppose that's the real beauty of semi-scale: no-one can say "That's not right" (I bet someone will though !).

[ashley needhamParticipant @ashleyneedham69188]

But Dave…just think of the propwalk with only ONE prop! 🤭

Ashley

[Richard SimpsonParticipant @richardsimpson88330]

Posted by ashley needham on 25/08/2021 09:01:09:

But Dave…just think of the propwalk with only ONE prop! 🤭

Ashley

Yes Ashley but when you become familiar with the effect you can use it to your advantage, particularly when docking and undocking.

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