Twin Prop question?

[PoppaParticipant @poppa]

Hi all i have a question about twin prop craft.

Does it affect the steering on a boat if both props rotate in the same direction?.

Will it tend to make a boat go more left or right according to which way the props rotate?.

My reason for asking is that i’m currently building a Brede class RNLI lifeboat, and it should have twin props but ive only built it with one center mounted prop, this is  because i didn’t know the answer to the above question as ive never built a twin prop boat before, so sooner than take a chance which might prove costly i opted for the single prop.

My thinking is that if twin props rotating in the same direction DON’T affect the steering then i might just alter the boat to twin prop, and power it off one motor, i know this would be awkward but it’s possible for me to do.

I would be Grateful for any help

[Andy BaileyParticipant @andybailey80218]

Hi , on a full size boat it does effect the steering but have never tried it with a model though i think it will be the same

[Paul TParticipant @pault84577]

Hi

Yes it does effect the steering on a model, it also effects the model when going in a straight line as the boat will tend to veer off to left/right depending upon the rotational direction of the props.

Contra rotating props (i.e. one that spins right and one left) are available at most model shops or try the prop suppliers that advertise in Model Boat mag.

When twin props/motors are set up correctly they can assist with steering.

Hope this helps.

[PoppaParticipant @poppa]

Cheers Guys, it’s as i suspected so i think i will stick with the single prop.

Many thanks….

[Alexander ForbesParticipant @alexanderforbes90192]

So how do you set them up right

[neil hpParticipant @neilhp]

what do you mean by "setting them up right",Alexander?

Usually the port side prop rotates anti clockwise with a left hand prop, and the starboard side prop rotates in a clockwise direction with a right hand prop for forward motion.

[ashley needhamParticipant @ashleyneedham69188]

Chaps. The convention for twin props is as neil states. This apparently gives better efficiency than having them the other way round…I read in a book on Destroyers. I must say I have experimented with my Battleship and it doesnt seem to make that much difference on a model. Viz one prop or two, if you think about it, just one prop rotates in all the same direction (!) and would give a torque reaction to a boat, whereas twin counter rotating props are self-cancelling in this department. Its horses for courses really. Most of my models regardless of type are single props as it easiest, or am I just a skinflint?   Ashley

[Charles OatesParticipant @charlesoates31738]

The effects of twin props are more obvious on a short beamy boat than on a long hull. i.e a pilot boat and a destroyer. Twin props are more scale, and appropriate to some boats, especialy if the prototype is  very manouverable. If you want your model to turn on a sixpence, useing two props, motors,and speed controls will enable you to have one motor ahead and one astern, and the model will spin round. Obviously this only looks right on certain protptypes, such as some lifeboats.

To do this properly one favoured contol method is to use two cannels and a mixer for the motors, so costs will rise quite a lot. There are some other ways of doing it but they all add to the cost.

   If your model is of a tug that had twin screws, using a twin arangement on the model wil give more ‘grab’ on the water, usefull if you are going to tow.

 Me? I usualy go for one prop so much easyer, and I’m a Yorkshireman with a Scottish mum so costs matter. My only exceptions have been a pilot boat and model of Sri Perlis a Malaysian patrol craft. Neither looked right with one prop.

 I hope this helps

chas

[Ian_G HughesParticipant @ian_ghughes13480]

Every single screw vessel "carried helm" but this varied according to ship’s draught and was most noticable in calmer weather. Invariably it was port helm that was "carried " in view of the starboard torque of a right-handed prop. This information was passed on from one helmsman to the next as his trick at the wheel expired.

Worst combination was triple screw arrangement as evidenced by the "Olympic" class. The "inwash" from this arrangement was notorious and on one occasion "Olympic" dragged a merchant ship from its pier moorings in New York and only superb seamanship saved the day. Unfortunately, when her sister "Britannic" went down this inwash was the reason for the only fatalities, the lifeboats being sucked in by props rotating and well out of the water, the ship being down by the head.

[PoppaParticipant @poppa]

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