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Old 18-12-2009, 01:15   #16
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I have a Yankee 30 with a right hand prop that is directly behind the fin keel (motor is midships). Without influence from wind or tide, the boat WILL NOT back to Port, yet pulls to Port at cruising speed in forward. The latter maybe created by wash over the rudder, but the propensity to back to Starboard is just strange!Yes...I'm sure it's a right hand prop. Other owners report the same characteristics.
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Old 18-12-2009, 02:31   #17
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In the northern hemisphere, the water is lower on the RHS side of the boat so you will move to PORT going forward. Either that or you need a wheel alignment....I dont know!!!!

It must be the pitch - is it standard or one you put on?
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Old 18-12-2009, 05:46   #18
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To me a right-hand prop when viewed from the rear will turn clockwise when driving ahead - propwalk or paddle-wheel effect will try to walk the prop to starboard, making the boat turn to port. The OP must have a left-hand prop (turns counter-clockwise when driving ahead). The offset between the shaft and the rudder is to counteract lateral thrust (I think that's what it's called). This is a well known effect with the pilots of small single-engine planes; the prop causes a whirling vortex that pushes on the side of the rudder (right hand prop pushes against the left side of the rudder, left-hand prop against the right.) The lateral thrust works in the same direction of the prop-walk - that is both make the boat turn in the same direction, but it is the effect that is most likely being observed by the OP, as it would also tend to turn the rudder. Dockhead, I assume the prop is left (counterclockwise) turning?
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Old 18-12-2009, 06:04   #19
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Originally Posted by Dockhead View Post
Yes, the prop is located between the fin keel and the rudder, like most bigger sailboats. It will be washing on the rudder for sure. But it's a right hand propeller -- wouldn't prop walk going forwards with a right hand propeller ordinarily pull the boat to port?
Apparently,it's RH.
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Old 18-12-2009, 06:33   #20
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It probably warrants having a visual check to confirm if it's a left or right-hand prop. From what's been said so far, it's not clear if the OP needs to counter the yaw or just hold the rudder from swinging to starboard. It could be a right-hand prop, and the lateral thrust hits against the port-side of the rudder, pushing it to starboard, which would cause the boat to turn to starboard. I wonder how much play is in the steering gear (cables?)?
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Old 18-12-2009, 07:36   #21
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Would it be possible to make a small adjustable trim tab for the trailing edge of the rudder to compensate for the pull to starboard?My Mirage 25 pulls to the right under power.It has a right hand prop.

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Old 18-12-2009, 16:16   #22
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I have seen Trim tabs on a number of larger sailboat rudders.
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Old 18-12-2009, 16:55   #23
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if the boat sails without a pull to the right, don't do anything. Unless you plan on using the engine more often than the sails, and at full power. I have only been on a handful of sailboats that don't behave in some sort of undersirable manner while motoring. Most rudders that have been designed to be balanced under sail don't react all that well to a localized stream of swirling water.
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Old 18-12-2009, 18:14   #24
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I agree w/ the monkey.

Prop wash effect and prop walk effect are two different things. You have the first, and it's just a function of the design of your boat. Mine does the same under power, but sails fine.
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Old 18-12-2009, 18:27   #25
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The engineer who was with me told me that this is normal behavior.
If he can't explain why in terms that make sense to you get rid of him. You hired him for a reason, expect alot, trust your intuition.
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Old 01-01-2010, 16:56   #26
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if strut is off center to allow shaft to be pulled past rudder that could be a factor
sorry didn't read much on your rudder or keel but that does happen when strut aims prop to on side of rudder
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Old 09-01-2010, 11:43   #27
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I own a 1982 Sabre 28 MkII with a Westerbeke 13 and offset shaft (to port) with a RH turning folding (Flex-O-Fold) prop.

This combination produces the most bizarre, yet predictable behavior when backing under power.

If I am motoring forward and throw the transmission into reverse while there is still way on the boat, the stern will walk to port.

If, however, the boat is at a dead standstill and I engage reverse, the stern walks to starboard.

This makes backing and filling impossible in the normal way. To get the stern to swing to port in reverse the boat must first be traveling forward. From a dead stop the boat will back to starboard, erasing any gain to port. It's weird, but at least it's consistent.
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