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Steering while running under Engine

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Lippe View Drop Down
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Joined: 05 September 2009
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lippe Quote  Post ReplyReply Direct Link To This Post Posted: 04 November 2023 at 11:29
Panos had already referred to reason to tendence for boat turning while under engine. Lower part of propeller turns the boat more than upper part. In bigger propeller the effect is bigger. If the boat goes straight probably the S-drive installation is not straight and compensates the propeller walk. 
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WEmmens View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WEmmens Quote  Post ReplyReply Direct Link To This Post Posted: 05 November 2023 at 09:10
Though this a rather old topic: Since new we had the same issue and also while sailing the boat still had a slight tendency to turn to starboard. After about 3 years I got fed up with it and it appeared that the port and starboard side of the rudder had a different profile. 
I had a new rudder made by a specialist in the Netherlands and now the steering is perfect (apart from some prop wash).
Happy steering
Wilko
Hanse 400, Mona Lisa, #337, 2007, Yanmar 3JH4E, Flexofold 3bl.
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landlocked View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote landlocked Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2023 at 17:13
It was interesting reading the accounts in this thread.   I've always had this tendency to turn to starboard under engine power (both with a 3-blade folding and 3-blade feathering prop).   I never wondered why because with the asymmetry of a single rotating prop it seems natural and would be surprising if the boat didn't have a bias (as with prop walk in reverse).   Since the propeller sends a spiraling slipstream back over the rudder I expect the upper and lower parts of the slipstream washing over the rudder don't just happen to balance and cancel each other out, so it tends to turn the rudder.   Once the boat starts turning it requires a counter-force on the rudder to bring it back to a straight course and if your hand is off the wheel it seems natural that the boat will just keep turning.  So I was surprised to read that some boats with the same hull, prop, and saildrive don't see this effect!  Some posts suggest it could be an asymmetry in the rudder but I have no such effect when sailing in light winds - I can let go of the helm and the rudder stays centered and the boat continues to track straight.  Incidentally, single engine aircraft have to turn their rudder during takeoff to compensate for the propeller slipstream pushing against one side of the rudder.  As their speed increases this effect on aircraft is diminished but on our boats I think the propeller slipstream is always a significant part of the flow across the rudder.
"Kerkyra" 400e #042
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Lippe View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lippe Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2023 at 17:55
Hi Landlocked. My theory like wrote above is that if the boat does not tend turning under engine the s-drive installation, and consequently the propeller thrust,  is not exactly inline with boat centerline generating compesationg force to propeller walk.
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landlocked View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote landlocked Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2023 at 21:58
Hi Lippe:  It would seem remarkable to me if an offset in the saildrive placement would manage to nicely balance the bias caused by the propeller wash; but I can't think of any other theory to explain how some boats of this design stay on a straight course when the helm is released.
"Kerkyra" 400e #042
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Arcadia View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Arcadia Quote  Post ReplyReply Direct Link To This Post Posted: 07 November 2023 at 00:49
I think a sail drive has less of an effect on steering since the prop is much closer to the keel than the shaft drive prop. This would give the sail drive considerably less leverage to turn the boat compared to a prop which is further aft with a longer lever arm to act on the hull.
Leon / ARCADIA
2018 Hanse 588
Sag Harbor, NY
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Lippe View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lippe Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2023 at 14:53
Hi Kerkura,
I didnt mean linear offset but an s-drive/propeller thrust angle compared to boat centerline generating force component left/right.

Hi Arcadia,
Maybe I didnt understand what you mean? I mean S-drive with the propeller. >Arnt propeller walk and thrust components of the propeller born from the same distance from keel.
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Arcadia View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Arcadia Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2023 at 15:19
I believe that in all these cases it is the boat which is turning the rudder, not the other way around.  The turning force is generated at the propeller. The further aft is is, the stronger the turning force will be. The hull generally pivots about the keel. 
Leon / ARCADIA
2018 Hanse 588
Sag Harbor, NY
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Lippe View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lippe Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2023 at 15:30
I partly agree but we talk about slightly different issues here.
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