Yacht pulling to starboard

[Kerenza]

Morning.
Boat back in water yesterday. New featherstream fitted in place of LH volvo 3 blade folder.
MD2030D saildrive, deep high profile fin and rudder. 11.5m waterline, 3.7m max beam. Doug Peterson design.
During testing in the bay, zero wind and tide, the boat pulls off to the right under motor.
Apply 1deg of port helm cures it, but hands off the tiller and round in circles before you know it.
Helm feels just like rounding up under sail, lots of pressure.
Previously the most stable boat I've ever been on.
Original 17 x 11 now 16 x 12

K

 

[awol]

Change to a Yanmar and It'll go to Port!

 

[Moodysailor]

If the only change is the prop, then the 'smoking gun' is right there... ;-)

 

[Stemar]

Jissel did this constantly under power. Just something I got used to. I'd stand to starboard of the rudder and let it push against me, steering with the pressure of my leg. It really wasn't a problem once I got used to it.

 

[Kerenza]

It is the only change, but my suspicions were the increased pitch might be exacerbating a tiny misalignment previously undetected with the saildrive.

 

[anoccasionalyachtsman]

Firstly - hull cleaned, so not differential weed growth?

Secondly - presumably the rudder didn't get bent during the lifts?

Thirdly. The water going into the propeller disc arrives at different speeds due to hull drag - generally slow near the hull and in the keel's wake, faster near the bottom and sides. That means that the speeds of the water coming out of the disc vary, and because the outflow is now partially a rotating column you can end up with faster flow on one side of the rudder. The prop change has affected that. I can think of a few ways to fix it, but they're all relatively expensive. Unfortunately it's quite common.

 

[Kerenza]

I use hydrophobic silicon and have for quite a few years, new layer applied.
The new prop is closer to the saildrive than the volvo by about 10cm due to the hub being smaller.
Thus 10cm further from the rudder, which is roughly 2m astern.
Could be the horizontal column developing more I guess.

 

[Kerenza]

 

[dunedin]

Morning.
Boat back in water yesterday. New featherstream fitted in place of LH volvo 3 blade folder.
MD2030D saildrive, deep high profile fin and rudder. 11.5m waterline, 3.7m max beam. Doug Peterson design.
During testing in the bay, zero wind and tide, the boat pulls off to the right under motor.
Apply 1deg of port helm cures it, but hands off the tiller and round in circles before you know it.
Helm feels just like rounding up under sail, lots of pressure.
Previously the most stable boat I've ever been on.
Original 17 x 11 now 16 x 12

K

Every boat I have had will go off in a swerve under power if the helm is let go of. Seems to be a natural effect if the spinning propellor and the hull shape.
Engine on then autopilot on is second nature.

 

[johnalison]

Every boat I have had will go off in a swerve under power if the helm is let go of. Seems to be a natural effect if the spinning propellor and the hull shape.
Engine on then autopilot on is second nature.

It sounds normal to me. My saildrive pulls slightly to port. Mine is accentuated by the balanced rudder, meaning that the helm cannot be left while under power or the diversion will rapidly increase. Curiously, my boat pulled hard to one side under sail at the end of one season. There was no sign of damage and it disappeared after re-antifouling.

 

[Graham376]

When I replaced 2 blade fixed with 3 blade Featherstream on shaft drive, no difference in helm, still like it's on rails. Longer keel and skegged rudder though.

 

[Kerenza]

This is a new phenomenon, only since launch yesterday. Previously tracked really well.

 

[st599]

Could it be torque steering? The top of the propellor is in a lower water pressure than the bottom so small powerboats exhibit this all the time.

 

[Daydream believer]

View attachment 126405

Bavaria Have you checked if the keel is still there? Looks a bit bent in that picture. First sign of failure.

 

[Bilgediver]

It is the only change, but my suspicions were the increased pitch might be exacerbating a tiny misalignment previously undetected with the saildrive.

The increase in pitch could increase the paddlewheel effect!

 

[Kerenza]

Thanks all for the interest, a few things to consider, although I suspect its something to learn to live with or go back to Volvo prop. As long as the sailing performance isn't affected, I think the Bristol Channel will mask the motoring issue.
K

 

[Slowboat35]

My long-keeler went from being on rails to exactly what you describe upon - fitting a featherstream! At full speed holding the wheel is hard work.
I also get a great deal of rumbling from the prop area that increases with speed that no-one seems able to explain.

 

[jwilson]

Fascinating. My old long-keeler with a mighty 7 hp single cylinder Volvo with fixed three-bladed right in front of the large rudder pushing 8 tons had almost dead neutral helm under power. Current AWB with 27 hp fixed two-blader pushing not much more displacement, has constant slight helm presssure under power. Let go of the wheel though and you are thrown into a hard-on full-lock turn in about a second. I have always assumed it was the price you paid for being able to steer astern....

 

[Kerenza]

Slowboat 35, thanks . now you mention it I thought there was more rumbling particularly when waiting for the prop to grip when changing from ahead to astern, than I'd heard before, something I was going to pay more attention to on the next test. I wonder if this is a cavitation type of problem.

 

[penfold]

The prop vortice is most likely striking the rudder at a slightly different place than it did with the previous prop, further from the axis of the tiller stock increasing the servo effect. Live with it or fit a different propellor.