Starboard Weather Helm

[Noreastern]

After switching over from wheel to tiller on our full keel 38' Pearson Invicta we found that we had excessive weather helm on starboard tack. We also found that the key-way on rudder shaft is offset about 5 degrees counterclockwise when rudder is positioned straight. While motoring boat "pulls" to starboard and continues to do so after motor is put into neutral (eliminating prop wash).

We pulled the boat to clean bottom thinking one side may be fouled more then the other. We also verified the key-way (and hence tiller) offset. We also checked rudder with a straight edge and verified it was true and not warped. After cleaning bottom we still experience excessive starboard weather helm.

Starting to think these where problems either from when the boat was built or when the hull was damaged and repaired on port side in 1978. The key-way offset and weather helm problems both could be masted when boat had wheel steering.

Are we missing something? In September we are planning on a year long refit to prepare boat for full time cruising. However this may be a show stopper for using this boat.

Appreciate any thoughts.

[Noreastern]

This is the offset with tiller positioned straight.

[IdoraKeeper]

If you cannot see a hull or rudder issue with the boat...it may be your rig. All of my boats have a preferred tack. Idora sails better on the starboard tack...mostly because the galley is on the starboard side and she is a little stiffer on that tack.
Look for asymmetry in the rig.

Todd

[Noreastern]

Thanks Todd. Originally we tried different sail trim/combinations, center board up/down and making sure rig was true. However now understanding that boat is pulling hard to starboard in flat water on an even heel while motoring we believe it is a problem with hull/rudder form.

A small difference in the amount of of weather helm port/starboard I believe you can find on most sailboats. In our case it is a very large difference. We are talking weather helm that makes steering the boat on starboard tack in over 20 knots of wind almost impossible!

[frank_f]

If it's a full keel, could you not run a line (like a chalk line) from the forefoot to the deadwood just before the rudder on each side and pull it taunt? I would think that if there was a problem, it would be 'bowed' out on the starboard side causing a slower flow of water and pulling the keel in that direction. Or the port side is 'hollow' causing higher pressure on that side and pushing the keel to starboard.

That would show you the keel itself. You could repeat the process from the forefoot to the rear edge of the rudder (while in its neutral position) to see if the rudder is offset.

Might not work but it may show something less obvious.

[Noreastern]

Worth a try Frank. Boat has to be hauled next week for some estimates and will give it a try. Thanks.

[Adelie]

Asymmetrical prop wash is at least half of the problem when motoring.


Since the problem is bad when sailing to me is sounds as if your hull is not symmetrical.

I can see a number of ways to check this with the boat out of the water, all time consuming.

[frank_f]

Originally Posted by Adelie

Asymmetrical prop wash is at least half of the problem when motoring.


Since the problem is bad when sailing to me is sounds as if your hull is not symmetrical.

I can see a number of ways to check this with the boat out of the water, all time consuming.

What if the prop itself was slightly off to one side?

Not a bent prop shaft (although that is possible) but more of a misalignment where the motor, tranny, prop shaft and prop are all aligned but the entire setup is a few degrees off axis to the centre line of the boat.

[Adelie]

Originally Posted by frank_f

What if the prop itself was slightly off to one side?

Not a bent prop shaft (although that is possible) but more of a misalignment where the motor, tranny, prop shaft and prop are all aligned but the entire setup is a few degrees off axis to the centre line of the boat.

That would have some effect. Asymmetrical helm when motoring is mostly related to the down angle of the prop shaft, the blade on one side sees a different angle of attack to the water flow than the other blade. The effect is especially pronounced at low speeds.

If the boat pull hard on one tack when sailing, look at the keel shape or at the shape of the whole hull.

[Noreastern]

Scout's shaft is horizontal ( no pitch). Also it pulls to starboard even when engine is temperary put into neutral.

[frank_f]

Originally Posted by Noreastern

Scout's shaft is horizontal ( no pitch). Also it pulls to starboard even when engine is temperary put into neutral.

I was thinking of a possible angle if you were on deck looking down through the boat with your x-ray specs on .

The centreline of the boat and the centreline of the propulsion system might be out of alignment with the motor slightly to port and the prop slightly to starboard. The prop would then present more surface area to the starboard side and less to the port side even when the motor was off or in neutral. It would be a constant drag on the starboard side.

This is all speculation of course.

[pete33458]

I had this problem on my Hunter36 as well. Never did figure out exactly why, but my suspicion was that it had to do with differences in heeling due to uneven distribution of loads, especially fuel and water (which were on the same side). When mostly unloaded (except fuel and water), my boat listed noticeably, even in the slip. This would be expected to add to heel angle on one tack and subtract on the other, which would significantly affect weather helm. Again, I had no way of proving this (other than going through an exercise of trying to balance the hull...), but my question would be: does your boat list at the dock? pete

[Noreastern]

Pete,
Thanks for the response. Scout does list slightly to port on her mooring. It would make sense this would be less desirable on starboard tack. I have always thought this is due to the 16' wooden main boom most always being pulled over to port with a preventer while at dock or mooring. We will center boom and see how she lists this weekend. Lucky for us, we have two 40 gallon water tanks port and starboard so we should be able to adjust some if there is still some list. Will write back with results.