Laminar Flow
Well-Known Member
Going downwind in a following sea is the most difficult course to steer. On the wind a boat is inherently aerodynamically stable. Downwind the rolling forces and those of a quartering sea can easily put demands on the rudder that are 300% above normal. Some rudders are not able to cope with this and beamy boats are more likely to experience an imbalance when heeling (rolling).
I do not know how efficient your rudder is, but we had all the same issues with our boat which has similar design characteristics to yours and they have been solved.
These included excessive (uncontrollable) weather helm and very high rudder angles that would lead to an early stall of the ineffective rudder profile.
Once we had modified the rudder and deadwood, even our 40 year old decrepit rags were able to cope with what was an inherently unbalanced sail plan.
Last year we added a bowsprit and increased our sail area to well over twice that of the standard model. She now will self steer to windward without us having to touch the helm.
Downwind we ran for some 70miles under spinnaker and mizzen in a rising and quartering sea with our old wheel pilot at the helm. We were doing well over hull speed and it was blowing between 25 and 30 kts. The max rudder correction when the steep following seas caught us was under 4 degr.
To increase lift in an existing rudder and without modifying it you have 2 variants: angle of incidence and speed. Lift increases with the square of the speed. Rudder angles over 5 degrees are slowing you down. I might pay to have a long, close look at the rudder profile and deadwood/rudder gap and transition.
Also, it has been often found that cutting out the turbulence generated by a fixed prop over the rudder, by switching to a feathering or folding type, has either removed or lessened the effects of persistent weather helm.
If you have trouble steering downwind with just the genny set, perhaps you need to increase your speed.
The bagginess of the sails has no bearing on weather helm when going down wind.
The Spray design has been made to sail with any number of rigs and ol' Josh's sails would have been super baggy by contemporary standards. The Spray model, with it's blunt, buoyant bow and easy run should be the perfect candidate for fast downwind runs and a number of replicas have been clocked at over 12kt doing just that.
I used to own a large cruising cutter and the key to performance was the correct setting of the stay sail. It is very easy to oversheet this sail and the correct trim is not necessarily intuitive. I found this would noticeably increase crease weather helm and make the boat cranky. Downwind I found the rig less effective as one or the other head sail would end up being blanketed.
On the wind. To move CE forward, try flattening the main, take some rake out of the mast or even rake it slightly forward, if you have to. Open up the stay sail just a bit more than you might think is right.
Generally sails should be trimmed for performance rather than purely for balance. Conversely, it has been argued that an imbalanced boat can't be fast.
A boat as beamy as a Spray probably wants to be sailed upright.
Some pics of her underwater configuration and rig might be helpful.
I do not know how efficient your rudder is, but we had all the same issues with our boat which has similar design characteristics to yours and they have been solved.
These included excessive (uncontrollable) weather helm and very high rudder angles that would lead to an early stall of the ineffective rudder profile.
Once we had modified the rudder and deadwood, even our 40 year old decrepit rags were able to cope with what was an inherently unbalanced sail plan.
Last year we added a bowsprit and increased our sail area to well over twice that of the standard model. She now will self steer to windward without us having to touch the helm.
Downwind we ran for some 70miles under spinnaker and mizzen in a rising and quartering sea with our old wheel pilot at the helm. We were doing well over hull speed and it was blowing between 25 and 30 kts. The max rudder correction when the steep following seas caught us was under 4 degr.
To increase lift in an existing rudder and without modifying it you have 2 variants: angle of incidence and speed. Lift increases with the square of the speed. Rudder angles over 5 degrees are slowing you down. I might pay to have a long, close look at the rudder profile and deadwood/rudder gap and transition.
Also, it has been often found that cutting out the turbulence generated by a fixed prop over the rudder, by switching to a feathering or folding type, has either removed or lessened the effects of persistent weather helm.
If you have trouble steering downwind with just the genny set, perhaps you need to increase your speed.
The bagginess of the sails has no bearing on weather helm when going down wind.
The Spray design has been made to sail with any number of rigs and ol' Josh's sails would have been super baggy by contemporary standards. The Spray model, with it's blunt, buoyant bow and easy run should be the perfect candidate for fast downwind runs and a number of replicas have been clocked at over 12kt doing just that.
I used to own a large cruising cutter and the key to performance was the correct setting of the stay sail. It is very easy to oversheet this sail and the correct trim is not necessarily intuitive. I found this would noticeably increase crease weather helm and make the boat cranky. Downwind I found the rig less effective as one or the other head sail would end up being blanketed.
On the wind. To move CE forward, try flattening the main, take some rake out of the mast or even rake it slightly forward, if you have to. Open up the stay sail just a bit more than you might think is right.
Generally sails should be trimmed for performance rather than purely for balance. Conversely, it has been argued that an imbalanced boat can't be fast.
A boat as beamy as a Spray probably wants to be sailed upright.
Some pics of her underwater configuration and rig might be helpful.
