Rudder balance

[MrChris]

Originally Posted by Cheechako

Any weight you try just added anywhere will just "leverage" the rudder. You wont know if the bouyancy is the issue unless you know exactly where to add that weight so it's neutral balance, but heavier than it was. Hard to explain!

One cubic foot of air is 64 lbs displacement. Are you sure 90KG (198 lbs) is correct? That would be over 3 cubic feet of rudder (if it was all air).

Still ...at 2 knots, water pressure will overwhelm any unbalance in the rudder I think. Water creates a lot of force. Try dragging a thin board through the water on edge, then with the broad side against the water.
JMHO!

No I have not checked my math because the test process will do that for me, and it is certain that the rudder weight (mass) is less than the water displaced. The 98kg is a guess at the displaced water at 1.5x.5x.1 which is around 0.1 m3 or 100kg. With the weight of the rudder underwater at around half of that, and allowing for the additional bit of weight above water, the uplift is around 45kg which, when it all goes one side, will certainly turn the boat at speeds under 2.5 knots.

[ilCigno]

Originally Posted by GrowleyMonster

Remove your tiller and see what happens. If there is improvement, then make a new, lighter tiller.

I certainly agree on this. If the laws of physics apply also on this boat, any weight in the tiller worsens the situation. I would recommend to make a tiller as lightweight as possible, i.e. made of carbon. Painted white of course.

[MrChris]

Originally Posted by ilCigno

I certainly agree on this. If the laws of physics apply also on this boat, any weight in the tiller worsens the situation. I would recommend to make a tiller as lightweight as possible, i.e. made of carbon. Painted white of course.

The tiller is not heavy relative to the rudder, and the situation does not change with the tiller standing vertically, ie, no weight to either side. This is a 3.5 tonne boat, the tiller could well be involved if it were a dinghy.