Bill's question of the day: Why do H14s and H16s rake their

[DanBerger]

Bills comment from another post:

"Relative to your first statement, question of the day: Why do H14s and H16s rake their masts so far back?"


I have heard many explanations, but the way it 'feels' to me on a Hobie is that it moves everything back on the boat. By that, the pivot point of the hulls is farther back and you tend to pitchpole less--but you have to sit farther forward or you will go over backwards and sailing at the back of the boat is very slow.

I have a feeling that it really has something to do with the bannana shape of the hulls and the lack of forward buoyancy.

I can tell you that they point MUCH better than with a straight mast, but downwind performance suffers.

The windurfers sail upwind with their sails pulled (raked) back very far, too.

[Bill Roberts]

Hobie 14s and 16s and windsurfers are all doing the same thing. They are moving the CE in the sail closer to the rudder. This forces the rudder to be loaded somewhat like a centerboard. The rudder is a much more efficient sideways lifting body than the hulls. Therefore any side load that can be transferred to the rudders is less side load on the hulls and they make less drag. The hulls are lousey side force generating shapes. The 16's underwater aspect ratio is roughly 6 ins deep by 15 ft long or 1/30. Dagger boards 3ft deep by 1ft wide have an aspect ratio of 3.0. In the induced drag equation, aspect ratio is in the denominator. As you can see the H16 induced hull drag due to generating a side force equal and opposite to the sail side force will be several times greater than a centerboard boat. This is why it is such a large benefit to get the rudders to carry even a little bit of the hull's side force. This also makes H rudders have a strong tendency to stall. What can I say; it comes with the terrtory.
Bill

[SC15Av8or]

So then why not rake the mast on the Supercats then Bill. Or was that all taken into consideration with the shared lift concept ???

[Bill Roberts]

That's right Grogman. Shared lift designed the hulls on all SC boardless boats. It is also why the SC15 and 17 have such large rudders, steering centerboards. The SC15 and 17 are also the source of "drive them bows" expression. The the bows on the 15 and 17 generate 50% of the side force for sailing to windward. If the sailors on the boat are sitting aft on the boat with the tramsoms down and the bows up, the boat is not going to sail to windward very well.