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  #21  
Old 04-01-2012
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Re: Windward performance

Quote:
Originally Posted by AdamLein View Post
Are you wondering about hydrodynamic effects on the leeward side, or aerodynamic effects on the weather side?

In the first case, if you're heeled over that far you have other problems. In the latter, I can't imagine it would have much affect on windage.
I am wondering about the hydrodynamic effects. For instance, does pronounced tumblehome produce a lift to leeward? Or maybe it helps the leeward hull side "stick" in the water and reduces leeway?

The boat with pronounced tumblehome I have sailed on is a Catalina 38 which points and goes to windward very well, and buries the rail (and of course the tumblehome) when there is sufficient wind. It seems to like that.

The tumblehome was part of an S&S race design as I understand it, so I am assuming it was done very purposefully. But why?
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Old 04-01-2012
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Re: Windward performance

Quote:
Originally Posted by kulokoo View Post
I am wondering about the hydrodynamic effects. For instance, does pronounced tumblehome produce a lift to leeward? Or maybe it helps the leeward hull side "stick" in the water and reduces leeway?

The boat with pronounced tumblehome I have sailed on is a Catalina 38 which points and goes to windward very well, and buries the rail (and of course the tumblehome) when there is sufficient wind. It seems to like that.

The tumblehome was part of an S&S race design as I understand it, so I am assuming it was done very purposefully. But why?
It may have been for looks, reminiscent of when tumblehome kept the weight of the cannons closer to the center-line and helped deflect cannon-balls. Not all design features are for performance. These links might help:
Tumblehome, stability, and performance

Boat Design Forums

From the link above:
"There are several advantages to tumblehome: as already mentioned, it reduces inverse stability; it allows outboard shrouds to be moved in relative to overall beam and thereby reduces sheeting angles; since a curved panel is stronger than a flat one for a given scantling, one can achieve greater strength with less displacement. The disadvantages are reduction in side deck area and a slight increase in tooling costs. Since offshore racing boats do not utilize outboard shrouds, one can only assume that the reduction in side deck area was a safety factor considered more important by the developers of a rule intended for crewed vessels. Brad"
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