Angus, I’ve noticed that you favor tumblehome in your designs. Could you tell us what advantage you see in it?
Thanks…Bill H
Angus, I’ve noticed that you favor tumblehome in your designs. Could you tell us what advantage you see in it?
Thanks…Bill H
OK – take a very deep breath.
Premises:
Given this we need a hull that does two things
Achieving (1) means that we must maintain the full waterline length as the boat heels rather than rolling the ends (particularly the stern) out. Reducing the waterline beam with heel helps reduce heeled drag. For obvious reasons, tumblehome reduces roll out.
(2) is closely related. We must not trim head down with heel (or no more than we can avoid). This generally means a narrowish stern and a fullish bow. It is easier to get the volumes right with a fair hull shape if we go along with tumblehome amidships. This is not easy to explain, but if you try drafting a hull of this type you will very quickly see what I mean.
Please note that with Footys (overall length rule) this applies only with relatively fat, heavy boats. The much lighter, narrower Freedom and Prometheus designs that are about to escape from the drawing board have slight flair throughout.
Thanks Angus…well articulated and understandable. Your point about midship volumes on wider boats is well taken. I may play around with the tumblehome thing a bit more myself. I’ve used it on a couple of Stollery-inspired designs, but not in a really thoughtful way.
BTW, I have achieved a state of tune on my Razor and American Footy that will sail hands-off to windward for long enough that my Footy is farther away than my comfort level. They hunt the wind, occasionally luffing slightly, then bearing away slightly to continue. Admittedly, this is in reasonable wind conditions…it doesn’t work in reallly gusty winds. So it might not yet be perfect, but it’s pretty darn good.
Bill H
One thing I probably should have added.
Quite apart from the fact that I think a Footy should essentially sail like a vane-steered or totally free sailng boat, I have a reason for being careful about lift out of the stern. The ‘Mariner’ type immersed transom is probably a tetchy brute. If we’ve got it right in a particular design, I don’t want to complicate matters by roll-out or head trim. if we’ve got it wrong, we’ve got it wrong!