Tumblehome

[ESP]

I have been trying to surmise the advantages and disadvantages of increasing tumblehome on a canoe. It appears that by doing so the boat retains less water when executing a roll and potentially it is drier when running through river features. What do all you experts have to say? Looking for both advantages and disadvantages please.

[Cheeks]

I may be wrong - I often am - but I think think tumblehome actually acts as a scoop and brings more water in

[RobertM]

I have nearly zero experience in OC, (all my canoes need skirts), but from a theoretical perspective, for the same below water shape, (with no boat lean), maximum beam and hull depth, increasing tumblehome should decrease secondary stability. Also, again for the same max hull depth, it seems like it would make for a wetter ride.

John Winters (no, not the actor/comedian, at least I don't think so) gives a fairly straightforward explanation of this in his "The shape of the canoe". The book is aimed at flatwater design, but it makes interesting reading.

2 cents (at most) from somebody who likes boat math but doesn't paddle an OC1 (yet, my knees are starting to complain about the saddle in the C1)

RobertM

"One fish Two Fish"
"Red Fish Blue Fish"

[Bob P]

Tumblehome allows the advantages of a wider boat - stability, water shedding - without the disadvantage of the paddle shaft being pushed way off the boat centerline by the outside gunwale.

[pblanc]

Shouldered tumblehome, in which the hull flares out to a "shoulder" of maximum beam a few inches below the sheer line and then sharply recurves in to the gunwales, offers the advantages of a flared hull in that it sheds water well and has good secondary stability, but reduces the width at the gunwales. Since you often have the boat heeled a bit toward the side your paddle is on, the outside edge of the outwale often winds up directly above the maximum beam at the shoulder allowing your paddle stroke to be quite vertical yet still close to the hull.

Smoothly curved tumblehome as is found on a lot of Wenonah flat water boats tends to have a maximum beam just above the water line. That is OK for a flat water boat, but when you heel a hull like that and go past the point of maximum beam, the secondary stability disappears rather abruptly.

[RodeoClown]

I may be wrong - I often am

You are. ESP hit the dryness and rolling advantages of it. The disadvantage is it's makes it tougher to mold in some materials.

[eddyhops]

The three rotation motions of a vessel- pitch, roll, yaw

Traditional tumblehome can decrease primary/increase secondary stability and helps prevent swamping due to boat roll in seas/chop. However, wave blocking is less dry with traditional tumblehome... hence some of the progressive 'shouldered' tumblehome canoe designs... best of both worlds.

BTW, in canoe design it does help to not have to reach further out with the shaft for some strokes, but most powerstrokes should be vertical, eh?

Also, tugboats don't use paddles



Interesting historical perspective-

http://en.wikipedia.org/wiki/Tumblehome" onclick="window.open(this.href);return false;

[Cheeks]

I may be wrong - I often am

You are.

Ouch brah...what a stupid I am!

Oh well, last time I listen to the internetz before shooting my mouth off

[RodeoClown]

I may be wrong - I often am

You are.

Ouch brah...what a stupid I am!

Oh well, last time I listen to the internetz before shooting my mouth off

It is a bit counter-intuative- it seems like more tumblehome would scoop more water, but that's not how it works. The Ion prototype had less tumblehome, and scooped water like it was going out of style. With the gunwales pulled in, it rolls much drier.

[Bob P]

BTW, in canoe design it does help to not have to reach further out with the shaft for some strokes, but most powerstrokes should be vertical, eh? ...

Absolutely. But turning is caused by the distance the paddle is from the boat centerline. If the paddle isn't forced outward by the width of the gunwale, there's less (yaw) turning torque.

[TNbound]

Also, having the gunwhales closer together with tumblehome = less smashing of knuckles on them. I think that is my favorite part, although rolling up in my Option with about 4 inches of water is pretty nice, too.

[ian123]

It is a bit counter-intuative- it seems like more tumblehome would scoop more water, but that's not how it works. The Ion prototype had less tumblehome, and scooped water like it was going out of style. With the gunwales pulled in, it rolls much drier.

I would guess the side wall foam and other floatation help with the scooping. Does it still roll drier without side fall foam??

Adding MORE sidewall foam definitely makes it roll drier.