Tumblehome - why have it?

[mharrall]

What is the idea behind the 'tumblehome' feature that some open boat have?

Martin

[Dave Thomas]

My understanding is that it as least partly to facilitate solo paddling by making it easier (for a given waterline beam) to place strokes over the gunwales while sitting centrally. But there may be other reasons/plus-points?

I guess one minus-point is that, if the boat is edged far enough for the tumble-home to reach the waterline, secondary stability can become compromised!

Dave Thomas

[mharrall]

Thanks, that makes sense.

Martin

[Andy(verygrubby)]

I see Dave's point and I've heard the same thing, but this assumes that the shaft of the paddle is almost touching the gunwale, at a slight angle to the vertical. In reality, I thought the paddle shaft had to be vertical for the first half of the J-stroke. If it is to be vertical, you still have to clear 'the fat bit' at the waterline which means your top hand and the shaft is a few inches out from the gunwhale. This makes having tumblehome irrelevant surely ? I am inclined to think it might be more to do with secondary stability, but I'm not sure.

[Chris Bolton]

I'm not sure either but have 2 suggestions:

You get a greater waterline beam but the weigh to any gear in the boat is nearer the centre. This thought is prompted by the only other vessels I can think of with tumblehome, Nelson-era fighting ships, with heavy canons on the upper decks.

It allows you to get the paddle shaft very close to the waterline beam, without catching your bottom hand on the boat/gunwale.

I don't know if Jim Wallis reads this section of the board - we could do with a Naval Architect's view!

Chris

[Geoff Seddon]

What about "It looks right" usually a good test of design, or curves are stronger than flat sections. Beware, usually any post I make has the effect of killing a thread stone dead.

[Crofty]

Hi
Is it not something to do with edging the boat over so you still have a round hull shape in contact with the water.
Crofty

[mharrall]

Is it not something to do with edging the boat over so you still have a round hull shape in contact with the water

That also sounds plausible. Are there any level 5 open boater coaches out there that can give a deffinite answer?

Martin

[adrian j pullin]

Web search throws up these:

Tumblehome gives a narrower beam at the gunwales and allows for easier paddling, however stability will be decreased. [http://suoc.syr.edu/suoc/paddling/canoe_design.html]

The inward curve of the sides of some canoes is called tumblehome. It's used for two reasons:


1. Floppy materials like sheet aluminum need some curvature for strength. The alternative to tumblehome may be more ribs, hence more weight.

2. Tumblehome reduces the width of the canoe at the gunnels. Thus, you don't have to reach so far over the sides to paddle.
[http://gorp.away.com/gorp/publishers/ics/how_cano.htm]

Tumblehome and rough water do not mix. It literally guides waves into the canoe. However it does have its place as it allows you to place your paddle close to the hull when paddling which is the most efficient way to do it.
[http://www.hpcanoes.bizland.com/articles/equipment/hulldesign.html]

and about 500 others. All that I have read say some mix of the above.

[mharrall]

Many thanks. I suppose I could have done that myself, just lazy I guess.

Martin