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Old 28 January 2008, 11:24   #1
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Transom Deadrise

Hi,
sorry if its a stupid question but i'm sure it'll neither be the first nor the last here.

My understanding of transom deadrise is the angle from the center of the transom going up from horizontal. Horizontal being zero.

I've been told that the Humber Assault is a medium-v hull and that the Destroyer and Ocean Pro are deep-v. However, i've read and since measured the the hull of my boat, an Assault, and the deadrise is 30 (if i've measured & read correctly), wheras the Ocean Pro and Destroyers are 25.

So what is the deadrise ? Are people confusing the comfort of a ride with depth of V or are there things that i'm missing?

PS. I realise that the depth of the V is not everything and that setup and tube height play a large part in going over waves at speed.
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Old 28 January 2008, 12:27   #2
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This is how I understand things:

Deadrise is measured at the transom. You are correct; it is the angle off horizontal that the bottom of the transom rises from the keel to either side.

The V part of it has to do more with the front of the hull; a deeper will have a "sharper" hull than a shallower V. Pretty much all modern boats have a variable V if you measure not just at the bow, but progressively back towards the transom.

Higher deadrise numbers will give a softer ride, but will roll more when stopped, and require more power to plane.

jky
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Old 28 January 2008, 12:49   #3
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heres a sketch of my understanding. the angle alpha in the picture would be the deadrise measured at the transom.

humber actually claim the assault is a deep V (although I am not sure there is a definite opinion on what angle is definitely deep and what is not). http://www.ribworld.co.uk/assault.html
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Old 28 January 2008, 13:57   #4
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I wouldn't call the assault a Deep V by any stretch of the imagination although the biggest problems with the hull are more the low sheer and low bouyancy of the bow combined with a relatively shallow hull.
It is Dam**d hard into any kind of chop r wave, speaking from experience.....
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Old 28 January 2008, 15:16   #5
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I thought I read somewhere that shallow V was less than 15 deg, medium V was 15 to 20 and anything over 20 was deep V but I can't remember where I saw that now.
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Old 30 January 2008, 04:26   #6
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Quote:
Originally Posted by BruceB View Post
I wouldn't call the assault a Deep V by any stretch of the imagination although the biggest problems with the hull are more the low sheer and low bouyancy of the bow combined with a relatively shallow hull.
It is Dam**d hard into any kind of chop r wave, speaking from experience.....
Maybe you should measure it. Humber claim that its 30 and thats the angle I came up with. I'm not saying that it's not a hard ride. I've not even tested it in any waves yet and i've not got enough experience to make any real comparisons. I'm not even trying to defend my boat. But I think that we too easily decide that a hard ride is a shallow V and a soft ride is a deep one when there are obviously plenty of other parameters that come into play.

That said, what is a "low sheer" ?
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