deadrise

Is deadrise measured at the transom or throughout the hull?

 

deadrise means the deadrise of the floors. it can be given anywhere from frame one to the transom, but usually people commonly say transom, a boat may have a very shallow dearise aft and very deep v entry so you cant say a deep vee at stern will necessarily be deep at the entry. flatter sections aft help th boat , esp, downwind and weather

 

...yes, as LJ suggests, whilst the deadrise can be given for any section of the bottom, if it's not otherwise stated, then it's usually at the transom.

 

Thanks guys.

Can the deadrise be the same for say more than half the length of the hull. Will the hull on a convex vee be stronger than a straight or concave vee.

 

Yes, the deadrise can be as consistent as you want, or even reverse, or whatever. That doesn't mean that all ideas work well. A hull that is 'prismatic' or a 'monohedron' has a consistent deadrise from near the transom to somewhere near the forward waterline when on plane. You see this on a lot of river boats for example, but they tend to pound too much in a big chop. A 'warped' or 'modified V' (and we're getting into semantics here) has a higher deadrise forward which continually transitions to a lower deadrise as you go aft. Sometimes all the way to a flat bottom at the transom. An easy way to get a feel for what a particular hull has is to look at the amidships deadrise versus the deadrise at the transom. For example, one boat that I know of has a 17 degree deadrise at amidships and 12 degrees aft, while another has 14.25 degrees amidships and 13 degrees aft. The first hull is warped to a certain extent while the second is closer to being a prismatic hull. Which is better depends on the intended operating conditions (warped hulls quite often work well offshore) and what the deadrise values are (prismatic hulls with higher deadrise can work just as well.)

In answer to your other question, yes, a convex hull form is typically stronger (other factors remaining equal) than one with flat or concave sections ...but it doesn't really matter. You can design around anything you want and have adequate strength. The bigger issue is how the various shapes _work_ in the intended operating conditions.

Brian

 

I'd have to disagree with Brian regarding the suitability or otherwise of constant deadrise boats for offshore work. Indeed, one of the original constant deadrise boats was that developed by Ray Hunt - the deep v, which swept away all the (warped plane) opposition in offshore racing in the mid 60's.
In theory, a warped plane hull will suffer from greater resistance than a constant deadrise hull, due to the way in which it must "twist" the water as it travels aft. However, in order to exhibit any reasonable seakeeping ability, a constant deadrise hull will generally have greater deadrise throughout the aft sections, so will require more power to travel at a given speed.
On practice, warped plane, low deadrise hulls are better suited to low to medium speed work. The faster you go, the greater the advantage that the constant deadrise hull will have.
But as Brian quite correctly points out - there are good and bad examples of both!

 

Actually we agree completely ...but in my already too-long post, I didn't bother to cover different examples.

Brian