Dead rise

How do I calculate the dead rise angle of my hull?

Deadrise is the vertical distance between a line horizontal to the keel of a vessel and its chine usually measured at the transom. You can measure it on the hard by laying a horizontal string from the keel out to past the chine using an iPhone or Android bubble level app or a real bubble level. Then measure from the chine down to the string.

Or just drop a measuring tape down from the chine and sight along your bubble level (or app) to meet up with the keel and note the distance from the chine.

It is also referred to as deadrise angle which can be measured with a protractor at the bottom of the keel at the transom.

David

Measure A and B
(Use a level to make sure the horizontal and vertical are true)

Calculate B/A

That is the tangent of the angle....then use a calculator, tangent table or website to calculate the angle.

Here's a website that will do the conversion from Tangent to angle:
http://www.rapidtables.com/calc/math/Tan_Calculator.htm#calculator

Donna said:

How do I calculate the dead rise angle of my hull?

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It's a moving target. In most cases the angle changes from bow to stern.

Why do you need to know?

If you have a smartphone, download iLevel or similar app.
Zero degrees is flat bottom. The bow is 50-60ish degrees. And check both sides in case the boat isn't sitting level.

Deadrise really has no "use" in a non planing hull...or a hull that only travels at displacements speeds. It is the angle defined by those above. But it is stated in literature and as a selling point for boats that can plane. It is usually a measurement that helps define how much better a planing boat will ride in rough conditions.

Ideally a boat would have a completely flat bottom. That is the most efficient hull form for a planing boat. More planing area...lifting surface. Obviously, a flat boat does not ride well when the water gets rough so we introduce "V"...or deadrise. Deadrise acts counter to lifting surface so you are losing efficiency but it is necessary to smooth out the ride on a planing boat. Large sportfish boats have tons of deadrise carried all the way aft. It is one of the reasons why a sportfish may have 5000hp and still "only" top out at 45 knots.

Deadrise in a boat like yours may cause your boat to have less "static stability"....static stability meaning its initial tendency to remain stable. A completely flat Marine Trader hull will resist roll(at rest/at the dock) more than one with a little deadrise. But that is the only use for that measurement on a hull like yours. Again, it is the "V" measured at the transom.

Way more than you wanted to know????....

I just googled "what is deadrise" and this was the answer....I was damn close!!!

<<Deadrise is the amount of V-shape on the bottom of a boat’s hull, measured in angles at the transom of planing powerboats. In general terms the larger the degree of deadrise the more V-shape of the hull, so a flat bottom boat will have a deadrise of 0 degrees, while a boat with 24 degrees of deadrise will have a deep V hull.
In terms of performance the greater the V-shape the better the boat will slice through the waves. The shallower the V the more it will push over them. So a big deadrise is better for rough water conditions and a small deadrise is better for smooth water. The more a boat slices through the waves the more energy it will use. Thus boats designed for rough waters have a greater degree of deadrise and are slower. Boats designed for smooth water have a lower degree of deadrise and are faster. For example, a ski boat designed for speed and water sports, used on a lake will have between 10 and 17 degrees of deadrise. On the other hand, an offshore sportfishing boat used on the gulf stream off the coast of Florida will have a deadrise greater than 20 degrees.>>

Baker wrote;
"Deadrise really has no "use" in a non planing hull...or a hull that only travels at displacements speeds."

There are lots and lots of FD flat bottomed boats both sail and power. There are very few boats considered dories that are not flat bottomed .. w no deadrise.

But deadrise has nothing to do w fore and aft lines. Only transverse across the bottom. And it's true a flat bottomed boat is usually not associated w seaworthyness but one of the most seaworthy boats ever has no deadrise and is flat bottomed. That's the St Piere Dory. The Skipjacks may be another.

Nomad Willy said:

Baker wrote;
"Deadrise really has no "use" in a non planing hull...or a hull that only travels at displacements speeds."

There are lots and lots of FD flat bottomed boats both sail and power. There are very few boats considered dories that are not flat bottomed .. w no deadrise.

But deadrise has nothing to do w fore and aft lines. Only transverse across the bottom. And it's true a flat bottomed boat is usually not associated w seaworthyness but one of the most seaworthy boats ever has no deadrise and is flat bottomed. That's the St Piere Dory. The Skipjacks may be another.

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Eric, I put the word "use" in quotations for a reason. I was not saying that full displacement boats cannot be flat. I was just saying that it is not a selling point like deadrise is on a planing boat. IOW, NO ONE talks about deadrise as it relates to a non planing hull. It is a term strictly related to a planing hull and somewhat of a marketing term.

You still need to know the deadrise angle in a displacement boat if you are going to install tilted transducer for a depth finder. I have a digital angle gauge that I have used to measure the angle on my boat. I find a level surface by the boat and zero the gauge. Then measure the same place on both sides of the boat and average the 2 measurements. That way if the boat is hanging in the hoist unlevel, you will account for that by measuring both sides and averaging the results.

I had never seen the level apps for an iphone...thanks to this thread I have a cool new app on my phone !!

I installed a depth finder today with the help of Home Depot. They actually sell a digital angle level!

Pulling wires tomorrow!

But you could have used a free app !!! The app would also telll you how far your boat is heeling over !!

Donna said:

I installed a depth finder today with the help of Home Depot. They actually sell a digital angle level!

Pulling wires tomorrow!

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Ah, in that case you want to measure the dead rise at the point you're going to install the transducer, which I assume you did, not at the transom.

Capt.Bill11 said:

Ah, in that case you want to measure the dead rise at the point you're going to install the transducer, which I assume you did, not at the transom.

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Yes absolutely! And now I have a new tool to add to my collection! I can see further use in the future.

Obviously, and more comfortably, you can measure the deadrise from inside the hull where you want your transducer. A couple blocks of wood (for shims) and any level will do the job. Measure 12" from the end of the level resting on the hull and then straight down to the hull. You could also simply trace the level with a bit of cardboard sitting on the hull and use that template to make your mounting blocks.

Although, a good excuse for a new tool is always welcome.