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Old 12-23-2011, 06:23 PM
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Default transom deadrise

so when a boat's specs are listed, a part of that is deadrise at transom. i understand deadrise but why is it important for the transom spec to be listed? does it directly relate to another spec, i.e. am i expected to relate that number to another measurement of deadrise somewhere on the boat? i understand that increased deadrise relates to an ability to operate easier in rough water but also becomes less stable when at rest in increasing seas.
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Old 12-23-2011, 06:32 PM
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People want to know what it is and when measured at the transom it can be easily compared to figures fr other boats.
It doesn't relate to another spec.
You're not to relate it to another measurement on the boat.

Figure I'd write these down to see if any calls BS on any of my answers.

Good luck,

J
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Old 12-24-2011, 05:25 AM
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Transom deadrise will affect the way the boat rides, and lands in the water. What most people dont realize is that the degree of entry and mid ship deadrise combined with the deadrise at the transom is what you need to pay attention to. That will give you a better idea of what the hull will do in any sea condition.

A shallow V at the bow will result in a bow happy boat that doesnt slice on plane.
A shallow V mid ship will pound at slower speeds.

Basically, if a boat was 24 degree from bow to stern, it would ride like crap at some point.
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Old 12-24-2011, 05:53 AM
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so just because a boat is spec'd at 22 degrees deadrise at the transom it doesn't directly correlate to the deadrise at the bow or mid-ship? why aren't those listed? without starting a "my hull is better than yours" war is there a general rule/range on amount of deadrise a boat in about the 25'-30' range should have to handle 2 to 3 footers without losing a filling in my teeth? i can handle some movement since my job requires me to be up and moving in a military cargo aircraft while scooting around at 250knots at 250 feet.
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Old 12-24-2011, 06:28 AM
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The only "consistant" way to compare deadrise is at the transom.

You could have 60 degree deadrise at the bow, and a flat bottom at the transom, and the boat would beat the hell out of you.

You could have manufacturers comparing "bow" and "midship" deadrise, but what exactly is "bow" and "midship"??? they would eventually bend the rules just like everything else.
They'd be measuring at wierd spots that gave higher numbers.

Just like the length of a boat. Does it include, brackets, pulpits, motors, etc...?

Transom deadrise is one of the few things left that can still be compared fairly on the specs of a boat, without the marketing guys screwing with the numbers.


You'll have to go ride the boats, and check the hulls yourself to get the real scoop on how that boat is going to run.
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Old 12-24-2011, 06:32 AM
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Originally Posted by ken2 View Post
You could have manufacturers comparing "bow" and "midship" deadrise, but what exactly is "bow" and "midship"??? they would eventually bend the rules just like everything else.
Therein lies the issue.
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Old 12-24-2011, 06:41 AM
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I agree with above commentary for planing hulls, but in general it is not that simple and it is a bit different for semi-displacement designs like downeasters. In fact, some lobster boats have zero deadrise at the transom but are considered the best sea boats of all. Beam, keel, speed, displacement, engine location, chines and many other factors determine the final ride.
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Old 12-24-2011, 06:45 AM
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Originally Posted by mackidaddy View Post
I agree with above commentary for planing hulls, but in general it is not that simple and it is a bit different for semi-displacement designs like downeasters. In fact, some lobster boats have zero deadrise at the transom but are considered the best sea boats of all. Beam, keel, speed, displacement, engine location, chines and many other factors determine the final ride.
very true.

I was just thinking of planing hulls.
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Old 12-24-2011, 08:02 AM
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Deadrise measurement at the transom allows a comparison point between boats.

The amount of transom deadrise indicates the amount of 'V', so the higher the degree
of deadrise, the more 'V' in your hull.

A high degree of deadrise helps the hull cut through waves, but at the cost of more
side to side motion. A lower degree of deadrise will be more stable, but will pound
more in a chop.

The deadrise at the transom is normally indicative of the hull's overall 'V' throughout,
so it is a good comparison point between boat hulls.

Only Sea Hunt, that I know of, gives deadrise readings of the transom, midships, and bow.
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Old 12-24-2011, 01:57 PM
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thanks for all the replies...
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Old 12-24-2011, 07:12 PM
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Default Deadrise

Yeah if your gonna be in 3'+ seas i dont recomend less than 22* on a planing hull. The Formula 233 offshores' are 24* My 1969 25' Atlantis is 27* with trim tabs and hard chines, she rolls a little more than i'd like on drift but can't beat it in a head sea. Smooooth! A 22* deasdrise, i think is a happy medium.
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Old 12-24-2011, 09:02 PM
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Transom deadrise is a good quick indicator but there is a lot more. Actually, the deadrise of the bow and middle sections are more important because this is where the hull first meets the waves, usually.
Other factors besides deadrise include how fine the bow is and deep the forefoot is. Too deep and the boat will bow steer in a following sea.
The shape of the midsections can be concave(dry but hard riding), convex(softer but wet) or straight(a good compromise) or even a combination.
Keel pads, strakes and chines are another factor to consider. These features generally add lift which increases speed and fuel economy.
An important factor often overlooked is the length to beam ration. A longer narrower hull will be more comfortable and fuel efficient. I think too many boats are too wide now IMHO.
Also, a heavier boat will generally ride better but will need more horsepower and gas.
As you asked, with some hulls, the transom deadrise can be carried forward generally to just forward of amidships where the deadrise increases up to the bow. A modified-v generally has a flatter transom deadrise and is used for heavier planning boats. A warped-v changes the deadrise constantly throughout the hull and generally rides at a more level trim angle.
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Old 12-24-2011, 09:33 PM
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Default hey Fireboat

Nice explination, My 25' is a 27* deadrise stern pretty narrow too. Wondering about addind a strake? It only has one strake on each side and hardchines. Being the DEEEP V it must sit low in water cruising. I think adding one would raise it and boost economy. Most have 2-3 strakes each side. Your thoughts?
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Old 12-25-2011, 12:09 PM
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I was talking to my buddy about how different boat hull bottoms are. I was cleaning the bottom of a 32 sea vee and the center lifting strakes stop half way back on the hull and it also has a flat spot that is 4 to maybe 6 inches wide starting about 3/4 of the way forward yet still has a 25 degree deadrise. So the deadrise is there but the flat part on the keep helps create lift along with the lifting strakes. And because the most inboard lifting strakes stop half way back the back of the boat squats more and stays in the water. The fountain was an entirely different animal with a 22 degree deadrise and the center part was actually extended down an inch lower than most of the hull to help create even more lift and of course the steps are a lot more involved. Lifting strake carry to the first set of steps etc.
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Old 12-25-2011, 01:39 PM
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The transom deadrise reveals quite a bit about the underwater shape of the hull, assuming you know something about the entry, and allows you to make certain assumptions about its potential performance. The deadrise indicates the amount of "twist" in the bottom since deadrise is never flatter amidships than at the transom (I know - never say never).

Therefore, 24 degree deadrise at the transom indicates a true deep vee - the softest high-speed ride in waves but with big power requirements and a snappy roll at low speed or rest. Generally, deep vees let you run faster in rough water but require a lot of power to plane and aren't very efficient or comfortable off plane.

Less deadrise generally equals a fair amount more twist in any boat with a fine enough entry to not slam in waves. Big Carolina SF boats are an example with transom deadrise angles ranging from maybe 10 to 20 degrees (more or less). Twist is a compromise between speed, comfort and fuel efficiency with none of the three being really outstanding but collectively, they are acceptable. Generally, less twist (deeper deadrise at the transom) makes a softer ride but takes more power and fuel. More twist (flatter at the transom) is potentially faster in smooth water with less power and less snappy at low speed, but is a harder ride in waves.

Zero or near flat deadrise at the transom coupled with a fine entry (like a lot of DE boats) generally results in good fuel efficiency but a lower top speed (at least in waves).

On the other hand, the differences between say, 18 and 20 degrees would be a lot harder to assess and you'd have to take all the other design features into consideration at the same time. Weight, beam, chine design, cross sections and other factors all have a big effect on performance and handling and have to be considered in your evaluation but in the big picture, transom deadrise angles suggest quite a lot about what the design was intended to do as well as what it probably actually does. And as the others said, transom deadrise is measured at a defined point, making it understandable and consistent from one design to another.
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Old 12-25-2011, 06:01 PM
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Default Another Question on the subject?

Maybe i'll star another thread for this....... Whats Your Deadrise At Transom? I;ve never heard or seen another boat wioth a 27* as mine has? So what about adding a lifting strake?
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Old 12-26-2011, 03:28 AM
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Quote:
Originally Posted by 19cape View Post
so when a boat's specs are listed, a part of that is deadrise at transom. i understand deadrise but why is it important for the transom spec to be listed? does it directly relate to another spec, i.e. am i expected to relate that number to another measurement of deadrise somewhere on the boat? i understand that increased deadrise relates to an ability to operate easier in rough water but also becomes less stable when at rest in increasing seas.
The standard accepted deadrise begins with deadrise at the transom. A "kinda sorta" number you can play with is deadrise at the transom, X 3 will give you a more or less V at entry.
Beginning in the early 60's, designers like Jim Wynne and Walt Walters, the "233", Carl Mosley "variable" Sea Craft, designed the 24 degree at the transom, and builders like Mr. Aronow "Damn Donzi", and Mr. Genth "Formula 233" made the 24 at the transom the hallmark as to offshore racing and offshore design that continues today. The same designs are still used.
It's all a compromise as to hull vs deadrise at the transom vs the customers intended use of the product. A 24 degree at the transom is not for everyone and that also has to do with the LOA of the hull your considering.
Measurement at the transom is also a way of keeping it all honest and straight forward. A way of offering true comparisons, hull vs hull.
A very worthy competitor of mine once had a larger hull that was very popular, sold well, but was horrid offshore. It had an 18 at the transom, was not a good offshore hull. Thus, some of the salesguys would not state the deadrise at the transom as an 18, they would do a smoke and mirrors offering the deadrise in a very confusing way bow to stern so as not to have to say it was an 18 at the transom.
As I said, there are compromises to be considered and there is no one deadrise at the transom that will satisfy everyone. Quite the contrary.
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Old 12-26-2011, 03:34 AM
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Quote:
Originally Posted by mike carrigan View Post
The standard accepted deadrise begins with deadrise at the transom. A "kinda sorta" number you can play with is deadrise at the transom, X 3 will give you a more or less V at entry.
Beginning in the early 60's, designers like Jim Wynne and Walt Walters, the "233", Carl Mosley "variable" Sea Craft, designed the 24 degree at the transom, and builders like Mr. Aronow "Damn Donzi", and Mr. Genth "Formula 233" made the 24 at the transom the hallmark as to offshore racing and offshore design that continues today. The same designs are still used.
It's all a compromise as to hull vs deadrise at the transom vs the customers intended use of the product. A 24 degree at the transom is not for everyone and that also has to do with the LOA of the hull your considering.
Measurement at the transom is also a way of keeping it all honest and straight forward. A way of offering true comparisons, hull vs hull.
A very worthy competitor of mine once had a larger hull that was very popular, sold well, but was horrid offshore. It had an 18 at the transom, was not a good offshore hull. Thus, some of the salesguys would not state the deadrise at the transom as an 18, they would do a smoke and mirrors offering the deadrise in a very confusing way bow to stern so as not to have to say it was an 18 at the transom.
As I said, there are compromises to be considered and there is no one deadrise at the transom that will satisfy everyone. Quite the contrary.

Why are you afraid to say Sea Hunt.
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Old 12-26-2011, 04:13 AM
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Why are you afraid to say Sea Hunt.
I was not talking about Sea Hunt.

Also, I dont do that, however, the hull I'm talking about was bigger than any Sea Hunt built, and was offered before Sea Hunt began production.

Deadrise is a great subject.

To me, there is nothing better than a 24 at the transom, conventional V, however, depending on the hull and the intended purpose of the hull, the LOA of the hull, the customer, a 24 at the transom could be the best choice, or the worst.

To me, that's what always makes deadrise at the transom a fascinating subject.

BTW:
We build 24 at the transom with all of our models at the moment. But, as much as we'd like it, everyone is not a Bluewater customer.
Beginning at Miami, maybe Stuart, we're introducing some Flats N' Bay that will include some 15 at the tranom. Inshore models, not offshore.
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Old 12-26-2011, 05:43 PM
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Deadrise also affects draft. Less deadrise will usually result in less draft. An 18 deadrise
isn't best for slicing through waves offshore, but it will most likely give you a nice shallow draft
for bay waters.

Some of the Hydra-Sports midsized boats seem perfect in that regard. With a 20 deadrise,
they still maintain a nice draft of only 15". If you fish shallow bays, that is a nice feature.
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