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Hull comparison

Old 03-01-2007, 07:34 PM
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Default Hull comparison

The hull I have now has a 60 degree entry, variable to 18 degree with a pad at transome.
This boat I'm looking at has a 70 degree entry and 19 degree constant deadrise.
What handling differences will be noticed and how much will the fuel mileage suffer with the constant deadrise?
Thanks
Ken

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Old 03-01-2007, 07:59 PM
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Default Re: Hull comparison

i am not very farmiliar with this type of boat. generally, how does she ride in rough water
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Old 03-01-2007, 08:05 PM
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Default RE: Hull comparison

What lenght and beam on each boat?
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Old 03-01-2007, 08:55 PM
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Default RE: Hull comparison

Length on the existing boat is 27 ' with 9ft beam.
Contemplated boat is 29 ft with 9'6" beam.
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Old 03-02-2007, 03:12 PM
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Default RE: Hull comparison

Hey guys
Don't be afraid to comment because they are Aluminum pilot houses and rare in most places.
The info I'm interested in is the comparison of the Variable and constant deadrise hulls.
Lets hear your thoughts.
Ken
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Old 03-02-2007, 03:37 PM
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Default Re: Hull comparison

I would guess that you fuel consumtion and handling would be about the same if the boats weigh the same. One degree is nothing and they both have a pretty flat running surface in the back. If you tab the bow way down I'm sure the 70 degree will slice better.
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Old 03-02-2007, 03:38 PM
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Default Re: Hull comparison

Some believe that constant deadrise is more efficeint than a modified V where the ultimate deadrise at the transom is the same. I think the reasoning behind that is - if both bottoms end up at 19 degrees at the transom for example, the modified version has progressively more surface area going forward by virtue of the changing deadrise. In your case, it's tough to quantify becuase your current modified bottom ends at 18 where the constant vee ends at 19. Thats so close , and there are so many other variables like the boats size, weight, power, center of gravity, lifting strakes, at what speed your running, running angle (how much of the hull is in the water) YADA YADA... it would be an outright guess to say I had any idea if they'd feel different or the same.

I do beleive hull design has progressed somewhat and when Ray Hunts constant dearise deep vee hull made history, it was a proven and well earned achivement in offshore racing hull design. I don't think it's the best hull form for every boat application, but it still has it's place. Likewise, there have been a few noteable hull designs that promised a lot and have not achieved the same historical acceptance - like the Deltaconic, warped plane etc. I believe hull design is part science and part art... You can calculate somethings but others just have to be seen and felt.
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Old 03-03-2007, 11:25 AM
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Default RE: Hull comparison

Jav
Wouldn't you also have a steeper deadrise with the variable at midship, creating a better head sea ride?
Also the pad should aid in planing and efficiency, no?
I don't think I have a perfect understanding of the differences, I thought there would be noticeable differences.
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Old 03-05-2007, 10:49 PM
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Default Re: Hull comparison

It is likely that at some point going forward, the deadrise will be the same and then the modified V will indeed have more deadrise beyond that point. How that impacts ride depends on a lot more than just the deadrise (I believe) since the boats wetted surfaces change dynamically with speed. One of the limitations with modified V designs (not likely the case here as 18 deg aft is still pretty substantial but) some modified V boats (like mine) that have an aggresive entry angle and a modest transom deadrise, can bow steer in some headsea conditions if the stern gets light, or is too far out of the water due to tabs. There's always more variables at work than just deadrise or hull form. For example, how much weight is forward in relation to the bows entry/bouyancy. Not to offend any Blackfin owners since I think they are pretty incredible sea boats but, a few years ago I was talking to a captain that just wasn't used to the very steep entry angles and heavy nose on his recently acquired BF 32. The boat rode great but in a big head sea, and at certain speeds, the nose would submarine since the relationship between forward weight and entry angle (which really smoothed out the ride), wasn't what he was used to since he came from boats that had lighter and more heavily flared bow sections that rose quicker to meet oncoming seas. It really freaked him out and to this day, I think he's the only one I've ever heard complain about a Fins seakeeping abilities. Thats why I say somethings are science and some are art... I cetrainly don't know enough to give you any real idea of how the two hulls will differ. I would suggest they will be more similar than you think and that what differences there are, will likely be negated by your experience running one or the other.
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