Hull Design vs Powerplants vs Weight etc.

[Carver370]

It was recently brought up in another thread by another member when discussing similar power in very different boats while they still make the same cruise speed and fuel consumption.

This is a quote from that thread:
390x Wrote:
"I've had 4 boats with Mercs, and one with Crusaders. The Crusaders are better engines, period. I just rebuilt a pair two winters ago, and they truly were better engines to begin with. On big blocks they're only 4-bolt mains, have better gasketing and forged pistons. On mercs, not all are 4-bolt mains and forged pistons. Go to yachtsurvey.com and see what Pascoe has to say about the Crusaders vs the Mercs. He's definitely a fan. My parents have an '87 38 Carver and it has been an absolutely fantastic boat. I know that they're 87 38 Carver has many things that are better than my 39. I would love to have it explained to me how their 28,000 pound boat with a keel can have basically the same engines as me, swing 24" props (handles fantastic), go basically the same speed as me at WOT, and get basically the same fuel economy. Meanwhile I weigh maybe 18,000 pounds, only swing 20" wheels (handles like sh*t) and have no keel. Point being they got it right, and Sea Ray didn't. You'll like the Carver very much. They make a good boat, and they can go out in anything that a comparable sized Sea Ray can. It also won't be any tipsier than any other bridge boat of the same size. "

I should say that this thread is NOT intended to be a brand vs brand bashing post, but more of an education for those who may not have run a different style boat than they may own. It also should be informative to show how different hull designs net different handling qualities, fuel efficiency, or speed. For instance, an aft cabin (of any brand) isn't always a dock queen or intended for small inland lakes or rivers.

I intend on taking some pictures tomorrow of some different hulls outside my office that I know the particulars on and it would be interesting to see what people think of the different hull designs and what their characteristics would be. I hope to have a pretty diverse crowd.

Hydro-dynamics fascinate me, and the post 390x made confirmed I am not the only one noticing this. My boat for instance fits the above statement exactly.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

Bring on your thoughts as to what brands these boats are or styles.

 

[Carver370]

Pics added.

 

[390x]

Well, I can start by saying I hate prop pockets. I understand that they result in reduced shaft angles, and lower draft, but they just absolutely kill performance. Again, I can reference the weight disparity between my boat and my parents boat, but WOT performance that is basically the same. Also, because of the pockets, I have small props which result in much greater prop slip. At 1500 RPMs, my boat is only turning about 7mph, and it's wanting to start planing. They're about 9mph at 1500 rpms. It also wants to fall off plane at anything less than about 3400. Theirs starts planing at 2200, and will hold plane with full tab all the way down to about 3200. That means they can run at trolling speed much better, and quicker than I can, and then hold plane at a lower speed than me, with a much, much larger boat, and the same power. I'd gladly give up my reduced draft to have the performance characteristics that they have.

 

[390x]

Also, without knowing exactly what they are, boats 1,4, and 9 would be vastly superior rough water boats, at least when heading into big seas with the sharp entry they all have. At least they'd all be much better than mine!

Also, #3 is an odd hull. I've never seen lifting strakes that go parallel to the keel instead of the chine like that. I'm not sure exactly what that would do. The whole point of strakes is to provide lift, and reduce suction by stopping the water from traveling up the hull.

 

[Henry Boyd]

It was recently brought up in another thread by another member when discussing similar power in very different boats while they still make the same cruise speed and fuel consumption.



Hydro-dynamics fascinate me,
Bring on your thoughts as to what brands these boats are or styles.

Suggest you get a copy of "Principles of Naval Architecture", Volumes I, II and III from the Society of Naval Architects and Marine Engineers. I don't know what the current revision is, I acquired my copies in 1988 when they were revised by the Society. I have not seen any notices of an updated version. The original version was published in 1939 and the first revision was in 1967, so the 1988 revision may still be the most current.

They are tough sledding though, the calculus is pretty involved. The reason that math is complicated is that the subject matter is complicated. There are many critical inter-related factors. As a result, eyeballing a hull form is not a realistic method of performance analysis. (Unless one also measures automobile performance by the number of chrome accessories!)

Henry

 

[Loneranger]

I am not sure what you are looking for without knowing more specifics like weight, beam, center of boyancy, etc except for general statements like this is a deeper V hull which should do better in open rough water than a shallow hull. Anyway, for those interested you could model your own hull via the program below:

http://carlsondesign.com/software/add-ons/shareware/hull-designer

I have not used the program myself but it is used on a site that I have used to get plans for plywood boats that I have built in the past from here:

http://koti.kapsi.fi/hvartial/

John

 

[Carver370]

Several people own some of these hull shapes on here, its more or less just for fun to see how people think their boats handle vs others.

For instance, some of these hull shapes above might surprise you as to their manufacturers. The statements often made here and other places are "this boat handles like this" or "this boat needs this power" or "this manufacturer doesn't handle well in a beam sea, head sea, etc.", sure some are but not all.

 

[390x]

Henry, I don't think you're trying to start anything, and neither am I, but I don't need to be a naval architect to see that a sharp entry is going to handle rough water head on better than a flat entry. Again, I don't mean that to sound pissy, but it probably does.