Warped Bottom Designs

[wdnboatbuilder]

There seems to be little to no information ( books ) on warped bottom boat design. anyone here know where I might find info. I guess I want to know why designs have gone to the deep V and not spent more time with the warped bottom? I have had alot of rides in both deep V and a warped, Modified, V and I will have to say that the softest ride I have had yet in a pretty rough sea was the warped bottom so why don't I see more of these bottom in the market? can some one help me out here?
thank you for your comments

[gonzo]

Carolina Sportfishermen, lobster boats and others are still using the warped bottom or rotated wedge design. It is good for semidisplacement speeds.

[KCook]

True deep-V (constant deadrise) is very rare in pleasure boats. Virtually all bowriders, cruisers, deckboats, ski boats, etc, are some flavor of warped bottom. Though they love to slap the "deep-V" label on anything with 20 deg deadrise at the transom.

Kelly Cook

[wdnboatbuilder]

I was always taught to leave the water as you find it. ok what is the semi-displacement speed, less than 2.0 speed to length ratio, right? please correct me if I am wrong. The 44 that we built for LUHRS I believe it ran 48knts thats not semi-displacement speed. it was all wood, I'm not sure what LUHRS is getting out of her. But you look at the flats boats and even small open fisherman and they are all constant or of the deep V bottom. Just seems to me the leave the water as you find it therory is blown all to hell and I see a lot of lifting strakes tryimg to get the boat some lift. sorry if it seems i'm rambling but it's early mornig and just had my first sip of coffee.

[KCook]

Ski boats raise the least wake for their speed. They are definitely a warped bottom type. But most folks in the pleasure boat market refuse to even consider them. Can't stand the harsh ride.

Kelly

[LP]

I think it's a performance issue. A lot of designs from the 40's-50's (?) have a warped bottom. The thinking being that a deep-vee forward gave a smoother ride while a flat surface is most efficient at planing. Thus, the transition to a flat afterhull. This configuation actually assists in keeping the bow down. It was discovered later that the constantly changing section proflie created more drag because the waterflow around the hull is constantly being changed thoughout the whole lenght of the hull. By going to a constant section shape somewhere around midship, the accelerations are removed and more energy is available to make the boat go forward. Lift strakes encourage water flow to separate from the hull earlier to reduce the amount of wetted surface.

[tom28571]

Bruce,

Most planing boats are either deep V, monohedron or warped bottom. Warped bottom hulls are very numerous.

Monohedron means that the deadrise is constant from about station 6 aft.

Some tests have shown a slight advantage to the warped bottom at low planing speed while the advantage goes to the monohedron at high speed. I have made towing tests that have not shown any measurable difference in drag between the two but do show an instability in the warped hull at high speed. Assuming that there is no convexity in the aft buttock lines, a warped bottom should get on plane a bit easier.

The thought that a warped bottom is easier riding than a deep V in waves is contrary to all evidence that I know of.

[KCook]

Thanks Tom. Hadn't heard that "Monohedron" term before. But that would describe most I/O bowriders on the market today.

Kelly

[Willallison]

Originally Posted by KCook

True deep-V (constant deadrise) is very rare in pleasure boats. Virtually all bowriders, cruisers, deckboats, ski boats, etc, are some flavor of warped bottom. Though they love to slap the "deep-V" label on anything with 20 deg deadrise at the transom.

Kelly Cook

How true... for me a deep-vee is anything over about 24 degrees deadrise. My personal pet hate is the current favourite of the marketing folk - the "modified deep-vee"....
Oh... and then there's my other pet hate - the term "trawler", which apparently nowadays means anything that floats and has squarish windows...
Oh... and then there's.... phew! Seems I'm turning into a grumpy old man!

[wdnboatbuilder]

Thank you all for your imput. interestingly enough that you say from sta6 or i would assume that would be amidships. So what your saying is the chine and keel run paralell or flat up to admidships? I have notice in the last 15 yrs there is a flat in the chines about the last 3-4' in a 15-28'ters open fisherman/flats boats. One interesting note that the builder/designer i worked for, built and ran the Daytona's and according to him if you use lifting strakes or trim tabs then you have a piss poor design. Now don't any of you take offence to that statement he was serious old school, but I also have to say you ask anything about the designing of his bottoms and you got cussed out and damn sure never got an answer. you had to be one of those guys that understood what he was doing and he seem to always got the person with the least knowlege to help him loft. I got caught on the loft floor once with a folding rule and got my asss chewed not for being there but because I had a rule in my pocket and was there. I enjoyed every minute I worked for him and learned alot, but some questions that never got answered. Thanks for your imput
hey i hit 100 post i'm a senior member now, not that that means anything still a junior train of thought.....lol

[tom28571]

OK, maybe I should have said from 60% of LWL aft of stem waterline. Many designers, maybe most, use 11 evenly spaced transverse station cross sections to describe the shape of the boat. That is starting at station 0 at the stem waterline and going to the transom waterline for station 10.

Anyway, you got the idea right. I do kind of agree (but not completely) with your taciturn mentor about the addition of trim tabs to correct for some bad behavior of the boat.

[wdnboatbuilder]

nonetheless they are running paralell with eachother. Yea Bob was an interesting person, would answer some questions depending how close you were to the idea or concept. it only took 2.5 of the 4 years i worked for him to figure that out.
I would finish my classes at Westlawn but really lost interst when I has to start figuring out sailboat designs nothing personal against sailboaters but I want to get somewhere quick and just never had an interest.
Thank you Tom I was not trying to hold you to admidships I have an idea of the 60% same idea that thats where you want your CB. (aproximate)

[Gilbert]

Personally, I have never had any clients with enough money to let me do all the research I would need to do to satisfy the question about which style of planning hulls were the best.
I feel fortunate in having met a few designers who have had the good fortune to do that type of 'personal' research. It has usually been for the government. The most enlightening comment I've heard from them is that to go fast in all weathers you do want to have a warped bottom. "But you don't want it warped very much." That was as specific as the advice got. So I guess we are at liberty to decide for ourselves what not very much means.
I believe that no matter what style of planning bottom you have, if the waves are bad enough, you will come to the point where the boat can take more punishment than the crew can, provided it is a well built boat. And so the limitation is how much discomfort the crew is willing to suffer. I guess that's why a lot of us have philosophically aligned ourselves with what many folks consider a slow boat. And I am not trying to imply that the crews of slow boats never suffer any discomfort.

[tom28571]

Gilbert,

There may be some confusion in this thread about what is meant by a warped bottom. Nearly all planing boats have a warped bottom in that the bow deadrise is much greater than that at the transom. If you want the boat to enter waves without pounding badly, a sharp entry is absolutely necessary and if the boat is to plane efficiently, the stern section deadrise must be small. Therefore some warp is inherent in all planing boats other than flat bottomed ones and constant deadrise ones.

What I meant by a warped bottom is that the aft planing sections are also warped. Even when up on plane and in smooth water, the water flow is still experiencing some twisting action as it leaves the transom. On the other hand, the monohedron hull has no twist to the after sections so that water flow is much more uniformly horizontal leaving the transom. Within these boundaries, you get the comments by your designer friends and it gets almost to a personal preference. I'm sure you know this but I wanted to clear it up a bit.

[KCook]

Good point Tom. And I expect most ski boats would meet this warped bottom description. With the deadrise changing even across the aft planing sections.

Kelly