confused about hull form and chine

Hi,
I am working on a powerboat which has characterstics like
L oa :21m. B: 5.45m. T:1.2 m. with Aluminium material. I am confused about V shape and chine line. Can anyone help about transom and midship deadrise angles and the chine height at aft and forward?
I am going to use 1000bhp x 2 engines and targeting a speed over 35 knots.

 

You're going to have to be a lot more specific about your needs if you expect any reasonable replies.

 

thanks PAR
for example
Dead rise at transom = 30 deg
LCG = 6.1
With the figures above hull is showing extremely high trim angles resulting in very high resistance numbers.
I can't figure out the relation between midship deadrise angle and transom angle, and the location of chine line.

 

You will likely have to study powerboat design some more. 30 degrees deadrise at the transom is way too much. Of course the trim and resistance numbers are high with that high of deadrise. Most high-speed craft have transom deadrise in the neighborhood of 20 degrees, plus or minus. Also, if your measurement for LCG is from the transom, it is probably way too far aft. If it is measured from the stem, it is way too far forward.

The mid-ship deadrise will depend on how you shape your bottom. It will be some angle more than the transom deadrise. It could be a few degrees more, and a lot of degrees more--it depends on your final hull geometry that you come up with. Personally, I like midship deadrise to be only a few degrees different from transom deadrise, but there are many other factors that go into bottom design.

The chines should be horizontal and just under the waterline aft when the boat is at rest in still water. They should rise in a gentle curve going forward up to the stem. There is a lot of art and intuition involved in chine design, and I have been known to mention to students and researchers that a really good Masters thesis or Ph.D thesis would be to characterize the science of chine design into something useful that others could rely on. I have designed chines into both my powerboat and sailboat designs in my career. I see they are becoming popular now on sailing yachts such as in the late Volvo round the world race.

Eric

 

I went for a run in a 21 foot powerboat that had 30 degrees deadrise at the transom many years ago. I was quite young, but it had an amazing ride in rough water as I recall. No doubt a bit power hungry...

http://www.boatpoint.com.au/boats-for-sale/details.aspx?R=3079567

Eric is correct about most deeper-V's having around 20 degrees of transom deadrise, though a true deep-V is generally considered to be 25 - 26, like those you'll find on Cigarette's and the like.

 

Mr. Sponberg, thanks for the useful informations you have written. My questions are mainly replied. I am new at this kind of boat type design, so as you said of course i have to work more about it.

Mr. Willallison, thanks for your answer and interest, too.

 

There are many more detailed texts, but have you read Dave Gerr's Nature of Boats? It will give a good, basic understanding of hullshapes, plus a lot of other interesting information about boats in general.

 

Eric, I too want to study more about chines. You have a suggestion where information can be found?

 

a place you could view
googel Don Shead
and Don Senior
Dons deep vee gameboats have deep vee entry, and only 7-9 deadrise aft
your 30 deadrise will make the boat really unstable, particularly down wind, as Eric said way too much

 

The suggestions already posted are geared more toward the layman. For more science-related help, you can contact the Society of Naval Architects and Marine Engineers in the US (www.sname.org) or the Royal Institution of Naval Architects in the UK (http://www.rina.org.uk/) which have published many many papers over the decades on powerboat design. For example, two papers that I rely on regularly are:

"Seakeeping of Hard Chine Planing Hulls", Technical & Research Report R-42, by Daniel Savitsky and Joseph G. Koelbel, Jr., published by SNAME, November, 1992. This gives a thorough look at the best design characteristics that are important in good powercraft design.

A much shorter version of this report, and easier to digest, appeared in the RINA's journal, The Naval Architect, in March, 1979, titled "Seakeeping considerations in design and operation of hard chine planing hulls," pages 55-59.

There are many other books and sources written by a number of other authors, which besides Savitsky and Koelbel, include Donald Blount and Peter DuCane. DuCane wrote a book first published in 1951 called "High Speed Small Craft" (4th and latest version printed in 1973). This book is long out of print and extremely hard to find. He is one of the few who even speaks about longitudinal chine shape in a powerboat hull form, and even then, it is not very much.

The point is, while there is a lot of science written on powerboat hullforms, very little is devoted to the 3D shape of the chine. This is why I think it is worth a graduate or post-graduate thesis and degree--no one's done it, yet.

The chine shape is necessarily tied to overall hull shape and more specifically to bottom shape. For example, let's say that you have three chined powerboat hulls: Hull #1 has a chine that starts low on the hull at the transom, and it rises gently as it goes forward to a point 1/4 the way up the freeboard on the stem. On Hull #2, the chine rises to 1/2 way up the stem. On Hull #3, the chine rises to 3/4 the way up the stem. Which hull form will have the best seakeeping characteristics and/or the lowest drag? I don't think anyone knows?

And what about sailboat hull forms? I put a chine on my open 60 design Project Amazon which had very little rise on the chine. She has very low deadrise, about 8 degrees at the transom, 15 degrees amidships, and I deliberately kept the chine low because I had another spray strake further up on the hull to help shed water from the hull. Project Amazon was extremely fast, in part, I think, due to the bottom shape and chine design.

Interestingly, you cannot design a true powerboat chine design into a modern open class 60 because of the design rules. A true powerboat chine will have some "reverse deadrise", if you will, up forward--that is, the outside edge of the chine is physically lower than the inboard edge in the forward end of the chine. The reason for this is to push the rising water on the hull back down and off the hull which causes a change in momentum of the water flow which, in effect, causes lift on the bow, pushing the bow higher out of the water. This dynamic lift reduces hull drag. Well, the Open 60 design rules prohibit any point on any station to be lower than any other point on the station closer to the hull bottom centerline. That is, the rules prohibit reverse deadrise. So you can't design chines on sailboat hulls to maximum effect. I got around this by making sure that the outboard edge and the inboard edge of the chine were at the same vertical height, and I had clearance for this by the race rules committee for the Around Alone race. Nevertheless, in the latest running of the Volvo 60, there were examples of chines on the sailboat hulls. Also, my design Bagatelle has a chine in the after end of the hull which disappears at amidships going forward. I am not the first designer to incorporate chines in sailing hull designs, but I have had some success with it.

So I think some research has to be done to further optimize the shape and 3D geometry of chines. There is a lot written on powerboat design, too many papers and books to summarize in this small space. You will have to do your own research to come up with the best sources. This at least points you in the right direction. I hope it helps.

Eric

 

There is one volume of Peter DuCane's High speed Small Craft available at Amazon for $185. I got my copy a few years ago for much less.

A boat of the size, power and projected speed that the original poster proposes requires some knowledgeable input, whether professional or advanced non-professional. It is beyond the scope of this medium to do more than add to an established knowledge base for such a project.