Which Hull Shape?

[monrosm@shrewsb]

Im quite new to this site and only 16 but i was wondering if any one could possibly help me with a problem i am having on a current Designing feat of mine. I need help on finding the right hull shape for a boat. I am designing a 95ft power boat which needs to be able to do about 40-45 knots cruising speed and 50 knots absoloutley flat out. This may be hard to picture so if you need more of an insight as to roughly what this should look/be like go to www.sunseeker.com (you need flash player 7 to enter) and enter the site then click on performance motor yachts and have a look at the Sunseeker Predator 95-100 as a base model for this design. The kind of information i need about the hull is weather to have a displacement, or semiplaining, and how deep the v hull should be (if it should be a v hull) and what sort of chine and deadrise angles i would need to make this Yacht stable but also capable of the speeds quoted previously. Also how many and where the positioning of the Strakes should be.
I know this is a big 'Ask' but any help would be appriciated even if you only are able to advise me on one of my specifications.....
Thankyou
Stefan Monro

[SailDesign]

Stefan - it would be easier to just buy the Sunseeker
However, if your heart is set on designing something like it, you will definitely want a full-on planing hull. A displacement hull on a 100-footer will be good to about 13-14 knots only, flat out, maybe 11-12 knots max cruise. The semi-planing will work to about 25-30 kots, but may be a stretch at the high end.
As for the other stuff, you could ask 10 designers about deadrise and strakes, and get 20 different answers. There is no one "right" answer.
If you can find a copy of Peter du Cane's book "High Speed Small Craft" in a library, take a peek - it is techie but useful. Also Colin and Rosemary Mudie's "Power Yachts" is well worth reading, and not so tech-based.
Good luck - let us know how it turns out.
Steve

[messabout]

Stefan;
Why does your design need to go so fast ? As speed capability increases, structural difficulties multiply exponentially. Required horsepower will be enormous for that size boat at those speeds. Lots of power means collossal fuel consumption. Few people, short of oil sheiks, could afford to operate it.

If you must have a large "go fast" boat then you might explore the hydrofoil concept. There are a number of them in operation in various places. I am thinking of a foil borne vessel that operates between the Maine coast of the US and Nova Scotia. It's big, it's fast (not as fast as your boat), and fairly comfortable to ride.

Best of luck in your quest.

Gene

[mark424x]

It all depends on what kind of interior space and load you need to carry.

For that size and speed, one thing to consider is a catamaran hull with passive foil systems. for example: http://www.hydrospeed.co.za/index2.html
A lot of large ferries use a system like this - see the 76m ferry at 55Knots. http://www.hydrospeed.co.za/10.html or the the 36m yacht at 38knots http://www.hydrospeed.co.za/9.html I'm sure the 38knot limit was due to it being a retrofit.

You might also consider a trimaran if you don't need all the much interior space.

[SailDesign]

messabout, Mark,
If you were selling cars, and someone came in saying "I want a Ferrari", would you sell them a Yugo because it was safer and cheaper to run?
If the answer is "No", why not go back and read the question again? Stefan is looking for advice on how to go about designing something like a Sunseeker Predator 95-100. I have to agree (sorry, Stefan) that the beast is too big, too flashy and not something I would own even if I had unlimited funds and mooring space. But that is what floats his boat, so to speak.
Hydrofoils are fine in their place, but have a lot of draught at rest, which is when they need the least (close to shore...) They are also speed-limited by cavitation, and even super-cavitation has its limits.
Catamarans and trimarans, for all their vaunted speed and grace, etc., are limited by a great deal of beam, and let's face it, the lack of spray-throwing and bouncing at speed is a big drawback to the whole wave-jumping woo-hoo thing.

Offering advice is a great thing to do, but please let's read what is asked before grinding any axes.

Steve

[mark424x]

Woah Steve, get up on the wong side of the bed this morning?

Originally Posted by SailDesign

If the answer is "No", why not go back and read the question again? Stefan is looking for advice on how to go about designing something like a Sunseeker Predator 95-100.

Actually, what Stefan said was "I need help on finding the right hull shape for a boat. I am designing a 95ft power boat which needs to be able to do about 40-45 knots cruising speed and 50 knots absoloutley flat out."

I don't know that he was actually trying to design a Sunseeker clone, do you? This was a representative example. His requirement was the length and speed. Here is a young guy who might only know what he sees in the boat mags. I was just trying to expand his horizons a bit. Sheesh.

Originally Posted by SailDesign

I have to agree (sorry, Stefan) that the beast is too big, too flashy and not something I would own even if I had unlimited funds and mooring space. But that is what floats his boat, so to speak.

Gee Steve, I must have misread the question, I didn't see the part where he was asking for opinions about this boat. If you were selling cars, and someone came in saying "I want a Corvette", would you tell them that beat is "too big, too flashy and not something I would own even if I had unlimited funds"?

Originally Posted by SailDesign

Hydrofoils are fine in their place, but have a lot of draught at rest, which is when they need the least (close to shore...)

Really? have you looked at the Hysucat designs, or those of Teknicraft or Morelli and Melvin? They use a foil between the hulls of the cat, no extra draught. By the way, where did Stefan say draught was a requirement, or did you forget to actually "read the question" The ferry out to the Channel Islands National Park uses a Teknicraft design that runs at a pretty good clip and goes to San Miguel 2-3x a week with it's shallow rocky exposed landing area.

Originally Posted by SailDesign

Offering advice is a great thing to do, but please let's read what is asked before grinding any axes.

Well, I'll admit that my response was a bit tangential, but a legitimate alternative. But the beauty of these forums is that folks present ideas that you might never have thought of. I'll admit that I like to grind my "anti me-too design" ax, but I guess you have a anti multihull ax in your closet.

If you get hall monitor credit for the day, feel free to put my photo with a red X through it on your locker, I've been duly reprimanded.

Just funnin with ya Steve, hope you having a better day today.

[SailDesign]

Mark,
Yup, probably right. I don't do Saturday's well... especially early-ish in the morning when the next-door neighbour's lawn mower wakes me up. 'Nuff said on that one - please accept grovelling apologies, although I still maintain I had provocation

Stefan did state that if one was fuzzy about the concept, the Sunseeker would show what he was thinking, though, so that was really part of it.

Hysucats are interesting, but a bit of a camel*, IMNSVHO. My Dad always had a sign on his drawing board lamp that said "Simplify" Anyone can design something complex (like, f'rinstance, a SLICE-type SWATH thingy, but it takes hard work to design something simple and efficient. What I would call an "elegant" design.

Steve "humble pie for breakfast"

*Camel = a horse designed by committee

[mark424x]

Hey Stefan, sorry to hijack your thread. I think Steve's original response is the best approach.

Steve, the combination of an early lawnmower and some nut suggesting foil cats will do it everytime, I take equal responsibility.

While on one hand I agree with you about keeping things simple and refined. One of the things I always liked about the passive hysucat system was the notion that you could decompose the design of the element that provided dynamic lift from the element that would slice the waves or for that matter provide low speed/static bouyancy. Sounds good in theory.

I've fought the design by committee problem many times - I know the pain.

[water addict]

You can get powering/resistance numbers using series 62 or series 65 planing hull forms from Principles of Naval Architecture from Society of Naval Architects and Marine Engineers.