Optimal hull?

[Robbi]

Hello there!

What is an optimal hull for a high speed powerboat (not tunnel boat design)?

Are there any good literature on the subject? Boat and yacht design books most oftenly only present sailboats. In "Principels of Yacht Design; R.Eliasson & L.Larsson" was a small chapter on powerboat design but I would like to see more.

An example problem:

A boatmanufacturer (custom boatbuilding) has developed a reasonably good hull design for a customer and then another would like to have a similar design but 2 metres longer. How should the hull be changed in order to maintain the good dynamical properties?

How should a problem like this be handled most efficiently in order to get the boat built and delivered? Tank testing? CFD? Calculations?

I'm not YET a builder or designer, just interested in the topic.

Robbi

I fear there is no (or very few) studies for small powerboats hull. (ie smaller than patrol boat). Simply putting a bigger engine gives better perf. And in that range of power (say under 2* 600 hp), you have a bunch of truck, offroad, industrial engines marine engines are derived from. So, it simply costs less to put a bigger engine than to optimize the hull.

It is my strictly own personal opinion.

[CDBarry]

There is a ton of material in professional level sources such as SNAME and RINA. For example, Blount & Fox, 1976, Blount & Koebel, etc. and the Small Craft CD.

Unfortunately few yacht designers look at these sources. I would start with Savitsky type calcs, and then if I needed to, use a Zarnick entering wedge analysis.

However, the process requires looking at the whole boat - how does the weight and CG change, etc.

[tom28571]

High Speed Small Craft - Peter DuCane
Naval Architecture of Planing Hulls - Lindsay Lord
Problems in Small Boat Design - Society of Small Craft Designers

There are a couple of others that slip my mind at the moment. All are sometimes available from ABE (American Book Exchange). Just google it.

The MotorBoating Ideal Series - If you can find it.

[Robbi]

Tank you for the references!

So RINA is similar to SNAME and located at www.rina.org or is it the wrong page?

What's on the Small Craft CD (=SNAME CD?)? Is it possible to obtain it in some easy way?

Would be interesting to see more about "Savitsky type calcs" and "Zarnick entering wedge analysis".

[D'ARTOIS]

Just curious.... What's the relevance of this question? Architects, - Shipyards, Scientists are spending barrowloads of money finding out, and you would like to have an answer for free?

[Robbi]

There sure is a relevance in this!

More CAD/CAE/CAM is becoming available to boatindustry and the technologies should be used both in design and manufacturing.

I can't get a simple ANSWER for FREE. There seems to be much to learn in this field. I'm looking only for references in order to see what has been done.

You must preserve a number of dimensionless groups to scale the model up accurately. I.e. Reynolds Number, Froude Number, etc.

[D'ARTOIS]

Sorry Robby, I did'nt want to be that cynic. If you look at the most optimal powerboat hulls available on the market, then the question arises what is more important - to stomp a vessel at ultimate speed through sea state 8 or to keep the crew alive?
There is no such thing as an optimal hull - although one is tending to believe it.
To give you an example: a sailingboat, even an America's cupper, runs better on the starboard tack than on the port - or vice versa. And that is a zillion-dollar affair. The America's cupper I mean. You make already a great advance in this field if you are capable to manufacture a fully summetric hull.

Nick Keig developed some years ago the VSV. A super fast vessel, going in any sea with 70 knots / hour; I better say through any sea. A boat almost radar invisible or stealth as they say in the US, 1000 nm range, a nightmare to drugrunners, waterpolluters and any other spoils of the sea. A sensitive, highly developed design.
Commercial value? Nada Zero. If it comes to basic terms, nobody is interested to chase drugrunners unless they have a least the power of a 1000 ton Coastguard vessel or the like to impress the bravo's in their cigarette's or high powered cougars.

The optimal hull as you call it, is in basic theory already available. Make a sum of your requirements, go to a knowledgeable design bureau and they will meet you with a proposal.
In the academic field, a tremendous source for the naval architect, one needs always brainpower to develop new ideas so, join that field, make yourself familiar with the papers from Delft, MIT and thelike. However, the secret of performance is not the hull, but the propulsion system, 100 times more important.......

[Robbi]

This discussion gave me some interesting feedback about hull design.

It was once said by a boatdesigner that "If you can't build a boat - you can't design one". This is probably true regarding hull and stability aspects of the boat. The aestethics can anyone design that knows a little about what pleases the buyers eyes.

More advanced mathematical calculations should only be applied if it's worth.

Well, I'm going to try to learn everything about boatbuilding and designing starting from Herreshoff's and Chapelle's knowledge. Hopefully I someday can establish a profitable boatmanufacturing company or design firm.

Merry Christmas and a Happy New Year!

Robbi

Sorry to heavily insist in my opinion ...

But savitsky papers are 40 years old. That does not mean at all they are wrong. But the tested range was what could be built forty years ago.

Gerritsma Keuning sailboat papers that can be found public on www.rina.org.uk are only 6 years old.

And for engines, a cummins b370 or cat 3126 is in 1600-1800 lbs range for 350 hp. A mercedes V8 cdi is 650 lbs for 310 hp continuous (aircraft figures). There is a german company marinizing this engine, but I could not found it on the web to get correct weigth and power figures. NB : This engine is old enough to have marine and aircraft versions, but BMW and VW have similar weight/power diesel engines.

Just guess now how 2000 lbs weight diff will change your hull form for about the same power (2 * 350 hp). Especially if your boat is built from core materials with prepegs, and/or vacuum bagged. (as environmental law pushes you in europe, hand laying resin in open air leading to too much nocive vapours).

WE ALL NEED A GOOD LAUGH EVERY SO OFTEN. I submit my first real woodie made of 1/4" Occume ply ( Holland ) except for the keel and 2 engine stringers, dash and transom. More or less. Sides and deck 1/8", braced.-- bottom 3/8". Interlocking slot of frames and all stringers and keel with diagonal opposite glued 1" x 1" triangular gusset blocks should be like a honeycomb as to rigidity. Engine mtg. beam is 4" X 4" X 3/8 SS angle same for trans. and thrust bearing. 21' X 4' 8" Wide X 3' deep 24 degree constant deep V, blended up into a cleaver bow. Please wait in line for your turn.

I have a pamphlet that tells of high speed hulls and how to go faster. 80' X 20' X 6' 50 ton 43 knots 4,500 hp or: 55.95 knots ( 65 mph ) just by adding 6 steps. Done in 1944.

[CDBarry]

Savitsky still works reasonably well to optimize basic parameters.

Google POWERSEA for Zarnick material.

Be very careful with steps. They can produce interesting dynamic instabilities.

As alaways though the question always comes to trade offs and it is improtant to follow a rational process in the design.

I am referrig to WW II PT boats. The data is from a historicaly accurate military manual. It is obvious to all of us now that no one will ever make a signifigant improvement in hull design because we have designed out 98 % of the problems. 1 % on a pleasure boat means little to the owner. 1 % to a container or super tanker owner, is a extra house or mistress, both highy prized. Much of today's improvement's are the nit picking refinement of the basics. This includes light weight composite furniture on mega-yachts. Mega-yachts today do not have exotic woods, silks, gold leaf, silver, and so forth. SPEED is the only thing. Is 1/2 the cost for the propulsion a fair estimate? They are really trying to build offshore racing yachts. Woops! There is room for more than 1 % improvement. I thought I was always right.