# Consceptual design

Discussion in 'Boat Design' started by Mik the stick, Dec 8, 2012.

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### Mik the stickSenior Member

I have a book on aircraft design by Dan Rymer it lists design formula. For example if you are designing an aircraft of 1350lbs to withstand 6G there is a formula to predict wing weight, fuselage weight, landing gear weight etc. I know Dave Gerr's book has a prop weight formula. Are there similar formula to predict hull weight for certain dimensions and materiels, engine weight for power, fitting out allowances etc to arrive at a final projected displacement.

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### philSweetSenior Member

Yes there are, and I want to thank you for consceptual. A terrific addition to the language. I may just submit it to Mensa's annual new word comp. http://www.yelp.com/topic/new-york-mensa-contest-winners

There are scattergram charts showing the values of nearly every design parameter you can imagine. Displacement and LWL are the two most common x-axis values.

But as far as weight goes, you really need to NOT take any shortcuts. You need to know the weight and location of every bit in order to figure how she will float and how stable she will be. So metrics don't really help you that much with respect to component weight.

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### Mik the stickSenior Member

I can pick an aircraft weight then draw its dimensions then use fomula to predict wing/ fuselage weight etc whats left is available weight for fuel.
If I know my boat will be 30ft x 9ft Its surface area might be 900ft^2 if everything is 0.75" thick. if wood was 0.55lbs per cubic foot 675 x 0.55 for a hull weight of 372lbs if an engine weighs 180lbs fuel and tank 360lbs, the empty boat cannot weigh less than 912lbs. Where can I find these charts for things like Prop shaft weight, rudder and controls, internal fittings, instruments etc.

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### philSweetSenior Member

Start by looking at a thread called the design spiral. It shows you the general order of march when designing a craft. The important idea here with respect to the forum is that if you come in with a specific question, Most folks here are going to assume you are on the right spot on that spiral to be asking that question, and will expect you to have the answers to the questions that pertain the problem. As far as hull weights go, you will need to work your way through a scantling rule which will size the structural and shell pieces based of the size and type of vessel. Some of these are quite involved and others are more-or-less cookbook style. Vessels are not often built as light as possible. The cost goes up very fast as you try to shed weight. Weight has to be tracked accurately, but is of far less importance to the average recreational boater than it is in an airplane. The sort of boats I'm interested in weigh about 10,000 pounds at 30'. What sort are you after?

found it - http://www.boatdesign.net/forums/boat-design/design-spiral-where-start-building-boat-28580.html

see the document attached to the first post.

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### Mik the stickSenior Member

Thank you
I am interested in boats/ships of all types. I enjoy technical stuff. I thought I would write a set of wargames rules for WW2 coastal warfare. Prediction of speed and required power led me to buy Dave Gerr's propeller handbook and an excellent book it is. I have loads of info on WW2 ships but thought I would like to be able to design a boat/ship in a conceptual way which i can do for aircraft, if I had the money this could then be presented to the likes of Dave Gerr to be improved upon. I have a thirst for knowledge on subjects which interest me.

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