# Boat cross section determination

Discussion in 'Boat Design' started by sudeb.roy, Jul 30, 2016.

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### sudeb.royJunior Member

I am a newbie and would like to know how to determine the cross sections of the boat along the longitudinal axis.
My boat is to be 12 meters LOA and would have about a 2 meter beam.

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### keroseneSenior Member

If I understand right, they could be:
V, U, |_|, or many other shapes...
Besm and length are hardly enough for determining hull shape

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### sudeb.royJunior Member

I understand that for this kind of beam it is wise to stick to a V type hull because I would be taking it out on the high seas too. I like the concept of a Caroline type of hull (Concave surface) and that of stepped hulls. I am a experienced 3d modeler and would easily loft the cross section. But, I need to know how to calculate the cross sections and what would be the appropriate deadrise angles at bow and aft.

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### PARYacht Designer/Builder

Welcome to the forum.

What you need to do is open a book or two and learn a wee bit something about hydrodynamics. I'm not trying to insult you, but selecting a midship section determines quite a bit and some decisions need to be made first, based on the type of midship section you want. These decisions are based on the goals of the design (SOR). In other words, there's no appropriate deadrise angles bow to stern, just satisfactory compromises based on how close you can hit the targets in the SOR.

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### sudeb.royJunior Member

Yes Sir, absolutely! Any suggestion on a few books? I am not in a position to back to school at the moment.

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### TANSLSenior Member

There are many boat designers who unfortunately do not know much about hydrodynamics, so do not be put off by that and you start to study other things not so complicated, before it would be better to know something, for example, about fluid statics.
If you talk about "cross sections of the boat along the longitudinal axis" maybe you're referring to the longitudinal profile of the boat, which do not need to know the deadrise. But for this and any other section of the boat, you need to do what we all do: copy a similar boat.
Of course, it is essential, following the advice of PAR, to have a SOR and with it, draw a boat General Arrangement. Try to find space inside the boat for everything you want to take.

Last edited: Jul 30, 2016
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### latestarterSenior Member

I would recommend "The Nature of Boats" by Dave Gerr.

It is packed with information, well written and easy to understand.

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### gonzoSenior Member

Let's narrow it down first. Is this a powerboat, and if so, what is the target speed and intended load.

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### sudeb.royJunior Member

Thank you all for the interest. I sincerely appreciate it. I would like to target 54kn, but is that a bit of an over reach for a newbie? Load would be about 4 to 5 tons maximum.

Last edited: Aug 1, 2016
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### gonzoSenior Member

What is the intended use? For example, pleasure, fast patrol boat, etc.

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### PARYacht Designer/Builder

An SOR would help define the general shapes you'd likely employ. Simply put, some midship sections would be wholly inappropriate, based of the goals of the SOR, while others would be beneficial.

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### jehardimanSenior Member

That's not a boat, that's a weapon system.

First, see how many vessels go 54 knots....That is beyond the capabilities of a Boeing 929 jetfoil...Waaayyyyy beyond a "newbie".

Start here...https://en.wikipedia.org/wiki/High-speed_craft

or here... https://en.wikipedia.org/wiki/Surface_effect_ship

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### sudeb.royJunior Member

Speed cutback

Well alright then.
Let's I cut it down and target 35kn.
The intended purpose is to have a high speed leisure boat that can be stored away in a 40' container when not in use. Hence I mentioned a beam of approximately 2m. If it's any bigger, I might not be able to make it at all.

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### Mr EfficiencySenior Member

Sounds like a Cigarette-style boat.

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### sudeb.royJunior Member

YES! A Cigarette style of boat would be awesome! I have observed a few stepped hulls but it wouldn't be suitable for easy cruising. I'd have to gun it all the time.

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