# HELLLPP!! SWATH Design

Discussion in 'Boat Design' started by persianmj, Nov 21, 2014.

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SWATH Design

This thread is written to kindly seek some information for bellow topic :

I need some information on calculation of new design SWATH type ship "main particulars" from a mother vessel. (basically the formula's)
As I suppose the readers of this forum are well aware that twin hull vessels have a different way of calculation from single hull vessels.
Therefore, any material that has information on aforesaid matter would be highly useful.
Mother vessel is a 400T hydrofoil small water plane area twin hull, and the intended design vessel is the same type with 1000T displacement.
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Determination of the LA, LPP, B, D, T1 (draft) T2 (draft), Xb1, Xb2, Zg, Xg, U, Lb, Lbe, Lbp, Db, Displacementb, Sb, Ls, Lse, Lsp, 2to (strut thickness), Hs.
Overall calculation, Main Body calculation, Strut calculation, Upper Hull calculation.
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KIND NOTES: After couple of comments by dear friends at boatdesign : I have made a mistake in typing above thread, but I decided instead of editing the above, just write a correct in below here: the new to be designed vessel is also a HY-SWATH!.

Last edited: Nov 23, 2014
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### TANSLSenior Member

The calculation of a Swath does not have to be different from any other hull. You have to get the ratios and coefficients of similar boats and apply them to yours. However, it does not seem a good idea based on a hydrofoil to design a Swath. It has nothing to do one thing with another.

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### rxcompositeSenior Member

Buy the book published by SNAME "Swath Ships" bulletin no. 7-5. Agree with TANSL, hydrofoil is a different design and has nothing to do with swath.

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### milo12Junior Member

I can't help with the OP question but he can Google HYSWAS, it is a hybrid SWATH-hydrofoil design. Is retains the seakeeping of a SWATH but improves efficiency by reducing wetted area since the hydrofoils support 30-50% of the mass.

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### keroseneSenior Member

Reduce wetted area on a swath? By adding wetted area in the form of foils.

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As already noted the type of vessel is irrelevant.

It's is called a GEOSIM....in naval architecture. If you are unfamiliar with such a term and its concept, then you should seek a naval architect. It is a 5 second calculation!

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Dear TANSL
thanks for your reply, it was a mistake by me, the new vessel to be designed is also a HY-SWATH. My problems is the ratios and coefficients of HYSWATHS.

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It was a mistake by me, the new vessel to be designed is also a HY-SWATH. My problems is the ratios and coefficients of HYSWATH to be used in calculation of the main particulars of the new vessel.
I am a naval architecture grad student , I am new to HYSWATH vessels.

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### rxcompositeSenior Member

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Type of vessel is irrelevant. Scaling from one hull to another is the same.

Open your book and look up the word geosim and understand what it means and how it is applied to a vessel and another vessel using the same hull but a different size. That's it. Once you understand this, it is a 5 second calculation.

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Thanks, yes I meant kindly please confirm if it is the book you meant for SWATH! thanks, I will look into it!!

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### rxcompositeSenior Member

#### Attached Files:

• ###### Geosim.xls
File size:
85.5 KB
Views:
155
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To be honest, I only mentioned twin hulls calculation be different from monohull is , as a student, since I am new to many things, I was doing some research and studies on HYSWATH type vessels from published papers, and I read somewhere that the calculation of a new vessel from basic vessel in twin hulls is different than single hull, so therefore, I mentioned in my above thread. I went through the papers to find the aforesaid matter and share it here, but unfortunately I could'nt find it.

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### rxcompositeSenior Member

No offense meant. I was talking matter of factly.

Personally, I don't think geosims work. It is easy to scale a drawing down to size in acad to get the desired proportion. In doing so (scaling), the froude number will change since the length has changed. Froude number, like Taylors number is related to length of ship and speed. The change in froude number will require that all ratios and coefficients of the hull to change in order to be within optimum range.

What works for the hull 100 feet in length will not work for a hull 60 feet in length. It will not be optimized if the ratios and coefficients remained constant. For twin hulls, there is an optimum ratio of hull spacing to length for every given Fn number.

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