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Old 17-05-2020, 00:46   #1
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Location: SPAIN - PHILIPPINES
Boat: philippino 'banca', 26m
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hull-design

hello!
any naval architects out there?

I have a question regarding hull-design: i’m planning to build a 7.5m cat, el.motor, with slender hulls (14:1 ratio). I was thinking to build ‘box-style’ hulls, double ended. Main reasons is shallow draft & ease of building. deck&keel parallel to waterline. Vertical stem&transom. Fibre-over-ply. Now, what I see much more often are V-type hulls, what would be the pros&cons of V versus BOX ?
I will reduce draft slightly in last quarter of hull to facilitate turning.


thanx for some hints - smooth sailing!

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Old 17-05-2020, 02:09   #2
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Re: hull-design

Wetted surface. Round bilge most least, V middle, box most. Some V hulls have the bottom flat a la Wharram.
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Old 17-05-2020, 17:46   #3
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Boat: 50' aluminium power cat
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Re: hull-design

Not an architect, but also try the boatdesign forums - there certainly are qualified people there. Also have a look at Harryproa's .
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Old 22-05-2020, 23:40   #4
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Re: hull-design

Thanx for d feedback; Harryproa, exciting designs indeed!
Regarding wetted surface area, I have to disagree. Round hull least, then box hull, V-hull has biggest wetted area; about 10% more compared to box; with a V-angle of 60° and equal displacement , that is.
V-hull has advantage of biggest lateral resistance, so deep-V multihulls get away with not having a daggerboard or similar.
I was wondering wheather box would have much more drag because of eddies/swirls forming around d chine-line. mind you, not a speed-boat, i’m looking at ~10 knots.
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Old 23-05-2020, 04:33   #5
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Re: hull-design

Yes, I agree wetted surface varies depending on if it is related to displacement or beam. There is and excellent article here.

Multihull Dynamics, Inc. - News Article

What about the option of a single deadrise, often used on powercats, very shallow draft and some lateral resistance.

Harryproas are excellent boats, cheap and easy to build. You might also check out a couple of builders, NZ guy just outside Bonbonon and you might like to contact Andy Smith in Bohol, he builds (used to build?) excellent Wharram cats
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Old 31-05-2020, 22:10   #6
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Re: hull-design

we’ll build ourselves. Not difficult, they’re just 2 hulls with a platform, to move divers around d island.; 4th edition. 1st was V-hull, 2&3 both developped round-bottoms, now probably a box as I see no big drawback but much easier to build. Hope to reduce drag by eliminating transom and reducing volume of last quarter.




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