# Constant deep V deadrise. Powering up angle.

Discussion in 'Powerboats' started by cyclops2, Sep 18, 2011.

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### m3mm0s ribSenior Member

daiquiri Glad to understand the whole of the building. As for the speed might be greater according to the theory. That is why 6200 rpm / 1.75 * 27 * 0,254 * 60/1852 = 78.715705 knots with hydroplaning 5% amount we do;

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### daiquiriEngineering and Design

You can use Crouch formula for a rapid estimation of high-speed powerboat performance. There are several versions circulating around, this one was used by Sonny Levi for his designs: http://www.boatdesign.net/forums/boat-building/50-knots-levi-triana-25-help-34749.html#post400951 . LWL in feet, SHP in horse power, weight in tonnes. Steps will add some 15-20% more speed to the figure given by that formula.

There's a handy on-line tool based on Crouch formula, where weight is expressed in libs, and the K factor has been correspondingly modified into hull-type C factor: http://continuouswave.com/cgi-bin/crouchcalc.pl

Cheers

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### m3mm0s ribSenior Member

daiquiri Thanks for the information but we are talking about something completely different. Sure there are some standard in all construction But this is changing many times in practice

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### daiquiriEngineering and Design

I'm affraid physics is the same for all planing boats.

This one is similar to your boat in size and weight: http://www.m-ribs.com/index.php/MR-900-Cargo-Rib.html
2x350 HP to make it go at 70 kts. Crouch formula gives 65 kts at 2.2 tonnes (light boat + 2 persons + some fuel) with K=1.6 (2 outboards). It's just 7% off from the declared max speed (if manufacturer's claim is correct) - not too bad for such a broad formula.

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### m3mm0s ribSenior Member

daiquiri Here we say for racing rib with lift, sport master foot and this is not 2,2 tones but only one +motor 250 kg+two people 180 kg

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### cyclops2Senior Member

Here are the 2 views of what I am building.
The deep V is required due to very choppy area I boat in.

Frames are 1/4" marine. Full depth, flat floor design for strength on 12' centers. Engine & keel stringers are also solid full depth plywood with some holes. All the frames & stringers are notched 1/2 way, so that they interlock into position. 1' x 1' pine triangular gussets solidify all right angle surfaces. Only way I can be sure the hull can resist twisting .
Covering boards are 1/4" marine plywood. Then vacumm bagged wood veneer as a last step.

Marine plywood was the only material that was easy, strong, and cost effective to use on a 1 boat build.

Does this shape, constant 32 degree deep V, have the soft ride I want.

Funny how a 21' x 4' boat looks so much like a modern offshore racer.

Engine will be the BOP 215 CI V8 300 pounds, first. Then a 350 CI V 8 650pounds if needed.
Machinery locations will be done with bags of stone to find correct water line.

The boat will ONLY have the rear bench seat for driver & passenger.

What % from the transom should the V begin to tuck to the VERTICAL bow?

The goal is a look very old wood runabout that can handle choppy water far smoother the the original "wraped / twisted" flat stern area.
40 to 50 mph is plenty of speed.

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### m3mm0s ribSenior Member

OK cyclops but tell us the weight and the top speed if you want.

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### cyclops2Senior Member

1500# with the Buick aluminum 215 CI and 2000# with a 350 CI V8.
Speed is 40 to 50 mph. I am GUESSING that because the boat is 1/2 the width & less than 1/2 the weight of a wood boat the sam length, I will easily reach 40 mph at lees than WOT.
All of the constant triangular deep V frames are solid 1/4" marine ply. The side frames are seperate sawn pieces. They are on 12" centers.

Medications are not good. Sometimes I do not catch mistakes after 3 proof readings of what I have written.
Thanks for all the help .

Rich

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