Constant deep V deadrise. Powering up angle.

[m3mm0s rib]

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;

[daiquiri]

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: 50 knots from a Levi Triana 25 Help! . 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

[m3mm0s rib]

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

[daiquiri]

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.

[m3mm0s rib]

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

[cyclops2]

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.

[m3mm0s rib]

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

[cyclops2]

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