TEOTWAWKI Boat

I'd certainly have a leg up.

 

I'll bet the interesting part of that ride was when he throttled down and came off plane, and the leading edge of that tabletop dug in.

 

I'll bet you're right.

 

We need Submarine Tom's special expertise . . . I've been down a mine a few times but not on water.

 

I don't think the front would dig in. The back would get deeper,I think it would just sink from the backwash.

If he throttles off slowly keeping back wash to a min and he shuffled his weight forward a bit he might just make it float.

Don;t forget --he started off somehow.

 

Hoyt,

From the picture, It does look like your boat have a "bow up" attitude. I don't think what you said about "very little resrve buoyancy at the bow" is the problem. More like a CofG problem. I remember most of the 22-27 footer we made and tested, speed can be increased by shifting weights or varying the trim of the motor. With an electric trim installation, we gain more speed (at planing condition) at less throttle, by reducing motor trim.

It also appears from the photo that you have installed the motor with the negative angle, which is good. But have you played around with the angle? That is if your outboard mounting brackets have this trim adjustment by repositioning the cotter pin.

I drew the principles of trim and some possible remedy. Since the boat is already made, you have very little options. If you want further info, you can ask for a reprint of ProBoat article "Trim Control" by Dudley Dawson and Donald Blount", Feb-March 2002.

 

Thanks, rxcomposite.
Motor bracket is set at 12 degrees per motor specs. I raised it up to the specified 22.2 inches height(I had it 2.2 inches too low) but have not glassed it yet. Once done I will test it again. Moving weight forward did help trim. I still haven't built the tiller extension.

 

???. Hoyt, this is not Ad Hoc but his disciple. Rx

 

Just a brief look at the basic dims.

You have an L/B of roughly 5...should be much higher
The L/D ratio is circa 4.6, better above 6.5 (you'll have a very high hump resistance).
And the CL to Cl is below 0.2L, thus plenty of interference.

Sadly the signs are not good

The remedy, is to widen distance between the hulls, and lengthen them, given the power you have. Another would be to make her a "displacement" catamaran. Don't try to make her plan, just let her push through the water. But again, you need to increase the L/D ratio for that which means increasing the length. Then just make into a simple round bilge, like a constant radius.

 

Too bad Michlet will not be of help to you. Your demihull is assymetrical and creates assymetrical wave patterns. Leo gave me a link regarding the study on this assymetrical hull but after browsing through it, gave up as my project was over,

Just curious, what wave pattern is giving you problem? The ones crashing into each other. Is it the divergent waves or the transverse waves? What is the distance between your hull and the length waterline?

Maybe my spreadsheet will help as it also consider transverse wave but it is for symmetrical hulls. AH probably has a better information on this (Vollheim (1968) and Miyazawa (1979)- displacement type cats and assymetrical hulls).

 

Oops! It was too early for me and I was still half asleep. Sorry. I fixed it.

 

I have learned the failings of my design but will continue to use it as a slow but dry and stable fishing platform. In 2014 I will start my garvey to fit the same motor and trailer.

 

Distance between hulls is 2 feet(0.61 meter). length at waterline is about 7.5 feet(2.29 meters).

 

I agree that if he came down carefully and watched his trim, he might have gotten away with it. But I'll bet it was an interesting balancing act....

 

Actually backwash is no problem due to a combination of a decked over stern with the additional benefit of a 2 inch coaming set 1.5 inches in front of rear cross-beam. Whatever little manages to wash past the crossbeam never makes it into the boat.