Quick blast around the Solent yesterday

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with legs at +1/+2 the boat started to porpoise a bit when we hit some shallow swell. Trimming in to -1/-2 stopped it completely, with no noticeable effect on speed.

[/ QUOTE ]I guess it's not WOT you're talking about here, and if so what you're saying is perfectly normal.
At cruising speed, the engine(s) can deliver more power than the hull actually requires, so they're capable to keep the same rpm even if the resistance increases a bit. Even more so in a boat like yours, which is pretty highly powered.
It's only at WOT that you should see the slight speed increase I previously mentioned.
Some porpoise btw is not a problem: it just shows that the props are throwing water backwards, not downward - which is what they're supposed to do. Of course you can reach a point where they start cavitating, which should be avoided like the plague, but that's very different from some porpoise.
 
what is being meant by porpoising? I always took it to be when the boat gets into a sort of rhythm of going bow high, and ducking down, but NOT for the reason that you are climbing a wave or gentle swell every 15metres or so.
I dont have the photos of the sea conditions on my work pc on this thread so I cant tell, but I ve never had a Windy porpoise, as I ve defined it. Did happen on smaller USA sportsboats if it was trimmed way way out.
But, you are right on the point that the zero gauge may not be set up for zero, as ideal. I ve had the sensor on the leg on another boat twist a bit, so it was out of line. Just a simple screw,and twist it back again.
 
yes, but of course it's more comfortable if it doesn't porpoise, even if that's at the expense of a knot or two. It's been a few years since I last had a boat with outdrives, so a bit more experimenting is obviously needed.
 
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what is being meant by porpoising?

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You'll know it when you feel it. I had a Sealine 305 which was very good at it. In flat calm water at certain speeds, the bow would bob up and down in a slow even motion (like a porpoise). To get rid of it, I had to slow down, speed up or trim down and it never happened in choppy conditions. I can't explain why it happens
 
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Get in!

Cheers
Jimmy

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Good Fun though and just as you speced it. Well done on your choice Nick! /forums/images/graemlins/cool.gif

Enjoy. /forums/images/graemlins/smirk.gif
 
I have KAD300's, 285 hp each. They run well, but are a bit smokier than I expected when you first fire them up, although they're clean once they're warm. The Windy guys I spoke to said you don't need D6's in the Khamsin, so the best option now is D4-300's.
 
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