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Harry Krause wrote:
Eisboch wrote: Short Wave Sportfishing wrote in message . .. On 21 Nov 2004 17:35:54 -0800, (Big Daddy) wrote: Hello. I have a 29' Chaparral (great boat) with twin v-6's and Volvo duoprops. It comes on plane extremely fast if I work the trim tabs full and use the outdrive tilt. You almost don't even know the bow is raising! My question is...in lieu of the damn gas prices, I'm wondering if I could get better mileage if I added larger trim tabs so that the boat would plane at a slower speed. Right now, I have to get it to 3,000 rpm's to bring it down on plane. Any thoughts? Based on my experience, I've never used trim tabs to bring a boat on or off plane. On my Contender, it's more a question of lateral balance in unfavorable sea conditions and for keeping proper bow entry in seas. Then again, I have outboards, so the conditions may be different. I don't think larger trim tabs are going to help much because of drag issues. I'm not all that familiar with I/Os, but with outboards, plane is more a function of proper engine trim and throttle setting. On my Ranger, a 20 footer which doesn't have trim tabs, it's all about engine angle and throttle setting. On the Contender, I hardly twitch the tabs unless I absolutely have to. I would think that larger trim tabs would create more drag, thus less performance, thus more gas used. Later, Tom IMO and personal experience, the results of using trim tabs and probably their optimum size varies from boat to boat, so there is no generic answer. Like Tom pointed out, trim tabs are primarily for lateral positioning due to heeling into the wind or unbalanced lateral loads. Many boats that are under or marginally powered benefit from lowering the tabs to help get on plane, but it is a balance of lifting the stern and generating more drag. If the OP's boat is underpowered, my guess would be that larger tabs might help lift the stern to get on plane which will the significantly reduce overall hull drag. Once on plane, he should slowly raise the tabs back up, while watching his tach until he finds the "sweet spot" of max RPM for a fixed throttle setting. Somewhere I think I remember reading that tabs should have an inch of width for every foot of boat length. Just my opinion. Eisboch When, exactly, is a boat on plane and how can you tell, precisely, when this happens? It certainly is easy enough to tell in small boat, but it's not always so easy to tell on a larger one. My Parker, for example, breaks onto plane at around 17-19 mph, but seems to remain on plane down to about 13 mph...in that the bow is still raised a bit, the wake still is fairly flat, and if there is any chop, the spray is tossed off in the usual manner. But that exact moment of being on or off plane seems difficult to determine... Crumbs this lying idiot doesn't even have the brains to properly understand the magazine test he tried to steal this from, as self serving evidence he owns a boat:-) Too too sad:-) K |
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