Formula Jr
04-18-2001, 06:11 AM
Looking at Scott's beautiful restore got me to thinking about Trim Tab placement last night. So I thunk some, and then I thunk some more and this is what I've resolved and want feedback on.
First, there are two entirely different ways of looking at trim tabs and trim tab placement.
There's an accepted, traditional use for trim tabs and, there's also an un-sanctioned, non-traditional use of trim tabs.
The traditional use, the one that Bennett and other tab makers can sign off on, involves application on hulls that do not exceed their design limits. This use is the commonly understood use of controlling boat trim, list, lowering the planing speed etc.
The Non-traditional use, is where tabs are used on boats, particularly older Deep Vee designs, that are being driven far over the speeds they were designed for. In this un-sanctioned application, the tabs are really acting as extentions of the hull and become critical planning surfaces. Lets say you got a boat made in '66 that was never intended to go over 50 mph.
Now you stuff, wedge, shoehorn or otherwise squeeze in an engine that makes 150 to 200 more hp than the boat was originally designed for. You're going to have handling problems since there isn't going to much in the way of a running surface to stablize the boat. This is where the non-traditional use comes in. The stability problem is because the "Point" of your running surface is the point of a V shape and the boat will try to fall over side to side in a chine walk. The drive is really your other "Point," but since its in line with the point of the V it doesn't add side to side stability. Now what if we add two flat running surfaces so that the V now
looks like this _ V _. And we run the two trims, drive and tabs, counter to eachother to push the transom chine area into the water. You have here, essentally turned a Deep Vee design into a high speed four point hydroplane and the rest of the hull is ill-relevant. Now I can understand why any trim tab maker would never advise anyone on this non-traditional use since the liabilty problems would be obvious, the practice exists none the less. But when you examine this four point concept, there are some things that immediatly come to view. One, you want long, extremely stout, tabs. You also want fine control of both the drive trim and the tab trim. And the traditional rectangular shape of the tab may be improved by a curved shape. You might also need some sort of safety mechanism that locks out fast trim changes or have a completely computer controlled progression of both the drive trim and the tab trim keyed to speed.
Well, the dentrites are getting a bit of a caffine jag so I'll stop here before I REALLY start babbling nonsense.
First, there are two entirely different ways of looking at trim tabs and trim tab placement.
There's an accepted, traditional use for trim tabs and, there's also an un-sanctioned, non-traditional use of trim tabs.
The traditional use, the one that Bennett and other tab makers can sign off on, involves application on hulls that do not exceed their design limits. This use is the commonly understood use of controlling boat trim, list, lowering the planing speed etc.
The Non-traditional use, is where tabs are used on boats, particularly older Deep Vee designs, that are being driven far over the speeds they were designed for. In this un-sanctioned application, the tabs are really acting as extentions of the hull and become critical planning surfaces. Lets say you got a boat made in '66 that was never intended to go over 50 mph.
Now you stuff, wedge, shoehorn or otherwise squeeze in an engine that makes 150 to 200 more hp than the boat was originally designed for. You're going to have handling problems since there isn't going to much in the way of a running surface to stablize the boat. This is where the non-traditional use comes in. The stability problem is because the "Point" of your running surface is the point of a V shape and the boat will try to fall over side to side in a chine walk. The drive is really your other "Point," but since its in line with the point of the V it doesn't add side to side stability. Now what if we add two flat running surfaces so that the V now
looks like this _ V _. And we run the two trims, drive and tabs, counter to eachother to push the transom chine area into the water. You have here, essentally turned a Deep Vee design into a high speed four point hydroplane and the rest of the hull is ill-relevant. Now I can understand why any trim tab maker would never advise anyone on this non-traditional use since the liabilty problems would be obvious, the practice exists none the less. But when you examine this four point concept, there are some things that immediatly come to view. One, you want long, extremely stout, tabs. You also want fine control of both the drive trim and the tab trim. And the traditional rectangular shape of the tab may be improved by a curved shape. You might also need some sort of safety mechanism that locks out fast trim changes or have a completely computer controlled progression of both the drive trim and the tab trim keyed to speed.
Well, the dentrites are getting a bit of a caffine jag so I'll stop here before I REALLY start babbling nonsense.