Moderated Discussion Areas
ContinuousWave: Whaler Performance
|Author||Topic: trim tabs|
posted 07-08-2001 01:56 PM ET (US)
How do you operate trim tabs on a outboard power boat.Do you set engine trim one time and than use trim tabs only to adj.boat trim? Or do you use a comb. of adj. trim tab and engine trim together. Thanks for advise.
posted 07-08-2001 02:05 PM ET (US)
On a 22' Revenge I adjust both as needed. I usually use engine trim to adjust the attitude of the bow and the tabs primarily to adjust against port or starboard lean which is usually caused by the prevailing conditions and load.
posted 07-08-2001 04:01 PM ET (US)
In general, one goes to the step of adding trim tabs because the degree of trim desired at a given speed can't be achieved by trimming the motor, or the motor has to be trimmed so far to gain the desired trim that it (the motor) is running more inefficiently than desired by virtue of propellor thrust being at too great of an angle from parrallel with the water surface.
In general then, once you are up on plane, the motor is trimmed to its optimum angle of thrust, and the rest of the fore and aft trimming and adjusting is accomplished with the tabs, not the motor. One or the other tab can be adjusted up or down to counter act windage lean or uneven side to side weight distribution. I find on my boat that what appears to be the optimum trim angle for the motor once on plane, when I am ready to have the tabs take over the fore and aft trim operations, is a little too high to bring the boat up on plane from idle speeds without some slippage. So, I am in the habit of trimming the motor down some as I bring the boat down from planing speed, and then trimming the motor back up again the next time I bring the boat up to planing speed. Other than that, there is typically no need to fuss with motor trim, and beyond that, to do so defeats one of the central reasons the tabs were added to begin with.
posted 07-09-2001 09:18 PM ET (US)
With Whaler hulls there seems to be a tendency for the boat to lean into the wind. If you have trim tabs this is easily corrected. You can also move a passenger or two around to correct lateral trim, too.
What about this problem:
Trim tabs seem like a natural for causing the boat's bow to come down, but how can a trim tab help move the bow up? I don't think it can make the bow have more lift than it would if there were NO trim tab. Am I right about that?
posted 07-09-2001 09:37 PM ET (US)
Jim - You are right about that. Trim tabs can only LIFT the transom, forcing the bow down. They cannot depress the transom thereby raising the bow. Engine trim or a high rake propeller are the way to raise the bow above a "non-trim tab equipped" attitude.
posted 07-09-2001 09:42 PM ET (US)
The water movement is under the trim plate. Therefore lowering the plate can affect the flow of water, lifting the stern from a "neutral" point" up. In order to lower the stern/raise the bow more than a neutral position, the water would have to flow over the trim plate. This does not happen, so trim plates are not effective in lifting the bow from a normal/neutral position.
posted 07-09-2001 10:07 PM ET (US)
I think you are right. My tabs do not "pull" the bow up, they only push it down. And on a Revenge 22, there is really no need for the tabs to push the bow down as the Revenge tends to ride more bow heavy than the Outrage due to the additional forward weight of the cabin. For my purposes, the tabs are only used for lean correction. Motor trim is used to set bow attitude as best as the motor trim can do.
posted 07-09-2001 10:53 PM ET (US)
I am installing trim tabs purchased from Boat US today to try and correct a slight lean to port at some throttle settings and if I am operating boat correctly to try and cut down on amount of times I make engine trim adj.Sting ray type fin on motor helped me get on plane at lower rpm setting.The Whaler is a 21ft. Conquest.Will post results of performance with tabs.
posted 07-11-2001 10:35 AM ET (US)
Trim tabs have a similarity in application to a cavitation plate fin (ie doelfin, etc), that is raising the stern by providing an additional planing surface. What I wonder is if the tabs have been reported (in real usage, not the manufacturers hype) to decrease or increase fuel use and top speed. While the cavitation plate fins all say that they increase the top speed, I don't get the impression that this is the case.
posted 07-11-2001 11:31 AM ET (US)
trim tabs are great! Have them on my 24' Baja. I use them to correct lean angles and to push the bow down in rough seas to stop the banging. Doel fins work on some boats, do not need them on small whalers(with trim) in my opinion. They will slow you down. Tabs will not because they are up when achieving top speed. Biggest problem is the parts are expensive on the tabs.
posted 07-15-2001 10:02 PM ET (US)
Sorry to report trim tabs do not give me the control of the boat I expected.I had trim tabs on a 31ft Trojan and a 23ft Pennyan they would trim the boat with more response than they do on Conquest.I think Sting Ray fin on cavitation plate of motor got boat on plane at lower rpm setting .Maybe sting ray fin and trim tabs over kill please advise me.
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