Need some advice on how to use drive trim properly

[Donzi GT250]

Need some advice on how to propery use the drive trim on a I/O.
When I have the boat on plane and crusing at 3200rpm how can I tell when I have the drive trimmed for optimal performance?

 

[HT32BSX115]

Re: Need some advice on how to use drive trim properly

Need some advice on how to propery use the drive trim on a I/O.
When I have the boat on plane and crusing at 3200rpm how can I tell when I have the drive trimmed for optimal performance?

Howdy,


It's fairly easy..... Just do your "hole-shot" with the drive almost all the way "IN" or "DWN"

Push it up to 3000 RPM or so and slowly "bump" the trim OUT until the speed increases. The boat will speed up as the drive reaches optimum position. (change your speed and the trim position will change slightly)

Run the drive OUT (or up) too much and you'll either experience "porpoising", produce a slight "rooster-tail" prop cavitation and you'll slow down a little. (Obviously your past the optimum drive position)

Change the center of gravity of the boat (move stuff or people from front to back in the boat) and you'll need to change the drive position slightly.

Don't rely on the gage.....you'll do it by feel mostly.

Some outboards have it even better since they can also change the vertical position of the "drive".





Regards,


Rick

 

[Silvertip]

Re: Need some advice on how to use drive trim properly

The seat of your pants is the best indicator of where best trim is. You should feel the boat suddenly take a very significant smoothness and slight speed increase at that point. If your butt is not particularly sensitive, then try your ears. Listen and watch the spray coming off the boat. Properly trimmed you will notice the rush of water suddenly become significantly quieter when the boat reaches proper attitude. Now you have two indicators. Try and translate what you see and hear to what you feel when on plane. Generally trimming up until porpoise starts, then backing down a couple clicks will put you at best trim. That setting my the way is not the same as load increases or decreases so the only real value the trim gauge has is to let you know where the drive is. It has no bearing on what the proper setting is.

 

[DuckHunterJon]

Re: Need some advice on how to use drive trim properly

Silvertip has it - you need to go by the "seat-o-pants meter". After a few times out, you'll get a feel for it and not even think about doing it.

 

[Brentathon]

Re: Need some advice on how to use drive trim properly

For my 23' mid-cabin, rpm's and speed are not good enough indicators.......I use SOUND (from load on engine).
I ALWAYS have the drive trimmed all the way DOWN when getting up on plane, once on plane, I pulse the trim switch UP until the engine suddenly gets a little quieter, then I usually give it one more pulse UP on the switch. If I'm not sure whether I trimmed UP enough, I lower it and repeat the process. I can always hear the motor "groan" more when I lower it; my engine doesn't like when the prop shaft is not parallel to the incoming water.

 

[Donzi GT250]

Re: Need some advice on how to use drive trim properly

So I gather that as long as you don't see a roster tail or have proposing you are in the safe zone and don't have the drive too high?
BTW after 28 years of marriage my Seat O Pants meter is pretty well worn out.

 

[Silvertip]

Re: Need some advice on how to use drive trim properly

"Safe Zone" is not a measure of trim! There is no safe-unsafe trim setting as far as "proper" trim is concerned. On some boats you couldn't get a rooster tail if you tried yet the opposite of that is still being trimmed down too far. Experiment with trim. That's what it is there for. You will learn what setting is best. Think smooth and quiet.