A Tutorial on Trimming?

[brianwrites]

I've read several posts here and articles on trimming outboard motors, especially for bass boats. I have a 1990 Procraft Fish and Ski. In the beginning, I accelerated with the trim all the way down accelerated then trimmed the motor way up. After popping wheelies, I quickly learned that I only had to trim the motor up for 1 or 2 seconds. My question is, I get the boat on the pad, trim it up just a tad and it hot 35 mph at about 3500 to 4000 RPMs. But the steel wheel torque is still pretty heavy. I read the wheel torque is very easy when the boat is trimmed perfectly. Is that right. Also if I get to about 40 mph, I'm at 4500 to 5000 RPMs. When should I be concerned about RPMs, hitting 5500, 6000? Thanks for any help you guys can provide.

 

[cr2k]

Re: A Tutorial on Trimming?

Your torque can be offset somewhat with the trim tab on your drive. As for trim you are on the right track, up till it porpoises then back till it stops. You are after the least wetted surface under the back of your boat for least water resistance.
How you load your boat can affect this too.

 

[oops!]

Re: A Tutorial on Trimming?

you might be over propped bud......i think the magic number is 5500....but i might be wrong....could be more.

to trim it.....start in the down position....

get her up on step....then start hitting the button.click click click...

if you start to wheelie.....(porpus) click down till it stops.

you will hear the rpms go up ....

when you are trimmed so you dont "bounce" and the rps are higher than full down.....you are in the sweet spot.

 

[Chris1956]

Re: A Tutorial on Trimming?

The zinc anode (on Mercs) or other small fin on the antiventilation plate can be adjusted to counter most or all of the torque, at a given trim setting and speed range. It will not usually counter torque on all settings. So I would recommend you set it to counter torque on the trim setting and speed you use most often.

BTW- Most motors will pull right at low trim settings and left at higher trim settings. Is that what you are feeling?

I do not know a better way to do this than trial and error, unfortunately...

 

[steelespike]

Re: A Tutorial on Trimming?

What motor are you running?Give us the details on boat and motor,prop etc. Normally you wouild trim for the most rpm and speed at a given throttle setting,lightly loaded.
Motor should be setup and trimmed for the upper end of the max rpm rating.If it can't make max rpm at wot something is wrong with the setup.Possibly prop selection but many other things enter into max performance.

 

[metriccrescentwrench]

Re: A Tutorial on Trimming?

You didn't mention what engine you have, but you want to be to be propped so you're able to get near the upper end of the recommended rpm range with a normal load. If you can't get the engine to turn that fast then you'll need to find a lower pitched prop. Being overpropped (lugging the engine) will cause more harm than anything - (higher combustion pressure, carbon buildup).

As for trim, when you're running more or less straight just experiment some. As others have said you'll notice the engine speed pick up and maybe some porpoising when you've gone higher than optimum.

The best trim setting for straight line cruising isn't going to work when you turn. You need to think ahead of the boat and trim down some as you start to turn, then trim back up to the original position as you come out of the turn.

 

[brianwrites]

Re: A Tutorial on Trimming?

All great comments. As for the prop type, pitch, etc. I'm afraid I don't know. The boat is a 1990 Procraft Fish And Ski. 150 HP Mariner engine. Boat is 18 ft long. Interesting that I'm supposed to adjust the trim and I go into a turn. Never knew that. Thanks for all of your expertise.

 

[Chris1956]

Re: A Tutorial on Trimming?

Brian, Not all boats will require trim changes while turning. If your boat has a pad that it will run on when travelling straight, you may need to trim down in a turm. Most other boats won't require trim changes for turns, unless you are trimmed to the max and running high speed. Obviously trial and error will give you the answer.

 

[DuckHunterJon]

Re: A Tutorial on Trimming?

I too have a Procraft Combo (20.5' with a 200 Merc). I do find this hull is a bit finnicky about trim, but once you have it, it will fly. My experience is trim all the way in (down) for hole shot. Once it pops up, trim all the way out (up) for straight running (with the 200, the trim can't overcome the prop force to go from trim to tilt - so I can just hold it till it stops). For turns, I have to trim in a bit or the prop blows out. Trial and error is your friend. Find a day when the water is calm and find a place where you have some room to play. Lot's of starts and stops, tight turns, etc till you get a feel for it. Then just when you think you have got it, it may change when you load a bunch of people/coolers/fish on board.

 

[cyclops2]

Re: A Tutorial on Trimming?

Good advice from DuckHunter. There are lots of unusuall handling boat hulls out there. Bass boats seem to have a LOT of different handling hulls. Even in the SAME COMPANY. Some years of the same model handle differently. No reason for that.

Practice VERY carefully !! Slowly build up speed after each set of SHARP TURNS EACH way. Hopefully the boat will not roll over in a sharp turn.
I STILL WILL NOT make a sharp turn above 40 mph in the Chaparral. I simply run the object over. log, pole or a shoal. CRUNCH & make a MAYDAY CALL....THIS IS A REAL emergency.