not enough trim?

[junkyardwarrior]

I have an '87 Tidecraft 16' bass boat, 88 model 90 Mariner 3 cyl with PT&T. Seems like I can't trim it "out" enough. I trim it all the way up but it seems like the boat could use more. It keeps speeding up until it won't trim out any more, seems like it could go more and benefit. Trim rods are fully extending (verified). It appears that the transom is 18 deg. At one time I did have a jack plate on the boat (6" back, 6" lift manual). All the way up (5" from bottom of boat) it was "ok" but not worth losing the hole shot, so I pulled it back off. Even with the jackplate it seemed like it could have been trimmed more.

Not sure if this is the right forum for a question like this.

Is there anything that can be done?

 

[Chris1956]

Re: not enough trim?

Lots of things can be done. Trim effect is a function of speed, motor height and hull shape. If you cannot get the boat to porpoise at max trim, I would think you could install transom wedges to increase trim angle. You might experiment with some home made wooden wedges, or get some cedar shingles.


Another thing to look at is to see if the motor needs to be raised or lowered on the transom. Since the motor doesn't blow out at max trim, this may have no impact, but be sure the antiventilation plate is above the water, while on plane. Make sure the hull is not hooked, and nothing is hanging down on the transom, to give the effect of a transom hook.

 

[junkyardwarrior]

Re: not enough trim?

I actually tried raising the outboard 5". No effect, other than losing the holeshot (it was extremely hard to plane with 2 people...approx 400 lbs). Top speed did not change and neither did anything else, other than adding 30 lbs to the transom. After pulling the jack plate off I tried all the way up, all the way down, no difference whatsoever in any position. I am currently about in the middle of the adjustment holes, which puts the AV plate about an inch high. I also noticed that one of the trim rod "seats" (the two threaded pieces that go into the swivel bracket-they provide a place for the trim rods to contact) was falling out. I tightened it, then thought it might be nice to add a couple washers to "move" them out a little, which gave me another couple degrees of trim-and that added 6 mph with no other changes and a LOT better fuel economy. Makes me want to make a couple seats that have more adjustment (maybe a modified 3/8-24 bolt and a pair of jam nuts) and try that. Does that sound feasable?

 

[Jdeagro]

Re: not enough trim?

What I hear you saying is that You can not trim the bow up enough when you are on plane to maximize your speed. Is this correct? Do you have any planing devises on the boat or motor?

 

[Capt'n Chris]

Re: not enough trim?

Mercury seems to have less overall trim angle than others which create issues as you have described. Aluminum (adjustable) wedges are made that will fit inconspicuously between the motor bracket and the transom. I would certainly try those before putting anything else on your boat in an attempt to correct the problem. You'll have to pull your motor, but will be worth the effort.

 

[junkyardwarrior]

Re: not enough trim?

What I hear you saying is that You can not trim the bow up enough when you are on plane to maximize your speed. Is this correct? Do you have any planing devises on the boat or motor?

Yes that's right. It keeps gaining speed as I trim up but never blows out or porpoises (at wide open throttle). It will porpoise a little at lower speeds with too much trim, though (obviously). It does have a "whale tail" on the AV plate, but it is not in the water when the boat is on plane. Verified it the other night at the river. The only "hook" might be the transducer for the FF and the speed sensor. I guess I could pull them off once to see if it makes any difference.