trim gauge problem

[rayaa3]

Hello all. It's that magical time of year when we are all figuring out what new work has to be done on our boat, and what isn't quite working right since being put up for the winter.

I have a 1998 Mercruiser 5.7 250, and alpha one gen II outdrive.

About 5 years ago I had my trim sender and limit changed - the gauge didn't work at all. Everything has been fine since.

This year I noticed something new - the trim sender works - the guage moves, the limiter works (well, I haven't blown my drive yet). However, the gauge is 'off'

when I'm fully trimmed up, the gauge only reads about 1/4 trim up. When I fully trim down the gauge moves down to the bottom, at about half trim, and keeps at the bottom as I finish trimming it all the way down.

I don't think my calibration is off, I think my gauge is wonky.

So I looked at this: http://www.boatfix.com/merc/Bullet/92/92_12.pdf

and for the steps of calibrating the sender on page 6 step 11, it starts with trimming the unit all the way down, and then moving the trim gauge needle all the way down....

ahh what? Moving the needle all the way down? Like with Harry Potter Magic? Is there suppose to be some kind of adjustment knob or technique on a standard trim gauge?

I think that's really the problem here, if I can get the needle to accurately show 'full down" when it is really fully down, but some how adjusting it - then my trim gauge would be accurate.

I know there really isn't much harm in the gauge inaccuracy...as long as it doesn't let me over trim up, and as long as my trim actually works....which it does. However, this is the kind of stuff that will bug me, and if it's easy, well I'll fix it. Easy generally means less than an hour effort. If it's going to eat 3 hours of a saturday, then the gauge is just going to be wrong.

-Ray

 

[Bt Doctur]

you loosen the 2 mounting screws and turn the puck, the trim limit if working correctly prevents that

 

[khe]

The adjustment for the gage is on the starboard side. You'll need a helper to work the trim controls. It is a very coarse adjustment - you probably won't get it exact but it should be closer than 1/4 of the full indicator movement.

With the drive in the full down position, remove the two screws that retain the starboard side sender and verify the index marks are aligned on the sender. It is possible they were not aligned when the sender was replaced?

 

[rayaa3]

OK, I got it. Took about 20 minutes to get it just right. I was able to do it myself, based on an opening near the back of the boat to the swim platform I could see the gauge cluster and read it clearly (thank you PRK).

It was never really perfect before, but it was better than it was now.

However, now I've got it dialed in.

The gauge has a full up and full down, with 'red' zones at the last 1/6 or so in both extremes (is it even possible to over trim down?).

Now, when I trim full up, it ends about the beginning of red up zone. When I trailer up, it enters the red zone and ends on full up.

when I trim as far down as it lets me, it ends at the begnning of red down zone.

Before I was full up going just north of the red down zone, and full down was, well, off the guage full down.

thanks for all who advised.

 

[achris]

(is it even possible to over trim down?).

YES! And it will cause you to bow-steer which, in a following sea, can be very very dangerous.

The way I 'tune' trim gauges is to trim the drive so the anti-cav plate is perfectly parallel with the bottom of the boat, then turn the trim gauge sender until the needle is exactly in the centre of the trim range (see picture). Makes it easy to know if the drive is slightly up or down before you drop the hammer.

Chris........

 

[rayaa3]

LOL - sea, that's so cute. Dude I live in Oklahoma The lakes around here get rough, but only from Okie wind.

In all seriousness, I knew it was possible to overtrim down in terms of performance and steering, but really I meant can you damage the drive, like you can by over trimming up.

I will however, heed this advice and go see where on my trim gauge is parallel with the hull.

Since we are on the subject of trim, I never really felt like I was taught the right explanation for proper trim. Here is what I was taught: to be the most efficient you should trim up as far as you can before you lose 'bite' and RPM start to rise.

The reality is that I'm usually trimmed pretty far down.

It might be helpful to understand: 20 f 1998 deck boat with a tri-hull like design (not the true tri's of the 70's and 80s) that is usually either making a run across the lake to a swimming cove, or towing the kids on tubes. The boat is overloaded most of the time (the rating is for 11 people, but if you look at the weight, it's 11 very skinny people who don't pack a crap load of coolers) Even with our 5 fat adults, and 5 skinny children, and countless coolers - the boat still pulls 25-30mph easy w/o going over 3000-3500 RPM. With 2 people on it does it in 3000RPM.

So really trim, what's my goal?

ray

 

[drolds72]

You are looking for efficiency. If you notice in Achris's pic, he has a GPH flowmeter. He probably trims for fuel consumption on a calm day. I trim for highest cruising speed vs a static RPM, while maintaining good steering and ride.

 

[achris]

Mostly I trim for comfort. Which in this boat is slightly bow up, mostly. Heading into short chop needs the bow down though. But most definitely bow up running with our long swells.