Proper Trim Angle

[rgreenwell8962]

So it's my fifth season boating in my 2001 2500 SCR Bravo III (brand new transom assemble and drive) and I feel a bit embarrassed to admit, but I still do not think I know how to "correctly" trim the drive. How much is too much? How much is too less? Do I need to raise it more or lower it? When I get up on plane, I tap it up a notch at a time until the "growling" or the "vibration" noise lessens. If I go too much one way or the other the sound comes back so I try and find the sweet spot. I figure this is the way to do it but after a day out on the sound this weekend I have begun to question my tactics, or maybe the integrity of my new Bravo III drive. On my way back to Elliot Bay from Bremerton the water was calm, the tide was coming in at 4.4 and there were long gradual rollers, no chop. Maybe I am just being a bit paranoid after dropping the cash to replace the drive, but I couldnt quite get that noise to disappear. At one point, for a very brief brief moment, the vibration actually was very loud until I slowed down and adjusted the trim a notch or two. Even so, it seems as though there is always some noise besides the regular engine noise. I want to say that it was always this way, even with my old drive. All the fluids are topped off so I kow I am not leaking anything which could cause something to happen. The engine ran great whether I was at a constant RPM of 3800-4200 and was cruising along a bit over 30 mph.

I sure don't want to hurt this new drive. Any thoughts?

Thanks everybody! Hope you are all out enjoying the water!

Rich

[ss3964spd]

Rich,

If yours is like mine there should be a detent that you have to push the toggle past to raise the drive all the way up. The toggle has a a range of motion prior to pushing past the detent. That small range is actually the pre-set drive trim and it is supposed to trim the drive up to exacly the correct angle once the boat is on plane. I have not had to fuss with the trim sensors on my boat but I believe one sensor is used to set the proper planning trim angle and the other only feeds the trim gauge.

If set up correctly it works like this in operation: Toggle the drive all the way down and throttle up to get on plane. Once the boat is on plane thumb the toggle lightly - make sure you don't push past the detent, to raise the drive to it's pre-set limit. Even if you hold the switch "on" (but without going past the detent) the drive won't raise any further. If you drop off plane simply thumb the toggle down again.

Dan

[rgreenwell8962]

Dan,
Good to know. I will try this. I had no idea.
Thanks!

[ss3964spd]

No problem Rich.

Whole purpose of trimming the drive is to get the horizontal surfaces of the drive, as well as the center line of the props, horizontal in the water. Otherwise they produce drag.

Come to think of it you can actually test yours. With the engine off, drive all the way down, and battery(s) on lightly hold the toggle switch. You should hear the drive trim pump run for about 5 seconds (ish) and then the pump will simply stop running. If everything is set up correctly the drive will be trimmed to the correct position when on plane.

Dan

[tackleshep]

Rich,

I'm a little concerned. You shouldn't get any weird noises or vibrations unless you have trimmed to high. For short trips and rougher water I'll go times without touching the trim and just use my tabs.

Just to make sure were on the same page. You are starting the boat with the trim all the way down....right? Lowering the trim should never get you weird noise or vibration only taking the trim to high should cause you any grief?

[ss3964spd]

Very valid TS. Agreed - if the drive is all the way down it shouldn't be making any noise or vibrations.

[rgreenwell8962]

I am starting the boat with the trim all the way down. Once I jump up onto plane, and get going for a bit, that is when I play with the trim adjuster. When it is in the full down position, there is a slight low pitch noise. If I click it just once, maybe twice, it goes away. It was like this with the old Bravo III, and is the same with the new Bravo III, which includes everything new aft of the engine.

Hmmmmmmm

[tackleshep]

I really think hoping on another similar sized boat and listening would help.

Like we said before you shouldn't have any unusual noises while trimmed down.

Now you just need to define unusual. .

For many of us we've been on numerous boats and when u say low pitch noise that could be a problem or just your ears.

[tjwieseler]

I agree, there shouldn't really be any pitch change when trimming until you get to the point of cavitation.

I have a 2400 SCR with a 5.7 EFI Alpha Gen II. When getting on plane I set the trim tabs all the way down and the drive trim all the way down. Once on plane I will raise the trim tabs all the way, unless I am a little uneven on the load, then I will level out with the trim tabs. Once the trim tabs are up all the way then I will tap the drive trim up a little at a time until I start to porpoise (bow bouncing up and down by itself) then I will back the trim back off a little. Sometimes in calm waters you can get the drive to cavitate then trim the drive back down. I just try to get the best RPM/MPH at the same throttle, with the combination of the trim tabs and drive. Sometimes you can get a little better MPH with the trim tabs down just a little. Each boat has it's own "Sweet Spot", so experiment with yours and see where it is. The drive doesn't always have to be fully trimmed out, most of the time just a little does what you need. It all depends on your load in the boat and where it is at.

The only time I get any different tone is when the propeller is cavitating.

Terry

[Warpa1]

Probably a silly question but i take it the prop is in good order along with the diffuser ring? If any damage or the ring is missing can sound like the trim is too high and creating the vacuum. Like the others have said though it sounds more like a serious problem as with the leg up or down there should be no noise or vibration.

[seapuppy]

on a B3 drive, the proper way to start out is drive down...tabs down if needed...hit the throttle and as the boat comes up on plane...reduce tabs first..adjust throttle rpm......then bump the drive up until you feel the boat free up...and your rpm's increase by a few hundred rpms....at this point your on plane...your at the least resistance...and your drive angle is set properly to drive the boat on smooth water...if the drive is too far down..meaning in the down position....your bow will be digging in....if it's too high..(and the b3 drives are easy to get too high)..the drive will cavitate thus loosing effeciency....the comments about a detent and all....those maybe applicable to the volvo drives ..but merc's will tilt up until it hit the stops..then you need to use the trailer button to raise the drive further...there is no detent on the mercruiser drive throttle quadrant.....
if you put the drive angle too high...the drive will cavitate...aka produce bubbles ...and make the noise and of airation...it will loose effeciency ...you will slow down..the rpms will increase...and about the only thing it will do is produce a rooster tail out the back....
is it bad for the drive??...no...won't hurt it...but it does waste alot of gas.....

On a B3 drive..if you bump once...and the drive starts to cavitate....there is a space or what they call the "Celery stick" on the pivot of the drive..that will have to be pulled out by a tech and flipped over to allow the drive to tilt down further.....but most of the time that isn't a problem....that's just an fyi....


SP

[ss3964spd]

Steve,

The drive trim toggle switch on my control lever absolutely has a "detent" (for lack of a better word).

If the drive is all the way down, if I maintain light pressure on the top of the toggle (the toggle only moves a little) the drive will raise just a little bit - then it simply stops at it's pre-set angle and the pump stops running even if I hold the toggle on. I can, of course, position the drive at any angle within that limited range. For how and where I boat I am able to simply trim it to it's max preset range and it never cavitates unless I turn very sharply.

To raise the drive more I have to press the top of the toggle harder to over-come the detent. It's almost like a snap that you can feel in the switch.

Dan

[seapuppy]

hmmm...interesting....must be something new then....all 3 merc drives don't have this one...even my 340 with the b3 drives just has a simple toggle for each drive...up...down.....then on the dash is a "Trailer" button..which brings the drives all the way up..

SP

Originally Posted by ss3964spd

Steve,

The drive trim toggle switch on my control lever absolutely has a "detent" (for lack of a better word).

If the drive is all the way down, if I maintain light pressure on the top of the toggle (the toggle only moves a little) the drive will raise just a little bit - then it simply stops at it's pre-set angle and the pump stops running even if I hold the toggle on. I can, of course, position the drive at any angle within that limited range. For how and where I boat I am able to simply trim it to it's max preset range and it never cavitates unless I turn very sharply.

To raise the drive more I have to press the top of the toggle harder to over-come the detent. It's almost like a snap that you can feel in the switch.

Dan

[rgreenwell8962]

Thanks for all the great input. I believe I am hearing the cavitation. I tried the detent, but mine does not have that. All I get is al up or all down, with no auto stopping in between. The detent is for trailoring on mine.

Thanks again. Love this forum!

Rich

[seapuppy]

one weekend give me a call and we'll go out and double check....


SP

[ss3964spd]

Really interesting. No "Trailer" button on my dash. Must all come down to differences in the control stalk.

[rgreenwell8962]

Sounds like a plan! Thanks for the offer! We are heading into the salt this weekend, though not sure where yet. It depends on the wx.
[
QUOTE=seapuppy;16741]one weekend give me a call and we'll go out and double check....


SP[/QUOTE]

[seapuppy]

come up north to Everett...I'll meet ya there...