Trim operation question

[john crowe]

Please...someone....explain to me in basic terms the function of the trim system, Here is what i have and why i wonder.

Today...i got my trim motor installed and trim working. When i take off, the nose of the boat raises high....front of engine is all the way down.

As i accellerate....I raise the front of the engine using the trim....however the nose of the boat doesnt go down. Is is suppose to???

So i guess the question is what should be happening and what is the trim for?

The boat is a 78 glassmaster 18ft , the engine is a 3.0, the drive is a model 400.

Please let me know other info that might be needed.

 

[freddyray21]

Re: Trim operation question

not all that familar with the those drives, but on a Mercruiser you leave the drive all the way down until you are on a plane (nose of the boat down) then you trim it for speed.

 

[john crowe]

Re: Trim operation question

not all that familar with the those drives, but on a Mercruiser you leave the drive all the way down until you are on a plane (nose of the boat down) then you trim it for speed.

drive down...meaning front of engine should be high as possible?

my issue seems to be the nose is always up when i start moving at any speed and doesnt seem to come down

 

[john crowe]

Re: Trim operation question

Did alittle reasearch. Seems im doing it opposite of how it should be done. Still...the nose of the boat never lowers.

http://www.boatsafe.com/nauticalknowhow/trimtilt899.htm

 

[f_inscreenname]

Re: Trim operation question

It sounds like it is underpowered or over propped. You also may need to move some weight to the front.

 

[freddyray21]

Re: Trim operation question

What pitch prop? I needs to have enough power to bring it on a plane (nose down) Assuming the motor is enough and if it came with the boat it should be and it's tuned and running properly. How long since you had it tuned? Carb clean? , but assuming the motor is running as it should be you need to go down in pitch on the prop, but I would start with the motor. Running good at an idle is alot different than running good under a load. I have a 1972 Searay SRV 180 with a 120 hp Mercruiser and we pull skiers with three or four people in the boat.

 

[john crowe]

Re: Trim operation question

how can i find the prop pitch? Im sure its same as it was made with. the engine really turns up the rpms and seems to move across the water great.

 

[jimhen]

Re: Trim operation question

I think I can help. I am a former O/B operator that got ahold of an I/O with power trim a few years ago, The whole concept was foreign to me. Check your boat out of the water to be sure the moter goes all the way down. unlikely this is not happening but if you look at it you should be able to see how when you hit the gas it will just push down a little on the bow. As you come up in speed and approach plane it take a little touch but you gently lift the engine a little to keep the bow from plowing in. If this isn't you then maybe the last couple of comments are right on. If you aren't all the way down with the moter your nose will be up

 

[jimhen]

Re: Trim operation question

the pitch and dia are stamped on it somwhere around the hub I think

 

[john crowe]

Re: Trim operation question

the pitch and dia are stamped on it somwhere around the hub I think

Heres what ive found to have:

#172490
Dia-14.00
Pitch-13
3-SST
OMC 24 - 31 mph

Recommendations on a prop to get more speed also?

 

[thrasher]

Re: Trim operation question

I will let people with more knowledge than me chirp in here, but that prop seems tiny for your boat. I have a 4.3L and am running a 14.5" prop with 23" pitch.. I am guessing that the prop might be too small and that will prevent you getting up to planing speed, which is why the nose never drops.. The boat will probably pull anything, but its not going to have much speed.. I suspect you need something with a 15 to 17" pitch, but that's just a guess. See what the more knowledgable people on this site suggest.

Gary

 

[john crowe]

Re: Trim operation question

i was also thinking the prop is kinda small....but of course i know very little about the aspects of boating thus far...but im slowly learning

 

[QC]

Re: Trim operation question

This sounds like an OMC 400 stringer drive. Define the "front of the motor". If this has power trim (unlikely) then interestingly enough it is the front motor mount that goes up and down. If the front motor mount is not a motorised screw jack thing, then there is no power trim and it only has tilt . . . However . . . if it has manual/fixed trim, the front mount can aslo be raised and lowered (adjusted) to change the fixed trim position. It could be set too low and no matter what you do, you can't get negative trim (for starting off). Please take a look at the front motor mount and tell us if this is what is going up and down. If not, then we have to start this discussion over . . .

 

[freddyray21]

Re: Trim operation question

I am running a 17 pitch on my 120 hp Mercruiser. I can run a 19 or a 21 and still plane the boat. The lower the pitch the more power generated, but too low a pitch and the rpms on your motor will be too high. Pitch is defined on how far it is supposed to move the boat in inches for one revolution in theory. A 17 pitch is 17 inches. I think a 13 is way too small.

 

[john crowe]

Re: Trim operation question

yes it has power trim (selectrim) I can raise and lower the front of the engine with a press of the button

 

[QC]

Re: Trim operation question

yes it has power trim (selectrim) I can raise and lower the front of the engine with a press of the button

Cool!! Not a lot of those out there. Are you getting the "tilt" all the way down before you go anywhere? i.e. there should be a substantial "clunk" when the drive completes the downward tilt range. I also agree that the 13 pitch is too low, however it should "jump" up on plane with the front of the engine all the way up ("down" or "in" trim of the drive) so something else is causing this bow high condition. Could be a few other things, but I would start with weight balance etc. I would not touch this prop until you figure out why it won't plane. It is, however, possible that this prop is marked wrong and is actually a much higher pitch, but that, like most of this, is speculation . . .

 

[john crowe]

Re: Trim operation question

thanks for the help.

the tilt is all the way down. No problem there.

Ive tried all I know other then changing the prop to fix this bow up condition.

I looked and i can only change the prop pitch...not enough room to change to a bigger "size" prop.

Should i try a 17 pitch prop?

 

[ricksrster]

Re: Trim operation question

To determine the proper pitch prop for your boat and motor you will need a tach. Your motor has a max RPM range for WOT. If your RPM is over the max you need more pitch. Is it is under the max range you will need less pitch.

 

[john crowe]

Re: Trim operation question

To determine the proper pitch prop for your boat and motor you will need a tach. Your motor has a max RPM range for WOT. If your RPM is over the max you need more pitch. Is it is under the max range you will need less pitch.

Simple enough...boat has a tach. Ill see what it does

 

[QC]

Re: Trim operation question

I want to keep this from getting too far from the beginning . . . When you start out, the drive is down (front of engine up). Give it all the throttle you have. What happens? Detailed description, with RPM and speed info. Does the bow initially go up and then as speed increases it comes over (down) a little and the boat goes faster? We need to know what happens without any further adjustment to the trim, keep the front of the engine all the way up and tell us what happens.

I think it is a little ( a lot) premature to start talking about pitch if we really don't know if this thing is planing. This problem may be engine performance . . . you can do a few little things in this area initially. Have someone confirm that you are getting the throttle all of the way open at the carb when you push the throttle handle all of the way down. We need to confirm that the engine is doing everything it can, tune up, all that kinda stuff before we can determine the proper pitch. If there is anybody that you can borrow a prop from to get an idea as to whether or not that 13 is actually a 13 that would help too i.e. if you borrow a known 17 and the problem is worse, then we are close to confirming that is really a 13" prop . . . But again, if you really do have a 13 now, and it won't plane, or the bow will not come down, then trying to figure out what the "correct" pitch should be is, well . . . uh . . . stupid

BTW, don't spend another minute thinking about diameter. That decision is already made, nothing you can do about it . . .