Propeller, trim tab adjustment, or something else?

[skipdave]

About a week ago I bought a 1984 Century Mustang 195. It has a 140hp 4 cylinder Mercruiser engine. This is my first boat. The propeller that was on the boat when I bought it had hit some rocks and the edges of all three blades were jagged/missing chunks. The previous owner said he had done this hitting rocks but had been running it for some time since he hit the rocks. I noticed a vibration/shaking at times on acceleration and when stopping at certain speeds there was shaking/vibration. I only took the boat out once with the damaged propeller. Today, I replaced it with a brand new one and at first it seemed to accelerate more smoothly. Fairly quickly though, I noticed that the boat pulled hard to the right at faster speeds. Even at slow speeds, it seemed to be easier to turn to the right than it was to turn to the left, but at higher speeds I had to compensate for a strong pull to the right and if I let go of the wheel the boat would start to quickly turn right. I didn't notice this pulling before changing the propeller. I am wondering if it is because of the new propeller? I also read about adjusting the trim tab, but I cannot find the adjustment screw or bolt to get the tab to move. It is centered now. But, I also noticed that when the boat is out of the water and the prop is raised, it seems easier to turn it to one side that it does to turn it to the other. Also, when I turn the steering wheel all the way in each directoin with the boat trailered and prop up, it returns itself just slightly off center one way, but very off center when turned the other way and let go. Should I just try adjusting the trim tab? If yes, how do I get to/find the bolt to loosen it to adjust it? Or is it possible that something is wrong with a steering cable? Definitely a novice here, so good descriptions/photos would be helpful. Thanks

 

[Texasmark]

Re: Propeller, trim tab adjustment, or something else?

Behind and above the prop is a thing called a trim tab. It's job is to trim the boat to offset the torque of the prop. By changing your prop, you apparently changed the torque the engine was applying to the water and caused your experience.

The tab is held in place with a bolt that does down through the anti vent housing and into the tab. The bolt may be visable, or you may have to pull a plastic plug to see it.

To correct, loosen the bolt, turn the tab in the direction of the error looking forward. If your boat goes easily to the right turn the rear of the tab toward the right (starboard side of the boat).

Lock her down and try it. Usually there is enough there to solve your problem; some times you don't have to go all the way to one side. The higher the pitch of your prop, the more you need. Additionally, this is usually trim sensitive and I usually set mine for the least torque on the steering at the trim level where I usually run.

HTH,

Mark

 

[skipdave]

Re: Propeller, trim tab adjustment, or something else?

Thanks for the help. The bolt to adjust the trim tab was under a plastic cap- found it and adjusted it all the way. This helped somewhat, but there is still a noticeable pull to the right at faster speeds. It is also still much easier to turn the steering wheel to the right, and there is still resistance when trying to turn left. I think I might try loosening up the propeller bolt. Maybe I over-tightened it and that is what's causing this?

 

[craze1cars]

Re: Propeller, trim tab adjustment, or something else?

Over-tightening the propeller is not your problem.

Hitting rocks with propeller usually means hitting rocks with your skeg as well. So I'm curious what is the condition of your skeg? Does it look like this?:
http://www.google.com/imgres?imgurl...&sa=X&ei=u5o4Tv2qHMv_sQLp8s05&ved=0CCIQ9QEwAw

or like this?
http://www.google.com/imgres?imgurl...&sa=X&ei=9Zo4TvL4MYbDsQLQ8_0e&ved=0CBkQ9QEwAA

Sight down the skeg from the rear of the boat. See if it is bent one direction or the other. It should be straight as an arrow. Any bend in one direction or the other, or any good sized missing chunks, will mess with your steering pretty bad....

All that said, 3 blade propellers can sometimes create a lot of torque steer. Every design is different. Often using a 4 blade propeller will greatly minimize/reduce it, although I realize you've probably already purchased a 3 blade...

The fact that you are feeling substantailly more resistance at the steering wheel in one direction and not the other while completely out of the water tells me you may have a steering issue. Is this a hydraulic steering system? Cables? Any idea? Might need new steering system....they do wear with age & time and can do strange things. Reputable manufacturer of that sort of stuff:
http://www.teleflexmarine.com/products/hydraullic-new/sterndrive-steering-new/

 

[Fed]

Re: Propeller, trim tab adjustment, or something else?

Too much negative trim will make it pull to the right also.
Now this following part I just don't understand?

But, I also noticed that when the boat is out of the water and the prop is raised, it seems easier to turn it to one side that it does to turn it to the other. Also, when I turn the steering wheel all the way in each directoin with the boat trailered and prop up, it returns itself just slightly off center one way, but very off center when turned the other way and let go.

That I'd like to see, are you sure you have described it correctly?

 

[skipdave]

Re: Propeller, trim tab adjustment, or something else?

Here's a couple photos of the skeg- it's got a guard or shield on it which I didn't put on, but looks straight to me. There is a small gash on the front edge but I don't think that would be causing the problem.

I'm starting to think it must be something with the steering. I'm not sure if it's cables or hydraulics, but I know it does have the same resistance when turning the wheel left and the same ease when turning it right when the boat is out of water.

 

[skipdave]

Re: Propeller, trim tab adjustment, or something else?

Fed- when the boat is on the trailer, out of water and on level ground, I center the prop at the back of the boat. Then I turn the steering wheel all the way in each direction and let go- the steering wheel spins back and the prop ends up in a different return position depending on which way I have turned the steering wheel. The boat itself obviously does not turn or move at all. What I was describing is that it seems like there is more tightness or tension against turning left even when the boat is out of water. Also, when trailering the boat, if I center the prop/skeg inline with the center of the back of the boat before taking off, it always shifts or tilts to the right or starboard side during trailering and stays there- which supports the fact that for some reason there is tension against turning left which is causing pull to the right, even out of water.

 

[craze1cars]

Re: Propeller, trim tab adjustment, or something else?

Skeg setup is adequate, not causing this problem. Might want to experiment with the trim tab a little more and not be so aggressive with it and try a few different positions...normally no more than 5 degrees one direction or the other....going too severe just creates drag and messes with things.

BUT, it sounds like you have a strange deal with your steering wheel wanting to pull to the right no matter what...even when out of the water.

Suppose if it were my boat, I'd delve deep into the steering system and try to figure out why...disconnect the steering wheel and see if it freewheels both directions...then disconnect the outdrive hookup just inside the transom and see if the outdrive freewheels both directions when steering system is disconnected. If yes to both, then there is some sort of tension wtihin the steering system itself. Most likely hydraulic I'd think, and presumably this 3.0 does NOT have power steering lke most of the larger Mercruiser's do. But sorry I don't know very much specific about those systems to advise any further...

 

[Fed]

Re: Propeller, trim tab adjustment, or something else?

A couple of things Dave, firstly have you tried trimming out?
Too much negative trim will definitely cause it to pull to the right.

Secondly, is that skeg guard stainless steel and if that white stuff on the gear case the start of corrosion I'd ditch the skeg guard and get the skeg welded/repaired with a new piece of alloy.

But, I also noticed that when the boat is out of the water and the prop is raised, it seems easier to turn it to one side that it does to turn it to the other. Also, when I turn the steering wheel all the way in each directoin with the boat trailered and prop up, it returns itself just slightly off center one way, but very off center when turned the other way and let go.

Do you mean when you turn the wheel from lock to lock there is a lot more travel in one direction than the other at the leg?

 

[skipdave]

Re: Propeller, trim tab adjustment, or something else?

A couple of things Dave, firstly have you tried trimming out?
Too much negative trim will definitely cause it to pull to the right.

Secondly, is that skeg guard stainless steel and if that white stuff on the gear case the start of corrosion I'd ditch the skeg guard and get the skeg welded/repaired with a new piece of alloy.


Do you mean when you turn the wheel from lock to lock there is a lot more travel in one direction than the other at the leg?

The pull to the right might actually be because I'm not trimming out enough when going faster. There is no trim gauge and I'm always afraid I will trim out too much and flip the boat. I've read/heard that can happen.

When the boat is out of water and I turn the wheel all the way right and let go, it spins back, and when I turn the wheel all the way left and let go it spins back. Each time I do a right turn, the propeller/outboard is always re-positioned at the same angle after it spins back and each time I do a left turn and let it spin back it repositions itself at the same spot. But the spot it stops at after a right turn is different from the spot it stops at after a left turn. After a left turn, it returns itself in a way that if it was in water would turn the boat to the right. After a right turn and I let go of the wheel, it spins back just slightly off center. That's why I thought maybe it was something to do with a cable or hydraulics. I still don't know which my boat has.

 

[craze1cars]

Re: Propeller, trim tab adjustment, or something else?

The pull to the right might actually be because I'm not trimming out enough when going faster. There is no trim gauge and I'm always afraid I will trim out too much and flip the boat. I've read/heard that can happen.

You have read/heard incorrectly. Quite the contrary. In fact, NOT trimming out for higher speeds causes "bow steering" which is very unpredictable and can be dangerous. It might be exactly what you are experiencing. If you trim out too far at high speed only one thing will happen...the prop will blow out of the water and you will lose speed...nothing more. It is not dangerous in the least and will absolutely NOT cause you to flip the boat...in fact it might prevent it by eliminating your pull! The only "danger" is that you want to get out of the throttle or lower the trim as blowout starts to occur, so the prop bites again before the engine over-revs.

So the correct way to use trim, with or without a gauge at high speeds (gauge is completely unnecessary...trim should always be done by feel/sound/experience...gauges are notoriously inaccurate anyway), is to start with the trim down (for max holeshot), and then as soon as the boat planes out go ahead and start trimming up. When you notice the prop start to blow out of the water a little bit just trim it back down a little bit. That's your sweet spot. I might actually completely correct your steering problem if you trim out farther like you're supposed to.

For obtaining proper trim at ANY speed, you are essentially looking for the "most efficient" trim location. This always occurs when your speed (and also RPM) is maximized at any given throttle position. So for example if you like to cruise around a 2/3 throttle, just leave it there for a while and play with the trim button. If you go up too high, speed will drop...usually when the prop starts to lose bite with the water. But if you go down too low, speed will also drop, because the bow starts to dig and plow water. And somewhere in the middle you'll find a spot that gives you max speed for that 2/3 throttle position. This is the trim position where you'll get the most speed/distance for your gallon of gas, with the least amount of wear/tear/strain on the motor and boat. You don't need a trim gauge to find that spot...you just need a working tach or speedo.

 

[skipdave]

Re: Propeller, trim tab adjustment, or something else?

Thanks for the information. I will try this the next time I take the boat out.