175 list at high speed

[kingkeith]

i bought a 2002 175 with a t-top and 90 Johnson a few months back. I can't find a marking on the prop for size so I'm thinking its on the backside of it by the hub and I'll have to take it off to see.  I think it's over propped. In gear at idle it drops to 500rmps. Im Usually the only one on the boat. its on a plane at 3500 doing 20 Kts and level. At 4200+ the boat leans to the left a lot. I max out at 5000, maybe 5100 rpms. I removed the t top cover thinking it was acting as a trim tab in the wind and it still did it. It sits level at the dock. I was told something about prop slip, that there's not enough of it and it's making the boat lean as it grabs the water. Any other reasons this would happen?  If I need a prop, what size is recommend?  If I measure diameter, I think it's 13 3/4.

[mshugg]

First off, I would check, just to verify that there isn’t a hook in the hull bottom.  A hook that is more pronounced on the right side could cause this.  More than likely it’s normal function of your right hand rotating prop. Prop torque pushing down on the water can cause some shift in light boats.

As for your prop, how are you trimmed?  Lightly loaded and trimmed out, you should be at the upper end of the RPM range.  I think the recommended RPM range for an OMC 2 stroke was 5500 to 6000 RPM.  Verify this for your engine.  Dropping 2-3 inches in pitch should bump you up to the correct range.  They usually start out propped closer than you seem to be, so before I started switching props, I’d run it at different trim positions and make sure the boat hasn’t gained weight.  Was it propped before the addition of the t top? Or is the foam water logged?

[kingkeith]

The foam is dry. I checked that prior to purchasing because I looked at another that sat very low and the foam was soaked. This boat has also had the list since the day I bought it and it was out of the water for at least 8. I the prior. Sits level at the dock. I bought the boat with the t top, however, they must have used the boat to wakeboard a lot since there was board racks on the t top which I removed. I've played with the trim and that doesn't help.  Where can I find out the max rpm range for this engine?  And where do I get the engine info from? The tag on the mount?

[RickK]

Yes, the tag on the engine mount and then google will help.  As for the lean, at 5000 rpm (which is low) there shouldn't be much of the boat in the water anymore. Just the aft 3 or so feet of the hull and the lower unit/prop.
As mentioned, lay a straight edge from the transom edge going forward and look at the hull on both sides.  If the trailer is not fit correctly to the hull (bunks under the stringers), or if it is a roller type trailer it may have deformed the hull a little over time.

[Woodeneye]

+ 1 for investigating the hook, for clarity a hook is a negative hollow in any area of the boat that is meant to have a dead straight run aft. Which they all should, pretty much. A hook as little as 1/4" can have marked effects. Also check the bottom isn't flexing under load (busted stringer?). Check both sides.

The fact that it is level at 3500rpm then leans over at 5100rpm make me wonder if the bottom is flexing under the increased load.

Also, perhaps a silly question, but......have you checked the motor is mounted plumb in the boat? ie is on the exact centre line and is vertical?

[kingkeith]

Woodeneye, it looks plumb, I questioned that too, there are not any old marks from mounting bolts so im assuming it's an original factory boat/ motor. It's still in the water as I was bass fishing yesterday so l'll put the straight edge on it when it comes out for the winter. I did adjust the trailer when I bought it. It is a load rite with the Aquasport logo on it. It has 2 2x6 bunks. They were on edge and I adjusted them to be flat and adjusted the heights of them.

[kingkeith]

I was hoping the issue was the transducer acting as a trim tab. I adjusted it the second day I had it but it didn't change anything. I even pulled it up so it wasn't in the water so the ducer isn't the issue.

[kingkeith]

Upon last inspection, I did not notice any stress cracks at the transome or the corners. If they were there, that would suggest the transome flexing, correct?

[mshugg]

As long as everything checks out with the hull, it could just be propellers torque.  Here,s a short article that talks about causes of list: https://www.boatingmag.com/how-to/tips-to-alleviate-lean-list-and-heel

A small set of electric trim tabs would be an easy fix for the list.  As far as prop, the boat was most likely propped before the T top was added, so drop a couple of inches in pitch should get you up to a more efficient RPM range.

[RickK]

Upon last inspection, I did not notice any stress cracks at the transome or the corners. If they were there, that would suggest the transome flexing, correct?

To check the transom, after you pull the boat up on the trailer tilt the engine at about a 45 and press your weight down on the lower unit while watching the transom. Bounce a little and watch the transom.

[wingtime]

Without a doubt this is due to engine torque.  This is why at higher power settings the list is worse.  Ever wonder why boats with a side helm have the helm on the starboard side and not the port side?  The reason is the drivers weight on the starboard side helps counteract the engines torque.  On a center console with you standing on the center line of the boat you don't have that weight on the right side to help level the boat out.  On my 170 with a 90 HP Ocean Pro I tend to sit a tad to the starboard side.  Adjusting the little trim tab on the engine can help with this a bit.  But adjusting it too much can induce strong steering loads too.  The only real solution is trim tabs.  Other wise try shifting some of the weight on the boat to the starboard side.

[Aswaff400]

For engine not reaching full rpm, one thing most people overlook is engine height. The factory and dealers hang the motors on the low side. Generally the top or second from top holes. Simply raising the motor a hole or 2 will bring the rpm up, especially once you trim out... I generally like to set boats up with the cavitation plate an inch above the keel for boats under 50 mph, and 2 inches above the keel for boats over 50 mph to start with.

On my fountain my motors where mounted second hole from the top, wide open throttle was 5400 rpm at 65 mph, I raised the motors to bottom holes, wide open rpm went to 5800 which is where they want it to run with a top speed of 69.9mph with the same props. Then I played with props and gained another 3 mph and turn 5900 rpm

[CTsalt12]

My 175 does the same thing.  I think they all do.  No big deal. 

[Woodeneye]

Its a bit of a big deal in a seaway. It makes steering interesting when you are dancing from chine to chine.