Boat tilts to the left at full power

[rbiggins]

I just restored a 1964, 15' Redfish Runabout with a 1964, Merc 650, 65 horse. The boat runs out good until after about 2/3 power. After that, it lists to the left. It doesn't pull to the left, it lays on its side and continues to run forward. I have adjusted the trim tab to every possible position but it doesn't make much difference. It also is not a weight distribution issue. I tried many different combinations as well. It does have a hydrofoil stabilizer on the motor. I had the same problem without the hydrofoil.

Any Ideas?

 

[QC]

Re: Boat tilts to the left at full power

Most single screw boats list opposite of the prop rotation. Your hull could also contribute to this if it had a hook that was more pronounced on the starboard side, or rocker that was more on the port side. I am leaning (pun intended) towards some hull imperfection. You should lay a straight edge down both sides. Also can you give us your prop dimensions. Prop torque obviously contributes, and may be the whole issue, it just seems odd that you don't feel it as you first apply power. That's where I typically notice it on my boats.

Good job testing with and without the foil. Eliminates that from the discussion

Oh, and welcome aboard!!

 

[rbiggins]

Re: Boat tilts to the left at full power

The numbers on the prop are 48 37900A3 15F. It is not the original prop.

It NEVER does it at lower speed.

 

[QC]

Re: Boat tilts to the left at full power

It NEVER does it at lower speed.

I would not expect it at all at "displacement" speeds, but how about as she begins to plane? Not full speed, but as you come onto plane.

 

[rbiggins]

Re: Boat tilts to the left at full power

It planes out great with the hydrofoil and I can cruise as long as I want at 2/3 throttle. As soon as I give it more power, it lays on its side.

 

[QC]

Re: Boat tilts to the left at full power

Have you played with trim? Higher (out) may solve some of this. And again, similar issue without the foil, right? Cruises along OK on plane, but then heels over when you mash the throttle?

 

[rbiggins]

Re: Boat tilts to the left at full power

Exact same problem without the hydrofoil. My problem with the trim is; I can only adjust it to the lower three of six settings. I have to take the rod out every time to release the motor and then move the rod up or down. I would like to try the higher settings but without the release, the (shock absorber type pistons) on the side block the pin from being removed. Where is the release?

 

[QC]

Re: Boat tilts to the left at full power

Hopefully someone with older Merc OB experience will chime in. I'm not that guy . . . I would certainly like to test this out at higher trim levels before I panicked. Straight edge is easy to check too. Again, with my boats,m the list happens as you throttle up, and then can also get worse at higher speeds, but yours seems awfully pronounced from what you describe.

 

[rbiggins]

Re: Boat tilts to the left at full power

Trim release problem solved.

 

[QC]

Re: Boat tilts to the left at full power

Retest.

 

[rbiggins]

Re: Boat tilts to the left at full power

10-4 this Saturday.

 

[QC]

Re: Boat tilts to the left at full power

Might be good to check the bottom as I suggested as well. If we had the bottom condition out of the way, then we could concentrate elsewhere. Also, can you confirm the motor is mounted straight on the transom. If the motor was leaning to Starboard slightly as viewed from behind, this could cause this as well.

Also, set the lower unit trim tab to where she is comfortable to steer both directions at a typical speed. The tab is used primarily to correct for steering tension. Need that out of the way too. Typically we want to change one thing at a time, and retest, but since the tab seems to make no difference we should put that back where it should be. Looking at the motor and the bottom are not really "changes", but info. Unless of course the inspection shows something significant.

 

[rbiggins]

Re: Boat tilts to the left at full power

Motor is straight. I'll look at the bottom. What should I be looking for?

 

[QC]

Re: Boat tilts to the left at full power

Anny irregularities. Rocker (convex) or Hook (concave) length wise are the most commons issues. Again, this is probably more of a prop torque thing, but it is the high speed only thing that makes me wonder. Usually you can actually feel the "twist" as you apply power, and they would not usually list hard as it seems you are describing.

 

[Jdeagro]

Re: Boat tilts to the left at full power

Most likely the problem is prop torque. I am a bit surprised that it is the same with or without the hydrofoil. In any event I am guessing that the boat runs flat (bow down) at high speeds. This would indicate that you are getting too much stern lift. The stern lift is either from the Hydrofoil or the motor trim, or a combination of the two.

 

[rbiggins]

Re: Boat tilts to the left at full power

I will try it with the trim lifted this weekend.

 

[emilsr]

Re: Boat tilts to the left at full power

I also think it's a stern lift issue.

We chased this on my brother-in-law's bass boat; ran flat (port-starboard) at WOT, but at lower throttle settings (and on plane) it would lay over on the port side. He installed a hydrofoil (despite my objections) but it didn't fix the problem. After trying about a dozen different props we found one that provided lots of bow lift and that ALMOST fixed it....he wound up trading the boat to his youngest son and his 350+lb butt in the driver's seat fixed it the rest of the way. Fast forward a couple of years; next door neighbor had the same issue with his 18' tinny, and a bow lifting prop also resolved most of the problem.

Different boats of course, and they both had power trim so it may not be the same type of issue, just throwing it out there FWIW. My boat does the same thing with a neutral or stern lifting prop at certain speeds, so I think jdeagro may be on to something here.

 

[Jdeagro]

Re: Boat tilts to the left at full power

The sharpest section of the "V" hull is in the front, and pushing the bow down too much makes the boat rock on the forward keel like a teeter totter. The engine rotates clockwise so the boat tends to unwind counter clockwise. Very common issue with hydrofoils. They lift the boat from the center and lift more and more as the boat goes faster, driving the bow down. Just a few degrees is all it takes.

Most common issues we deal with every day are these (in order of volume):

1) time to plane (hole shot)
2) porpoising
3) port side listing

Although the specialty prop may alleviate the problem, it may not be the best overall solution from an efficiency standpoint.

Aluminum boats are most prone to listing.

 

[QC]

Re: Boat tilts to the left at full power

ran flat (port-starboard) at WOT, but at lower throttle settings (and on plane) it would lay over on the port side.

The reason I was looking to other possibilities was the OP's reporting the opposite to this AND, no difference with and without the hydrofoil. He has noted now that trim may be fixed too far in so far. We will see after some more testing.

 

[emilsr]

Re: Boat tilts to the left at full power

The reason I was looking to other possibilities was the OP's reporting the opposite to this AND, no difference with and without the hydrofoil. He has noted now that trim may be fixed too far in so far. We will see after some more testing.

BIL's boat started to flatten out at speeds over 45mph, the neighbor's at about 40. At lower speeds (like where the OP is running) his boat (and the neighbor's boat) would lay over on the port side. Neither would "carry" the bow which is in the end what necessitated a prop change on both boats.

Trimming out is definitely the first thing to try. That'll be the cheapest/easiest fix.