Boat Rolls at speed

richnle · Post by **richnle** » Mon May 02, 2011 5:18 pm

My 16ft Penn Yan (75 hp Johnson) rolls to the left at planing speeds, even when driving straight. I can manage the issue by driving slower and trimming the motor out more, but at full throttle, it rolls regardless of trim. Anyone ever experience the same handling issue?

Rich

Torchie · Post by **Torchie** » Mon May 02, 2011 7:22 pm

What shape is the hull in. By that I mean are there any Hogs in the bottom.
These cause boats to do strange things.
Karl.

richnle · Post by **richnle** » Mon May 02, 2011 8:38 pm

The bottom does have a minor hook. The funny thing is that I used the boat twice with a different engine prior to refinishing her over the course of a year, and I did not notice this rolling with the previous engine. The previous engine was a 1983 Johnson 70. The current engine is a 1965 Johnson 75hp. The two times I used her previously, she handled fine, but there was significantly more weight in the boat. The roll to port is now very consistent at speed, but I am not positive if it will be noticeable if the boat were loaded with more people. Can a hook lead to rolling when going straight? Is there anything about the different engine, smaller dia prop, etc, that can be contributing to the problem in addition to the hook?

Torchie · Post by **Torchie** » Mon May 02, 2011 11:18 pm

I know that hooks or hogs in the hull can cause the bow to plow down into the water don't know about the roll though. This may seem like an odd question but is this engines prop rotation different from the other? Also did you change anything else besides the motor like gas tank location , battery, ect. Wonder if it is weight related. What side of the boat is the steering on? Hopefully someone else will weigh in on this.
Karl.

richnle · Post by **richnle** » Tue May 03, 2011 4:35 am

Good point. Gas tank is 11 gallons and is on the left of this very round bottomed boat. The gas tank was empty during the test runs and we ran on a temporary 6 gallon tank in the center of the boat. The strange thing is the lean definitely gets worse and worse the faster I go, to the point where it feels unsafe. It feels like more than a weight distribution issue.

richnle · Post by **richnle** » Tue May 03, 2011 6:02 am

To be clearer - the 11 gallon tank on the port side of the boat was empty when the boat handled well with the previous engine. It is now full with the replacement engine and the boat rolls left.

W Guy · Post by **W Guy** » Tue May 03, 2011 2:55 pm

Maybe it's time to lift it or go underwater and see if something came loose or attached itself to the hull????? (just a thought)

JoeCB · Post by **JoeCB** » Tue May 03, 2011 2:58 pm

I'm guessing that you are seeing the effect of a torque reaction from the prop. Looking from the rear,your prop is turning clockwise the reaction on the hull will be counterclockwise, hense the roll to the left (port side).
That 75 hp is a pretty big motor for a relatively light 16 ft boat.
Joe B

richnle · Post by **richnle** » Tue May 03, 2011 5:41 pm

Thanks Joe - that makes sense based on how the boat felt as I increased power. Any thoughts on how I can stabilize the boat if this is the issue? I have thought about adding smart tabs or fixed trim tabs (if I can find any), but I hesitate to throw the bow down any more with the slight bottom cupping issue. I know newer engines have an adjustable anode / "trim tab" to counter torque, but I do not think there is anything available like this for the old 75.

Phill Blank · Post by **Phill Blank** » Tue May 03, 2011 6:58 pm

Rich,

I can not see where the 5 more HP would make the differnece and cause the handling problems you are talking about. But the additional speed you are getting could be.
There is a wieght differnece between the older 75 HP motor and the newer 70 HP which might have some effect.
I also can not see the prop torque causing the handling problem you are talking about.
But I think your slight hook you mentioned in your second entry is your main problem. With higher speeds hooks and hogs will cause the boat to be squirrelly and handling becomes a big problem.
Hooks and hogs cause the water flow under the hull to become disturbed and this will effect handling as the boat is trying to go in the derection the water flow is driving it.

My advise would be to correct your slight hook and I will bet the problem will go away.

Good Luck,

Phill

Torchie · Post by **Torchie** » Wed May 04, 2011 4:19 am

The faster you go the less hull that is in the water. So the boat tends to get more squirrely(sp)and less stable. I agree with Phil on The hook issue. You wouldn't think that 5 more HP would make a difference. But Joe also has a valid point as well in regards to the prop torque.
So my vote goes to it being a combination of a lot of little things. Small hook plus bigger motor and perhaps some balance/weight issue's. It all adds up.
If the hook is not too deep you can take care of it with some fairing compound.
Start with that and then see what happens from there. Process of elimination. That's how you trouble shoot a problem.Keep us posted.
Karl.

richnle · Post by **richnle** » Wed May 04, 2011 5:03 am

Thank you all for your help. I agree that the problem is probably a combination of the hull hook and torque prop and weight distribution. The hull is very round bottomed which is not helping. The funny thing is that the handling is very predictable . She starts out level and from 20mph up it starts to roll left. The faster I go, the more she leans. It does not feel squirrely. I think I will add smart tabs for this season and work on the bottom in the winter. Thanks again

Rich

LancerBoy · Post by **LancerBoy** » Wed May 04, 2011 6:02 am

do you have a big mother-in-law? have her ride with you and move her from one side to the other at various speeds. see if she makes the boat cease its roll while sitting at such and such locaiton.

if you find a "sweet spot", have her on retainer for all future boat rides!

andreas

john · Post by **john** » Wed May 04, 2011 2:29 pm

Your old 1965 75 has less prop shaft hp than your newer 1983 70hp. The 1983 should be 5 mph faster!

How fast are you running? Any idea of max rpm? If the engine is over proped, it is possible to cause the boat to be twisted to one side. RPM @ wot should be 4500+, if boat run but 30 mph, a 10 inch pitch prop is what you need, could esily have a 12 inch pitch.

Have your tried raising the tilt pin? or raising the engine on the transom?

Other wise the bottom is at fault.

richnle · Post by **richnle** » Thu May 05, 2011 10:08 am

John - I do not know the max rpm, but I do know the engine came off of a much heavier 18ft T&T, so I tend to doubt the pitch is too much for this boat. It does lean less the higher I trim the motor. I have not tried raising the engine on the transom. Thanks for the thoughts.

Rich