How to get my boat to stop porpoising...

[Zq8 Blazer]

My 16ft Monark modified-V aluminum boat has a BAD problem with wanting to bounce out of the water even if the water is smooth. I originally had a 75hp motor on it that didn't have power tilt/trim and I had a bad problem with it not wanting to plane off so I installed a whale tail. Since then I've put on a 60hp with power tilt, but it doesn't have trim. I added the whale tail to this motor too. It has always rode rough in the water, but now it's very bad. Short of a jack plate what can I do to remedy this problem?

 

[JASinIL2006]

Re: How to get my boat to stop porpoising...

SmartTabs?

 

[Drowned Rat]

Re: How to get my boat to stop porpoising...

Yes, smart tabs. Problem solved.

 

[UncleWillie]

Re: How to get my boat to stop porpoising...

Tilt/Trim more DOWN and/or move more weight forward.

You need to get the bow down!
It will plane sooner and will cut the waves with the bow instead of slamming the bottom into them.

??? Tilt = Trim ??? Is there a difference?

 

[Zq8 Blazer]

Re: How to get my boat to stop porpoising...

Thanks guys, I'll look into that.

Tilt/Trim more DOWN and/or move more weight forward.

You need to get the bow down!
It will plane sooner and will cut the waves with the bow instead of slamming the bottom into them

I've tried it tilted at various locations and nothing helps. I don't have much up front, but the rear is pretty loaded down. Passenger, battery, two 6ga tanks, and the motor.

 

[jestor68]

Re: How to get my boat to stop porpoising...

Is it still porpoising with the "whale tail" or just riding rough?
Have you checked the bottom for straightness?
What sort of "whale tail" are you using?
A 16 ft mod V Monark will tend to ride a little rough in a chop, but it shouldn't porpoise if trimmed properly.
A better description of the boat/motor might help. What year; what kind of motor. etc.

 

[UncleWillie]

Re: How to get my boat to stop porpoising...

...I've tried it tilted at various locations and nothing helps. I don't have much up front, but the rear is pretty loaded down. Passenger, battery, two 6ga tanks, and the motor.

Start with it ALL the way down.
The prop shaft should be pointed slightly uphill with the prop trying to lift the stern.
Then move some weight up front. The passenger is the easiest.
If you are still porpoising with that trim level, something else is amiss.

 

[Zq8 Blazer]

Re: How to get my boat to stop porpoising...

It's doing both with the whale tail. I haven't removed it from the new motor because it was so hard to get it to plane out with the 75hp I just figured it needed it on there.

I've had the boat up in the air when I painted it and everything appears to be nice and straight.

This is very similar to the one I have:

Start with it ALL the way down.
The prop shaft should be pointed slightly uphill with the prop trying to lift the stern.
Then move some weight up front. The passenger is the easiest.
If you are still porpoising with that trim level, something else is amiss.

Ok thanks.

 

[LippCJ7]

Re: How to get my boat to stop porpoising...

If you would like I can offer you my 300 lb Mother in Law cheap......

Cheaper then tabs anyway if your boat porpoises simply put her on the bow if your boat digs in put her on the stern and adjust her mouth....






or I could pay you....

 

[jestor68]

Re: How to get my boat to stop porpoising...

If you would like I can offer you my 300 lb Mother in Law cheap......

Cheaper then tabs anyway if your boat porpoises simply put her on the bow if your boat digs in put her on the stern and adjust her mouth....






or I could pay you....

:lol: :lol: :lol: The snow must be getting deep. :lol:

 

[LippCJ7]

Re: How to get my boat to stop porpoising...

:lol: :lol: :lol: The snow must be getting deep. :lol:

You have no idea.....

 

[jestor68]

Re: How to get my boat to stop porpoising...

Does your boat look something like this?

 

[Zq8 Blazer]

Re: How to get my boat to stop porpoising...

Basically. It's a jon boat so the hull is the same design.

 

[jestor68]

Re: How to get my boat to stop porpoising...

Basically. It's a jon boat so the hull is the same design.

What I meant was does your boat have a console with a steering wheel?

It won't hurt to place a couple of 50 lb sacks of (whatever) in the front to see what it does for the weight distribution. That will tell you whether or not shifting weight will even make a difference(it should).

As far as the bottom goes; the only way to check is with a straight edge. These things can develop over time by(for example) not being supported properly on the trailer.

 

[tazrig]

Re: How to get my boat to stop porpoising...

If you would like I can offer you my 300 lb Mother in Law cheap......

Cheaper then tabs anyway if your boat porpoises simply put her on the bow if your boat digs in put her on the stern and adjust her mouth....






or I could pay you....

Hey, Al Bundy, I think you might just have something there! :lol::laugh::lol:

 

[Zq8 Blazer]

Re: How to get my boat to stop porpoising...

What I meant was does your boat have a console with a steering wheel?

It won't hurt to place a couple of 50 lb sacks of (whatever) in the front to see what it does for the weight distribution. That will tell you whether or not shifting weight will even make a difference(it should).

As far as the bottom goes; the only way to check is with a straight edge. These things can develop over time by(for example) not being supported properly on the trailer.

Yes it has the console.

I don't really have a way to check to see if it's straight with it on the trailer

 

[Captain Caveman]

Re: How to get my boat to stop porpoising...

I'll make the basic assumption that your specific jon boat is rated to support a 60hp or 75hp motor. I might be tempted to follow jestor68's advice. Throw a couple of heavy sacks, old batteries, useless mother-in-laws, or whatever in the front to see if ballast is the issue. Try different weights as well, not just 20lbs and not just 300lbs.

Also, I'm not familiar with tilt-only motors but can you still manually trim the motor? If so, I'd make sure that it is trimmed all the way in (down).

 

[Outsider]

Re: How to get my boat to stop porpoising...

Porpoising occurs when the bow rises (for whatever reason), but runs out of lift. It them falls back down and repeats the process. Too much aft weight is common on tin-can console boats and exacerbates the problem. Try starting with the tilt pin in the lowest hole (motor will be trimmed all the way in). If that doesn't improve the problem, adding bow weight might ...

 

[Zq8 Blazer]

Re: How to get my boat to stop porpoising...

Okay I got a set in. I have a question though. Should I be able to manually push the actuators down like a shock on a car? Also I am suppose to remove the dorsal fin from the motor while I have these on, correct?

Oh and it doesn't tell how far apart the bottom bracket and top bracket should be from one another and the degree that the tab should be from the hull. I know the degree will be adjusted, but I figured there would be a starting point.

 

[ezmobee]

Re: How to get my boat to stop porpoising...

Should I be able to manually push the actuators down like a shock on a car?

Yes.

Also I am suppose to remove the dorsal fin from the motor while I have these on, correct?

Yes. Don't run both.