Need help with Porpoising

[Ol Sarge]

Hi everyone. I've got a problem that I just can't figure out. I took my 16ft Javeline Bass Boat to the lake today for the first time and it's porpoising really bad. The boat has a 70hp Johnson outboard with a Stingray Hydrofoil and Tilt &Trim. With the motor trimmed all the way down it comes up on plane really quick but when it reaches about 20 to 30 mph it starts to porpoise. Trimming the motor out only makes it worse. Adding more throttle makes it worse. I tried to power through it and it damn near threw me out of the boat. The only weight in the boat was me, two 6 gal. fuel tanks in the rear of the boat along with 2 batteries also in the rear of the boat. Neither of these can be relocated forward due to lack of storage space. I tried and tried every conceivable solution I could think of with trim and nothing worked. I really need some wisdom to sort this out. Thanks in advance.

 

[Sprig]

This was your first time out in the boat? It could be a number of things but I’m thinking it may be the foil. Yes I know what the foil is suppose to do but Try your boat without the foil. Your boat with your engine should not be doing that especially trimmed all the way down. Try it without the foil first..

 

[Ol Sarge]

This was your first time out in the boat? It could be a number of things but I’m thinking it may be the foil. Yes I know what the foil is suppose to do but Try your boat without the foil. Your boat with your engine should not be doing that especially trimmed all the way down. Try it without the foil first..

Thanks Sprig, I just bought the boat 3 weeks ago and had a few issues to work out before I could put it in the water. I was thinking about taking the foil off and trying it but wanted to get more info from some folks that know more about it than I do. It gets up on plane really fast with trim all the way in but not long after that is when it starts to porpoise. It's also pulling to the right and wants to roll over to the right. I'm thinking that may be the trim tab needing adjustment. The boat rides pretty good if I can just get the porpoising situation figured out.

 

[MTboatguy]

I would take the foil off of it and start with the basics and then start narrowing things down, always start with the simplest configuration you can, then you have a baseline to build from for any options you want to add, do them one at a time and that way you have a road back if you add something and it goes goofy. The KISS principle always applies with boats.

 

[Tassie 1]

As above
but is it also possible to try the boat with just one battery and one fuel tank?
Just a couple of up and down runs would be enough.

 

[82rude]

Seeing as how this boat is new to you id say maybe your water logged.Nauticus trim tabs will help as a quick and dirty fix till you can address the problem.

 

[Scott Danforth]

take the fuel tanks out and then weight the boat and trailer. from there, subtract the weight of the trailer and the weight of the motor and compare to the spec weight for your boat. that will tell you if you are water logged.

I would also try it without the foil.

which prop is on the boat. you may have a bow-lift style prop.

 

[spoon059]

I would see if you can add some weight to the front to stop the bouncing. All your weight is in the rear, that's never gonna ride right.

 

[Sprig]

Waterlogged is definitely a possibility. That could be the reason the prior owner put the foil on, because it was heavy in the back and the foil helped him get up on plane. I’d contact the previous owner and ask him about the problem you are having. It was obviously happening before you purchased the boat.
Im thinking you didn’t do a water test drive. I learned the hard way many many years ago to always do a 20 or 30 minute test drive. Let us know what’s up when you get it figured out.

 

[JimS123]

Its not the foil and its not the trim tab. You got a hull problem. Sight down the keel from the transom and I bet its not straight. Next look at how its set up on the trailer. Is the hull properly supported?

Lastly, look at the motor to be sure its truly trimmed in all the way.

Nauticus tabs may help, but what you really need is a set of fixed tabs to bring the bow down. The boat was designed with the battery and gas tanks where they are, so moving stuff around is just a Bndaid to fix a basic problem.

 

[robert graham]

Move the bracket pin that the motor rests against into a forward position.....most motors have 3, 4 or 5 different settings.....

 

[capecodtodd]

Does your boat do this every time you get up to speed? My 1901 stingray with a I/O porpoises on occasion and there is no fixing it so I back off the throttle to stop it then bump it back up. I also have a stingray foil on the out drive. It can happen with 2 or 5 people plus gear in the boat so it has to be some combination of the trim combined with water conditions like a bit of wake that starts it hopping. I suspect you have too much weight in the back so try stripping it out as others have suggested.

 

[garbageguy]

...I'm thinking that may be the trim tab needing adjustment...

It has one trim tab? Some pics of your rig and where your (outboard?) sits with respect to the rest of the boat when trimmed down would likely help you get more help.

 

[JimS123]

Does your boat do this every time you get up to speed? My 1901 stingray with a I/O porpoises on occasion and there is no fixing it so I back off the throttle to stop it then bump it back up. I also have a stingray foil on the out drive. It can happen with 2 or 5 people plus gear in the boat so it has to be some combination of the trim combined with water conditions like a bit of wake that starts it hopping. I suspect you have too much weight in the back so try stripping it out as others have suggested.

Stingray's are noted for that. That's why a few years ago they started offering fixed tabs as an option. I thought they should have them as standard equipment. I put a set on mine and they worked like a charm.

 

[JimS123]

It has one trim tab? Some pics of your rig and where your (outboard?) sits with respect to the rest of the boat when trimmed down would likely help you get more help.

Trim tabs are there to correct steering (propeller) torque. They don't fix porpoising.

Yes, show us a pic of the motor bracket and a side view when its trimmed down.

 

[JASinIL2006]

SmartTabs help with bringing down the bow and with porpoising. You might be able to fix your problem via other means, but SmartTabs are pretty cheap (relative to most boating-related stuff) and they do work.