Unstable Super Jet

[Wake Rider]

Hey guys,

My Super Jet is pretty unstable when riding in a straight line. It has been shortened, reinforced, had tubbies added, and I'm positive the tray is waterlogged (it's really heavy in the back and water always comes out of the drain bolts a past owner installed). I've tried adjusting the steering nozzle and installed rear sponsons but it's still unstable.

I bought it a little less than a year ago with all the existing hull mods. Before owning it, I had a js550 that didn't feel this unstable. I even went and test rode a stock fx1 this week and it was more stable than mine!

Any ideas of what could be causing this?

 

[Mike W]

What kind of rideplate do you have?

 

[bored&stroked]

Ride a stock superjet and decide for yourself. You bought a highly modified ski that you already admitted was done poorly and waterlogged. Fix that first then ask questions.

 

[Wake Rider]

What kind of rideplate do you have?

I was running an ocean pro "ocean" (finned) plate for a while. Yesterday, I switched back to the flat carbon fiber one that came with the ski (it's cut flush with the back of the hull) and felt no improvement.

Ride a stock superjet and decide for yourself. You bought a highly modified ski that you already admitted was done poorly and waterlogged. Fix that first then ask questions.

Do you have a stock ski laying around for me to ride?
I never said the ski was built poorly. I bet one of the previous owners did the shortening/footholds when the ski was newer and still had good foam in the tray (it's a 1999). I'd already have the tray cut open and be yanking the foam out if I thought that was the problem. I've read numerous other threads about waterlogged hulls and none of them described the ski becoming unstable.

 

[Mike W]

Try an extended rideplate. A Riva Groovy or Worx is what I have experience with and help out quite a bit with the issue you are having.

 

[Vumad]

Hey guys,

My Super Jet is pretty unstable when riding in a straight line. It has been shortened, reinforced, had tubbies added, and I'm positive the tray is waterlogged (it's really heavy in the back and water always comes out of the drain bolts a past owner installed). I've tried adjusting the steering nozzle and installed rear sponsons but it's still unstable.

I bought it a little less than a year ago with all the existing hull mods. Before owning it, I had a js550 that didn't feel this unstable. I even went and test rode a stock fx1 this week and it was more stable than mine!

Any ideas of what could be causing this?

How fast are you going when it is unstable? It might not ride that good at high speeds with those hull mods.

Also, how is it unstable? Is it rocking side to side? Falling over? Porposing? Back sliding out?

Rocking side to side can be chine walk from sponsons being mounted too low.

Falling over can be imbalances such as a very heavy battery and a lighter aftermarket pipe, wet foam more on one side, rider imbalances loading one side of the ski too muc, etc.

The back sliding out can be helped by using rear sponsons. Think yaw on an airplane. They are usually held on with just a few bolts so you can easily remove them for the days riding.

Porposing is likely caused by the shortening, and is mostly unfixable except with practice. You could try adjusting your pole or steering length.

Ultimately short skis are not built to go fast. You may need to consider what kind of riding you want to do. I never shortened my ski because I was riding a lot with racers even though shorter would have better in the surf, I had to be able to keep up with my friends.

 

[jetx]

How much has it been shortened...I'm guessing you don't have muh tray time on it and really just need to keep riding and get use to its characteristics

 

[Wake Rider]

How much has it been shortened...I'm guessing you don't have muh tray time on it and really just need to keep riding and get use to its characteristics

It has been shortened about 3 inches. I'd love to blame it on tray time, but I'm not the only one in my family that thinks it's pretty unstable. Also, the ski I learned to ride on was a 300sx, so I'm pretty used to short skis.

Vumad,
It's definitely rocking side to side/falling over unstable and it doesn't really go away at any speed. It does float with the carb side lower than the pipe side. I'm starting to think that the tubbies are mounted too low like you said.

Here's the ski in case someone knows more about it's past:
http://www.x-h2o.com/index.php?threads/carter-b-built-1999-yamaha-superjet.164041/

After I bought it, I found out from Carter that it was actually built by a friend named Matt under his supervision/guidance.

Thank you everyone who has chimed in so far.

 

[Harbor]

What made my 01 RN unstable in smoother water was destroyer sponsons and an intake grate that has a large center rib and deep scope.. It Would rock side to side while riding in a straight line. Also hook and touce you off over the side at slower speeds. Felt to unstable to reach full speed/throttle

Your sponsons are they destroyers? Yours look similar but look larger with that bulge, ski may be pivoting/turning/hooking on those large sponson bulges

 

[Vumad]

It has been shortened about 3 inches. I'd love to blame it on tray time, but I'm not the only one in my family that thinks it's pretty unstable. Also, the ski I learned to ride on was a 300sx, so I'm pretty used to short skis.

Vumad,
It's definitely rocking side to side/falling over unstable and it doesn't really go away at any speed. It does float with the carb side lower than the pipe side. I'm starting to think that the tubbies are mounted too low like you said.

Here's the ski in case someone knows more about it's past:
http://www.x-h2o.com/index.php?threads/carter-b-built-1999-yamaha-superjet.164041/

After I bought it, I found out from Carter that it was actually built by a friend named Matt under his supervision/guidance.

Thank you everyone who has chimed in so far.

On a stock boat it's called chine walk. Think how ailerons effect an airplane. Those sponsons wouldn't be easy to move up because they are molded in.

I would start with addressing the list and try time. The list is usually caused by 2 things. 1) water in the exhaust outlet (which does not affect riding) 2) imbalance in the ski (which does affect riding). Water in the exhaust outlet is only a factor so you are not chasing your tail. If you have a stock exhaust outlet which is at the top right side of your bulk head, it wont list for that reason so you can look at weight imbalances. If you do have a different exhaust, make sure a lack of flotation isn't causing the list. This will not affect you while riding, but it can throw you off when trying to balance your ski.

My personal experience with imbalance was caused by changing pipes. The stock pipe and battery are both very heavy. The FPP pipe is much lighter than the stock pipe. My ski would load on the right and turn very poorly to the left. I went to a smaller battery (just a narrow gel cell, not an expensive lithium battery), but it still listed and turned poorly. I added a plate over my motor mounts (hull side) that was 4-6lbs. The ski does not have the "gangsta lean" while floating, and turns exceptional both directions now. imbalances come from other things, like wet foam, that's just where mine came from.

Rider position also is a major factor in chine walk. Just because everyone agrees with you that the ski walks does not mean any of those people know how to ride it. We tend to favor one side and you may just need to practice more on that particular ski.

Those are just some inexpensive suggestions. Its hard to say without riding it. I don't get out much right now or I'd offer to ride with you.

 

[Freakie]

Its your sponsons that are mounted too low...they are most likeky flush with the lowest seam on the hull on each side.....great fir surf riding....crap for high speed flat water...creates chine walk at anything over half throttle on FLat water......they needto go up about .5 to .75 of an inch or cut away from the base and remoulded there to achieve an even seam slightly higher than the hull itself....aerodynamics 101 or what Vumad also said ........look no further