nautica ribjet 10 plowing, undriveable

[bbar]

Hi, 2001 nautica ribjet 10. Yamaha jet driveline. Got this as a basket case and have put it back to running order; but have a problem I can't figure out. As I increase speed, hull comes down(as it should) but keeps on going too far and starts to plow and hook into sharp turns, etc. I can get about 24 knots out of it before it becomes undriveable and tries to throw me out of it. I have changed jet nozzles from 0 degree to 5 degree up angle (which should have kept the nose up) but no change. I have deflated the tubes (maybe a very little bit better). There is no hook in the hull and everything is exactly how it was made. This thing has the 11 gallon fuel tank way up front and the motor sits forward of center. Is this just a bad design???
What can I do to the hull to keep the nose up? Some kind of chine? Sponsons? Need help. Thanks.

 

[Ronnie]

Maybe you can move the fuel tank to the stern and/or add ballast to the stern.

 

[tdonoughue]

Had to go look up just to see what the thing looks like. Do you have any pics of the vessel? Particularly the jet drive?

 

[zipper]

This has been going on for 3 years. We are going to need pictures of the hull and jetpump like @Julian asked for 3 years ago.

https://jetboaters.net/threads/handling-issue.22725/#post-388907

 

[jocolo21]

 

[zipper]

View attachment 183812

I get that part, I am asking for pictures of the underside of the hull and the jetpump assembly. The bow should not be digging in at speed. There must be a trim alignment issue. There was another guy, a sailor, who had one of these with a cavitation issue that ended up being his bow line connected to the eye had fallen overboard and was interfering with the intake causing his cavitation.

Anyway my dinghy is ass heavy, I have to sit forward to keep the bow down getting on plane. My trim is adjustable. The shape of his hull should keep the bow up while underway unless trim is way out of whack.

 

[jocolo21]

I get that part, I am asking for pictures of the underside of the hull and the jetpump assembly. The bow should not be digging in at speed. There must be a trim alignment issue. There was another guy, a sailor, who had one of these with a cavitation issue that ended up being his bow line connected to the eye had fallen overboard and was interfering with the intake causing his cavitation.

Anyway my dinghy is ass heavy, I have to sit forward to keep the bow down getting on plane. My trim is adjustable. The shape of his hull should keep the bow up while underway unless trim is way out of whack.

Gotcha, that jet drive moght be pointing slightly down to do that

 

[bbar]

I hadn't tested the different nozzles when I posted a similar thread a couple of years ago. Thought I would start new with that info. I will get some pictures added tomorrow.

 

[bbar]

Here are some pics. Current jet nozzle is 0 degree. As stated in previous, I tried a 5 degree up angle with no change.

 

[Julian]

Hard to tell, but is there a gap at the front edge of the ride plate/intake grate?
Can the gas tank be moved back? How big is it, how much does it weigh? Have you tried with two people in the back and does it do the same thing.
How far off the top RPMs at 25mph are you?

 

[Cobra Jet Steering LLC]

POWER HOOK IN HULL fiberglass is flexing under power usually caused by a bad center stringer. just in front of the ride plate go under and push up with your hand and see if it flexes

 

[bbar]

hello, thanks for response. Here are 2 more pics. there is no real gap between the 2 pieces. There is a step. The back of the intake is 1/2 inch lower than the start of the ride plate. This ride plate has always had me wondering. It was with the thing when I got it but never bolted up well. I had to open the holes up some to get it bolted up.

Other info- gas tank is under deck, can't be moved. It is 11 gallon and I have run with various amounts of gas in tank (down to 1/4 tank) with no change. Tach says I'm doing 3000 at 25 and I'm at about 1/4 throttle (if throttle lever is accurate). Its on the edge there but if I countersteer ahead of what it tries to do,I can keep it kinda under control (although the steering response is very long so I can't be near anyone or anything. Any faster and it starts catching and skidding almost sideways and is out of control. Have tried 2 cinder blocks strapped to the rear "swim platform". That in tandem with the tubes deflated felt a little better. Have not had 2 people on it cause nobody wants to possibly get flung into the water. (can't blame them I suppose).

 

[Cobra Jet Steering LLC]

those have a history of getting power hooks in the bottom of the hull so be sure that is not the problem because it is definitely the symptom check the search records I vaguely recall someone else having the same issue years ago

 

[tdonoughue]

What are the round plates to either side of the jet? Mostly curious there...

You are likely smart enough to have crossed this one off, but just in case: anything in the bow at the bottom that was not there at stock? Like a huge anchor? Or a lot of water? Like I said, assuming not, but...

When you changed the angle of the nozzle, how did you do that? Have you tried 10 degrees up? To me, given where the jet is up/down on the craft, if it is nosediving, has to still be an angle thing. It is below center, so it should be torqueing the nose up, not down...

While the lip there at the ride plate is not ideal, I would figure it would slow the boat more than cause nosediving. My guess.

 

[bbar]

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