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Absolutely Impossible To Tune Jet Boat.

5K views 38 replies 17 participants last post by  GRoper 
#1 ·
OK heres the deal.........

Have tried to go out with 15 YO son in his Rogers Dragstar and tune the boat.

The engine is running fine.

Trying to tune in the pump/boat combo after a crude throw together get the entire thing going project.

If I am in the boat. It porposises like the biggest piece of shit on the water. To the point of unbearable to ride in.

When I get out, it runs and takes a set and goes like crazy.

What is the deal ???

We drilled the intake to take pressure readings. I can't ride in the boat to monitor them because the boat will not accept a rider.
Damn, Talk about a sensitive setup.

This is the damndest thing I have ever seen.
 
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#5 ·
I'll see what I can do for pics this weekend Tom. I am going to speed coat the bottom.

We did build the boat to race but damn. Would be nice to ride in it lol

The boat handles fine with Info Jr in it by himnself.
 
#3 ·
Best bet is to talk to people who have run that Rogers hull and get their setup info, and then make minor adjustments to suit your setup, weight/hull etc as even boats out of the same mold will respond differently at times.

You could get the GPS out and work on max speed, but your best bet is to try and make minor adjustments at the track and use the first season as a learning curve. Season two you can start pouring it on.

I assume you tried to trim the porpoise out?My dads boat has a nasty porpoise to it after a complete re-rig. Boat came with cav plates and no ride plate. Maiden voyage We left the cav plates off(ran out of time) and the rideplate too(forgot it). We are hoping the rideplate will fix the problem as the porpoise could not be trimmed. If it doesn't, we will know why the cav plates were on it to begin with...
 
#4 ·
Sounds like the boat needs something to sit on, put a ride plate on it.

My old Avenger did the same thing, the ride plate made a world of difference along with adjusting the nozzle angle.
 
#9 ·
This is probably overly obvious ....but as far as watching the gauges maybe you could rig up a vid. camera to record them. I do that when I go out because it's impossible for me to drive wot and watch the a/f, oil pres, tach,pump pres, water pres,ect,ect....
 
#18 ·
OK Tom here a few pics. Showing where everything in the boat is located. Boat mfg recommended the engine be installed right where it is now. The pump shaft angle compared to the top of the stringer measures 6 degrees.

Held the straight edge on the keel to the ride plate It hit the shoe on the way back. . The back cut shoe prolly needs to go.

Let me know what to measure and I'll take a pic.

The bottom is a different color now. lol :)devil
 

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#19 ·
Last one.

Yes it is ugly. This is the first time we had no regard for the way it looks. We are going to make it run then we will make it look nice.

And when we are finished pulling the transom plate off we will goop it up nice.

All of the hardware is as we bought the boat. Except for the ride plate and impeller. And the nozzle mod we did. And loader duh.
 

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#21 ·
You want me to put the straight edge on the keel, extend it across the small area immediately in front of the intake and up to the loader?

There is a short area immediately in front of the intake that does not have the round dropped keel. It's flat. You can see daylight between the straight edge and the bottom of the boat in the one pic.

I'll measure it when we get back from town take a pic and post it up
 
#23 ·
OK loader blades 1/2 inch below keel
front of loader pad to middle of shoe 16"
But here is the big deal. Shoe dead even with the keel in the center and the back cut portion above keel.

I'll be needing a shoe and shims ASAP.

"Have never had the boat and this long straight edge in the same place before. And also been a little confused on exactly where to lay the straight edge.

It's ugly up that inlet. Ride plate is off to seal up a leak

Were headed out to thrash it some. Don't have any hardware to make corrections with.
 

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#25 ·
Why no one else said....

Why on earth would you buy your son a jetboat?

Brian
 
#36 ·
Update

So in the last month we have ..............

Found out the intake was way too big at 15" Moved the shoe fwd to squeeze it down to 13 1/4" Unfortunately that moves the pump setback fwd that amount.

Had the wrong loader in it. Took the loader that came with it cut out the center blocker and cut it back to just above keel.

Put in a "B" impeller and inducer

Put in new packing and a prime a jet.

Shoe and loader in and out countless times. Pump apart 4 times.

Yes Info Jr. is becoming quite a boat wrench.

Improved the ET by 1/2 second and 4 or 5 MPH

OH and for whatever unexplained reason. Getting the intake pressure up to 40 lbs changing all of that made the 2 person porpoise problem go away.
 
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