--> Yamaha GPR Platform - Inherent Hull Safety Issues

[Shibby1485]

By reading a few threads, some memebers requested there be a thread created structly about the GPR hull safety issues, both for stock skis and highly modded skis. (ie scrap the stock grate, pump pressure, etc)

Please use this thread to post links to other important safety criteria as well as having good in-depth conversation regarding these issues as we all come up with solutions to protect the lives of others and ourselves.

[philip_gpr]

Safety Issues

The GPR has several major areas that have to be addressed when building a modified ski capable of 80+ mph.

1) Intake grate

The stock intake grate is unsafe at any speeds above 65 mph

There have been numerous reports of Riva/R&D intake grates breaking

The ski has been known to buck using a stock Worx or Pro-tec grate

This means there really isn’t a safe intake grate available.

On my ski I have resorted to building my own intake grate using billet aluminum pieces welded together. I also use a Worx grate that I have modified. The modification involved having a piece of aluminum welded to the rear of the wing to close in the notch.

2) Intake Grate Bolts

The intake grate bolts need to be upgraded to the next larger size

3) Inserts (pump shoe, rideplate and intake grate)

All of the OEM inserts need to be replaced with replacement inserts that are made from flat pieces of aluminum. The flat bars spread the force over a large area making it impossible to pull the insert through the hull.

4) Pump Tunnel Reinforcement

The pump tunnel needs to be reinforced. This can be done with a fiberglass reinforcement piece, a R&D carbon fiber reinforcement kit or with layers of fiberglass cloth and Epoxy resin. With the SMC hulls any glue or resin used must be epoxy based in order for it to stick to the hull. If you have a 2003 or newer hull I would suggest you use the fiberglass reinforcement piece or the R&D carbon fiber tunnel reinforcement kit.

5) Pump Pressure Relief

The faster you go the more water gets forced into the pump tunnel.

The more angle you put on the rideplate, the higher the front of the hull rides in the water which opens up the pump tunnel more to the water which forces more water into the pump tunnel.

These 2 forces act together and cause the pump to get over stuffed – this commonly happens at speeds around 78 – 80 mph. When the pump over stuffs the ski bucks, it is like you ran over a log, the rear bounces up, here is where it gets real nasty, sometimes the front chines dig in and the ski does a violent left turn.

One fix to this problem is to add pressure relief fittings to the 2 inch pump spacer.

http://www.greenhulk.net/forums/showthread.php?t=29686&highlight=pressure+relief

http://www.greenhulk.net/forums/showthread.php?t=29092&highlight=pressure+relief

http://www.greenhulk.net/forums/showthread.php?t=37409&highlight=pressure+relief


6) Steering Nozzle

Steering nozzles. The cheap plastic POS that sits in the sun everyday needs to be replaced every couple years or switch to a R&D or Pro-Tec aluminum model.


Modified Rideplates – a few comments

After a R&D or old style Riva rideplate has been modified by Jim or Island Racing quite a bit of material has been machined off the plate. Doing this significantly reduces the strength of the plate. I believe it is possible that one of these plates will fail at high speed. It might fail on its own or maybe it will be helped by hitting something floating in the water, but it could fail. For this reason in 2008 I will be working with a new style Riva plate. This style plate does not require as much material to be machined off.

[addicted]

A few notes

Info on bolts
http://www.mcmaster.com/param/html/A...crewmaterials/

Some of the cheap bolts available at local hardware and home improvement stores is weaker than the stockers. Make sure you know what you are buying.

updated brackets for ride plate & shoe are available through sources for oem parts for model year 2005 and up.

Island racing also has crazy overkill billet inserts.

[JFizzleJR]

Island racing also has crazy overkill billet inserts.

Saw them yesterday in person and they will do the job for sure.

&

Excellent post Philip

[beerdart]

[spaceman]

If you are replacing/buying stainless steal bolts.. make sure you get A4 grade.

[JFizzleJR]

So, after reading I think I have a decent handle on the pump pressure issue. Correct me if I'm wrong on the consensus:

Install a pressure gauge to read pump pressure.
Use 800 grate rather than 1200.
Drill and tap for dual Jetworks valves fitted to the 2" spacer.
Shim Rideplate and Trim Tabs accordingly.
Send pump shoe to Ben Herman for his mod? (or get done somehow).
Drill 2 strategically placed holes in the pump shoe. (Kerry mod).
Shim intake grate down if necessary. (depending on shoe mods).

[addicted]

Fizz, you have about 3 different methods n there. Read up on all of them, and choose one.

basically, you need to relieve pressure no matter what. Here are the 3 most common ways.
1-jetworks
2-holes in shoe
3-Ben's mod

shim your plate/tabs/grate as needed.

Pressure guage is neat, but not necessary.

1200 grate is better for holeshot and safer than the 800 at speed. aluminum 800 grates have been know to break, hence the reason that Jerry is having them cast out of stainless.

Did you try calling Hop? He can explain all this to you.

[jpa1300]

Is the ride plate shown in RIVA's catalogue the 2008 version??

jp

[JFizzleJR]

I read up on all of them and found people are combining them. Maybe 1 is good for 80 mph, but with speeds of 90+ I figured more than 1 method is necessary? Some are saying holes in the shoe do nothing. Some are saying the jet works valves are not enough..etc.

I've got 2 jet works valves now.. and the pressure gauge was already in the hull when I purchased it so that's why I listed it. I will call Dan if I need help.

Thanks for trying to straighten things out for me Mike.