What .... more Jet Jon questions ! Say it ain't so !

[Kman1775]

Hey Guys thanks for having me .... I'm sure i'll enjoy being had !

Quick introduction.... I have many years fabracating and building high performance stand up jet skis. If you have a little time on your hands check out X-h20. Much like this site the sky is the limit when it comes to build ideas and creativity. I really enjoy river fishing and have been running a 1760 jet tunnel with a 50 Hp outboard jet for years. It gets the job done ,but in reality it's a slow gas drinking a$$ dragger that can barely get out of it's own way. I have though about upgrading to a larger jet , but the ineffiency of these motors make that idea undesirable. I have a complete 760 wave raider I plan on using for a doner ski and have found an old bass tracker that I think would be suitable for a hull. For simplicity I'm thinking I'll use the grafting method. Now on to the questions ....

1. What are the drawbacks for using the grafting method ?

2. Pump angle is critical .... is there a prefered angle or degree you all have found to be better or worse. I realize the angle can be manipulated with a variety of reduction nozzles from 0 to 6 degrees. Additionally you could use a drop nozzle for hols shot lift ( very important to get on step in a short distance in some river situations ).

3. Cavitation issues .... General rule of thumb is that jet sleds have a minimum dead rise of around 6 degrees from front to rear. This allows the air bubbles to split and escape to the edge of the chine giving the pump a smooth laminer non aerated flow . How much of the grafted hull do you allow to penetrate below the aluminum hull ? I assume this affects handling as well.

4. Debris in the intake ... this is a big concern . Intake grates come in 1000 different shapes and sizes . I understand most are using flat bar style river grates, however there are much better options for with regard performance (cavation reduction ,handling ) . How are you all dealing with pump obstructions that don't require a diving mask ?

5. Pump flush or exposed ? Certainly pump protection is part of that consideration , but I assume leverage / handling comes into play at some point.

6. General pit falls.... THE DON'T DO'S !

7. Conversely , What are the MUST DO'S or as they say in parts of Alabama , Georgia and Tennessee .... " What you Ort do's "

8. Eight ....Eight .... I forgot what Eight was for .... but nine ( bonus points if you get the reference )


Sorry for the first long winded post .... Just figured getting some specific detailed answers from you highly qualified jack leg ,shade tree tinkerers would help me fast track . So from one
jack leg ,shade tree tinkerer to another .

Thanks for your help,

Kman ( I'm in Georgia )

 

[CedarRiverScooter]

Hi, I'll give it a shot. I grafted in a 750 polaris twice (1st time had bad cavitation), then upgraded to 4 stroke 1100 Yamaha. 16 foot jon.

1. What are the drawbacks for using the grafting method ? You compromise the structure of the hull & have to splint it back together with braces. Also, in a hard rock strike, guess where it will split open. (Been there).

2. Pump angle - I have found 5 degree to be minimum, but how much beyond that is per the weight distribution. I had to add trim tabs to mine to eliminate porpoising. I tried to down angle the nozzle, which helped porpoising but made steering feel odd.

3. Cavitation issues .... My 1st install was flush for minimum draft, but that cavitated badly. I found 2 inches down to be ok. Use the natural deadrise of the jet ski hull for that purpose, the farther you extend that V towards the front, the better.

4. Debris in the intake ... Stay away from top loader grates, they let big rocks in. I haven't had any problem with OEM grate.

5. Pump flush or exposed - It would be nice to have the extra 8 inches of interior room to have engine slid back & pump stick out back. It would take extra structure to support the thrust forces. I would do this if I could start over. Give nozzle angle an extra degree if down due to more weight towards the back.

6. General pit falls.... Use as much of the OEM controls & fuel system as possible, otherwise the budget will get out of control. Use lots of sealant (5200) as pinholes are hard to track down later. Buy a big bag or earplugs for running that 2 stroke. Also budget for gas, it will drink 5+ gallons per hour.

7. Conversely , Check into the registration issue, you will no longer meet the HP limit on you mfg certification plate. I changed to 'homemade' status.

8. Eight .... I recommend 4 stroke engine. Yamaha has great engineering, made the Polaris look like a high school shop project. It may be more money to buy a 4S, but it is a lot of work to install so don't do it twice like I did.

 

[Kman1775]

Thanks for the reply Scoot .


Looks like I'll have to just roll my sleeves up and start fabricating. I agree on the 4stroke ,but I have the Radier just sitting there. One redeeming factor is that it has mounts for 1200 cc two stroke as well if I wanted to up grade the power. As far as rock strikes , You could put a false bottom on the part protruding through the hull using 2 part foam and epoxy /glass to reduce the risk actually putting a hole in the bottom. They make a 16 pound two part foam that drys super hard . I plan on using some variation of that to support fiberglass graft .... my gears are turning ....

Any of you guys use Mag pumps ? They provide Max hook up and seriously improve hole shot . Theres also a ton of after market pipes to improve preformance ...... hell while we are at it let's a run total loss ignition system ....... What a rabbit hole ! This could get stupid fast !

Man

 

[CedarRiverScooter]

No doubt 2S has wicked better hole shot. My rock strike tore open a hole because the overlap was minimal, the alum folded back. The weakest link of the chain got hit, go figure. Even with the hole we planed back to the ramp, it had suction pulling the water out.

A couple inches overlap is the way to go.

Good luck on your project, sounds like you have the right skill set.

Please post pictures for our entertainment!

 

[Kman1775]

Well .... got down to the lake today to look at the wave rider up plan on using. The height of the motor is 19 1/2 inches the total length of the pump and motor mounts is around 70 inches from front to rear. The pad is about 24 inches wide and it’s relatively flat.


Thoughts :
I could cut up an old super jet and reduce the length by probably 2 feet. Not sure what that does to the weight distribution. Additionally, the hull runs on a flat area about 12 inches wide . I feel it would need to be modified to more of a v to help with cavitation. Two part foam and heavy glass would be much stronger that the factory SMC (sheet molded compound) just a little FYI only use epoxy resins with when working with SMC. Vinyl esters and polyesters will not adhere well .

I think I have found the bass tracker doner hull.... tracker 1648 she a real Beauty....