big jet boat

[PSG-1]

This would be the first twin engine jet john project on this site, as everyone else has gone with single engines. It will be neat to see how it turns out!

 

[KGouty]

here is a pic of the under side of the cut out jet ski.......i was thinking of mounting the pump totally outside the hull and only having the intake in the boat. comments? suggestions?

 

[PSG-1]

I think that's how they build "New Zealand Style" jetboats, with the majority of the pump being off the transom, and just the intake being set into the hull. It should work just fine like that.

I see that it's a fiberglass intake, not aluminum. Since fiberglass isn't my field of expertise, I'm gonna have to yield the floor to the experts on this one.

 

[KGouty]

Ok been thinking a lot about my project and need some advice before I cut into my boat. Bottom of boat is not flat , so should I mount motors with contour of bottom of boat or make them level? If I install them with contour of bottom will that affect engine performance? Help?

 

[Ranchero50]

Design time eh?

STILL need pictures from the back of your hull showing the dead rise of the bottom and one from the side showing the angle of the transom... It's hard to give decent advice when you won't provide the basic info needed.

You really haven't offered up much data on what you have vs. the stuff you expect help with. Honestly any dang fool with a sawzall can hack up some stuff and cobble something together with 5200 and lag bolts. Most of these build fail because the builder is pretty clueless about what they are doing.

 

[KGouty]

Sorry thought I posted it......I will get it on here asap

 

[KGouty]

hope this helps

 

[KGouty]

PSG hope this is pic you wanted

 

[KGouty]

Inside the lines i had thought about having that area protrude from the bottom of the boat......would be approx 0" to 2" taper

 

[PSG-1]

KGouty » 51 minutes ago[/url]"]PSG hope this is pic you wanted

Actually, the one of the transom is better. It looks like your hull has about the same degree of deadrise as my Duracraft, probably around 10 degrees or so.

I think you've got the right idea as far as how to cut and splice, but again, I've never done one like this, so, I don't know the idiosyncrasies about it like people who have done the cut-and-splice method.

If you're still going with twin engines, you'll need to measure from the keel, to the gunwale on each side, and make sure you have enough room for 2 fully assembled engines to sit side-by-side before cutting. If so, then your next step is to figure out a centerline for each side, (measure off the keel line to get this) and do your layout work in preparation for cutting into the hull.

 

[KGouty]

measurements so far........jet ski parts to be graphed in are 22 5/8" wide......boat is 60" inside.....

 

[KGouty]

so total width to be installed in boat is 45 1/4"....with 60 " of room........that leaves enuf room for exhaust boxes and everything......fuel tanks to mounted in front of motors under bench seat that i will add

 

[riverrat174]

Too cool!!!! I cant wait to see the finished product.

 

[Ranchero50]

The deadrise looks really shallow so you may have trouble with the outboard engine cavitating on hard turns. With a wide flat base I'd expect the wetted surface to move around a lot as the hulls rolls to change direction. A deeper V like a ski boat will keep more of the rear of the hull submerged.

I'd try to get the engines as close together as possible and leave the jets hang off the rear. That way the intakes should be submerged most of the time and it should perform better.

For the hull grafting I'd only cut out on your hull wide enough for the flat section where the intake grate is mounted to sit flush. I wouldn't sink the ski hull through the boat hull as I think you'll have water control problems with it.

Google-fu some of the Yamaha wake boats to see how they did their intake but be aware that a Yam hull is designed to run heavy and site deeper in the water.

 

[KGouty]

OK thanks Ranchero......will do my best.

 

[KGouty]

Ranchero here is a link to a jet jon build and it shows how much ski hull is below boat....this is the idea i had......let me know what you think? Thanks


https://www.youtube.com/watch?v=XFajwYm6VKc

Ranchero here is another link that shows the pump hanging off the back.....is this what you meant?

https://www.youtube.com/watch?v=4J31xB45GVk