Mini OB Boat conversion to Mini Jet Boat

2 powerplants, two pumps, independent throttle control I can imagine youd have some amazing maneuverability with a setup like this....not to mention monster holeshot!

 

Last night I ground the bottom surface of the hull behind the motor mounts to lay some new glass. We really hadn't laid a good amount of fiberglass in this area and we wanted to really reinforce this spot. Here are some photos after I ground and laid the glass. You can tell how thick it is now by the color. Also, there used to be kind of a step there, now it is more gradual due to the amount of glass added.








Then we encased the rib with glass to seal and reinforce this area.





The last one was almost finished, but you can see some fiber that hadn't been completely wetted out. It turned out very nice and smooth and we laid a LOT of glass here too.

More soon!

 

Couple questions for the boat builders here...

1) What adhesive should be used to attach the deck of the boat to the bottom of the hull? After using recommended adhesive will I need to fiberglass the boat together from the inside as well or will the adhesive be plenty strong for my application?

2) What foam should be used to fill the underside of the deck for buoyancy? Is the "Great Stuff" brand expandable foam in a can the stuff I should use or is there a better alternative for marine use? I have West Marine stores very close if they might have something better.

 

I bet that would be a blast with twin jets. You could definitely show up some of those SeaDoo boats in the spin department.

Looking awesome.
I didn't know we had a West Marine in the cities.

As far as the foam goes, I'm nowhere near an expert on it but I'd say don't use the Great Stuff.. Look into marine pour foam probably. That will fill the cracks better I'm sure and it will probably hold up to moisture.

 

From this website.. http://www.aeromarineproducts.com/boat-foam.htm

Q. How do I know how much foam I need to float my boat?

A. Great question! Get your calculator ready, you will need it. A cubic foot of polyurethane will float about 60 pounds of "dead weight". The wood parts of your boat will probably float, so you don't need flotation foam to offset that weight. The fiberglass parts of your boat will barely sink, so you really don't need much foam to offset the fiberglass- maybe one cubic foot of foam per two hundred pounds (or more) of fiberglass hull. The metal parts of your boat are what you really need to account for. A small (4-6hp) outboard may weigh 45-55 pounds. A 50hp outboard will weigh about 200 pounds.

So a 16 foot fiberglass skiff with a 50 horse outboard will need about six cubic feet of urethane foam to keep it afloat. A 12 foot plastic kayak will only need one cubic foot. A 30 foot fiberglass sailing sloop with a diesel engine and lead keel would need about 150 cubic feet of foam. Actually, very few 30 foot keelboats have positive foam flotation, but it's not out of the question- especially when you consider all of the air pockets that would exist, as well as all of the wood interior components that provide some positive flotation.

 

That's really helpful man, Thanks!!

 

Where did you get the wrecked jet ski for this project?

 

It was not wrecked. It was a ski hull that had been used for parts. The engine, pump, and all other parts were taken from miscellaneous skis in a performance shops grave yard. The shop is called RSI (Race Shop Inc in Shakopee, MN). The motor and pump were also fully rebuilt by the owner Rob Schatzle.

 

Created a level battery tray to mount my Optima YellowTop. I think the pics tell the story. A belt will keep the battery tied down. Let me know if you have any questions.

 

Yep it sure is

 

Engine length

Awesome project, I just bought a 14ft RIB that I am planing to fit with a Sea Doo power plant. What is the length from the inside of the transom to the end of the motor? Trying to figure how much of the interior I will have to modify.
Thanks for any help, and great posts on your project.

 

Give urself about 40". Thats uf u want to chop off the tunnel so the pump sticks out the back. From my transom to the front of the motor its 36" but i made the pump shoe stick out the back about 4"...thats why i say 40".

 

I templated and cut the fuel tray today. I still have to glue it together then fiberglass it in.

 

looking sweet!

always wanted one of these small boats haha, and this conversion ticks all of the boxes
should be a heap of fun to drive

 

We taped the fuel tray pieces together then glassed them together.






Then we placed it in to the boat and glassed it in place using the battery to weight it down and keep it in place.






We decided to flip the tank so the fuel pick up is near the rear. That eliminated the need for a downward slope toward the front, so we cut 2" from the rear wall of the fuel tray to lower it down.






She is ready for bed-liner on the interior/bilge!

Tonight we also modified the hub of the WetJet steering wheel. The hub is angle cut from the factory which was making the wheel point downward at an awkward angle. We modified it so we could flip the hub 180 degrees to allow the steering wheel to angle upward at a more natural angle. I'll take pics of that later.