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[flatlander]

Greetings all, I have a question on setting up a outboard jet engine.

The jetboat hull has a 25" transom.  I bought a Yamaha proped longshaft outboard (20" shaft) and am planning to replace the bottom end with a Outboard Jets lower unit.  Outboard Jets says that I need to lift the outboard approx 6" for the jet lower unit as the jet intake leading edge of the intake needs to be flush with the boat bottom.  Can I get away without using a jack plate for the outboard or is a jack plate still required?  The outboard mounting holes allow me to raise it a few inches off the transom which could give me some additional room.  Also is it necessary to attach a plate to extend the bottom of the boat back to the jet intake to control water height reaching the intake if a jack plate is not used?

Thanks 

[Jamison Jay]

First: I am no expert............that said, before you get into Jack plates, it sounds like your transom is already at the right height. Being that a typical transom for long shafts is 20in. I would see how the motor lines up with the jet on th bottom. as for the cavitation plate I would run one from the back of the boat to ther jet, they can help big.

[flatlander]

Thanks JJ, I was hoping to get away without using a jack plate and save some $$$$.

[jetboatjim]

http://www.outboardjets.com/index.html

[flatlander]

Thanks Jim, I'll be picking up one of their lower unit jets next week.  I've already read their FAQ's.  I wasn't sure though how accurate I need to be in aligning the jet intake.

[jetboatjim]

what kinda boat are you putting it on?

[scuntor]

Pose your question to this forum http://www.riverjetmagazine.com/fusetalk/forum/index.cfm?forumid=11 if you want a larger jetboat audience. I've asked a few questions and guys have given some great advice.

[steelhead]

No matter what you're transom height ( 20-25-30") is you're pump leading surface must be 1/4" ABOVE the bottom of you're boat. Figure a 25-30% loss in horse power. IE 60/40, 90/65 115/80 & so on. BE SURE to if anything, you OVER power ,,,,cuz you can really lose with extra weight ,,,,,extra people ETC. The thrust is completely different that of a prop. I run a 90/65 Etec on a 700 lb 17' flat bottom boat and its a perfact setup.

[steelhead]

I have run Jets since the 70's and the biggest mistake made is too little power. Some of the best installers in North america are down near thew Skagit river Washington. They stock pumps and install all the time. Valley RV in Mt Vernon has the BEST staff in that area. You'll love you're rig if its set up correctly ,,,but if not it can be pain.

[jetboatjim]

[flatlander]

Thanks all for the info.

Jim, the boat is a 18' Alumaweld Super Vee LT.  Putting on a 115/80 which is the maximum rated horsepower for a 2001.

[steelhead]

That's a good rig ,,,how big is the motor you'll put on it ?

[flatlander]

Steelhead, a 115 yammie two stroke is going on the hull.

[umpo4]

I had to have a transom extension riser welded on transom for the new motor ,,,,raised 5" . They did it out of Alum. andf works fine ,,,aprox 150.00
Steelhead/umpo4

[umpo4]

By you're pic.s ytou may not have to add anything. 25" from top of trans. to bottom is perfact unless that Yam. is an extra long shaft which is kind of rare on the smaller boats like yours & mine.............