I HATE to throw COLD water on your project, but you are going to be very DISAPPOINTED with the performance of the rig you are building -- I have been running OB and inboard jets for twenty some odd years
First off lets look at your motor -- in ALL jets EVERYTHING you do is with POWER to get on plane -- ALL OB jets are DERATED 30% at the jet output, all inline jets are derated 15% -- so if you intend to use a 50HP ETEC head your actual HP at the jet Pump will only be 35HP -- I expect that hull will weigh in around 500#, add your weight plus gear and motor for another 400#, if you intend to carry a buddy another 200# -- so you will be pushing ` 1200# loaded -- thats asking A LOT from 35 ponies == you will be LONG to get on plane and you will find you have to STAY in the throttle to get any performance at all -- this will shorten your motor life
If you intend to fish out of it alone mostly you still will just barely operate in the motors best RPM curve -
You will really need at least 60 HP output at the pump - that means at least 80HP at the head.
AS far as transom height, and tunnel -- ideally the tunnel itself should be NO LONGER than 18" and no deeper than two inches -- no wider than the Jet foot itself, your transom should allow for set up motor height to where the Foot rides IN the tunnel - this will be slightly ABOVE the hull level INSIDE the tunnel --
Sponsons normally are needed if the boat is NOT properly set up as a jet boat -- all jets when sitting IN the water, with gear and driver should sit LEVEL, not nose down and not transom down
Jet boat performance is little understood in this part of the country
Look at Allweld jet tunnel hulls
Go to Rockproofboats.com talk to the owner of the company
Look at Snyder boats.com
These guys are the pros in this part of the country
Here is a good example of a jet OB properly set up
You will thank me later for saving you some serious disappointment
DO your homework
Water Jet propulsion works on POWER, you are throwing water OUT not AGAINST anything which provides forward momentum -- - the faster you can accelerate the water stream, the more thrust you have, water does not compress you have to throw it HARD for thrust.
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