outboard jet motor intake position

[kozar]

I am looking at buying a 1998 20HP Mercury jet motor. It is a short shaft (15"). I do not have a boat for it yet. I am looking for somthing that will go thru less than a foot of water. What position should I expect the intake screen to be relative to the bottom of the boat keel? <br />Flush?, Below?, above?

 

[snapperbait]

Re: outboard jet motor intake position

Initally, you want to start with the leading edge of the intake flush with the botom of the boat...<br /><br />It takes a few test runs to find the optimum setting for the engine height and trim... Start out with the motor in a near vertical trim position...<br /><br />If it cavitates (over revs, loss of thrust) then the motor needs to be lowered... Make adjustments in 1/4" increments..<br /><br />If good performance with initial setting, raise the motor in 1/4" increments untill you get some cavitation... Once you reach the point where it wants to cavitate, proceed to lower the motor 1/4" below the setting where cavitation occours... That will be the optimum setting..

 

[Skinnywater]

Re: outboard jet motor intake position

Before you buy it, know that the boat you put it on will have to be very small and lightweight. And this includes passengers, tackle and icechests. <br /><br />That 20hp is going to act like a 12hp at best. <br />And if you can't get on plane that jet will never swim in less then a foot of water.

 

[Link]

Re: outboard jet motor intake position

snapperbait <br />and Skinnywater <br />Have given you good information except I think Skinnywater was being too kind... he said that your 20 HP was going to perform like a 12 HP at best..I would say a 9.9 HP at best..

 

[kozar]

Re: outboard jet motor intake position

I appriciate all the input. Very helpfull. The motor ID tag states that it is a 25HP motor. The cover states 20HP jet. I would like to get at least a 14ft boat. If this is not going to be possible I guess I will have to pass on this $900 motor deal. I was planning on trying to keep the boat light and simple. Am I going to be better off with a modified vee or a flat bottom jon boat style hull?

 

[Terry H]

Re: outboard jet motor intake position

If the jet came from Mercury with the pump on it it would have been a 30hp motor had they installed a prop on it so it could actually give you the 20hp it says it will. A light aluminum hull with a shallow vee , 12-14' long should work fine...if it's a converted prop motor, then the 10-12hp would plane maybe a light 12 footer...just a Thought