Javelin 350/Johnson 40hp setup:

[CalicoKid]

Last post I was looking for a stainless prop for my 15.5' Javelin. I've since purchased a Stiletto Triad for it. With my OMC aluminum 17" pitch prop I was getting 33mph@5600rpm at best efficiency. With the stainless I am getting 33mph@5400rpm at best efficiency. To determine best efficiency I am watching my gps and tach while slowly trimming out and stopping trim out at the point at which speed stops increasing but rpms continue to increase. I think I need to be getting more rpm out of this motor.

Boat and motor are 1992; Javelin 350 angler 15.5', Johnson 40hp twin.

The hull is quite light. It has a built in setback of 7" but no pad. I think my motor is much too low, the AV plate is about even with the bottom of the hull (not the bottom of the setback). I am getting a lot of spray between the transom and motor bracket. How far should I theoretically be able to raise the motor? Since a pic is worth a thousand words, here's a few grand worth:

 

[JUSTINTIME]

Re: Javelin 350/Johnson 40hp setup:

looks right to me
av plate should be level with bottom of hull

 

[walleyehed]

Re: Javelin 350/Johnson 40hp setup:

...Not with that much set-back...
The AV plate should be about 1.5" above the pad as a starting point with 7" of set-back.
Let's try 1 hole at a time and test.

 

[Crownie2]

Re: Javelin 350/Johnson 40hp setup:

I second that motion...d

 

[Ron G]

Re: Javelin 350/Johnson 40hp setup:

i third that motiondd

 

[Silvertip]

Re: Javelin 350/Johnson 40hp setup:

That engine performs best with a prop that allows it to turn 5800 RPM. It's being lugged with a 17P.

 

[CalicoKid]

Re: Javelin 350/Johnson 40hp setup:

Thanks all, I will hopefully get it out tomorrow and raise the motor and test some more. I might bring a jack down to the landing so I can raise it one hole at a time without coming home. The ramps are dead this time of year so should be no problem. And yes 5800 is more or less my goal, I just want to get the height closer to where it should be and check rpms before switching props again.

 

[walleyehed]

Re: Javelin 350/Johnson 40hp setup:

"That" is why we are doing some testing of raising the engine with a better prop. Pitch is not important until we maximize what he has...
Here's my theory=if we raise the engine, say 2 holes, gain 150-200RPM, we will likely gain some speed, right? Well, if we gain some speed, we "should" end-up with less wetted area, adding more speed AND RPM. Less drag requires Less HP. If we can get it up and free, the RPM will follow, and yes...with the 17.

 

[CalicoKid]

Re: Javelin 350/Johnson 40hp setup:

That's what I'm hoping for Kenny Fingers crossed!

 

[CalicoKid]

Re: Javelin 350/Johnson 40hp setup:

Well today didn't go so well. I got the motor raised and went to the lake but the motor wouldn't run right. It was flooding badly. When I pump the bulb I can hear gas rushing at the carbs and if I then turn the flywheel by hand gas pours out of the exhaust around the prop. I'll be rebuilding the carbs sooner than I had planned now and since it is getting so cold here and I've been so busy I doubt I will get a chance to test the boat out until Spring. Oh well....

 

[walleyehed]

Re: Javelin 350/Johnson 40hp setup:

Sorry to hear that, C.K......
email me when you get time....
Kenny

 

[CalicoKid]

Re: Javelin 350/Johnson 40hp setup: (It's alive!)

Re: Javelin 350/Johnson 40hp setup: (It's alive!)

I rebuilt those carbs over the Winter and did a preliminary sinc and link according to my OMC manual. My father and I took the boat to the lake and dialed in the carbs and timing and need to make a couple fine adjustments to the timing before the next time out but the motor is running better than it ever has.

The last time I had it out before the float stuck I had raised the motor two holes to see what would happen. Well good news here: The big spray is gone. It doesn't ventilate any worse, but I didn't seem to pick up any rpms either. It seems this prop just doesn't hold well if I trim past horizontal and it still has a tendancy to slip all at once rather than losing bite a little at a time. I didn't take the GPS but I did look over the transom while my dad drove to see what was happening. As I said the big spray off the leg is gone but I believe the motor is still too low. The AV plate is still running 1-2" below the surface, there is a small plate above it that is running right at the surface. The guy who had the boat before me mounted a transducer on the transom with epoxy and it is throwing a lot of spray so I need to take it off. Why he put it on the hull and not IN the hull is beyond me.

So I need to do the final timing adjustments and clean up the transom, possibly raise the motor to the highest hole and bring my GPS out and get some more numbers. Will post them.

 

[CalicoKid]

Re: Javelin 350/Johnson 40hp setup:

OK 2 holes up and getting 34mph at 5400rpm. So I picked up 1mph, still no decent rooster and can't trim over 5400rpm without blowing out (trimmed pretty high). Cav plate is running below the surface as posted above. I need to raise it to the top hole and see what happens. I might need to put a jackplate on eh? I'm likely overpropped though and underpowered, I'd love a 70hp triple.

 

[CalicoKid]

Re: Javelin 350/Johnson 40hp setup:

I raised the motor to the top hole and took it out again. This time I had my dad with me so I can't compare precisely with my previous results but I am more likely to have another person with me than not so it's good to know how the boat will perform.

I was getting around 32mph and 5200rpm. If I trimmed to the highest speed and rpm the prop would easily lose bite and send the engine revving. Maybe it's the prop and maybe it's my hull but I wish I had more gradual slippage. With the motor in the highest holes there is a lot of torque steer so I think dropping it one hole again would be best for now. The holeshot is pretty lame and the engine bogs in turns also. In short I'm overpropped.

I have two aluminum props that the boat came with and have tried those in the past with the motor at it's lowest. The 15" was not enough pitch, RPMs much too high. The 17" was a good one, 33mph @ 5600rpm. That prop actually had better slip characteristics than this Stiletto stainless at least from a handling perspective. I might put that on and see what happens but I'm afraid it won't handle the engine height.

It is interesting how two 17" props yield 200rpm difference. If I swap the 17" Stiletto for another pitch should I go with a 16" or a 15"? I wish there were a prop that ran at the surface better for this motor. Any comments welcome.
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[CalicoKid]

Re: Javelin 350/Johnson 40hp setup:

I put the 17" aluminum back on and gained some RPMs and lost some MPHs.. I'm at about 31-32 mph and 5600 rpm max before it loses bite. I think the motor is a little too high now to run an aluminum prop. The boat handles good and turns nicely if I trim it in properly for the turn. It still loses speed and rpms when I horse it into the corners though which is no good on the river. Although if I keep it trimmed just a little high I can keep the Rs up by slipping the prop through the turn and it hooks up once I'm straightened out. I do prefer the aluminum prop over the Stiletto stainless for this kind of driving since the aluminum seems to slip more gradually where the stainless holds on solid and then blows out suddenly and drops the boat. The holeshot is not good with either prop since I've only got 40hp but the aluminum is a little better. Whichever prop I end up with finally I will consider porting it.
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