looking at a jet convesion

[JoshKeller]

hi guys, i have a riveted 1648 alumacraft mv. powered by a 2001 johnson 35 hp 3 cylinder outboard. boat weight is approx 600 lbs with batteries, trolling motor, motor. I have found some jet lowers for my motor, and am wondering if it will plane/push my boat well. going by 30% powerloss, it turns my 35 into a 24.5 hp jet. I did have a 25 hp merc prop on the boat before and it ran 28 mph with two people. i will be keeping my prop lower for the majority of my fishing, but would really love to have the jet option for certain areas of the potomac. thanks guys.

 

[Lil' Blue Rude]

Won't be a speed demon but it should get you up and down the river. I've known of people running the 25hp 2 cylinder omc on boats that size and some even bigger.

 

[dhoganjr]

+1
It will get you where you need to go. Should plane out and run fine.

Keep in mind, if you haven't run jets before, that the jet is going to need to be mounted higher. So if you're going to swap back and forth you will probably need a jack plate to make it easier to adjust the height.

Good luck and have fun with it!!!

 

[JoshKeller]

my motor uses the same mid section for the 15 and 20" models, they just use a 5" extension. my plan was to order the short shaft jet pump and remove the extension, and when wanting to go back to prop, just adding the 5" extension back in.

 

[JL8Jeff]

I was thinking about doing the same thing with my 40 hp Evinrude but ended up finding a Mercury 60/45 jet with the short shaft for cheaper than the conversion. I have yet to mount it up on the boat though, everything is packed away for the winter for now. If the jet works out well, I can sell the 40 hp prop and reduce my cost. But my 40 seems to run really well so i might just keep it if I ever need it for another boat.

 

[JoshKeller]

yeah, i thought about buying a jet already made, but the pump brand new is $1700. i can remove the lower unit on my motor in under 5 minutes.

 

[JoshKeller]

i'm looking at the chart on outboardjets.com and it says powerhead horsepower - is this the old crankshaft hp rating, or the newer at the prop measurement? from what im hearing my 35 is actually closer to 40 hp at the prop, and around 45hp at the crank, which puts my boat weight well within the chart for its weight assuming 30% powerloss for the jet conversion.

 

[Ranchero50]

I'd just call them and bend their ear for a bit with what you actually have and how it's loaded to see what they suggest.

 

[JoshKeller]

yeah, i called, he said it would push it, but didnt have much more information than that, since my motor is pretty rare. does anyone with a short shaft jet happen to have the measurement from the area where the jet pump mounts to the motors mid section, to the foot of the jet where it needs to be flush with the bottom of the hull? would like to check my measurements and make sure i dont need to redrill some holes in my static transom riser.

right now i have it set so that my 20" prop motors cavitation plate is dead even with the bottom of the hull, with one bolt hole available to lower the motor, and 2 more to raise it.

 

[mphelle]

That motor had a short production run, did the people at OBJ tell you what size pump/impeller it was fitted with? Need to know which one to measure.

 

[JL8Jeff]

My short shaft 60/45 Mercury measures around 9-3/4" from the front of the jet foot to where it bolts to the midsection and the rear measures around 11". The foot is angled so it's higher in the front to allow the water in.

 

[JoshKeller]

he told me it was model AM.

just measured my motor, and with the motor all the way down, it is 9" from the midsection of the motor, to the bottom of the boat.

the center of my boat has a chine and the drain plug. will this be a problem? just mount the motor so the front of the intake is in line with the lowest point of the hull?

 

[mphelle]

Looks like it uses the same medium pump and 5 7/8 impeller as the model Q which is used on the J/E 20-35hp. I have a 83 Johnson 35 jet over at my shop, I'll get you a measurement later tonight.

 

[dhoganjr]

I've never mounted one on a mod-v but I would put a straight edge beside the chine. Board, ruler, or whatever you have handy. Mount the leading edge of the jet foot at that height. Will be trial and error from there, might be able to go up about a 1/4" or so. May have to come down a bit, depends on if you get cavitation from the chine being lower. If it is too low the foot is going to drag in the water slowing you down.

Hope this helps.

 

[mphelle]

1983 Johnson 35 jet

 

[JoshKeller]

spent an hour today at the river and deserted ramp messing with motor height on my prop. it runs best there its currently at, and i just went and measured - 8.5" would put the front edge of the intake approx 1/16" below the bottom on the hull.

 

[dhoganjr]

Since it is that close, put the pump on and see how it performs. You can adjust from there if you need too. Once you get the pump on, you'll be able to get exact measurements. Since you have 2 holes higher to go, raising it one might put it right where you need it.

 

[JoshKeller]

so it will certainly work with the setup i have? height tweaking may be required, but it will work? since the bottom hole of my motor bracket is a slot instead of individual holes, i have no objections so drilling another hole in the extension bracket for one of the top 4 bolt holes to line up if i need to infinitely be able to adjust the height.

dhoganjr » 1 minute ago[/url]"]Since it is that close, put the pump on and see how it performs. You can adjust from there if you need too. Once you get the pump on, you'll be able to get exact measurements. Since you have 2 holes higher to go, raising it one might put it right where you need it.

 

[dhoganjr]

It should work, I've only dealt with flat bottoms, but they have a strake in the center to. Some are built without them and some people remove a couple of feet, but they run fine with them. Once you get it mounted and run it, you can fine tune it from there.

 

[JoshKeller]

Excellent. Most say it works. A few say it won't. Called outboard jets to figure out exactly how much it will cost, and the girl swore up and down it wouldn't plane, even though another guy from there said it'd be fine. If it planed out easily with a 25 prop, does that mean it'd run approximately the same speed and plane as easily if it was 25 HP at the jet pump?