hey guys,

i'm a wisconsin smallmouth and steelhead guy and seriously need of some outboard help...

getting tired of blowing up lower units on the rocks here and i'm trying to outfit a 14' mod-v lowe jonboat with a Merc 25/20 jet outboard.

problem is, nobody runs them here and dealers can't tell me all that much, either.

my boat's transom height is 15", and according to the one dealer who had (very little) experience with them, that's 7 inches too short for the motor. apparantly if mercury lists the shaft lenght of their 25/20 hp jet as 15-16", that still means i need a 22" transom? that makes little sense. can any of you explain?

i'd like to get into a more indepth conversation about this to see if it's even feasible to run a jet on this boat. i see no reason for it not to work. if you don't mind sharing your expertise, mail me at bacon_to_fry@hotmail.com.

thanks much, as this is getting really frustrating.

-jason

My 16 ft. Grumman wears a Merc Jet 30 on its 20.5 inch transom. So if you build up your transom 5-6 inches it will work just fine.

You will want to put a 'riser' on your transom that raises the engine to a point so that about 2/3s of the jet 'shoe' are below the bottom edge of the hull. (how's that for a run-on sentence)

My other input would be on the size you are interested in. If you typically travel light, a 25 may work ok for you but it works out to be about 17hp at the nozzle, not 20. That may not sound like a big deal but it is. I ran a 40 hp, 28 at the jet, on my 14' footer and it was a nice combo. I think you are on the right track with what you are trying to do.

Steve

XStldr, those other fellas are going to hate you when you get your rig dialed in! Who knows you may even start a revolution!

How far you from Black River Falls?

FJ...out.

fish jesus,

i'm about 1 1/2 hours from black river falls. been up there in driftboats a few times and wailed smallmouth, as well as a few muskies.

thattype of river is exactly what i'm trying to set this rig up for. long, unproductive pools inbetween awesome bank eddy stretches.

thanks to all who posted. do you happen to know of any aftermarket transom risers? or do i have to make one myself (not the best welder in the world...)

-jason

Actually Wooldridge makes transom extensions. Had to have one done on an older Valco to accomodate a newer jet. Not sure about the sizes they offer. Might check with them.

www.wooldridgeboats.com

The transom extension bracket is pretty easy to build if you have an aluminum metal shop in your home area. I had to have one built to put on my jet motor to a 20" transom. Had to raise it over 8" to make it right.

Make sure you silicone all the bolt holes before putting together because they have a good chance of leaking if you don't.

Your boat should run with the jet unit but you are going to lose about 25 to 50% of your speed.
Heavy loads a little more and light loads a little less.

You might have to do a little up and down moving to get it just right. You will know when it is there.

fp

You will be very happy with a Jet 30. My 16-ft Grumman flies with that motor, and we have planed four serious silver fishermen at times. Plenty of power.

Thumper...were those fully developed males?

FJ...out.

Thumper, is that a 16 foot grumman canoe? I have an 18 ft Formula Vee with a 115 Yamaha jet and wish I had a 150 (Prop HP of course).

XSTLHEADER, I don't know what kind of river that you will be running, but suspect if it is not like the waters we run here in the northwest, that you may be better of with a "macs" propguard. I have these on both of my kickers and they have saved the day many times.
Like they were saying, you lose ALOT of power when converting to a jet pump. I often reinstall the lower prop unit on my sled and it will hit about 53 mph top speed (Best conditions) but with the pump, I am lucky to hit 35 mph. It takes much longer to get on a plane also, and I have a stainless impeller to boot.

Seriously guys there is plenty of power with this combination. Now when I say the boat goes plenty fast I'm talking about basically a Jon boat. Twenty mph would be heart-stopping. This ain't your big sled. Hey --- it goes upriver as fast as I want to go.

Oop! Grass Hopper just reminded me that Xstlhdr is talking about a Jet 20, not a Jet 30. Hmmm. Tell us Grass Hopper, what should he do??

And runs shallow too. No prop boat can ever compare and I can't believe a jet sled man recommended a prop guard. If you want to run a Fiberglass ski boat I can recommend a glass repair guy too. But if you want to run shallow you better buy the jet! I always recommend more horsepower but if your boat gets the job done with a 20 hp prop then a jet with a true 20 hp rating will do the same just come out or the hole a little slower.

Xstlhdr, I see that your boat has a modified vee. A jet pump requires a flat spot at the back of the hull or it won't perform at all.

Grass Hopper, you would notice that I said that I did not know what kind of rivers that he intended to run, and with his type of boat...(a small jonboat) a prop would work just fine in a river such as the lower Chehalis for instance. I would not think of using one in a river like the nisqually or even the Cowlitz in low water conditions. And Grass Hopper, I suppose that your kicker is a jet too, probably not, wonder why?
Regardless, does he realize what can happen when that small boat is roaring along and hits something? I have seen this done in good sized sleds and even saw a guy and his dog go swimming once on the Cowlitz below the mouth of the Toutle.
By the way Grass hopper, know what happens when your sled sucks up too much of that grass....she's dead in the water....err grass!

Xstlhdr,
When your motor is mounted at the proper hight,the part of your shoe that is closest to the boat should be 1/4 - 1/2" below th bottom of the boat. Transon hieght is all irrelevant until you accomplish this. And the trasom angle of a Jon boat is a little less than a big alum sled, so I would go with 1/2" or it will cavitate alot.

XStlhdr,

Another quick comment on power. I understand Grasshopper's reasoning above but it isn't accurate (don't mean to disparage you GH). I had a 14' boat that had a 20 Merc prop on it that was quite fast. I changed it to a 40 hp head/28 hp at the shoe jet, and it was not as fast as the 20. Power at a prop and power at a shoe can't be correlated to speed in the same way due to how the water exits each. A prop pulls the boat through the water, a jet pushes it. Because of this, the horsepower is used in two separate ways and you are trying to compare an apple to an orange.

As far as this setup working on the mod-v Lowe jonboat, I just looked at those at the Sportsmans show out here with a friend who needed a new boat. They have a little bit of v built into the nose and are flat as a pancake in the back. This is identical to my boat that I jetted. You will find that the mod-v is a joke once you are on step. The entire v part of the boat is out of the water and you are riding on the flat bottom. My boat used to porpoise if there wasn't any weight up front. If you can, throw your battery and tanks in front of the center seat to help resolve this.

This will be a Very fun setup when you are done. I miss mine frequently.Good luck,

Steve

many thanks guys for the help you've given me. at the beginning of yesterday, i was pretty much throwing the whole jet idea down the tubes. not anymore...

you've really helped me get some confidence that i'm not going to put 3000 bones down on a motor i can't use...

here's answers to a few question i saw.

the boat's a mod-v, but it's very flat for 2/3 of it's lenght. i was hoping the V will help me get up on step, is all. from there, i can run upriver like a mad crazy jedi.

also, i'm only about 160 pounds and will likely fish with a friend who's about 180. couple that with a few rods and gear and that's not very much weight in the boat, in my opinion, so i'm thinking i can get by with a 25/20 jet.

the rivers i'll be fishing are very shallow in many spots, yet there's really no serious water to move through. we don't have the gradient like you do out west. in fact, i'll not encounter much current except when in the shallows.
l
ast, do i need to remove, like 24 inches of the keel in front of the intake? an article i read said it's essential to reduce cavitation.

again, thanks. you guys really helped, even if you are a bunch of wacked out, nut job steelheaders.

-jason

Jason --- Don't worry about the jet application. I had a jet on a 16 ft. Klamath which had no flat area at all. Handled great and ran well in the skinniest of water. You are going to like the set-up a lot.

I would stick the motor on and see if you have a cavitation issue before messing with the keel. Very well may not be required.

Xstlheader, good luck with the new motor and let us know how it works out for you. The best test will be the real test, hands on and throttle down!
Have fun with those smallmouth, never been to Wisconson, but sounds like a nice place to live. Although, I would really miss living in a place with no saltwater.
Later,