# motor height setup - mini-jacker install. Looking for speed!



## srimes (Sep 23, 2011)

I'm hoping yall can give me some good advise on this. I searched on google and that's how I fount this forum, a few posts from pappy telling people how to set up jack plates on jon boats.

I have a 97 grumman 14' with a 25hp johnson. It has a 20" transom, but the cav (anti vent) plate sits 2" below the bottom and a lot water shoots up the leg. If I set the trim pin in all the way it sprays up so much water I can barely see the motor! So I order the mini-jacker from basspro to raise it up, along with a tach and water pressure gauge.

I installed the gauges (not the jack plate yet) and borrowed a gps and found that the boat did 27mph with the motor in the highest trim setting. The tach showed 4600 rpm but I had it set at 6p when it should be 5p, so I think it was really turning 5500. That works out to 13% slip with the 10 x 13 prop. I think I can get this at least in to the low 30s, if not mid 30s. I ordered a solas amita 4 blade 10x15 prop. I went with the 4 blade as I figure it'll let me raise the motor higher because it'll have more bite than a 3 blade.

So how high should I set the motor? The mini-jacker isn't adjustable itself. I saw a post where pappy suggested 2-2.5" above the bottom. Since I'll have a 4 blade prop I was thinking of starting at 2.5". Any thoughts?


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## Skidz (Sep 23, 2011)

Your speed sounds good for what your are running. If you are at 5500 or so with the 3 blade 13 pitch prop, the 4 blade 15 pitch will pull your rpms way down. You want to be running wot at or as close as you can get to max rpm's, which for this motor I am assuming is 5500.

I would say the 2-2.5" above the keel that Pappy mentioned is about the max you can get away with. The most important thing is maintaining adequate water flow. The less lower unit in the water, the less resistance and more speed, but if you aren't getting good water to the engine, it's all for naught. If it were me, I would start at 1" above the keel and work from there. Maybe use a piece of wood as a spacer you need until you find that magic height.

I am interested as to your set-up of the water pressure gauge; I also own a 25 Johnson, but the only place I could find to install one is on the tell-tale, which wouldn't tell me anymore than if I just glance back there and see it.

HTH, 
Skidz


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## FuzzyGrub (Sep 24, 2011)

I'd raise the motor and retest with 3 blade, before buying another prop.

What are the hole spacing on the mini jacker? I thought they were 1" spacing. If so, select mounting holes that will give plus minus one inch. So if you go with starting point of 2", you also have 1" and 3". As mentioned above, you can usually block a motor with 1/2", so you would also have 1 1/2", 2 1/2", and 3 1/2". Starting at 1 1/2", gives 1/2" flexibility from 1/2" to 3". 

Look forward to seeing your results.


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## srimes (Sep 25, 2011)

Skidz said:


> I am interested as to your set-up of the water pressure gauge; I also own a 25 Johnson, but the only place I could find to install one is on the tell-tale, which wouldn't tell me anymore than if I just glance back there and see it.



Mine is hooked up to the tell tale, here's where I asked about it on iboats: https://forums.iboats.com/showthread.php?t=513597

I only got 8 psi at wot, but the water pump on this motor had never been changed :shock: and I haven't put in the restricting nipple. I put in a new pump last night and I'll check the pressure before install the nipple.

I'm still working on installing the plate. Nothing went right yesterday. The biggest disapointment is that the plate only nets about 1 5/8" of lift, so I'll have to mount it overhanging the transome about 2.5" to get the lift I want. If I had know this I would have tried a different route. Hopefully it won't look too bad.


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## lckstckn2smknbrls (Sep 25, 2011)

Mounting the mini-jacker above the transom cap is what you want to do. Just drill out a few more of the dimples.
In my pictures you can see where I used a piece of wood to help me find the correct height then I moved the mini-jacker up 2 more inches.


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## srimes (Sep 25, 2011)

I finally got the [email protected]#&*! mounted! Some projects go smoothly with everything falling in to place, and this was not one of them. 

Finding the SS hardward to mount it was tough and very expensive. I spent over $50 at lowes for the bolts, nuts and washers.

I painted the plywood insert that came with the mini-jacker so that it'll last longer. After the first coat my dumb yellow lab snatched it off the sawhorses and chewed it a little before leaving it in the dirt. No real structural damage but it sure was ugly. I stuck it under a heat lamp to speed drying and then sanded out all the dirt/grass/leaves stuck to it and filled the chewed parts with bondo. Put on another coat and let it dry in the shop, away from the dog.

Pulled the motor off with a come-along hung from a tree. Clamped the mini-jacker in place and found that it hit a hole in the transom, which had a lip and wouldn't let the bracket sit flat. Back to lowes for a stick of 1/8" x 2" bar to make shims. 

I thought I figured out how high to mount the bracket. I made the shims and clamped everything in place, with the minijacker 1 3/8 above the transom. The bracket gives 3" lift, and with 1 3/8 more I'm looking at over 4" of lift, right? Wrong! I break out the square and measure only about 3" of total lift! I measure and measure every which way to figure out what is going on, and finally go in to sketch it out. Turns out the setback on the bracket (4") reduces the lift because of the transome angle, so the bracket only nets about 1 5/8" of lift. I end up mounting the bracket about 2 3/4 above the transom.

Drilling the holes went well, other than fighting dead batteries in the drill. I did 4 holes and test bolted it, then decided to go ahead and do 2 more as the instructions that came with the minijacker said. It also said to use 3/8" bolts, but the hardware store didn't have long enough ones in 3/8 so I used 5/16. So I bolt it back on, drill 2 more holes, and when I try to remove the bolts on of them siezes up! I planned to use anti-sieze before final assembly but it was too late. I had to break out the angle grinder and cut the bolt, and as I didn't have any extra I made another trip to the hardware store. Lesson learned, always use lube on SS bolts first thing.

Anyway, It's all buttoned up except for the cables and wiring, I didn't try to run them neatly yet. I sealed the bolts with 4200. Where my motor bolts on there are 2 holes spaced 3/4" so I can adjust height that much with drilling. I mounted it high to start with: the bottom of the vent plate is 2 7/8" above the bottom of the boat. It's probably a little high, I just thought I try it since I'm putting on a 4 blade prop. At least that went on easy, and the new water pump was fine too. I'll post pics in a minute.


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## srimes (Sep 25, 2011)

Here are the pics of the thing all bolted up.








Here you can see a shim and why it was needed.


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## link7 (Jan 21, 2012)

hi srimes, sorry to revisit an old post, but I joined this forum because of the pics of your motor with the mini-jacker. 

I've got a 2002 Mercury 25HP on a 14' gregor and the cav plate sits about 6" below the hull (short transom, long shaft motor). I see you've got the mini-jacker set well above the top cap of the transom. I'm thinking of doing the same thing. Has the height caused any problems for you? Is the transom flexing a lot?


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## srimes (Jan 21, 2012)

It didn't flex. If your transom flexes you need to fix that. I had to lower it down a bit 'cause the prop slipped too much. I don't have pictures, but iirc I lowered it 2 holes.


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## link7 (Jan 21, 2012)

Ok. Thx. 

I haven't done it yet. Just planning it out and I wanted to see if it worked for you. 

My transom is in pretty good shape, so it should be fine.


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## flatboat (Jan 22, 2012)

if you are gettin a 4 blade i would run it where it is and try it .if its stainless you can cup it so it holds onto the water a little better,don't cavitate nearly as bad . aluminum don't like it high theres no cup in them .most of them will cavitate pretty bad up high .but if you want speed stick with a 3 blade and work it a little .... then turn your hat round bacards and haul a%%


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