Jack plate questions

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catsmith

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Please tell me your experience with diy jack plates on a jon boat. I know I have to raise my motor approx 1 inch to line up with the hull. The boat will run skinny water. It almost sits on top of the water at full throttle.

My motor is the limiting factor of my draft. How does all this work with lifting the motor on a jack plate. I've read alot of information but I'm looking for your experiences please.
 

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I used a 1"and 1.5 thick pieces of hard wood on top of the transom for testing motor heights.
There is also set back of the motor which lets you get the motor higher.
 
you're only going to lift it so far before you run into prop ventilation.

one can play with props to get it higher, but not recommended unless you have a way to feed the water pump inlet.

How skinny? If inches, get a jet and be done with it. That's all they're good for.
 
About all you can do is set the cavitation plate height to what the manufacturer recommends in relation to the bottom of the boat and go from there. Easiest way is shim between the top of the transom and the outboard clamp bracket, but you'll soon run out of room to still clamp/bolt the upper part of the clamp. Usually you'll be able to go an inch up before problems. All kinds of vinyl products at home improvement stores to make shims. Higher than an inch usually will mean a jack plate. Your outboard will work its best at a certain height on your boat. It's all about how the water flows from behind your boat. Going too high will cause tiller steer and cavitation.

My old flat bottom had a big outboard that liked to be low in the water to run right. I started on the transom and it ran fine, but had a big spay off the sides. Tried an inch shim and the spray was way better and still ran fine. Tried 2" up and the tiller handle pushed towards me (tiller steer) once on plane and started to cavitate the prop in rougher water and on higher speed turns. Dropped it back to the 1" setting and bolted it to the transom. You'll have to go through a similar process to find your outboard's perfect height. Best of luck.

Sent from my SM-G973U using Tapatalk


 
typically as you set the motor back from the transom the higher you can run the the motor, so long as the prop doesn't ventilate (blow out). So with many small jack plates, which are 5-6" setback, you can gain up to 3" of lift. Ideally you'd want a hydraulic jack plate such as the atlas micro-jacker. I have installed these on river boats that are used locally. They work great. The problem with a manual plate is that there is ALWAYS a compromise. Manual plates require tools to lift the motor. There is a point where the motor is lifted too high to plane, it blows out before you get on plane, but if/when you ever do get on plane it's fine. So ideally you'd want to raise the motor a little AS you are throttling up, drop it so it don't blow out while planing, then once on plane, lift it. You can't obviously do that with a manually adjusted jack plate or even a fixed jack plate. This is where hydraulic is handy!

4 blade prop will run shallower than a 3 blade of the same exact design. A prop with some cupping will run shallower than one without. A 4 blade with some cup specifically designed to run at or above the surface will let you run the motor high enough to uncover the water pump intake holes on most standard outboards, hence the need for low water pickups. I've seen some locals run 4 blade cleavers which are not cheap by themselves, then pay someone to mod the foot for low water pickup, just so they can run in a foot of water. By time that amount of investment is made, they'd have been better off with a jet and a lot of these guys will end up buying a second boat that is powered by a jet.
 
So I ended up blocking it up and bolting thru the transom. Runs great now. Shaped a pretty piece of wood for the final block.
 

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That doesn't look like a lot of purchase on those clamps, I'd think chances are good that your motor could go for a swim fairly easily. Maybe not right away but over time with the vibration they will lose their grip, just my opinion. I would strongly caution against that. your best bet would be a mini jacker, that's what I did and absolutely loved it.
 
I put a mico-jacker on a customer's boat the other day, and tested (and adjusted) afterwards.

BIG improvement. Runs real shallow but it adjustable on the fly. Nice setup. Little expensive but worth every single penny in his case.

one could also try a power tilt plate. With that (I run a PT35), you can tilt way in when needed, gets on plane like instantly, then trim out as you start increasing speed. The second benefit is that as you trim "out" the motor raises, and along with that there is a 5.5" setback (on mine anyway) so that you can raise the motor about 3 1/2" on the plate just by itself. On mine I can trim out underway just before it starts to porpoise I can look back and see the entire top of the av plate completely out of the water, and can just start to hear the prop surfacing. I can't see it (obviously) but I know what's happening. If I wanted to raise it any more, I'd have to go with a 4 blade cupped prop and that's really more than I need to be doing with it. It will comfortably run in just under a foot of water-I call it 11"--at full throttle. Maybe shallower but I haven't actually measured or tried (yet).

bob's has a tilt-and-jack, it is a jack plate and a power tilt-all in one neat little unit. Made for smaller outboards. I ain't messed with one yet.
 
Colorado1135 said:
That doesn't look like a lot of purchase on those clamps, I'd think chances are good that your motor could go for a swim fairly easily. Maybe not right away but over time with the vibration they will lose their grip, just my opinion. I would strongly caution against that. your best bet would be a mini jacker, that's what I did and absolutely loved it.

Apparently you glossed over the part where he said that he BOLTED motor to transom
 
MDCrappie said:
Colorado1135 said:
That doesn't look like a lot of purchase on those clamps, I'd think chances are good that your motor could go for a swim fairly easily. Maybe not right away but over time with the vibration they will lose their grip, just my opinion. I would strongly caution against that. your best bet would be a mini jacker, that's what I did and absolutely loved it.

Apparently you glossed over the part where he said that he BOLTED motor to transom

Nope, I read that all right. Apparently you glossed over the photo showing it isn't bolted, or maybe you just weren't sure what you were looking at, that's ok too. there's a saying about believing what you hear vs what you see. Some people always look for something to whine about though I guess. hope it works out for him.
 
Colorado1135 said:
MDCrappie said:
Colorado1135 said:
That doesn't look like a lot of purchase on those clamps, I'd think chances are good that your motor could go for a swim fairly easily. Maybe not right away but over time with the vibration they will lose their grip, just my opinion. I would strongly caution against that. your best bet would be a mini jacker, that's what I did and absolutely loved it.

Apparently you glossed over the part where he said that he BOLTED motor to transom

Nope, I read that all right. Apparently you glossed over the photo showing it isn't bolted, or maybe you just weren't sure what you were looking at, that's ok too. there's a saying about believing what you hear vs what you see. Some people always look for something to whine about though I guess. hope it works out for him.

Been a bit, but just got back on site. Apparently its' YOU that glossed over the photo, maybe YOU just aren't sure what you are looking at.

I've drawn a red arrow pointing the BOLT the OP was speaking about which goes thru the outboard bracket (you can't see in pic, but if you know OB's you know this it where the thru bolt hole is located) and thru the transom, thus BOLTING it to the transom. (I also turned the pic so that it's easier for you to see) I'm SURE it's working out for him.
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