# Adjustable Jack Plate



## alfaguy (Nov 7, 2011)

I finished fabrication and mounting my version of an adjustable jackplate on my 14 ft Rhino today, and thought I would share the design with the group. It was built using the Bob Dillion Racing plans, but I needed it to be adjustable from a single point, so I adapted the Vance Engineering type adjuster, but using a 1/2 inch x 8 inch long piece of all thread. I used 4x4x1/4 angle for the boat attachment part, and 3x3x1/4 angle for the motor portion. 

With the motor board I have a 6 inch setback and it will adjust up and down 3 inches. I still have room to cut the slots longer if I need it.

I will try to load photos below.

Dave A.


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## lckstckn2smknbrls (Nov 7, 2011)

Very nice work.


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## aeviaanah (Nov 7, 2011)

Very nice, im getting ready to make one myself! Im glad you posted this. Does the allthread go through both plates and you just turn the top nut to adjust? Then lock it down with nylock jam nut? How is the allthread mounted at the bottom? Is the nut welded to the allthread?

Great job!


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## alfaguy (Nov 7, 2011)

The allthread goes through both cross brackets. The top one is cut from 3x3x1/4 angle and the bottom is from 2x2x1/4. I used a double nut on the top to create a long bolt because I could not find an 8 inch bolt with long enough threads for the length of adjustment needed. I made a steel bracket to capture the nut under the bottom cross piece. It is rivetted in place. There are different ways to do this but I thought it was important to allow for misalignment in the assembly and the captured nut seems to work good as it can move about some. 

Dave A.


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## aeviaanah (Nov 7, 2011)

alfaguy said:


> The allthread goes through both cross brackets. The top one is cut from 3x3x1/4 angle and the bottom is from 2x2x1/4. I used a double nut on the top to create a long bolt because I could not find an 8 inch bolt with long enough threads for the length of adjustment needed. I made a steel bracket to capture the nut under the bottom cross piece. It is rivetted in place. There are different ways to do this but I thought it was important to allow for misalignment in the assembly and the captured nut seems to work good as it can move about some.
> 
> Dave A.


What are the lengths of the angle irons? How well does it perform? Is there anything you wouldve done differently?


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## alfaguy (Nov 8, 2011)

The neat thing about making your own jackplate is tailoring the size to your boat and motor combination. My transom is 15 inches tall, and the clamp mount on an Evinrude 25 hp is 10 inches wide. The Dillon design uses 12 inches for all components, which would have worked good on this size engine but my cavitation plate sat 1.5 inches below the bottom of the boat, so my beginning point needed to bring the motor up to that level. 
I changed the basic dimensions for the boat side angle aluminum pieces to 11 inches, and the motor side to 13 inches. My overall width is 12 inches, but I should have made it 12.5, to give me a slightly wider motor board. I would not change anything else. 
I should point out that I bought a Vance 4 inch unit, so I had the benefit of seeing exactly how they did it. It is a great unit, but is just too big for a lightweight boat. It is 16 inches wide, weighs 23 lbs, and is rated for 225 hp. I will keep it in case I ever get a bigger boat, because their engineering is great and at $173 plus shipping, you cannot go wrong if you need a big one.
One curious thing about working with aluminum angle is that it is not exactly square. You will see this when you mount the boat side brackets to the motor side brackets. Each piece measured 0.060 out of square. I emailed Bob Dillon about this and he replied that when you draw it up with the clamping bolts it all works ok. He has made plenty of them so he knows. But I lessened some of the gap by inserting a 5x1.25x 1/16 piece of teflon in each side to act as a friction surface. 
I do not think it is a big issue for a non-bolt adjustor jackplate but when you add the cross pieces and motor board the non square issue becomes more apparent. (I may be a little anal about this).
Sorry for the long post.
Dave A


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## fender66 (Nov 8, 2011)

VERY impressive! =D>


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## aeviaanah (Nov 8, 2011)

Thanks for the post man! So the cav plate should be at the bottom of the boat at the lowest adjustment point? My motor is coming in this week 

I happen to work in a metal shop as well 

What size hardware did you use?


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## alfaguy (Nov 8, 2011)

The side clamping bolts are 1/2 in carriage bolts, where the square part fits in the 3 inch slots without the bolt turning. The bolts to the transom are 3/8 in. The bolts attaching the adjuster cross pieces are 5/16 inch. The 3/8 and 5/16 bolts, washers and nylock nuts are stainless, but I could not find 1 1/2 inch long 1/2 carriage bolts in stainless but the nylock nuts and washers are.
In cutting the 1/2 inch slots, I drilled multiple 1/2 holes and used a sawzall to connect them. It will take lots of file work to smooth everything so go buy a new file for the job.

Good luck and share your experience.

Dave A.


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## JBooth (Nov 8, 2011)

Very nice work! Have you tested it yet?


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## aeviaanah (Nov 8, 2011)

alfaguy said:


> The side clamping bolts are 1/2 in carriage bolts, where the square part fits in the 3 inch slots without the bolt turning. The bolts to the transom are 3/8 in. The bolts attaching the adjuster cross pieces are 5/16 inch. The 3/8 and 5/16 bolts, washers and nylock nuts are stainless, but I could not find 1 1/2 inch long 1/2 carriage bolts in stainless but the nylock nuts and washers are.
> In cutting the 1/2 inch slots, I drilled multiple 1/2 holes and used a sawzall to connect them. It will take lots of file work to smooth everything so go buy a new file for the job.
> 
> Good luck and share your experience.
> ...


Thanks for getting back to my with that information. And what about the cav plate height? Should the lowest point of the adjustment make it so cav plate is equal to bottom of transom?


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## alfaguy (Nov 9, 2011)

Others should join in, but the starting point for adjusting the position of a motor should be to have the cavitation plate even with the bottom of the boat surface. The motor can be raised from that point until it starts loosing cooling capacity, or the prop starts acting strange. Water conditions will impact your set up too so any final setting will be a compromise. 
From what i read on line, cooling capacity can be quantified if you have a water pressure gauge, but small motors do not have them and I think cost may be prohibitive for most of us. 
I installed my jackplate 3 days ago and have not run the boat with it yet. I have two friends with hydraulic controlled units (one with a tunnel) and they like them a lot. Our Florida rivers have plenty of snags and logs so it helps to get the motor as high as possible.
I am headed to the river for a weekend hunting/fishing trip tomorrow, so I can report back to the group on Monday.
Dave A.


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## aeviaanah (Nov 9, 2011)

alfaguy said:


> Others should join in, but the starting point for adjusting the position of a motor should be to have the cavitation plate even with the bottom of the boat surface. The motor can be raised from that point until it starts loosing cooling capacity, or the prop starts acting strange. Water conditions will impact your set up too so any final setting will be a compromise.
> From what i read on line, cooling capacity can be quantified if you have a water pressure gauge, but small motors do not have them and I think cost may be prohibitive for most of us.
> I installed my jackplate 3 days ago and have not run the boat with it yet. I have two friends with hydraulic controlled units (one with a tunnel) and they like them a lot. Our Florida rivers have plenty of snags and logs so it helps to get the motor as high as possible.
> I am headed to the river for a weekend hunting/fishing trip tomorrow, so I can report back to the group on Monday.
> Dave A.


Right on, Ill be waiting around to hear how it performed. Do you think you will notice a difference? What size motor is that anyway?

Thanks for the help. I'm wanting to start on the jack plate but I dont have the motor. It is a 2011 15hp Mercury 4stroke. I need the know the width. Or maybe I dont, any suggestions? I appreciate all you have helped me.


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## alfaguy (Nov 10, 2011)

You can tailor the width to your motor. My 25 Evinrude has a 10 inch wide clamp bracket, and the 12 inch wide jackplate is good for it, but a 15 hp Johnson measures 7.5 inches, so it can be smaller. You should measure your new motor - may be able to use a 10 inch wide version, and use 3x3x1/4 angle on the boat side too to keep the scale reasonable. It is up to you. 
With a smaller, lighter motor, I don't think I would bother with a screw adjustor either. My Rhino is a 14x48 welded boat, and the 25 hp is fairly heavy. I wanted to be able to adjust it on the water. 
Dave A.


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## aeviaanah (Nov 10, 2011)

alfaguy said:


> You can tailor the width to your motor. My 25 Evinrude has a 10 inch wide clamp bracket, and the 12 inch wide jackplate is good for it, but a 15 hp Johnson measures 7.5 inches, so it can be smaller. You should measure your new motor - may be able to use a 10 inch wide version, and use 3x3x1/4 angle on the boat side too to keep the scale reasonable. It is up to you.
> With a smaller, lighter motor, I don't think I would bother with a screw adjustor either. My Rhino is a 14x48 welded boat, and the 25 hp is fairly heavy. I wanted to be able to adjust it on the water.
> Dave A.


Do you think a jack plate is a benefit for a 15 hp motor and 12' boat.

Howd that thing perform?


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## alfaguy (Nov 14, 2011)

My jackplate worked great on Saturday, but I did not get a chance to fine tune it due to motor reliability problems. The boat was faster with the motor raised so the cav. plate was even with the bottom of the boat though.

I have a 15 hp on an 14 foot Monarch jon, and if I were to make a jackplate for it I would do a quick version without the screw adjuster and may just drill holes for different positions instead of taking time to make the long slots. For your case I think it is worth while to do.


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## alfaguy (Nov 6, 2014)

I am revisiting my old post and can't believe it started 3 years ago. The jack plate is working great and I would not have done anything differently other than using all stainless steel fasteners. I have a couple regular cadmium plated bolts and they are showing some oxidation now.

Having the jackplate adjustable is good for me as I usually boat by myself, but when i plan on adding a passenger I can fine tune the motor height for best performance.

I am curious about how others fared with their project though.


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## surfman (Nov 6, 2014)

I was wondering how you did the slot, that's the hardest part. I made mine by just drilling a bunch of holes, sounds simple enough but, they all need to line up no matter where you move the bracket and that is not so easy to do. It is also a pain to adjust because I need to remove the motor to move it. I have a F20 on my 1448. and that little motor still weighs in at about 100 lbs.


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## alfaguy (Nov 7, 2014)

I made the slots as you did, by drilling a series of holes and sawing and filing between them. I was careful to locate the hole centers and center punched the locations so they would be precisely drilled. A couple new files helped cut quickly.

You can make your unit adjustable like mine by installing a long bolt/allthread between the two sections. Look at my photos to see how I did it. It works well on the water. Just be careful to not drop your wrenches overboard.......


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## alfaguy (Nov 7, 2014)

Here are photos of the adjustor from today. The middle photo shows how I captured the bottom nut, so it could move a little to self align itself. The jackplate is bolted together without any welding.


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## surfman (Nov 7, 2014)

Looks real good. SS is always best.


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## alfaguy (Nov 15, 2021)

This thread was fun to work on, and the jack plate has worked perfectly for all these years. I will be moving this jack plate to another boat, and making another one for the Rhino boat, which will be sold. The new boat is a 14x48 Scandy white with a tunnel hull - it will want the adjustable jack plate. Since I have the Rhino sorted out, I will make the new one with the slots, but it will not have the screw adjustor. 

Keep those tin boat projects going!!! :---)


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