DIY jackplate

I have an idea of bolting 2 pieces of angle to the back of the transom and running a "riser" board between them directly over the top of the transom to get my cavitation plate even with the bottom of the boat. Does anyone think that the "riser" would flex more than the transom and crack my mounting bracket on the motor?

Great minds think alike. Others have done what you describe. Using angle for a riser is even commercially available (see below from T-H Marine). I like your idea of using a 2x board across the top of the transom. You don't mention size of boat & outboard. Obviously you will need to use beefy angle.

How much do you need to raise the motor? If it is a clamp on motor, can you temporarily shim it up to see if it is a worthwhile change?

How big motor are you running? Here is what I did with my 4hp. No flex at all. In pic it is screwed, but after I got the height adjusted I thru bolted it.

LDUBS said:

Great minds think alike. Others have done what you describe. Using angle for a riser is even commercially available (see below from T-H Marine). I like your idea of using a 2x board across the top of the transom. You don't mention size of boat & outboard. Obviously you will need to use beefy angle.

How much do you need to raise the motor? If it is a clamp on motor, can you temporarily shim it up to see if it is a worthwhile change?


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That is exactly my plan but with a 2x stringing across the top for my clamps to clamp to and I will also bolt mount to transom. That way i dont have any setback, well other than the angle. 1436 jon bare bones, no trolling motor, no battery, 2x10 on top of both benches with seats mounted to them,15hp johnson tiller pull start. Its a clamp style with 2 bolt holes towards the middle/lower third of mount bracket. Already tested it shimmed and i estimate i gained close to 10mph. It also gets on plane way faster, it doesnt plane where it sits now until about 3/4-WOT. With me, my 5 year old, 6 gallons of fuel, small cooler and tackle bag it goes about 22mph down river and 19mph up river. I temporarily raised it 1 1/2" and I need about 2. The problem is at 2" the "washers" on my clamps are gonna be hanging off the top of the transom or close to it. Therefore I was gonna build a riser and and maybe run a beefy aluminum plate from the 2x riser to the transom just so the motor clamp won't be half on the transom and half on the riser. If that makes sense. Also the main reason I'm asking is because I've read where some people say the using a 2 piece "jack plate" can crack your mount.

MDCrappie said:

How big motor are you running? Here is what I did with my 4hp. No flex at all. In pic it is screwed, but after I got the height adjusted I thru bolted it.
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That actually is a smart idea. Might look into doing that instead.

I know you don’t want any set back, but here’s a picture of my bracket. I haven’t seen any issues with flex or stress on the transom. Works great.

Makaw said:

I know you don’t want any set back, but here’s a picture of my bracket. I haven’t seen any issues with flex or stress on the transom. Works great.

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How thick is the aluminum angle and what size motor?

lckstckn2smknbrls said:

How thick is the aluminum angle and what size motor?

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2.5" aluminum angle. 1/4" thick. Motor is a 20hp Johnson short shaft, roughly 90 pounds.

Makaw said:

I know you don’t want any set back, but here’s a picture of my bracket. I haven’t seen any issues with flex or stress on the transom. Works great.

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They were talking about this style 2 piece jackplate. Where you bolt the motor directly to the separate angle pieces. One side flexing more than the other is what they were saying could crack your mount.

I like your idea of the cross piece and beefy plate. That provides a. lot of added support/rigidity to the whole thing.

Back when metal was cheaper, I made several of these from 3/16" and 1/4" aluminum angle. Now, it would probably be cheaper to buy them pre-made. Metal has gotten stupid-expensive lately.

thill said:

Back when metal was cheaper, I made several of these from 3/16" and 1/4" aluminum angle. Now, it would probably be cheaper to buy them pre-made. Metal has gotten stupid-expensive lately.

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I was gonna use some 1/4" steel that I got laying around. I have plywood on the water side of my transom where the motor hangs so it won't contact the motor bracket or aluminum transom.

rebeldrummer96 said:

I was gonna use some 1/4" steel that I got laying around. I have plywood on the water side of my transom where the motor hangs so it won't contact the motor bracket or aluminum transom.

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I don't recommend mixing steel on an aluminum boat but if you put many coats of paint on the steel or put a piece of aluminum bar stock between the steel and the hull, but you need to keep an eye on it.

lckstckn2smknbrls said:

I don't recommend mixing steel on an aluminum boat but if you put many coats of paint on the steel or put a piece of aluminum bar stock between the steel and the hull, but you need to keep an eye on it.

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The steel is going to be bolted up against 3/4 plywood thats on the back of the boat with stainless bolts so there won't be any contact with the steel and boat at all.

Pros and cons.

Pros: Save as much as $25 cost of square foot of 1/4 aluminum plate. Save time sourcing aluminum.

Cons: Potential for rust/corrosion (the plate will be subject to rust regardless of what it is against and don't forget your outboard will be clamped/bolted to this plate). Extra weight (about 3x aluminum plate).

Doesn't mean you can't do it. Like @lckstckn2smknbrls says coat the steel (including the bolt holes).

rebeldrummer96 said:

The steel is going to be bolted up against 3/4 plywood thats on the back of the boat with stainless bolts so there won't be any contact with the steel and boat at all.

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Remember don't use pressure treated wood.