Need 4 more inches!

**DEN** · 04-23-2019, 04:46 PM

Over this last weekend, I bolted up all the hardware for my new manual jackplate.
Jackplate screw is low it can go. Can not re-postion JP on trans.
I knew this was going to be close on my length and I was right.
I need to lower my OB 4 to 5".
What are my options?
longer midsection (25" now)
lower?
I really don't want to physically lower the whole OB, this will change
mounting.
If I have to, I will.
OB is a 97 Merc, 225hp.

Options?

**keefallan** · 04-23-2019, 05:02 PM

Show some pics so that we can see with our eyes and be able to give suggestions..............please.

**SS Minnow** · 04-23-2019, 05:23 PM

So, you have a 25" mid and a jack plate, AND you still cannot get the motor LOW enough?
Yep, need pictures.

**mrichartz** · 04-23-2019, 05:35 PM

Yea what's it on etc?

**DEN** · 04-23-2019, 07:03 PM

I guess I should have done this 1st....after all , I was confused.
I have attached side views of the transom so y'all can see the profile why it is impossible to lower the JP with one exception. Ill get to that later.
As you can see, my transom was built right over the last rib of the boat, which is vertical. Transom angle is 12 degrees.
Also, JP is 14" vertically, so I can NOT just bolt it on, the angle would interfere.

So what I did was bolted 2" x 4" x 12" (1/4" wall) aluminum rectangle tubing,basically, just a pair of standoffs, than bolted the JP to the tubing. (see pic)
This gave me enough clearance so the JP wouldn't interfere with the angle. (I now can see why your confused)
From the top (there are 2 top holes using the bottom hole ) mounting holes in the JP, to the bottom of my sponsors is 25 1/2" (also see pic)

On the OB, top mounting hole to center line of prop shaft is 30"
With a 14" (15") prop diameter, this leaves (14") 2 1/2" to (15") 3" of the prop will be above the water line when on plane.
Now to the exception, I could get longer standoffs, use the same bolt mounting pattern on the trans, then mount the JP lower on the standoffs.

I really don't want to go the "exception" way, but that might just be the cheapest.....but I don't want to lose my OB either. (it will be chained down either way)
Hope this clear up some confusion!

**dtmeeks** · 04-24-2019, 12:32 AM

I would say use a low water pickup and a surface piercing prop. You should have room to set the prop shaft about even with the bottom of the sponsons. I'm not the biggest fan of the offset tubing you used but I see your problem. I dont have any experience with a setup like that but I also tend to overthink things. Maybe someone else will chime in on that.

**SS Minnow** · 04-24-2019, 08:28 AM

Is it possible to use a jack plate with more set back?
When I put a 6" setback on my checkmate I was able to raise the motor higher and gained more top end, and some low end.
If you move your motor back and leave it at the same height, is that not almost the same as lowering the motor?
With that, do you know the ideal set back for a rig like that?

Just brainstorming here.

**KIRCHNER** · 04-24-2019, 08:56 AM

YOU cant predict where water line will be, when on a plane. an educated guess at best. i would get the prop haft even with sponsons, or higher. thats how i have my cat set, 2'' set back. on a momo hull u have water being compressed in front of prop, not on a tunnel. bobs makes a liteweight convertible JP.

**Chaz** · 04-24-2019, 10:21 AM

Redrill the pattern in the motor side plates ..... after you turn them upside-down

**KIRCHNER** · 04-24-2019, 12:39 PM

Originally Posted by Chaz

Redrill the pattern in the motor side plates ..... after you turn them upside-down

Looks to me boat needs a 20'' no JP, LOW intake, 4 blade and let her rip! theres 50 lbs. off to start!

**stokernick** · 04-24-2019, 02:31 PM

25 inch mid section ?????

**DEN** · 04-24-2019, 05:06 PM

Thanks for all the input guys, I really do appreciate it .

Has for surface piercing prop, which I have never heard of...great idea...but very expensive, after doing some research on it.
As for adding more setback, a good enough idea to look into. I plotted the transom (triangle) into my cad. With 2" standoff and 6" JP.
The math said this will not work for my setup. simply put, 12" total setback would give me just short of 1" drop. With a 12 to 1 ratio, that would not be good.

Yes, I now have 25" midsection.

My OB will not bolt right up to the transom, mounting surface area of the OB is 13 1/2" is vertically, (see pics)
Now Kirchner has a great thought!!!!! This boat has not been in water (yet) He is very correct...Do I really know where the water line will be when on plane?
I do NOT know this.

So that said......I am going to leave it all where it is right now and drag out my go pro , mount so I can see where and what the prop is doing when I get this on the water.
I still have a lot of little thing to do before I get to that point, but I will certainly "prop my results"

Thank you all!

**Merc 2.5** · 04-24-2019, 06:14 PM

Originally Posted by DEN

Over this last weekend, I bolted up all the hardware for my new manual jackplate.
Jackplate screw is low it can go. Can not re-postion JP on trans.
I knew this was going to be close on my length and I was right.
I need to lower my OB 4 to 5".
What are my options?
longer midsection (25" now)
lower?
I really don't want to physically lower the whole OB, this will change
mounting.
If I have to, I will.
OB is a 97 Merc, 225hp.

Options?

Need 4 more in. Chit,,,that's what she says , I say bolt it ,run it, and go from there , seems to me u could use a 20in mid and setback?

**Chaz** · 04-24-2019, 06:36 PM

Originally Posted by stokernick

25 inch mid section ?????

The powerhead gotz ta fit up there nice ~N~ purdy tweenst the bilboards ..

Has for surface piercing prop, which I have never heard of...great idea...but very expensive, after doing some research on it.
As for adding more setback, a good enough idea to look into. I plotted the transom (triangle) into my cad. With 2" standoff and 6" JP.
The math said this will not work for my setup. simply put, 12" total setback would give me just short of 1" drop. With a 12 to 1 ratio, that would not be good.

Yes, I now have 25" midsection.

I don't have a Cad / Cam , but I did gradG-ate from .. err .. no that's a lie .. I'm still attending G.O.B.I.T. Good Ol Boy Institute of Technology.
I'm gonna hafta say lookin at my reverse engineerin de-vice .

It leaves bout that much of 15" exposed ...

That takes care of the mid section can / clamp bracket part ...

And about that much for a lower unit ...

Which is only ... 10" from propshaft to mating face ...

Don't bury that lower unit under water ... you'll hate that boat . How it runs , how it handles .. everything about it . Plenty of pictures on this site on where it should be for best results ..

**DEN** · 04-24-2019, 09:06 PM

Hey there Chaz
I love that reversed engineering tool in your hand, I got one too..lol
But honestly, I don't follow you in the top 3 pics...but the end result
I believe your trying to tell me is only stick the tip in right?

One other thought here, I still debating to myself, what prop would y'all put on this 1st.
middle of the road performance to start.
choice between 14"/15" and lots of chooses on the pitch.(15 -23P)

(1997- merc, -carb- 225hp 15 spine)