DIY static outboard bracket
 

I am purchasing a used 175 offshore merc with a 25" shaft. I have a 20" transom. Thinking of making my own bracket using 4 pieces of angle bracket.

Motor weighs about 400 lbs, i think (per NADA) Smokeonthewater recommened 3x4 angle, but should it be 3/8" or is 1/2" safer? I Like overkill. Stainless? Or is Aluminum better? How many bolts should I use to attach one angle to another? 2 or 3? And what size bolt? What grade bolts? How many bolts to attach the bracket to the transom? How many to bolt the motor to the bracket?

Any thoughts appreciated.

I edited my suggestion on the other thread w more details... ALSO you can buy one ready to bolt on for $100 .. ish

https://www.google.com/shopping/prod...d=0CMkBEPMCMAQ

I've seen that one on several sites. I have never seen a weight rating for it, only a HP rating (150, which the motor exceeds). I would think the weight capacity is important, I personally can't bring myself to trust it until I know.

whoops!.. I was thinkin you were getting a 150.... my bad

Check out the specs on that bracket...what thickness material..alum or SS...how many bolts and exceed those numbers for your 175

Here's my 2 cents worth:

Any Stainless angle over 3" x 3" x 3/8" for outside, Inside I would use a full plate 1/4" thk across the transom to disburse the force on the transom. The plate should be a minimum of 4" larger than the distance across and above the outside area of the angle frame dimension. Bolts 5/16" dia minimum 2" down/inside from each end and then spaces about every 8" apart. Grind the extreme ends of the angle where they lay against the transom. All welds should be full penetration for the bracket and ground smooth on the side against the boat. This will not allow any brunt force against the fiberglass.

Do not use aluminum, you would need to beef up the thickness from 5/16 to 1/2" thick to compensate for strength and it would need to be out of billet aluminum.

remember also, you need lift, not necessarily set back, although set back requires less lift(rule of thumb is 2 inches set back covers one inch lift), I made a lift only bracket for a 70 by using two pieces of angle aluminum, I used the original mounting holes in the transom to mount the aluminum angle use flat head bolts so they fit flush), and drilled new holes thru the angle and transom for the engine mounting bolts. The top bolts were not supported by the transom, they only went thru the angle, the bottom bolts went thru the angle and hte transom

Thanks for the detailed reply. I'll have to see what the local scrapyard has for stainless angles. Its not inexpensive.

I assume the inside plate can be aluminum since it's basically funtioning like a giant washer. Would you think that a 6" or 8" square plate for each of the bolts would serve nearly as well, or would you stick with your recommendation of a giant plate? I think an 18" 6061 aluminum plate 1/4" thick can be had for around $40.

The old motor was bolted to the transom with 4 bolts. OK to bolt bracket to transom using just these four?

I'm confused by that statement. If the transom is angled down towards the water, wouldn't the setback due to the bracket require more lift, not less?

water is "higher" the further back from the transom you go. the deepest hole your boat makes in the water is at the transom.

now your really confused