280 k planes, what hardware for mounting?
 

Hello all.

I have a nice pair of 280's but no mounting hardware. The mounting holes appear to be drilled for 3/8 bolts.

Are they supposed to be mounted with stainless 3/8 bolts or grade 8 3/8 bolts?

Are you guys using any backing plates on the inside or just using washers?

Thanks, rob

We use SS 3/8" bolts and custom 3" aluminum stringer type washers on the inside of the transom.

I'd got to mcmaster for some 316 SS hardware. They're 70ksi and Id' think that'd be plenty to mount some planes.

Don't forget antiseize.

My 280's take 1/2" bolts for mounting. Double check the ID of the four factory holes per mounting plate. I do not think that 3/8" bolts are adequate, and it is too easy to snap them by over torqueing them. Most ss fasteners are low on tensile strength. I would use thick ss fender washers on the inside of the transom. I also overdrill the holes in the transom for all mounting bolts and epoxy a fiberglass tube into the oversize holes. The ID of the tube is the bolt size. By doing this there will never be any water intrusion into the transom core. I suggest that you do this above and below the waterline. Seal the bolts with 3M 4200. Do not use 5200 in case you ever need to remove the bolts. Good luck.