Outboard Bracket Mounting

[menissam]

Hello,

I'm in the process of mounting a adjustable kicker bracket on the transom of my 27' C&C. I am positive I will be needing a backing plate, on both sides of the hull. My first thought is aluminum, because that is the bracket material and when i use stainless fasteners I can use Isolators between them to avoid corrosion. Marine grade plywood is my other option, though it will have to be thicker. That being said, my transom is curved, and I'm not sure how to mount my bracket on a curve like this. Older forums mention using shims (probably wood) as well as some epoxy based sealant. Ideally I'd have the curve measured and get a plate made to match that curve but that sounds expensive as hell. Does anyone have any tips on how to do this right?

Cheers,
Sam

 

[Project_Mayhem]

What's wrong with your inboard? You'll need some marine plywood tabbed to the backside of the fiberglass. I'd recommend 1" or so. You can double up two 1/2" sheets. I thought i would need some on the outside but four years later, there's no signs of spidercracks. My transom has a slight curve to it as well

 

[menissam]

Thanks for the reply!
My inboard seems to have governor issues, but I need to move to another marina so I'm going with an outboard for now.

1" of marine plywood on the inside would definitely help, but if I just mount the bracket bare to the fibreglass transom, it wouldn't sit flush. if I tightened the fasteners the fibreglass would probably flex... I'm thinking for the outside to use a handful of hardwood shims glued to a ½" piece of marine plywood. I can then coat that whole wooden assembly with something that'll waterproof it. I was thinking of using Sikaflex or something similar to fill any gaps... not sure what the limitations of caulking are.

Thoughts?

 

[BAD ORCA]

Hello,

I'm in the process of mounting a adjustable kicker bracket on the transom of my 27' C&C. I am positive I will be needing a backing plate, on both sides of the hull. My first thought is aluminum, because that is the bracket material and when i use stainless fasteners I can use Isolators between them to avoid corrosion. Marine grade plywood is my other option, though it will have to be thicker. That being said, my transom is curved, and I'm not sure how to mount my bracket on a curve like this. Older forums mention using shims (probably wood) as well as some epoxy based sealant. Ideally I'd have the curve measured and get a plate made to match that curve but that sounds expensive as hell. Does anyone have any tips on how to do this right?

Cheers,
Sam

You could probably get away with stacking washers on the outside of the hull instead of a backing plate between the hull and bracket if the curve creates gaps under the bolt holes of the bracket itself, and you dont intend to leave it on permanently. The entire bracket does not need to be flat against the transom as long as its secure and flat where it bolts through. If its going to be a permanant arrangement and you are going to leave it on, a good machine shop or 3D printer should be able to make tapered backing plate. On the inside where no one will see, you could epoxy in blocks of G-10 or FRP blocks with really thick epoxy and bolt the bracket to the transom as the epoxy is still uncurred. This will squeeze out excess epoxy and force it to fill in the gap between the backing blocks and the hull. You could do the same on the outside if you wanted to by putting a thin piece of polyethelene sheeting on the hull surface first so the epoxy doesnt stick permanently to the hull. Coat the back of your plywood shim/backer with peanut butter thick epoxy, bolt it all together and let the epoxy squeeze out conforming to the hull. Remove it when its curred and clean everything up and repeat on the inside. Would be a bit of work to do but not technically very hard to do. Also, i think McMaster Carr has angled washers (leveling washers) if you go this route and want to fine tune it. They also have slotted, tapered shims and tapered shims from aluminum.

 

[Project_Mayhem]

For a quick and dirty short term solution you could use rubber washers. I've sway bar link bushings a number of times for similar applications. Like Bad Orca said, it doesn't have to be perfect.
For the interior, think about how your deck is constructed. Two layers of fiberglass with a scored sheet of balsa in between. Assuming that your transom is a simple (one way, not complex) curve, then you could potentially cut the plywood into strips and tab it to the hull. On my boat, they slapped some filler on the transom before plywood. This took care of the slight curve in the transom. I'd probably apply a bunch of layers of 1708 to make it even enough to tab in the plywood. Much less messy and far stronger.

What model is your inboard?