Shim an outboard motor mount?

Apr 23, 2014
54
Irwin 28 Long Island
Hey everyone, I am trying to install a Garelick outboard mount on my slightly curved transom and I am finding that the curve is causing the bracket to not sit very flush.

Seems I have to shim at least one corner of the bracket mount to sit flush against the transom.

Is this considered a good idea? I know I could use UHWPE sheets to shim it but I cannot really find anywhere online where anyone is talking about this kind of problem.
 
Nov 9, 2012
2,500
Oday 192 Lake Nockamixon
Necessity is the mother of invention. If you need to shim in order to get a good fit, than go ahead. It's more about a snug fit and decent force distribution… If I were going to shim an outboard bracket, I'd probably make the shim a bit oversized for load distribution.

UHWPE could probably be used, but PE is a plastic that will deform under load. Near as I can tell, Starboard is a high density PE. Probably the higher the density of the PE, the less of a problem deformation under load would be.

There was a recent article in Good Old Boat where a guy replaced teak riser pads for deck hardware with Delrin. He said you could get offcuts from a plastics place on the cheap.
 
Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
shim away.... but if you are using small washers, do it on the top of the bracket.
if you must do it on the lower holes, then an oversized shim would be best.

properly, if you do it on the bottom of the bracket, you can also use a piece of delrin (best), uhmw, aluminum, or stainless that would span the distance across between both lower holes... put this spanner piece against the hull and shim with washers between the bracket and this support.

when the outboard is pushing the boat into the wind and waves, the pushing force will be on the lower holes, and you want a good bed so that the hull is being pushed against evenly on the lower part of the bracket.... fiberglass is very forgiving and im sure you could pull the glass of the transom to the bracket without any problems and be fine, but a better aligned support with a larger footprint will allow for a more solidly mounted motor.

on the inside of the hull, use 3/4" x 2 or 3" oak for spanning the distance between each top hole and each bottom hole, as back up supports. it makes a big difference in how solidly mounted it becomes.
 
Apr 23, 2014
54
Irwin 28 Long Island
shim away.... but if you are using small washers, do it on the top of the bracket.
if you must do it on the lower holes, then an oversized shim would be best.

properly, if you do it on the bottom of the bracket, you can also use a piece of delrin (best), uhmw, aluminum, or stainless that would span the distance across between both lower holes... put this spanner piece against the hull and shim with washers between the bracket and this support.

when the outboard is pushing the boat into the wind and waves, the pushing force will be on the lower holes, and you want a good bed so that the hull is being pushed against evenly on the lower part of the bracket.... fiberglass is very forgiving and im sure you could pull the glass of the transom to the bracket without any problems and be fine, but a better aligned support with a larger footprint will allow for a more solidly mounted motor.

on the inside of the hull, use 3/4" x 2 or 3" oak for spanning the distance between each top hole and each bottom hole, as back up supports. it makes a big difference in how solidly mounted it becomes.
You mean a sheet of Delrin like this? http://www.travers.com/98-131-516?C...u2orUlO-NoPdMoPO92JiXKw0CfG3xbTkgQaAg-U8P8HAQ

Put that behind the mount holes directly on the fiberglass, shim with washers between that and the bracket, a strong oak backplate on the inside of the transom, stainless steel hardware, clean silicone job and I think I should be good. Let me know what you think.
 
Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
your method of application is absolutely spot on.... but i would recommend using 1/4" delrin... it has the strength of 1/4" aluminum.
the 1/8 stuff has a bit of flex that wont allow as much support.
 

capta

.
Jun 4, 2009
4,935
Pearson 530 Admiralty Bay, Bequia SVG
I would not shim one side or corner of your outboard mount if this is what the mounted outboard will be on when using it, not storing it. Build a spacer that is flat on the face for the outboard bracket and curved to the shape of the hull on the other, incorporating all the holes in the bracket.