Fitting the mounting pads
When installing components or upgrading systems, it is obviously crucial to be able to provide secure mounting points. Sometimes existing bulkheads or suitable bonded timber reinforcings can be used: if not, it is necessary to fabricate suitable supports. I think a main reason why the heater was installed in the cockpit sole was that there was an existing framework in there to which it could be attached, making the job easier but prone to future problems.
However, there was an area in the aft battery locker which would provide the more suitable space required. Here it would be both reasonably accessible and, more importantly, not as subject to condensation from being in a bilge locker. The problem with this position was that the transom skin laminate would not be thick enough for the fixings required to mount the heater and electronic control unit. The solution was to make up mounting pads, and the method shown here can be adapted for a variety of installations.
The transom has a slight reverse counter, so the first job was to establish the angle required to shape a pad so it would fit properly. This was done with a sliding bevel and a protractor. If not available, on a calm day a short plum bob can also be used.
The pad was made out of a single softwood pad, 6in wide and 5½in high. It was 1½in thick at the base and 1in thick at the top, cut at angle of roughly 85°. It would be bonded with a thickened mix of epoxy and the pad ‘tacked’ in place with fast-setting epoxy.
The area where the pad was to be fitted was washed, left to dry and masked off to the dimensions needed. It was abraded with 60-grit paper and cleaned with Sika Cleaner. The second layer of masking tape at the top was put on: the strip where the fast-acting epoxy would be.
Masking tape was then put across the top of the pad to leave a strip for the fast-acting epoxy after the regular thickened epoxy mix had been applied. It was not possible to use hard fixings on the pad, so Five-Minute Adhesive was used to hold it in place while the regular epoxy cured.
To ensure a good bond, the thickened epoxy mix should make contact with the whole surface; and any excess squeezed out can be cleaned away afterwards.
Remove the tape while the mix is still wet. The pad was left for 24 hours to let the adhesive cure. To protect the pad, it was coated with a straight resin/hardener epoxy mix. Once the epoxy had cured, the mounting bracket was screwed into the pad with 4 12-gauge 25mm s/s pan-head screws.
An area was prepared in a similar way to mount a wooden pad for fitting the electronic control box.
From the way the pad sat I could see that parts of the laminate were slightly irregular. This isn’t a problem with thickened epoxy designed to fill surface irregularities, but a good flush bond for the fast-acting epoxy would be needed, and one end was better than the other for this so I used a double band of tape. The thickened epoxy was applied first, and the clear space at the end could then be used for fast-acting adhesive to tack the pad in place while the rest cured.
The pad for the control box is bonded in place on the laminate and, once again, the epoxy is left to fully cure.