Electronics, GPS and VHF, Part 4: Installation of Mahogany Panels

The Garmin GPSmap 541s dry-fitted into place
When you construct panels for the flush-mounting of a GPS on the cabin trunk of your boat, you can't fully install them until you've cut the hole into which the GPS will be mounted. This cutting of the hole is a relatively simple task, yet one that must be approached with patience and attention-to-detail. It is not difficult at all to create an ugly cut-line with chipped gelcoat all along its edges, if you approach this job hastily or with the wrong type of saw or saw blade. In this brief posting I describe how I made the cut, and how I dry-fitted the mahogany panels and the GPS on Oystercatcher, my Ericson 25.
I mentioned in the previous posting that I had to purchase the Garmin flush-mount kit separately from the GPS itself. This kit cost me about $24 online.
The mahogany that I used to construct the panels was between 3/8 and 1/2 inch in thickness. What you see below are the backs of the two panels. Notice how there are cut marks here and there at various angles? These were scrap pieces of mahogany from an earlier project. With help from of a friend, who specializes in traditional woodworking, I had split a 5/4 board, i.e., a 1.25 inch thick board, into two halves that were around 1/2 inch thick. I did this to save some money. I needed two boards that were 1/2 inch. Southern Lumber in Charleston, South Carolina, where I live, does not sell rough-sawn lumber in thicknesses less than 4/4. Therefore, if I had not split this single 5/4 board into two halves, then I would have had to buy two different boards and plane them down to the thickness that I desired. For more on how I split (or I should say my friend split) this piece of mahogany, see my article, "V Berth, Alcove Box, Mahogany Trim."
The cabin trunk, marked and ready for the cut.
The flush-mount housing for the GPS.
The back of the housing with the GPS dry-fitted within it.
For making the cut, I used my Makita brand jig saw. I love this saw, and I have used it on many projects in the refitting of this boat. Not only can you control the speed of the blade, but also you can control the amount that it oscillates, if any, while making the cut. For cutting fiberglass, I always set the speed low, and I always turn off the oscillating switch, so that the blade moves perpendicularly to the surface. Likewise, I always use Bosch brand reverse cut blades with 10 TPI (teeth per inch). The stock number on these blades is as follows: T101BR. These blades help reduce your chances of chipping the gelcoat.
With the saw set as I describe it above, it takes a good bit of time to make the cut. The results, however, are worth it - nice and clean.
In making this particular cut, I had to cut through the two layers of glass at the same time. The outer layer, of course, was the cabin trunk itself. The inner layer was the hull liner.

The flush-mount housing fit well within the new hole.
Likewise, the GPS.
The interior panel wasn't really necessary from a practical standpoint. From an aesthetic standpoint, however, it was. Could anyone really be proud of this work?
Much better.
All in all, this project was progressing well, but there was still a good bit of work that remained. For one thing, I needed to figure out where I would install the VHF, and I needed to figure out the infrastructure for the DSC (Digital Selective Calling) that would join the VHF and the GPS. Likewise, I needed to figure out how to install the through-hull transducer that would be joined to the GPS. These sub-projects are the subject of my next two postings in this seven-part series.
This ends this posting on how I cut the hole and installed the panels for the GPS on Oystercatcher, my Ericson 25.

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