Through Hull Replacement, Part 3: Prepping the Holes

The plastic liner within the original chamfered hole
The original chamfered holes in the hulls of some old sailboats contain a plastic liner. This liner, I suppose, was intended to protect the hull from blistering, in the event that water ever seeped into the gap between the head of the flush-mounted through-hull and the hull itself. Such a leak would only occur, of course, if the sealant for the through-hull happened to fail. When I removed the original through-hulls from Oystercatcher, my Ericson 25, I discovered that the chamfered holes that housed these original through-hulls contained these plastic liners. I also discovered that in the almost forty years that this boat had been in existence it was these original plastic liners themselves (and not so much the sealant) that had begun to fail. Therefore, before I could replace the original through-hulls with new ones, I first needed to remove the plastic liners that were original to the hull. Although this sounds like it would be a difficult task, it was actually one of easier parts of this multi-part project.
The original bronze through-hulls
The first area on which I concentrated were the two holes that serviced the head, i.e., the toilet.
The waste-outlet hole (to the left in the picture above) was to house the new 1.25 inch Groco brand through-hull (left below). Conversely, the raw-water intake hole was to house the new .75 inch piece of hardware.
The head of the 1.25 inch through-hull was almost a perfect fit for the original chamfered hole. Around the edges of the head of the new through-hull you can see the white plastic liner. This liner had a flange of sorts that extended beyond the chamfered edge of the hole. How far it extended, I do not know. I did not want to remove all of the bottom paint and the epoxy barrier coat to find out.
One thing I needed to do, in addition to removing the plastic liner from the raw-water intake hole, was to enlarge the original .5 inch hole to accommodate the new .75 inch through-hull. You can see in the picture below the original hole compared to the new through-hull.
Here's the new hole after I enlarged it. I used a hole-saw for this job. The plastic is from the backing-plate job I was concurrently preparing to do in the interior of the boat at this time.
Here's the new .75 inch through-hull in the newly-drilled hole. As you can see, the head of the new through-hull is significantly smaller than the chamfered recess.
When the time came for me to extract the plastic liner from the chamfered holes, I discovered that the bunk of the trailer would hinder my work.
I had no choice but to try to move the bunk from its original position. The 3 pound hammer was useful for this, since the bunk board was quite stubborn.
I marked the aluminum casing in pencil for the purpose of remembering how many threads were visible prior to my adjustment of the bunk. It's important not to tighten these bolts too tightly, lest the bolt damage the aluminum bunk stand.
Below we see the three tools that I assembled for the removal of the plastic liners from the chamfered holes: an ice pick (yes, this is a tool, and a very handy one at that); an old dental instrument (purchased at a local hardware store); and, finally, a chisel. The latter would prove to be the most useful.
I started with the raw-water intake hole. All I had to do was poke at it with the chisel. The plastic easily chipped and crumbled.

In case you're wondering, the hull is 1/2 inch thick in this area of the hull. If it weren't this thick, I can't imagine that a flush-mounted through-hull would be a possibility. The only alternative would be a mushroom-head through-hull, whose head would rest on the exterior of the hull.
After I had removed all of the plastic, I sanded the hole in order to clean it up as much as possible.
Then it was time to move to the waste-outlet hole.

Next, I wiped down both holes with toluene to remove any wax or other residue that might remain.

Having finished both of the holes for the head, it was time to move aft to the hole for the galley sink drain.
This hole was not an easy one on which to work, given its proximity to the bunk.
The plastic in this hole was also more stubborn than the plastic in the other two holes.
It required lots of little pokes and proddings with the chisel.

As with the first two holes, this one also received a good sanding once the plastic was gone.
Toluene again served to clean up the chamfered hole.
A quick wipe or two and this hole was finished.
This ends this brief posting on how I prepped the holes on Oystercatcher, my Ericson 25, prior to resizing them with thickened epoxy to accommodate the new Groco brand through-hulls that I had purchased to replace the original ones.

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