Plumbing, Bilge, Part 3: New Through-Hulls, Installation

The new stainless steel through-hulls for the bilge pump hoses
Having determined exactly where I wanted to route the three new bilge hoses for the three bilge pumps, I could install the three new through-hulls in the transom. The steps I took to accomplish this installation on Oystercatcher, my Ericson 25, are the subject of this posting.
The plastic through-hulls that came with the boat when I purchased her in October 2009 were in pitiful condition. I can only guess that they were original to this 1975 vessel. When I attempted to remove them from the transom, they crumbled. That's how brittle they were from years of exposure to the elements.
For this reason, and for aesthetic reasons, I did not want to replace them with new plastic ones. Therefore, I went with stainless steel - much more classy and a material that would stand up to almost anything. These were Groco brand through-hulls, and they were designed for the 1-1/2 inch, 1-1/8 inch, and 3/4 inch hoses that I would be installing for the pumps.
The location of the two existing holes in the port side of the transom worked well with my plans to install a swim ladder on this side. If you look closely in the picture below (click to enlarge), you can see that I've drawn a line to indicate where the bottom of the platform for the swim ladder would be located.
The existing hole for the manual bilge pump through-hull was just the right size for the new through-hull. The existing hole for the old electric pump through-hull, however was a bit too small.
To remedy this problem. I broke out my Dremel and sanded the perimeter of the hole with a 50 grit sanding drum.
This was all it needed.
Now I needed to figure out where to make the new hole for the emergency electric pump that I would be adding to the boat. I needed to make it somewhere near the existing holes, so that it would not encroach on the swim ladder.
I decided that the most aesthetically pleasing location would be directly above the small through-hull.
After I marked the spot, I used a plumb line to check my work. As you can see in the picture below, I was slightly off.
Therefore, I drilled the pilot hole slightly to the right of my circular marks.
Then I installed a hole-saw attachment on my drill and began to make the cut. I started with the drill set to Reverse. This ensured that the damage to the gelcoat would be minimal.
I normally don't use the detachable handle on this drill, but I used it for this cut to help me make the hole as perpendicular to the transom as possible. A friend stood by and checked my alignment on the perpendicular axis.
After I finished the cut, I cleaned up the rough edges with the Dremel.
The hole was in just the right place relative to the vertical reference line I had drawn with regard to the plumb line.
If I had had a blank transom and the opportunity to position these through-hulls in any arrangement of my choice, I would have positioned all three of them side-by-side centered on a horizontal reference line. This was the best I could do with what was available to me.
From afar, these three new though-hulls didn't look too bad. Never mind the rectangle on the transom. That's something I added to the picture to cover the hull ID number.
I was pleased to see that the swim ladder fit well in the space above the through-hulls and that the through-hulls did not encroach on this space.
Now it was time to install the through-hulls. First, though, I needed to remove the remnants of the old sealant. The large hole looked like it had received Dolphinite, or something like that, during the installation of the large through-hull. I know the original shop manual for this boat often spoke of Dolphinite.
The small hole had silicone around it. This made me think that the previous owner had rebedded the plastic through-hull at some point in the past. He was very fond of silicone sealant - you know, the stuff that some people use for sealing things in household bathrooms. I can't stand the stuff anywhere, on land or sea. It does a lousy job a sealing things, and it's difficult to remove from any surface, especially gelcoat.
Here's how the holes looked from the inside of the cockpit locker. My plan was to put anti-siphon loops in the hoses prior to joining them to the through-hulls.
There were remnants of sealant on the backside of the large hole. It was a royal pain to try to clean up this area inside the cockpit locker. I bridged the space between the two cockpit lockers with the lid from the large locker in the V-berth. Then I lay down on the board in the prone position and reached my arm back toward the transom.
After I had removed as much of the old sealant as possible, I cleaned up the area with xylene - the solvent best suited for the removal of old wax and adhesives.
I then used the xylene on the exterior side of the holes.
This worked well, but I really thought that it would be smart to lightly sand the gelcoat around the holes with some 220 grit paper. This would ensure that any remaining impurities would be removed.

This light sanding around the small hole was especially needed. A thin film of silicone will remain even after you've removed what appears to be all of the silicone. I would later deal with the silicone contamination issue over and over in my reinstallation of the deck hardware that I had removed.
After I had finished the sanding, I hit the holes again with xylene.
Then I cleaned up the through-hulls with acetone. This would remove impurities from the machining of these pieces of steel.
I did not neglect to clean the nuts for these through-hulls. If you look closely, you can see the grime on the white rag. Yes, this cleaning process is a necessary step.
I used Sikaflex 291 LOT for this installation. The LOT designation stands for Long Open Time. This means that you have a little more time to get your work done before this stuff starts to set. I used this Sikaflex 291 LOT for the installation of quite a few items on this boat in my lengthy refitting of her. The bronze through-hulls for the head and for the galley sink come immediately to mind. The benefit of this polyurethane, as opposed to the 3M brand polyurethanes, 4200 and 5200, is that it clings less tenaciously to joined surfaces. It's tensile strength is 200 psi (pounds per square inch), whereas 4200's and 5200's tensile strengths are 300 and 700 psi respectively.
The installation of these through-hulls was definitely a two-person job. While a friend held the through-hull, I applied the Sikaflex.

He then held each through-hull in place while I tightened down each nut on the other side of the transom.
We cleaned up the exterior of the transom with paint thinner immediately afterward. Yes, Sikaflex 291 LOT does allow you some time to adjust the hardware that you are installing, but it doesn't allow you much time for clean-up. It quickly begins to skim over. Removing the film quickly from the surface of the gelcoat is important.
This Sikaflex quickly becomes sticky and tends to smear as you work to clean it up. If you're not careful, you'll get it all over your gloved hands and everything else that you touch.
We didn't attempt to clean up the other side of the transom. I probably would have cleaned it up, if it had been more accessible. I couldn't even get my hand back all the way back into this space.
I was only able to install these nuts because I could hold them in place with the channel lock pliers while my friend turned the through-hulls with a tool on the exterior of the boat. It was his opinion that I would never be able to install the hoses on these through-hulls, if I did not install some sort of access hatch on the side of the cockpit locker. I definitely saw the logic in his argument, and I eventually did install a small circular hatch. That is the subject of another posting in this series.
I my next posting, I address my work on the original, bronze strum box for the manual bilge pump.
This ends this posting on the steps I took for the installation of the new stainless steel through-hulls for the new bilge hoses on Oystercatcher, my Ericson 25.

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