Through Hull Replacement, Part 10: Flange and Through-Hull Installation

Installing the new bronze through-hull
Of all the steps associated with the replacement of old bronze through-hulls, the final steps, which involve the installation of the new through-hulls, are perhaps the easiest. As anyone, who has properly painted anything, knows, it's all about the prep work. The same, I believe, can be said for the replacement of through-hulls on a boat. The prep work is about 90% of the job. Once that is complete, the rest of the job is not that difficult. With a little patience and attention to detail you can bring this project to completion. In this, the final part of my ten-part article, I describe the quick and easy steps I took to install both the flanges and the new bronze through-hulls in Oystercatcher, my Ericson 25.

I began with the most accessible of the three holes - the one devoted to the intake of raw water for the marine head. A quick wipe of the backing plate and the bronze flange with acetone, and these parts were clean and thus ready for the application of adhesive/sealant.
Outside, my buddy cleaned each of the bronze bolts with a brass brush to remove any dirt or residue from the threads.
Afterwards, we wiped all of the hardware with acetone.
Then I grabbed a tube of Sikaflex brand polyurethane adhesive/sealant. Sikaflex makes a variety of polyurethanes. This one was Sikaflex 291 LOT (Long Open Time). As I have said in numerous places in this ten-part article, I often followed the suggestions of Maine Sail, whose article on his Compass Marine website, I found to be quite helpful. Maine Sail used Sikaflex 291 LOT, so I thought it wouldn't be a bad idea to do the same. Here's a suggestion of my own that I can add: be mindful of the fact that this product is stamped with an expiration date. If you grab the first tube off the shelf, or if you buy a tube from a bargain basement online store, you might find that you've purchased an old one. About half the tubes at the local West Marine were expired. Some of these they had marked down. Others they had not. The one pictured below I ordered from Defender, the big online retailer based in Connecticut. It was a good one, the expiration date of which was well removed from the date of purchase.
We began by applying the Sikaflex to each bolt.
The amount that we applied to the first bolt seemed like overkill, until, that is, we pushed it into place.
As you can see in the picture below, there was not a lot of excess.
On the subject of hardware, before going any further, I should mention where I obtained the bronze nuts, washers, and bolts. In several parts of this ten-part article I have consistently referred to the bronze machine screws as "bolts." I have done this simply because the word "screw," tends to make most people think of pointed wood screws, whereas the word "bolt," tends to make most people think of flat-ended pieces of hardware onto which they can screw a nut. To get technical, I'll tell you that I used 5/16 inch x 2-1/2 inch silicon bronze, flat-slotted, machine-screws. These I ordered from Jamestown Distributors in Bristol, Rhode Island. I opted for Jamestown, because they sold these screws individually (instead of in boxes with quantities far greater than what I needed). I ordered 10, even though I needed only 9. I learned long ago that it's always smart to have an extra piece of hardware on hand. As far as the nuts and washers (flat washers and lock washers) were concerned, I opted for Top Notch Fasteners out of Mankato, Minnesota. For some reason, Jamestown Distributors will sell screws individually, but will not sell nuts and washers in this fashion. Top Notch Fasteners, on the other hand, will not sell 5/16 inch screws individually, but they will sell nuts and washers in this fashion. Make sense? I didn't think so. The take away from this is that if you're planning on doing this project yourself, you might have to forget about one-stop shopping.
As far as the application of the Sikaflex to the flange was concerned, I again followed the suggestion of Maine Sail. I laid down a large bead around the threaded hole and then around each of the bolt holes. I would only stress that you should not hold back on the Sikaflex. Even though this might look like overkill, it was not. I almost didn't get a full and consistent squeeze after I bolted the flange into place.
My buddy and I worked in tandem on the flange. He stood outside with a large slotted screwdriver. I knelt inside the head and tightened down the nuts as much as possible . . . with my fingers.
Leaving the nuts in this finger-tightened state, I went outside the boat and applied copious amounts of Sikaflex to the through-hull itself while my buddy slowly rotated it around his finger.
He then slid it into place and began to screw it into the flange.
He screwed it as far as he could by hand.
Then, he grabbed the large screwdriver, and I grabbed the wrench, and together we worked to fully tighten the nuts on the flange. We used the same technique that people commonly use when tightening the lug nuts on a car tire. We tightened one a little bit, then another a little bit, and then another. Eventually, the flange was fully snugged-up to the backing plate and the nuts were firmly in position. I took care not to force the nuts once they felt nice and firm. This was a point that Maine Sail made. I suppose it's not hard to strip the threads on bronze. That would be one excellent reason to have an extra bronze bolt on hand, wouldn't it?
Outside the boat, my buddy began to screw the through-hull firmly into place. Instead of using a step wrench he used the head of a closed-end wrench and a pair of vice-grips. This was something that he had come up with earlier during our dry-fitting of the parts. This make-shift step wrench worked well and saved me a lot of money. The head of the closed-end wrench gripped the nubs on the interior of the through-hull very well. No slippage whatsoever.

After he was finished, I stepped in with a plastic putty knife and began to spread the Sikaflex in a smooth and consistent manner.

I then cleaned up some of the excess Sikaflex with mineral spirits, the solvent recommended by the manufacturer. I took care not to get the mineral spirits too close to the joints. Obviously, I did not want to weaken the sealant in these areas.
Afterwards, we moved on to the through-hull underneath the galley sink. This went quickly.
All that was left was the large, waste-outlet through-hull in the head. This too went quickly.

I would leave these areas undisturbed for a week while the Sikaflex fully cured. Later I would sand and paint these areas as part of the final steps in the post-boatyard bottom-painting process. Note, for instance, that the patches, where the jackstands had stood, were still in need of paint.
The replacement of the old, bronze through-hulls with these new ones, was a relatively easy task, once the more difficult preparatory work was complete. Was it worth it, you might ask, given the difficulty of that prep work? Peace of mind is, to me, almost always worth the toil, whatever the project might be.

This ends this ten-part article on how I replaced the through-hulls on Oystercatcher, my Ericson 25.

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