100R

thruhulls

21.05.14
North Saanich BC, Canada

We closed 5 thru-hulls: the galley raw water sink intake, head intake, head outtake, sink drain and macerator.

We kept most of the thru-hulls in the galley (sink, fore/aft cockpit drains and engine intake) but replaced all fittings.

Removing the thru-hulls

Three of the thru-hulls and piping in the head were seized, we had to use a grinder to cut them out. Both the macerator and galley sink fittings came out readily. We used a large pipe wrench to twist the fittings off from inside the boat.

It is easier to twist the thru-hulls out by first applying some heat (heat gun) to soften the sealant around it. In a thru-hull there are slots for a step wrench, a useful tool to keep them from spinning when trying to undo or screw in fittings from inside. We do not own this tool, but the chandlery at the Westport Boatyard lends them out.

Thru-hull replacement fittings

Having never replaced fittings before, we weren't sure how to size them. While unscrewing the ball valves, we found the number written on the side:

The numbers were still clearly visible, even if the metal was old and worn. Most marine gear measurements in Canada are imperial, because of our proximity to the United States.

We bought bronze replacements that are rated for marine use. It is tempting to buy cheaper fittings at a regular hardware store, but they stock yellow brass and won't last. Yellow brass and marine bronze are not galvanically compatible. Brass fittings appear more yellow in color and have a smooth machined finish rather than a rough one (due to sand casting). We had difficulty finding bronze hose barbs (hose adapters). The local chandlery did not stock them, we had to order them out.

We bought Groco flush-type thru-hull fittings (it's what the boat came with), although it was difficult to find. The chandlery had one 1 1/4 bronze thru-hull in stock, but we needed a second. They called other stores in the area and could find none. The chandlery had thru-hull intakes with a screen, so we bought that instead and cut the screen out (it worked out quite well). We drilled a hole into the screen, and pried it off with pliers.

We agonized over the mismatching of threads when planning our new plumbing. We'd read it wasn't smart to combine NPS threads with NPT because they don't match as well (less contact area). To fix this common issue, Groco sells thru-hulls with a NPS / NPT combination thread. The peaks of the threads are machined off so that it is easier to match with a fitting with an NPS thread (common with ball valves, street elbows). Of course, this only works if you don't cut down the thru-hulls. We did not have to cut down ours in the end, we dry-fitted each part and found that they all fit under the floorboards. Our final setup was as follows: a Groco thru-hull fitting, a lock nut, a street elbow (to reduce vertical clearance), a ball valve, hose barb and a hose.

For a while, we considered getting the type of fitting with a base supported with screws, but had to abandon that idea because of our lack of vertical clearance.

We dry-fitted all of the parts to make sure that they fit well. Then, we took them apart again and squirted the outside of the hole with some Sikaflex 291 marine sealant, popped in the thru-hull fitting, added sealant from inside, inserted a step wrench into the slots below to keep the thru-hull from spinning while someone was inside threading the lock nut in, screwing it on tight. Even if our threads matched up, we added teflon tape on all threaded connections.

Closing thru-hulls

Pino's hull is thick fibreglass, thicker on the floor behind the keel (where the galley thru-hulls are located). We closed the macerator hole first as practice, then we moved on to close the other 3 in the head in one go.

To make a good patch, it's necessary to sand the fibreglass around the hole down into a bevel. A good bevel will provide strength. The size of the bevel depends on the thickness of the hull (measure the thickness with a caliper). The rule is to multiply the thickness of the laminate by 12. Say your hull is 12.7 mm, multiplied by 12 is 152.4 mm, which is the diameter of the bevel. We marked out the diameter on the hull, taped some wax paper on the inside of the boat with a weight overtop, and used a sander with 60 grit sandpaper to fair out the hull.

To sand, we wore protective gear:

We also covered the boat with plastic sheeting from the waterline down to keep fibreglass dust from blowing around the boatyard. The boatyard is right near a bird sanctuary (poor choice of location), the last thing we want is to blow dust around where they eat.

We prepared our sheets of cut fibreglass beforehand. On a piece of wax paper we drew the outermost circle (of the diameter we measured earlier), and then drew circles of decreasing size within that one until we matched the size of the hole in the hull. It is better to cut the circles beforehand, because when you start applying epoxy it gets messy, and you don't want to waste time cutting more sheets. Using the pattern drawn on the wax paper, we cut out each circle (cutting into the pattern until we were down to the last, smallest circle). We cut circles of both biaxial and woven fibreglass fabric. Biaxial helps to add thickness quicker than if we were using just woven matting.

This is what we used to apply the sheets:

We cleaned the dust off the area with acetone, and mixed some epoxy thickened with the 406 colloidal silica (to a peanut butter-like consistency). We applied thickened epoxy into the hole, and layered on sheets of fibreglass fabric from the smallest circle to the largest (alternating between biaxial and woven), careful to line up fibres when layering woven matting. We used a glue brush to apply the epoxy onto the sheets, applying one sheet on the hole at a time. We also had a fibreglass roller, a useful tool to spread the epoxy around evenly and to pop air bubbles. Others (like our good mentor Gerry) like to prepare mat 'sandwiches', which involves laying a few layers on a piece of cardboard, and adding epoxy to wet them thoroughly before applying them on the hull. Applying dry sheets on the hull directly just means that you have to add more epoxy so that the sheet layered over top will stick to it, this is what we did and it worked out fine. It is better to pre-soak biaxial with epoxy though, since they require more epoxy than woven fibreglass.

We let the patch dry. When dry the patch will develop a waxy whitish haze known as amine blush. It is a chemical reaction that occurs between water, carbon dioxide, and the amine component of epoxy coatings. Nothing will stick well to amine blush. We scrubbed off the surface with a scotch pad, water and a bit of dish soap to remove the blush. We let it dry, and sanded the area lightly, again, cleaning the dust off with some acetone. Then, we mixed up more thickened epoxy to fill out the rest of the holes. We used plastic scrapers to apply it, brushing off the excess with one scraper, scooping it up with the other and applying it back. Having a wide scraper is necessary for this job, so that we could use it to match the bevel of Pino's hull.

We also added thickened epoxy to the inside of the hole. It would have been better to add fibreglass sheeting to the inside too, we did it for the macerator hole, but we did not think it was necessary for the rest.

The holes are barely discernible with bottom paint! We're glad we took the time to do this job, it was a good learning experience. We had good mentors helping us along the way (thank you Gerry and Rick), but we also referenced a lot of the West Systems videos on fibreglass repair on YouTube. Their videos are very thorough and helpful.

We also enjoyed the posts on Marine How-To. Their posts on how to replace thru-hulls proved essential, and we used some of their wording throughout this text (especially about yellow brass).

We removed all the thru-hulls in the head so we could switch to a dry toilet.