Replaced Thru-Hulls and Seacocks-Down the rabbit hole

I hauled Aeolus out last week to do bottom paint and replace all my below the waterline thru-hulls as well as install proper seacocks and backing blocks. My bottom paint lasted two seasons and was finally tired. I recoated with West Marine PCA Gold and expect another couple years. Slime appears on it over time, but it has appeared on every paint I have ever used here in the NW, including Trinidad SR. Anyway, bottom paint is straightforward and not the topic of this post.

No, the topic here is the big kahuna of cutting big holes in the boat and filling them in. I'll try to put some order to this process as it was pretty epic.

Gulf 32 Thru-Hulls and original equipment
When we bought Aeolus she still had plastic gate valves screwed directly onto the thru-hulls with only a 2"X2" and 1/4" backing square and the nut that comes with the thru-hull. Dreadful. I replaced the plastic gate valves with Marelon ball valves back in 2007 even though I knew the mating of bronze and Marelon was less than ideal, because it beat the hell out of what had been. Although none of them leaked, I had reason to doubt the condition of the meager backing blocks and the status of the bronze itself, and I was of course anxious to get proper flanges installed and redo the whole works. I put this project off from my last haul out because I had a lot going on and I think I was a bit intimidated by the scope of what would be involved. My concerns about the thru-hulls, and project, turned out to be justified. The photo below shows the sink drain thru hull before being worked on.

Turns out that all thru-hulls on a Gulf 32, and I presume on all Capital Yachts boats like Newports, are glassed in flush head fittings. That's right, glassed in, flush head. I'm sure these were used on Gulf's simply because they were used on the faster Newport boats and they had them laying around the shop. However, this installation method is unusual, and means that they are impossible to replace without major surgery on the boat. Most every other boat in the boat yard, especially cruising boats, will have mushroom head thru hulls. If that had been the case on Aeolus, I would have been able to do the whole job in two easy days, no problem. Instead, I had to tackle a major deconstruction and reconstruction project for four full days of 12 or more hours each.


Removing the old thru hulls

To remove the old thru hulls I used a trick from Don Casey that worked really well. But first, you must remove the valve and nut that backed down onto the meager backing block. I started with my engine water intake as it was the most accessible. As I put my wrench on the nut and began to turn, after having let the nut sit in some PB Blaster for a few minutes, I was stunned to find the entire top of the thru hull laying in my hand as it had snapped off just as easy as you please. A textbook example of nightmare scenario. In this photo you can see the entire unit removed from the boat and with the backing block removed. You can just make out in this photo the green color of corrosion at the breaking point and the metal looked soft and spongy. And this was my raw water intake. The one you exercise most often. This whole thing was just days away from from snapping off altogether and though easy to plug, it would prevent easy use of the motor without some creative work arounds. After seeing this, I knew I could not trust any of them no matter how they looked. These are 23 years old as she is a 1988.

You can see on the head of the thru-hull that it has had one edge cut straight. This was so that when they glassed it into the hull it would not turn on them when they tightened the ball valve on the inside.

Before being able to pull the thru-hull out, the fiberglass surrounding the head of the thru-hull must be removed. This is the serious part. No boat owner likes to take a hammer and chisel to the hull of their boat to make a large hole, but that is exactly what had to be done. I used a chisel to cut a hole around the head of the thru-hull and then my dremel tool (more on that later) to excavate the proper circumference of the shape. It was such a dramatic and irrevocable act. 

This photo shows the Don Casey apparatus to remove the thru-hull once the area around the head has been excavated. On the inside of the boat the long bolt has a nut and large washers to prevent it from pulling through. Then you simply tighten the nut on the outside and it pulls the thru-hull right out. There is a lot of force involved, and when these popped it was clear they were being held in very firmly.

Once they were removed it was possible to see how they had been installed. Apparently the hull had been laid up completely, and probably solidly, and then the holes were then cut for the opening of the thru-hull. On the inside, making this whole thing stranger, they had then had to glass over the inside of the thru-hull to provide some strength, which they did with a fairly light treatment of glass and lots of polyester. The result of this was a raised, pimple like protrusion on the inside of the hull that the meager block perched upon. This had to all be sanded smooth in order to accept the larger backing blocks.

Prep for new thru-hulls

This photo shows the engine intake thru-hull hole after I had done a serious amount of sanding to get it flat. 60 grit paper on my good disc sander did the trick. The single most important piece of equipment on this whole project was my Dremel. I want to write an Ode to Dremel here soon to express my appreciation to this great little instrument. Having a Dremel with the little cutting heads let me do the rather artistic work of shaping the area for epoxy work and then sculpting the epoxy for final prep.

Once the hole was flush and cleaned on the inside, I then had to take the Dremel and prep the outside area of the hole for the new head and the epoxy I would need to use to make it solid. This involved grinding away any loose material, and getting good edges and angles.

After all this grinding and sanding and prep work, I cleaned the whole area repeatedly with acetone to remove all dust and oils and such. Lots of white rags turned brown.

Then I mixed up some West System epoxy with fast cure and painted the outside area with the unthickened epoxy in order to fill in any micro gaps and provide a good foundation for the thickened epoxy coming next. I let this dry for a few hours, or until it was still soft but tacky. I then came back with colloidal silica thickened to the point of peanut butter and filled in the edges of the hole in preparation for using the thru-hull as a mold. This was necessary because the new thru-hulls were not the same size as the old ones, wouldn't you know it.

The photo here shows my approach. I took the thru-hull and wrapped the threads and the head with duct tape. I then coated the whole thing with Vaseline as a mold release. I then pushed the thru-hull into the thick epoxy like this and seated the head from the outside nice and flush. I used duct tape on the outside to hold the head in place until the epoxy set up. Before the epoxy had fully cured but after it was quite firm, about 6 hours or so, I carefully removed the thru-hull. This worked well, and the epoxy did not stick at all to the vaseline. In retrospect I might not have needed the duct tape in addition to the vaseline but I hadn't wanted to take any chances of epoxy bonding to the bronze.

I then had to take my dremel tool again and finely shape the epoxy and remove any burrs or bumps left over from the ridges in the tape. I then wiped the whole thing with acetone again to remove any debris or dust and the vaseline and it was then ready for installation of the new system.

New backing blocks

Back at home I had fabricated some new substantial backing blocks from 3/4 inch exterior plywood. A friend of mine let me use his band saw which made this quite easy. I then used a hole saw matched to the size of each thru-hull to make those holes and then coated the whole thing with unthickened epoxy. I set them aside to dry on the first day.

I should say a few words about the choice of plywood over fiberglass backing blocks. First, there is no question that fiberglass or epoxy glass backing blocks would be more permanent. You can make them yourself, or buy stock from McMaster Carr. I chose to use plywood for a few reasons. One is that it was sufficient to the task of being rigid and bonding well. This is the primary purpose of backing blocks: to provide rigidity and stability to the area of the thru-hull to avoid any flexing. Second, I chose plywood because it was cheap and easy to work with. I knew I wouldn't be through bolting the block (no need for extra holes in the boat to prevent the block from turning) and I don't have a drill press for perfectly vertical bolt holes that unforgiving fiberglass requires if you seat the bolt heads underneath the glass block but on top of the hull. Finally, since I fully coated these in epoxy and expect they will remain solid for many years, they more than meet my expectation for the life of the system. I will be pleased to get 10-20 years from this set up, and expect to replace the thru-hulls again at that time. All these locations are easy to inspect since I will be exercising the ball valves regularly, and can check for any signs of corrosion or softening of the plywood.  It will be a small matter to replace these backing blocks at the same time as the new thru-hulls then. All this to say, fiberglass is a gold standard for backing blocks, but not the only or best choice for my particular situation. 

When it came time to use them I first took some rough sandpaper to the surfaces to prep them for better adhesion. My adhesive of choice for this project was 3M 4200 Fast Cure. I needed fast cure because I only had about 24 hours between my last installation and being put back in the water. 4200 is also less permanent than 5200 but much stronger than even Sikaflex 291, which gets good reviews. I wanted the extra strength, and needed it because I did not through bolt these backing blocks into the hull.

What you see in the picture is a whole lot of 4200 gooped onto the backing block as it is prepared for placing over the hole. When I pushed these down on the hole, the 4200 oozed out around all edges. I would then go outside and insert the thru-hull and tape it in place to hold the backing blocks at the proper position. This took a few hours to set up firmly enough that they would not move when the thru-hull was removed.

Installation of new harware

For this project I decided to go with the Groco system using their IBVF flanges. I was convinced by the good arguments about the advantages of this system, including the ability to change ball valves without removal of the entire works, as well as the thread compatibility of the whole thing.

When the backing blocks had firmly dried I then threaded the thru-hull into the Groco flange to make sure everything lined up properly, and to determine if I needed to cut any extra threads off the heads of the thru-hull. Turns out I did have to do the latter on three of the five. I then predrilled the pilot holes for my bronze lag screws. I decided to use lag screws to prevent the flange from turning as I believe they will be more than sufficient for the job and much easier than through bolting. I then took it all apart, and coated the inside of the flange with 4200 and secured it in place with the lag screws.

The photo here shows how much I had to cut off the thru-hulls to ensure they fit well with the flange. The flange only accepts a finite number of threads, and so the extra must be removed in order to have them tighten down onto the backing block together.

From the outside, I cleaned off any 4200 that was in the way of the thru-hull and then coated the thru-hull flange with 4200. I put a thin bead of vaseline around the top 4-5 threads so that they would not bond too tenaciously to any 4200 that was that high up the shaft. There would be plenty of 4200 on the bottom to prevent any movement and provide sealing. Using my step wrench, I then tightened the thru-hull into the flange good and tight. Lots of 4200 oozed out and cleaned this up and smoothed the exterior nicely. It is worth noting that where the previous thru-hulls had been glassed under, these are mounted on the surface. It will allow for removal 20 years from now without doing major glass work again. 


Ball valves and final installation

I used Groco ball valves on the flanges and hope for many years of good service.

Altogether this project involved replacing:

• Engine intake thru-hull

• Sink drain thru-hull

• Sewage pump out thru-hull

• Sewage diret overboar thru-hull

• Sewage water intake thru-hull

This was all painted over quite nicely before I was put back in the water. I shed a lot of skin, and got a lot of bruises doing this project, but it gives me an incredible piece of mind knowing that these thru-hull systems are now absolutely solid and no longer a concern. I've been on countless boats, new and old, that don't have proper seacock systems and I'm very glad that Aeolus now joins the ranks of those few who have it done right.

*A quick note on bonding. Everyone has an opinion on this, especially around boat yards, but I went with the wisdom of Nigel Calder and my own experience which is to not bond them together. Of the five I removed, only the engine intake had any corrosion. By not bonding them I let them each stand alone and not suffer corrosion shared among them all. All the hoses are rubber insulated and so there is no electrolysis between them and the engine. I expect to get another 20 years from the thru-hulls and to replace the ball valves more often.