My boat isn't much different than most of its vintage. Back in the day it was pretty common to fit gate valves directly to through-hulls. Unfortunately, this practice has not stood the test of time, and for reasons I won't elaborate on here, it's a bad situation. This project was one of the top entries in my safety category.
The first step for me was to inventory my seacocks and hose sizes so I could begin spec'ing out the shopping list and comparing the prices of my options. Here's what I came up with:
- Cockpit Drains (2): 1-1/2"
- Engine raw water intake (1): 1/2"
- Galley Sink Drain (1): 1"
- Head Sink Drain (1): 1"
- Head Toilet Intake (1): 3/4"
- Head discharge (1): 1-1/2"
Selecting a Replacement Product
There are a lot of different choices for proper seacocks on the market. They range from moderately expensive to insanely expensive and everything in between. Of course, since seacocks are a marine product, there is no such thing as inexpensive options.
After reviewing the options I was extremely interested in the Marelon Forespar line. I really like the idea of eliminating corrosion from the list of concerns, and if plastic is strong enough for my hull, it's hard to argue that the through hull and valve need to be stronger. The problem I encountered is that Forespar's Marelon line does not include seacocks in a very wide range of sizes. To use Marelon throughout my boat I would need to either increase or reduce the size of many of my through-hulls, then convert hoses as needed. This was an integration hassle I really didn't think was justified in the end. With that, I abandoned my Marelon dreams and moved on.
As I was researching alternatives, I stumbled on a lot of forum postings about Groco's line of Flange Adapters. The idea with this product is that the valve is a separate unit from the flange, and thus the mechanical part of the through-hull assembly can be changed without having to remove the through-hull itself. This is good considering that the through-hull is typically bedded quite firmly, while the valve is threaded on with pipe dope. After comparing prices, I realized that using flange adapters would be just about the same cost, or less, than using traditional seacocks. The Groco line is very complete with respect to available sizes and fittings, so I decided to go with flange adapters and in-line ball valves.
Reuse or Replace Through-Hulls?
Reusing my existing through-hulls would save me a lot of work. However, I've found that many of the items on this boat were not installed in a manner I'm pleased with. I also noted that some of the through-hulls had gobbed bedding compound left on them, which doesn't sell itself as a professional installation.
The second consideration which pushed me over the edge was concern over metal quality. I just don't know what kind of through-hulls are on the boat now, whether or not they are quality, and whether or not they have been corroding over their 30 years. Reminding myself that I would probably not have to do this job again as long as I own the boat, I decided that the right course of action was to remove the existing through-hulls and replace them. In the end I would have 100% Groco matched products, with known compatible metal types in a known to be good bedding job.
Peace of mind for the cost of around $20 per hole.
Planned Modifications
There are two modifications I wanted to make during this project. Upgrading the engine raw water intake from 1/2" to 3/4", and installing a diverter valve in the head discharge to create a better (less stagnant) path for the black water.
The engine raw water intake, while adequate at 1/2" made it tricky to find seacocks. Not too many are made in such a small size. Moving to 3/4" brings me up to the "standard" small size. The extra capacity will also help to offset any flow which might be impeded when I add a raw water strainer. This is probably irrelevant, but it also can't hurt.
The head discharge plumbing is a bit of a mess. Rather than a diverter, there is a strange mix of gate valves attached to plastic fittings with cracking hose cuffs on poorly sealed thin walled hose. . The routing also leads to a number of positions where black water may not be fully flushed through the system. By adding a diverter valve closer to the toilet I can fix routing issues and simplify the plumbing considerably.
Removing the Original Through Hulls
The plan for removing the original through hulls is to use threaded rod, a big nut, and blocks of 2x4. The strategy comes from a
Don Casey article on replacing seacocks. In place of the threaded rod, I happened to have an automotive spring compressor that would do the job...
In a few cases I really needed the leverage this set up provided, but in others I think I could have pried the fixture out with a toothpick. Yes, I'm really glad I tackled this project because more than half of the through-hulls had nearly failed sealant / adhesive. Yikes! I tightened the clamp down slowly with the intend of letting the adhesive fail by stretching out without cracking the outer layers of fiberglass. In the end, only the engine raw-water intake was damaged. A few passes with the grinder and 2 layers of fiberglass will bring this spot back to new.
The old through-hulls really weren't in bad shape at all. I saw no visible signs of corrosion, cracks, or thread damage. This is no doubt due to this being a fresh-water boat, but I'm pretty confident they would have been fine had I chosen to only renew the sealant. I'm still going to replace them all though.
Making New Backing Plates
The original backing plates throughout the boat were plywood. I don't think the plywood was ever sealed in epoxy as some of it is in rough shape. I decided to go with fiberglass backing blocks. Rather than spend time making laminates, I ordered 2' x 2' x 1/2" thick
sheets of premium Fiberglass Reinforced Plastic (FRP) from
McMaster-Carr. While not cheap, they saved me a lot of time.
After finding two circle-shaped random items in my workshop (one for the smaller through hulls, one for the larger) I made tracings and cut out the plates using a jigsaw and very high quality blade. If you try this with a economy grade blade it will last for about 15-20 seconds. Seriously. I burned though all my blades and had to go buy a nice set of bi-metal carbide tipped DeWalt blades. Major difference - don't try to cheap out when cutting fiberglass.
The most efficient plan would probably have been to use a large hole saw and a 1/2" drill. I didn't have a hole saw that size, nor a drill with that much torque. In the scheme of things, it would have taken no time at all to pick up a sacrificial drill at Harbor Frieght and a decent hole saw at Lowes. It really doesn't matter in a structural sense though. What I did will work just fine, and the small imperfections in my cuts won't ever show. I made a roughly-centered 1/8" guide hole as well. This will help to align the hole saw when I cut out the through-hull opening in the center. That will take place after mounting the plates in the hull.
In each case I made about a 3-pump mixture of West epoxy and thickened it with colloidal silica. I then pressed the plate into place with a hugh nail sticking through the guide hole. I climbed out of the boat, and used that nail to eyeball it into the center of the old through-hull hole. I used my gloved finger tip to make a nice fillet on the outside, then went back in and did the same there.
I'm very, very happy with these things. They look great and are bullet proof.
Installing the new through-hulls
The first step was to re-drill the through-hull hole since each one now had a backing plate blocking it. I picked up some cheap Husky hole saws at Lowes which I really don't like at all. They worked, but they dulled quickly and didn't feel very precise. A cut a few holes with a Milwaukee hole saw that cut like butter and felt better. Not sure how else to describe the difference, but if I were to do it again, I'd only use the Milwaukee saws.
I discovered that no matter how you orient the flange adapter, you can get the in-line ball valve to align as you wish with a pipe wrench. The easiest thing for me turned out to be wrapping the flange adapter with teflon tape, then scissoring two pipe wrenches to cinch it down. This assembly was then put in place and dry fit with the through-hull screwed into it.
In all cases the through hull was too long and needed to be shortened. I used my Dremel tool with a large cut off wheel because it gave me a lot of precision and let me grind off the burrs when I was done. Having tuned the lengths, I threaded them into the flange adapter to test fit everything. You don't want to discover a problem AFTER you put in a bead of 4200, so blow the time and dry fit it first.
While I'm at it, here's another tip: Don't try this without a through hull wrench. Just buy it as it's not worth trying to go without.
Back inside the boat, I fine tuned the flange adapter's orientation and drilled the holes for the bolts. In some cases the space was tight, and I needed to remove the flange adapter (after marking the hole!). I then drilled it out with a Dremel tool and angle adapter. I then enlarged the hole from the outside 1/6" at a time where I could use a full-size drill. A real angle drill would have been preferable since the little Dremel was really straining to make the necessary torque to drill through almost an inch of FRP. With patience, it did the job though.
Outside the boat again, this time with a 5/8" counter sinking bit. This took some fidgeting. You need to bury the bolt deep enough to have a reasonable thickness of fairing compound over it, but not so deep as to compromise the hull integrity. Do a little bit at a time and check it. Creep up on it until the bolt head is about 1/16 below the hull surface. Don't forget to use only bronze bolts. This is no place for stainless steel.
Finally, it's show time. I loaded up the flange adapter with 3m 4200, then did the same on the through-hull. I pushed the bolts through from the inside to keep the flange adapter aligned, and then ran outside the boat to thread in the through hull until it was moderately tight. Then I went back in and pulled out the bolts. Running back down the ladder (this was getting comical!) I pushed the bolts in properly, then ran back inside the boat again to tighten the nuts down. Final step was to give the through hull another crank and clean up the excess 4200.
Whew, done!
New Hoses (Non-Sanitary)
The existing hoses were in pretty sad shape. The sanitary hose was corrugated and cracked bilge hose. Nothing could be worse. The cockpit lines were badly cracked. Both sink drains were not quite cracked, but definitely not good. The only one that was decent was the engine raw water intake. I'll keep it around as a spare.
I wanted to use the same hose throughout the boat as much as possible for consistency. It also stands to reason that all of the through-hulls have the same structural demands placed on them, so what's good for one is good for all. The only exception to this is the sanitary and fuel line plumbing.
For all but the sanitary I chose Shields Flex II Water Exhaust Hose. This stuff is very highly regarded, and it is amazingly flexible compared to the sanitary hose and some of the existing lines. Can't deny that the blue stripe looks good as well. Each hose end will be finished off with dual stainless non-perforated hose clamps. I'm sure some of the existing clamps are still OK, but I have no benchmark so I wanted to start fresh. The non-perforated clamps are much stronger and preferable for below-waterline use.
| Hose Location | Diameter | Length |
| Cockpit Drains (need 2) | 1-1/2" | X |
| Engine Raw Water Intake | 1/2" (upgrade to 3/4") | X |
| Galley Sink Drain | 1" | X |
| Head Sink Drain | 1" | X |
| Toilet Intake | 3/4" | X |
New Sanitary Hoses
I went through many deliberations on what to do with the black water plumbing. Ideally I'd love to have a dual-diverter configuration for complete flexibility. That's not going to happen. My budget and schedule are too tight for non-essential modifications. The other consideration is the hole in my hull. Should I fill it and go with a tank-only configuration? There's a lot to be said for that simplification. But do I have the time and motivation to fill a 1.5" hole in my hull? That's a lot of fiberglass layers, and a lot of grinding mess.
In the end, I ran out of time and got sick of fiberglass work. In installed a through-hull, a threaded coupler, and cap to seal off the through-hull. At some point when I recover financially or psychologically I'll have the yard fill the hole and remove the through-hull. A tank only set up is best for me as it will work for the majority of my sailing and increase the safety and simplicity of my boat.I still need to run hoses from the head to the tank, and the tank to the deck pump-out fitting, and to select a holding tank... ...
Build custom electronics cabinet: I want a sleek built-in look for the primary electronics. There should be plenty of room right next to the wet locker on the port side. it will just shorten the shelf area a bit. No big loss.
Super-insulation of Ice Box
Primary De-watering Pump
