Thru-hull Flange Plate and Marelon Flanged Valve Installation.

I just want to say one word to you.

Just one word.

Are you listening?


Plastics!

A detailed description of how we replaced standard bronze seacocks with their flanged Marelon equivalents.

When we last left our heroes [see our blog post titled Thru-Hull Valve Reduction Project] they had removed several thru-hulls (and their associated valves) and plugged the holes left behind in the hull.   They had also decided, wherever they kept a valve in place, to substitute the bronze seacocks and mushrooms with their Marelon equivalents...

We decided to use Marelon valves instead of bronze for a number of reasons, but I should first point out that this is a very controversial decision, and only time will tell if this was the right decision or not.  Many, many people still use bronze or stainless, some use even use titanium, and I do not wish to suggest that our solution is the "right and true" one, it isn't.  There are clear disadvantages to using a composite material in lieu of metal, and we researched this idea extensively and spoke to as many marine professionals, boat builders, sailors and other trouble makers as we could find before deciding on this solution.

Before jumping on our bandwagon, you should be aware that we don't think Marelon is as strong or reliable as bronze under certain conditions, but that no thru-hull/valve combination, regardless of material, should be used unsupported.  Metals like steel, aluminium, titanium and bronze are ductile and tend to handle shock loading better than plastic (which under the right conditions will shatter) and people often do install valves directly off the thru-hull, but (in our very inexpert opinion) that seems like a recipe for disaster.   Any forces placed on the valve, or the hoses leading from it, can exert a significantly magnified force on the thru-hull, which isn't designed for those kinds of loads.

That is especially true for the Marelon thru-hull mushrooms, and we strongly advise you not to use one without a fully supported valve.  One that will not place shearing, twisting, bending or torquing loads on the mushroom thru-hull.  In other words, don't use a valve unless it is either held in place with some sort of bracket, or is internally flanged and mechanically attached to the hull.

On the other hand, Marelon will not corrode when exposed to galvanic currents, which means that you won't need to worry if the metal in your valves is slowly ebbing away, but our real reason for using a flanged valve and creating a backing plate wasn't our worry about the strength of the valve material itself.  We were concerned about the bending force placed on the thru-hull whenever the valve was operated. We'd seen how easy it was to crack off the old bronze valves once they corroded, and we'd seen first hand how easy it was to snap off a plastic mushroom if the valve itself was torqued.   Because we weren't relying on the compression fitting created between the thru-hull mushroom and valve (which would normally be the case) we believed that we had avoided the problem of placing our faith in one particular piece of plastic (what you might call a single point of failure) from keeping the boat from flooding.

Our thinking is that even if the thru-hull broke off completely from the valve, the valve should retain its watertight seal between the flange and the hull.  Of course, this is all probably just wishful thinking on our part, but we felt better knowing that we'd made every attempt possible to prevent a broken thru-hull from flooding the boat. Our only regret is that we didn't take this approach initially with all of the valves in the boat.

We did use this for the 3/4" salt-water (toilet) intake and the 1.5" holding tank output valves located in the bottom of the maintenance cabinets, but didn't for the engine intake valves (in the engine compartments) and sink drain valves (under the sinks on the outer facing hulls), which were both 1" diameter.  At least we did not take this approach initially, but wish we did.

Our approach was to use a flanged Marelon valve, that we mechanically attached to the hull via a backing plate that we chemically bonded to the hull.   Below is a cross sectional view of the  hull (blue) with the flanged valve (black), backing plate (yellow) with embedded bolts (orange), and thru-hull mushroom (green).

The advantage to this approach was two-fold: it eliminated any metallic plumbing parts being exposed to sea water (which meant that we wouldn't need to worry about electrolysis as much) and (if we used the flange plate style valve) it reduced the likelihood that a broken, cracked or leaking thru-hull could result in a complete failure which might leave a large opening in the boat.

One thru-hull removed, one to go...

In fact, if you somehow managed to completely shear off the thru-hull mushroom cap on the outside of the boat (perhaps by driving over a reef), or cracked the threaded mushroom stem (perhaps through a collision, or boat flexing from significant wave action, or just incorrect installation), the valve itself would still remain in place, directly attached to the hull via the bolts and nuts holding the valve flange to the fiberglass backing plate, and keeping the hull intact and water-tight.

[editor's note: This is all supposedly true, at least in theory.  The problem with theory is that in theory, theory always works, where-as in practice, theory often turns out to be less reliable. ]

The obvious downsides are that it was more expensive than bronze (about twice as much) and a relatively newer technology with less of a track record.  Another downside is that we had to make and install custom flange plates on which to attach the valves, which took time (and money), and was a bit tricky to do. Originally, we wanted to somehow embed nuts into the plates, but it was easier (and we believe a bit stronger & more secure) to have bolts sticking up out of the plates instead. We used two pieces of stock 1/4" thick fiberglass plates just slightly larger than the footprint of the flange, and glassed them together, making a triangular plate slightly thicker than 1/2", with three bolts sticking up out of it, and a large hole in the center.  

The two thru-hull backing plates installed.

To do this, we first drilled matching 5/16" holes in the plates for the three flange bolts and a slightly larger than 1.5" hole in the center for the thru-hull opening. On the bottom piece we extended the holes on each side, creating a slightly larger slotted opening, and then ground stainless steel bolt heads to fit into it (which would mechanically prevent the bolts from spinning in place should they break free from the fiberglass) and then glassed the the two plates together, and glassed the bolts in as well.

[editor's note: this is actually harder than it sounds, because you need to make sure that the three bolts are perfectly aligned and square to the plate.  We recommend making a 1/2" thick template flange (out of some other material that won't stick to fiberglass) that matches the hole pattern of the valve flange.  Using this, instead of the valve, means you'll be able to install the plates without having to readjust the bolts later on.]

This allowed us to have a backing plate with threads sticking up out of it, that would eventually be glassed (chemically bonded) onto the hull itself, making a relatively secure means of keeping the valve in place, even in the event of a catastrophic failure of the mushroom.  In order to get a strong bond between the fiberglass backing plate and the hull, we had to glass the plate to the hull before the valve was installed.

Kelly's ingenious solution of running a pipe clamp
through the opening and clamping the backing plate
to the hull as the fiberglass hardened.  It helps to protect
the bolts with tape (shown above) and to make sure you
get a complete bond between the plates and the hull.

To clamp the plate to the hull Kelly (the fiberglass specialist at Napa Valley Marina) came up with the brilliant idea of using long pipe clamps, with the pipe running through the thru-hole.   That allowed us to put a large amount of clamping pressure onto the backing plate as the epoxy hardened, creating a strong chemical bond between the backing plate and the hull.  Once hardened, we had a means of attaching the flanged valve to the boat.  We used BoatLife caulk to create the seal between both the Marelon mushroom and the hull, as well as between the valve flange and the backing plate.  


[editor's note: One of the best pieces of advice we got from the Kelly was this: if you are going to use any kind of sealing caulk, get the white color instead of black.  The reason being that, despite your best attempts, it will get on everything, and all over you, and the white doesn't show up as bad, especially if you have to go to work the next day.   Sounds silly but that really did turn out to be great advice, because this stuff is horrible to get off your skin, and if it weren't for exfoliation, I'd still be stuck to the hull.]

We could only find Marelon flanged valves in the 3/4" and 1.5" sizes. Rather than enlarge the openings, we decided to instead use their 1" valve for the sink drain and engine intake.  That was, in retrospect, a big mistake for which we paid dearly.   Perhaps it would have gone better if we'd build a support bracket for the valves themselves, but given our experiences (see below) with the Marelon thru-hulls cracking, we don't believe that is the proper solution either.  At least for us, your mileage may vary.

First pass at cutting an opening.  We later
cleaned this up and added a door panel.

But we digress...back to eliminating the holes in our boat.  In attempting all these changes, we realized that the maintenance closet door, which was at least two feet above floor level, meant that any work we needed to do on the thru-hull valves (or bilge pumps) at the hull level meant hanging upside down, arms outstretched, inside a deep hole.  Being that I've already suffered an IRS tax audit, a Barium enema, and have been divorced twice, I figured I'd already had my share of suffering and could skip that step.  And since the forward toilets would no longer be in the way, there was no reason we couldn't just cut the door opening down further, and add a larger door.

But we couldn't find a 1" Marelon thru-hull valve with a flanged base plate.  Which meant that we used the thru-hull "mushroom" screwed on to the standard valve to create the seal (along with caulking) between the hull and the ocean.

Unfortunately, we also used Marelon thru-hull mushrooms, which we realize now, are not strong enough for this application, at least not in our opinion, and apparently some other netizens think so as well.  Unfortunately, the sink drain holes and the engine cooling water intake holes were both 1" diameter, and we ended up using the standard valve & thru-hull mushroom fitting without a flange plate.  Although we made sure we had as good a fit as possible, the mushroom cracked as we were trying to install it.  We weren't comfortable with the possibility that the mushroom could shatter and expose a 1" hole to the sea, but we were assured by the folks at the marine supply store that the Marelon could handle it.   Perhaps this is true for some other installations, but it wasn't the case on our boat, and we should have listened to our gut.


Unless you have an absolutely orthogonal [at perfect right angles] fit between the mushroom head, the outside skin of the hull, the inside skin of the hull, the valve base, and the sides of the hole going through the boat, you will ultimately place slightly more pressure on one side of the mushroom's lip than the other, putting significant bending force on the part and transmitting those stresses into the threaded shaft as well.   Worse still, any bending force introduced at the valve (by operating the valve lever for instance) would be magnified and transmitted into the mushroom, which isn't really designed to withstand those kinds of pressures.

The problem was that all of the holes in our boat are in curved surfaces with uneven side dimensions. For bronze or titanium thru-hulls this probably wouldn't be an issue at all, as the ductile strength is adequate, but for plastic [even Marelon], where the material has a tendency to shatter, this is a horse of a different color.  More to the point, it is entirely possible, just from the operation of the valve handle, to theoretically place enough force on the mushroom to potentially cause it to crack, if not shatter or fail complelety.


[editor's note:  we learned this "the hard way" by trying this very approach.  It ended with us noticing that one side of our boat was a bit lower than the other, mostly due to water continuously leaking in one night while we slept.  Apparently the thru-hull mushroom in the starboard side had cracked, and it slowly but surely flooded the bilge.  We hope you learn from our mistake.]


We're not exactly sure when this happened, but the leak was discovered only a few weeks after installation.  Given that we had not installed any plumbing yet (the far end of the valve was plugged) it could only have been caused by improper installation and/or hull flex.  The crack probably occurred when we installed it, but went unnoticed because the caulk kept enough of the seal intact.  That probably worsened while we were sailing about on the bay, perhaps even on returning back from the yard, but it didn't leak at all for the first few days.  Eventually it did, and at some point it became fast enough to significantly flood the starboard bilge before we noticed the problem.

Worse still, the valve was in a cramped area with little elbow room.  When I tried to fix it (and because the mushroom stem was so badly damaged already) the valve broke off completely from the mushroom, leaving a gapping hole in the boat and a fire-hose of  water streaming in.  This is one of those moments where being your own mechanic leaves you wishing you had someone to fire besides yourself.

We eventually removed this valve and replaced
 it with a flanged version with backing plate.

So, our advice (for whatever it is worth) is that no matter how good a fit you think you can make, we'd recommend NOT using a Marelon (or any non-metal) thru-hull mushroom unless the valve it is attached to has an integrated  flange plate AND you have added a supporting base plate to the hull to which it can be attached, effectively eliminating the structural requirements (and stresses) on the thru-hull mushroom itself.   That may sound like a bit of a religious statement, and to be honest it probably is, but I sleep better at night knowing this is how the boat is configured.

The picture to the right is of our engine compartment's seacock.  Eventually we removed these 1" valves and replaced the engine valves with their 1.5" flanged counterparts, which required enlarging the openings and adding a backing plate.  To see the description of how we sealed the thru-hulls under the sinks, go to the blog entry titled Thru-Hull Valve Reduction Project.  We also removed and sealed up the sink drain thru-hulls completely, eliminating two more holes in the boat.

We did learn a valuable lesson or two.  First, always assume that every thru-hull in your boat is going to break open, and be prepared to have everything you need to stop the leak at hand, preferably lashed right to the valve.  To that end, you should have an appropriately sized wooden plug fastened somewhere close by, several rolls of emergency tape, and a bucket of StayAFloat readily available.  We also think a few Nerf footballs are good to have lying around, as they can be stuffed into just about any oddly shaped hole that you need to plug.

Thru-Hull Reduction Project

Twenty Holes, One Boat

A somewhat detailed description of how we eliminated eight (below the waterline) thru-holes.

We own a 45' Robertson & Caine "Leopard" catamaran. That means we bought a boat with twenty holes below the water line, all of which are potential leaks. "No way, there can't possibly be that many!" you say. Well, it breaks down like this (and because it is a catamaran, there are two hulls, and consequently twice as much of everything) . . .

Triton afloat in Trinidad

2 holes for the 2 rudder shafts.

2 holes for the 2 drive shafts.

2 holes for the 2 engine coolant water intakes.

2 holes for the 4 toilets' salt water intake (I'm surprised there wasn't 4, but the two toilets in each hull share an intake).

2 holes for the 2 holding-tank gravity drain outputs.

4 holes for the 4 toilet outputs.

4 holes for the 4 head sink drains.

2 holes for the instruments, both in the starboard hull (1 for the knotmeter, 1 for the depth sounder).

Too many hoses in this cabinet to make working on it easy!

Plus, there is a rat's nest of plumbing, valves, filters, pumps and hoses all stuffed into the maintenance cabinets behind the forward heads and in the engine compartments. Most of that is hard to get to, and if something started leaking, it would be a nightmare to fix, especially in a heavy sea.

But wait!  There's more!  That is only the stuff below the water line, as if that wasn't enough keep you up at night checking the bilges.  Above sea level there are another 20+ drain holes for various bilge pumps, galley and locker drains, engine exhaust ports, propane vents, diesel vents, holding tank vents and all are great places for water to get in.


Makes you feel warm and dry, doesn't it?   We really were concerned about them, and thought it was high time we did something.  But back to the underwater thru-hulls and valves, of which there were 14 we cared about.

The view from under the bridgedeck.  Lots more holes.

They were all bronze on our boat, and all original equipment as of 2000. The nice thing about bronze is that it is really strong and if handled properly will last years. . . right up until the point that galvanic corrosion or electrolysis eats away at it. Then it turns into a lovely copperish substance with all the holding strength of hard cheese, which you might not notice until it is too late.

What got us started down this road was the somewhat nagging worry that we might now have a problem.  We noticed that a few of our thru-hull valves were starting to show signs of wear, and had significant amounts of bluish green rust growing around them. Many of the values would no longer close completely. The last time we had hauled out was when we bought the boat [in 2006, it was now 2011!] and although they looked great at the time and we'd been regularly having the boat bottom cleaned and the zincs replaced, we'd been in a lot of different ports, marinas and anchorages since then and we're not sure all of these places had proper electrical grounding.  In other words, we were concerned that our valves or thru-hulls might be turning into brie.

Yes, Virginia, there is a Santa Claus on board.
2008 Alameda Lighted Yacht Parade

 So we decided it was time to haul out and have a look for ourselves, and do something about the absurd number of thru-hulls.   And unlike our typical bay sailing excursions, where we often had twenty drunken Santas aboard at a time and glad we had enough heads to accommodate them all, we  felt that the existing plumbing arrangement [designed for the charter trade, with four separate bathrooms all expected to be in constant use by at least eight over-fed customers and an underpaid captain & cook] was hard to justify and didn't represent a realistic view of how we would live on the boat.  We felt that once we were out cruising we'd probably only need two toilets, one in the captain's berth, and one in the aft guest berth.  More than that seemed like overkill, and we didn't expect to have that many guests aboard at the same time.

Typical crew size.  We rarely had more than this aboard.

For what it is worth, we sailed from Tortola in the BVI's, to Trinidad, then along the coast of South America, through Central America, then back to San Francisco, usually with anywhere from four to seven people on board, and found that only two working heads were more than adequate.   Yes, it was great to have more, provided you didn't mind constantly fixing them.  [editor's note: If you feel differently, we welcome your input and, most importantly, your efforts in maintaining our marine toilets.  You are welcome to come fix them, preferably during the hot, humid season.  We will gladly watch and offer comments and criticisms while you hang upside down in the bilge.]

We were already comfortable with the rudder post mechanism because the fiberglass rudder sleeve terminated above the waterline and didn't represent as much of an issue.  We cleaned and rechecked the seals and they looked good.  We'd also tackled the drive shaft seals early on [see Propeller Shaft Mechanical Seal Replacement] and replaced them both with PCI mechanical seals, with which we've been very happy with ever since.  We also knew that the holding tank outlet thru-hull and raw water intake thru-hull would require a new fitting and valve and planned for that.

Now to solve the big problem, eliminating unnecessary thru-hulls.  Our first action was to decide which of those thru-hulls were absolutely mandatory, and which weren't.  Keep in mind that we intend to do a lot of blue water cruising, coastal navigation, and gunk-hole sailing in off-beat places and countries where we wouldn't necessary have easy access to a boat haul-out lift or well-equipped repair facility.   

By removing a head on each side, and eliminating the
direct pump-out, dramatically reduced our maintenance. 

Our desire was to limit the amount of plumbing and maintenance as much as possible, especially where items could rust or corrode, and to reduce our need for haul-outs.   Our justification was that every hole we removed from the boat made it that much easier to inspect, cheaper to maintain and safer to operate.  Less things to fail, less things to overlook, less things to fix, fewer boat yards to depend on, etc.

J.D. points out the holes we will seal.

We also decided we would eliminate of all four of the toilet's direct pump out ports.  Our thinking was that we could always pump directly into the holding tank instead, which had a gravity drain through the hull, achieving the same effect without relying on a joker valve ALWAYS working, but reducing the likelihood that a mechanical failure could flood the boat, and reducing by more than 66%  (because there would be only one large thru-hull & valve per side instead of three) the chance of a leak or mechanical failure.

That meant we'd be eliminating four of the 1.5" holes in the boat, four large thru-hulls, four large (and very expensive) seacocks, as well as four large (and also very expensive) anti-siphon valves and four of the (very expensive) three way valves (which were annoyingly hard to reach) and at least twenty feet of very expensive hose.  Hooray for us!

We also thought we could get rid of at least two of the four bathroom sink drains.  Since we wouldn't be using the forward bathrooms as much, it seemed like a good idea to tie the two lines together and only use one thru-hull.   In retrospect, we wish we'd taken out the remaining two sink drains, which we ended up doing anyway, about two months afterwards.

The sink drains run to the thru-hull ports just below the waterline along the outsides of the boat.   Our dear friend J.D. [pictured above-left pointing to three of the four holes (per side) we would initially patch] is also standing next to the one hole we regrettably left in place.   But to start with, we removed the two toilet thru-hulls and the aft bathroom sink drain thu-hull, and created a fiberglass "plug" for each of these holes.

The railway lift, Napa Valley Marina

But our first task was finding a marina that could haul us, somewhere within sailing distance of Emeryville. After much searching, we eventually brought our boat to the Napa Valley Marina, just up the Napa River, in beautiful Napa, CA.  Once we were up out of the water we were able to easily inspect the thru-hulls and valves.  

We were shocked at what we found. Several of the thru-hulls had corroded so much that the valves broke off in our hands as we tried to remove them. We were amazed at just how fragile they were, and a bit dismayed at the thought that a valve could have easily come apart while we were out sailing on the bay, or worse, miles away from land in a bad storm, leaving us with a 1" large (or better) hole in the boat.

We also discovered that both engine value thru-hulls were jammed up with fishing hooks and lines inside the valve and the tail piece elbow. This really surprised us, but it explained why we weren't able to close those particular valves completely. We're not sure how, when or where we picked these up, but it had to happen somewhere between La Paz and San Diego, because that is when we first noticed the problem. What is amazing is that it didn't seem to interfere with anything else. The engines didn't seem to run any hotter and we didn't seem have any problems with fishing line in the strainers, or worse still, anything working its way up to the impellers.

What was most distressing to us was the amount of deterioration in the valve's bronze that had taken place without us noticing. The valves had all been professionally inspected during our survey (and by ourselves as well) and they seemed fine at the time. Both the surveyor and I had independently examined each and every valve, and scraped the metal both inside and outside the boat. At the time, things looked great. Since that time we had been quite religious about keeping up with the zincs on the boat, changing them regularly, and we were very careful about properly connecting our boat's electrical system, and had it checked frequently.

But what we couldn't protect against was a stray current from another boat or dock. We really have no idea when it took place, but we assume it was during our trip back.  It seems unlikely it happened once we got home as our local marina is one of the most stringent in the bay area, especially where electrolysis and stray current/voltage is concerned. Every dock in our harbor has an in-water electronic monitoring system that can notice when a boat is improperly wired, and the marina regularly checks each boat's shore power lines for stray or improper current. Nonetheless, we ended up with very badly corroded valves and thru-hulls in the space of about four years and we didn't have much warning that it was happening.

Marelon 1.5" valve with flange plate.

That was quite a scary realization and it helped us in deciding to use non-metalic valves and thru-hulls wherever possible on the vessel. To that end, we elected to use Forespar's Marelon Valves. These are valves made out of a corrosion free/electrolysis free material that has a strength comparable to bronze, although I would caution you against assuming the same is true of their other products.  [For more on this, see Thru-hull Flange Plate and Marelon Flanged Valve Installation.]

But before we could do anything else, we needed to plug the thru-hulls we intended to eliminate.  One of the best assets of Napa Valley Marina is their staff, and especially their fiberglass expert, Kelly Howell, pictured here, trying not to laugh at the idiot in the bunny suit.

Kelly Howell on right, the Wonder Bunny on left.

Because we had only limited experience with fiberglass, and this was such an important and critical job, we didn't feel comfortable taking on this project by ourselves. Kelly was happy to explain everything we needed to do, and work with us acting as an instructor and foreman. He made sure the project was done right, and we used the least amount of his time to achieve it. If you need to do a big fiberglass project where most of the work can be done yourself, hiring him to help out and keep you on track is a great way to cut costs and still buy piece of mind.  But if you are going to do this, our advice is to make sure that you don't try to schedule that effort along side any other task.  We tried to get a bunch of stuff done simultaneously, and we found that the responsibility of keeping an entire crew of friends busy made it very difficult to also efficiently make use of his time & expertise.  We often had to deal with emergencies that cropped up, which meant having to let Kelly do the work for us.  Less of a savings than we had hoped, but at least we knew the work was being "done right the first time".

A clean, well lighted place to epoxy.

One of the most valuable lessons we learned from Kelly was to get everything prepped ahead of time, to always work in a clean, organized manner, and to only do as much of the project at one time as is reasonable.  Getting prepped meant starting with a reasonable work area, and preparing the work site, including cleaning up anything you've been grinding on with acetone.  Another great tip we got was to have a small plastic bowl of acetone handy, filled about 2" high.  Make sure you are wearing protective gloves (in fact, wear two sets of them so that if you hands become hopelessly sticky you can pull off the outer set and still keep going) and as you are working the fiberglass, dip your fingers into the bowl to clean off the epoxy and mat that sticks to them.   [editor's note: Epoxy chemicals are quite toxic, make sure you are wearing the appropriate gear, including eye protection, gloves, long sleeved clothes, respirators, etc.  Don't take on a project like this without adequate supervision and training.  Consult a professional before modifying your boat, and don't assume anything we say here is correct, complete or concise.]

Thru-hole to be patched, just after
we'd removed the mushroom.

We needed to plug the existing thru-holes that we weren't using any more, and to do so we would create a "rivet" of fiberglass (think of an upper case letter "I" turned sideways, that encased the hull]) which would fill the entire hole but also overlapped the hull skin on both sides and be bonded with it inside and out.   To do so, we needed to first prep the hole.  This meant first removing the thru-hull and any caulk or sealant, then scoring back the balsa core a bit but leaving the hull laminate intact, so that there was about a 1/4" of balsa removed.

The area surrounding the thru-hull mushroom will be filled with some form of caulking or sealant.   If you're lucky, the prior installer won't have used the dreaded 5200, or some other type of glue, which can make removing things quite annoying, but in any event, you will want to grind out enough core that you create an interior cavity between the two hull skins larger than the existing opening.  This will also allow you to examine the core itself for signs of damage or water intrusion.

[editor's note: The thru-hulls on many of these boats were "supposed" to go through an area of laminated marine plywood, but unfortunately not all of them did.  Sometimes the installers missed when they installed the core hole, especially on the holes along the side of the boat.  Sometimes they put the core hole into only half of the plywood.  Don't be surprised if the hole through your boat exposes balsa core, or plywood, or some combination.  Regardless, the balsa and/or plywood should be dry and intact.]  

Make sure you scrape back the balsa about 1/4" from the edge
of the hole, grind the hull surfaces inside the hull to achieve a
good bonding surface as well.  This hole went completely
though the balsa and missed the  plywood entirely.

You'll need to cut back whatever you find there from the edge of the hole.  We tried several different tools to do this, including a chisel, a drill, but what worked best was an air powered hand grinder with a small enough grinding bit that it could fit in the hole.  What didn't work was an allen wrench placed in the end of a drill chuck, which sounded like a great idea at the time, but turned out not to work as well on the plywood as it did on balsa cores.

When coring out the balsa, do be careful, it is very easy to take away more than you intend to, especially near the hull laminate.  Go slowly, and don't cut away the hole edge or enlarge the opening.  You want to remove about a 1/4 inch of balsa/plywood back from the opening of the hole edge only.  Make sure there is none of the old sealant or caulk remaining, and that you sand the fiberglass inside the hole so that the surface is roughed up.  Then sand down to the fiberglass (past the gelcoat) around the hole on both exterior surfaces, creating a smooth circle about 6 inches around.  Make sure you get down past the gelcoat and that you don't gouge up the surface.  Try to feather back the edges of the gelcoat slightly as well.  This means attacking the job from both inside and outside the boat, and it turns out to take way more time than you think it should, but this is one place you really want to go slow and be methodical.  Clean the surfaces completely with acetone when you are done.

Grind the surface around the hole back past
 the gelcoat, leaving a smooth surface.  You
can see the plywood core as well as the
balsa on this opening.

We used polyester resin, fiberglass mat, and MEK-P hardener for much of this project.  We probably could have also used the West Systems two-part epoxy, but polyester resin was the appropriate choice of material for our boat.  It was also less expensive.  Be aware that when bonding to existing fiberglass, not all materials work the same, and if you aren't sure, seek the advice of an expert before attempting to modify your boat.  It is important to create a strong chemical bond, and while epoxy will stick to polyester, the opposite isn't true.  [editor's note: The hardening agent (catalyst) we used for the polyester resin is called MEK-P, and it should be treated with the utmost care.  If you get this in your eyes or skin it will cause intense burns and can result in blindness.  Do not use this without proper safety equipment including eye protection, gloves, respirators and protective clothing.   If you do come in contact with it, rinse the area immediately with water and seek medical attention.]

We then needed to create a thick fiberglass putty for the project, which we would eventually use to plug the holes.  We poured enough resin into a 1/2 gallon tub to fill it halfway, then added equal measures of West Systems 404 high-density filler and 406 colloidal silicate to it.  This thickens (and strengthens) the resin and makes it into a putty like material.  Be careful, these materials are a breathing hazard and will fly away in the lightest breeze; make sure you are wearing a respirator when working, and avoid closed spaces.   We needed to add enough of the fillers to create a peanut-butter like paste that did not "flow".  We set it aside in an airtight container (and didn't add the hardener yet), because we would be using this in small batches to plug all the holes.   We were able to keep this around for the length of the project, only adding hardener to small portions as we needed it.


We then cut four circles of fiberglass mat for each side of the hole, ranging in size from 3 inches to 6 inches and labeled them 1 through 4 in order of increasing size.  We made a complete set of these for each side of every hole we were going to patch.

We filled a pint container about half way with resin, then added an appropriate amount of hardener.  You'll notice the color of the resin change slightly when you do so, which is a good reminder whether you've added it or not.   It isn't uncommon to forget if you've added hardener and if you do forget you'll wonder why your patch is still gooey the next day, if you add twice as much hardener you're epoxy will harden far too fast, and if you really add too much it will even catch fire!  Fortunately, if you aren't sure, you can tell by what color it is, so make a mental note of this the first time you mix the two.

We used a small (cheap) paint brush to paint the interior facing fiberglass hull (the skin inside the boat that we had already roughed up with sandpaper) with Smith's two-part penetrating epoxy.  That helped create a surface that the patches would adhere to.  We then placed the four concentric circles of mat on a cardboard box and saturated them with the resin/hardener mixture, making sure to completely soak the mat.

You can see the sunlight shining through
the mat before we'd filled the hole with
epoxy paste.  We also sanded this down
   and painted it with gelcoat to finish it.

The mat should become translucent when it contacts the fiberglass, and any air pockets will appear as small opaque bubbles.  Place the smallest circle of mat over the hole on the inside of the hull, then work out any air bubbles that have been trapped between the mat and the hull surface, using your paint brush and/or a squeegee, and work them out towards the edges.  We had to work quickly (before the material started to set) so that we could then place the next larger circle over it and repeat the process of removing air bubbles, until we'd built up a series of plates that overlapped each other and extend out beyond the hole's radius by at least 3 inches, and allowed them to harden completely.

Build up the surface layer to meet the gelcoat, so that there is
as little sanding as possible required afterwards.

We allowed the patch to harden overnight.  We needed to wait for the dew to burn off every morning before we could begin the next step.  The temperature and humidity matter greatly when working with fiberglass, so take that into account when using this material.

We next gently roughed up the inside surface of the patch (from outside the boat) with a small sanding wheel, to allow the plug to bond to it better, and painted this surface and the rest of the interior area with the two-part penetrating epoxy, which is thinner than resin and will saturate into the balsa and help create a good chemical bond with the hull skin.

Filling the holes with the resin putty.
Work quickly, as the mixture will
become difficult to use as it hardens.

We now had a pocket we could fill in (from the outside of the boat) with the thick paste we made earlier.   We divided out enough of the paste to fill one hole completely, then put it into a smaller plastic container.


[editor's note:  Months before you start in on any fiberglassing project, begin by saving your plastic yogurt and cottage cheese containers, as these work great for epoxy trays.   The boat yard makes a small fortune selling you "special" plastic tubs; you could buy the two containers filled with delicious food for what they will charge you for an empty one.


That same markup, by the way, applies to sand paper, paint brushes, rollers, tape, cardboard, etc. Try to have as much of this stuff on hand as possible, before you begin your project, and if you need to, go buy it at a hardware store instead.  Make sure you have lots of paint brushes, paint stirrers and fiberglass mixing sticks on hand, as you'll go through these faster than you think ]

Kelly next to the first plugged hole.

We added the hardening agent and mixed thoroughly, then filled in the hole with the mixture until it was just slightly sticking out past the hull on both sides.  We smoothed off the surface so that we had as clean a match to the hull as possible, with about 1/16" excess above the surface, which we later feathered back with a grinder using 36 grit sandpaper.  We allowed it to harden completely.  Once dry, we ground this flush with the hull surface.

Next, we repeated the same process (but from the outside hull) of adding the circles of glass mat to this plug, overlapping each circle and building the final layer up to just above the level of the gelcoat.   Ultimately we wanted to get as smooth a surface as possible, to reduce the amount of fairing (grinding back the excess fiberglass to achieve a smooth surface) we'd need to do.   Since this patch was below the water line, and we were going to add an epoxy barrier coat over it anyway, so we didn't need to worry about using gelcoat on the outside.

We really wish we'd have plugged all four holes the first time.

We did grind smooth and cover over the interior patch with gelcoat, so that the surface wasn't rough to the touch.   That turned out to be more important than I realized at the time, as any small imperfections or bits of fibers sticking up out of the patch are like little razor blades.  We wanted to knock these down with a grinder and then cover the area with gelcoat to get a smooth finish.

We now had plugged holes, that should be as strong, if not stronger than the hull itself.  Providing we'd properly (chemically) bonded the new glass mat with the old, and that there was no initial water damage to the core, this plug should be just as water-tight and last the lifetime of the boat.  It will definitely outlast the owner, given the amount of fumes and dust we've breathed in during the process.

That left us ready to add the flanged valves and their backing plates, finish grinding off the old paint, add an epoxy barrier coat, and paint the hull.  Now I know how Sisyphus felt.