Seacock Removal and Replacement
boat was built several years back so it was not a surprise to me that it
had several types of seacock valves installed on the thru-hulls. What did
surprise me however was finding myself alone in the boat with a seacock
valve in one hand and trying to stop old faithful from sinking the boat
with my other hand. The valve had broken off at the thru-hull fitting as
I was closing it. Luckily there was a toolbox nearby. I retrieved a screwdriver
from the toolbox with my foot and with my free hand a towel that was located
on top of the galley sink. I could barely reach it. Suddenly I began to
laugh because it reminded me of the Twister game that kids play. I wrapped
the towel around the screwdriver handle which I forced into the thru-hull,
handle first. This seemed to slow the waterflow down to a trickle and it
gave me time to wrap the broken thru-hull fitting to the screwdriver shank
with duct tape. With a feeling of great insecurity I hurried to a local
marine store to see what could be done. I was handed a set of tapered softwood
plugs and was told, “that is all you can do until you haulout.” I rushed
back to the marina and to my relief the boat was still floating-it hadn’t
sunk! I decided to put the plug in the thru-hull under the boat instead
of on top. I didn’t have confidence that the plug would stay in the top
position for any length-of-time. With the wood plug and hammer in hand
and in my underwear I made a dive over the side and drove the plug into
the thru-hull. Cold and embarrassed, I thought to my self “talk about not
being prepared” and maybe a few other unfriendly words.
seacock that failed on my boat was a gate type valve which is considered
to be a garden variety valve and was not marine grade. The problem with
gate valves is that you cannot determine by looking at one weather it is
open or closed. Any piece of debris caught in the gate gives the impression
that the valve is closed, because the handle won't turn any further, in
fact, the gate may still be half open. I found out later that this type
valve was used to save the builder dollars. If you have gate valves, especially
below the water line, consider replacing them immediately.
There are several types of marine grade valves. The three most common
seacock designs are tapered-plug type, expanded-rubber-plug type, and ball-valve.
The ball-valve is the latest design and practically maintenance free. A
dab of waterproof grease once or twice a year and occasional turning of
the handle, will prevent it from seizing. I made it a habit to close all
the valves when I leave my boat. This solves two problems, 1) it eliminates
seizing and 2) the boat will not sink if a hose fails. The other type valves
require annual disassembly maintenance. Even if you have ball-valve seacocks
it is a good idea once a year while the boat is out of the water to remove
the tail piece and inspect it for foreign material and with a dab of grease
on the end of a wood dowel grease the ball. Turn the handle several times
to make sure the grease covers the ball. Repeat the same greasing procedure
through the thru-hull from out of the boat.
Every thru-hull should be mounted through a backing block that is shaped
to fit flat against the inside of the hull which has a surface area greater
than that of the seacock flange or the thru-hull flange nut. For improved
strength, the flange of the seacock should be thru-bolted to the hull or
blindly fastened with screws to the backing block to prevent it from turning.
All seacock tailpieces should have barbed ends to prevent the hose from
slipping off. If the valve is below the waterline the hose should be double-clamped
to the tailpiece.
remove a seacock you will need to borrow a step wrench from the boat yard
(Figure 1). This tool is tapered to fit into the thru-hull from the outside
of the boat. It fits snugly against the two knobs protruding inside the
thru-hull. With a large wrench unscrew the thru-hull fitting out of the
boat. If the flange is not thru-bolted or screwed onto the backing block
a second hand might be needed on the inside to hold the valve from turning.
If for some reason you cannot locate a step wrench try a metal wedge
that will fit into the thruhull so that it will lock onto the knobs. If
the knobs are gone due to corrosion you will have to cut the thru-hull
out with a reciprocating saw. Remove the valve before cutting, place the
blade inside the thru-hull fitting from the outside; and cut to the edge.
Make several cuts to ensure that the thru-hull will collapse inward try
not to cut into the fiberglass. Another method is to drill the thru-hull
out because the hole will require a large bit and you will most likely
have to borrow a bit and drill from the boat yard. With all this borrowing
going on it would be a gracious gesture to take whom ever you are borrowing
from out to lunch. It’s a minor concession if you need to borrow again.
Once the thru-hull is out, remove the seacock or flange nut from the
backing block. If the flange is thru-bolted to the hull, scrape off the
bottom paint in the area around the thru-hull and find the plugged holes.
Chip the filler out of the holes to expose the bolt heads and remove them.
If the flange is not thru-bolted and will not come off the backing plate
or the hull, try applying heat to the flange with a heat gun and slide
a putty knife under the flange to break the bond.
Before installing the new seacock and thru-hull, inspect the
backing block for rot. If you need to replace it, cut the backing block
out of a marine grade plywood with a surface area larger than the flange.
Bore the hole for the thru-hull in the middle of the block. The marine
plywood is fine as long as the end grain is sealed with epoxy resin to
keep moisture out.
There are two types of thru-hull fittings; 1) mushroom the most traditional
and requires no special tools for installation and 2) flush mounted thru-hull
primarily used for racing. A special counter sink tool is used to bevel
the hole for the thru-hull to fit flush (Figure 2).
Some thru-hull fittings are sold with a flange nut that is separate
from the seacock (Figure 3). If you decide to use the flange nut to install
the thru-hull the installation is quite simple. Apply a generous amount
of underwater bedding compound to the inside of the thru-hull flange between
the backing block and the hull, and between the flange nut and the backing
block. Because the thru-hull is not thru-bolted, some owners have used
3M’s 5200 as a bedding compound for extra strength. The only problem using
5200 as a thru-hull bedding compound is it increases the difficulty
for future removal. Use plenty of bedding compound, clean-up is easy with
a razor after the bedding has set. To install the thru-hull, have someone
outside holding the thru-hull from turning with a step wrench, and
another person in the boat tightening the flange nut with a wrench. Once
the thru-hull is tight, and with the step wrench still held in position,
install the valve. Use some plumbers tape on the thru-hull threads this
will assure that there will be no leaks.
more stable and reliable installation method is to use a flange that is
part of the seacock valve and is thru-bolted through the hull (Figure 4).
In most cases, the thru-hull will be too long and will require cutting.
Measure the thickness of the hull and backing block. Mark this measurement
on the thru-hull starting from the inside face of the thru-hull flange.
Then thread the thru-hull into the seacock as far as it will go and put
a mark on the thru-hull. Unthread the thru-hull and count the threads it
took to bottom out. Add this number of threads, less two to the initial
mark on the thru-hull. By subtracting two threads, you will be sure that
the assembly will tighten up before the thru-hull bottoms out inside the
seacock. After cutting off the excess from the thru-hull, clean the threads
and make sure the threads will start into the seacock. On a work surface,
set the seacock on top of the backing block with the thru-hull in place
to keep everything centered. Next mark and drill the holes for the thru-bolts.
Back at the boat hold the backing block against the hull, centered on the
hole for the thru-hull, than mark, drill and countersink the holes for
your thru-bolts. Before applying the underwater bedding compound make sure
that everything assembles properly. With this type of installation do not
use 5200. After applying the underwater bedding compound insert the thru-bolts
through the hull, backing block and the seacock flange. Start the thru-bolt
nuts, but do not tighten until the thru-hull has been partly threaded into
the seacock. This will make sure that everything will align. After the
thru-bolts have been tightened, turn the thru-hull with a step wrench until
I learned a few things from this adventure. Seacocks are the sort of
mechanical devices that are reliable and simple enough to invite neglect.
It is a good idea to routinely inspect all seacocks and thru-hulls annually.
Make sure they are marine grade. Check to see if each seacock is mounted
on a backing block and fitted with a proper tailpiece. Evaluate how easy
they operate and make sure that no leakage occurs anywhere in the fittings.
Keep them in good condition all year, know their locations and have a softwood
plug available in case of failure.
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