Re: [Paddlewise] pressurize the boat

Dave Kruger wrote:

>>>>As Robert Livingston said, it is not that hole which allows water in; it
is
any hole in the outside of the hull in regular contact with water.  In my
boats, I do not see leaks into the _bulkheaded_compartments_ any more;
rather, I get water "pumping" from the hull flex mechanism, operating on
the opening the rudder cables demand, _into_the_cockpit_, where they exit
the hull-deck seam.  The cables run along the inner edge of the H-shaped
rubber extrusion which "seals" the hull and deck.*  The hull and deck are
mated with a structurally sound overlap of mat and resin on the inside;
but, the cables have to penetrate that mat/resin overlap, and after a few
hours of rough water travel, I'll have a quart or so of water sloshing
around in the cockpit.

That quart of water has never been a problem; I know from rescue practice
that even a couple gallons of water is not enough to materially affect the
handling of my boats.  I get wet some from the leakage; but, it _is_ a wet
sport, after all.

- ---------
*That H-shaped extrusion is laughable as a "seal"; it just makes the
hull-deck seam look good;  I think its main function is to maintain
registration when the real seal (the mat and resin overlap on the inside)
is bedded in place at manufacture.  Once, I replaced most of the overlap in
a boat which had been oil-canned in surf; the H-extrusion helped me mate
the halves, but that was about all.<<<<<<<<<<<<<<<<

Your asterisked section above is an astute observation. Those are the
H-shaped extrusion's functions. With a vacuum-bag mold the cockpit opening
is closed and must be cut open later to put the cockpit in. That means the
kayak can not be seamed together when it is still in the molds (by bolting
the mold halves/boat halves together after the edges are trimmed flush with
the mold and seaming the inside through the cockpit hole). Therefore, the
much thinner boat parts have to be held together somehow, in register, and
sealed such that the resin in the seams can't leak out though the gap
between the hull and the deck. The vinyl H-molding (and several strips of
masking tape to temporarily hold things in place) provides those functions
and also means that the seaming job is completely finished once the masking
tapes are removed. This is a very efficient and labor saving way to seam a
fiberglass kayak together and you end up with a very crisp looking seam.
With vacuum-formed plastic kayaks the hull and deck are just glued into the
extrusion so no inside seam is even necessary.

Contrast this with what must be done with a vacuum-bagged kayak otherwise.
The parts must be trimmed and removed from the mold as before but without
the vinyl extrusion they must be carefully butted together and taped with
masking tape every 4 to 6 inches in a manner that doesn't start to generate
a twist to the hull. Next long strips of masking tape are put along the seam
to seal it for putting on the fiberglass inside seams (which is pretty much
the same job for both types). Once the seams have cured a lot more masking
tape must be removed with the non-vinyl extrusion type (outside seams). Now
some way must be found to cover the raw edges of the seam where they butt
together. In early fiberglass kayaks this was often covered with a long
strip of plastic electrical type tape. The downside was that later handling
often resulted in the tape getting moved and looking bad. It was pretty easy
to replace though. Today most kayaks that don't use vinyl extrusion in the
seams are made with fiberglass outside seams. This requires two new long
strips of masking tape be placed along the seam at an equal distance apart,
by eye, on each side of the kayak. Next someone must sand the shiny waxed
gelcoat surface between the strips of masking tape so the fiberglass resin
has a roughened surface to get a good grip on when the fiberglass outside
seams cure. A layer of fiberglass "selvedge edge" tape is wetted out with
resin and laid down between the masking tapes and the masking tapes must be
peeled up while the resin is still runny or it won't leave a clean edge (the
cured resin overlapping it will tear the tape or the gummy resin will make
strings that will mess up a clean edge appearance when the tape is removed).
The resin was often pigmented black or some other color and a liquid wax
(known as "surface agent") was added to make the outside seams cure
completely so they weren't gummy on their surface. When resin cures in
contact with air the surface layer of resin molecules are air inhibited and
never cure. The downside of this was that the outside seams were pretty
rough and could abrade other boats they rubbed against on say a car rack (or
ones knuckles if scraped across them). The selvedge edge (where the fibers
fold back toward the center to form the tape edge) would often protrude a
little above the grade of the rest of the tape aggravating the problem. To
solve this many builders mask off the area again and sand of any rough spots
that stick up above grade and then cover the whole thing with gelcoat that
has a smoothing agent and a surface curing agent in it, making another step
in the long process.

As you may have guessed fiberglass outside seaming certainly isn't a very
efficient process. One builder told me there was eight man hours of labor in
just the fiberglass outside seams of his kayaks. A strip of vinyl extrusion
doesn't cost as much as even a half hour of labor so why don't those
manufactures just use the extrusion? Nobody has a patent on it.  If you
order the extrusion with a hole down the middle you can even eliminate the
plastic tubes that the rudder cables need to run through otherwise (to keep
the cables from sawing through the fiberglass where they enter the kayak,
any bulkheads they pass through, and your rear compartment's gear bags when
worked back and forth as you use the rudder).

Now, why is the title of this thread "Pressurize the boat"? Oh yeah, to find
leaks. Leaks have been a major problem for H-seams. As Robert described,
anywhere that water can puddle, where there is also a tiny hole, the flex of
the boat and resulting pumping action draws water into the boat. Dave,
above, blamed that process for the water getting into his cockpit but I
think he is mistaken about that unless he has a taut and airtight spraydeck.
I think his leak is one I observed once in trying to stop multiple leaks in
a kayak. The rudder cables working back and forth as they do move water
inside the rudder cable tubes until it is running down into the cockpit. My
suggestion to Dave is to inject some silicone sealant into the tube where
the rudder cables emerge near the back of the kayak and let it cure. This
will make the cable hole a lot smaller there (and as the silicone sealant is
sawn away enough by the cable that the leak reappears replace it again). The
main problem with the H-seam is that the upper half hold water and if there
are any pin-hole leaks in the inside seam that water can be pumped into the
closed compartments and replaced in the "gutters" by the next wave high
enough to lap over the seam. One manufacture even admitted there was a
problem with the early H-seams but claimed his new seams fixed the problem.
The new seams had the uneven lengths of the H-seam switched around. The
shorter side was on the outside. I think the theory was that way there would
be no head of water since the water on the outside would pour over the edge
of the tape before it could get high enough to go through any holes and pour
over the inside of the tape. If I'm correct in that speculation, he didn't
count on Robert Livingston's pumping action observation as the new seams
were leak prone just as the old had been. So why can't the inside seams
adequately seal the kayak with H-molding? Well, sometimes they do. But then
again, sometimes they don't. I think the problem is partly due to the inside
edge of the H itself. When the inside fiberglass seam tape bridges across
that H edge to seam to the hull or deck a bubble line in the resin often
forms along the bridged gap. As the resin cure some of those bubbles break
and form pin-holes. The other problem is that someone seamed the ends of the
kayak by reaching in with a brush on the end of a long stick and having done
this many times I can attest that you don't have a good enough angle to
really see how well you have done at getting the bubbles out near the ends
of the kayak or maybe even in getting the fiberglass seam tape completely
saturated way down there. Coincidentally, or not, most seam leaks are near
the ends of the kayak. While hatches on many kayaks are not very watertight,
if a kayak has H-seams and is getting water inside I'd check the seams first
as they are the most likely leak site. Rather than pressurizing the
compartment though, I'd just put several gallons of water inside the kayak
and rotate it around to see where it leaks out (or stand the kayak on end
and fill up the lower three feet of so to give the water a little head to
increase the water pressure to help it find the leaks for you.

If you find that your H-seams leak, don't despair, there is a rather simple
fix. Get a tube of silicone sealant and cut the long applicator tip at an
acute angle, like a hypodermic needle. Fill the top half of the H with the
sealant by injecting it in as you move your "needle" slowly along the seam.
If the vinyl of the H is too stiff to get your "needle" into, warm it up
some with a hair dryer to soften it temporarily. Don't bother trying to seal
the inside seam with thickened resin, as is often tried. Most likely you
will just add several pounds to the kayaks weight and find it is still
leaking some.

Matt Broze
www.marinerkayaks.com
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