Outdoor storage wasn’t a problem with my first
boat. Little cartop boats can live happily upside down and my
piccup pram started out propped up by some landscape timbers.
After it got buried in snow the first winter, I built an elevated
facsimile of the car’s roof rack on posts in the back yard.
It worked well.
But, trailer boats are a different matter. I thought I had it
all figured out too. The masts lived in crutches inserted into
the two mast steps and these provided the ridge pole for the cover
tarp. Along the sides of the trailer, I had cleverly welded tarp
hooks every foot or so. All the ingredients for a tarp that could
really shed some water! I even fitted the heavy-duty polytarp
to the boat and installed grommets every foot or so.
But, all was not as well as it seemed. The tarp easily stretched
under the weight of snow or rain and I inevitably had pockets
of trapped ice next to the masts. Of course the melt water would
find its way though the tarp and refreeze in the boat. Then I
would later be breaking up the icebergs in the bottom of the boat.
It was easier to remove them whole, but they inevitably encased
some stray lines.
I was not going to do that again, so I dealt with the defenses
in reverse order. Hull drains ensured that any leakage would escape
before too much ice could accumulate. For details see here.
I even built this ramp to make sure the boat would tilt the right
way to drain.
But this wasn’t perfect. Leaks over the mast steps still
let water into undrained compartments. After a year or two in
the sun, even the heavy duty polytarp starts springing some serious
leaks. I needed better support.
The most important consideration was to prevent the tarp collapsing
next to the ridgepole. I’m a little embarrassed to think
of the overbuilt options I considered when all I really needed
were battens. I used ½” CPVC pipe. It’s cheap
at about $3 per 10 foot section.
But notice that there needs to be quite a bit of downward force
on the ends to flex these battens into a snow-shedding arch shape.
Batten pockets would force the cloth to take all this force in
a rather destructive way.
Again, I went through a series of overbuilt options. The simplest
was to tie down the battens separately from the tarp. This completely
removes the batten strain from the tarp and eliminates any need
to sew batten pockets of any kind in the tarp. This is good given
how fast tarps wear out in the sun. It also lets the fabric stretch
as necessary regardless of the frame beneath.
Obviously this sort of batten requires a ridgepole to be sturdy
enough. If you can’t manage a ridgepole, the next best option
is probably to bend bows from steel electrical conduit and use
standard bimini fittings.
So let’s get to how we do this two-step tying-down.
First the battens are tensioned in place with 1/8” Dacron
line and taut line hitches. The small “beads” (also
PVC pipe) are only there to keep the line more or less on the
hook if the knot slips. They probably aren’t really necessary.
I found that I only need five battens on this 23-foot boat. Setting
up the battens takes about a minute, with my wife and me working
together. Alone it’s maybe three minutes.
In case you have the same idea, my first approach was to use
tensioner toggles, like many tents use. My version made from CPVC
pipe wasn’t very secure. Maybe it would work better in wood,
but I didn’t try it.
The toggles you see in my version are simply to keep the loop
from jumping off the hook while I pull it tight from the other
side of the boat.
After the battens, the tarp is tied down by pulling loops of
a continuous line through the grommets and down to the trailer
hooks. Right now I cross over the boat with this line at each
batten, but it would be faster to have a separate line for each
The aft end of the tarp is sort of sewn to hooks on the light
bar and then cleated.
I have used it like this for a couple of years. It handles highway
speeds fine, doesn’t collapse under the weight of snow and
the tarp is much less prone to leaking rain during the summer.
But there was still room for improvement.
Faster tying down
Note the duplicated effort above. First we tie down the battens
and then the tarp. Batten pockets were not a great option, but
I thought of another way to eliminate the redundancy - permanently
lashing the battens to the tarp’s grommets.
||Tarp new lashing
I also sped things up by simplifying my Dutch lacing. I had a
long line that fastened the tarp at the forefoot, then went aft
to fasten one side and the first batten, jumped over the boat
to do the other side, then went aft to the next batten and so
on. This is a lot of reeving every time I went sailing. Let’s
cut that line up into more manageable pieces that can stay with
the cover tarp.
Here’s the taut line hitch at the bow. I took an extra
turn around it to increase the mechanical advantage, but I’m
not sure it's necessary.
||Front tie down
At each batten, we have an eye on one side to engage the hook
on the trailer frame. On the other side we have a simple taut
line hitch. Actually, I use a taut line hitch on both sides in
case I need to adjust it side-to-side. Make sure the batten is
long enough or the lashing will slip off the end when the tarp
stretches under tension.
|| Tarp new loop
By the way, did I mention that tarps come with lousy grommets?
It is well worth putting in good brass ones. I did for most of
them and should have for all of them.
||Tarp new loop
Then at the stern we have the same setup as before, but only enough
line to do the stern.
||Tarp new stern
Much quicker and easier! This reduces tarping from about 15 minutes
I had a feeling that even bad fabric will be a lot better with
this frame. But the tarp was pretty well rotten. I screwed up
and ordered the wrong size tarp, but I turned this into an experiment.
The aft part of the new tarp is silver tarp and the front is white.
The silver tarp seemed to succumb to sunlight just as fast as
fast as the white stuff, but it does block a lot more light.
|Silver tarp Sep 2008
So even though it doesn’t last as long, any varnished parts
under it will go longer between refinishing. I call that a win!
What's more, it works okay even as it is dissolving if you have
hull drains. Keeping maple seeds out is more important than keeping
rain out. Rain can get out through the drains, but leaves and
maple seeds will plug them better than any rubber stopper.
That said, even a year after the above photo it was still keeping
water out reasonably well.
Some folks will want to try better fabric, but I’m not
sure it’s a as good an idea as it seems.
The normal boat cover fabric is Sunbrella, which is an Acrylic
awning canvas. It is excellent at what it does, but it is heavy
at 9.25 oz per square yard, and expensive at around $13 per yard
in the 46” width. I’d need around sixteen yards for
the light schooner and for that price I could buy about nine of
the heavy duty polytarps ($23 at tarps.com) I made the first cover
out of. I guess Sunbrella would have to last sixteen years to
be worth it. And, it probably would! But I wonder if the boat
will even last that long stored outdoors.
Why not use lightweight ripstop tent fabric? We now have a frame,
so why wouldn’t thin fabric work? Well, there’s a
few things to consider. First, nylon breaks down from the sun’s
UV rays nearly as fast as polytarp, especially the lighter colors.
It also offers little UV protection to any varnish underneath
- again, especially the lighter colors. Finally, nylon stretches
when wet. In our application, you can count on it sagging between
the frames in rain or snow! It is probably better with a good
waterproofing, but still not half as good as even the cheap thin
However, you can also get ripstop polyester. It has more UV stability
and blocking ability than nylon and it is stable when wet. But
ripstop polyester made for tents does not seem to be available
in consumer quantities at present. Not all ripstop is waterproof.
It pretty much has to be tent fabric and you have to periodically
treat it with waterproofing spray. A lot of it! I think it is
just as easy to rebuild them from cheap tarp if you’re not
willing to pay for Sunbrella.
Some might also think of using Tyvek house wrap. This would be
a wonderful idea, except that it last far less that a year when
exposed to UV.
Some will be tempted to get ingenious (cheap) and use painter’s
canvas drop cloth and treat it with paint or something like Thompson’s
Water Seal. Or the time honored waterproofing for canvas - sealing
wax in turpentine heated in a double boiler and brushed on. The
folks in Society for Creative Anachronism (you know…they
dress up medieval and play with fake swords on weekends…)
have already tried these and they don’t work well. The weave
is too loose and it won’t hold the waterproofing. It will
mist on your boat in a heavy rain. Worse, once treated it rips
easily. The canvas from fabric stores is the same stuff, as far
as I can tell.
The cheap cotton might be acceptable if you don’t care
about rain misting. As I mentioned above, it is more important
to keep out leaves and seeds than water. I suppose it is also
good that it breathes when it’s dry. Remember that there
is little or no mildew resistance with plain cotton.
You can get good quality traditional cotton 10 oz cotton army
duck from Sailmaker’s Supply for $5.50 per yard, 36”
wide. Then you also have the traditional problem with capillarity.
Touch the inside of the cotton with anything during a rain and
it will leak at that point. I think, for the cost of army duck,
I’d rather make the jump to Sunbrella.
With any cotton, be aware you need to wash it and dry it before
sewing or treatment. Also, be aware that it will change dimensions
as it gets wet and dried. You will need to keep an eye on the
fastenings so it doesn’t destroy itself by pulling too tight.
I think heavy duty polytarp is probably our “sweet spot”,
as long as your cover design doesn’t require too much sewing.
How did it work?
The test? This spring I found dry bilges! Even with record snowfall
this year (over 100”!). I never had to shovel snow out of
pockets in the tarp. Snow removal was more like brushing off the
car, which is a lot easier. A push broom usually works. I frequently
didn’t even bother with that, reasoning that some snow cover
would reduce the degradation from UV rays. (I don’t think
it helped much.)
I suppose the “Cadillac” approach would of course
be to build a bow shed from Stimson
Marine’s plans. But for now I’m renting,
so that will have to wait. It might be a good thing too, since
we both know I would just store this boat outside and start building
another one in the shed - wouldn’t you?
Madison, Wisconsin, USA