By Rob Rohde-Szudy - Madison, Wisconsin - USA


Outdoor Winter Boat Storage:
The Fine Art of the Tarp


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.

Trailer ramp

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.

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.

Batten tying

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.

Tensioner toggle

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 side.

Tarp tying

The aft end of the tarp is sort of sewn to hooks on the light bar and then cleated.

End cleating


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 to five.


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.

Better Fabric

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 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 polytarp.

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.

Cheaper fabrics?

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?

Rob Rohde-Szudy
Madison, Wisconsin, USA


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