Monday, July 29, 2013

DIY Non-skid Surfaces for Plywood Boats

"Slippery when wet." How often don't we see that on notices and signs along footpaths, in shopping malls and in other places where a surface is too smooth to allow a good grip and could become dangerous?

Boats are also such places, with the additional factors of regularly being wet right where you need to be and also jumping around in reaction to wind and waves. Despite that, it is a common problem that a boat has inadequate texture on the deck or other walking surface to allow a good grip for deck shoes or bare feet.

Of course, maximum grip will come from maximum texture, or the roughest surface. However, people also sit on these surfaces and the roughest surfaces are the toughest on clothing and also on bare skin. The trick is to come up with a surface that allows secure footing on a wet and heaving deck but will not wear through the seat of your pants or skin your elbows and knees. Add to that the need for it to be applied by an amateur builder, not break the budget and to be attractive in appearance (or at least to not detract from the aesthetics of the boat) and you have a fairly difficult set of requirements to satisfy.

I have had mixed results from the various methods that I have used over the past 40 years of building my own boats. I will run through them and give the successes and failures of each of them.

In the 70s and 80s I used a rather nice non-skid deck paint that was made by a UK (I think) paint company under the trade name "Helmsman". It had a fine grit that was soft on clothing and skin yet gave reasonable grip. Problem was that the colour faded badly and it did wear down, so it needed to be redone very year or two. It was a really good product that seems to no longer be available.

In about 1975 I saw a very attractive deck finish done by a friend of mine on a plywood Cobra catamaran that he was building. He used a simple open-weave petticoat lace and bedded it into the first coat of paint on the deck, then painted over it. It added some non-skid properties that were adequate for the particular boat, which would be sailed sitting on deck or trapezing on the gunwale. It would not have been good enough for a deck that was to be walked on when wet in big seas.

That set me thinking on how to increase the non skid properties of this method, when building my first big boat. My solution was to buy woven polypropylene tree netting. The one that was available to me in South Africa had a honeycomb-shape mesh of about 20x30mm (3/4"x1 1/4"). The strands were also woven from fine strands of polyethylene and were about 2mm thick with a woven texture. I bedded it down into the second coat of epoxy on my deck surfaces, laying it in panels that I marked off with masking tape. Once that coat of epoxy had cured I cut through the strands along the panel edges, removed the offcuts and tape then applied another two  coats of epoxy. The resulting surface was very effective for grip but rather harsh. It was tough on clothing and skin so I  sanded the rough spots off it. With the roughness removed and the deck painted with polyurethane paint, some of the grip had gone, so I painted over it with the Helmsman paint mentioned above. The final result was extremely good grip but the honeycomb pattern could be uncomfortable to lie on.

While effective, this netting method is very time-consuming because of the need to pull the netting so that it has an attractive appearance, with the cells of uniform shape and in straight lines. The netting can also lift off the epoxy in places before it hardens, so I had to return to each panel repeatedly as the epoxy started to set, running a steel roller over the netting to press it down into the epoxy until it stayed there.

Many boats have non-skid surfaces done with paint, with a grit of some sort sprinkled onto the first layer while it is wet, then finished with an extra layer or two of paint applied over the top. The grit is usually fine river sand, which has round grains to give nice grip without being sharp. Beach sand tends to have sharp corners that make it very harsh, so is not suitable.

For my Paper Jet I used a non-skid paint additive that is available from International Paints. You can adjust the texture by using more or less of the additive. The additive grains are clear, so can be added to varnish also. While suitable for dinghies, the finish is too fine for larger boats, not providing enough grip for safety on a heeled and heaving deck with waves washing over.

For my Didi 38 "Black Cat" I used a variation of the grit method. Instead of grit, I sprinkled coarse Epsom salts onto the wet paint. When it had dried, I painted another coat or two of paint over the salts. After a few days the paint was hard enough to be lightly sanded, to expose the tops of the grains. Once opened up, the salt grains are rinsed out by rain or spraying with a hose, which leaves little craters. The texture of the surface can be adjusted by light sanding to create as much grip as you want. You can also choose the desired texture with the amount of salt that is sprinkled. For good ocean-going grip the salt crystals should almost totally cover the first coat of paint.

This last method was the best of all that I have used. The texture is formed into the finishing coats of paint so slight wear on the texture doesn't wear through the colour. The grit can be Epsom salts, course table salt or even sugar. Basically anything that will dissolve in water and rinse out of the craters will work. I wouldn't recommend the sugar option because there is likely to be a sticky residue on and around the boat for awhile, attracting ants and other insects.

You can also go the route of gluing textured sheeting onto the deck. There are cork-based deck materials that give excellent grip and are available in a range of colours. They are fairly soft, so easy on bare feet but can wear quickly if constantly chafed by a rope that crosses over a cambered deck or cabin roof.  There are also imitation teak products that can be glued down either in sheets or in plank form. They do a very close impression of teak decking and require little maintenance.

For localised spots that require more grip than elsewhere, for example on the top of a bowsprit, a good solution is self-adhesive strips that are much  like very coarse sandpaper. These strips can be painted to blend into the deck. They give very secure footing but can be harsh on your skin if you choose to sit there naked. That is good reason to reserve this method for the "must have grip" dangerous spots on the boat.

Of all of these methods, my all-time favourite is the Epsom salts method. It is versatile because you can set the level of grip yourself and it has the big advantage that some wearing of the texture doesn't make the deck look tired by exposing base layers of a different colour.