There’s more than a little irony in the need to keep a fiberglass boat away from water. The reason revolves around chemistry and the fact that water is the universal solvent. Given enough time, H20 will dissolve granite. Fiber reinforced plastic (FRP) is a much easier target, partially because it relies on filaments of glass fiber being coated with a sizing in order to create a resin to fabric bond. Glass filaments are never saturated, they are only surrounded by resin.
The best defense against moisture intrusion is a well-executed, void free layup. A half century ago, the heroes of hull molding were those armed with serrated rollers who forced the resin into contact with the sizing that coats glass fibers. Their efforts improved the contact between inorganic glass and organic resin. Today, resin infusion and vacuum bagging are often used to further decrease the voids in a laminate.
Gel coat is another moisture blocker, but voids and porosity can become a weak link. This is why barrier coating has become a worthwhile effort aboard new and older vessels. For decades PS has been testing high solids epoxy barrier/primer coatings and their performance has been encouraging. Bottom line? Products like Interlux-Interprotect, Pettit’s Pettit Protect, Sherman William’s Seaguard are worth the trouble.
We just concluded a 10-year test run of Interprotect and Seaguard on a Chesapeake Bay based 41-foot sloop. The vessel winters wet stored and conditions on the bay include a staggering range of water temperature and salinity variation. The summer to winter temperature flux spans ice water at 30 degrees F to summer bath water at 84 F.
At the same time, mesohaline bay water and river flow bounce salinity through equally wide variations—ranging from 2 or 3 parts per thousand to 18 parts per thousand. This physical change of water chemistry combines with summer sunlight to encourage a biological attack on bottom coatings. The net result is a barnacle and bryozoan utopia and a real test of antifouling capacity along with an adhesion test of the bottom paint as well as the barrier coat. In short, the region is a good test bed for underwater coatings.
In 2009 the time had again arrived for me to remove Wind Shadow’s failing bottom coatings. The scrap-by-scrape details are spelled out in PS March 2009 issue. A decade later, in 2019, it was once again time to face another bottom ordeal. It’s a process I’ve become familiar with—a once-a-decade woe. But having owned Wind Shadow for 45 years, the 2009 redo held a nice surprise.
Once the biological demons—barnacles, bryozoans and tunicates were removed from the surface, along with some ablative antifouling residue, I discovered that hull areas protected by either Interprotect 2000E/2001E or Sherwin-Williams Seaguard 5000 barrier coats had done their job and the bottom was in far better shape than it was in 2009.
Your personal preference. If there aren’t that many layers of bottom paint, you can sand them off with an 8-inch, dual-action orbital sander and 60-grit sandpaper, but this is hard work and requires careful safety precautions. Overzealous sanding can lead to dings and divots in the gelcoat.
Another option is using a chemical paint stripper like Peel Away or Franmar Soy Strip (PS, October 2011). Chemical paint strippers break down the paint’s adhesive bond on the hull and make it easier to scrape down to clean substrate that can be repainted. This is messy and noxious work, but it’s less back-breaking than sanding. We’ve found that the strippers performance varies by boat (and temperature), so review the articles on strippers to see which one best fits your scenario. And if you’re not happy with one product, you might want to try another before giving up.
Both of these methods will be time-consuming on larger boats. Before tackling this project, check out our October 2011 article, “A Mathematical Decision Maker,” which outlines a formula for determining whether the DIY approach is right for you. On boats in the 40-foot range (or larger), we recommend looking into soda-blasting the hull (PS, October 2011). If you’ve got an old barrier coat that needs renewing, and are still considering a non-blasting regimen, then you’ll first want to read Ralph Naranjo’s account of his barrier coat removal project.
For owners of older boats with unknown, well-adhered coatings, a tie coat can help make sure successive coatings stick. The major bottom paint manufacturers—Interlux, Pettit, and Sea Hawk—all have priming/tie-coat products. One that we’ve recently used with success is Sea Hawks 1277 Barrier Coat Primer, a chlorinated rubber compound. Pettit’s version is called Tie Coat Primer 6627. Interlux markets its Primocon for this purpose.
How long you wait to strip down the old paint depends on how bad the adhesion issue is and your tolerance for a rough bottom; work boats go years without stripping. Eventually though, adhesion will suffer. The rough surface will also mean more drag in the water and slower boat speed. If you do start fresh, regular application of an ablative paint-one to two coats for a single season, no more than three for long-term cruising—can prevent paint build up. For help in selecting an ablative bottom paint that is best suited for where you sail, check out our March 2013 report on favorite bottom paints by region.
The durability of the 2009 barrier coating effort was quite apparent. The adhesive quality of Interprotect and Sherwin-Williams Seaguard epoxy were both excellent as was their ability to function as a moisture barrier. The dry film thickness of the Interprotect was greater than the Sherwin-Williams barrier coat, but after 10 years, this variant did not seem to affect barrier coat performance. Both coated sections revealed a minimal number of intra-paint layer minor blisters, only a dozen or so included sub-gelcoat penetration and the largest of these was only about one-half inch in diameter.
I tried a chemical barnacle base remover (On-Off) but preferred dry sanding with wire-grid sanding pads. A final 80-grit sanding with the Fein orbital vacuum sander, and I was ready to clean up, tape off, and apply a batch of new products to test.
This time I rolled and tipped two coats of Pettit Protect—an easily applied, high solids epoxy barrier coat. And followed up with two coats of Trinidad Pro bottom paint. Fouling has become so problematic in the summer months on the Chesapeake Bay, that I decided to see how a hard surface, high copper content paint will cope with the biological onslaught and increasing water temperature.
A year has gone by since last summer’s (2019) DIY bottom paint revamp and the initial results are quite encouraging. I haven’t scrubbed or hauled and washed down the bottom. During a recent dive and in situ inspection there were no barnacles, no tunicates and only a couple of spots on the rudder where a few small clusters of pioneering bryozoans were attempting to gain foothold. A sponge, not a scrub pad, evicted the intruders. Down the road we’ll see how the barrier coat fares.
Former boatyard manager and safety expert Ralph Naranjo is the author of “The Art of Seamanship: Evolving Skills, Exploring Oceans, and Handling Wind, Waves, and Weather,” available at www.practical-sailor/products.