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Bye Bye, Blisters!


A bad case of blisters can penetrate the skincoat and go deeper into the laminate.

Except for one dispiriting little detail, the boat was exactly what I'd been looking for. She was meticulously maintained, reasonably outfitted, and cosmetically impressive—a perfect example of the model I'd been lusting after for years. In fact, when I described her to friends during bouts of pre-purchase euphoria, I was wont to use the phrase like-brand-new, often blissfully leaving aside the fact that she'd been built and launched in the late 1980's.

The survey took seven grueling hours. And actually the little detail that cropped up at the end of it was way more than dispiriting, at least at first. I swear, as the TraveLift operator at Sassafras Harbor Marina in Georgetown, Maryland, hoisted my prospective acquisition gently free of her element, my heart dang near stopped. Bottom blisters! A whole bunch of the little jewels, each about the size of an old-fashioned silver dollar.

Accredited marine surveyor Fred Wise calmed me down, sensing the deep emotional attachment I'd already formed for the lovely objet d'art hanging in the slings as well as the gloomy sense of demoralization already setting in. I'd lived aboard a variety of vessels during the '80's, and if there was anything that spread universal dread among boaters back in the day, it was blisters, especially scads of 'em. Wanna toss and turn all night while dreaming about delamination and structural devastation due to the horrors of laminate hydrolysis? Venture back in time to, say, 1983 or 1984, and have your friendly neighborhood boatyard manager hit you with a money-sucking apres-haulout observation like, "Yup, it's boat pox."

"So let's see what's goin' on," said Wise upon securing agreements from the seller, the broker, and me that some areas of bottom paint might be removed to facilitate preliminary moisture-meter readings. Pawing and scraping ensued. Then finally Wise made a pricey but reasonable recommendation, and negotiations moved forward.

Certainly, my initial horror had not been total paranoia, however. After the blister problem hit the boat biz at the start of the '80's, it spread like wildfire during the ensuing ten years. Forums, seminars, and symposia were convened during major boat shows, with boat manufacturers and dealers on hand as well as fiberglass-materials purveyors, organic chemists, composites experts, and safety-minded representatives of the U.S. Coast Guard. Exactly why the problem hit when it did remains a matter of conjecture even now, although there's a theory that sudden, subtle, under-wraps changes in refining processes at major oil companies negatively impacted the chemical/molecular nature of resins across the board, a development that knocked lamination technology off track until boatbuilders figured out what was going on.

In any case, the Coast Guard decided to fund a study in 1985 and handed the project off to the American Boat Builders and Repairers Association (ABBRA), which in turn handed it off to Thomas J. Rockett, Ph.D., and Vincent Rose, Ph.D., both chemical engineers at the University of Rhode Island. The Causes of Boat Hull Blisters, subsequently compiled by the two scientists with help from graduate students over the next two years, remains to this day the definitive word on the subject.

According to Rockett and Rose, blisters are simply bumps on a hull, usually below the waterline. They range in size from a few millimeters to several inches in diameter and normally occur between the cosmetic layer of exterior gelcoat and the first outer layer of fiberglass composite (usually called the skincoat), although they can dig much deeper in some instances.

While there are a couple of types of blisters, it's possible to generalize the formation process. It starts with the movement of water molecules through the gelcoat, a porous material typically subject to water permeation no matter how technologically sophisticated. The next step entails the link-up between said water molecules and small clusters of water-soluble materials in the skincoat. This evil alliance then forms or fills pockets in the skincoat with an acidic solution that features molecules too large to go back through the gelcoat and return to the water. Osmosis (the tendency of a solvent to pass through a semipermeable membrane into a solution of higher concentration so as to equalize concentrations on both sides of the membrane) cranks up, with more water molecules moving into the pockets through the gelcoat in an attempt to dilute the highly concentrated acidic solution within them. Eventually the pockets bulge, blisters form, and a repetitive process begins that if left unchecked can ultimately hydrolize or "corrode" a laminate severely and do structural damage.

Fortunately the marine scene's changed lots since the '80's. Many of the root causes of blistering pointed out by Rockett, Rose, and others have since been addressed by boat and chemical manufacturers. Highly water-resistant, uniformly blended vinylester resins have replaced cheaper general-purpose polyesters in skincoats. Lamination techniques have been refined and standardized. Control of on-site working temperatures, humidity levels, cleanliness, wet-out procedures, catalyzation rates, and other critical aspects of skin-coat layup have been generally improved. And barrier coats have been developed that all but nix osmosis. So fortunately boat-bottom blistering today has all but faded from the scene, with only a comparatively few new boats evincing problems. Indeed, according to Greg Davis, chairman of the Yachts and Small Craft Technical Committee of the National Association of Marine Surveyors (NAMS), the only serious blister problem NAMS surveyors have dealt with over the past 15 or so years occurred in a vessel built in the late '90's. "And we're talkin' over 50,000 surveys conducted on all kinds of vessels across the country," he adds.

Such glad tidings would leave owners of vintage vessels like me feeling just a tad left out if it weren't for savvy guys like my surveyor. Undeterred by my lingering blister-related anxieties, Wise suggested an up-to-date bottom-repair job as well as a solid and reputable craftsman to do it, Mark Lenox of Lenox Company in Sudlersville, Maryland.

I did some checking. At the time Lenox had been in the business of blister and bottom repair in Maryland for more than 20 years, and his list of satisfied customers was lengthy, with folks taking ailing boats to him from as far away as Florida. Moreover, Lenox's company offered a written, ten-year warranty.

The five-month repair job took place in a large, climate-controlled tent at Duffy Creek Marina on Maryland's Eastern Shore and cost $10,000, a sum the seller helped absorb. After first abrading the bottom of my boat in spots with a power grinder to accurately profile the depth and degree of blister damage, Lenox peeled approximately 1⁄4 inch of infected fiberglass down to hard, solid laminate with an electric peeling machine and a sand blaster. Then he let the laminate dry for a month or so, thereby releasing most of the water remaining inside. Next came reglassing the entire bottom with 1.5-ounce mat, some roving here and there, and lots of vinylester resin, a material that's only slightly less resistant to water than epoxy but much more compatible with the polyesters used throughout most '80's laminates. Then finally, after adding six layers of pure vinylester resin as a barrier coat, Lenox applied isophtalic gelcoat and two layers of bottom paint.

The result? I recently had my boat hauled at a boatyard in North Florida for an antifouling renewal. Once she was cleaned and awaiting fresh paint, her bottom looked as smooth and solid as it had in Lenox's tent in Maryland. There wasn't even a hint of a blister!

Is this a validation of modern repair techniques for what consitutes the last bastion of the dreaded boat pox: older vessels, mostly built in the '80's? Not by a long shot—blisters can sometimes take ages to reappear based on any number of factors, among them gelcoat thickness, immersion time, salinity levels, opeating stresses, and ambient water temperatures.

Is it a groovy, confidence-inspiring development, though? Yes indeed, especially since my pride and joy's bottom has been immersed for almost two years now without incident.

New-Boat Blister Blues

According to surveyors I talked with while researching this story, bottom blisters can and sometimes do pop up on new boats. Such problems typically arise from poor manufacturing practices (lack of cleanliness, uneven resin catalyzation, sloppy roll-out procedures, etc.) typically centering on skincoat layup.

Blistering in new boats is admittedly a rare problem, but according to Capt. Ric Corley, a long-time marine surveyor in Destin, Florida, owners should still keep an eye peeled during haulouts. "If you see one or two blisters, don't freak out," he adds. "Simply continue to haul every year, keep track of the darn things by taking pictures for comparison's sake in the future, and if your blisters seem to be increasing in number and/or size, have them ground out and filled immediately by a reputable repair guy or repair facility."

Of course, Capt. Corley is not talking about a serious case of boat pox here, with literally hundreds of comparatively large blisters. Such vexations typify older vessels and can be addressed in the manner described in the main story.—B.P.

This article originally appeared in the April 2008 issue of Power & Motoryacht magazine.