R 22

Rhodes 22



When my surveyor explained to me the significance of the blisters below the waterline of my '90 Seaward Fox, I think I was too excited about buying the boat to even pay attention; he gave the boat an unequivocal "thumbs up", and that's all I needed to know. However, I do think blistering and gelcoat delamination can be a serious problem if not treated properly. That being said, I thought I'd forward a blister explanation to the Seaward list. For those of you who own 80s/early 90s Seawards that have been consistently slipped in water, it might explain a thing or two. (Special thanks to Bob Proctor of the S2 6.7 and 6.9 owners' who wrote the article.)

"Blisters" that occur below the waterline of fiberglass boats are craters in the resin that vary from the size of a grain of rice to about the size of a manís glove. The craters are sometimes referred to as "osmotic blisters" and as being formed by osmosis. Biologically, osmosis refers to the movement of a liquid through a semi-permeable membrane to achieve equal concentrations on both sides of the membrane. Semi-permeable means the membrane allows certain solutions to pass through it but other solutions cannot pass.

Dried prunes, for example, have a skin (membrane) through which water can pass in but the sugars inside the skin, even when dissolved in water, cannot pass out. When the prune is put in water, it swells as the water outside goes through the skin "trying to achieve" an equal concentration of water on both sides; the prune gets juicier and plumper. But if we put the dried prune in a sugar syrup, no liquid passes through the semi-permeable skin; it wonít allow sugar solutions to go through. You donít have (as youíll see) water passing through the boatís hull, so principles other than osmosis are really involved. But just as you sometimes figuratively use osmosis to refer to a gradual, diffuse process (as in "he learned by osmosis"), so itís also used non-technically in this case.

Fiberglass (FG) hulls get almost all their strength from their glass fibers. A resin is used to bind and hold these fibers in the desired shapes (hull, cabin, etc.) and to provide a smooth exterior and colored finish (gelcoat) on the FG. Until sometime in the 1980s, the resin that was typically used for all FG marine construction was a polyester resin. It was originally thought that FG hulls constructed with polyester resin as the binder to the FG (i.e., cloth, mat, and/or chopped FG) were as impervious to water as is a steel hull. But after about twenty years experience and the industryís discovery of the "blister" or "osmosis" problem, it was found that FG hulls are NOT impervious to water, they are just "relatively impervious".

When there is long term immersion, water very slowly seeps into the material but itís at such a very slow rate that FG hulls can be considered waterproof for all monthly or seasonal purposes. As water migrates in, it sometimes chemically reacts with the polyester resin under the surface to form an acid (liquid) in various size globules. The resin binder has dissolved in those spots in reaction with the water. The acid may further dissolve intact resin that it touches. Many of these globules eventually grow large enough and close enough to the surface that they break through the gelcoat. These are the blisters that are typically found on the outer surface of the boatís hull below the waterline. They are usually within the gelcoat and resin layers down to the layers of structural glass (cloth, mat, chopped FG).

Blisters can also form on the inner surface of the hull if that region is exposed to prolonged water. And on a few boats, blisters have been found to have penetrated even farther, into the structural FG of the hull itself, although fortunately, that seems more rare.

There may be many factors that determine when and where blisters will form. The one that Iíve commonly heard of that promotes blistering is the contamination of the polyester resin by dust and other chemicals. When the polyester resin and all FG is kept meticulously clean, almost surgically sterile, during building, less blistering-- or none--occurs. Any contamination apparently supports the formation of the acid.

In the early days of boat production with FG, this was unknown. This contamination theory is one explanation of why some boats of a particular model may have much blistering while others may have little. For example, if the bolts of FG cloth or mat came fresh out of the box just before layup, there may be few blisters; but if portions of cloth picked up shop dust before layup, then where the resin came in contact with it on the FG, there may be many blisters.

Other factors also encourage blistering. Long-term immersion is an important factor; the less time in the water, the less opportunity for blisters to form. Mooring in warmer waters seems to increase blistering, colder water to retard it. Fresh water is said to foster blister formation more than salt water. As older FG boats accumulated years (time) immersed in water, the FG marine industry gradually became more aware that there was a widespread, generic blistering problem and it was not, as first reported, isolated among just a few boats or brands. This awareness slowly dawned mainly in the late 70s and early 80s.

This was an issue affecting boats moored in the water-- larger sailboats and powerboats. The thousands of smaller, trailered boats didnít show the symptoms. It also greatly affected the chemical and FG industrial suppliers and, of course, builders and dealers of larger boats. Happily, some vinylester and epoxy resins were found that were suitable for marine FG fabrication and that were also much more water resistant than polyester resin. However, those alternative resins were also more expensive and were limited in their capacity to bond to other plastic resins.

A number of companies revised their manufacturing techniques and switched from using polyester resin to vinylester or epoxy resins for building their hulls. Since prolonged immersion was necessary to produce blisters, typically the industry has continued to use polyester resin for molding smaller boats and those parts that wonít be continually in the water.

Boats with hulls made with polyester resin that will be wet slipped (moored in the water) should have a barrier coat of epoxy (or other suitable water resistant material) applied to the bare hull before the usual bottom painting. The hull should first be suitably dried and any blisters properly repaired.

The following references will give some information about repairing:


The company below is still in business and while their info doesnít seem to me to be quite as knowledgeable or well written as Osmocureís was, itís still worthwhile:


And thereís also a book about blisters (~ $20) that I havenít seen, but itís described at:


For a credible discussion of hull blistering go here:


Bill Sparhawk
Spokane, WA
Sailing Lake Pen díOreille, Idaho

It's been a long time since I posted a question to the Rhodes list, but a discussion about blisters, delams and "osmosis" in used boats on another list to which I subscribe has made me a bit uneasy. Needless to say, the topic generated a lot of discussion. My understanding is that prior to the early '80s, the boatbuilding industry used polyester resin extensively (I think vinylester may be used now, but I'm not sure.) Hulls that were produced too quickly--i.e., mass produced, and cored hulls in particular--did not have the resin cure properly, and that lead to voids and acid production when water infiltration occurred. The end result is blisters and delaminations. The folks at gbi address this on the website, where it says that only two owners of R22s have reported any blistering. Given that R22 hulls are solid and not cored, and that a LOT of care and time is taken in the lay-up of the hull, I guess that I shouldn't be suprized that only two owners have reported any problems.

So...my questions to your collective wisdom, and mostly to those of you who have recycled R22s:

  • 1. Have you ever had a blister problem?
  • 2. If so, how were the repairs done, and how costly were they?
  • 3. What type of resin was used in the R22 around '85-'90 (& should it even matter to me)?

I hope to ask Elton about this on Saturday at Strictly Sail when I see him. I don't remember that this topic has come up in the time I have been a list subscriber, and I am really quite interested in it. Thanks for your help!

Dave Scupham
29 Jan 2001

I am the proud owner of one of the two boats with blister problems. The reason being, the previous owner did nothing to protect the fiberglass, not even an anti-fouling coating. My understanding is that fiberglass hulls without any coating were meant for dry sailing or boating, not to be left in the water. My boat has been in the water year around for almost eleven years. The correction isn't all that bad. A little time out of the water to dry once the blisters are cut off, repair the holes and two finish coats. One to protect the fiberglass and the other is an anti-fouling. Total cost I've been quoted is around $600.00. NOT BAD.

29 Jan 2001

We have a 1995 Rhodes and keep it in a fresh water lake here in sunny California from April to December. We also trailer to salt water locations for short trips of two to three weeks. We have found blisters on the hull and rudder when we pull the boat for the past 3 years. Not many but definitely there. Interestingly, the rudder had more then the hull this last Dec. We have not had any repairs done. The blisters tend to "fade" pretty quickly sitting out on the trailer.

Our previous boat was an O'Day 23. It was the first "big" boat we owned and we didn't recognize the blisters on the hull when we bought it in 1987. The bottom looked more like the paint job had gone bad or the boat had a bad case of chicken pox.

Sacramento, CA
02 Feb 2001

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