Wet Rudder Repair
My friend Chris bought a 33' fiberglass sailboat, a Cal 33, to use as his family cruiser. Because it was an older boat, he knew he had a few projects ahead—including drying out the rudder. Here in Michigan, we haul our boats out of the water for the winter and it gives us a chance to do repairs and inspect under the waterline.
After hauling out the boat and storing it in the barn for the winter, Chris asked me to advise him on repairing the rudder.
We found two smaller delaminated spots on one side of the rudder and a sizeable one on the other, along with a 6" crack near the rudder shaft. After drilling a few ⅜" drainage holes through the fiberglass skin and into the foam core, we saw that it was still in good shape even though the foam was wet.
A Temporary Fix
With the boat already in the barn and not blocked high enough for us to remove the rudder, we made a plan to do a temporary fix to get through the next sailing season, then could wait until the next fall to complete permanent repairs.
Over that winter, I had Chris use heat lamps whenever he was at the boat in order to help dry the rudder as much as possible. In the spring, we chamfered the ⅜" drainage holes and sanded the chamfer with 80-grit sandpaper. We then filled the holes with WEST SYSTEM® Six10® Thickened Epoxy Adhesive and smoothed it with an 808 Plastic Spreader. The next day, we sanded the cured epoxy and painted the rudder.
Getting the rudder completely dry was not the plan because we knew it would absorb more water over the summer, but we did it to prevent further damage during the winter freeze. Rudders can hold enough water to make them crack open from the ice expansion in cold weather.
Identifying Delaminated Areas
The next fall we took the rudder off the boat and brought it into the Gougeon tech shop. First, we sounded out the areas of delamination. For this high-tech operation, we used the handle end of a screwdriver and a felt tip marker to mark delaminated areas. I followed the marker lines to cut and remove the delaminated fiberglass skin with an oscillating saw. I also drilled out some of the drying holes we’d temporarily filled to get through the summer sailing season.
The rudder was wet, but not as bad as I thought it would be. It still had water in it, but it wasn’t running out like it had the year before.
Drying Out the Rudder
The most basic way to dry out a rudder is to drill a hole in the bottom and let gravity do its job. This works well for draining most of the water and should reduce moisture content enough to prevent ice from cracking the rudder open during the cold months. If you store the boat outdoors, a good method to dry the rudder is to tape a black plastic bag over the rudder. On sunny days this will increase the temperature of the rudder to help it dry. This works great in temperatures around 25°F (-3.8°C). The added heat brings the wet rudder above freezing to provide it with extra days of drying.
Taking the rudder off the boat and bringing it into a temperature-controlled environment, like a basement or heated workshop, is another good way to dry it out. Warm, dry air will help the moisture evaporate. If there is damage or delamination to be repaired, remove the fiberglass skin to expose the foam core. The more exposed the core is, the faster the rudder will dry. A heat lamp warming the area will also help.
The most efficient way to dry a rudder is to vacuum bag it. This works best with the rudder off the boat and placed in a controlled environment. This is how I dried Chris’s rudder. At a vacuum pressure of 29 inches of mercury (Hg), water boils at only 76°F (24°C). This lets you boil the water out of the rudder without causing damage from excessive heat. It still takes some time, and I had to open the vacuum bag (which is like a big envelope) to dry out the breather fabric a couple of times. After the bulk of the water was out of the rudder, I added a heat lamp because our shop was at 72°F (22°C) and I was only pulling a vacuum of 27
Hg. At 27 inches Hg, the boiling point moves up to about 120°F (49°C), which is still cool enough to prevent damaging the rudder laminate. Drying the rudder this way removed all but the last little bit of moisture. For more about vacuum bagging, see “Vacuum Bagging Basics” by Rachael Geerts in Epoxyworks 49.
The moisture meter indicated the bottom of the rudder was still wet, so I removed some of the fiberglass in areas where the readings were still high. It turned out that the high moisture readings were from the laminate. The foam core was now mostly dried. Ideally, I’d want the moisture meter to read 0 but a reading anywhere in the green is good.
I didn’t remove the bottom paint and what looked like one coat of VC Tar2TM osmosis protection primer before trying to dry the rudder. When I did sand down to the gel coat, I found that the rudder had a few gel coat blisters, which we would need to sand open and fill with thickened epoxy after the laminate was dried. This would account for the moisture reading in the laminate.
With the rudder dry, it was time to put it back together. In some cases, you can reuse fiberglass skin that was previously removed. We outline this procedure in our Fiberglass Boat Repair
& Maintenance manual in section 5.2.1 “Re-bonding the skin.” However, the skin I’d removed from Chris’s rudder was deformed and couldn’t be saved, so I had to replace the fiberglass laminate.
Replacing the Fiberglass Laminate
In order to calculate the thickness of the fiberglass replacement laminate, we first needed to measure the original laminate thickness. Grinding back the fiberglass that was still attached to the rudder allowed us to count the number of layers. We measured the laminate with vernier calipers and it was 0.070" (0.0625" is 1/16"). Taking off a little for the gelcoat makes it an easy number to work with.
For a typical fiberglass repair, you taper back the existing fiberglass 12 times the thickness (12:1 taper). In this case, the 1/16" would be 12/16" (¾") all the way around. It’s not a bad idea to taper more than 12 times on thin skin laminates. You want a nice even taper over ¾".
Determining the Number of Fiberglass Layers
Once we knew the laminate thickness, we had to determine how to match that thickness for our laminate repair. How many layers of a given weight of fiberglass would we need?
It’s not surprising that different weights of fiberglass cloth have different thicknesses. But even the same weight of fiberglass can vary in thickness depending on the amount of epoxy applied to the cloth.
For example, saturated or laminated, 10 oz. fiberglass can range from 0.0014" to 0.0019" thick. The range in thickness adds a degree of difficulty to calculating the number of layers of fiberglass required to match the thickness of an existing laminate. For example, 10 oz. fiberglass that’s 0.0014" would reach a laminate thickness of 0.056" with four layers.
But if the 10 oz. fiberglass you had on hand was actually 0.0019" thick, it would reach a total thickness of 0.057" with only three layers laminated.
Using fabric weight alone to determine the number of layers means estimating the repair laminate thickness. The result may be a laminate that’s too thin, requiring you to buy and apply additional fiberglass. Or the laminate could be too thick and need to be sanded down, turning the epoxy and fiberglass you paid for into sanding dust, not to mention the “fun” of sanding fiberglass.
The method I used to determine the fiberglass weight and layers is simpler and more reliable. I made a laminate thickness gauge.