Friday, January 25, 2013

This Old Hull Update

Soft decks are a very common problem with old Lasers.  Over many years, the weight of the sailor in the middle of the deck leads to delamination of the sandwich structure.  Instead of a tightly bonded sandwich of fiberglass – foam – fiberglass, the top layer loses the bond with the foam.  This leaves the sailor supported by a 1/8” thick piece of fiberglass.  The affected area widens over time with the repeated flexing of the soft deck. 

Recently I have had two lasers suffering from this condition.  Rather than attempt to cut a hole in the cockpit sidewall, and grind out and rebuild the sandwich construction, I elected to use the epoxy injection method described in Eric’s This Old Hull.

Unlike Eric, I had no confidence that I could maintain air pressure in the hull for 24 hours.  I was using a pump designed to inflate water toys like ski tubes.  The nozzle fit quite well into the transom drain hole, but I had no way to keep it there except tape.  To control the pressure in the hull I taped over an inspection port and put small holes in the tape until the air pressure lifted the deck to flat, but no higher.  I didn’t trust this crude pressure control system for more that 2 – 3 hours, which dictated a much faster process than Eric used.

Instead of a slow cure hardener (all West System products), I used a fast cure hardener.  This meant I had to work a lot more rapidly.  I got a helper to double the rate at which the holes could be injected with epoxy.  I also used bigger holes, 1/8”, to get epoxy into the space faster.  I used several batches of epoxy (4 pumps of resin and 4 pumps of hardener per batch) and between mixing and injecting, the two of us were still racing the clock to beat the set up time of the epoxy.

I was repairing two boats on both sides so I had four tries to perfect my process, and I tried to learn something each time.  My primary concerns were making the process simple and straightforward and controlling things that affect the aesthetics of the finished product.  I tried hard to hide the repairs and avoid the machine gun bullet holes look.

First, I used a 2” x 2” rectangular grid because it was much easier to lay out and I thought it looked a little less distracting to the eye than Eric’s 60 degree grid.  On the first deck, I started by covering the entire area with masking tape and drawing on the tape.  I then drilled the holes through the masking tape.  Each time the depth stop on the drill bit hit the tape, it made a small tear in the tape.  I learned later that this meant that some epoxy got on the deck, undermining the masking process.  I also learned that until the tape comes off, you don’t really know how well it worked.  TAKE IT OFF BEFORE THE EPOXY IS SO HARD IT CAN’T BE REMOVED.

Aesthetically, it is very important to keep excess epoxy off the deck.  Much easier said than done.  I spent more time on this than on the rest of the process.

As a result of what I learned on the first try, I resolved to drill the holes first and then apply the tape that protects the deck from epoxy overflow.  I didn’t want to draw all over the deck, so I had to mask first, drill, remove the first tape and re-tape it.  Half way through this I realized I could make a template for the holes and save a lot of time and trouble.  This made a lot of sense with a second boat to fix.  After drilling the holes, I taped the entire area with blue painters’ tape.  I then punched holes in the tape.  Just like Eric did, I clamped pieces of wood into place to keep the deck from arching upward when air pressure was applied.

Lessons learned for the second side:
Hanging chads from the tape can get stuck in the epoxy and leave little blue marks in the holes.  Use standard masking tape.
When taking the tape off for a cleanup before the epoxy is cured, you have to work around the wood struts that hold the deck down.  Plan carefully where the wood is located in relation to tape strips and holes.
Clean-up is a painstaking operation if you want a clean deck.
If you can catch the epoxy at the stage where it is still rubbery, but not rigid, you can used a razor blade scraper to remove excess.  If there is a bump where a hole was filled, the scrapper cuts it off flush.  This is the perfect way to get the holes completely filled and absolutely flat.

I learned another good lesson when I went to West Marine for more resin and hardener: 
There is an additive for the epoxy which makes the color white.  It turns out that mixing the slightly yellow resin/hardener solution with white additive yields an almost perfect color match for off white decks.  When done well, the filled holes can be just about invisible.

Employing all the lessons learned so far, I advanced to side one of boat two.  In the universe’s unrelenting desire for me to learn new things, a new problem arose.  The process of putting epoxy in one hole, forcing the air out of the next hole until epoxy came out of that hole, broke down.  With several of the holes, the air never stopped coming, and, in fact, was a steady stream of perceptibly moving air. As I injected epoxy into these holes, air bubbled through the epoxy until the epoxy settled and disappeared.  There was a break somewhere between the pressurized hull and the bottom side of the sandwich.  This was undermining the ability of the pressure inside the hull to push up the bottom half of the sandwich and make a tight seal.   With no good solutions apparent, I had no choice but to keep filling the holes trying to fill as much of the void as possible.  This used a lot more epoxy and made the clean-up that much more tedious.  The next day the deck was firm, but a few holes still remained and had to be filled.

With some of the imperfections, I thought I would try gel coat to pretty up the filled holes.  There are three pitfalls to this.  It can be difficult to achieve a color match.  It is difficult to apply one drop of gel coat and achieve a not concave, not convex, but flat finish.  The scraper method of clean-up does not work at all.  When the gel coat is rubbery, it all comes off in a ball, and when it is firmer, the blade can’t cut through it.  Over all, I concluded that gel coat was more trouble than it was worth.  (Gel coat is required to prevent breakdown of the epoxy from ultraviolet light.  Because I keep my boats covered when not in use, I don’t think either I or the boat will live long enough for this to become a problem.)

Side two of boat two went smoothly.  When all was said and done, both boats have rock solid decks (at the cost of a couple of pounds of weight gain) and cosmetically acceptable scars, some better looking than others.

Standard masking tape, white epoxy additive, and using a razor blade scraper at the right time are the keys to getting the best look.


  1. Yarg, you have advanced the art! The deck in the last picture looks pristine. Great job!

    I would love to see a picture of a cross section of soft deck from a destroyed Laser if anyone has one. I wonder how much of the foam in the sandwich survives, or is it just powder.

  2. Looks great, I must admit that you do seemed to have perfected this! I agree the deck looks very smooth, you must have great patience, sir.

    First Class Sailing

  3. Is this blog dead, or what? No updates since January?