If you are unfamiliar with Epoxy or polyester resins than let me briefly introduce you to  what they do and what they are.  Polyester resin is the stuff most boat hulls are made of these days.  A mold is made in the shape of the outside of the hull and in one of several ways, a mixture we refer to in general as fiberglass is formed into the shapes we dream of as boats.  The deck and inner linings are made in the same fashion.  We call any combination of resin, and structure, fiberglass, however, that's incorrect.  Other combinations may create what should be referred to as Epoxy glass, or carbon Epoxy, etcetera.. There are many types of polyester resins and an overwhelming number of epoxy resins on the market.  It is important to know a couple of the types of polyester resins that are probably in your boat.  First off is the gel coat.  This resin is the smooth colored finish you see on the outside of your hull.  It contains a´ large amount of wax that allows the polyester resin to fully cure.  Left to open air, polyester resins often stays sticky.  Next up is laminating resin.  This resin is the main structure of your hull and would be worthless without the fibers added to it.  These fibers and the way they are laminated make the difference between great ocean-going vessels and flimsy low priced intercostal cruising clones.  Hand laid sheets of woven polyester fiber cloth, that were laminated to complete saturation, with the exact amount of catalyst for the temperature, and worked until there were absolutely no bubbles, using high density resins make the strongest hulls with the lowest chance of delaminating.  Boats that use a chopper gun to spray a combination of resin and chopped up matting into a mold yield the cheapest most likely to blister, you can keep it, type of hull.  Mat can also be hand laid.  Woven cloth can be poorly laminated and vacuum seals can press things into shape.  In the long run, the most work yields the best product.  The old boats, like those out of Jensen mar Marine in Costa Mesa mesa such as Cal, Ranger, etcetera, still get the most respect from me.  You can tell the difference by looking in a locker or in the bilge to what the pattern in the mix looks like. (matting or chopper gun on left and woven cloth on the right)

Epoxy resins are newer, lighter, stronger resins and come at a much higher price tag.  Epoxy is easier to work with and often more resistant to chemicals.  They harden in different times depending on the hardener used,  there by making them more versatile. They dry with out leaving a sticky finish, and best of all, they  penetrate much deeper than polyesters so they can saturate the inside of wood as opposed to polyesters barley sticking to the outside when laminating wood. 

Epoxy can be mixed with all kinds of powder to make all kinds of putty.  I've used everything from silica powder that is stronger than  *^#~+*#!!! ,  to Baby powder or corn starch that is strong but makes a fantastic sanding or faring compound.  The trick is to make the putty into the right consistency for the job, usually that means a paste about the consistency of peanut butter.  Epoxy will harden nicely over the top of polyester resin but polyesters will not cure over epoxy.  The molecular structure of epoxy lets it cling tenaciously to just about anything, in fact.  It is so trust worthy that I never use polyesters any more. 

Before you get started using epoxy you should become familiar with the safety tips provided by the manufacturer.  Respirators are a heath choice as are gloves and goggles.  As long as the epoxy is still wet, you can clean it up with white vinegar.  Do not kill your self with acetone because it does not come close to vinegar. 

Here are a few simple project that use epoxy to up-grade your boat.

Try saving a few bucks on you next air conditioning or refrigeration job by making your own ducking instead of buying the factory pieces for some enormous amount. First,  you have to take a cardboard box and cut it to shape or just cut out pieces that will make the shape you want.  Tape the pieces together and ad pins if you have any.  Prepare a surface to laminate on and start painting on the epoxy.  Let the outside harden and then laminate the inside.  You have just made an epoxy board duct would have cost a bundle and you did it for pennies.  Connect it  with duct tape (probably the first time you will ever use duct tape for what it was made for).

Would you like to install a transom mounted depth sounder inside your fiberglass boat like the through hull type without punching a hole in your boat?  The depth sounder companies know all about this way of installation but can not tell you about it because it reduces the sensitivity of their machines a little. (My sounder that cost $99 in 1992 and  promised a depth range of 400 feet rarely gives me a signal past 280 feet).  First, you have to select a location for both the transducer and the unit in a way that avoids wiring such as VHS antennas and alternators.  The transducer can shoot strait though fiberglass as long as there are not a lot of air bubbles in the glass.  If you put the transducer near the center of the boat a false echo can occur, especially in shallow water, when the signal bounces of the keel of shaft of your boat.  Prepare the surface by cleaning it and washing it off with acetone of some other cleaner that does not leave a residue.  Mix about five or six ounces of epoxy in a small cup.  Mix in what you plan on using as structure, such as baby powder, and do not be surprised at how much powder seems to fit in that cup before the mix starts to get thick.  Then,d form a box with walls about two to three inches tall and about a half inch to one inch wider on all sides than the transducer.  do not make a floor in the box.  Baby sit your box until it stiffens up or you will come back to a potato chip.  After your box hardens, Place the transducer in it and mix up a clear batch of epoxy.  Mix enough to fill the void around, under and up to the top of the transducer.  The epoxy will seep down into most of the air pockets and some of the air bubbles on poorly laid boats.  I have seen many boats rigged this way and they all have had positive results.

Non-skid decks have been known to become very slippery after they get painted.  To counteract the slipperiness of my decks I made epoxy non-skid for the side decks.  I used powdered non-skid for the foredeck because I did not want to kneel on a rough surface. 

For the shape of the non-skid I wanted, I used plastic fluorescent light covers with the diamond shaped pattern.  I had to look around awhile for the pattern that was sunken in and not lifted up.  The difference is that if you use a lifted up pattern as your mold, your casting will be sunken in and will collect water and every bit of dirt and scum that comes in contact with it.  I used cloth for support and an epoxy putty to adhere the mats to my decks when finished. 

Here is how I did it.  After finding the plastic covers, I lined them up and taped them together on the back.  I laid them down on a sheet of plastic  to catch any spills.  I sprayed them with a releasing agent,  which in this case was a can of Pam.  I mixed up a big batch of epoxy and mixed in a little silica for strength (not so much as to keep the epoxy from flowing easily).  I pored the epoxy in to the mold and laid on a piece of 2 ounce cloth  for strength and allowed the excess epoxy to wick up into the cloth.  Before the epoxy hardened,  but after it started to cure, I lifted the sheets and cut them into the correct shape to be fitted on my side deck and attached them quickly with epoxy putty.  That is a mouthful and needs to be planned out well in advance or you will be trying it more that one time, I promise.  The putty under the newly formed non-skid will ooze out as you press the non-skid down and into shape.  What oozes out should be smoothed out along the edge of the non-skid with a wood stick.  Form it into a bead and the smooth it like caulking leaving a little to be sanded off later.  If you use baby powder to make your putty, it will sand off easily and make a nice finish.  Before you paint your decks, wash the new surface with a scrub pad and an abrasive cleaner to take the oil film off.

A common problem with boats seeing a lot of action is bulkhead tabbing separation.  Rebuilding the tabbing is not that big of a job if you use epoxy.  If you can get access to the edge of the bulkhead then you need only lightly sand and clean it, and lay up a new piece of cloth.  Fiberglass cloth also comes as tape and rope.  Pins and masking tape help a lot with this project.  If you suspect you need tabbing repair you should get on it before other permanent damage happens to your boat.

One quick last project I want to mention is actually and additive to other projects.  The next time you want to permanently screw something down, try dipping your screws in epoxy.  the holding strength goes up incredibly and if you need to you can still get the screws out, it is just a bit harder.