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GELCOAT DAMAGE BELOW THE WATER LINE. How serious is this?When you pull your boat at the end of the season it is not uncommon to find chips, scratches and gouges below the water line. The question is do the repairs really require immediate attention, the short answer is yes but not right away. I will explain!
First lets cover why you would wait to complete the repair this time of year. When you hauled your boat out, the hull was and still is wet. Every hull has a moisture content or the amount of moisture the lamination has managed to pick up. Each hull will have picked up a percentage of moisture content over the years. In the case of a new boat the humidity may have been very high the day that they laid the fiberglass material in your boat, thus creating trapped moisture there from day one. Not to worry any thing below 6% is considered very dry. There is a tool to measure this level of moisture, (moisture meter). Surveyors love them, but half the time they are not calibrated right or the operator doesn't know how to read it correctly.(Moisture meters are a whole other topic we will get into later). In the winter weather conditions are dry after the freeze, dry cold air, this air will help dry out the damaged areas in preparation for your repair(s). Drying the hull will make for a higher quality repair! The dryer the repair area the more likely it is that the bond of the repair will be better and the gel coat patch will not become contaminated. So take advantage of the cold dry winter weather, let it dry out the damaged area.
So what's the big deal a couple of chips cant be that bad? There are two common trains of thought.
1- Fiber glass cannot rot
2- Fiber glass is water proof.
Both of these statements are incorrect. Fiberglass material can rot. This happens when the material gets so damp that mold and mildew starts to break down the mechanical bonds between the layers of material used to build up the thickness of your hull or deck. You can actually pull the black rotten fiber glass layers apart like a layer cake. Water will also break down the resin which surrounds the fiberglass strings in the material.( There is a tell tale sign that this is happening. The water in the material starts to smell like vinegar when you break through to these areas). This is called wicking, the water will break the resin down and actually flow up hill from the water line toward the deck and hull joint.
The second misinformation is that gel coat is water proof, it is not! As soon as you breach the resin rich surface, the gel coat can be penetrated by water and this causes damage such as blisters and high moisture content developing and spreading through the hull. (A foot note: When you sand the bottom of a boat in preparation for antifoul you are breaching the resin rich surface. There are several great sand less primers on the market, use these product instead of sanding. You will need to use the same brand of primer and paint. I have done over a hundred bottom paint jobs this way in the Pacific North West and it will work great provided all instructions are followed). Maintaining a resin rich and unbroken gel coat layer below the water line is very important to the life of your boat.
Back to the question, Yes these repairs below the water line are important to complete for the above mentioned reasons. Any repair work below the water line should be your priority, just remember that the outside of the hull is not the only area to the hull which can be chipped or damage. Boat owners often over look the inside of the hull in the bilges, damage in these areas have the same effect on the hull as exterior damage as the bilge usually always has water laying around in it. The hull will draw moisture from the inside or out. Damaged gel coat (referred to as base coat on the interior of the hull) can also lead to rot of structural components and water contaminating the floatation foam areas.
Where do these little chips and gouges come from? Well there is an answer for this. Most of the damage will come from haul out and launch. If you are using a trailer then you know how easy it can be to make an error in judgment and get on the trailer wrong and hit the trailer. If you are using a travel lift then little rubs and damage can occur. Areas that are exposed in most cases are the factory voids. These are areas where they did not roll out the material behind the gel coat very well and these areas have opened up. We refer to these areas as air voids, this type of damage is very common on edges of lifting strakes and hull steps where there are tight 90 degree edges that the material must try to lay in. Of course you may have ran over some debris that was just below the surface or hit the hull with fishing equipment such as down rigger weights. The most common damage to the hull, bar none is beaching damage. The boat owner will run the bow up onto the sand. Causing the gel coat on the keel to be sanded away leaving and exposed area of material along the very bottom of the boat, this area could be several feet long and several inches wide (if this is common practice for you consider a keel guard purchase or have an extra couple of layers of gel applied in this area).
While we are on the topic of hull damage and the importance of keeping the area below the water line in good repair, lets briefly touch on epoxy barrier coating. One of my pet peeves, an oversold expensive product that does work, yet is applied more times than not, for no reason at all. Barrier coats are designed to prevent moisture penetration, this makes sense for new boats that have not been in the water for years. Dry hulls definitely benefit from a barrier coat system. However keep in mind if it won't let water in, then it only makes sense that it won't let water out. So if you apply it to an older boat not only are you are trapping the moisture content in the hull, but you are eliminating the possibility of air drying over the off season. You can dry the fiberglass material out before you install the barrier. This will require stripping all of the gel coat from the waterline down (a massive undertaking), having a controlled environment and several days with heater pods to dry the material. ( Just ask Black Line in Sydney BC they are the very best at blister repairs). So it may make you feel better. But are you not throwing your money away by barrier coating an old hull? Just think about it! If you currently have a barrier coat then it is important to remember it too must be repaired if you have gel coat damage.
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