prevent roting during winter

Question
QUESTION: No matter how dry my boat is when I take it to storage in Fall, by next Spring I will have some of the plywood floor rotten and a big job patching it with fiberglass. Is there a fungus killer I can spray or leave in the bilge of my 17' I/O during winter to kill those wood eating microscopic bugs? The hull is fiberglass so I am safe there, or am I? (the transom is wood wrapped in fiberglass, thus risking being eaten too). Thanks.


ANSWER: Hi Ever...thank you for selecting the undersigned to reply to your question.

It would have been helpful to know the yr., make, and model of the boat. However, the fact that it is fibergalss, I will presume it is also an older vessel, primarily because of the dry rot that is occurring.

In most cases, dry rot occurs from moisture that builds up during winter layup. Fall/spring warm day and cold evening temperatures create moisture to build up within the boat, especially when it is shrink wrapped and there is no ventilation whatsoever. Osmosis is another source for dry rot to occur. Gel coat, which is the exterior finnish, is permeable, and water can and will seep through it and into the fiberglass laminates, which separate when the moisture within freezes and expands.

In the event you've had an expert scan the hull and stringers with a moisture meter, and its been determined there is an exceptional amount of moisture within the hull, there's a strong likelihood repairs will be futile and uneconomical. Salvage what you can, if you so wish, sell off what is useful, then consider purchasing another boat with appropriate assistance and guidance from a qualified and reliable marine surveyor.

Safe Boating
Ron

---------- FOLLOW-UP ----------

QUESTION: Thanks for the quick answer. The boat is a 1995 Starcraft 1710 (17 ft) with a Mercruiser 3.0L, all in pristine condition except for the floor forward of the front seats, around the opening leading to the floor storage between the front seats. I have not measured moisture in the hull and stringers but I know is low because the boat sits on my driveway from April to October covered by a standard boat cover (not water tight). The boat is used in a lake or river on weekends only for a few hrs a week; I remove the plug on the transom so rainwater that manages to go through the tarp can drip off. From October to April it is stored in a warehouse without heat but otherwise well insulated. My problem is that the floor is made of plywood. I have replaced parts of it only to find it rot around the patches I made. Should I replace the entire floor? and if I do, what material should I use?

Answer
Hello again Ever...and thanks for clarifying a few aspects.

I'm surprised to hear a 13yr. old starcraft would have such a problem. Perhaps the plywood is not marine grade, meaning the glue that secures each laminate is not waterproof and permits delamination due to absorption of moisture or maybe the plywood wasn't dry when encased in fiberglassed.

Whatever the circumstance, replace the entire floor with a marine grade plywood that is properly cured/dry, then apply one layer of matt top and bottom. When resecuring the plywood to the stringers and framing, pre-drill a small hole, then insert an epoxy or silicone sealant into the hole, and don't forget to put some on the screw.

Dependant upon the type of floor covering used, it can and will retain moisture, which will promote dry rot. Never staple or use screws to secure the floor covering material. Always use a marine grade waterproof glue.

All of the above work should be undertaken when the temperature ranges around 70F and make certain the work area is well ventilated.

Safe Boating
Ron