preventing floor rot, how does water get under the deck anyway?

[tfret]

I'm planning a floor job and really want to get it right. I plan to go the extra mile by installing drainage channels and holes so that any water below deck will ultimately end up at the bilge and keep the under deck dry. I may even install a ventilation system to flow air through those channels. The floor I just removed was completely rotted and the foam was pretty wet on the bottom. The deck appeared to have rotted from the bottom side up. The top of the deck was glassed well. So I guess I'm a bit puzzeled as to how all that water got under the deck to begin with? Is this the result of years of condensation? It seems that rain or water from swimmers would simply lay on top of the deck and evaporate, or flow back to the bilge. I'm just trying to understand the source of this water so I can better eliminate it.

 

[Bondo]

Re: preventing floor rot, how does water get under the deck anyway?

It seems that rain or water from swimmers would simply lay on top of the deck and evaporate, or flow back to the bilge. I'm just trying to understand the source of this water so I can better eliminate it.

Ayuh,... Generally speakin',....
There's usually passages from the bilge, that you pump, 'n the bilge that's Under the deck...

If there's pumpable water in the open bilge area,...
There's also water under the deck, forward as far as the water level carries...

Boats Live in the water, they get wet...

Drainage with limber holes is Critical to the longevity of the hull...
Ventilating is probably Overkill...

Sealin' the underside of the deck is a debatable pay-back....

 

[oops!]

Re: preventing floor rot, how does water get under the deck anyway?

deck rot is caused by several issues....

first off....a properly foamed deck will not condensate......as there is no air space below the deck for water vapour to collect to.

however,,, a deck that is not fully filled with foam will condensate. The foamed areas, are totally enclosed...so there is no way for the vapor to evaporate.

The second and most common way for a hull to get water intrusion....Is from a hull penetration or thru hull fittings that are not properly sealed.

There is also always the chance of bilge or locker water getting thru a bad laminate between the hull stringer or an improper transom fitting.



The best way to ensure deck longevity is to fully encapsulate the deck in fiberglass...underside and over.....and make sure all screws to hold the deck down are pre drilled...injected with 5200, and then screwed and glassed over.

As far as air circulation below deck......it is a good idea.....but that also means the water can get into the area....so you must protect form it.
my school of thinking is to believe that water is supposed to be under the deck and build with proper drainage below.

In the link in my sig......and at the bottom if the index......is a way to foam a hull, leaving air passages and water drainage, with out worry of waterlogged foam.

However, a properly encapsulated deck...using standard build methods and care....will last 40 plus years.