I would look for the source of the leak up higher. Handrails, ports, fittings, etc.
A moisture meter could be helpful in locating the source, by tracking areas of wet core.

From our good friend from Maine
[url]http://www.pbase.com/mainecruising/moisture_meter[/url]

I bought one of these a couple years ago and used it when tracking leaks and when we were looking at Catalina 36’s to buy. Very helpful in ruling out the toads.

I use a pinless meter (like the one you mentioned) for initial analysis and then confirm with a pin moisture meter. I have to drill two tiny holes to insert the pins, but it is WAY more accurate. You are now directly measuring water content as opposed to measuring a "proxy" for water content. Pinless meters are basically just glorified "stud finders" from what I've read and from my own experience.

Do you really need to know if the moisture content is 20.000% or 20% or 18% to 22%? either way you got a problem. Comparing a known good site to a suspect area is an effective use of this type of meter, which is based on capacitance that changes with the moisture content. It is very easy to quickly ascertain if a boat has chain plate leaks, track leaks etc. with this type of meter.

Most boat sellers and owners would probably frown on having test holes drilled in their boats. It is not like we are measuring kiln dried lumber for a fine wood working project. We are interested in discovering if there is excessive moisture in a plywood or balsa core.

I'm just going to interject a thought here;
Does your intake for the head have a anti-syphon vent loop in this cabinet? Is the water of salt content or fresh. Perhaps this loop is the issue? Going from memory I believe I have two of these in that cabinet.

[QUOTE=VermontSailor;18371]Do you really need to know if the moisture content is 20.000% or 20% or 18% to 22%? either way you got a problem. Comparing a known good site to a suspect area is an effective use of this type of meter, which is based on capacitance that changes with the moisture content. It is very easy to quickly ascertain if a boat has chain plate leaks, track leaks etc. with this type of meter.

Most boat sellers and owners would probably frown on having test holes drilled in their boats. It is not like we are measuring kiln dried lumber for a fine wood working project. We are interested in discovering if there is excessive moisture in a plywood or balsa core.[/QUOTE]

Sorry but I don't agree about the first paragraph. Although I own and use both pinless and pin meters, the problem is that you can get COMPLETE false positives with pinless meters. I discovered this by googling and reading the various reviews of the meters and then trying it myself. It picks up metal and other odd solids within the deck core and such.

So I wouldn't reject a boat or start cutting just based on a pinless meter check, though I agree it's a good start, i.e. if the pinless shows all is ok then there is no need to go to the second step of drilling the holes to confirm. You can cover large areas quickly with a pinless which is a great advantage.

You are certainly right about the second paragraph, though once it's my own boat, I drill these TINY (almost invisible) holes and only on the inside where it does no harm. From time to time I run checks to see if any water has intruded (signif change in %).

I agree with you about the minor differences in percentages. Life is too short to focus on such. :-)

Is it possible that the hatch above the head is leaking and the water is running down under the top of the deck from there? Also, how about the port by the head?

Have you tried running water from a hose for a few minutes on suspected stantions, chain plates, etc. Start low and work your way up hill. I found the source of a leak in my aft cabin caused by a stantion that needed rebedding.