As previously stated, the most likely cause of a rotting bulkhead is water seeping in from the chain plates.
I recently replaced the main bulkhead (btw head and seating) in my 1970 E-35.
The bulkhead had rotted away at the chain plate and along the bottom where the shower sole is. I could stick my finger through the wood!
It is difficult to find the rotted areas because it is difficult to see the mid chainplates. These, which secure the mid and upper stays, are covered by "nicely varnished pieces of mahogany." ARG!!!
On the port side you can look at one side of the bulkhead from inside the head cabinet. You will get an idea how bad the rot is. Use an ice pick and push into the wood. Also, near where the bolts are that secure the plate to the bulkhead, you will notice that the bulkhead itself is "minimally" glassed in. This is, I think, A big flaw in design. The glass does not even cover enough of the bulkhead for the chain plate bolts to grab both wood and fiberglass. In fact the whole bulkhead was "tacked in" with fiberglass and not continuously glassed in.
On the Starboard side It is even harder to reach up and feal the back side of the chain plate bulkhead area. You have to reach up like a contortionist, through a dead space located above the "box" where your feet would be when you were lying in the stb. bunk. Then use the ice pick to probe around. At this point I just ripped out the "nicely varnished" wood cover. I did find some delamination here. Not lots of punky wood that your finger could go through. I plan to do a fix to this area soon. I will soak with Smiths penetrating epoxy (CPES) and then glass over the area. This should work well and be secure. I think this job will take about 8-15 hours.
Make sure to check the forward lowers too. They secure to the sides of the lockers in the head and stb. hanging locker. I have a bit of delamination here too.
As for the main bulkhead that I replaced. I hauled out at a great boat yard that could do the job if I had problems and would answer my questions (I had lots.) Svendsons in Alameda California.
The job went like this:
Pulled mast, and hauled boat out of water.
Dismantling of bulkhead: Took One full day (8am-7pm)
All tongue and groove siding out
seating against bulkhead out,
old bulkhead
compression post
Head cabinetry
Surface preparation (one full day)
grinding and chipping
cleaning up mess
Fabrication (Two and a half days)
templates
wood prep
Thinking a bunch (all night)
Fiberglass in bulkhead (One full day)
I paid the fiberglass guy at the yard to help me
with this step. I learned a bunch and the 2.5 hours
he helped was worth the $160
Assemble things back together.(One day)
compression post
fasteners
install chain plate
Big note: I still have to put back the seating area.
I plan to redesign it with more storage, new table
folding down from bulkhead, and sleeping area. Big
Job!!!
As mentioned earlier, do you really want to do this, or go sailing? I would rather be sailing a bit more than I am right now. But, I knew this boat had problems when I purchased it "salvaged" after a fire broke out inside. I paid little money for it and I was able to start sailing it with minimal work initially. Now that I am married and have children, safety concerns and cosmetics are beginning to become more important. I have put in a new engine, new full set of sails, dodger, and soon to come all new cushions. I am now wandering how much time and effort to put into this "salvaged boat." Perhaps selling it and buying something more suitable would be best. Ask yourself carefully ,(Off the boat), what you want to do with it right now, and in the future, also, what kind of maintenance you want. Good luck and let us know what comes from your visit to the boat.