What is deck coring under the mast step?

[roythomas]

I really want to know if the coring between the mast step and compression post is balsa. Considering the constant pressure at that one point I would be surprised if it were balsa but what do I know. My education is not in marine engineering.

[ebb]

I can confirm it is there on A338.

But had to replace it because it had gotten soggy. The clue finally was:
I noticed that the deck was flattened under the step. Checked it out
with a batten.
When Pearson drilled the holes thru the middle of the mast-base fitting
and mast step for electric wires, they forgot to seal the hole....Among
other things. Fresh water got in, which rots wood. A compsite with 1/4"
or more top layer fiberglass, with 3/8" vertical grain balsa, and another
1/8" interior glass, molded into a well-arched curve... has 100 times the
resistance of plain balsa, or foam, to a point load. Of course, if there is
failure, it's going to be under the mast where stays and shrouds are
always pulling the spar into the accommodation. Believe a balsa core
frp laminate is less prone to delamination than some other composites.
The endgrain wood soaks up resin and really bonds the glass layers into
a cohesive panel.

Fixed it by cutting out a holesaw rounded corner rectangle, with a Skill 6"
cutoff saw, blade set a little under 1/2" so as not to cut thru the deck,
not to cut thru the bottom glass laminate. Lite tapping on the deck told
almost where to draw the lines for cutting. Found mostly dry balsa.
Where it was dry and still attached to the glass it was a bear to remove
Started to dig out about 1/2" deep around the inside of the tray with a
bent nail in the drill. Crude, and for me a bad idea. Actually a 3/8" wood
chisel as a scoop was far easier and cleaner. This groove and the chamfer
around the shallow tray will make the repair successful. (Bulkhead and
strongback upgrade inside A338 now guarantees refusal to any movement.)

Feathered the top edges with a Makita angle grinder back about 1 1/2"
from the cavity. A338's cabintop is about 1/4" thick. Filled it with 24oz
Xmatt and 100% solids epoxy. Layerd in 10&6oz fabric over the chamfer.

Used a bending batten to get close to the original cabin top curve, and
noticed that after all these years the pressed-in top nearly returned to a
fair original curve. Used WestSystem 407 fairing compound (but not their
epoxy) to finish off to perfection. Pretty much ignored the gel coat because
I planned on painting the topsides.
If your circular laminated phenolic ply maststep is in good shape, the one
I had was curved perfectly to the curve of the new cabin top. Lucked out!

Believe your Commander maststep is different than Ariel. So before starting
repair to the deck by digging into it as above, check how your compression
post is. I'm unfamiliar with Commanders. Would check with battens how
fair the cabin top is inside. It would have had to be perfect when leaving the
factory. Has to be fairly easy with straight edges and bending battens. Will
show flat areas or unsymmetrical hollows or bulges. You can make doorskin
arch edge patterns to check where you want to end up outside.
A hard thin pattern like that can also be used to pull wet fairing material
across a surface...at least once!!... which will cut sanding to a minimum.

Checked fairness inside A338 with a batten, as the mast is off set a little from
the oak strongback running along the bulkhead. This strongback and bulkhead
is another problem in most Ariels. If you have to remove your strongback
for any reason, you'll find some other Pearson surprises. I'm not sure you
have a strongback in the Commander, if not, it'll make it easier to check how
fair the curves are inside BEFORE you dig the rotten balsa out from the top.

Pearson, at the factory, when they drilled holes thru deck and cabin did not
seal them. Some boats have had to replace the balsa on the whole deck
back to the coamings. Luckily, I found the only balsa rot on A338 under the
mast. Cabin top has quick drainage and few gear fastenings.
Except for those crazy holes under the mast. They probably provided bedding
under the step, thinking that was the only way water gets in. But, imco, they
forgot about the main sheave at mast top, where wind and water enters!
You know, not much... but 50years?

Clint Pearson probably never imagined his Ariels and Commanders would still
be around this long ! !! !!!