"engsol" wrote in message
...
Doug, thanks for your comments.

You may be correct re my being overly cautious.

My 'bible' is "Boatowner's Mechanical and Electrical Manual"
by Nigel Calder. He says on page 40 (2nd edition):
"The vent, (which leads outside, and *not* to interior boat spaces)
is at the top of the compartment, since the explosive hydrogen
gas given off during charging is lighter than air."

Just like the real Bible, any bible should be taken in the context of
reality.
Hydrogen gas is only explosive in high concentrations when
enough oxygen is present to provide an explosive mix. A reasonable vent
will allow the hydrogen to escape where it will escape quickly from the
interior
of the boat unless you have a really tight boat.

But later, on page 41 he states that a screen in the top of the
battery box lid is OK for ventilation. Later in the page, he quotes ABYC
to the extent: "There will be some form of a vent to allow
hydrogen to escape."

"Some sort of vent" is sufficent.

A quick google reveals (actually not much):
-------------------------------------------------------------------------------------
Code of Federal Regulations 33 183.420 Batteries:
A vent system or other means must be provided to permit
the discharge from the boat of hydrogen gas released by
the battery.

True.

"....excerpts from The American Boat and Yacht Council (ABYC) Standards
and recommended practices for small craft. E- 10 Storage batteries:
Battery boxes, whose cover forms a pocket over the battery, shall
be vented at the uppermost portion of the cover. For those of you
contemplating a serious offshore passage provide a means for
securing the top just in case things get upside down."

True. Not only the top, but the entire box. A heavy battery thrashing around
in
a boat that is rolling can be catastrophic. And also if you may get turned
upsidedown, liquid lead-acid batteries are the worst possible choice since
battery acid mixed with seawater liberates chlorine which is very nasty.

--------------------------------------------------------------------------------------

Given the vague "thou shalts" it probably boils down to the personal
hot-button of the boarding USCG Petty Officer.

The USCG is looking at PFDs, fire control, drugs, bells, horns, and not much
else.
Unless you are getting an official USCG certification for chartring, it
doesn't matter.
Matter of fact, Just venting the battery box in the normal way will suffice.

For the price of a few feet of hose...I think I'll vent it overboard.

Danger is that the vent hose may ship sal****er into the battery box. That
can make a more dangerous situation than the gas does.

My original question still stands....will silicone withstand battery acid?

Try an experiment and see.

Norm B


On Wed, 16 Mar 2005 19:22:23 -0500, "Doug Dotson"
dougdotson@NOSPAMcablespeedNOSPAMcom wrote:

I think you are being over cautious to the extreme. Sealing the lid of
battery box is unnessessary. Only containing spilled acid is really
necessary.
Venting overboard is also ovekill. Hydrogen will quickly dissipate if a
reasonable vent is installed. The cheapie thermometers may work well
if you can affix the probes to one of the battery terminals in a way
that has good thermal contact. But, your battery monitoring system should
be able to measure and display battery temperature.

Doug
s/v Callista

"engsol" wrote in message
. ..
I'm about to finish the new battery box. Just need to
put in restraints/hold-downs, and then epoxy the wood frames.
The three sides and bottom are fiberglass/gelcoat, i.e., part of
the boat. The top, 1/2 inch marine ply, will be epoxy'd also.

My plan is to put a fresh air vent near the bottom of the front
panel of the box, and another vent near the top to exhaust hydrogen
outside the boat. If you're curious, I plan to use panel mounted
cable clams for the two positive leads, the common, and
the battery charger leads.

Since I want to take the whole thing apart, if need be, I don't want
to seal the box up with glass or 5200...but planned to use silicone.
After the discussion re batteries exploding and spraying acid
around, (a bit paranoid now), I'm wondering if silicone will withstand
the acid. Anyone know for sure?

I should point out I'm also using the common plastic battery boxes, but
without the tops (lids?), so I have two boxes contained in a larger
box. Call it belt and suspenders, but the inner boxes should contain
the acid in the event of a split case.
I'm also considering using a couple of those cheapie indoor/outdoor
thermometers to provide a cross-check on battery temps.

Advice appreciated.
Norm B