Sport Today

At what change in elevation should a board be vented? Living at sea
level I never vent and forgot about it until going to the Gorge I
noticed a sign announcing the elevation as 5000'. I pulled over and
opened the vent on my board but heard no air exchange so was it
necessary to open it?

That trip to the Gorge is the only time I unscrew that thing since the
elevation at the Oregon/Cali border is around 4-5K.

Put the***in your universal base plate and close it so you won't
forget about it when you hit the water again.

You might want to read the Board Maintenance section of the BoardLady.com

Unless you're in one of those places where temps don't change more than
10 degrees ever, you're better off venting your board ALL THE TIME -
even if you don't have dramatic effects from the repeated pressure
changes inside the board, the constant expansion/contraction will over
time make delamination more likely. This is especially important for
boards with large volumes of foam (which contains tons of air and thus
expands/contracts a lot with temp changes) and relatively thin layups -
so formula and other large boards are more susceptible to damage; wave
or B&J sticks with bomber layups and low volume a little less so.

As for the elevation thing - 4000 feet is a large amount of pressure
change. Try this - take an empty plastic water bottle (the thick
polyethylene Nalgene bottles will do nicely for this demonstration) and
***it shut tight at 4000 feet. Drive down to sea level. Observe how
the bottle folds in on itself. Convinced that it's a fair amount of
pressure change?

The whole hissing thing is interesting - I've had board that hiss, and
others that don't. Not sure exactly why, but maybe it's about the
particular vent plug and o-ring. You're also more likely to hear a hiss
if there's a bit of moisture in the board from a previous mishap.

There are tons of things people do to try and remember to close their
vents before going out on the water. For me, it's become this routine
thing where I have a screwdriver in my hand and I fasten three screws -
two finbolts and a vent screw. When I set the board down for a longer
break and open the vent (advisable if it's really sunny), I often stick
the screwdriver in one of the footstraps to remind me before I go back
out.

People using two-bold base plates often stick theif vent screws in the
base plate - no way you can connect your universal w/o noticing. Still
others tie little streamers around their straps anytime they undo their
vent.

-Andreas

Google Groups provided an interesting link while I looked at this
thread:  a company that makes "breather valves", www.agmcontainer.com

Browsing the link, the Mini Immersion Proof Breather Valves look
interesting:
http://www.agmcontainer.com/immersion_breathers/immersion_breathers_m...
Their catalog also has a nice section on "Breather Valves Theory and
Characteristics" if you want graphs etc. on pressure differential
following changes in altitude or temperature.

rec.windsurfing has previous threads on Gortex covered board vents
which indicated these had some problems.  The mini immersion breathers
might provide a replaceable option to someone who wants to try this
approach.  Cost of these unknown, but you could email them.  They may
be quite expensive, some are used for missile and torpedo containers.

Me, I use a double bolt Chinook baseplate.  The baseplate pins slide
over to hold the bulky knot in a line whenever I loosen the vent screw.
 Works for me.

regarding the Goretex vents, they all state somewhere in their
literature that they are "immersion-proof", but not "vapor-proof". So
you might be good in the water, but once you zip up your wet board in a
foil bag and the water from padz and footstraps turns to vapor, then
this vapor will travel into the core of your board.
I just extracted 4oz of water from the immediate vicinity of a Goretex
valve that had been flawlessly installed in a custom Nelson board.
Everything worked as it should - but still took on a considerable
amount of water.
I get out ye olde screwdriver every time!
Eva

Per philo:

I don't have any technical knowledge to base it on, but my feeling is that
temperature is important too.

If I put my board inside a vehicle, I always open the vent plug.   Got some
spring clamps at Home Depot that I use as markers.   If the vent plug is open,
there's a spring clamp on the rear footstrap.
--
PeteCresswell

Eva,
How do you extract 4 oz. of water?  Spread throughout the interior of a
board that can't be very much water. Do you apply a vacuum?

Jim

Eva is absolutely correct.  However, if you leave the vent***open
when not sailing, water vapor can get inside the board.

What is interesting about the breather valves and why they are used is
that these are valves with opening and closing pressure differentials
(available from 0.3 to 5 psi)  This minimizes the amount of water vapor
entering a container.  To quote the company's "Breathing Valve Theory
and Characteristics" regarding moisture entering a container due to
cyclical pressure changes:

"At one time, "free-breathing" containers were considered as an
alternative solution to this problem. The theory, based on Ficke's
Law, was that moisture would not pass freely through tubes with lengths
10 or more times their diameters. However, this principle applies only
when there is no pressure differential between the two ends of the
tube. The method was found to be unsatisfactory in actual practice. In
fact, in tests conducted by the U.S. Army Tank Automotive Command, the
average water gain in three free-breathing containers was over six
times greater than a controlled breathing container with a valve which
sealed at 0.5 psid pressure and 1.0 psid vacuum (See Appendix - p.
22)."

I read the above with slight dismay because I leave my vent***
slightly loose when my board is stored.

The company's article gives some useful guidelines on how much pressure
differential occurs under various conditions.  An altitude gain from
sea level to 8,500 feet (equals aircraft cargo pressure) drops the
pressure from 14.7 down to 10.7 psi.  Temperature effects are in the
range of 1 to 1.5 psi per 30 deg F.  A 30 deg. F change is quite
possible within a closed car on a sunny day.  You could use the Ideal
Gas Law PV=nRT for a more exact calculation (see Wikipedia
http://SportToday.org/
http://SportToday.org/).

While these valves might be nice (even available with desiccant to
absorb water vapor entering via the valve), my guess is they cost a
significant amount for a minimal reduction in moisture entering the
board.

What I want to know is, if you go over a mountain pass with a board on
top of the car in recommended bottom down, tail forward, and opened
vent pointing up, what should you do if it starts to rain ?  The board
bag will probably leak water on to the vent hole.

I just returned from a trip to Punta San Carlos, Baja...  Realized
after I returned on the flight from San Diego, that I had forgotten to
open the vent***on my board.  Opened the board bag to find no
damage, delam or otherwise.  The only thing I can figure is my board
must not be airtight, because it should have exploded well below 30,000
feet!
Rocky

    I get the thing about not leaving your vent***open in a bag with wet
straps causing water intake in the board. But wouldn't the also take on
water  in a high humidity environment with the vent open . This makes me
wonder if its better to leave the vent***cracked just a little when
storing in the off season, or what happens if you leave the board vented in
high humidity environments.
     Do I need to construct a temperature and humidity contoled room for
board storage?

On Sun, 24 Sep 2006 09:19:13 -0700, "Charles Jutkins"

You *do* have a dehumidifer on the roof racks, I hope..

Per Rocky:

From posts about air-shipping pets and other animals I get the impression that
the cargo hold is pressurized.
--
PeteCresswell

Yes but I think its the same as the Cabin which is normalized enough so
people can breath . I wonder how much that is like 5000 feet

See post above on breather valves.  Air pressure inside the cargo hold
is stated as 8500 ft, reducing it from nominal 14.7 psi at sea level to
10.7 psi.  Since one of the markets for these valves is the military
(company site has photos of Patriot shipping case, Harpoon shipping
case, and Stinger shipping case) this may be a military aircraft cargo
hold's pressure.

"...Figure 10 shows the 767 cabin altitude schedule. At a 39,000-foot
cruise altitude, the cabin pressure is equivalent to 6,900 feet or a
pressure of 11.5 psi (about 450 feet less than Mexico City). In
addition, as the airplane changes altitude, the outflow valve
repositions itself to allow more or less air to escape. The resulting
cabin altitude is consistent with airplane altitude. This is
accomplished within the constraints of keeping pressure changes
comfortable for passengers. Normal pressure change rates are 0.26 psi
per minute ascending and 0.16 psi per minute descending...."

Temperature inside the cargo hold per
http://www.inamarmarine.com/pdf/LossControl/Air%20Cargo.pdf
"Temperature- Aircraft cargo compartment temperatures normally range
between 30F and 70F (-1C and 21C). However, cargo aboard an
aircraft parked in freezing or very hot weather will be subjected to
unusual cold or heat conditions."

If there is a temperature drop, this increases the pressure
differential about 1 to 1.5 psi per 30 deg F drop per same post above.