At 10:47 11/1/2000, PSavage wrote:
>it's hard to imagine the actual weight on this 3" diameter unit

Just to keep the details straight -- a 3" vent installs in a deck fitting
with a 3" hole.  The vent itself is somewhere btw six and ten inches in
diameter, and screws into the deck fitting.

As to the weight, it may very well not be a factor.  However, it should be
borne in mind that these units are normally installed on surfaces that
expect to have people walking on them, not on thin resonant panels where
they would act to drastically lower the resonant frequency of the panel --
and the shock/vibration regime in a Westy is considerably different than a
sailboat.  This may not be an actual issue...but it might.

>And properly installed, allowing for differences between a
>Westy's fiberglass roof & the normal installation of these units
>on sailboat cabin tops, I can't see why they would leak!  They

If you take green water over the roof there will surely be a deluge
<g>.  These vents are not meant to be used in heavy weather underway, they
are to help keep the cabin dry when the boat is closed up.  Bearing in mind
that ordinary driving in a Westy amounts to a near-hurricane in a sailboat,
I would expect possible issues with noise and possibly unwanted inflow
depending on the pressure zone where the vent is installed.

Thought needs also to be given to the possibility of snow/ice dams -- I've
experienced leaks through the regular skylight from this cause.

Of course all of the above is avoided by removing the vent and substituting
a blank deck plate when under way and during snow season....

david
David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"