Yup. Pete has said all of this before and I don’t know why debate over it comes up time and again. There are lots of vents on the market. If it’s a concern or even a maybe. Use one. I haven’t vented these EPS Shortboards, because I just don’t see the need. I have three SUPs I need to glass, they will all be vented. Will probably place one vent up in the mid forward point of the board and will use Pete’s Cadillac vent. If it’s good enough for Dave Mel’s boards, it’s good enough for mine. So remind me next time I am down there Pete to pick up a few. I’m starting to wonder about things like future gatherings and the Coronavirus though.
Covid-19 is indeed a real concern. Without the old, confused, misinformed bastards like me and McDing, who will become the new targets of scathing criticism from both domestic and international communities?
Hey Pete, Really appreciated your comments regarding thermal contraction of EPS surfboards. Full disclosure, Pete’s gortex vents are top notch. I use them on my start to finish builds and also use FCS SUP handle vents with customer request.
Back to the thermal contraction. Remember when Clark Foam closed in Dec 2005? I was already balls deep in making EPS blanks on oahu. had 2lb and 1.5lb density available. Tried to promote it with shapers and got the cold shoulder from most. Finally had 3 bigger surfboard/SUP manufactures buying blanks from me. The ride lasted about 18 mos before other EPS blank sources became readily available and competition made it not viable for me to make money doing it and employing 3 people. My biggest surfboard customer soon came to me complaining about my foam and how they were having problems with with water absorbtion in foam. They were using FCS early generation 2006 plugs. I tried to explain that a warm eps board going into colder water causes a vacuum in the board and will pull water into board from any micro hole that is in the board and usually around the fin plug of the FCS. I used o’fish’l and futures 99% of the time for my boards and NEVER had a problem cuz I placed boxes pre glassing with a patch and they just didn’t leak at that spot.
My First SUP board board came to me that year on a shaped blank, 1 lb foam. that I would balsa laminate, glass, and place a home made gortex vent in.I used brass fittings with gortex based on an experiment I pulled off in my hot tube with a prototype. The finished board was extremely light weight, had lots of pics taken of it in barrels in waikiki and was just a beautiful board. 13 years later this same board come back to me for a referb sale . Gortex vent still there. no signs of leaks on this well used board. Glassed over old gortex vent and places handle vent per customer request. I had no clue what I was doing with the vent but it did the job,or…the glassing was so tight and sealed it was not even necessary at all in our consistent, tropical climate??
Pics of board 2019
PeteC is correct. This is basic physics – Gay-Lussac’s law, Boyle’s Law, Charles’ Law.
The lower the foam density, the higher the gas content. A glassed foam board is basically the equivalent of a fixed volume.
Simple experimental verification. Take an empty plastic milk jug and place it on the roof of your car with cap removed on a hot sunny day. Allow it to sit there for 5-10 minutes. Replace the cap tightly. Then place the sealed jug in the CA Pacific Ocean. Watch the jug collapse inward.
Now do the reverse. Take an empty plastic milk jug and place it on the surface of the CA Pacific Ocean with the cap removed (without submerging the opening). Keep it there for 5-10 minutes. Replace the cap tightly. Then place the sealed jug on the roof of your car on a hot sunny day. Watch the jug expand like a balloon.
Yup. Good visual Stoney.
That goes to show the quality involved in what you do. Durable darn board.
BTW foam/blank temperature at the time of glassing will affect the type of internal pressure (positive vs. negative) an unvented board will be most affected by.
I’ve always installed vents in all of my EPS boards; all utilized 2 pound EPS. However, I’m finishing up a 70 liter longboard with a 1.7" wide wood stringer. I want to put a through-box leash attachment and forgo the vent(s). The board has no color. This is a board for me and I take care of my boards. I appreciate all of the feedback I was able to glean from this thread. I’m going no-vent. Will post as soon as I get a delam 
Thanks again.
