Hi Turtlehunter, if you are in hot conditions it's a good idea. Buy a goretex vent and epoxy it into your board or get a repair place to do it for you - you don't need to worry about remembering to open and close it.
Shapers have them www.shapers.com.au
I don't think they are shown on the web site but give them a call they do have them, I just don't get why some boards have them and some don't.
Here is a quote from Eva Hollman AKA The Board Lady
boardlady.com/She really knows what she is talking about, there is heaps of info on her site about repairs and a lot of stuff that's relevant to making boards too.
"
And speaking of vent plugs: opening yours whenever you are off the water is the single most effective thing you can do to prolong the life of your board. Leaving it closed will cause the EPS foam core to expand and contract at least once a day. You take any substance, no matter how stout, and you push and pull it continually, at least 365 times a year, and it will fail. Guaranteed!
It's not that much, you say? I just measured my Trusty Old 9'-4": typical summer day, near sea level, early morning, cool 60 degrees, it was 4 15/16" thick. Then the day warmed to 89 degrees, a thermal low developed, and the board expanded to 5 3/16". That is a whopping 1/4" change, or 5%!!
Get into a routine, where you tighten the vent screw just before you put on your harness, or some such thing, and it will become second nature, and you will not forget. But DO IT!"
