Some emails cause our hearts to skip a few beats.
Checking in from our cross-country road trip. We stopped by a lake in Colorado a couple of days ago to take the PT11 out for a sail and noticed something very alarming... The back seat buoyancy tanks have bowed - like the air in the tanks expanded. They have returned to the normal shape again, but the fiberglass strips on the tank joints probably couldn't handle the pressure and have cracked - see pictures attached.
This boat was built at sea level in NYC and the tanks were expanded at roughly 10,000ft. The good news is that they did not explode nor do they appear structurally compromised, thanks to wood/epoxy as a construction method.
Most of our clients have used their boats near where they built them but others have taken their boats from sea level proximity to higher altitude lakes. (These two videos are thanks to Randy and Kim Kerr)
https://www.youtube.com/watch?v=jdLN_QaQrv4. Ross Lake (1,519 ft)
https://www.youtube.com/watch?v=LJV8MJJv6pU&t. Chilko Lake (3,845ft)
Randy replied to my inquiry about his lake trips: "We've never really taken our PT11 higher than 4000' and didn't notice any bulging in the buoyancy tanks personally. I could imaging customers that span 10K feet in altitude difference could easily see bulging or compressing."
Because Russell and I initially imagined our boat builders using their PT 11 dinghies primarily for ocean cruising, the influence of high altitude on the air buoyancy tanks simply did not come up but once in 15 years. That customer installed a relief valve but we never heard exactly what type or how well it worked. We imagined that as a one-off but we are also under the constraints of the USCG rules that prohibit access ports or any compromise of a sealed air tank if it is to be counted as buoyancy. Hence we moved on.
Times are changing however, and it appears that more PT 11s are on road trips and out lake sailing so, it seems prudent to address the air pressure question for anyone planning altitude differentials of more than 4-5000ft with their PT 11 or SPEAR dinghies.
There is an argument for drilling a 1/4" hole on the vertical face of each of the three air buoyancy tanks and filling them with thickened epoxy. (This keeps moisture from reaching raw wood.) If you then notice any expansion at altitude, you have a safe spot to drill a very tiny hole to relieve pressure. The hole could then be taped over until the boat was back at its normal altitude when the new hole could be filled. You would have to choose a time and place with a stable temperature to fill these holes. In an emergency, go ahead and drill tiny holes to keep damage from occurring. Just know that refilling those holes in a way that keeps the wood dry will be important.
One builder currently working on his PT 11 is planning to use it almost exclusively on mountain lakes and had already researched the pressure valve question before I reached out to ask about it. Have you heard of Gortex Dots? He has generously shared his in depth research and conclusions in this PDF article. An Idea for the Vented Volume Dilemma
The standard rule should still be noted for air buoyancy tanks: no access ports or compromise of the seal unless you plan to fill the voids with flotation foam. These dedicated air tanks (forward of the mast step and the aft seat boxes) are not intended as storage and using them as such could present a serious safety risk if you flood the boat. If you truly need to modify the design to fit your intended use, how you manage that is your responsibility, so be informed, do your own research, and think 'safety first'.