We have a PSS dripless shaft seal installed in our h36 and I ran the vent tube up in the engine compartment into an overflow bottle per Mainsail's suggestion. The top of the vent hose is about 14" above the waterline. The overflow bottle would catch water on our h30 due to aggressive use of reverse gear, but this does not typically happen on our h36, maybe just a oz or two. So I was surprised to find the bottle full and overflowing a few times over the last 3years we owned the h36 and I was mystified.
Turns out that when changing the zincs in the water, air begins to collect in the scalloped area where the shaft log exits the hull and bubbles up around the shaft into the PSS bellows. The trapped air in the bellows then pushes water up thru the vent tube into the overflow bottle to escape. No kidding. It works like an old aquarium filter. The scuba air rises thru the vent tube, pushing lots of water ahead of it, easily filling the bottle in the time it take me to change the zincs. The Admiral watched it happening and emptied the bottle when I surfaced for the second zinc. So next time I'll either plug the vent line or let it overflow into a bucket.
Turns out that when changing the zincs in the water, air begins to collect in the scalloped area where the shaft log exits the hull and bubbles up around the shaft into the PSS bellows. The trapped air in the bellows then pushes water up thru the vent tube into the overflow bottle to escape. No kidding. It works like an old aquarium filter. The scuba air rises thru the vent tube, pushing lots of water ahead of it, easily filling the bottle in the time it take me to change the zincs. The Admiral watched it happening and emptied the bottle when I surfaced for the second zinc. So next time I'll either plug the vent line or let it overflow into a bucket.