First off I don't prefer a "wet" system, I prefer an effective shaft seal that isn't a constant source of worry. The traditional shaft seal is more than up to the task of keeping an R-21 bilge virtually dry, especially with the new packing materials now available. A fast boat with the engine turning at 5-6000RPM's and a slow turning diesel boat like the R-21 have much different needs and that is why the PSS type of "Kinda-sorta" dry system was developed.
drawbacks with old type packing in the R-21 ...
1) requires an adjustment once in a long while 2)if it drips while shaft isn't turning, the bilge pump may come on for a few seconds once a month or so (if boat is in the water and for some reason you don't want to adjust it to Not drip). 3) if the 6 ply heavy-duty almost bulletproof rubber hose attaching the box to the sterntube gets chopped several times with an axe or cut with a saw you would have a severe leak. 4) because the setup is soo forgiving of engine mis-alignment you may not know why the cutlas bearing is wearing out prematurely...but other than an annoying vibration it's no big deal.
drawbacks of a mechanical (pss type)system...
1) doesn't require adjustment other than when the carbon faces wear out, or the springs fatigue, or the bellows get stiff, or the retaining disks set screws loosen or strip, or the salt crystals that form between the mating surfaces cause it to drip. 2)if it drips while shaft isn't turning the bilge pump may come on for a few seconds once a month or so (if boat is in the water and you don't want to adjust it to Not drip) unless the drip is due to salt crystals or someone touching it and you need to run the engine in gear for a while to re-seat it. 3) if the 1 ply bellows gets old and cracks underway or is damaged by a dropped screwdriver, or a piece of fishing line finds it's way to the bilge and gets wrapped around it, you would have a severe leak . 4) because the setup is soooo UN-forgiving of engine mis-alignment you may not realize the cutlas bearing has worn out prematurely because all the water pouring into the boat has you distracted.
Pluses of the "old system",...cheap, easy to maintain, chance of catastrophic failure...almost 0. Properly adjusted and using Gor-Tex packing your bilge will remain dry when at rest and almost dry when in motion.
Pluses of a PSS type system,...Marina guy's kids can go to the "good" school, you learn to work under pressure, Properly installed your bilge may remain dry when at rest and almost dry when in motion.
disclaimer:I have had several boats over the years and experienced living with both types of shaft seals...If you want a dry bilge you need a boat with an outboard motor. Also, The R-21 cockpit drains go to the bilge and unless you never get rained on and never get splashed the bilge is going to get wet.
