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plenamar

Dripless seals

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Are "dripless seals" any good? I read that the can fail catastrophicall & result innboat full of water/sinking.

Any opinion?

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Properly maintained they're a huge upgrade over a conventional stuffing box and the risks ate quite low. Generally speaking, I'd say they're less maintenance than a conventional system.

Be sure to take a look at the Manecraft seal, which has several advantages over the pyi product.

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"Properly maintained" is the key term, for a piece of gear that's pretty much out of sight and too often out of mind, sort of like your steering gear...

You trade a small risk of catastrophic failure of the bellows, for the slow drip of a traditional packing gland. 

If you use it and haul it out regularly, and have all thru-hulls inspected, & serviced every time, including your Rudder & prop shafts you are probably ok... 

If your boat sits ignored for years in the water, growing a waterline beard and the prop is slowly going away due to electrolysis perhaps not so much. 

 

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I won't ever go back to a standard stuffing box. I suggest you contact the various yards in and around BA and ask them if they've seen any dripless failures and the associated circumstances. There's no substitute for actual data.

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If you're worried about catastrophic failure, then replace the bellows (PYI) every 5 years. They last much longer.

Also put a hose clamp in front of the s.s. collar since you will get copious flooding if the collar slips forward. And then you'll have to replace your starter in a few months after the seawater bath. And you will spend Thanksgiving weekend anchored 1/2 mile from shore in 40 knots of wind with waves slapping the underside of your catamaran because the stupid starter died. And nobody will want to cook the turkey because it will be too rough. And your guests will not like the experience. So install the hose clamp.

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3 minutes ago, Zonker said:

If you're worried about catastrophic failure, then replace the bellows (PYI) every 5 years. They last much longer.

Also put a hose clamp in front of the s.s. collar since you will get copious flooding if the collar slips forward. And then you'll have to replace your starter in a few months after the seawater bath. And you will spend Thanksgiving weekend anchored 1/2 mile from shore in 40 knots of wind with waves slapping the underside of your catamaran because the stupid starter died. And nobody will want to cook the turkey because it will be too rough. And your guests will not like the experience. So install the hose clamp.

Who amongst us hasn't had this experience, amirite?

FWIW, I used a shaft anode butted up against the collar instead of a hose clamp but the principle is the same. Also, I think PYI got rid of the sketchy stacked grub screw collar fixing arrangement and went with a split stainless collar instead, which probably eliminates the risk of the collar slipping. Mucho mejor.

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That's highly debatable, especially now that PYI calls for the split collar behind the solid one. I know the PYI solution will run dry far longer without self-destructing and I suspect it has a much greater range of shaft thrust tolerance due to its bellows design.

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I have nothing but good things to say for the PYI system, installed quite a few of them and never had any problems, well except for one customer who never trusted it and would constantly "burp" the bellow as he didn't believe the engine was pushing enough water to it. Turns out that if you keep jacking the bellows and you don't make sure it mates squarely with the stainless steel ring, it leaks. Who would thought (well except everyone).

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I went from PSS to Tides lip seal. So far, so good. I have bad access to the box due to a v-drive, so the spare lip seal on the shaft is nice 

 

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Have a pare of Tides on the vessel, run ~500 hours a season on the engines, very happy with them.

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One thing you DO have to do, is burp it when you launch (if it doesn't have a vent hose). The reason is air gets trapped in the shaft log with no way out. On mine, I also broke it loose after any long rest. A few weeks and the carbon disk sticks to the stainless ring. When you put it in gear, it will tear it loose but it is a bit more violent than it needs to be. Simply wiggle the carbon ring (or shaft) by hand to make sure it is free. Mine was in the boat for 15 years, no maintenance or replacement other than that, no leaking. 

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I tried the Volvo version when I first switched from a sail drive, and even with burping the boat's forward motion (and gravity) would ultimately drain the shaft log of all water down to the water line.  It resulted in really high temperatures when running in gear.

Switched over to the vented version of the PYI with a bit of a weight penalty, and have been happy since.  Agreed on the hose clamp insurance policy. 

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