Dripless seal

[a64pilot]

Originally Posted by s/v Jedi

Hmmm the cutlass bearings that I know will allow water to pass through... are there types that don’t?

Not that I am aware of, even a standard stuffing box needs water to be cooled.
Read step #15 in the instructions, I’ll also post a screen shot of the instruction page
https://www.shaftseal.com/pss-instal...tructions.html


I’ve been contemplating a dripless seal myself and with the problems with owners having a boat out of the water and forgetting to burp the seal etc. it seemed prudent to just plump a water supply to one from the engine. On my boat I believe I can simply remove a drain from the heat exchanger and put in a nipple and connect a hose.
Plus mine is difficult to access as I have a very deep and narrow bilge back there where the shaft log is.

[a64pilot]

Originally Posted by s/v Jedi

Hmmm the cutlass bearings that I know will allow water to pass through... are there types that don’t?

My assumption is that they will allow water to pass, but it’s a dead end, with no flow and maybe it’s easy to get an air bubble in there that won’t clear?
If the vent hose would let air out, why do you have to “burp” a dripless seal on a boat that has sat for more than three months in the water or one that had been hauled?

Now I’m just theorizing and assume the requirement to plump water to one with a cutlass bearing in the log is a change?

[s/v Jedi]

Originally Posted by a64pilot

My assumption is that they will allow water to pass, but it’s a dead end, with no flow and maybe it’s easy to get an air bubble in there that won’t clear?
If the vent hose would let air out, why do you have to “burp” a dripless seal on a boat that has sat for more than three months in the water or one that had been hauled?

Now I’m just theorizing and assume the requirement to plump water to one with a cutlass bearing in the log is a change?

No only the types without the hose need to be burped. When vented, the air is forced out by water pressure and water will stand up in the vent hose at waterline level.
Edit: so it’s not a dead end, it’s open to the atmosphere.

[GILow]

Originally Posted by s/v Jedi

Hmmm the cutlass bearings that I know will allow water to pass through... are there types that don’t?

I wondered the same thing when that change to the installation instructions for the PSS were introduced.

I confess, I have two cutless (cutlass) bearings and I do not feed raw water to my PSS. I have tested it under various conditions including running at the top end of my speed range and the water flow from outside into the seal is very fast. I even fitted a length of clear PVC hose to see if there was evidence of a vacuum effect that I might have been missing. There MAY have been a slight drop in the water level in the hose when under way but it was small enough to be hard to tell as the motion of the boat through waves was enough to cause the level to jump up and down erratically.

Maybe, as your question appears to suggest, there are bearings that restrict water flow enough to be a problem. But not on mine.

[BBViper]

I have the PSS dripless, think its great. My mechanic installed it, said while yes, it is meant to be a source of lubricating water for high speed boats, also recommended connecting it to engines water system for sailboats. Helps with lubrication AND best to not let it be open or loose as it is an open line to the water. No sense having a potential leak on board.

P.S. - i did have the hose laying flat in the bilge once when the boat was splashing after bottom job. forgot to connect. water came pouring in !

[a64pilot]

Originally Posted by s/v Jedi

No only the types without the hose need to be burped. When vented, the air is forced out by water pressure and water will stand up in the vent hose at waterline level.
Edit: so it’s not a dead end, it’s open to the atmosphere.

I wasn’t aware of any that didn’t have a hose, but I’ve only started looking myself.
I feel sure the PSS has a hose, and is required to be burped.

Currently I have Teflon packing in my stuffing box and it doesn’t leak, but I’m concerned about possible scoring of the shaft.
A dripless seal that has the sealing surfaces not on the shaft ought to eliminate the scoring concern.

I’m leaning towards a Lasdrop Gen II or Elite, but can’t determine the difference between the two.

[GILow]

Originally Posted by s/v Jedi

No only the types without the hose need to be burped. When vented, the air is forced out by water pressure and water will stand up in the vent hose at waterline level.
Edit: so it’s not a dead end, it’s open to the atmosphere.

Actually, I have the vent hose, but if I do not burp mine after a haul out, it squeals when it turns until I burp it.

I THINK the burping, in this case, actually wets the faces of the bearing, rather than simply letting the air out, which as you note, is done by the vent house.

[Wotname]

Regarding the PSS item.

The hose that is open to the air above the waterline is to allow water to fill the seal on relaunching, nothing more, nothing less.

The hose that is feed with a raw water supply is to maintain an adequate supply of water to the seal when underway at higher speeds (~12kts IIRC). At these higher speeds, enough water is potentially pulled from the stern tube (past the cutlass bearing) by prop / keel action to cause insufficient water at the seal face.

I dunno about other dripless seals!

[2fast2nick]

I had one of those in my ski boat. I had the water line tapped into the engine water feed.

[GILow]

Originally Posted by 2fast2nick

I had one of those in my ski boat. I had the water line tapped into the engine water feed.

Well, a sub 12 knot ski boat would probably not be a lot of fun.

[a64pilot]

Originally Posted by Wotname

Regarding the PSS item.

The hose that is open to the air above the waterline is to allow water to fill the seal on relaunching, nothing more, nothing less.

The hose that is feed with a raw water supply is to maintain an adequate supply of water to the seal when underway at higher speeds (~12kts IIRC). At these higher speeds, enough water is potentially pulled from the stern tube (past the cutlass bearing) by prop / keel action to cause insufficient water at the seal face.

I dunno about other dripless seals!

Now, I don’t have one, so take this for whatever it’s worth, but plumbing a water supply to a seal would also seem to keep it flushed clean, silt etc build up is an issue with a standard stuffing box, and I’d assume a dripless seal that has no way to be flushed clean may also trap silt over time.
In other words, it’s would seem that as PSS requires a water line to all boats with a bearing in the shaft log, regardless of speed etc. I see no downside to having one and possible advantages like not ever having to burp one.

[s/v Jedi]

Originally Posted by a64pilot

Now, I don’t have one, so take this for whatever it’s worth, but plumbing a water supply to a seal would also seem to keep it flushed clean, silt etc build up is an issue with a standard stuffing box, and I’d assume a dripless seal that has no way to be flushed clean may also trap silt over time.
In other words, it’s would seem that as PSS requires a water line to all boats with a bearing in the shaft log, regardless of speed etc. I see no downside to having one and possible advantages like not ever having to burp one.

Again, burping is only for non-vented version to remove the air bubble. I own Jedi 17 years, have used a water feed to the PSS for 10 years, then found out the water is siphoning through engine and seal 24x7 as long as engine seacock is open (galvanic action?), then decided we only go 12+ kts under sail and went to vented to thruhull fitting into cockpit bulkhead for the past 7 years. Temperature of carbon ring is exactly the same, everything sounds the same.

Maybe PSS changed documentation after an incident with a claim from a clueless customer but my documentation is clear and came with the seal as installed.

[Wotname]

Originally Posted by a64pilot

Now, I don’t have one, so take this for whatever it’s worth, but plumbing a water supply to a seal would also seem to keep it flushed clean, silt etc build up is an issue with a standard stuffing box, and I’d assume a dripless seal that has no way to be flushed clean may also trap silt over time.
In other words, it’s would seem that as PSS requires a water line to all boats with a bearing in the shaft log, regardless of speed etc. I see no downside to having one and possible advantages like not ever having to burp one.

I also can't see any downside to having a water feed except perhaps some slight added complexity in the raw water circuit (which is certainly no biggie in the grand scheme of things IMO).

FWIW, my first PSS was way back when the vent spur was solid, if you wanted a hose fitted to it, you had to drill it out - this was possibly mid 80s IIRC. I left it without any vent and just burped at every relaunch as part of the relaunch checklist - never had a problem.

My last PSS was vented to the air although I did have a bearing in the shaft log - I had fitted the PSS before the change in instructions regarding a water feed. I never bothered to go back and refit a water feed - again never had any issue. I suppose a sample of one is not conclusive evidence though

[Wotname]

Originally Posted by s/v Jedi

........

Maybe PSS changed documentation after an incident with a claim from a clueless customer but my documentation is clear and came with the seal as installed.

Yep, the documentation has changed over the years while the seal has (apparently) remained unchanged.

The cynical side of me concurs with your assessment of the reasons why .

[a64pilot]

Still, the directions have apparently changed, I doubt it was due to one complaint, but more likely several in service issues.
Lasdrop recommends plumbing in a water line in all installations, but doesn’t require it.
I’d bet that once in a blue moon there are problems, but if there is pressurized water flow, there isn’t.
As I’m investigating a dripless, I’m looking at and reading instructions.
My current stuffing box has had for three years Teflon packing and it doesn’t leak at all, but I’m beginning to become concerned at the long term possibility of scoring of the shaft.
It doesn’t appear to be that big a deal to plumb into the raw water side and provide water, assumption is it doesn’t require much flow.
I have no idea of the pressure in the heat exchanger but as it’s an open ended thing, I wouldn’t expect much at all.