Drip less Shaft Seals

D

David M

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Long story short. RW pump seized; loud screech, threw the serp belt on the port side. Shut down the engine and completed the trip on one screw at hull speed with port transmission engaged.

Got to my destination ans needed twins to get into the slip.

Started the port engine and got her in the slip and shut her down before the temp gauge hit 140.

Woke up at 2:00 AM with the OSH!T thought. Shaft seal!

Thoughts and recommendations please.

TIA
 
probably didn't run long enough to do damage. Is it leaking?
 
It should be ok at slow speed. A bigger concern would be hot spots in the engine since the circulation pump wasn't running. The guarge may have shown 140 but with no coolant circulation it would have been much higher near the cylinders. Running FWC engine for a few minutes without the raw water pump is ok as coolant circulates and won't have time to get too hot, but without the circulation pump is a lot more risky.
 
I wouldn't worried to much about it. The shaft seal should be fine. And I've done that same, "run the other engine just long enough to dock" a number of times without any problems. So I'll bet once you get things sorted out your engine will be fine as well.
 
Most twin-engine's shaft seals are (or should be)set up with a "T" crossover in the seals' RW supply from the engine . If one engine is not running, the other one still supplies cooling/lubing water to both it's own shaft and the free-wheeling one. Same even if both are running but one has lost it's RW pump like yours..at slow rpm.
If yours is not yet "T"-d , as long as you kept speed slow as you should anyway to protect the down engine's transmission, it is probably OK after both free-wheeling and the very brief docking maneuvers, but I would certainly check the RW pump impeller and housing and watch the temp gauge. The dry impeller can be damaged quickly, particularly if it is not the somewhat more forgiving blue Globe type. And, of course, check the shaft seal early on during the next cruise to ease your concerns.
 
quote:
Originally posted by Sandy

The dry impeller can be damaged quickly, particularly if it is not the somewhat more forgiving blue Globe type.

Click to expand...


If the belt that broke is driving both pumps the raw water impeller would not be turning so there would be no damage to it from running dry.
 
The reason for the water hose to the shaft seal is to overcome the water getting sucked out at speed. Sail boats don't have them. If you were just doing slow speed maneuvering, there would have been plenty of water cooling the carbon and SS rings.
 
Ditto on the cross over plumbing. And if you don't have it I am thinking it is in your future.

Edit: If you do not have it I am willing to bet that the seal enclosures have a plug where the cross over tube goes.
 
David how did you make out overall?
Is everything ok with the motor?
Bill
 
quote:
Originally posted by Sandy

Most twin-engine's shaft seals are (or should be)set up with a "T" crossover in the seals' RW supply from the engine . If one engine is not running, the other one still supplies cooling/lubing water to both it's own shaft and the free-wheeling one. Same even if both are running but one has lost it's RW pump like yours..at slow rpm.
If yours is not yet "T"-d , as long as you kept speed slow as you should anyway to protect the down engine's transmission, it is probably OK after both free-wheeling and the very brief docking maneuvers, but I would certainly check the RW pump impeller and housing and watch the temp gauge. The dry impeller can be damaged quickly, particularly if it is not the somewhat more forgiving blue Globe type. And, of course, check the shaft seal early on during the next cruise to ease your concerns.

Click to expand...


===========================================

OK - I get the cross plumbing concept, however....

in the case of the PORT engine running at, say 2000 RPM with the STBD engine off, what keeps the water pumping over to the STBD engine from backing up and dropping into the rearmost cylinders via an open exhaust valve?

RWS
 
quote:
Originally posted by Sandy

Most twin-engine's shaft seals are (or should be)set up with a "T" crossover in the seals' RW supply from the engine . If one engine is not running, the other one still supplies cooling/lubing water to both it's own shaft and the free-wheeling one. Same even if both are running but one has lost it's RW pump like yours..at slow rpm.
If yours is not yet "T"-d , as long as you kept speed slow as you should anyway to protect the down engine's transmission, it is probably OK after both free-wheeling and the very brief docking maneuvers, but I would certainly check the RW pump impeller and housing and watch the temp gauge. The dry impeller can be damaged quickly, particularly if it is not the somewhat more forgiving blue Globe type. And, of course, check the shaft seal early on during the next cruise to ease your concerns.

Click to expand...


===========================================

OK - I get the cross plumbing concept, however....

in the case of the PORT engine running at, say 2000 RPM with the STBD engine off, what keeps the water pumping over to the STBD engine from backing up and dropping into the rearmost cylinders via an open exhaust valve?

RWS
 
I m looking at the install instructions on the PSS seals as I am about to install one on the sailboat I'm building.

It says that boats that do not run over 12kts on a single engine do not need a crossover line as there isn't enough suction in the stern turbo to suck water out of the seal. Interestingly, for boats no exceeding 12 kts and which do not have a cutlass bearing in the shaft tube, then you don't even need to connect a water source to the fitting, instead just run a vent hose to a point 2 ft above waterline.

In my case, I decided to go with a PSS to reduce friction compared to a conventional stuffing box to maximize the electric motor efficiency both for propulsion and for regen.
 
quote:
Originally posted by PascalG

In my case, I decided to go with a PSS to reduce friction compared to a conventional stuffing box to maximize the electric motor efficiency both for propulsion and for regen.

Click to expand...


You could save some money and just use a traditional stuff box with GFO packing. GFO is very slippery stuff. :-)
 
quote:
Originally posted by RWS

quote:
Originally posted by Sandy

Most twin-engine's shaft seals are (or should be)set up with a "T" crossover in the seals' RW supply from the engine . If one engine is not running, the other one still supplies cooling/lubing water to both it's own shaft and the free-wheeling one. Same even if both are running but one has lost it's RW pump like yours..at slow rpm.
If yours is not yet "T"-d , as long as you kept speed slow as you should anyway to protect the down engine's transmission, it is probably OK after both free-wheeling and the very brief docking maneuvers, but I would certainly check the RW pump impeller and housing and watch the temp gauge. The dry impeller can be damaged quickly, particularly if it is not the somewhat more forgiving blue Globe type. And, of course, check the shaft seal early on during the next cruise to ease your concerns.

Click to expand...


===========================================

OK - I get the cross plumbing concept, however....

in the case of the PORT engine running at, say 2000 RPM with the STBD engine off, what keeps the water pumping over to the STBD engine from backing up and dropping into the rearmost cylinders via an open exhaust valve?

RWS

Click to expand...


It's a good question!
But since I believe the water is supplied to the aft side of the seal & out the shaft log I don't see how it is going to back up into the dead engine unless perhaps the boat is towed backwards.
I can't easily picture that happening, but I'm sure it could. In the event that is required, I'd suppose a vise grip clamped on the dead engine hose would prevent any potential backflow. It's good you brought that up.
Normally, engine running or not, any RW supplied to dripless seals should be getting sucked out by fwd hull movement through the water.
The "tee" junction is down low on the hoses on my boat too, so it would have to fight gravity and suction to back up. That's my best guess FWIW.
 
quote:
Originally posted by Capt. Bill1

quote:
Originally posted by PascalG

In my case, I decided to go with a PSS to reduce friction compared to a conventional stuffing box to maximize the electric motor efficiency both for propulsion and for regen.

Click to expand...


You could save some money and just use a traditional stuff box with GFO packing. GFO is very slippery stuff. :-)

Click to expand...


For a 1" shaft it s only $230... Yes GFO is slippery but there is A lot of friction from 3 or 4 rings around the shaft compared to just the face seal of the PSS
 
quote:
Originally posted by Billylll

David how did you make out overall?
Is everything ok with the motor?
Bill

Click to expand...


The Mech finally got to Saint Max last week. No biggy, she was getting new front canvas. Motor is OK Bill. She is pumping tons of water out the sides. Off for the 1/4'ly visit to Mom's next week then take her to her new home around the first week in July.
 
quote:
Originally posted by PascalG

quote:
Originally posted by Capt. Bill1

quote:
Originally posted by PascalG

In my case, I decided to go with a PSS to reduce friction compared to a conventional stuffing box to maximize the electric motor efficiency both for propulsion and for regen.

Click to expand...


You could save some money and just use a traditional stuff box with GFO packing. GFO is very slippery stuff. :-)

Click to expand...


For a 1" shaft it s only $230... Yes GFO is slippery but there is A lot of friction from 3 or 4 rings around the shaft compared to just the face seal of the PSS

Click to expand...


$230 is pretty cheap. But still almost twice the retail cost of an old school 1" packing box.

It would be interesting to know the difference in friction loss between the two systems. I'd be surprised if there is a significant difference.

But in your case every little bit will help I guess.
 
quote:
Originally posted by KiDa

quote:
Originally posted by Billylll

David how did you make out overall?
Is everything ok with the motor?
Bill

Click to expand...


The Mech finally got to Saint Max last week. No biggy, she was getting new front canvas. Motor is OK Bill. She is pumping tons of water out the sides. Off for the 1/4'ly visit to Mom's next week then take her to her new home around the first week in July.

Click to expand...

Glad to hear it David. I finally got around to starting my motors from being winterized last weekend. Everything is fine but I'm concerned I have about 200+ gallons of Ethanol in the tank that is 9 months old. I better burn it off and get some fresh gas soon.
Bill
 
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