Dripless seal - water injection needed?

[mlydon]

I'm planning on installing a lasdrop gen ii - the folks there mentioned that for a sailboat I can get away with simply 'venting' the seal. Some reading I've done states that if you have a cutlass bearing in the stern tube (I do), you need to inject for sufficient cooling.

What say you? my boat will likely do 8 knots or so at cruise, has a LONG stern tube. In addition, my engine is down below the sole, so venting requires a good 10-15 ft of hose, one way, injection we're talking about 30' of hose and a vented loop.

For those who are going to comment that traditiional stuffing boxes are wonderful - NOT in my case - major acrobatics to get anywhere near it, never mind adjust the f(&*er.

Matt

[Montanan]

Reference article: https://www.passagemaker.com/technic...ng-shaft-seals

Snipets there from:

The hose connecting the seal to the stern tube fills a critical role: It is below the waterline and failure could lead to sinking. On most face seals, the hose provides the compression needed to hold them against each other, which is the reason for the bellows. . . . while the LasDrop hose, made of military-grade vulcanized silicon, has a 10- to 12-year replacement interval. The LasDrop Gen II seal takes a different approach. A spring located in the face seal provides the compression, eliminating the need for a bellows hose. This reduces the cost of a replacement hose and simplifies service and installation.

Additionally, the instructions caution against re-using the set screws, because the cupped points become flattened and lose their effectiveness. These guidelines are critically important. If the stainless collar becomes loose on the shaft it can move away from the carbon face, allowing water into the bilges. Face seals are reliable and easily maintained when the faces are kept clean. If the boat sits for long periods or if you run through sandy shallow water, particulates on the face can damage the seal. Clean the surface with a rag as needed. If the carbon face seal needs replacing (some can be refaced), you will need to haul your boat and pull the shaft from the coupling so that the replacement can slide onto the end of the shaft. Loss of water flow to the seal is the number one cause of failures, followed by particulates getting caught between the seal faces. Properly maintained, replacements are not common, and the manufacturers report more than 20,000 to 30,000 hours of use on a single carbon seal in commercial applications.

Water Flow To The Seal

Dripless or not, all three types need water for lubrication and cooling. In some cases, water inside the stern tube is adequate, but a pressurized source of water is generally required. Most conventional stuffing boxes do not require the following modification, but if you cannot keep your box cool enough, you probably need it.

For a source of water most boats tap into the engine’s raw-water loop. A small port is added to the loop and directed to a hose fitting on the packing gland. Depending on the location of your engine relative to the waterline, the injection line may require a vented loop to keep the stern tube water from back-feeding into the engine at rest.

Failure to provide a good flow of water is the number one cause of failure to face seals and lip seals. For boats that do not exceed 10 to 12 knots and which have no bearings inside the shaft tube, the PYI and LasDrop recommend either a vent line attached to a nipple on the seal housing, or water injection as described earlier. The vent line prevents air entrapment at the seal and a vented loop might also be required. For boats that run above 10 to 12 knots or boats that have a bearing inside the stern tube, water must be injected from the engine’s raw-water cooling system. Duramax specifies water injection for all installations.

Twin-engine boats present a complication. If each engine directs water flow only to its respective shaft seal and you have to run on only one engine, the shaft on the non-running engine will freewheel, overheating the seal, and likely ruin it. One solution specifies a crossover hose from one seal to the other, so that water from either engine will flow to both seals. You also can plumb the raw-water line from each engine to both seals. This method provides an extra measure of protection, since the loss of flow from one engine would not lead to an overheated seal. For all of the details described above, refer to the manufacturer’s instructions.

Given the importance of injected water to these seals, your annual maintenance should include inspection of this component. Make sure the hose and nipple remain in good condition and remove the hose from the nipple with the engine running to make sure there is good flow. The fittings and hose are small in diameter and debris can easily obstruct the flow.

Seal The Deal

Boat owners have three good choices. For simplicity, field service, and ruggedness, a conventional stuffing box can’t be beat. But, you’ll have to accept water in the bilge and keep an eye on temperature and drip rate. If you want a dripless seal, face seals can provide thousands of hours of operation. Replacement of either of the main components will require a haul-out and removing the shaft from the coupling.

[Bill O]

I believe once you put it back in after a haul out you would "burp" to remove the air, then you are done (if you don't have the water injection) for the basic models of dripless shaft seals..
We have an older Lasdrop with the water injection with the heavy duty orange bellows and has been working well. We do not have to burp ours to remove air after haul out.

Maybe I'm missing something here, but they do sell the Gen II w/ the water injection so why not just get what you want?? Lasdrop has different styles to choose from besides the Gen II.


Bill O.

[mlydon]

Bill,
My point was that the lasdrop people said “just vent it”, and passagmakers says you have to inject if you have a cutlass bearing (the bearing didn’t come up in my conversation with lasdrop). I had a pss 2 boats back - instructions said to vent, period. No discussion of cutlass bearings. The passagemaker article contradicts that

So, who’s right? Or more to the point, what has the real-world community to say about their setups and experience?

Thanks,

Matt

[Bill O]

Well, our real world situation w/a very long shaft w/a cutlass is use the engine water injector to ensure no air and water flow thru the shaft/cutlass. Been working for years for us.


Bill O.

[daletournier]

I would go the vent not the injection.

I hydrolocked an engine due to the siphon break salting up. I just don't think the injection is needed on a yacht and it offers a unnessary potential problem.

I've had two ventless pss seals, Ive had problems with air getting in there underway. Personally I'd go a tides lip seal over a pss if your shaft is ok, much stronger connecting tube (compared to bellows). I'm actually going to a stuffing box next haul out.

[Montanan]

Originally Posted by mlydon

Bill,
My point was that the lasdrop people said “just vent it”, and passagmakers says you have to inject if you have a cutlass bearing (the bearing didn’t come up in my conversation with lasdrop). I had a pss 2 boats back - instructions said to vent, period. No discussion of cutlass bearings. The passagemaker article contradicts that

So, who’s right? Or more to the point, what has the real-world community to say about their setups and experience?

Thanks,

Matt

Both the bearings and the seal are lubricated and cooled by water. The alternative is to use oil as a lubricant which requires replenishment and obvious environmental issues. Without water they will have considerable friction which will lead to rapid wear and heating. Venting passively removes air from the system that otherwise would block water flow. Water injection basically actively vents by displacement of the air but also forces water into the friction zones and also flushes contaminates.

From the Frequently Asked Questions site of Lasdrop:

Q. Do I need water lubrication?
A. At hull speeds of 8 to 10 knots and above, a vacuum is created in the stern tube that draws the seawater used for cooling and lubrication. At slower hull speeds, no water lubrication is necessary. The supply hose can instead be used to purge the air out of the seal when the vessel is put back in the water. If there is no water injection, ensure there is water to the seals at all speeds. Lasdrop does, however, recommend water injection for all seals and speeds.
I am totally unclear as to how one could "ensure there is water to the seals at all speeds", if there is no water injection.

Instructions related to shaft seals would not necessarily include references to lubrication of further downtube shaft cutless bearings as mounting and lubrication of cutless bearings is its own distinct issue.

From discussions with the Lasdrop customer support they indicated that at the low hull speed of most sailboats there shouldn't be the formation of enough vacuum pressure to suck out the water from the stern tube, bearings and seal to result in lack of presence of lubricating and cooling water in the contact areas of the bearing and seals. The technical service representative indicated that he believes about 90% of sail boats are just passively vented and about 10% utilize active water injection. The open end of the vent line needs to be fixedly positioned well above water line, [else you won't float your boat] and he recommends that it should remain open so as to continuously vented and thus not require "burping" which is something that boaters sometimes fails to occur when boaters refloat their boat after hauling out and forget about the need to purge the air from the shaft. The open end needs to not become blocked else it will lose its venting functionality.

He indicated that if direct injection is readily achieved that would be the best method which is consistent with their FAQ answer.

I suspect that one could on occasion force air through the vent line to be sure it remains clear and purged of potentially blocking contaminates, but that is only an intermittent fix and a blockage might arise between such preventative measures. An water injection system does provide a degree of assurance that contaminates are being forced from the stern tube and clearing the cutless bearing. Boats that come into contact with the ocean bed, such as which dry out due to tidal changes would seem to have much great opportunity for sand and shells to enter the stern tube. I wonder if marine growth could be an additional cause for inadvertent or even intermittent blockage of the bearings or a vent tube.

Review the Duramax website linked here which shows the function and importance of flowing water on their cutless bearings to provide lubrication and to remove contaminates.

http://http://www.duramaxmarine.com/bearingLine.htm

Call the Lasdrop manufacturer and ask for technical advice, if you continue to have doubts.
Office hours: M - F 8:00am - 5:00pm EST

1 800 940 7325 - Toll-free in the US
1 810 388 9718 - Direct and for International calls

Clearly one does not desire for the bearings or seals to run dry.

I have read on another forum post [copied below] that the on some boat's designs the propeller may induce a low pressure zone that could draw out the water from the shaft tube and cause dry running of a cutless bearing and up tube seals. The formation of a low pressure zone may be a result of the proximity and action of the specific configuration of propeller itself and not just a factor of hull speed. I can also imagine that a a sizeable current added to hull speed could be cumulative in nature to the formation of adequate vacuum pressure to result in dry running. By way of comparative example, a wide diameter, high pitch propeller derives torque at a comparatively lower rpm then does a smaller diameter, lower pitch propeller. It seems to me to be a very localized area of low pressure at the aft exit of the stern tube is of key parameter.

"the propellor's action causes a low-pressure area in the water immediately astern of the bearing, as a result most of the water which has percolated into the stern tube whilst sat on anchor will be slowly sucked out once the propellor begins turning and not replaced until the engine next stops.
He suggested that active sea-water lubrication might help: - fit a 6mm/1/4" T junction into the flexible engine cooling water pipe just before the point where it connects into the exhaust elbow and tap a 6mm/1/4" connection into the propellor tube where it emerges into the engine bay (just astern of the existing oil-filled seal) then connect a hose between these new fittings which will then take a proportion of the expended engine cooling water out via the propellor bearing.
Read more at Cutlass Bearing Lubrication


Another useful reference article from passagemaker regarding Dripless Shaft Seals DSS.
https://www.passagemaker.com/technic...ss-shaft-seals

Other useful knowledge from the FAQ:
Q. How long should a seal last?
A. The DrySeal model will last three to five years before the inner lip seal must be changed. If a back-up seal is installed during the original installation, the seal can be easily installed without removing the shaft from the coupling. The “Original” Bellows and Generation II models will last as long as eight to ten years before servicing. Both models would most likely require refurbishing of the seal surfaces. In addition, the bellows on the “Original” model should also be inspected and replaced, if necessary. As in any part, they should be routinely inspected.

Q. Does a Lasdrop seal wear a shaft like the stuffing boxes do?
A. There is absolutely no shaft wear from the "Original" Bellows and Generation II. Because it is a lip-seal design, the "DrySeal" model produces very little wear on the shaft.

Snipets from passagemaker article linked above:

"While a DSS may be "dripless," it is definitely not maintenance free."

WATER INJECTION HOSE

Most DSS units have a small barb fitting on the graphite flange where a hose can be connected to ensure that water is always present right up to the rotor. From the fitting, the hose runs either to a place high above the waterline, or, in the case of higher speed vessels, into the engine's raw-water cooling system. (The instructions for the PSS Shaft Seal, for instance, make a distinction between boats that run above and below 12 knots.)

In most of these installations, the water injection hose runs unsupported from the flange to a nearby stringer, floor, or bulkhead, where it is attached. It is important to use underwater-rated hose, which is quite durable but also flexible.

Best wishes for a dry bilge.

[bharney]

I would definitely go with water injection on any shaft seal. I had a lastdrop seal w/o water injection and ending up destroying it due to it overheating and put a deep groove in the bronze propshaft which then had to be replaced. I then installed a pss shaftseal with water injection, it's been 10 years now with no problems

[Montanan]

Another insightful passagemaker article.

https://www.passagemaker.com/technic...ng-shaft-seals

[Elie]

My shaftseal do not have water injection hose. Once ;aunched, I simply pull once on the bellow and nothing happens. That.s it. I figure that since it is under water, that is more then enough, considering the slow revolutions of the shaft. I check it and it never get warm. so... it must be ok.

[sailormed]

I am not familiar with the lasdrop seal. I have a Volvo dripless seal installed, burp it when you get back in the water after a haulout and that is it. Two rubber lips for sealing, one cooled by seawater the other one by grease. So grease the seal when out of the water, burp when back in the water.
For the rest of the time accumulate dust in the bilge.

[Boatyarddog]

Originally Posted by daletournier

I would go the vent not the injection.

I hydrolocked an engine due to the siphon break salting up. I just don't think the injection is needed on a yacht and it offers a unnessary potential problem.

I've had two ventless pss seals, Ive had problems with air getting in there underway. Personally I'd go a tides lip seal over a pss if your shaft is ok, much stronger connecting tube (compared to bellows). I'm actually going to a stuffing box next haul out.

Definitely agree with this statement, look at the flexible bellows thickness, this should scare you.
If anything tears or twists this bellows open, and there's a lot of things that can accomplish just that, now you have a lot of water coming in where you may not be able to do anything about.
Sorry, give me a pain in the arse, solid packing gland anytime.That tube hose is 1/2"to 5/8" thick, multiple plys.
The new flax Teflon impregnated packing seats fine and the leak rate is close to Zero.
Cheers
SV Cloud Duster

[Frugal]

A note of caution. The water injection model fed from the raw water supply can be a source of back pressure while sailing and the prop shaft freewheeling. I have experienced water ingestion in the motor a couple of times after long rough passages. Solved the problem by disconnecting the feed and allowing it to become a vent.

[Montanan]

Originally Posted by Boatyarddog

Definitely agree with this statement, look at the flexible bellows thickness, this should scare you.
If anything tears or twists this bellows open, and there's a lot of things that can accomplish just that, now you have a lot of water coming in where you may not be able to do anything about.
Sorry, give me a pain in the arse, solid packing gland anytime.That tube hose is 1/2"to 5/8" thick, multiple plys.
The new flax Teflon impregnated packing seats fine and the leak rate is close to Zero.
Cheers
SV Cloud Duster

The Lasdrop Gen II Dripless Shaft Seal [DSS] does not have any bellows, instead it utilizes a spring to put force against the face seal. Accordingly it does not have any bellows to replace or to become damaged. Indeed a bellows is soft and flexible by design intended to be able to be axially compressed and thus give an axial force to aid in sealing. Reference image below of the Gen II product and its enhanced design. The tube hose on the Gen II appears to be made by Trident is also thick and multiply. The debate is thus mostly about what the seal material is and its relative robustness.

Per LasDrop website:

Friction ring assembly uses carbon graphite sealing surface
Cutlass bearing ensures proper alignment to the shaft
Clamp and pressure assembly secures assembly around the shaft, preventing galling or damage to the shaft
Seal ring floats on ball-bearing drive, maintaining complete contact with carbon seal surface
Seal ring features a rubber/fiber ring that rotates with the shaft

[txg]

There is another way to do it, when we repowered the yard that changed the engine plumbed the shaft seal in parallel to the engine raw water inlet so cooling water gets sucked through the stern tube.



This works fine now for about 800 hours. What i like about this idea is that there is a second (yes, it's smaller) cooling water inlet. If the main inlet gets plugged there should be at least enough water coming in to run the engine at slower speeds without overheating.