Dripless shaft seal maint.

On mine it would have to plug the lines from both engines to overheat, I think most are set up with a crossover. I guess if one side plugged up, I wouldn't know until the other side plugged and it overheated. Anyone have a technique for checking flow in both lines all the way through the fittings in the seal?

Crossover lines are a must , cheap insurance.

They cut your odds by half I suppose, but how would you know if one side was plugged? I didn't think plugging of these was that common. I did have an impeller disintegrate, and never checked or back-flushed that part of the raw water system.

It's usually scale build up in the nipple. Take the hose off of the nipple at the dock and water should shoot out like a water fountain. Generally the major issues I've had were tide seals, had nothing to do with cooling, more to do with sitting. On several boats, I've had them swell and freeze on the shaft, then literally rip the cooling hoses off and play weed eater......on one boat it cut a bunch of bonding wires. On another boat it cut the cooling lines for the chillers.

Yeah, pull the hoses at the dock. No need to back the nipple out, water should shoot out of the nipple if it's clear.

I always install a filter screen on the line running from point on the engine (gear) before the hose to the dripless. Most of the crud caught is pencil zinc debris, easy enough to add to your maintenance schedule.

https://www.mcmaster.com/#standard-strainers/=1bfshwq

Seems like that filter plugging up would be no better than the line plugging up, and more likely...?

I guess it would be good to pop that line on each seal to let air out when I put the boat in the water, good time to check flow.

There's a lot more cross sectional area of the screen than the 3/8" line itself.

Thanks for sharing the builders solution, it is helpful to have an easy to check inline solution.

I would think that this would go on any boater's maintenance plan to be checked once/twice a year.
So how would you plan on lubricating the shaft seal when one of your twin engines goes down and you have a long run home on one engine?

I have in the past locked the shaft with a rope in some cases. On some yachts I installed a T on both lines and ran a crossover line to the other shaft......that way, if either engine was running both driplesses would get cooling water.

What mesh size? As long as it only blocks particles too big to pass harmlessly through the shaft seals, it is beneficial. If it blocks smaller particles, it becomes the critical component that can fail your shaft seal by plugging up. I think my sea strainer blocks particles big enough to plug my shaft seals, the only other source of particles is the impeller.

All the dripless shaft seals I've looked at have two connectors, one for the crossover allowing either engine to provide water.

On another forum we were talking about transmissions freewheeling and was that healthy? One guy kept his boat moored in a river with a 15-knot current. He contacted Regal about his Velvet Drives, and they said it wouldn't hurt them. He had dripless shaft seals, hadn't thought about those, no problems in ten years in that river.

I doubt the seals will get hot running at rotation speeds likely, while dragging at hull speed. The shaft itself will provide a lot of cooling, and if the air has been purged there is water and turbulence at the water side of the seal.

These lip seals are the same as the lip seals used on crankshafts and output shafts, keeping oil in your engines and transmissions on cars and boats. They aren't simple rubber seals, they are very wear resistant, heat resistant, they can tolerate grit and abrasives. That is why I'm surprised to hear they are failing, I guess I'll add checking my cooling lines to my list.

I use the "20" mesh size and order the monel versions for replacements. Most of those dripless lip seals are Nitrile rubber and cooled by water injection behind the seal so yes, small particles usually pass through with no problems. Most of the reported failures though are traced to zinc chips clogging at the hose nipple going into the dripless seals. If that happens you also lose the crossover feed water. Those zinc chips are coming off the engine and transmission sacrificial zincs and any in the heat exchanger cores, all those are after your seawater intake strainer!

Interesting. My shaft seal water comes off my exhaust manifold, Tides specifies it come off the raw water line before the engine. Maybe I'll change that. I was considering putting valves on those lines, they are the only connection between raw water systems. If one raw water line blows, you can shut off the seacock for that engine, but will get a steady stream of water through that crossover. I'm not sure at what pressure, I just noticed it when changing my impellers. Had to shut off both seacocks to stop the flow on either engine.

Very interesting! Tides drawings show tapping (using one of their tees) off the hose going to the mixing elbow which is very commonly done. Alternative locations I've also seen are the transmission cooler or an unused fitting towards the end of the seawater cooling circuit before the exhaust dump.

I've also done a few installations in trawlers and sailboats with exhausts or engines below waterline which have a different set of requirements due to siphoning or lift mufflers but that's another discussion.

Tides are THE ONLY dripless I've had issues with over and over. If the boat sits, the hard rubber (plastic whatever material) part that rides on the shaft swells, locks onto the shaft, and then plays weed wacker with the cooling hoses.

Thanks guys, so many new things to worry about!

How long sitting would result in sticking seals? I'm surprised the seal has enough strength to rip the bellows loose, does it rip the bellows or just spin it on the stern tube? The seal surface is tiny compared to the bellows. These should be very high-carbon rubber, shouldn't easily stick to things. Could anything be getting into the seal that would dry into a glue? Dried salt? I'll shoot an email to Tides asking about this.

My boat sat a lot in Canada, 300 hours run time in 12 years, but probably not much more than six months sitting. Maybe cold weather helped? Or maybe with low hours, the seals haven't worn grooves into the shafts, which would've made seizing more likely? Or maybe running anti-freeze through the raw-water system put just enough lube in them to not stick? I'm using heated storage, so I'm not doing anti-freeze. I've not heard of seals sticking to shafts around here, but I'll ask a friend who owns a marine service company, repairs and stores a lot of boats.

Perhaps a little mineral oil in each seal would preserve them, assuming the seal material is oil-safe.