The Offshore Voyaging Reference Site

Seacock Lubrication Tip


The ice has finally gone out of our inlet here at Base Camp and we are getting Morgan’s Cloud ready for launching. Here’s a neat tip that my friend Bob (a fellow charter member of the anal retentive boat owner’s club) taught me.

Why You Should

Metal seacocks should be lubricated every year before launching. If you don’t grease them they will eventually seize up, and since Mr Murphy is always in charge at sea, you will find that state of affairs when you try to close the seacock after a large water hose ruptures.

It’s even worth lubricating the relatively new “maintenance-free” seacocks—those with teflon mating surfaces. Why? Well teflon (PTFE) is also manufactured with oil imbedded as an additional lubricant, but that’s not what they use for seacocks. The point being that if teflon is good, greased teflon is better.

Even if your seacocks don’t seize up, if you don’t lubricate them they will eventually stiffen up so that when working them open and closed you will be putting a huge load on the mating surfaces where the actuating shaft (that connects to the handle) and the ball bear on each other. Eventually, slop will develop in this area and the ball won’t fully close-off the seacock—a scary problem since we might assume a seacock is closed to the deep blue when, in fact, it’s not.

As an aside, the seacocks on a lot of older boats have this problem, and so we should all check for it regularly and look carefully. We have had to replace two seacocks on Morgan’s Cloud for just this reason, that looked and worked fine on casual inspection.

The Hard Way(s)

OK, now we know we have to lubricate, but how exactly do we go about doing that?

Sure we could pull the hoses off to lubricate the ball by squirting a spray lubricant in with the seacock closed…lots of luck with that. Ever tried getting a large hose off a tail pipe it’s been clamped to for even just a year? Good way to burst a blood vessel.

Or we could squirt some spray lubricant in from outside, but it will drip all over our boat’s newly painted bottom.

Worse still, some spray lubricants contain solvents that will dissolve bottom paint. How do I know this? Well, it wasn’t pretty, and resulted in a lot of sanding and repainting.

And anyway, spray lubricant won’t last long.

Some seacocks have a plug you can remove—ostensibly there for draining, which is, if you think about it, a pretty useless “feature” for most of us since said seacock will drain when you open it. But you could temporarily replace said plug with a zirk fitting and use a grease gun. What a hassle.

The Easy Way

Or you could do it Bob’s-Easy-Way:

  1. Close all the seacocks.
  2. Paint the balls from outside the boat with Lubriplate 130-AA grease, which lasts great underwater, using an acid brush (see photo above).
  3. Work the seacock through its entire travel a few times.
  4. Repeat as necessary.

The above process is faster and easier with two people, one working the seacock from inside the boat and the other outside the boat painting the balls.

One caveat: If you have the old fashioned seacocks with the tapered cylinders, you should probably completely disassemble them for service every three years or so since they depend on a clean well-greased mating surface on the cylinder and casing to remain waterproof. Having said that, Bob’s trick will work fine for the interim years.

Thank you, Bob.


Do you have any cool pre-launch maintenance tips? ‘Tis the season, at least for us northern residents. Please leave a comment.

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Dick Stevenson

Hi John,
Good suggestions in part because it is almost exactly what we do. The difference is Ginger sprays our grease in from the bottom while I work the seacock, the former being what you advise against. I believe in the US we were able to find a spray Lubriplate, but over on this side of the pond I have settled for CRC White Lithium Grease which has seemed to work fine. It does dribble a bit so I only do the spray after the bottom paint is done and dry. The dribble has not affected my bottom paint (usually Micron) in any noticeable way. In any case, I see no reason that spray grease, well worked in to a moved back & forth seacock, should not last as long as a brushed on grease, similarly worked in (maybe spray Luibriplate is less thick?). That said, brushing sounds likely to be more thorough and less messy with over-spray.
My best, Dick Stevenson, s/v Alchemy


Doesn’t this just lubricate the half that’s exposed to the outside while leaving the inside half unlubricated?

Marc Dacey

That’s what the back-and-forth is for. The action puts the greasy part of the ball on the inside mating surface, and some will get on the other side with enough action.

I also use lithium grease. I will switch to Lubriplate for salt water as it appears more tenacious.


Marc, it might just be the model of Groco seacock that I have but mine only allow 90 degrees of motion on the handle so there’s virtually no overlap.

I’ve also not figured out a better solution than painting the outside with grease so that’s what I do too.

Eric Klem

On some seacocks, you can actually get them to turn a full 360 if you remove the handle and use an adjustable wrench instead. If you look at how they are put together, the stops are usually built into the handle.


Todd Huss

Eric, great suggestion! My solution has been to fully open and then close the handle ever so slightly. I then reach a brush up to get some grease on the leading upper edge (the inaccessible side) of the ball in the hopes that the closing action will spread the grease on that side.

However, it’s always bugged me a little knowing one side is properly greased and the other is very slightly greased (but not enough to remove the hose from every seacock). You’re absolutely right that removing the handle will allow a full range of motion to do the entire job from the outside of the boat!

pat synge

I suggest using Silicone Grease.
I’ve always used the Molykote brand (others may be just as good) which is extremely water resistant and tenacious. It’s also useful for O-rings, sail slides and all sorts of other things.
Good stuff to have on board.


I developed a corollary to my law: “If anything can go wrong, it already has: you just don’t know about it yet.”
Westbrook Murphy

Patrick Genovese

Any suggestions on alternatives to Lubriplate for us on the other side of the pond ? 🙂

What about marelon sea cocks.. I’m thinking of changing some of my seacocks to marelon.

pat synge

Hi John
Why do you refer to the ‘consumer line’ of Forespar seacocks as being ‘junk’?

I’ve inspected dozens of boats with these seacocks and, despite the stories, have only ever seen one that has failed. The handle broke – probably because the valve was never opened/closed and had consequently seized and was then forced. I’ve come across many that were stiff to operate but then most people don’t maintain (or even use) their boats correctly. I would like to think that most AAC members are not in that category.

Forespar seacocks may not be foolproof and you probably shouldn’t stand on them but the vast majority of seacocks are located in spots where you would have to a contortionist to do so (though with a claimed tensile strength for Marelon of 27,000 psi they should not be much less strong than the equivalently dimensioned bronze fitting).

Yes, like any other valve they should be greased annually and, ideally, opened/closed occasionally in the interim but in my opinion they are far better than most of the so called “bronze” ball valves I see installed. Many of which I would call junk.

They may not be the very best but I suggest that they are far from being ‘junk’. At least they have a readily accessible flange to make life easier for the installer!

pat synge

And did you note the price of the Marelon lubricant, John?
Gold plated!

Silicone grease will do the job very well (and dozens of others on board as well from battery terminals to sail slides as well). $40 for 400g (including postage if you are in US).

It doesn’t say it’s suited for marine use, of course. It would probably cost at least twice as much if it did!

pat synge

You’re absolutely right about being wary of using just ‘any old lubricant’ on plastic and might be interested to know that Synco provide useful information about their lubricants’ compatibilities with a wide range of plastics.

This why I was suggesting having this specific lubricant aboard: because it is so versatile and compatible with such a wide range of polymers. The fact that it’s relatively inexpensive is a bonus.

Alan Teale

Patrick, K99 Water Resistant Grease by Morris Lubricants, Shrewsbury, is compatible with plastics. It is widely available in chandleries in the UK. It is recommended by the manufacturer for use in stern tubes., etc.. We use it to pack our rudder tube and we will be trying it in our Marelon seacock. Alan

Tim Good

Interesting. The general consensus in the UK seems to be NOT to grease seacocks for fear of attracting dirt that will wear away the ball valve. Then again, a lot of the blogs I read from the US, people seem to be using blakes whilst most boats I see in the UK seem to have standard ball valves screwed directly to a skin fitting.

I say this with relatively limited knowledge given that you guys have seen a hell of a lot more boats that I.


It is an odd one I agree, looking at the differences in practice. But even the likes of Hallberg, Najad, Nauticat etc have been using ball valves as seacocks and they are regarded to employee the best boat builders in the world.
I agree though, the Blakes style do look the way to go but I have never had a boat with one to compare.

I haven’t seen a chandlery blindly selling brass seacocks and skin fittings. I think it is commonly known here that it is bronze or DZR brass for a seacock. I suppose the total success of DZR is still yet to be seen maybe?

Neil McCubbin

We lubricate our marelon seacocks with olive oil
I am a bit shy of lubricate on plastic, although it works well in our Maxprop

Neil McCubbin

Ball valves vs Seacocks
Agreed 100% that brass is a bad valve material for seawater, whether in a ball valve or the gate valves used by the cheap builders in the past.
However, ball valves are used widely in industry for fluids dramatically more corrosive that seawater. When buying form an industrial source, the full specs are available and reliable, which is not true for all products in the yacht market.”Seawater resistant bronze” is a meaningless term, for example.
One issue with most ball valves is that they have NPT female threads (outside diameter tapering), which are unreliable when screwed on the parallel (NPS or BSP) threads on a standard through hull fitting. The unfortunate issue is that the NPT thread fits, and is watertight with some Teflon tape. However, the joint is structurally weak, and is liable to wiggle and leak.
The solution is to tap the NPT thread out to NPS (easy if you have the tap) or to buy a valve with the proper thread.

Wilson Fitt

Hi John

I fully endorse going for the best seacocks available, damn the cost. When originally equipping my boat, I went with Buck Algonquin flanged seacocks because they were the stock items at local chandleries and appeared to be good marine quality gear. But in less than a year one of them stuck half closed (the head discharge of course) and over time they all became difficult or impossible to operate. It seemed that the chrome plate on the ball was pitting. I contacted B-A about the first one and they replaced it, but did not provide much of a reason for the failure and my confidence was lost.

I replaced all the seacocks with Grocos at great expense. Ten years later and without any maintenance whatsoever, the Grocos still operate like new, but being a good ACA disciple I greased them this week for the first time figuring it can do no harm.

Neil McCubbin

Choice of seacock depends also on hull material. With wood, and I suspect fibreglass, a good solid bolted flanges give great, and probably necessary strength.
In our aluminium hull, we have high quality reinforced plastic ball valves, which screw on to the threads of 8 mm thick tubes welded to the 8 mm thick hull. The tubes are same alloy as hull, machined with the appropriate pipe thread. No signs of corrosion after 10 years in the water.
I am much more scared about corrosion if I used a metal valve than physical weakness of the plastic. That said we installed a structure around each seacock that prevents any large moving object, or foot, from applying a load to the valve.
I will get some of that silicone grease Pat mentions above, instead of our olive oil lubricant


Of course a properly designed boat has a sea chest rather than a baker’s dozen holes drilled throughout the boat — typically in the most inaccessible of locations. And with one big valve for closure there is less temptation for the bean counters to “earn” their keep by replacing all the sea cocks with ball valves.

Of course even a ball valve is better than the sea chest on an Italian motor yacht I once worked on. One of the 4″ diameter engine feed lines had a 1/4″ diameter hole in it which someone had “fixed” by applying duct tape and painting it white.


Excellent thread. Just wondering if anyone has concerns about lightning strikes and what they may or may not do on boats with bronze vs. Marelon seacocks? We’ve all heard stories of boats sinking due to thru-hulls being blown out by a lightning strike…


Will there be a problem with the grease fouling watermaker membranes or filters?


Hi John,

It seems to me that whilst sea chests have advantages, one still has to be just as careful about siting and protecting the fittings/valves that go onto them. I have no experience in this regard, but looking at some of the images on the net, it would appear that these valves too could be dislodged by a forceful bump into them. With the tall narrow sea chests typically seen in the few yachts that have them, would this complicate the servicing and access to the valves? Looks like nothing will substitute for thorough planning and good engineering.

Marc Dacey

The equivalent plan on a standpipe would be to thread a strong monofilament or a light wire through those crushable plugs used as “soft bungs”. If a teed-off seacock fails or requires service, a sufficiently sized bung jammed down to the grate end of the standpipe (and secured with pressure from above if needed) should retard water ingress well enough to fix what needs fixing. The alternative for more customary seacocks is to dive on the boat, rubber mallet in a softwood bung if the absence of “ears” allows it, and drive the bung out an opened cock from above. I’ve done this, and it creates a nice fountain effect!

Marc Dacey

Yes, the standpipe terminates above the waterline, but the tee-offs are below the WL. To swap out or to service one of the seacocks for a) engine raw water, b) head intake, c) A/C circuit or d) seawater to the galley would involve plugging the bottom so I only had to drain the water in the “column”, so to speak, in order to remove, replace or service individual shut-off while still afloat. The upside is only two drain lines out (head and galley) and only the standpipe “in” below the waterline. I’ve seen some boats with a dozen holes in the hull, which I find anxiety-inducing.

Robert Snelling

I used Forespar LanoCote this year (first time); I had to warm it up prior to application as, when cool, has the consistency of beeswax; very difficult to apply. I’m going to try and reapply it once our Nova Scotia weather hits the double digits

Ee Kiat Goh

Dear all, Forespar Marelon Thru Hull. Does anyone knows if marelon is a reliable product to use under the waterline? Any bad experiences of them breaking off? Thank you.

Ee Kiat Goh

Hi John, I am using this thru hull with a Hansen ball valve from Australia. A very experienced sailor recommended Hansen industrial ball valve to me 10 years ago. I didnt know any better then so I had most of my plumbing fitted with Hansen product and I havent had them leaking sinced So far so good. Have you or anyone here used Hansen product with negative experience as I am trying to avoid a surprise failure. However, I am concerned with Marelon as an over confidence in the material has made me overlooked on its replacement (10 years old). How long have you used your Marelon gear below the waterline before you replaced them?

Ee Kiat Goh

Hi John, thank you for your advice. I will look into replacing my seacocks on the next haul out. Let me read your other article on “how to” install one.