seacocks & Thru-Hulls

My Thru-Hulls & Seacocks are 14 years old, and all appear to be in perfect shape. Is there a rule of thumb or test to determine whether they require replacement?

What sort of seacocks (why were they never called sea-roosters)?

a) bronze tapered-plug or cone valves (which some regard or used to regard as the ‘only’ acceptable seacocks; or
b) bronze full-port ball valves, with PTFE-coated ball rotating in a bronze housing; or
c) plastic (glass reinforced Marelon or Zytel etc); or
d) high-zinc content brass gate valves; or
e) high-zinc content brass ball valves; or
f) something else that I cannot think of at the moment.

Brass valves made from a high-zinc content brass meant for fresh-water plumbing were surprisingly common on low-priced production boats in some economies. UK boating magazines used to run a story a year (until about 2011) about the dangers of dezincification in brass seacocks. ** (late edit: seems the UK wasn’t the only economy using yellow brass/high zinc brass, and seems the practice didn’t end in 2011. See: for MaineCruising’s suggestion that brass components were still being used in 2011!)

I doubt that any BCC from Sam L Morse Co. was built with high zinc content brass.

Quality bronze seacocks could be expected to last 30 years or more, depending on use and maintenance.

Tapered-plug valves may need honing or re-plugging. And then another 30 years could probably be expected.

Full-port ball valves, with a PTFE stainless steel or bronze ball should last 30 years. I don’t know if enough experience has been gained on failure of the PTFE (theoretically it should not fail, but nothing else lasts forever so …). I’ve not seen anyone publish data on the wear/failure rate.

Same goes for Marelon/Zytel valves: I don’t know if they’ve been around long enough to show failures (except from side-loading causing the plastic to break and crevice corrosion on the stainless steel fixings).


Okay, you’ve convinced me that my Groco seacocks probably have another 15 years of service life as long as I maintain them properly.

My other question is “what’s the life expectancy of the thru-hulls?”

traveler Wrote:

My other question is “what’s the life expectancy
of the thru-hulls?”

If your thru-hulls are also Groco bronze, I’d guess they would outlast the PTFE-coated balls in the Groco full-port ball-valve seacocks: in other words, unless subject to galvanic corrosion or current leakage corrosion, the thru-hulls should outlast the GRP hull.


I would think/hope my thru-hulls are Groco as well. At any rate, I’m not going to replace them unless there is some sign of galvanic or current leakage corrosion like you mentioned Bill. I’ll post some photos later this summer once I complete the last of my refitting projects.

You are a wealth of knowledge Bill!

It sounds like you and your boat are not at the same place. I wouldn’t assume that your seacocks are Groco. Groco used to make rubber tapered plug seacocks (which Sam used in our head) and now make only ball valve seacocks. Sam used Wilcox-Crittenden tapered plug bronze seacocks on Shaula, in 1981 except in the head. If your seacocks are the tapered plug type, they may leak in the off position due to metal loss on the mating surfaces. This might not be noticed unless you removed the hose although if there’s enough metal loss, water will leak into the boat even when the seacock is turned off. This can be corrected by lapping, using grinding compound and a lot of rotation, most easily done after removing the seacock to a vice.

Bronze tapered plug seacocks should be disassembled during haul out, inspected and regreased. A common problem with seacocks is due to lack of use–the handle can’t be turned. It’s a good idea to work the handle from time to time to make sure it’s not frozen.

The forum has discussed seacocks several times in the past. You will get several opinions on threads using Search.

Hi Dan,

I checked my seacocks today and they are all groco (ball valves). They all exercise freely and will hopefully provide many more years of serviceability as long as I keep up with the periodic maintenance.

I did a search prior to my posting, but none of them addressed my specific questions like this thread has.

Thank you for responding Dan.