Holes in the boat
Let’s talk about seacocks and thru-hulls. No, contrary to what my coffee-deprived early-morning photoshop image below might imply, seacocks are not some strange water-based fowl. They are instead valves which control the flow of liquids or gases through the thru-hulls (through-hulls) in a boat.
When it comes to thru-hulls, they can be located either above the waterline or below it. The ABYC marine code dictates that all thru-hulls that could end up under water need to have a seacock attached to them. In a cat, that’s pretty easy to determine but in a monohull’s case, thru-hulls that are located above the waterline when the boat is at rest may in fact be underwater when the boat is heeled over. Something to consider.
In our boat’s case, there are only 4 below-the-water thru-hulls: one for the watermaker/head input, one for waste discharge, and one each for the speed and depth transducers. In the post where I described our latest head troubleshooting job, I mentioned that we had T-ed off the head intake for our watermaker input. In my mind, the fewer holes in the boat we have the better, especially ones below the waterline. As a comparison, the boats belonging to some of our friends have 14 or more!
This images shows three thru-hulls above the waterline and two below it. The other two below-the-water thru-hulls are located in the same area but are not visible from this angle.
Fortunately for us, all four of our below-the-water thru-hulls are confined to the same forward locker making it easy to inspect and control them. Thru-hulls are like any other moving part on the boat, they need to be exercised. At some regular interval, it is a good idea to open and close the seacocks that are typically left in one position, just to make sure that they do not seize up (something which is reportedly quite common). It’s also prudent to have nearby some method for plugging the holes in the event that the seacock breaks off, the traditional method being to have a wooden plug fixed nearby each of them that you could hammer into the hole to stem the flow of water. Because our thru-hulls are all confined in that one location, we go one step further and keep nearby a container of Stay-Afloat in addition to the wooden plugs.
Another prudent thing to do to prevent water intrusion from these sources is to use only high-quality stainless steel clamps on each of the hoses attached to them, and also to double up on them, using two clamps on each hose. Make sure that you inspect these too as just because they are labeled as stainless, it does not mean that they won’t rust. Remember, it’s stain-LESS, not stain-PROOF. During my last trip into that locker I found that the screw portion of many of the hose clamps had indeed rusted considerably, warranting replacement.
Hungry for more reading? A lot of info on thru-hulls and seacocks, including some excellent photographs, can be found on this page.