Keeping the Sea Out
Out of sight, out of mind That adage is so old it creaks, but that doesnt make it any less true. It was especially true of the cockpit drain hoses and gate valves on our 34ft project boat. Back when we acquired the boat, the surveyor looked at the ancient hoses and corroded gate valves in horror and suggested that we replace them before long. Three years later, before long still hadnt arrived and the same surveyor was due to give the boat its insurance condition survey. I knew I was in for a telling-off if he found the same old frozen gate valves and dilapidated hoses still in place. Time to act.
I had not done myself any favors by putting off this task. More than a few boats have gone to the bottom because of aged cockpit drain hoses. Ostara was built in 1973; the hoses looked as though they could easily be original. Apart from looking generally faded and grubby, they showed no visible signs of damage, but that didnt mean anything; they could well have been deteriorating from the inside out.
As for gate valves, they have no place on a boat, at least not below the waterline. It doesnt take long for marine growth to prevent the gate from closing. The wheels on my valves had been frozen open for as long as wed had the boat, and probably a lot longer than that. The fact that I had taped wooden bungs to each hose gave me some sense of security, but still, the gate valves had to go.
Now it was decision time: leave the original bronze through-hulls in place, or replace them? Bronze fittings can last for decades, but not all bronze alloys are created equal, and it is far from unusual for brass fittings to have found their way below the waterline, even on boats from reputable builders. There was just the faintest pink tinge to one of the through-hulls, indicating that some loss of zinc had occurred. Because of this, and because of their age, I felt I had no choice but to replace both of them.
There are two types of seacocks suitable for use in an offshore-capable sailing boat; the tapered plug, and the ball valve. The former must be dismantled and greased annually, while the latter is almost maintenance-free. One way to install a seacock is to drill a hole in the hull, insert a threaded through-hull fitting into it from the outside, screw a flange nut onto the fitting and tighten it against a backing plate, and then screw a ball valve onto the through-hull fitting. This is fast and easy, and its the method many boat builders use. That doesnt mean its the best way. As long as the flange nut cant come loose, and theres a decent backing plate between it and the hull, its an effective enough way to install a through-hull.
The trouble comes with the ball valve. The thread on many through-hull fittings is NPS (National Pipe Straight) and the thread inside most ball valves is NPT (National Pipe Tapered). This means youre mating a tapered thread to a straight threadnot a good idea. An NPT to NPS interface is typically held together by no more than three threads; it wouldnt take much of an impact to separate the two, much less the 500lb of weight, sustained for 30 seconds, that the ABYC says a seacock installation should be able to handle. In fact, I would not call such an installation a true seacockits an inline ball valve.
Forget about trying to save a few bucks by buying a nondescript ball valve. Most ball valves sold in hardware stores are made of brass. You want one with a bronze body and a stainless steel or chrome-plated bronze ball, which is why it would be wise to buy a seacock assembly that is made by a reputable supplier. These come with a flange that is screwed or through-bolted to the backing plate and hull, and the bottom of the seacock will have an NPS thread to mate with the through-hull. Groco makes a stand-alone flange that can be used with an NPS through-hull; its top thread is NPT, so inline valves can be used with it. The upper threadwhich takes the hose fittingon ball valves and seacocks alike is typically NPT.
There are excellent bronze seacocks available from Groco, Spartan Marine, Perko, Buck Algonquin and others but in the interests of saving weight and minimizing corrosion potential, I decided to install a pair of Marelon Series 93 seacocks from Forespar. These robust units are ABYC and Lloyds approved. Theyre supplied with matching through-hulls and have built-in flanges that bring a wide area to bear against the backing plate, thus making for a strong installation. Because of the different coefficients of expansion of the two materials it is not wise to use a Marelon seacock on a bronze through-hull, so the latter had to be replaced.
ALL HOSES ARE NOT CREATED EQUAL
I barely had to touch the ancient drain hoses before the tip of my knife penetrated the rubber walls. The spiral wire reinforcing had rusted in places and parts of the inner surface were crumbly. It was plain to see that one or both hoses could have failed at any time. Any markings on them had long since faded away, so I dont know their provenance, but I suspect they were perhaps not even marine-grade hose.
So, what should I replace them with? I had several lengths of sanitation hose in the basement, left over from replacing the head and holding tank. Would they do? A quick phone call to hose manufacturers Trident Marine reassured me that yes, marine-grade sanitation hose would do nicely. So would marine exhaust hose, but thats several times the cost. One thing I certainly would not do is use the thin-walled, corrugated stuff marketed as bilge-pump hose. Even if youre paying several dollars a foot for your hose, youll only need a few feet, and this is one area where theres no point in skimping. Trident 100, 110, 148 and Shields 101, 148, 149, 141, 144, 105 and 250 are all suitable for cockpit drains, as is Vetus exhaust and sanitary hose.
As it turned out, the sanitation hose Id hoped to use was too stiff and inflexible for the required bends between cockpit drain fitting and seacock, so I had to fork out another $20 for 4 feet of Shields 148, which eventually coaxed into place.