Archive for the ‘thru hull’ Category

That Sinking Feeling off the Baja Coast

Clark February 3rd, 2016

3 on deck
It was 1991, and we were three fools fresh out of San Diego State. Brian had bought an old Catalina 30, and we spent six months fitting her out. Against my protests, Brian changed her name to Break‘n Wind, a boat name I’ve encountered several times over the years, and never liked any better.

Brian’s artist buddy painted the new name and hailing port on the transom, along with some sorry-ass blue palm trees. I asked the artist, “Isn’t break spelled B-R-E-A-K?” He’d spelled it Brake’n Wind. The paint had already semi-dried, so we ended up with one E wedged in there somehow, and another E rubbed out with acetone, and it never looked quite right.
The overfilled cockpit, with fresh flowers from our bon voyage party.

We finally set sail and ran down the Baja coast at night, the boat laden with windsurfers, surfboards, a guitar, scuba gear, and enough food to transit the Northwest Passage. Tim, the third crewmember, was on watch in the cockpit while Brian and I tried to sleep on opposite sides of the main salon.

I was drifting in and out of sleep when the automatic bilge pump light caught my eye. It went out and I closed my eyes again, but ten seconds later the light came on a second time. When it lit the third time I nudged Brian, “Hey, the bilge pump has gone off three times.”

Brian flipped out of his bunk, turned on the lights, and ripped up the little floorboard in the middle of the main salon. Water poured into the bilge from somewhere aft. We opened the engine compartment, where a stream of sea water flowed past the engine mounts.

“She’s taking on water!” Brian yelled.
“What!” Tim peered down the companionway, wide-eyed.

We cleared out the quarter berth to get access to the packing gland, and Brian squirmed in with a flashlight.

“It’s coming from farther aft, and it’s a lot of water now! It must be the rudder!”

We were a good fifty miles off shore, following Captain John Rains’s advice to sail well outside the shipping lanes. Panic.

We tore open the cockpit lazarettes and scattered ridiculous piles of junk on deck: scuba tanks, fins, masks, wetsuits, spears, beach chairs, a barbeque, windsurfer sails, oars, and awnings. It was the adventure of a lifetime and, well, we’d overpacked. Occasionally the beam of the flashlight met the spooked eyes of a shipmate, and around us were only blackness and a cold winter westerly. We avoided eye contact as we moved the life preservers, the ditch bag, and the EPIRB.

The automatic bilge pump ran nonstop.

We emptied the aft lazarette, which gave us access to the rudder stock. In the aft lazarette we could also see the bilge pump’s thru-hull. Next to the thru-hull, unattached, lay the bilge pump hose, with water spewing out of it, into the lazarette.

“We’re saved!”

We slid the hose back on the fitting with a new hose clamp, and the bilge pump pumped the same load of bilge water for the last time.

Bug-eyed with the adrenaline of our first mid-ocean crisis, the voyage began in earnest, and our little ship seemed more plucky and devious. At our bon voyage party a friend had given us a bottle of single malt scotch that was much too good for a couple of twenty-one year olds. We took slugs out of the bottle and talked about near misses, what ifs, what-to-dos, and all the adventures we were about to have in Mexico.

Brian and Tim drifted off as I started the 3 a.m. watch, with my first sunrise of the voyage to follow.
Break’n Wind under sail

No-Nos and Good Practice with Thru-Hulls and Seacocks

Clark October 27th, 2013

A common boatyard misdeed is to install a thru-hull like this,
All images courtesy of Groco
then screw on a ball valve like this,
ibv wv 225
with an appropriate tailpiece connected to some item of plumbing below the waterline. This is done all the time, but it’s bad practice for several reasons:

1. The threads don’t match. I’m not the first to write about this: If you go here, on Compass Marine’s excellent technical blog, he has even cut a fitting in half to show the difference in the threads.

The thru-hull has straight threads (NPS, National Pipe Straight) and the ball valve has pipe threads (NPT, National Pipe Taper). They’re not meant to go together, but if you force them you can get 2-3 turns and a watertight seal. Two or three turns isn’t enough overlap for a strong joint.

2. The threaded part of the thru-hull isn’t meant to be exposed, at least not when it’s below the waterline. It’s meant to have a seacock surrounding it. Left naked, the grooves where the threads are cut make for thin spots, lots of them.

3. If you use this method you’re not spreading potential loads on the the thru-hull to enough of your hull. Even if you’ve got a good backing plate, the thru-hull should still attach to a flange of some sort, which is then thru-bolted to the hull. By the cheesy method, the only thing spreading the load of the thru-hull, and holding it to the hull, is the bronze nut that came with it.

The ABYC standard is for the assembly to withstand a 500-pound lateral load for thirty seconds.

The proper solution is something like this, a seacock:

It’s beautiful, isn’t it? That big, heavy slab of bronze, with its wide base. So seamanlike. It also retails for nearly $300 for a 1-1/2″ version, which is why so many people cram ball valves onto straight-threaded thru-hulls.

Condesa had two lingering ball-valve-on-thru-hull seacocks that I got rid of during my last stint in the boatyard. Mind you, both of these stood up to at least 12 years and a circumnavigation, but the longer I live and the longer I own my boat, the more serious I get about eliminating weaknesses that could sink her.

I’d been eyeing Groco’s flanged adapters for some time, and they ended up working as advertised:
187287 GRO IBVF 750 PPM
The idea is to give you the same solid, strong base as a proper seacock, but with pipe threads, which will accept a standard ball valve:

The combined cost of the flanged adapter and a quality ball valve is about half the cost of a bronze seacock of the same size. (A 1″ seacock retails for $180. A 1″ flanged adapter is $40; a good 1″ ball valve $40-$50.)

When the valve wears out, you can just swap out the the ball valve without replacing the whole seacock. The flanged adapter doesn’t look like something that’s going to wear out. For price and swap-ability, the flanged adapter arrangement seems superior to a bronze seacock.

Bronze NPT ball valves are available everywhere in the world. Bronze seacocks are not.