Thru-Hull Stats

[Plymouth Sailor]

I’ve been sailing for sometime now but it still surprises me that most boats have holes in their hulls in which upon failure of the mechanism - thru-hull - water may rush in, (my hull has no less than 7 below the waterline). Given this, I’m frankly surprised that we don’t see more boats sinking. Does anyone know what the percentage of boats are that have this problem?

 

[dlochner]

A high quality properly installed through hull will seldom if ever fail and flood. The failure mode for the valves, ball or seacock valves, is to seize either open or closed. This is particularly an issue with the old style cone seacocks. What can fail is the hose attached tot he seacock.

Improperly installed through hull can fail, had a through hull failure this fall. I didn't see it, however from the description I believe it was an improperly installed through hull. Some DIYers and some boat builders have been known to install the through hull and then just attach a valve to the through hull fitting and not a proper flanged seacock. The through hull fitting itself is pretty weak. The wall diameter is thin and when threads are cut in, it becomes thinner. Stepping on these through hulls or trying to move a sticky valve and bend and fracture the throughout. I believe this is what happened to my friend. A proper flanged seacocks will bury the tube inside the seacock and the flange which is secured to the hull will prevent the tail piece from bending and cracking.

With all that said, take a look at the BoatUS Insurance site, they sometimes provide this kind of information.

 

[Don S/V ILLusion]

Does anyone know what the percentage of boats are that have this problem?

I’ve seen data somewhere I can’t recall which essentially says 100% of boats with improperly installed or inadequately maintained ‘sea cocks’ can and may fail.
The moral of that story is ….

 

[Ralph Johnstone]

some boat builders have been known to install the through hull and then just attach a valve to the through hull fitting and not a proper flanged seacock.

I'm afraid that "some" should be replaced with "most". I started looking at through hulls at boat shows many years ago (back when we still had boat shows) after becoming aware of the danger. From what I remember, all Hunters and all Cats were not flanged. Some of the European boats, which escape my memory, were flanged but they were rare.

BTW, nope, haven't re-done mine yet. HOWEVER, I have pulled the hoses on several to inspect the internal circumference of the threaded portion, and after a wipe, they still appear corrosion free. Still no reason for not replacing .

 

[Ralph Johnstone]

But @dlochner , does your boat have flanged thru-hulls or no ?

 

[dlochner]

But @dlochner , does your boat have flanged thru-hulls or no ?

Yes. Groco Flanged Ball valves. Original from the factory. Unfortunately they were not installed in photogenic positions. Here's one for the head sink, the most easily accessible one.

I did replace one valve because a seal had begun to weep. It was not going to be a catastrophic failure, it just an annoyance. It leaked about a gallon a year if that. It was accessible so I just kept it closed except when being used.



Probablylea

 

[Ralph Johnstone]

Yes. Groco Flanged Ball valves.

Looking like that, you're going to want to protect the surface with some form of protectant to keep that bright bronze finish. Maybe Krylon spray on clear acrylic. My valves have all discoloured after 24 years.

 

[jssailem]

Failure modes need consideration:

• With a seacock located in an exposed (you can easily step on it or use it to control a fall when the boat is moving) position the action of crew/operator may cause failure.
• Seacocks that are rarely used can fail to work.. Crew wanting to open or close can attempt to exercise the valve, even using a tool to leverage their effort, can cause a failure.
• Corrosion of the metals - the valve, the thru hull fitting, etc can cause failure or contribute to failure. This maybe the most frequent cause as often the corrosion is hidden from view.

My example: The raw water seacock on my boat, age unknown at time of purchase. Seacock worked with out need for force and was serviceable right up to the point when I removed it.

Attempting to remove the valve from the thru hull fitting, the valve broke in to two pieces (as seen in the image). The pink metal shows that the valve had experienced galvanic corrosion from the inside.

Regular inspection and control of galvanic corrosion aboard your boat is critical to continued safe use. If you do not know the age of your valves or their quality, it may be time to replace them.

 

[Ralph Johnstone]

@jssailem , does your boat have flanged or no flanged thru-hulls ?

 

[dlochner]

Looking like that, you're going to want to protect the surface with some form of protectant to keep that bright bronze finish. Maybe Krylon spray on clear acrylic. My valves have all discoloured after 24 years.

Too late, the photo of the bright shiny one is a few years old. Not going to polish it.

 

[jssailem]

My boat came with a 3/4 inch thick solid fiberglass hull. The thru hulls are centered in a wood backing plate and reside in a dry area of the hull. No valve flange was used. The area of the hull is covered with a sole deck. The valves are hidden in their own compartment and not exposed to potential contact damage.

 

[Ralph Johnstone]

and not exposed to potential contact damage.

What about corrosion ?

Are you reeeeaaally sure there's nothing going on in there you should know about ?

 

[jssailem]

Good question Ralph. Sure. What is that when it comes to t boat.
I have taken all the normal precautions.
Galvanic Isolator, Grounding strap to metal through hulls, Zincs, occasionally performing corrosion potential survey on the boat.

Pretty sure having a "Flanged Valve" is still metal and if something is going on it will not be much different.

 

[Tally Ho]

I would guess more boats sink because the valves are left open and the hose or clamps fail…

I know my galley drain hoses, with a below the water line thruhull we’re pretty close to failure before I realized it…

I try to keep all of the below the waterline valves closed when not on the boat…but that was not always the case.

I do not have flanged thru-hulls, but an upgrade is on the to-do list at some point.


Greg

 

[Ralph Johnstone]

Pretty sure having a "Flanged Valve" is still metal and if something is going on it will not be much different.

Quite right indeed. Same old corrosion ............................ buuuuuuuuuuut, the seawater exposed parts in a flanged valve are much thicker, otherwise known as a corrosion allowance. I look at at the metal thickness at the thread roots on an NPS through hull or a combination NPS though hull (screwed into an NPT valve) and it makes me want to move my total through hull replacement project that much closer to the top of my TODO list.

I would guess more boats sink because the valves are left open and the hose or clamps fail…

That's what's allowed me to sleep nights all these years while having factory installed NPT ball valves, half screwed on to NPS mushroom through hulls. I'm religious about closing valves and all original hoses have been replaced with good quality hoses and all with double SS gear clamps. All that, and I always throw a few coins into the poor box every Sunday morning .

 

[RoyS]

Before launching a simple stress test of your below waterline hose connections is a good idea. Simply grab the hose and tug in all directions while looking for tears or bulges. Visually inspect for corroded clamps at the same time. If the hose connection survives a stress test it is unlikely to fail by itself during the upcoming season.

 

[Ralph Johnstone]

Simply grab the hose and tug in all directions while looking for tears or bulges.

.............................................. and just pray that the thickness at the thread root on the NPS mushroom head through hull hasn't corroded through !

I can't say this post has garnered a lot of responses as to HOW MANY PEOPLE HAVE THE DREADED NPS THROUGH HULLS.

I hope @Plymouth Sailor doesn't protest if I repost this again. If so I apologize in advance.

Easier to ask for forgiveness than ask for permission.

 

[JamesG161]

If your Valves are Marine Bronze, like my Propeller and Valves are, then your Shaft Zincs protect the Marine Bronze from...

Galvanic Corrosion.
_____

Stray Current Corrosion will eat you shaft Zincs then go after the Bronze.

Jim...

 

[Ralph Johnstone]

then your Shaft Zincs protect the Marine Bronze

I presume if they are all bonded ?

 

[Bob S]

I remember reading Rodd, Maine Sail, posting about the importance of exercising your thru hulls. It must have been 15 years ago as I was a newbe and very nervous boat owner. I use an acid brush coated in a waterproof grease (I use Lubriplate 130AA from my maxprop) applied from the bottom before launch every season. I also did this from inside when replacing any hoses. I always keep ours closed unless it's being used. Hang the key on the engine thru hull so I don't forget (only once) and they all can be activated by the 110lbs admiral!