[C320-list] Thru Hull Failure

[John Frost]

We had a scary incident on our 3 year old boat last weekend.

While motoring towards home, I lifted the starboard interior seat to stow an
item and was greeted with a garden hose spray of lake water.

It was shooting out the side of the holding tank thru hull, which is
normally wired shut.

I thought, no problem, I will cover it with my thumb, then put one of the
plugs I have in.

Unfortunately the handle  had broken free from the ball valve and left a
very irregular hole that I couldn't plug. All attempts just made it gush in
a different direction.

I had my wife go to warp drive in the direction of our marina, where a crane
resides.

As the water rose, I found that the broken handle did a partial job of
stemming the tide if held in place just right.

I was able to tape that in place and the bilge pump was keeping up as we
came screaming up to the marina.

 

Lots of luck helped. I had just replaced the bilge pump which had been dead
all winter. We were on board when it happened. The crane had just that day
returned from a week of repairs.

Best of all, my marina operator took my urgent call and had the lift ready
before I arrived.

 

Now to the apparent cause. The thru hull is by Forespar and made of Delrin.
It is UL certified and looks like new and turns freely. 

The failure mode was pulling out of the shaft and acorn nut that is molded
into the ball valve. This allowed the handle to shoot out opening up the
valve.

Forespar engineer was incredulous and said it was tested to 150 pounds and
could not break unless I stood on it trying to turn it the wrong way. I
assured him that was not the case.

After think for a bit, I think I found the cause.  I had put a plastic wire
tie LOOSELY around the valve handle and the large adjacent holding tank hose
in case I was stopped for an environmental inspection.

It appears that the adjacent hose had been vibrating (while under power). It
apparently tugged on the wire tie in a direction perpendicular to the normal
rotation force and eventually pulled the valve apart.

Lessons: 

1)      Don't let anything touch your thru hull handles, not even a locking
plastic wire tie.

2)      Check your bilge pump regularly and replace immediately if it dies

3)      Stay friends with your marina operator

 

By the way, Forespar sent a new valve for free

 

 

Happy Sailing!

 

John

2007 C320MKII

Hull 1118

Guntersville, AL