With regard to real seacocks, not Ball valve/thru-hull combinations, I agree with Jedi, if you have to have a hole in your hull
, do it right. A true flanged seacock, thru-hull and backing block are the best insurance
for you and your boat.
On a bronze thru-hull, the wall thickness is about .10” and that .10” is compromised by the fact that the threads are machined (notched) as opposed to cast or molded. The seacock housing and base distribute both static load stress and the base when used with a backing block and lag bolts diminish the potential effect of impact and shear on the thru-hull.
Take a look at Mainsail’s testing on a variety of thru-hull/valve combinations. Mainsail
did an excellent job at documenting his efforts and he recognizes they’re not perfect. They do, however, raise some real flags
with regard to the ABYC standards we now have. Several on this thread have provided valid criticize the ISO standards.
Something many of you might not know is that the reason for Mainsail’s tests. He had a situation where a spare alternator
broke loose and seriously damaged a thru-hull/ball valve unit, in particular the thru-hull. Because there is no ABYC impact test, so he used the static load test.
I feel the real questions and debate should be:
What forces (groups, etc,) have moved us from real bronze seacocks to, in the case of European standards, brass ball valves and thru-hulls? In the ABYC’ case it’s move from real seacocks to ball valves and thru-hulls. And what information was used to make those changes. Additionally, who and what influenced the standards as they now exist?
The other question is really, what are boaters willing to accept by way of testing and characteristics desired in seacocks and thru-hulls?
With bronze we have an known issue regarding corrosion
, it’s easy to identify and straight forward in it’s solution. Plastics are another matter. They don’t corrode; they degrade, some plastiics more than others. And it’s not as easy to identify the degradation level. In fact, most “experts” seem to give the plastics a pass.
So with bronze, it’s simply replace ASAP. With plastics, all you really have is: (is it breaks it breaks), or what the % of degradation level is over time. What % of degradation would you find unacceptable for a plastic thru-hull on your boat? Are there other known issues like impact that should be tested and what should the criteria be? Is there a bottom line for you, like PVC thru-hulls and ball valves should not be on boats?
If it wasn’t for the insurance
issue, there are quite a few boaters who would be happy with PVC. As they say, “I’ve never had a problem with PVC seacocks (ball valves) in the 20 years I’ve used them.”
I’ve always felt that Murphy and his laws were on steroids on a boat, and tried to act accordingly.