Hi there. I think its time for my 2c worth.
I am not going to expound the virtues of Corten Steel over blah blah...
I would like to tell you where we have had problems, and what caused them in order to prevent the same thing happening to you.
Gilana is fitted with an engine
driven HUGE Jabsco
pump. This is as an emergency bilge pump
and also feeds the fire hydrants and their 2" hoses. The suction side of the pump goes to a manifold where you can select, Forepeak, FWD bilge
, Aft Bilge, Engine
room, or the sea chest when using as fire pump.
All piping is in 2" 316 SS with 2" SS Ballvalves. The suctions are bell shaped with strum wires, to avoid vortices and clogging. The suctions in the fwd and aft bilges were misaligned and touched the inside of the hull in the keel pockets. The Stainless burnt a hole through the hull, well not quite through, but we found it and welded it up. We also shortened, and centered the suctions so they are in the middle of the well.
Case number two, our holding tank
is part of a double bottom design that includes the watertank and fuel tanks
. Any impact damage there will result in full tanks
but not sinking. BUT...
The inlet to the holding tank
from the head
is on the port side. There is a 3" plastic hose inside the tank leading to the STBD side, so there is no back-flow when heeled. This hose was held on by SS hose clamps. The "bolt" of the clamp, being of poorer quality disappeared in the soup that is in the holding tank. The clamp bands fell off, and by wave action landed up at the high tide mark in the "mud" inside the tank. There they lay for ???? long. When we hauled last year, (we only haul every 6 years) I pressure washed the hull, and noticed a spot that did not dry....
I put a screwdriver on it and hit it with a hammer, and out came poop...
So we had a hole in the hull right in the holding tank.
We pumped the tank into a biohazard tanker, and proceeded to lift
the tank lids, 244 8mm bolts. per lid. We found the remnants of the hose clamps exactly where I made the hole with the screwdriver.
Once again, 3 minutes with the welder and we were as good as new, but oh the poop in that tank...14 years of it, indescribable...!!
The moral of the story and the lesson learned is:
Although Corten A is several times stronger than mild steel (133kpsi yield) because of its Copper content, it is susceptible to electrolysis
. The electrical
junction made by the proximity of the stainless ate into it, with a perfectly round hole. IF the stainless was WELDED to the hull, NO problem, but, lying a few mm away even with 8 layers of epoxy
, the electrical current
between the SS and the Corten burnt a hole...
Be careful of dissimilar metals in proximity submerged in an aggressive electrolyte!
A small thing I have learned. I "grew up" in the navy
. We used traditional methods to fight rust, namely "Red Lead" and Alkyd Enamel paint. Then along came all these wonderful epoxies, and polywhatnots. Next it was conversion primers and all manner of things.
I have found that epoxy
is for new steel perfectly cleaned and blasted. BUT if you need to make a temporary repair, and cannot remove the last molecule of iron oxide, then don't use epoxy. The rust will come back, and pop the area off and it will spread under the epoxy. Rather use OSHPO, and then 24 hours later wire brush, then use Red Lead or equivalent, and then you can put an epoxy or polyurethane
over that. The Oil
based paint stays soft under the epoxy, and will only "blow" directly above the problem area the size of a pin head
, not the size of a quarter...
We draw 8'6" and in Current
Cut in the Bahamas
, we hit bottom, boy did we... Doing near 8 knots at the time. The damage was we lost
the paint on the keel shoe. See the photos here...
West Palm Beach to Cartagena de Indias
In the Azores
in 2002, we met a steel boat that hit a semi submerged container, it was apparently bobbing in a vertical position. They smacked it fair and square. The only damage was the bow section, and they had to run their anchor
over the side...not over the rollers.
All boats are a compromise....it just depends.....