Problem picking up Lobster pots with rudder - Page 2

sailingdog · #11 08-05-2006

I'd have to agree with camaraderie. Stainless steel is not really a great material for use under water. It tends to have galvanic corrosion and oxygen deprivation corrosion issues. Marine-grade silicon bronze, titanium or galvanized steel are better choices. Aluminum is also a good choice if properly protected from galvanic corrosion.

foxglove · #12 08-07-2006

We're in the Chesapeake where crab pots are almost everywhere. I've snagged pots on two occasions and tried unsucessfully to keep the float attached to the pot.

But is it not true that if I cut that line, the pot wanders unattached around the bay becoming a crab killing machine? Crabs swim in to feast on the remains of dead crabs who swam in to feast on the remains of the first dead crabs and so on until the pot disintegrates.

And would this be also true of lobster pots?

camaraderie · #13 08-07-2006

Foxglove..true. Good reason to TRY to avoid them AND securing the pot line before you cut it free from the boat. Would be nice if the lobstermen/crabbers would geep their posts out of marked channels too. But if it is a choice between me going in 50 degree water & potentially killing myself...I'll kill a few bugs.

sailingdog · #14 08-08-2006

It would also help if the lobstermen/crabbers would mark their buoys, so we could tell them when we do catch one an move it a mile or so, dragging it. However, I've noticed that many are not marked in any real identifiable way. I think they do this to avoid any fines or liability caused by damage from their lobsterpots to boats, after they've negligently placed it inside a working shipping channel.

svindigo · #15 08-10-2006

Isn't the propshaft stainless? If not what is it? Regarding using stainless to bridge the gap between the keel and rudder as referenced earlier it seems that a zinc attached to the plate would answer. Am I off here?
thx

sailphoto · #16 08-10-2006

I realized that stainless is no good underwater and already have made a little skeglet out of fiberglass, which with my keel and rudder arrangement shoud render my boat pot-proof. I think we'll still be working on avoiding them though.

SteveCox · #17 08-10-2006

Svindigo,
If I understand the situation correctly, stainless requires oxygen in order to remain "stainless". The oxidation is actually what protects it. In a oxygen depleted situation (underwater) that oxidation cannot form and the metal gets eaten away. On my boat I have a ring on the bobstay tang that has been half underwater and half above. The underwater part is over half eaten away while the other part is fine.

gc · #18 08-10-2006

The stainless situation underwater is very complex. My older son is a materials scientist and a sailor. He claims that there is a LOT of difference in different stainless alloys, but that there is also lots of oxygen in the seawater - as long as it is flowing freely. When the water around the stainless gets trapped, the oxygen is rapidly depleted. But there are also other effects. In short he says that stainless can be used underwater but not casually - it takes a lot of very knowlegable engineering analysis to determine if it is safe. Best general rule is to look for other materials to do the job.

sailingdog · #19 08-10-2006

Quote:

Originally Posted by svindigo

Isn't the propshaft stainless? If not what is it? Regarding using stainless to bridge the gap between the keel and rudder as referenced earlier it seems that a zinc attached to the plate would answer. Am I off here?
thx

Most better propshafts that are made of stainless are not 316 or 304, but DUPLEX stainless, which is both stronger and much more corrosion resistant than regular grades of stainless steel. Duplex stainless is a alloy of ferritic and austentic stainless steels.

IIRC, the zinc is only useful if the plate was bonded to the rest of the boat's underwater metal structures. Otherwise, probably not all that useful.

paulk · #20 08-10-2006

Woodenboat (and probably SailNet too) will sell you a boathook casting with instructions on how to add a wood handle so that if you drop it, it not only floats, but floats with the handle up, sticking out of the wate at a convenient height for you to retrieve it.