Through hull fittings

here is the sea chest from the above link

 

Thru hull fittings

Weld in stainless type 316 sch 40 pipe nipples for thru hull fittings, then paint her.Don't use anything else.
Sea chests usually result in a lot of extra lengths of plumbing inside a boat. SS nippes with SS valves cause no problems.
Brent Swain

 

Brent,
just curious about your wording. Are you suggesting to place thru-hulls where they are needed instead of using a sea chest?

 

Yes . Definitley. Far simpler . You can also weld thru hulls at whatever angle to the hull is most convenient , unlike in non metal boats .

 

Hi Brent,

Wouldn't an advantage of stainless steel pipes welded into the hull and then flanged/bolted onto a stainless steel seacock be that no isolation nipples, gaskest etc are required whereas if a mild steel pipe is used then the nipples gaskets etc are required?

 

Hi All first time post, We use 316 SS pipe nipples schedule 80 welded to hull plate. PTFE tape and Loctite 567 a SS ball valve on. (locking type). All you need. Or weld a SS table E flange to hull first and bolt your flange and ball valve arrangment on. We do a few this way also.

 

Hi Shipwright.

Thanks for your reply.

Can you provide some more details about "weld a SS table E flange to hull first and bolt your flange and ball valve arrangment on"..

Do you mean to weld the flange directly to the hull and then bolts through the hull to connect the flange with the ball valve?

 

Yes , Threaded bolt holes in flange which you bolt your flange and v/v to. Does not bolt through the hull. Its not as good as a Nipple type in my opinion.

 

and you did not use any isolation material to prevent corrosion because the stainless steel pipe niples and the ball valve are of the same material, correct?

 

All stainless yes

 

Make the stand pipe to hull skin attachment strong by having a flange on each side of the stand pipe. Weld the bottom flange to the skin, bolt the valve to the top flange . Remember the air purge valve on a sea chest and a nice detail is the ability to close the sea cock ,then flush the sea water from machinery with sweet water and a garden hose...add a purpose built nipple and fitting.

 

Galvantic Corrosion

I thought that galvantic corrosion occurred where an electrical path exists between disimiliar materials. I can understand that physicly separating mild and stainless steel with gaskets etc would work if the the two parts aren't submerged in salt water.
But stainless talls welded to a mild steel hull, must surely have an electrical path even if they weren't submerged in salt water, it seems to me that this must be the perfect way to rot your hull. Can somebody enlighten me?

 

Its always best to use steel to steel. Ive sailed with steel nipples and steel sea chest's...no problem..The next level up is a 100 percent ss sea chest. Maintenance is greatly reduced with a ss sea chest. The sea chest is a high maintenance item... Always opening and closing...always re anti fouling each year...always damaging the seachest lid gasketed flange. 100 percent SS, insulated from the hull with a gasket and anoded is best if you can afford it..

The pictured sea chest is square....not good, has no thru hull valve...not good, and required a many thru bolt pattern lid...not good. Go circular chest, ball valve and flange clamp.

 

It is good and it's a sea chest.. circular tube with a ball valve is a manifold..
The difference in practice lies in the fact that a sea chest can be cleared from the inside, for a manifold you got to dive..

 

Hi, nothing wrong with SS to mild steel weld. Its common. Much better than mild steel nipples, just keep an eye on your zincs and keep plenty of paint on everything and you be fine.