Through hull fittings

Correct...it should be a double flanged standpipe...one flange welded to the hull plating and the other end of the flange, bolted to a valve. Stainless ball valves work OK.

 

If a stainless nipple has given no corrosion problems in 40 years, it's not going to.Flanges make sense on an aluminum boat where corrosion of threads is far more likely, but not on a steel boat.
The hull plate and the wall of the ss pipe is a lot stronger than any plastic, or bronze through hull for that matter.
Doubler plates are a waste of time , like putting a half inch shackle on quarter inch chain to gain more strength. Neither the ss nipple nor the hull plate is going to break in a boat's lifetime. The slightest pinhole in the weld, and you have major corrosion between them.
With a nipple you can see everything, nothing is hidden. With flanges, you have a lot hidden.

 

Not true...I have seen nipples welded to hull plate fail at the skin weld, best to use a doubler or flanged standpipe. Bolt pattern flanges and valves are best and the easiest to service.

 

Sorry bout that PDW I should have been more clear about the isolation part.
It would be nice if they would standardize world wide
10 gage is a little over 1/8" and it mikes out 3.2 mm

I think what would be better than a doubler would be to insert a thicker plate where needed say double the hull thickness and 6" x 6" or 8" x 8"
spread the load out a bit and eliminate the potintial for corrosion between the doubler.
Tom

 

That's what I'm thinking. Cut out a circle (whatever) of hull plate and weld in a flange mount with blind studs (no through holes) of appropriate thickness. 2 easy welds inside & out, no worries about corrosion between doubler plates etc. Easy to maintain, minimal/no protrusion into the water outside the hull.

Stainless pipe welded through, I really doubt you'd ever get any problems from it either especially if you had a couple of braces to spread any shock load. At least you'd not have to worry about thread corrosion on the inside of the hull and with a decent barrier paint job, how much stainless steel is going to be exposed to the water anyway except the inside of the pipe (and you could swab paint up there during the build)? We had stainless welds to various bits of gear on the bottom of an icebreaker and never had any issues in all the time I worked there. I went to every dry docking for years so I had plenty of opportunity to see.

I like the standpipe arrangement myself, just not sure if it's practical in a hull of only 11.5m, space-wise.

PDW

 

Preiously you mentioned spray foam around them and condinsation not being an issue now you say a pin hole in the weld you can see it. Whitch way you going here are you spray foaming all aound it up to the pipe or are you leaving it open around it so you can see the weld ?
" Doubler plates are a waist of time" I think your the only one in this world that would make such a claim. "Backing up a critical joint" is a waist of time ? Interesting

 

Do it like this. If you line the inside diameter of actual hole thru the hull with a thin wall fiberglass sleeve , you will keep shipyard bottom crew guys with scrapers from going after barnicles in the hole and chipping your epoxy barrier coat and exposing bare metal

 

I think that's pretty much how I am going to do mine, except those studs are too long and would be better capped with acorn nuts to protect the exposed threads.

What do people think the best way of attaching studs is, given the lack of a stud welder? Personally I wouldn't use less than an 8mm dia stud and more likely would use 10mm.

Obvious options:

1. Blind threaded hole, loctite. Need thicker plate, thickness at least 1.25X stud diameter.

2. Blind threaded hole, stud welded on inner face (need to have matching gasket/flange not bear on weld bead, probably need to TIG weld them).

3. Through drilled hole, stud welded in deep countersink on outer face - leaves possible corrosion from inside around stud/hole. Wick-in loctite?

Other??? I've used all 3 at various times.

PDW

 

I think I would just go with the blind threaded hole with loctite. seems the simplest.
Tom

 

I'd weld the bolts, from which side depends on the flanges. If they have to touch, then the countersunk hole underside, if the flanges have a gap (thick seal or just machined that way) then weld both sides.

Actually if I'd build a steel boat, I'd use a short pipe to separate the actual bolting flange off the hull plate and use regular bolt and nut (and a flange with a gap). If you get a stuck bolt, just take the angle grinder and cut it in the middle.

Lurvio

 

Thats a good way to do it if you have the space and access.

 

True. However , one can always check the wall thickness of a bronze through hull, the kind which have been in use for about 200 years or more, from the bottom of the cut threads, not the top ,and compare that with the hull thickness. A chain is only as strong as its weakest link.
Using taper locks is an ingenious solution , their being cheap and already machined up. However ,when one bolts a flange to them, it is almost impossible to torque the bolts down without cracking the epoxy around them. Then, corrosion begins immediately, in a place where it's very likely to go unnoticed. There is very little mild steel around the hole holding things together, so corrosion to a dangerous level can happen quickly. The bolt holes are also tiny, but could be enlarged, at the expense of the amount of mild steel around the holes. . Corrosion around the bolts is another potential problem , both mild steel and oxygen starvation in stainless bolts. I prefer the well proven reliability of stainless, which I've never seen a problem with. .

 

Sorry, I should have been clearer myself this time. I use taperlock weld-on bushings to fabricate things like drive flanges, a flange for the top of my rudder stock and the like. I machine a recess in some 12mm plate then weld in the taperlock female flange fitting from both sides then put it in the lathe and take a facing cut across the mating face. Drill holes to suit whatever is getting bolted to it. All these are in the machinery spaces or on deck not below the water line.

Here's a pic of one ready to weld.

PDW

 

In years of scrounging stainless from scrapyards of pulp mill scrap I have never seen any corrosion or freezing on SS pipe threads although I have seen it on the pipes themselves. This despite pulp mils using far more corrosive chemicals that sea water. I don't know anyone who has. You can check this out yourself ,by taking your pipe wrench to the scrapyard and taking SS fittings off SS pipes and checking for corrosion and freezing. You wont find any.
You can check the possibility of weld failures by welding one to a plate putting a fitting on then testing it to destruction with a sledge hammer. If you are still skeptical, you can weld gussetts on between the pipe and the hull.

 

Don't you know there's some difference btw alkali and electrolyte..