Through hull fittings for steel hull (again)

[Lomax]

My apologies for brining up yet another topic which seems to have been argued to death - but I've spent a fair amount of time searching and reading about this, and although I found many lengthy discussions I haven't managed to narrow things down to a clear answer.

I am fitting two Whale Gulper 320 pumps as bilge pumps on a steel hulled boat - what material is best to use for the (above the waterline) through hull fittings? I understand that galvanic corrosion can only take place in the presence of an electrolyte, in our case (salt) water, and thus this shouldn't be a problem above the waterline, but I need to choose which fittings to buy and have the choice between brass, DZR brass, bronze, phosphor bronze, stainless steel and various kinds of plastic. I haven't been able to find any mild steel ones, or galvanized steel, so that doesn't seem to be an option. Purely from an aesthetic point of view I would prefer to use brass or bronze, but other than plastic what is the best choice from a durability/corrosion point of view?

 

[PaulRainbow]

Why not weld steel pipes in and have them flush on the outside of the hull ?

 

[Lomax]

Because while I can easily drill the holes, I do not know how to weld, nor do I have a welder... Also, I would still need a hose barb on the inside, of some material.

Edit: Remember, these are above the waterline - had it been below the waterline I would definitely have paid to have pipes welded, for a number of reasons. Seems excessive for bilge pump outlets though?

 

[Lomax]

Ok, let me put this another way: any reason I shouldn't use plain brass fittings for this?

 

[Tranona]

No reason at all if you insulate the fitting from the steel. Cut 2 washers from a plastic kitchen cutting board, one either side of the hull and bed the whole lot in plenty of sealant.

 

[pvb]

I fear this is all getting too complicated. As I understand it, the OP has a steel barge, which he's mainly intending to use on inland waterways. So why not just use a plastic fitting for an above-waterline through-hull?

 

[Tranona]

I fear this is all getting too complicated. As I understand it, the OP has a steel barge, which he's mainly intending to use on inland waterways. So why not just use a plastic fitting for an above-waterline through-hull?

He has expressed a preference for a shiny metal one for aesthetic reasons (last sentence of post#1). Just suggesting how he might achieve that easily! but of course plastic would do.

 

[Lomax]

I fear this is all getting too complicated. As I understand it, the OP has a steel barge, which he's mainly intending to use on inland waterways. So why not just use a plastic fitting for an above-waterline through-hull?

Her (current) home port is in brackish water actually, and I fully intend to take her across the channel at some point, but yes, otherwise mostly inland waterways. I guess plastic would be fine, except from an aesthetic point of view; all the ones I've seen are white plastic which isn't going to look very good against a black hull... I seriously doubt any paint would stick well enough to change that. There doesn't seem to be a massive price difference between decent quality plastic ones and cheap quality brass ones - unless there's a particular reason to avoid them in my case (i.e. galvanism) I would prefer to go with the latter.

 

[Lomax]

No reason at all if you insulate the fitting from the steel. Cut 2 washers from a plastic kitchen cutting board, one either side of the hull and bed the whole lot in plenty of sealant.

Thanks. So there is reason to take these precautions also above the waterline. I guess this was the real question. What about bronze then? Stainless steel? Do the same precautions apply to these?

 

[VicS]

Her (current) home port is in brackish water actually, and I fully intend to take her across the channel at some point, but yes, otherwise mostly inland waterways. I guess plastic would be fine, except from an aesthetic point of view; all the ones I've seen are white plastic which isn't going to look very good against a black hull... I seriously doubt any paint would stick well enough to change that. There doesn't seem to be a massive price difference between decent quality plastic ones and cheap quality brass ones - unless there's a particular reason to avoid them in my case (i.e. galvanism) I would prefer to go with the latter.

What about Trudesign ? Available from Leesan, https://www.leesan.com/shop/shop-by-brand/tru-design-plastics and others in black as well as white ? No worries at all about galvanic conflicts or any requirement to insualte.

 

[Motor_Sailor]

What about Trudesign ?

It's odd that you've discounted the best solution for steel on the ground of colour when both Trudesign and the marelon Forespar are available in black.

But if you don't want to use the solution that has proved perfect over the past 35 years, you can return to the good old days and insulate a metal fitting as above, although I would use washers cut from thin grp rather than breadboard. You can often find an old fibreglass dinghy laying around in the boatyard or laminate a new piece of grp 'plate' on a polished piece of window glass as a mould.

 

[David2452]

We've been using chromed brass fittings for the exhaust outlet on narrowboats for years with no issues. Marelon is not favoured on the inland waterways (well, canals anyway) for skin fittings mainly because of physical damage worries.

 

[KellysEye]

>what is the best choice from a durability/corrosion point of view?

Our steel boat had Marelon through hull fittings that can't corrode. http://www.forespar.com/marelon-marine-boat-plumbing.shtml

 

[Norman_E]

We've been using chromed brass fittings for the exhaust outlet on narrowboats for years with no issues. Marelon is not favoured on the inland waterways (well, canals anyway) for skin fittings mainly because of physical damage worries.

I like TruDesign fittings but on a canal boat above waterline they certainly risk damage. My own choice would be stainless steel because its closer to a mild steel hull on the galvanic scale than any brass or bronze, and is physically strong.

 

[Lomax]

I like TruDesign fittings but on a canal boat above waterline they certainly risk damage. My own choice would be stainless steel because its closer to a mild steel hull on the galvanic scale than any brass or bronze, and is physically strong.

Thanks, that might be the best option - typically cheaper than brass too. Shame you can't paint it though. Why can't I find plain iron/mild steel ones?

 

[rogerthebodger]

My apologies for brining up yet another topic which seems to have been argued to death - but I've spent a fair amount of time searching and reading about this, and although I found many lengthy discussions I haven't managed to narrow things down to a clear answer.

I am fitting two Whale Gulper 320 pumps as bilge pumps on a steel hulled boat - what material is best to use for the (above the waterline) through hull fittings? I understand that galvanic corrosion can only take place in the presence of an electrolyte, in our case (salt) water, and thus this shouldn't be a problem above the waterline, but I need to choose which fittings to buy and have the choice between brass, DZR brass, bronze, phosphor bronze, stainless steel and various kinds of plastic. I haven't been able to find any mild steel ones, or galvanized steel, so that doesn't seem to be an option. Purely from an aesthetic point of view I would prefer to use brass or bronze, but other than plastic what is the best choice from a durability/corrosion point of view?

I also have a steel boat that I fitted out and launched 8 years ago.



I used all stainless steel in my mild steel hull both above the waterline and below.

You can just weld half a 316 stainless threaded nipple to the hull and screw on a 316 stainless steel ball valve or you can use a flanged 316 stainless skin fitting if you prefer.

https://www.google.co.za/search?q=s...7tnbPTAhUrJ8AKHSd2DxwQsAQIIA&biw=1920&bih=901

I would never use a yellow metal(brass/bronze etc) on a steel hull. I have even replaced my bronze prop with a fabricated stainless steel. The only thing that is bronze is the bow thruster leg in a steel tube.

Have a look at the pics in the link in my sig below.

This is my main sea water inlet setup.

If you have a steel boat the best skill to have is to learn to at least to stick weld. It used to be easy to learn at night school run by you local technical college.

 

[Lomax]

You can just weld half a 316 stainless threaded nipple to the hull and screw on a 316 stainless steel ball valve or you can use a flanged 316 stainless skin fitting if you prefer.

Surely a ball valve is not much point on a through-hull that sits at deck level? Can't think of any situation where I'd want it closed off that a threaded blanking cap wouldn't work just as well for?

I would never use a yellow metal(brass/bronze etc) on a steel hull.

Roger that.

This is my main sea water inlet setup.

Holy crap, that's quite a set-up - impressive!

If you have a steel boat the best skill to have is to learn to at least to stick weld. It used to be easy to learn at night school run by you local technical college.

It's on my to-do list. Which is long.

typically cheaper than brass too

Jesus, where did I get that idea!? Must have seen something on eBay. Stainless seems to actually be about 150%-200% the cost of brass.

 

[rogerthebodger]

Surely a ball valve is not much point on a through-hull that sits at deck level? Can't think of any situation where I'd want it closed off that a threaded blanking cap wouldn't work just as well for?

Well yes if your skin fitting has a thread so that a blanking plug could fit from the outside. If you were thinking of a "blanking cap" on the inside of the skin fitting you would need to dismantle the pipework first.

My old boat did not have ball valves on any skin fitting above the water but when I careened my boat once to give the bottom a scrape water started coming in through above water fittings including my side engine exhaust as the tide was coming in which cause me to panic and had to disconnect and block all the skin fittings on the one side. This caused me to fit ball valves to all skin fittings including my engine and generator exhaust.

BTW I also only use 3 part ball valves so that they can be dismantled and services without disturbing any of the surrounding pipework. # part valves cost a lot more than the 1 part but you get what you pay for.

Jesus, where did I get that idea!? Must have seen something on eBay. Stainless seems to actually be about 150%-200% the cost of brass.

Yes but it is recommended by the AWB builders to replace "Brass fittings in contact with sea water every 5 years as far as I understand.

 

[Lomax]

Well yes if your skin fitting has a thread so that a blanking plug could fit from the outside. If you were thinking of a "blanking cap" on the inside of the skin fitting you would need to dismantle the pipework first.

My plan is to fit a 3/4" or 1" all thread through-hull (I think the 1" might be wise, to reduce outlet pressure), cut down to be just long enough for the fixation nut and a 90deg elbow, to which a 3/4 hose tail is screwed. A short length of hose from there to the Gulper's outlet, and a longer from its intake down between the stringers into the bilge, where it's attached to a stainless strum box. I've already got the hose, a 19mm inner dia steel reinforced PVC suction hose from Jaymac, which should be good for a lot of things. If I can find a stainless rotating barb to 3/4 BSP, disconnecting the pump should only take seconds. I will be using all 316 hose clamps throughout. Naturally.

 

[Lomax]

While we're on this subject, this is where the pump will be mounted (yes, the bilge is in the process of being re-painted):



Any good ideas for how to attach the pump to the inside of the hull? Welding some kind of brackets?