[david_japp]

I have an old (50 yrs) small (62ft) Feadship that I am restoring (Tiky 62ft). Some of the thru-hull and all of the deck drain outlets need replacing and I am concerned about corrosion if I use bronze fittings below and/or above the W/L. does any have any thoughts advice about whether to use a synthetic material fitting (such as Marelon) as an alternative to bronze?

[FISHTIGUA]

I have just found a range of synthetic scupper outlet and above waterline fittings that come with a detatchable chrome bezel. In Europe they are available from C-Quip Marine UK, a horrible website to use but they sell good kit.

For below waterline, stainless fittings and seacocks are available for a 'not inconciderable' price $$$$$$$$.

Fish

[david_japp]

thanks - I always understood that stainless fittings should only be used above the w/l and that in using them below the w/l there is just as much risk of galvanic corrosion with steel hull plating, as there is with bronze fittings????

[Capt. Bill11]

I would use Marelon myself.

[Capt J]

In all of my days, I've never had to replace a bronze thru-hull due to galvonic corrossion, and have replaced a few plastic ones that have broken due to age and brittleness........But I'm talking on fiberglass boats. One steel or aluminum, plastic thru-hulls make sense rather then having dissimilar metals.

I've worked on a steel yacht before and all of our thru-hulls were steel that were welded into the hull.....(I THINK). What material are your thru-hulls now? I think marelon/plastic thru-hulls would make a lot of sense......

[david_japp]

On all my wooden boats, I've always had bronze fittings. Currently, on my steel boat, all the below w/l thru-hulls are bronze. They were probably originally steel but presumably rusted up and were replaced at some point with bronze . I'm not concerned about the bronze thru-hulls themselves having problems, but rather about the hull itself, which is made of (less noble) steel

[q240z]

My aluminum Roamer has aluminum standpipes below the waterline and I'll use SS thru-hulls above the waterline for tank vents etc. The AC raw water discharge will be plumbed to a large standpipe that used to be the forward head discharge--no more splashing while the AC is running. If I wasn't already done with epoxy coating the hull, I would seriously consider one big seachest for raw water intake and just get rid of all the other thru-hulls.

[david_japp]

standpipes dont really provide a solution for the problem of having dissimilar metals in salt water - ie there's still a bronze and steel in salt water. in order to be secure and prevent risk of catastrophic flooding in the event of a valve failure, they need to come up above the w/l, which means they are not only often in the way but also wont be suitable for certain water intake requirements, where the negative pump pressure isn't great enough to get the water where it's needed.

[dennismc]

Marelon or hight impact pvc, personally, marelon is the answer.

[q240z]

sry, wasn't quite clear--standpipes to marelon ball valves is the way I went. Chris Craft originally used aluminum standpipes to dielectric fittings to bronze seacocks. I know others who use marelon flanged seacocks bolted straight to the hull. Any of these approaches seems to work fine, though none is perfect.

In the original configuration I thought you were describing bronze thru-hulls with bronze seacocks all secured to a steel hull with some sort of goop as an insulator/sealant, which I wouldn't recommend for obvious reasons.

[corinthian99]

Hi,
Everyone has oddly (to my mind) recomended using a synthetic material over bronze. Synthetics are a lot cheaper and won't give you corrosion problems but they are also not very impact resistant and have a nasty tendency to melt in a fire which might be upsetting. Synthetics also age and become brittle with exposure to UV light. All large yachts and ships use bronze side valves and they have lasted on thousands of ships for decades. What is important is that your valves are properly bonded (electrically) and that you maintain your zinc anodes. If you would like a good concise explanation I'd suggest buying Nigel Calders book which you will probably find very helpful regarding the many other issues you'll be coming across shortly. Thats my tuppence worth anyway. Hope you're enjoying your refit more than I am mine.

[corinthian99]

Originally Posted by david_japp

thanks - I always understood that stainless fittings should only be used above the w/l and that in using them below the w/l there is just as much risk of galvanic corrosion with steel hull plating, as there is with bronze fittings????

Hi Again,
The problem with stainless under the waterline is that it needs oxygen to maintain the protective layer that makes it stainless so to speak. If the fitting is in a de-oxygenated atmosphere stainless tends to pit. All depends on the specific local environment, shafts left idle for long periods can be badly affected by this, especially on their upper bearing surfaces. Stainless side valves are pretty good on an aluminium boat though - bronze and any other copper alloys should never be used on an ally boat.

[dennismc]

If you have UV light in the bilge, you have bigger problems than dissimilar metal contacts..lol...
Calders book is a must for on board library...

[Capt J]

Originally Posted by q240z

My aluminum Roamer has aluminum standpipes below the waterline and I'll use SS thru-hulls above the waterline for tank vents etc. The AC raw water discharge will be plumbed to a large standpipe that used to be the forward head discharge--no more splashing while the AC is running. If I wasn't already done with epoxy coating the hull, I would seriously consider one big seachest for raw water intake and just get rid of all the other thru-hulls.

A seachest works very well, providing you DO NOT have the ac pickup drawing off of it. When you plumb the a/c to it and there is a lot of waterflow through it, barnacles grow like wildfire in the seachest and clog all of your supply pipes that join it. you've got to take it apart and clean it every month.