Can I do this??

The watery and smelly sides of life.
puremajek
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Can I do this??

Post by puremajek » Sun Sep 20, 2009 5:47 pm

Hi Paul

I challenged a chandlery mob here in Brisbane about why they sold brass seacocks (as raised by 44C above) and their excuse was the freshwater market???????. It also blows me away why this is done knowing that the sale could easily see these units in a saltwater environment. There are also some units that are bronze with brass internal components????



Marelon is a proven line for non-steel seacocks below the waterline and while I did not go this way, we did located some on Ebay during our research phase. We have gone all non-steel (13 in total and similar to yours above) in the desalinator/freshwater/toilet systems, but all these units are above waterline. Worst case is that they empty the freshwater tank and give us a wet floor, or the toilet leaks. In the 8 months so far, we have been very happy with them, having had no problems. Their sizes have ranged from 20mm to 37mm. Happy hunting :lol:
James
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44c
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Can I do this??

Post by 44c » Sun Sep 20, 2009 6:13 pm

madaz wrote:Paul, I echo Alans opinion on those particular plastic valves. I have no experiance with them in terms of failure but a number of builders here who have built a couple of boats wont go anywhere near them and steered me to Philmac Valves.

You can buy philmac valves also, not sure how they compare with the one Alan mentions, you can buy them at rural supply/irrigation shops. MUCH MUCH better
pic below


The Philmac valves are very similar to the Hansen ones, (in price too) I actually got a couple of them by accident from the same supplier. The Hansen ones do have the slight advantage of being able to remove the handles.

mahnamahna
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Location: Gosford NSW

Can I do this??

Post by mahnamahna » Sun Sep 20, 2009 8:08 pm

Thanks guys, The section of the boat where this thru hull will go, without going into to much detail here, is in a place where it (the through hull) has to be above the sole, therefore it (the thru hull) is only just (100mm) below the waterline, so as a result, once I connect the 90degree elbow the stopvalve is actually right on the waterline. I think I will hunt out one of the other valves mentioned for this application, and use this one in the main toilet where the valve will be well above the waterline and easily replaceable.



Just one more question. I have coated my hulls with copper laden epoxy. Does this mean that I MUST use plastic through hulls because of electrolysis? (2 dis similar metals should not contact?) or does bronze have sufficient copper content to be considered a like metal?

madaz
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Location: Hobart, Tasmania

Can I do this??

Post by madaz » Sun Sep 20, 2009 11:02 pm

I had the same thought Paul. as I have coated mine also.



I am using all acetal nylon skin fittings and the valves we have been discussing. As i have outboards which will only be in the water when being used the question I asked myself is why introduce a metallic item under the water if there is no need to.



I am no expert on electrolisis (?) but if I have no metal in the water then I dont have a problem... i think anyway,

Smooth Cruiser
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Can I do this??

Post by Smooth Cruiser » Mon Sep 21, 2009 12:09 am

mahnamahna wrote:Just one more question. I have coated my hulls with copper laden epoxy. Does this mean that I MUST use plastic through hulls because of electrolysis? (2 dis similar metals should not contact?) or does bronze have sufficient copper content to be considered a like metal?


Short answer: No.



Long Answer: No - you can use bronze fittings with copper epoxy.



Explanation to long answer: Bronze is not a metal as such - it is a metallic alloy consisting primarily of copper and tin with possibly small proportions of other materials like silicon, manganese, aluminium and zinc. Typically though the bronze used in marine rated fittings will be almost entirely copper and tin, with tin making up about 2-10% of the alloy. Hence bronze itself is not and cannot be attacked, but the copper and the tin that make up the bronze can be.



The copper in the bronze isn't an issue in this case (worrying about bronze contacting the copper epoxy) - so the question becomes - will the tin in the bronze be "attacked" (oxidised) by the copper in the epoxy.



The obvious answer to this is no - otherwise the copper in the bronze would attack the tin in the bronze. Hence you can rest easy that marine grade bronze in contact with copper will not lead to galvanic corrosion.



To explain why copper and tin can co-exist so happily you can look at the galvanic potential of these two metals. Tin has a galvanic potential of +0.15V, copper has a galvanic potential of +0.159V. The two are almost identical in terms of electrochemical behaviour. Compare this to zinc which has a galvanic potential of -0.76V. Zinc will be aggressively oxidised by copper, and in fact by most metals, hence why it is used as an anode.



Hope this helps!

Smooth Cruiser
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Can I do this??

Post by Smooth Cruiser » Mon Sep 21, 2009 12:22 am

As an aside to the previous post - the same principle is why brass should not be used in and around salt water. Brass is an alloy of copper and zinc. When salt water is added as an electrolyte to complete the circuit the copper in the brass will oxidise the zinc in the brass meaning that brass will rapidly destroy itself - even when not in contact with any other metals. (Note oxygen is also needed - so brass competely submerged in still, low oxygen content water will last for a while). This is why people say don't use "yellow" brass in particular. Brass comes in a range of compositions distinguished by colour - red brass is very high copper content and low zinc content, while yellow brass has higher zinc content and hence will oxidise faster. Add into the mix stray electrical currents and brass valves with higher zinc content brass balls in them (harder and more wear resistant), and you have a recipe for disaster. The balls get eaten out of the valves relatively quickly, and following this the valve body will start to oxidise as well. Next thing you know is that your boat has sunk.

mahnamahna
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Can I do this??

Post by mahnamahna » Mon Sep 21, 2009 5:07 am

Thanks Smooth, perfect explanation. Work continues on my build, thanks.

44c
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Post by 44c » Mon Sep 21, 2009 5:41 pm

One reason to avoid bronze or stainless through hulls is the possibilty of a lightning strike going to ground through them.



It has happened that metal through hulls have been blown out and sunk the boat.



OTOH, they are less likely to be broken by mechanical forces inside the boat. You pays your money and makes your choice.

madaz
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Location: Hobart, Tasmania

Can I do this??

Post by madaz » Sun Sep 27, 2009 9:11 am

These are also available, and being made in New Zealand (like me :D ) they must be good :D







BLACK NYLON BELOW WATER SKIN FITTINGS

Black nylon below water skin fittings is designed and made in

New Zealand, skin fittings are moulded from Nylon glass

reinforced plastic. High-strength, high-modulus glass fibers

impregnated into the nylon provides dramatic increases in

strength and stiffness, toughness, and dimensional stability.

Feature

Glass Reinforced Nylon Polymer

Chemical resistance

UV resistant

Can be painted over

mahnamahna
Posts: 580
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Location: Gosford NSW

Can I do this??

Post by mahnamahna » Mon Sep 28, 2009 6:14 am

Thanks Tony, they look the goods, do you know where they are available?

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