Hey folks I'm talking about the seacocks not the thru hulls. I thought the seacocks were to be bronze, I'm not certen they are marlion or what ever you called it.... it looks plastic to me and scared me away. lots to be replaced.
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Marelon
John Thy're Marelon, distributed by Forespar from an Austalian original design. They're very good. Try a google. Stu
John Thy're Marelon, distributed by Forespar from an Austalian original design. They're very good. Try a google. Stu
The problem is electrolysis
The primary reason that “plastic” or Marlon seacocks are employed is that they can be used on thru hulls made of any material without the danger of electrolysis that occurs when a bronze thru hull has a brass seacock or a brass thru hull has a bronze seacock. Brass and bronze are different metals. When placed together, electrolysis occurs between the two. Because bronze is more noble than brass, the brass will wear away. Hence, a brass seacock placed on a bronze thru hull will eventually fail and leak. Likewise, a brass thru hull with a bronze seacock will fail and leak. Nevertheless, brass and bronze are similar enough that it is very difficult to tell them apart, although bronze is usually cast and shows a rough surface while brass is usually stamped and has a smooth surface. As metal thru hulls may be made of either brass or bronze, it is very difficult, if not impossible, to ascertain whether you have a brass or bronze thru hull and thereby need either a bronze or brass seacock. Getting it wrong will sink your boat. Hence, the use of Marlon or “plastic” seacocks which can be safely placed on either brass of bronze without any galvanic reaction or electrolysis. Marlon or “plastic” seacock handles are known to suddenly break. However, I truly believe this is caused by maintenance failure. The ball valves on these should be periodically greased with waterproof non-petroleum based or synthetic grease such as Super Lube. Super Lube (yellow cap) comes in a convenient spray that can be easily applied to the ball from outside the boat up through the thru hull and then from inside down onto the ball after removing attached elbows and or tubes. Because of the propensity of the Marlon valve handles to break, there are sailors who swear that only bronze and or brass seacocks should be used. However, this belies the very real danger of lurking electrolysis in the system. The electrolysis does not manifest itself readily, but when it does, you had better be quick with those wooden plugs. Further, you can only be quick if you are there when the failure occurs.
The primary reason that “plastic” or Marlon seacocks are employed is that they can be used on thru hulls made of any material without the danger of electrolysis that occurs when a bronze thru hull has a brass seacock or a brass thru hull has a bronze seacock. Brass and bronze are different metals. When placed together, electrolysis occurs between the two. Because bronze is more noble than brass, the brass will wear away. Hence, a brass seacock placed on a bronze thru hull will eventually fail and leak. Likewise, a brass thru hull with a bronze seacock will fail and leak. Nevertheless, brass and bronze are similar enough that it is very difficult to tell them apart, although bronze is usually cast and shows a rough surface while brass is usually stamped and has a smooth surface. As metal thru hulls may be made of either brass or bronze, it is very difficult, if not impossible, to ascertain whether you have a brass or bronze thru hull and thereby need either a bronze or brass seacock. Getting it wrong will sink your boat. Hence, the use of Marlon or “plastic” seacocks which can be safely placed on either brass of bronze without any galvanic reaction or electrolysis. Marlon or “plastic” seacock handles are known to suddenly break. However, I truly believe this is caused by maintenance failure. The ball valves on these should be periodically greased with waterproof non-petroleum based or synthetic grease such as Super Lube. Super Lube (yellow cap) comes in a convenient spray that can be easily applied to the ball from outside the boat up through the thru hull and then from inside down onto the ball after removing attached elbows and or tubes. Because of the propensity of the Marlon valve handles to break, there are sailors who swear that only bronze and or brass seacocks should be used. However, this belies the very real danger of lurking electrolysis in the system. The electrolysis does not manifest itself readily, but when it does, you had better be quick with those wooden plugs. Further, you can only be quick if you are there when the failure occurs.
Electrolysis not just on Seacocks
Given the preferences for Marlon due to electrolysis, how do you all feel about the typical bronze shaft, bronze strut and bronze props on your boats?
Given the preferences for Marlon due to electrolysis, how do you all feel about the typical bronze shaft, bronze strut and bronze props on your boats?
Here is more on the Brass - Bronze issue
Click on the link below. http://www.westmarine.com/webapp/wcs/stores/servlet/WestAdvisorDisplayView?advisor=bvsbfittings.htm One more point. For years I didn't think you could have a bronze thruhull and a Marelon seacock. I'm not 100% sure but I don't think the threads are compatible, but either way its was not suggested to do that. But now I guess it might be ok, but I still wouldn't do it. check out this link http://forespar.com/resources/tips/MarelonValvesOnBronzeThruHulls.htm And to read about MORE things about Marelon vis-a-vis everything - Here is a great resourse. http://forespar.com/resources/techtips.htm
Click on the link below. http://www.westmarine.com/webapp/wcs/stores/servlet/WestAdvisorDisplayView?advisor=bvsbfittings.htm One more point. For years I didn't think you could have a bronze thruhull and a Marelon seacock. I'm not 100% sure but I don't think the threads are compatible, but either way its was not suggested to do that. But now I guess it might be ok, but I still wouldn't do it. check out this link http://forespar.com/resources/tips/MarelonValvesOnBronzeThruHulls.htm And to read about MORE things about Marelon vis-a-vis everything - Here is a great resourse. http://forespar.com/resources/techtips.htm
Stu, shafts struts and prop are thicker walled
than a thru hull and the percentage of galvanic corrosion will not affect it as much. It takes a lot of galvanic corrosion to have a prop fall off. You would have lost your thru hulls by then. Plus you need the other mechanical properties of Bronze for the these items (and I would argue that stainless is actually better, but more expensive)
than a thru hull and the percentage of galvanic corrosion will not affect it as much. It takes a lot of galvanic corrosion to have a prop fall off. You would have lost your thru hulls by then. Plus you need the other mechanical properties of Bronze for the these items (and I would argue that stainless is actually better, but more expensive)
Do NOT screw metal into plastic on a boat...
Metal is harder, and with the boat's constant jostle, it will eat through the plastic threads. See my post on the other thread about marelon seacocks, for a relevant experience that sharpens my views on this. Metal and plastic also have different rates of thermal expansion, and that can't be good over the long term. I suspect screw and nut should have similar material properties: both plastic, or both metal, not one of each.
Metal is harder, and with the boat's constant jostle, it will eat through the plastic threads. See my post on the other thread about marelon seacocks, for a relevant experience that sharpens my views on this. Metal and plastic also have different rates of thermal expansion, and that can't be good over the long term. I suspect screw and nut should have similar material properties: both plastic, or both metal, not one of each.
Thermal Expansion Rates
Russell is exactly right - “Plastics” generally have a much higher coefficient of expansion than Metals. Hence, in colder climates, we never install plastic INSIDE metal - the transitions are always plastic OVER metal. In a water-tight application, such as Thru-hull to Seacock transitions, this will NOT be adequate. OMO - NEVER thread metal to plastic pipes in climates with wide temperature differences. Thanx Russell - I never thought of this before you mentioned it. I wonder what Forespar wouls say?
Russell is exactly right - “Plastics” generally have a much higher coefficient of expansion than Metals. Hence, in colder climates, we never install plastic INSIDE metal - the transitions are always plastic OVER metal. In a water-tight application, such as Thru-hull to Seacock transitions, this will NOT be adequate. OMO - NEVER thread metal to plastic pipes in climates with wide temperature differences. Thanx Russell - I never thought of this before you mentioned it. I wonder what Forespar wouls say?
Through hulls are resting in the sea. The temp
is near constant. I would expect the expansion differential to be nil. Did that make sense?
is near constant. I would expect the expansion differential to be nil. Did that make sense?
Gord - Forespar® Tech Tip - Your Answer??
Gord - Here's a link to a Forespar® Tech Tip about connecting their Marelon® valves to bronze metal thru-hulls: http://forespar.com/resources/tips/MarelonValvesOnBronzeThruHulls.htm Does this answer your question? If not, to the left of the web page is "Tech Tips". Click on that and see if there is anything that helps. If it were me, for a trouble-free installation I think the best solution would be to go 100-percent Marelon® and not use either stainless or bronze thru-hulls. On my boat the thru-hulls are flush-mounted so they don't protrude. There are a lot of precautions to take when using metal and the average boat owner is probably not that adept at the technical maintenance and inspection capability that is required. Using metal is only asking for problems (grounding, inspection, electrolysis, etc.). From a toughness standpoint, the Marelon® thru-hull is going to last as long as the fiberglass hull it's installed in, and since it will never have osmossis problems, maybe even longer.
Gord - Here's a link to a Forespar® Tech Tip about connecting their Marelon® valves to bronze metal thru-hulls: http://forespar.com/resources/tips/MarelonValvesOnBronzeThruHulls.htm Does this answer your question? If not, to the left of the web page is "Tech Tips". Click on that and see if there is anything that helps. If it were me, for a trouble-free installation I think the best solution would be to go 100-percent Marelon® and not use either stainless or bronze thru-hulls. On my boat the thru-hulls are flush-mounted so they don't protrude. There are a lot of precautions to take when using metal and the average boat owner is probably not that adept at the technical maintenance and inspection capability that is required. Using metal is only asking for problems (grounding, inspection, electrolysis, etc.). From a toughness standpoint, the Marelon® thru-hull is going to last as long as the fiberglass hull it's installed in, and since it will never have osmossis problems, maybe even longer.
Expansion
Fred: Not exactly. “Plastics” will be crushed or broken when they expand at a much greater rate than a surrounding metal (such as when they warm up after a very cold winter (Northern climes). John: The Forespar “Tech Tip” doesn’t address this issue of thermal expansion. I agree, that it’s best to maintain materials compatability - and I too, chose all Marelon. Regards, Gord
Fred: Not exactly. “Plastics” will be crushed or broken when they expand at a much greater rate than a surrounding metal (such as when they warm up after a very cold winter (Northern climes). John: The Forespar “Tech Tip” doesn’t address this issue of thermal expansion. I agree, that it’s best to maintain materials compatability - and I too, chose all Marelon. Regards, Gord
Expansion
Fred: Not exactly. “Plastics” will be crushed or broken when they expand at a much greater rate than a surrounding metal (such as when they warm up after a very cold winter (Northern climes). John: The Forespar “Tech Tip” doesn’t address this issue of thermal expansion. I agree, that it’s best to maintain materials compatability - and I too, chose all Marelon. Regards, Gord
Fred: Not exactly. “Plastics” will be crushed or broken when they expand at a much greater rate than a surrounding metal (such as when they warm up after a very cold winter (Northern climes). John: The Forespar “Tech Tip” doesn’t address this issue of thermal expansion. I agree, that it’s best to maintain materials compatability - and I too, chose all Marelon. Regards, Gord
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