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Old 18-11-2004, 23:00   #16
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Yep Greg, that's what I refered to in my post above. So they are NZ made? I didn't know that. So they are JUST a NZ found product??
The "plastic" materials are brilliant. There are two materials found here. One is a black fibre reinforced (I presume resin) stuff and is very hard and durable. The other is a tuff durable form of plastic, looks like it could be thermo-moulded. I have heard the name Marlon used. Not sure if that is the make or the material or something compleatly different.
I have used both over the years and never had a problem with either. They have never broken, cracked or deteriorated in anyway. They take a lot of punishment, although as far as tuffness goes, I would say SST would be tops. But SST is actually more prone to corrosion than anything else when fully submerged in Salt water. Bronze is actually better than SST. Silicon Bronze and another bronze that I forget the name of right now, is even better. But those metals are softer than SST and easier to break. Saying that though, they also tend to give a little more than SST.
Jeff, I have seen what you have described also. And yes it was the fact that a Bronze and a Brass component was used together. That is the only problem with those materials. It is darn near impossible to tell what is what, especially when the surface gets darker with age. When shiny new, it is a little easier, but most people don't realise that there even are difference between Bronze and Brass. Except price of course.


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Old 19-11-2004, 03:54   #17
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The NZ product in question is called Marelon and it is a propreitary product of the Forespar Corporation. I have had Marelon products on a couple boats including one that I owned for 14 years and sold when the valves and thru-hulls were 16 years old. I think that the Marelon products are all very well made and quite durable with the exception of the 'Y' valve. That said I have yet to find a durable 'y' valve made by anyone. Maintenance consists of operating the valve periodically and lubing the ballvalves when you can.

The plastic used in Marelon is a fiberglass reinforced nylon and is supposed to have equal strength to the bronze that it replaces. That said the Marelon is a lot softer and more flexible than bronze. This softness is important because it means that Marelon should never be used with bronze. The bronze threads will damage the Marelon threads. Also the Marelon nipples tend to be a little short on some of their fittings making double clamping more difficult.

Regular unreinforced plastics should never be used below the waterline or for critical systems. That includes the common hardware store nylon and PVC fittings and piping. Both of those materials will work harden and become brittle with time.

One issue with Marelon is that Forespar only makes ballvalve type seacocks and so these are 'use them and then dispose of them', rather than the higher maintenance but longer durability of a rebuildable tapered plug type seacock. Still and all Marelon has a very long lifespan.

My standard answer on this is to use Marelon if you are cruising areas where marine supply stores are easily accessible and to use bronze if you expect to spend long periods of time offshore or in remote areas.


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Old 07-12-2004, 15:06   #18
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Other areas to inspect

Take are carefull inspection of all rigging. Surveryors do a good job of checking, but it is important to verify and understand the various parts of your boat.

Inspect y our spares, extra lines, blocks, secondary anchors, tools, etc. A trip can turn into a disaster or at the very least an uncomoftable trip for the want of the some replacements.
Captain Bil formerly of sv Makai -- KI4TMM
The hunt for the next boat begins.
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Old 08-12-2004, 01:59   #19
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Ozskip & BC Mike

Oskip & BC Mike:

Stainless Steel is NOT generally recommended for use underwater*.
* As a General Rule:
304 - May be used for fully exposed components, frequently washed with fresh water
316 - May be used for all hull and deck fitting applications above the waterline
Duplex S/S: These are stainless steels containing relatively high chromium levels (between 18 and 28%) and moderate amounts of nickel (between 4.5 and 8%). Super duplex grades have enhanced pitting and crevice corrosion resistance compared with the ordinary austenitic or duplex types. This is due the further additions of chromium (over 25% cr) , molybdenum and nitrogen to these grades.
SAF2205 - Offers higher strength and lighter weight for the same applications as 316 and can be additionally used up to 60 degrees C in wet exhaust systems and in all submersed applications.
SAF2507 - Offers higher strength and weight savings and can handle all marine applications with no risk of corrosion in tropical waters (above & below the waterline) and hot, wet exhaust systems.

From “Flow-Induced Corrosion" - By: Dr. Harvey Hack
UnderWater Magazine Article reprint: May/June 2001
”I would also not recommend using stainless steel for continuous immersion in seawater. Most common stainless steels, including type 316, can suffer crevice corrosion in seawater which can lead to large leaks which could sink your boat at the dock. Although the stainless steels can be protected from corrosion by electrical coupling with aluminum, the aluminum will suffer galvanic corrosion in the process and the electrical contact between the stainless steel and the aluminum is difficult to maintain in seawater.” ... Either 316 or 316L are usually poor choices for long term immersion in seawater or more concentrated brackish water unless they are supplied with cathodic protection. Without cathodic protection they will suffer rapid crevice corrosion.”


NOBLE (Least Corroded)
ACTIVE (Most Corroded)
** The two positions of Stainless Steel illustrates how oxygen depletion affects its resistance to corrosion. The normal passive state is more noble than most other metals. However when the metal is in an oxygen deprived environment (underwater, sealed off, or in a crack) the less noble / active condition applies.

Forespar makes “Marelon” Thru-Hulls, Seacocks, and Ball Valves. Marelon® is a proprietary formulation of a reinforced, marine grade, engineered polymer (plastic).

Silicon bronzes are alloyed with 1-3% of silicon; about 1% of iron, nickel, manganese or tin can also be present. Although silicon bronze presents some fabrication difficulties, it has excellent chemical resistance and becomes stronger when worked, e.g. by rolling. Silicon bronzes are used for pumps, boilers, marine hardware. If bronze fittings appear bright and shiny, this is an indication that galvanic corrosion may be occurring. If bronze fittings are pink, this a indicates a dangerous condition known as dezincification - replace immediately!

Sacrificial Anodes etc:
Very rapid zinc loss that results in bright, shiny metal being exposed is a clear indication of electrical activity (stray current or galvanic), usually the former . Bright zinc in association with heavily corroded bottom paint means you have a problem that needs to be addressed immediately.
If you are getting white and/or green, or red/brown halos around your zincs or underwater metals, you have a stray current leak. Copper-based metals like brass and bronze leave green oxides, white for aluminum, and reddish-brown for stainless steels.
Underwater Stainless fittings will usually end up with rusty looking oxides around them when crevice corrosion is involved, but no telltale oxides when stray current is the culprit.
Gord May
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Old 08-12-2004, 08:26   #20
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Your last post would also be a good one to post under "Yacht Maintainance, Boat Building, Tips & Tricks" for future reference to those searching for info.
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Old 08-12-2004, 20:20   #21
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I have this friend, & his name is Murphy! If you do not anticipate his needs he will drop on you like a ton of bricks. you anticipate his needs in advance & are always prepared (boy-scout rule #1) he will have no reason to visit your vessel to see if you are prepared. Motto is: If you got it-chances are you may not need it!

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