through hole fittings

[Gavala]

Echo, over tightening plastic skin fittings is a common problem, god knows I had enough returned from people saying that the fitting was a fault, often returned with traces of PTFE tape within the threads in an attempt of resurrection.

Go metal and use Arbomast BR sparingly to bed them in.

[skipmac]

Originally Posted by Gavala

No, but it took some time finding a random sight that has no weight when it relates to 300 stainless and not 316!!!!

Come on.

I'm really struggling here to get through. Crevice corrosion is due to weld and the site you linked is for 300 stainless. Please.

That is for 300 series stainless alloys which includes 316, 304 and others. There is also a 400 series and others. All of the alloys within a series have similar components and similar characteristics which is why they are lumped together as a series.

And I can assure you that crevice corrosion exists and has nothing to do with welds. Stainless steel maintains its rust and corrosion resistant surface due to the production of Cr2O3, chromium oxide which is formed when the pure Cr in the SS alloy reacts with oxygen at the surface of the stainless steel. This is why SS welds rust so quickly, the chromium oxide coating is damaged and the surface contains a lot of free Fe.

When SS is in an environment with little or no oxygen like below the water line, it cannot maintain the oxide coating and rusts. I've seen it dozens of times. Most recently in a friends Westsail 32 where the SS bolts holding the stem fitting corroded in half where they passed through the hull and stayed wet. Outside where they were exposed to constant salt spray but also fresh air and oxygen, they looked perfect, but inside where there was no oxygen they rusted completely away.

If you don't believe in crevice corrosion ask any knowledgeable wooden boat owner why they never use SS screws to fasten planks to the ribs.

[Gavala]

Originally Posted by skipmac

And I can assure you that crevice corrosion exists and has nothing to do with welds.

It does exist, but only when the metal has been raped of its original form, something that 'turning' the fitting does not do.

Regarding the whole 300 series having 'similar' properties is where you're leading readers astray. 316 Is specific and why it is used for underwater profiles. 304 I wouldn't put within 100 meters of sea water!

Regarding your friends transom bolts, the problem was with the contact of air and sea water within the same fitting and being restricted of air.

Of course wooden boats do not have stainless plank fittings. I can appreciate the mention of Cr2O3 but we need to concentrate on the fact that these are underwater profiles and not transom or topside fittings, such as the dozens of stem fitting which you witnessed.

[transmitterdan]

I have seen stainless parts that were not welded come apart under load. It looked like 98% of the cross section was rusted and only a tiny sliver of metal was holding. Why use stainless under water when bronze is more robust and suitable?

[skipmac]

Originally Posted by Gavala

It does exist, but only when the metal has been raped of its original form, something that 'turning' the fitting does not do.

The metal does not have to be "raped" of its original form. Placing prime, polished, new SS turned or otherwise, in an oxygen depleted environment will cause crevice corrosion. Do a little reading.

Originally Posted by Gavala

Regarding the whole 300 series having 'similar' properties is where you're leading readers astray. 316 Is specific and why it is used for underwater profiles. 304 I wouldn't put within 100 meters of sea water!

Leading no one astray. Giving correct facts. Again, do a little basic reading on metallurgy. NOTE I did not say identical properties, I said similar. 300 series alloys are called a series for a reason. Their composition and properties are similar. Not the same, or they wouldn't have different alloys in the series.

Originally Posted by Gavala

Regarding your friends transom bolts, the problem was with the contact of air and sea water within the same fitting and being restricted of air.

First I said it was a stem fitting. Those are on the bow, not the transom, but otherwise, yes. That is exactly what I have been saying. No air, no oxygen. Just like in certain installations under water where the fitting is enclosed in the hull and not exposed to circulation of fresh water or air, just like the shaft of a thru-hull fitting where it passes through the hull.

Originally Posted by Gavala

Regarding your friends transom bolts, the problem was with the contact of air and sea water within the same fitting and being restricted of air.
.

You did notice that the OP said "all' his though hole [sic] fittings which I assume to include those that are under water, where it will be "restricted of air"

[HopCar]

"They're called 'skin fittings'."
On this side of the pond they are called Thru-Hull Fittings.

"Buy bronze ones if its within budget or stainless if possible as stainless contains no zinc / corrosion properties."

On this side of the Atlantic bronze is the standard for fittings in contact with salt water. This includes skin fittings, sea cocks and sea strainers. I'm starting to see some stainless used. It's not well accepted here yet. Groco is making 316 stainless thru-hulls now. I wouldn't even know where to buy a brass thru-hull in the US. I have seen European brass thru-hull / skin fittings but they just don't sell in the US. At this time bronze is less expensive than high quality stainless and as far as I can tell, baring electrolysis, it will last forever in contact with salt water.

EchoPilot, the only plastic thru-hull fittings suitable for use below the waterline are the ones made by Forespar of a material they call Marlon. I prefer bronze but a lot of people use Marlon.

[TopperHarley]

My engine raw water inlet fitting has started leaking and looks like this....



Its only a drip every 30 sec or so, but it obviously needs attention..... replace or repair ??

Can anything be done with the boat in the water ??

[robert sailor]

First of all have your present fittings carefully checked as they may still be just fine. I look for any pink in the bronze as a sign things are not so good.
If you find they do need replacing use bronze fittings. Yes I know many Europeans use brass in their new boats and for replacement but its a stupid decision. Brass will not last, you might get 5 years if your lucky and then you have to go thru the whole job again to replace them. Manufacturers do it simply to save a few bucks with no regard for the end purchaser.

[EchoPilot1975]

Originally Posted by TopperHarley

My engine raw water inlet fitting has started leaking and looks like this....



Its only a drip every 30 sec or so, but it obviously needs attention..... replace or repair ??

Can anything be done with the boat in the water ??

Where specifically is it leaking?

[TopperHarley]

Thanks guys....

There is no sign of any pink corrosion, only the blue/green stuff.

Its hard to tell where exactly is leaking/weeping but my best guess so far is that is around the black plastic fitting that is in between the bronze through hull and the hose. Its significantly worse when the valve is open / engine running

Im reluctant to play with it too much as im worried if it is weakened, I will break it and make the problem worse !! (although it still feels very sturdy).

[robert sailor]

Blue and green are just fine, its just what bronze will do. Consider closing the thru hull and replace the fitting that your hose attaches to with a bronze fitting and then reattach the hose if its in decent shape and use 2 hose clamps. That should end the leak.

[HopCar]

I second what Robert said. I'd look at that plastic hose barb first.
If you need to replace it, upgrade to bronze.
Next time you haul you might want to improve that installation by adding a Groco Flanged Adapter between the thru-hull and the ball valve. That will make it a much stronger installation.



Groco Flanged Adapter IBVF

If you can't find these in Australia, these are small enough that I can mail them to you and the postage isn't outrageous.

[captain58sailin]

I have used bronze thru - hulls below the waterline exclusively, since 1967, I have never had one fail. The rule here is below the waterline use bronze, above the water line it's okay to stray into alternative material. Marelon fittings have been making their appearance in the local chandlery, and I am sure there are some who are using it below water line, I will never be one of those. You do have to examine the bronze thru - hulls where the bell and the straight threaded part come together, on one refit after 16 years, I found several that had hairline fractures and replaced them all. I believe that was as much to over tightening of the fitting as any other cause.
While being just a layman in this discussion, I have always heard that SS below the waterline is a bad idea. I have seen on almost all of my above deck fittings rust emitting from behind my chain plates etc... I just hope they will hold together until I can replace them with bronze. I have researched bronze versus stainless steel for chain plates and deck fittings and from what I have learned of it the bronze responds much better to the stresses than stainless steel chain plates. I've also found support to the argument for galvanized wire for standing rigging is as good or better longevity than stainless wire. Of course the galvanized cable will require more maintenance, that is the trade off for a longer life span. I can keep a roll of it in my focsle and replace my stainless stays as they part.

[Watercolor]

Echo pilot - If you consider what you put to control the water flow that those holes in your create go with bronze (not brass). The bronze I'd look for is called Composition Bronze, 85-5-5-5, or Alloy 836.

If I had my choice I get either Perko, Buck-Algonquin, Spartan or Groco's US made real seacocks, they are flanged. These are the best and safest. Next would be the Apollo sea valve (full flange). After that you're into Chinese metal products.

But go with a full flanged real seacock.

Someone stated "the only plastic thru-hull fittings suitable for use below the waterline are the ones made by Forespar of a material they call Marlon." I would argue that Marelon does meet the ABYC standard, but a material that looses close to 60% of its strength in water is not a suitable material.

I won't go into any great detail here but the following thread may be of some help.

http://www.cruisersforum.com/forums/...-102317-6.html

CRITICAL UPGRADES - DO THESE OR ELSE!!!
Is this a dangerous thru-hull fitting/valve combo, or is this normal? MARELON

Fair winds

[Watercolor]

TopperHarley - If you read my earlier post this might seem like an about face.

My sister and her husband live in Wollstonecraft, NSW. I might have a more local solution for you.

If you read my post you'll know that I'm not a fan of nylon for thru-hulls or seacocks. However, not to far away in NZ is a company called TruDesign that makes ball valves and thru-hulls out of a far higher grade of nylon than the Forespar stuff.

I've talked to them at length. Their nylon material has better than double the glass as Marelon and the resin is far better at water absorption. Also, the ball valves are a far better design than Forespars. These valves are reasonably priced from what I can tell.

If it's a British boat, you might have an issue with the threads, BSP(GB) or NPS (US) on the thru-hull/skin fitting.