thru hull fittings
 

anyone knows why the ABYC does not recommend this fitting for below waterline fitting http://www.perko.com/images/catalog/...Fig%200333.jpg

I'm replacing all my bilge pump thru hull fittings with s/s and the below water fittings with the above item along with the scupper item below

http://www.perko.com/images/catalog/...Fig%200285.jpg
thanks
jet
:ski:

If their plastic they can break off (under the water line) and flood the boat. I have metal and once a year check them.
P/s use a check valve on the thru hull fitting, I put them on all mine.

They are the wrong plastic for below water line. You want MARELON.

The first link shows a scupper with a flap which would never be used BELOW the waterline. The second link is a deck drain

Although not the best, it would be reasonable to use the second fitting as your deck drain connected to the first fitting as a thru hull scupper just above the waterline.

THANKS, will work on looking for a bronze thru hull fitting.

NEVER have ANYTHING other than Brass, Bronze or SS under the water line as a thru-hull. Period. My personal choice is SS.

never use BRASS in ANY fitting that makes contact with seawater, ever. It contains copper and zinc and zinc "disappears" in salt water, weakening the brass.
Also, never use a Brass fitting on aluminum (such as fuel tank) because of bi-metallic corrosion.

Bronze contains copper and nickel and does not have the same problem, provided that you bond them in common with all other submerged metal( the motor and all other fittings). SS also needs to be bonded.

A big PRO for using MARELON is not needing to maintain a good electrical bond

Skunk, gotta slightly disagree with you. While what you say is true as to the make up of normal Brass, I've personally had DR Brass fittings in a boat for long years with no signs of degradation. The so-called dezincification resistant (DZR or DR) Brasses, (sometimes referred to as CR (corrosion resistant) brasses), are used where there is a large corrosion risk and where normal brasses do not meet the standards.

Additionally, part of the reason I've never had any problems might be that all my boats are trailer queens, so the bottom is never in salt water for long periods of time and is washed down with sweet water as soon as it gets back home.

Bronze is principally an alloy of copper and tin. But Bronze does not necessarily contain tin, and a variety of alloys of copper, including alloys with arsenic, phosphorus, aluminium, manganese, and silicon, are all commonly termed "bronze"

Wholeheartedly agree with you on dissimilar metals causing electrolysis, which is why it's so important to not neglect the sacrificial Zinks on your engine.

And I'll stand by my original comment that my own personal choice for thru-hull fittings is SS, which suffers from none of the aforementioned possible problems.

(I know that Marlon is a superior grade, glass reinforced plastic, and it's probably a great choice for just about everybody, but given my druthers, I still like SS better. I've never stripped the threads on a SS fitting like you can with plastic, so humor an old sea dog)

I don't want to seem like I am picking on you but in regards to SS it really isn't a great choice for an underwater fitting on a boat that stays in the water. SS is only stainless in the air. Underwater for long periods, it can develop veins of corrosion internally. You may have noticed that on underwater screws holding your transducer. I know I have.

And of course there are different types of SS. 304 is the most common(cheapest) and most likely to have crevice corrosion. 316 is better. 304L and 316L are even better. Add to that the fact that its all made in China now and probably doesn't really meet the spec.

Propeller shafts on inboard boats are usually Aquamet or Aqualoy. I don't think you'll find a thru hull fitting made of that.

As for me, I think the best underwater fitting is NONE! The only underwater hole in my boat is the original bronze garboard drain.

It's only by discussions and conversations that people learn things Skunk, so no worries about my being offended or anything. :butt:

Seriously though, I didn't know that about SS developing crevice corrosion. As stated earlier, all my boats have been trailer queens, so they are never in the water for any length of time. So I thank you for the info.
I still don't like plastic due to it's susceptibility to UV and climate degradation, but I may have to rethink my opposition to Marlon. :beer:

interesting thread....

This explains all the bonding done on the Bertram.