Raw water fittings: Bronze, SS, or plastic?

L

Luhrs28

Chief Petty Officer
Joined
Jul 14, 2010
Messages
423
Hi Guys. I'm wondering what material plumbing fittings I should use for all my raw water connections. (seacock, strainer in/out, oil cooler in/out, tranny oil cooler in/out, heat exchanger, etc.) I'm actually leaning towards plastic. I can get glass-filled nylon fittings that are very strong for a fraction of the cost of bronze. Seawater won't eat through nylon will it? I mean heck my raw water strainer has a plastic housing and bowl.

Do any of you see anything wrong with using glass-filled nylon fittings?

Thanks,

Bert
 
H

Hank496

Seaman
Joined
Jun 13, 2010
Messages
59
Re: Raw water fittings: Bronze, SS, or plastic?

I think all of the below waterline stuff has to be metal according to CG safety regulations. I would lean towards Bronze as the best choice. Properly bonded bronze will last for the life of the boat. I'd be concerned about galvanic corrosion with SS.
 
Brentathon

Brentathon

Petty Officer 1st Class
Joined
Dec 29, 2009
Messages
385
Re: Raw water fittings: Bronze, SS, or plastic?

My opinions:
Avoid stainless steel below waterline....and if there is any, it has to be protected with sacrificial anode.

My 20 year old bronze fittings look perfect, and are not "bonded" (there are sources that say isolated bronze should not be bonded).

I had a plastic thru-hull fitting develop a crack.......I would avoid plastic.
 
S

Silver Heels

Petty Officer 2nd Class
Joined
Apr 28, 2008
Messages
125
Re: Raw water fittings: Bronze, SS, or plastic?

I'm 99.99 percent sure the Coast Guard doesnt require metal below the waterline, I know for a fact that many boats at least in the recent past came with plastic through hulls. That being said, there is your run of the mill nylon through hull designed for above the waterline applications. There is also Marelon fittings, a plastic that is marketed for use below the waterline. Many do recommend this as it doesn't corrode and unlike nylon, is very tough.
 
Fireman431

Fireman431

Rear Admiral
Joined
Sep 17, 2007
Messages
4,292
Re: Raw water fittings: Bronze, SS, or plastic?

I have 4 underwater thru-hull fittings. All are bronze and all are bonded (because they go directly to the engines/genset/AC, etc.)

If you go plastic underwater, they will be come brittle very soon. Stay with the bronze and seat them with 3M 5200 or other suitable compound. Use a little pipe dope on the threaded portion to assure they unscrew at a later date.
 
barbosam

barbosam

Petty Officer 2nd Class
Joined
Aug 25, 2009
Messages
153
Re: Raw water fittings: Bronze, SS, or plastic?

I think that the carbon fiber reinforced Marelon fittings by forespar are great. No worries of galvanic corrosion and they are very strong. They were orignally intended for carbon fiber hull boats or carbon inner skin hulls where galvanic corrosion can be a big issue. Now they are used on a lot of fiberglass boats as well. There are a lot of top notch manufacturers useing these. My only warning with these is to make sure you do not overtighten them! They can crack if you really crank on them. As long as its sealed properly they really don't need to be much more than snug.
 
C

CaptainSkip

Seaman Apprentice
Joined
Aug 23, 2009
Messages
47
Re: Raw water fittings: Bronze, SS, or plastic?

As stated above, if you go plastic...use Marlon, it's CG approved below waterline.
 
dingbat

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
15,500
Re: Raw water fittings: Bronze, SS, or plastic?

Bronze below and stainless above the water line. Or you could go nuts and install titanium, everywhere.
 
C

crewscontrol

Seaman
Joined
Sep 15, 2010
Messages
52
Re: Raw water fittings: Bronze, SS, or plastic?

Given the choice between USCG approved plastic and bronze, I would choose bronze. Bronze will cost more but IMO it is much stronger than plastic. In my Sea Ray all through hull fittings are bronze. Many of them have reinforced hard rubber hoses attached. This hose does not bend very easily and it puts quite a bit of side strain on the through hull fittings. Personally I prefer the additional strength of bronze.
 
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