Raw Water Strainers Metal or Plastic?

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Pgitug

Pgitug

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Joined
Jan 4, 2015
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Usa
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Escapade
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Nordic Tug 37 2002
I need to order spare strainers. Which is the better way to go? Stainless Steel or Plastic?
 
I have very old plastic ones that are still serviceable....some stainless have come apart within the decade.
 
Pgitug said:
I need to order spare strainers. Which is the better way to go? Stainless Steel or Plastic?
Click to expand...

I put a plastic one in my 2" Groco strainer and have been very happy with it. They are recommended for high use time applications such as raw water for air conditioning. The one I removed had lost it's bottom through electrolysis. The alternative is SS and attaching a zinc to it for a sacrificial element.

Ted
 
I assume you are talking about the strainer baskets not the strainers themselves.

If so, I'd go with the plastic strainer baskets.

And I'd order extra baskets at least for the A/C and genset (if you have one) strainers so you can change them on the fly if need be. Then you can clean the dirty one at your leisure.
 
O C Diver said:
I put a plastic one in my 2" Groco strainer and have been very happy with it. They are recommended for high use time applications such as raw water for air conditioning. The one I removed had lost it's bottom through electrolysis. The alternative is SS and attaching a zinc to it for a sacrificial element.

Ted
Click to expand...

If your seacock was a Groco, it was silicon bronze. If your basket was 304/316 stainless then electrolytic corrosion was not part of the problem.

Electrolysis had nothing to do with it.
 
Last edited:
O C Diver said:
I put a plastic one in my 2" Groco strainer and have been very happy with it. They are recommended for high use time applications such as raw water for air conditioning. The one I removed had lost it's bottom through electrolysis. The alternative is SS and attaching a zinc to it for a sacrificial element.

Ted
Click to expand...

Would not the bonding of the strainer eliminate the need for a zinc on the basket? I've had stainless baskets for years and never had any issues in salt or fresh water. I do twist them once in to insure they are seated. Maybe I'm making better electrical contact that way. :confused:
 
boatpoker said:
If your seacock was a Groco, it was silicon bronze. If your basket was 304/316 stainless then electrolytic corrosion was not part of the problem.

Electrolysis had nothing to do with it.
Click to expand...

Must have been the stainless steel eating worms. What does the seacock have to do with it? The seacock wasn't bonded to the strainer; a rubber hose separated the two of them. BTW, the seacock was plastic. When I replaced the seacock and redid the plumbing, I installed a bronze seacock and tied both to the ships bonding system. Groco recommends the plastic strainer for applications such as AC where the pump has a high duty cycle. What to you think ate through the stainless if it wasn't electrolysis?

Ted
 
Capt. Jon said:
Would not the bonding of the strainer eliminate the need for a zinc on the basket? I've had stainless baskets for years and never had any issues in salt or fresh water. I do twist them once in to insure they are seated. Maybe I'm making better electrical contact that way. :confused:
Click to expand...

I don't know. When I reworked my raw water system, I tied the new seacock and the strainer to the ships bonding system. While I like stainless, after seeing the strainer basket bottom separated from the basket, I decided to try the plastic one. Think the plastic basket cost me $20 for the 2" strainer.

Clearly the corrosion didn't occur over night. So just thoroughly check the stainless each time you pull the basket. There may be enough bonding where it isn't a problem in your situation.

Ted
 
Never use a plastic strainer basket! They last way too long and I can't get rich selling replacement baskets! Seriously, the plastic does seem to last longer. The holes are usually a little bigger but I've never heard of anyone having a problem because of that.

Pgitug, I was on your side of the world last weekend. Had dinner at the Torch restaurant. Outstanding food!
 
O C Diver said:
Must have been the stainless steel eating worms. What does the seacock have to do with it? The seacock wasn't bonded to the strainer; a rubber hose separated the two of them. BTW, the seacock was plastic. When I replaced the seacock and redid the plumbing, I installed a bronze seacock and tied both to the ships bonding system. Groco recommends the plastic strainer for applications such as AC where the pump has a high duty cycle. What to you think ate through the stainless if it wasn't electrolysis?

Ted
Click to expand...

Electrolysis - A chemical change in an electrolyte due to the passage of current.

i.e. Electrolysis is what happens to the electrolyte, not the metals.
You may mean electrolytic corrosion or galvanic corrosion but again, "electrolysis" is irrelevant.

You may have simply had shitty Chinese "stainless" but silicon bronze and the stainless usually used in marine applications (304/316) are close enough on the galvanic (or Noble) scale to silicon bronze that any electrolytic activity would be extremely small and with virtually no measurable corrosion for many decades.
 
I will definitely pay close attention to them!
 
boatpoker said:
Electrolysis - A chemical change in an electrolyte due to the passage of current.

i.e. Electrolysis is what happens to the electrolyte, not the metals.
You may mean electrolytic corrosion or galvanic corrosion but again, "electrolysis" is irrelevant.

You may have simply had shitty Chinese "stainless" but silicon bronze and the stainless usually used in marine applications (304/316) are close enough on the galvanic (or Noble) scale to silicon bronze that any electrolytic activity would be extremely small and with virtually no measurable corrosion for many decades.
Click to expand...

I bow in defeat to the grammar police.

The stainless deteriorated above the plastic basket bottom to the point where the bottom fell off in less than 12 years. Haven't seen any after market stainless baskets for Groco strainers. On their advise, I went plastic.

In your opinion, what was the deterioration process of the stainless and how would you prevent it's reoccurrance?

Ted
 
I switched to plastic, the metal ones seemed to get deformed for some reason.
 
No grammar involved. I believe correct terminology makes it easier for everyone involved. I often tell clients that if a "marine" electrician uses the term "electrolysis" they should hire someone else because they clearly do not understand electricity or corrosion.
 
My metal ones don`t degrade or deform, but do attack my fingers when I try to withdraw them for cleaning. They resemble a cheese/finger grater, lacking a moulding at the ends,leaving a cut sharp edge.
 
Perko strainers are supplied with stainless strainer baskets. Boats which run their airco's 24/7 often eat these baskets. Installing plastic ones may appear to be the answer, but I would like to know what is eating the stainless in case it is a symptom of a bigger problem.
 
That is a valid point. A few years ago I was dealing with a corrosion problem, and I said "electrolysis". The marine electrician asked me if we were looking at a situation regarding the removal of women's body hair. I have been careful to use "GC" ever since.

boatpoker said:
No grammar involved. I believe correct terminology makes it easier for everyone involved. I often tell clients that if a "marine" electrician uses the term "electrolysis" they should hire someone else because they clearly do not understand electricity or corrosion.
Click to expand...
 
Ted, I believe the failure of the stainless baskets with plastic bottoms (maybe other than plastic also) might be from (help me Boatpoker if I use the wrong terminology) crevice corrosion. The bottom of the strainers usually have some junk in them after awhile and the stainless just loses its protective barrier. Maybe also from the plastic interlock.


18-8 Stainless steel, 304, 316 Stainless Steel Corrosion


2. Crevice Corrosion - this is a problem with stainless fasteners used in seawater applications, because of the low PH of salt water. Chlorides pit the passivated surface, where the low PH saltwater attacks the exposed metal. Lacking the oxygen to re-passivate, corrosion continues. As is signified by its name, this corrosion is most common in oxygen restricted crevices, such as under a bolt head.
 
I have a stainless rudder on my charter boat. Without a zinc, it pits and deteriorates. With a zinc, there is no noticeable pitting or corrosion. What is the process that causes this deterioration and how is it any different than what happened to the strainer basket?

Ted
 
When an "expert" uses the term "electrolysis" I know that marine corrosion is not their field of expertise. In my tenure with ABYC I helped develop the ABYC Marine Technician Corrosion course. In boats, the corrosion we most often deal with is galvanic corrosion. An application of sacrificial anodes is usually involved. We sometimes see stray current corrosion, but not very often. With stainless steel in salt water we sometimes see crevice corrosion. Adding anodes will not make any difference if crevice corrosion is the issue. As one who has SS sea strainer baskets, I see the corrosion start at the welds. This is a good indication that the issue is indeed crevice corrosion. Our boat was built in China in 2008 and some of the sea strainers are US products and some are Chinese. I have fewer problems with the baskets from Buck Algonquin, and can order replacements. I cannot seem to find replacement baskets for the Chinese knock off sea strainers.
 
tadhana said:
When an "expert" uses the term "electrolysis" I know that marine corrosion is not their field of expertise. In my tenure with ABYC I helped develop the ABYC Marine Technician Corrosion course. In boats, the corrosion we most often deal with is galvanic corrosion. An application of sacrificial anodes is usually involved. We sometimes see stray current corrosion, but not very often. With stainless steel in salt water we sometimes see crevice corrosion. Adding anodes will not make any difference if crevice corrosion is the issue. As one who has SS sea strainer baskets, I see the corrosion start at the welds. This is a good indication that the issue is indeed crevice corrosion. Our boat was built in China in 2008 and some of the sea strainers are US products and some are Chinese. I have fewer problems with the baskets from Buck Algonquin, and can order replacements. I cannot seem to find replacement baskets for the Chinese knock off sea strainers.
Click to expand...

Since this deterioration isn't at or near a weld (plastic bottoms on the basket), are you thinking it's more likely galvanic corrosion?

Don't know if that "expert" swipe was directed at me; am not one and never claimed to be one.

Ted
 
My comment was not directed at anyone here. I interact with the cruising/boating/boatyard community in many ways and many levels. The professionals I wor with in the field of marine corrosion do not use the term electrolysis
 
Moonfish said:
We will be replacing our original raw water strainers with these marelon units from Forespar:

https://youtu.be/00xpK1C9ktY
Click to expand...

I used them and hate them because they clog easy.

Everything else is nice, but the tripod top holder allows fairly small objects to clog them....and then they are a bitc* to clean out.

Yes, outside the hull thru hull covers may prevent that, but I prefer an open thru hull for excellent reasons and other strainers wouldn't clog like the Forespars.

If I was in the market again, I would look closely at the Raritan strainers.
 
Moonfish said:
We will be replacing our original raw water strainers with these marelon units from Forespar:

https://youtu.be/00xpK1C9ktY
Click to expand...

My generator had one of those when I bought the boat. Lid was cracked from the retainer hole out to the edge. Be careful not to over tighten the retaining nut.

Ted
 
HopCar said:
Never use a plastic strainer basket! They last way too long and I can't get rich selling replacement baskets! Seriously, the plastic does seem to last longer. The holes are usually a little bigger but I've never heard of anyone having a problem because of that.



Pgitug, I was on your side of the world last weekend. Had dinner at the Torch restaurant. Outstanding food!
Click to expand...


Their hours of operation are not consistent. But when you catch them open I have heard that their food is good.
 
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