Raw Water External Strainer Debate

[Captn_Black]

External and internal strainer, imo, you get these little guppy fish in some places that will block the pipes otherwise.

[Donald Bryden]

Most of the raw water inlets on my boat are attached to a sea chest. The opening at the hull is about 5 inches. I've always thought of covering it with a strainer, but in 22 years, I've never gotten around to it and have never had a problem. We have cruised west-about from the American east coast to the Mediterranean Sea, so have seen many varying conditions.

[sailingchiro]

Have external strainers, not a fan! It is much harder to clean barnacles out with the fins in the way. I try to break the fins off the strainer with screwdriver when cleaning the thru hull. In fact, I have had barnacles that couldn't be removed over heat the engine.

[Cyrus Safdari]

Originally Posted by sailingchiro

Have external strainers, not a fan! It is much harder to clean barnacles out with the fins in the way. I try to break the fins off the strainer with screwdriver when cleaning the thru hull. In fact, I have had barnacles that couldn't be removed over heat the engine.

I think it is now pretty standard to use external strainers that can be opened or removed (because they're hinged) so as to avoid this particular problem

The remaining problem is the difficulty in clearing a blocked external strainer.

So some say just avoid them and rely on the internal strainer which can be cleared without having to dive in

The round perforated hinged RSC style external or hull strainers by Groco are designed to fit over the intake thruhull on sailboats (not scooped) and are hinged so they can be opened when you're scraping the hull to get at anything growing under the grille (and Groco has patented it) They cover about 2.5 times the area of the intake they're protecting. So it seems to me that whatever can block the strainer would block the strainer-less intake too, so better have an external strainer...?

[rslifkin]

Originally Posted by Cyrus Safdari

They cover about 2.5 times the area of the intake they're protecting. So it seems to me that whatever can block the strainer would block the strainer-less intake too, so better have an external strainer...?

The non-strainer intake has a bigger hole, however, so that may help. And with no strainer, depending on the seacock and plumbing setup, you may be able to rod out the thru hull from inside if something clogs it.

[Inanna]

Originally Posted by rslifkin

I personally hate my external strainers and plan to get rid of them, or at least change them to oversize ones that are less likely to clog. If you clog one, you have to get in the water to fix it. With no external strainer, you can rod out the thru hull and clean the strainer from inside the boat.

Fully agree. Without external strainer, it's a five minute job to unclog. With external strainer, half an hour or more, unless you were already in the water or about to enter.

[YANDINA]

The ultimate raw water unclogger.

We always had compressed air at 100 psi for the air horns. To create a super fast unclogger we connected an air line to the downstream side of the strainer with a 1/4 turn ball valve. Periodically, or if water flow was restricted, a 2 second blast of compressed air blew all the trash out of the strainer and cleared any blockage from the through hull all without leaving the pilot house.

We did the same on the raw water for A/C and water maker but since they had centrifugal pumps we had to add a bubble extractor (Google it) to the strainer that automatically released all the trapped air as well as removing any air sucked in while underway.

[BoatBumm]

True story - had some vague overheating problems on my diesel powered sailboat with fresh water cooling. Did all the usual checks. Nothing apparently amiss. Seacock worked fine. Dove overboard with a mask to look at the intake - everything okay. Once the boat was hauled for the season started more trouble shooting. After checking every part of the cooling system and finding nothing wrong - gave up. Another project was to install a raw water foot pump to the galley sink. I decided to Tee off the engine intake line requiring removing the 90 degree curved tailpiece off the seacock and replacing it with a pipe thread T and hose barbs. In looking at the tailpiece once removed I found a very deceased, and now dried, small fish neatly stuck in the curved tailpiece. Like a sardine in a can. Before the boat was relaunched I installed a bronze strainer screen over the intake. No problems since.

[skipperguy]

Used a flat perforated bronze plate In the mating fitting retainEd by two screws in the mating fitting for port and starboard Perkins diesel’s for 26 years. Plate was approximately 5” x 7 or 8 inches and holes were approximately 1/8 inch diameter. Never a problem - just be sure to clean out after bottom painting. Standard fitting I’m sure - just don’t know from where

[steve_zissou]

I just had a new beta 38 installed on my sailboat. The installer told me that my warranty would be voided if I kept my external strainer. Something else to consider.

[Cynara]

We are from the west coast, but while sailing on the ICW our internal strainer got clogged with jellyfish

[a64pilot]

The whole purpose of a strainer is to get clogged, if it’s clogged, it’s doing it’s job.
The issue is how easy it is to clear an internal clog as opposed to an external clog, especially if it’s behind the external strainer.
About the only way your getting a barnacle out from behind an external strainer is by opening or removing the strainer while diving the boat and get in there with a screwdriver or something and dig it out.

If you have the external strainer just glued on with 5200, then you could knock it off with a broom stick or similar pushed though the thru hull from the inside, this would also remove whatever the clog was, even if it’s a barnacle.
This is more important for the cold water guys, or it’s my understanding that that there are large reptiles in some parts of the world that you don’t want to get into the water with, or even deadly jellyfish.

But for us Southern cruising the Caribbean types, we can just dive the boat.

[model 10]

[QUOTE=a64pilot;
But for us Southern cruising the Caribbean types, we can just dive the boat.[

I usually swim around the boat naked. This year there were jellyfish about the size of a silver dollar and kind of brown looking, and I was stung... It ruined the whole year for cleaning the bottom.

[a64pilot]

[QUOTE=Ecos;3173573][QUOTE=a64pilot;
But for us Southern cruising the Caribbean types, we can just dive the boat.[

I usually swim around the boat naked. This year there were jellyfish about the size of a silver dollar and kind of brown looking, and I was stung... It ruined the whole year for cleaning the bottom.[/QUOTE]

For those a wet suit or even a rash guard help.
We were diving with our Daughter about ten years ago, she was 12 at the time, when we were coming up, the jellyfish layer started at about 20 feet, she went to dive back down, but of course we had to swim through them and get stung, there was no other choice.

Some where in the world there is a tiny fish that will swim up your urethra, after reading about that, I have no desire to swim naked, even if it’s an Amazon River fish or something.

[thinwater]

I've cleaned external strainers with a screw driver. Not a big deal. I added them because fish kept swimming in and getting stuck in the seacock piping (they didn't make it to the internal strainer).


I'm sure this depends on the area and application. Only the AC intake required an external strainer. I figured the reasons were:
* constant flow
* boat not moving
Both of these combined allow fish that are grazing on the bottom to get caught in the suction.