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Old 11-11-2013, 08:24   #16
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Re: Adding External Strainer to Open Through Hull

Just Dreaming and Ziggy you should read the OP's original question. He already has an internal strainer and wants to keep fish out of it.

Vasco, it's important to use a fine strainer on a head intake to prevent organic stuff from getting into the rim of the bowl. A lot of head odors are caused by seaweed and small critters getting into the rim of the toilet bowl and rotting. The smell is usually blamed on the discharge hose but doesn't go away when the hose is changed.

I use an external strainer to keep out the big things like fish, jellyfish, plastic bags and octopus. I also have a fine mesh internal strainer to keep small bits of stuff from getting into the toilet. I use the same set up on my engine intake and my AC intake.
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Old 11-11-2013, 08:30   #17
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Re: Adding External Strainer to Open Through Hull

Quote:
Originally Posted by HopCar View Post

Vasco, it's important to use a fine strainer on a head intake to prevent organic stuff from getting into the rim of the bowl. A lot of head odors are caused by seaweed and small critters getting into the rim of the toilet bowl and rotting. The smell is usually blamed on the discharge hose but doesn't go away when the hose is changed.

.
If you flush enough, not a problem. In fact new visitors love to see the sparklies when they flush at night.
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Old 11-11-2013, 09:25   #18
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Re: Adding External Strainer to Open Through Hull

"If you flush enough, not a problem."
No true. There are types of sea grass that can make their way into the rim of the bowl but won't make the 90 degree turn to go through the holes in the rim. They just stay there and stink. Read Peggie Hall's book on boat odors. I had it happen before I put in the internal sea strainer.

If it's not a problem where you are, great you don't need a strainer. A lot of people do have the problem. In this thread alone they have mentioned fish, octopus and Jelly Fish getting into the system. The octopus was a new one for me!
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Old 11-11-2013, 10:15   #19
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Re: Adding External Strainer to Open Through Hull

I have never seen an octopus, but jellyfish, uug. We got stuck in the middle of a swarm of small box jellies in Trinidad so big we had to shut every thru hull on the boat. It took hours to pull them out of everything, and bits of them from all the plumbing.


Minaret,

A strainer (internal or external) needs to have a thru volume of x gallons/min @ Y head to feed whatever system it is plumbed to. Engines, generators, AC pumps, all have specced thru hull sizes based on the engines cooling demands. When you add a strainer (either type) you reduce the cooling water getting thru the system by some amount. That restriction amount is based upon the surface area of the strainer minus the surface area of the grid acting to keep stuff out.

A strainer basked has massively more surface area than an external strainer, so even tho they filter the same size particles the internal has a lot more water pass thru. As I mentioned it doesn't matter much for heads since water thru rate isn't critical, but for systems that need cooling it can be.
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Old 11-11-2013, 11:32   #20
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Re: Adding External Strainer to Open Through Hull

"When you add a strainer (either type) you reduce the cooling water getting thru the system by some amount. That restriction amount is based upon the surface area of the strainer minus the surface area of the grid acting to keep stuff out. "

If you look at the table in my previous post you'll see that external strainers have a lot more open area than the thru-hulls they are designed to protect.
For example the Groco APHS-1250 has 2.9 times the open area of an 1-1/4 thru hull.
This allows for any increase in resistance to the passing of water through the strainer and also for some blockage of the holes. If you're not comfortable with that, you can go to the 2000 size strainer which has more than 8 times the area of an 1-1/4 thru-hull. You can also choose the size of the openings but the ratio stays the same.
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