One for the Engineers

[bruce smith]

I do not use one.
From lookin at those photos, one can see why. One is obligated to remove the strainer every haul out/ paintjob. If the inside of the strainer is not anti fouled, it will attract growth. The strainer you made (post 8) has little bolts, you going to be removing that every time?
Much simpler to have a straight shot through the through hull and seacock for a stick from the inside.

[HopCar]

Groco makes a series of strainers that addresses the problem of cleaning inside the thru-hull fitting. You can open and close it without removing it from the hull.
Groco Round Strainer

Many boat builders are eliminating internal sea strainers and just going with external strainers that have holes the same size as a sea strainer. The idea is that they are self cleaning. Sea weed, bags, jelly fish just wash off.
Groco Perforated Hull Strainer

I'm not sure I'm comfortable with that method but a lot of builders are going that way and it seems to be working.

[SVTatia]

Originally Posted by HopCar

Groco makes a series of strainers that addresses the problem of cleaning inside the thru-hull fitting. You can open and close it without removing it from the hull.

Hop - Thanks for this info.

Question for everyone:

How do you install - the bolts that hold the strainer - do you thru-bolt them with a washer/nut on the inside or just screw into the fiberglass with epoxy?

[Stumble]

Tatia,

They should be through bolted. Nothing you ever want to stay on should be screwed into fiberglass.

[sailorchic34]

Originally Posted by GordMay

Since the area of a circle varies directly as the square of it’s diameter, a 40mm diameter hose will enclose four times as great an area as a 20mm diameter hose.

It only requires a 28.28 mm diameter opening (free area) to enclose approximately twice the area as a 20mm opening.

ie: Were your strainer grate to have 6mm diameter holes (28.313 square mm each), you would require approximately 11 of them to equal a single 20mm dia. (314.59 square mm) Hose, or 22 of them to equal twice the area (629.18 sq mm) of a a 20mm hose.

I actually knew that, but was too lazy to start up my HP50g calculator.

One other interesting fact, each orifice has a flow coefficient for the pressure drop across the opening.. If memory serves a flat hole is 0.64. Chamfering the hole reduces the inlet friction loss and increases flow through the orifice. The best opening looks like a velocity stack on Dellorto carburetor. Which is why velocity stacks work.

[Cheechako]

Based on how fast I've seen barnacles grow, a strainer plate like that could completely clog up in 2-3 weeks in the Caribe.

[GordMay]

Originally Posted by sailorchic34

I actually knew that, but was too lazy ...
... Chamfering the hole reduces the inlet friction loss and increases flow through the orifice. The best opening looks like a velocity stack on Dellorto carburetor. Which is why velocity stacks work.

Good point! I'd thought that was why, in part, you recommended doubling the capacity/size.
BTW: Earlier, I was only commenting on what you wrote, not on what you know.

[micah719]

The idea of the seachest and the stick to remove the critters in the inlet pipe gave me an idea....mount the stick to the strainer plate with a rotating blade....a few turns on the stick from time to time and voilá, a clean strainer. Hmmm, now the blade is getting deposits....aha, make it of monel!

[casual]

Quick question regarding water intake,I,removed a flush mount thru hull fitting,the hull was counter sunk to accept the thru hull fitting,I,wish to replace with a Mushroom fitting and fill the counter sink,this is a 1" thru hull raw water supply for a 56 hp Yanmar.Will the mushroom thru hull restrict water flow,was that the reason for using a flush mount?No strainer on the outside.
Thanks all.

[barnakiel]

It is suction, pulsation, on the 'lee' side of the hull. Turbulence, etc..

b.

[HopCar]

Casual, Flush thru-hulls are used to very slightly reduce drag and increase boat speed. You shouldn't have any problems with changing to a mushroom head thru-hull. Why do you want to change?

[capngeo]

Originally Posted by GordMay

Since the area of a circle varies directly as the square of it’s diameter, a 40mm diameter hose will enclose four times as great an area as a 20mm diameter hose.

It only requires a 28.28 mm diameter opening (free area) to enclose approximately twice the area as a 20mm opening.

ie: Were your strainer grate to have 6mm diameter holes (28.313 square mm each), you would require approximately 11 of them to equal a single 20mm dia. (314.59 square mm) Hose, or 22 of them to equal twice the area (629.18 sq mm) of a a 20mm hose.

Once again you beat me to the punch Gord!

[capngeo]

Originally Posted by micah719

The idea of the seachest and the stick to remove the critters in the inlet pipe gave me an idea....mount the stick to the strainer plate with a rotating blade....a few turns on the stick from time to time and voilá, a clean strainer. Hmmm, now the blade is getting deposits....aha, make it of monel!

Another variation (poor man's model) it to mount a "T" just above the valve where an elbow normally would go. Plug the "top" opening. When cleaning is needed, close valve, remove plug, insert rod, open valve, push rod down to strainer, wiggle like hell, remove rod, close valve, clean up mess!

[delmarrey]

Originally Posted by capngeo

Another variation (poor man's model) it to mount a "T" just above the valve where an elbow normally would go. Plug the "top" opening. When cleaning is needed, close valve, remove plug, insert rod, open valve, push rod down to strainer, wiggle like hell, remove rod, close valve, clean up mess!

My system, which can also accept a flush kit to winterize or just run the motor with fresh water. I can pull the top plug and push a ram rod straight thru to the strainer. Any thing left in the strainer one can dive under and finish by hand.