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Old 02-08-2012, 19:53   #1
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One for the Engineers

Water Intake Grill,

Is there any reason why it cant be flat?

Would the pressure of the hull displacement be enough make sure that enough water gets in to cool the motor correctly?

The diameter of the water intake thru the hull to my little yanmar ysm8 is 20mm and the plate that i'm going to put over it on the outside of the hull will be raised of the hull by 10mm and have a internal clear diameter of 120mm.

Basically it will be a stainless plate that floats of the hull on a polyethylene ring.

Next question is it it better to have hole perforated or slots cut?

If possible i will make a dish out of hard wood and try and reshape the grill to be rounded, but this may or may not be a success with the equipment that i have and the thickness of the plate that i was going to use.

Any advice or opinions would be welcomed.

thanks in advance

Matthew
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Old 02-08-2012, 20:01   #2
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Re: One for the engineers

Some are flat, some are angled, some are slotted, others perforated, some are rectangular, and a bunch are round. All of them are intended to keep critters, seaweed, and plastic bags from finding a hidey hole. The angled ones are often used on high speed craft to ensure that the water gets into the boat efficiently when under way (make sure the slots face forward). Slower boats don't generally need to "ram" the water in. All of them are a pain to clean. Many times they are unnecessary, since the seawater strainer is good for much of the work. Installing a "sea chest" manifold with a cap that can allow a push stick to clean out the intake is one cool way to handle issues with gobys, cleaner shrimp and striped mussels from taking up residence and blocking water flow.

Personally, I don't use them. It's easier to dive on them and poke around with a screwdriver to clean out the bore. But, of you have a drug runner, you will want to ensure that LOTS of cooling water makes its way easily into the water pump.
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Old 02-08-2012, 20:14   #3
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Re: One for the engineers

Flat is fine. Main thing is to have at least the same free area of openings as the diameter of the through hole. Good design would have the free area 2 X the opening of the through hole. So at least least 40mm total opening area in the cover.

Holes or slots or a mix work. Mainly used to keep the critters out of the through hole.. (fish, jellyfish, etc...
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Old 02-08-2012, 20:38   #4
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Re: One for the engineers

Interesting pics:

External Strainers - OMG Photo Gallery by Compass Marine at pbase.com
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Old 02-08-2012, 21:00   #5
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Re: One for the engineers

oh love the ones with the painted over holes...
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Old 02-08-2012, 21:37   #6
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Re: One for the engineers

Cool thanks for the replies everyone,

Now i wont feel bad if my attempt to subdue my stainless plate into a rounded strainer fails.

But pride and astetics ditate that i must at least try to make it round.

Ill post a picture when finished.

Matthew
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Old 02-08-2012, 21:50   #7
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Re: One for the engineers

BTW, sometimes you can get a chrome plated brass or SS floor drain strainer in the plumbing department at some Big box or hardware stores. Not sure about down under but probably near enough the same. May need to by the PVC floor drain then just pull the strainer. Plumbing wholesales would have just the stainer.
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Old 02-08-2012, 23:29   #8
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Re: One for the engineers

Ahhh, a thing of beauty, even managed a slight dome to it
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Old 02-08-2012, 23:43   #9
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Re: One for the engineers

My Google-Fu sucks today. Anyone know where I can get these in Stainless?

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Old 03-08-2012, 00:27   #10
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Re: One for the engineers

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Originally Posted by xymotic View Post
My Google-Fu sucks today. Anyone know where I can get these in Stainless?

And so does your picture.
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Old 03-08-2012, 00:44   #11
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Re: One for the engineers

I really don't get these strainers... Just use a sea strainer and get rid of them. They are too easy to clog, restrict water flow, and are hard to service.
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Old 03-08-2012, 02:31   #12
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Re: One for the engineers

And yet, just yesterday, a coworker of mine was late to work because he had to get towed in when his sailboat sucked a fish up the thru-hull that never made it to the strainer.
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Old 03-08-2012, 04:07   #13
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Re: One for the engineers

Agree with forumites that use straners, - you gotta keep the fish and plastic bags out. Do not use brass, the zinc will leach out and the strainer fall apart. Looks like you made a real good job of making your own. Well done to get all those holes drilled so evenly.
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Old 03-08-2012, 06:15   #14
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Re: One for the engineers

Quote:
Originally Posted by sailorchic34 View Post
Flat is fine. Main thing is to have at least the same free area of openings as the diameter of the through hole. Good design would have the free area 2 X the opening of the through hole. So at least least 40mm total opening area in the cover ...
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.
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Old 03-08-2012, 07:38   #15
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Re: One for the engineers

A copper one would be great. Keep the barnies from growing on it.
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