External Strainer Orientation

[Tellie]

On a watermaker intake, face it forward.

[dubema]

Hi,
I have been confronted to this straining question for some time now. On Tanzer sailboats I have seen sea slotted strainers oriented in both directions, and same on other sail boats. My belief is that when oriented aft the Venturi principle applies (same principles as intakes for monitoring instruments on airplanes wings or fuselage) and it goes on the sucking mode so your intake pump works more. When facing forward the inverse applies and the strainer takes in water with a positive pressure thus helping the pump. In the Yanmar support document they show and say that the seacock opening should be facing forward.
Tanks!

Originally Posted by Gaiamar

Greetings,

After reading many other threads I remain in need of knowledge and advise.

All 18 thru hulls have been replaced with new bronze. The problem is
that the contractor reversed the slotted strainers to face forward.
Original orientation was aft. Now they are glued and screwed in. There
were some words and now a standoff of wills.

The boat is a Beneteau 42CC and we sail at 6 or 7 kts. There are 3
external strainers 1 A/C (Not so worried here) 1 Gen and 1 Yanmar.

What is tha truth of the matter? Fore or aft.

Thanks Very Much

[wingless]

Originally Posted by delmarrey

My sea strainer is removable with 4 screws for cleaning. But.......

The through hull / strainer the factory used on my boat for the engines and A/C were the one piece scoop / through hull that did not permit cleaning, except by picking out crud through the slits, they were like these Groco STH strainers.

At the last haul out I replaced all of those w/ the APHS exterior strainer and a mushroom-type through hull. Now I can clean both sides of the screen and the through hull w/o any problems. An added plus is the change increased the water flow through the engines.

[HopCar]

Just to complicate matters, some new boats are going without internal strainers and just relying on external strainers with small holes. The theory is that the holes are as small as the holes in an internal strainer but the thing is self cleaning as the boat moves through the water. The Groco version also opens so you can clean growth out of the thru-hull.


Link: Groco Perforated Hull Strainers (APHS series)

I see wingless beat me to it.

[wingless]

When I installed mine I used one through bolt to permit electrical connection to the bonding system inside the boat. The rest of the fasteners were screws into the hull.

[roverhi]

As DelMarrey says, it's a power boat thing. On sailboats, have always seen the strainer facing aft where it won't pick up debris as easily and speed creating a vacuum is a non issue. Recently had a yard that almost exclusively does power boats change the head intake. The put the stainer facing forward. When I questioned the worker about it, he said it needed to be forward to force water into the strainer at power boat speeds. Had already invested money in that haul out so just left it facing forward.

[trantor12020]

I know this thread is old, nevertheless for the scoop strainer that is mounted wrong way (facing forward), has anyone consider cutting/extending the slots and do away with the scoop portion of the strainer to prevent hydrolock?

[delmarrey]

Extending the slots would help but it all comes down to its location, the speed of the boat and it’s ability to plane. Sucking air and/or forcing water in against the pump. One has to balance out the circumstances.

[donradcliffe]

Extending the slots will help, but unless you can do that underwater, it's better to turn the original around or replace it.