I have a problem with bits of driftwood clogging my yanmar raw water intake at the thru hull. I have a strainer on the hose; but I am planning on installing a strainer over the flush thru hull. Most race boats don't use a strainer. Do they have a problem with this? My problem is I want to use a marelon strainer and they only make the scoop type. This will probably flood my engine while sailing. I have seen some boats with the scoop on backwards but am concerned this will starve the engine for water while motoring. I have considered drilling holes in the back of the scoop. Anybody have any ideas on this?
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Raw water intake grate
"Race boats" probably want to eliminate drag & turbulence and ensure as smooth a flow of water along the hull as possible, thus .....no strainer. The scoop type you want to install won't flood the engine while sailing if you close the raw water seacock, will it ? Hang your engine key on the seacock as a reminder to open the cock before starting the engine.
"Race boats" probably want to eliminate drag & turbulence and ensure as smooth a flow of water along the hull as possible, thus .....no strainer. The scoop type you want to install won't flood the engine while sailing if you close the raw water seacock, will it ? Hang your engine key on the seacock as a reminder to open the cock before starting the engine.
Can't flood with scoop
As long as the engine is not turning no water can pass through the raw water pump. Now if you got her up to 50 kts MAYBE you could get a trickle to flow but even then I doubt it. Your raw water pump is a vane - positive displacement type and acts like a piston pump. No turnie - not water flows. If you have a centrifugal pump then you might have a problem as the impeller can pass water when it is stopped. I don't think this is even possible as the anti siphon loop would have to be gotten over and that would take 4-8 PSI which would mean once again ~50 kts.
As long as the engine is not turning no water can pass through the raw water pump. Now if you got her up to 50 kts MAYBE you could get a trickle to flow but even then I doubt it. Your raw water pump is a vane - positive displacement type and acts like a piston pump. No turnie - not water flows. If you have a centrifugal pump then you might have a problem as the impeller can pass water when it is stopped. I don't think this is even possible as the anti siphon loop would have to be gotten over and that would take 4-8 PSI which would mean once again ~50 kts.
Bill is correct, of course, but I also doubt that
the intake would starve for water if the strainer faced aft. A positive displacement pump will pump air as well as water, they are used as priming pumps for large centrifugal pumps. I'm pretty sure people run them facing aft to avoid scooping junk in and they'll let us know how it works in practice.
the intake would starve for water if the strainer faced aft. A positive displacement pump will pump air as well as water, they are used as priming pumps for large centrifugal pumps. I'm pretty sure people run them facing aft to avoid scooping junk in and they'll let us know how it works in practice.
scoops work fine
we've had the forward facing marelon scoops on our raw water intakes for several years with no problems-Bill's correct-you won't have water forced thru your engine at sailboat speeds
we've had the forward facing marelon scoops on our raw water intakes for several years with no problems-Bill's correct-you won't have water forced thru your engine at sailboat speeds
Aft-facing Scoop
I have used an aft-facing scoop for many years on several boats. It never starves the engine for water and it rarely ever fouls with eel grass or other junk. Check the Archives.
I have used an aft-facing scoop for many years on several boats. It never starves the engine for water and it rarely ever fouls with eel grass or other junk. Check the Archives.
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