Modifying Raw Water Pick Up

"1997, 7.4/300HP Merc., Bravo

"1997, 7.4/300HP Merc., Bravo III, closed Cooling System. For years this unit has shown signs of poor water pick up. I'm considering using the current Overboard Discharge, (Never used, as boat is a Bay only Vessel.), as the new Raw Water Intake. I'll need a Strainer, Bronze Valving for direction and Flush. My main concern is can I use the Thru Hull from the Over Board? Ideas and opinions welcome! (I'm using the Flush Thru Hull do to room constraints). Al W."

"As is, I think not. I doubt t

"As is, I think not. I doubt that the hose size on the overboard meets the minimum hose size for the inlet...for example, on a 5.7L the minimum inlet hose size is spec'd at 1-1/4". Furthermore, it is recommended that lines on the suction side of a raw water pump be wire reinforced to prevent collapse.
Another issue is placement of the discharge. It should be low enough down on the hull to insure that it always sees non aerated water. And finally (and this is fixable quite simply if this is your only problem) You need to have a scoop on the inlet to help create a high pressure point at the water inlet (There are some available with strainers on them) ...Otherwise water flowing past the discharge will actualy cause a vacuum at the water inlet that the pump will have to overcome. Since water does not perform all that nicely in "shear" you could end up with cavitation."

That's the part of this eq

That's the part of this equation I was looking for. My boat is a 97 Sundancer with the Vacu Flush System. I believe the discharge to be 1.25 so I may be able to go this way by adding a Strainer Scoop. Thanks Rob! Any one else? (Please). Al W.

"I know mastercrafts have used

"I know mastercrafts have used a scoop on the bottom, the side discharge may come uncovered when turing."

The water inlet hose on the 7.

The water inlet hose on the 7.4 is most likely larger than the 1.25" one I indicated for the 5.7L.