I've never asked before,

[walker45]

But for a lot of years I've made it my hobby to look at the water intake plates on outboards, the rectangular plate near the impeller. I've seen the little scoops facing both forward and backward and I'm sure I'd seen some facing up and down if it were possible. My question is. Is the scoops supposed to face front or back?

 

[F_R]

Book says this way----

 

[thatone123]

I don't know if there is a supposed to - to it as there are many different designs. I've wondered what is the most efficient for different circumstances etc. I would think the older OMC with the ones that are like in the photo or some that have the water entry under the cavitation plate would be best for my extreme shallow water running. The 15 2 stroke OMC is good even though they are on each side of the gearcase above the actual gear location. I was running in shallow drive yesterday in 4-5 inches of mud and weed water and no clogs. Often you can see mud coming out the pee hole that I have enlarged. (Northern Bush Trick) As for deep water, I wonder what jams the most water into the water pump housing or even is that necessary for super efficient cooling? Some Outboard Guru here must have some insight?

 

[F_R]

As said, there are many different designs. I guess I was assuming the question pertained to the kind in the photo. As for that particular type, the main water intake is on the leading edge of the exhaust outlet snout. Propeller thrust and forward motion through the water rams water into that main intake. Because of that ram effect, water actually flows out of those little holes in the pictured bypass plate during forward running. But during reverse running, the prop is sucking water away from the main water intake. That is the reason for the holes in the bypass plate---an auxillary intake for when running in reverse..

 

[walker45]

I feared it could turn into a question with many answers but after not noticing on one I removed years ago it turned into more than curiosity. Facing forward does seem to make more sense to me.

 

[walker45]

Btw, do a youtube search for Port Huron or Marine City if you have any interest in Great Lakes freighters.

 

[racerone]

Just looked at 4 of those 6 HP gearcases.----2 of them face forward.----2 face to the back.----Makes no difference.----And I know that if it was critical then the hole positioning on OMC parts would be so that it could only be mounted one way.----They did that thinking in the old days !

 

[Mohawkmtrs]

I also just looked at a 6hp in the shop...holes facing forward.

 

[F_R]

Six days a week for 24 years working in an outboard shop and I confess I didn't know how it is "supposed" to go without looking in the factory service manual. Obviously it makes no practical difference. But now the question is why the scoops in the first place? The part almost certainly was made in a punch press, almost instantly at each whack. So the time and material is the same either way. Only difference would be the tooling. And it took considerably more $$$ to make the tooling for scoops than plain holes. So new mystery, eh? Reckon we'll never know.