Motor flusher question

[boscoe99]

I think that the fwd motion of the engine as rpm increases is then forcing water in through the inlets and up to the WP inlet will have an effect on how the pump operates. Thoughts on that?

OP no pissing match going on here...we just like to debate the crap out of everything...and try to keep it civil as possible. Sometimes it becomes a pissing match, not often though.

I think the scoops (side or forward facing lowers) may help to deliver water to the pump but from there it is all on the pump to send the water up to the block.

Having said that, I suspect that in reverse, with no water ram effect to the pump inlet, the pump will still be able to satisfactorily cool the motor even at prolonged periods of high power reverse operation.

[TownsendsFJR1300]

With the inlets on the side of the leg and screens on them I do not see water being forced up to the pump

I have to disagree, at least while the boat is in motion...

Think of your pitot tube opening at the front of your lower unit and how small it is.

I flush mine after every run with a hose, and the end cut into a "V".

With approx 50 PSI out of the garden hose, my speedometer reads ONLY 17 MPH.

Imagine the force (in that tiny hole) to get the speedometer to read 48MPH (WOT for me)....

[zenoahphobic]

Two simple things:
Forward or backward motion on side screen pickups, will produce pressure. The shape there is an aero foil.

Two: much of the "centrifugal" affect is purely from the inlet being closer to the centre than the outlet, albeit by the larger diameter inlet hole. Swap holes the pump will work turning the same direction but push from the outlet back to the inlet. The concentric "positive" displacement affect will still have influence though.

If not for the relative smallness and inexpensiveness of this design, I cannot see why a simple "automotive" pump where the vanes don't touch, last forever, with sand, cannot do.

[boscoe99]

Most automotive water pumps that I am familiar with are centrifugal pumps. The vanes never touch anything. All of my water pump failures have been when the bearings give out.

https://www.google.com/search?q=auto...w=1229&bih=588

Maybe the outboard motor water pump needs to be a positive displacement type because water has to be lifted from down below and forced to the top of the block. Several feet perhaps. Maybe a bit more. I doubt a centrifugal type pump could move sufficient water at an idle RPM of say 550.

[99yam40]

I have to disagree, at least while the boat is in motion...

Think of your pitot tube opening at the front of your lower unit and how small it is.

I flush mine after every run with a hose, and the end cut into a "V".

With approx 50 PSI out of the garden hose, my speedometer reads ONLY 17 MPH.

Imagine the force (in that tiny hole) to get the speedometer to read 48MPH (WOT for me)....

you have to understand that the speedo hole is facing forward not on the side, so not much pressure

[99yam40]

Most automotive water pumps that I am familiar with are centrifugal pumps. The vanes never touch anything. All of my water pump failures have been when the bearings give out.

https://www.google.com/search?q=auto...w=1229&bih=588

Maybe the outboard motor water pump needs to be a positive displacement type because water has to be lifted from down below and forced to the top of the block. Several feet perhaps. Maybe a bit more. I doubt a centrifugal type pump could move sufficient water at an idle RPM of say 550.

I agree positive displacement pumps will pump water a lot better at low RPM than centrifugal
I always amazed me that centrifugal pumps run on ac motors out in the plants pull less amps when you pinched off the output.
amps go up the more water they pump,
raise the output pressure and lower the volume the amps drop
but then the RPM stays the same all of the time

[pstephens46]

Not much of a scoop on the side of the F150 lower. If it was a flat screen would the pressure inside the lower unit be higher than outside? Without the suction of the pump. Due to the water moving past at high speed.

[panasonic]

Pump inlet screens on my old little 20 are more than half way back on LU, sort of hiding bihind the thickness part of curved side of the casting.

But looking at the screen each little hole is formed like a little scoop to direct water into the inlet cavity. Some water has to be forced in while in motion from looking at it closely...

Now looking at my brothers seahorse 35 LU straight on from the front you can see the inlets sticking out the sides and they are shaped to scoop water in most definitely..water is being forced in to the pump inlet.

[zenoahphobic]

Most automotive water pumps that I am familiar with are centrifugal pumps. The vanes never touch anything. All of my water pump failures have been when the bearings give out.

https://www.google.com/search?q=auto...w=1229&bih=588

Maybe the outboard motor water pump needs to be a positive displacement type because water has to be lifted from down below and forced to the top of the block. Several feet perhaps. Maybe a bit more. I doubt a centrifugal type pump could move sufficient water at an idle RPM of say 550.

You will notice there are elements of "positive" displacement in those simple pumps, in as much as that they grab and push water and not just spin the water to make it fly out of the outlet.
You can design vanes with multi staging or pitch if you like to accomodate the rev range. The water mass required to circulate is quite small compared with closed radiator circuits because it has an infinite supply of cold water.
Cant be that hard , what do inboard car engined boats do when they use the water direct from the outside, no stupid complicated rubber impeller system.

[TownsendsFJR1300]

you have to understand that the speedo hole is facing forward not on the side, so not much pressure

Again, respectfully, I disagree..

The leading edge of the LU is extremely thin (and agreed, the pressure would be the highest there).

However, the LU side PU screens do have an ANGLE (recessed)* and will force water into those pick ups.

*Try putting your hand (better yet a thin piece of aluminum) SIDEWAYS in the water at say 15 mph (or higher). Now, turn it slightly outwards- that plate will have a BUNCH OF FORCE just with that slight angle..

Same as sticking your hand out your car window at speed aerodynamically, THEN slightly angled. MUCH more force.

And water (of course) is much more dense then air..


As you can see, the LU case is designed and the pick up's set back in a bit with casting directing water directly into the intakes. At speed, those pick up will scoop a bunch of water.


Just a side note, when I put my "Skeg Gard" on, I lost approx 1 MPH on the top end.

[99yam40]

I would be interesting to have someone cut the vanes off of an impeller, put the pump all back together and onto the lower,
make a bracket to mount it to so you can hang it on the back of a boat and run it threw the water to see how much water will come up and out of the water tube.

but that is not going to happen
so we just guess at these things

Inboard boats I have seen use a heat exchanger, not a direct raw water into the motor.
but I have only played with those in saltwater

[zenoahphobic]

Water pickups effectiveness is quite an aerodynamic science - requires the equivalent of wind tunnel testing. Often what you think happens does not. Eg. The leading edge of an airfoil like the outboard leg is not where the maximum pressure is.
I have had first hand experience with Radio Control boat cooling systems, none of which seem to be employed in full sized boats.
The pickups: there are basically three. One uses the rear under hull pressure. Second uses a hole in the side of the rudder similar to Townsend description photo.
And the third is simply a vertical tube with the end cut off at 45 degrees facing the flow of water. This one is where it is interesting. If you were to have bent this tube 90degrees with the end opening fully facing the flow of water (as seen on small outboards) the efficiency of this arrangement is abismal. The 45degree version is many times more effective! It has all to do about the turbulence, drag call it aerodynamics, at that opening!

[walleye1]

???????

[zenoahphobic]

And that Skeg guard, if you were to putty and smooth out the crevices and bumps you will get improvement. This will spoil the look though. But I suspect where the extra drag comes from can't be much improved, and that is at the guard's trailing edge. It has a dubious airofoil section (chord) not in harmony/compatible with the speed it travels at.

[zenoahphobic]

???????

Aerodynamics.
Get a matchbox and light a match and hold it facing a small breeze that won't blow the match out. Then place it in front of the matchbox, it won't go out. Place it behind the matchbox (you would think the sheltered side) and you can make it go out.
Now you can do this with greater wind where a match will go out, but move it closer to the front of the box facing the wind and it can stay alight ??????.!