water impellor direction

[Blue_Runner]

Probably the same reason we don't have permanent light bulbs.

[Destroyer]

Originally Posted by Blue_Runner

Probably the same reason we don't have permanent light bulbs.

Did you know there's a light bulb that has been burning almost continiously since 1901 in a firehouse? It's in Livermore, Ohio and has been the subject of several researches, investigations, and documentations. It started out as a 60 watt bulb and now burns as a low (4) wattage bulb. It doesn't give out much light, but even still... 110 plus years......
(And I have a 6v high intensity night light on my night table that I put a 12v automobile bulb in...that bulb has been on continiously for the 27 years we've been living in the house. It's not a lot of light, but works just great as a night light). Obviously the trick to long life for a lightbulb is the burn it at a lower wattage than it was designed for.)

[Blue_Runner]

That's pretty cool. My point was there would be lots of lost revenue in the aftermarket parts industry if we had impellers that lasted for the life of the engine. Seems like everything these days is made to wear out after a certain amount of time. I don't think it is a coincidence and in a lot of cases I don't think it is just because it would be cost prohibitive to make stuff more durable.

[THEFERMANATOR]

Rubber impellers are used because the yare self priming by nature, and are forgiving to debris going through them like sand, and provide good output at low RPM's. There are other optons, but the rubber impeller is still the best overall option for reliability, longevity, and durability.

[RWilson2526]

I'm still musing over the fact that Destroyer still sleeps with a night light

[Destroyer]

Originally Posted by RWilson2526

I'm still musing over the fact that Destroyer still sleeps with a night light

Ya,.. I got tired of stubbing my toes against various items in the dark.. The glow of a little light works just great. Beside, it lets me see other "business" in the dark.

[Destroyer]

Originally Posted by THEFERMANATOR

Rubber impellers are used because the yare self priming by nature, and are forgiving to debris going through them like sand, and provide good output at low RPM's. There are other optons, but the rubber impeller is still the best overall option for reliability, longevity, and durability.

Ferm, I know that you know your stuff, and everything you said it true,
but just for the sake of arguement, let me put forth the following. Both of my Seagulls pump a ton of water when they run. One is a 2 1/2hp and the other is a 4hp. Both have solid impellers similar to the kind found on just about any pedestal sump pump. I have a pedestal sump pump, and looking at it I find I was wrong, it's a 1/2hp motor, not the 3/4 I thought it was. Regardless, it still pumps to a 25 foot head. At 3 feet of head it will pump about 4000 gph. According to it's specs, it's designed to pass up to 3/8" solid debris, which is far more than any rubber impeller will.
You say that rubber impellers are self priming by nature, but if submerged, so is a pedestal pump. You would probably have to redesign the lower unit a little to get the pump impeller under the water intake ports, but other than that the self priming feature is pretty much a wash.
As stated above, the solid impeller will pass debris like sand and seaweed about the same as a rubber unit... perhaps a little better. Finally, my pedestal pump impeller is direct coupled to the motor via a shaft, turns at 1725 rpms and pumps 4400gph at zero head. That's a lot of cooling water at idle speed.

I know that this is all just conjecture, but it would seem to me that there's really no good reason to not use a solid impeller, especially given the fact that the British Seagull engines, (considered by many to be the best, most reliable small outboard engine ever built), use a solid impeller in their design. Really, I cannot see why they could not be used on larger engines. I wish some engineer could give me some hard facts documentation as to why the rubber impellers are used. (Other than the fact that it's just good business to make a unit that needs yearly replacement at about $35 per unit)... Multiply that by how many hundreds of thousands of outboards in use and that's really big business.

[THEFERMANATOR]

Originally Posted by Destroyer

Ferm, I know that you know your stuff, and everything you said it true,
but just for the sake of arguement, let me put forth the following. Both of my Seagulls pump a ton of water when they run. One is a 2 1/2hp and the other is a 4hp. Both have solid impellers similar to the kind found on just about any pedestal sump pump. I have a pedestal sump pump, and looking at it I find I was wrong, it's a 1/2hp motor, not the 3/4 I thought it was. Regardless, it still pumps to a 25 foot head. At 3 feet of head it will pump about 4000 gph. According to it's specs, it's designed to pass up to 3/8" solid debris, which is far more than any rubber impeller will.
You say that rubber impellers are self priming by nature, but if submerged, so is a pedestal pump. You would probably have to redesign the lower unit a little to get the pump impeller under the water intake ports, but other than that the self priming feature is pretty much a wash.
As stated above, the solid impeller will pass debris like sand and seaweed about the same as a rubber unit... perhaps a little better. Finally, my pedestal pump impeller is direct coupled to the motor via a shaft, turns at 1725 rpms and pumps 4400gph at zero head. That's a lot of cooling water at idle speed.

I know that this is all just conjecture, but it would seem to me that there's really no good reason to not use a solid impeller, especially given the fact that the British Seagull engines, (considered by many to be the best, most reliable small outboard engine ever built), use a solid impeller in their design. Really, I cannot see why they could not be used on larger engines. I wish some engineer could give me some hard facts documentation as to why the rubber impellers are used. (Other than the fact that it's just good business to make a unit that needs yearly replacement at about $35 per unit)... Multiply that by how many hundreds of thousands of outboards in use and that's really big business.

Your leaving out one KEY component in your equation that REALLY changes things, and that is speed. Your small engines are designed for engines that don't run that fast, and probably never experience cavitation while running. Now lets say you have that solid impeller and hit a wave and suck air through your water pickup. Now you've lost prime and quit pumping water, yet your still going on plane. Now you have to come off plane for it to pick up water again, and then you get that cold water hitting the hot cylinders that were just left dry for a few seconds and you get that nice steaming and stressing of the metal. I see what your point is, but in a high HP planing application the rubber impeller is king.

[spareparts]

keep in mind, you need to drop the lower unit every couple of years just to grease everything up, if you don't, when you really need it to come off, it won't

[Destroyer]

Originally Posted by THEFERMANATOR

Your leaving out one KEY component in your equation that REALLY changes things, and that is speed. Your small engines are designed for engines that don't run that fast, and probably never experience cavitation while running. Now lets say you have that solid impeller and hit a wave and suck air through your water pickup. Now you've lost prime and quit pumping water, yet your still going on plane. Now you have to come off plane for it to pick up water again, and then you get that cold water hitting the hot cylinders that were just left dry for a few seconds and you get that nice steaming and stressing of the metal. I see what your point is, but in a high HP planing application the rubber impeller is king.

Actually I had thought about speed but was hoping with a redesign of the lower unit that the impeller pickup could be placed somewhere where a wave/blowout would not result in anything more than the normal shot of air that even rubber impellers get occasionally. I'm sure there are good sound engineering reasons for using the rubber impeller over a solid type. (But I'd still love to see factory data)....

Looking at it from a different angle though, here's a thought/question I've always had. At speed, how much water does a rubber impeller really pump? Think about it. At low speed an impeller pumps whatever water is in the pickup. But at high speed, when you're up on plane and skimming along the surface like there's no tomorrow the water that's under your boat is hitting your lower unit water pickup with more pressure than a fire hose. Does the impeller continue to pump water at all, or does the extreme pressure flex the vanes out of the way and go directly to the engine all by itself? ... or maybe it is a combination of the two...pumping and pressure?

Originally Posted by spareparts

keep in mind, you need to drop the lower unit every couple of years just to grease everything up, if you don't, when you really need it to come off, it won't.

Excellent point also.