Running outboard "Dry" out of water

[Capt Popeye]

Yes I sort of get this argument - and I check the outboard at home with muffs. But, because I'm new to this, it seems feasible that you could test the engine at home with muffs, then drive 50 miles to the coast over bumpy roads, during which time you could damage or dislodge something in the electrical or ignition system, or the battery starts to fade. Then you drop it in the water and it won't start.

Like you lot I probably won't give it a second thought after I've been boating for a few years. But the problem just had me scratching my head a little bit. After 100 years of outboard development, you can still turn a brand new 10 grand motor to scrap by accidentally turning the key?

Humm well thank you tsf you speak wise words I say, my thoughts are that the Manufacturers are 'blind' to the situation, companies run by peoples with grease on their hands, and all is well, a sort of Engine Groupie, so suggest that any improvements are to come from those outside of main stream Outboard Engine Manufacturers.

The RNLI do appear to have given it some thoughts and they have their own way of dealing with this situation, maybe the water pump is lined with a Ceramic material so reducing the rubbing /shear stress on the Impeller blades.

As the response that OB run in water so where is the problem, well partly or even mainly true, but at the Start of a day afloat it is good to start the Engine when the Boat is out of the water, just to see that all is well, good practice I would say; not everyone wants to test it at home or at the garage, or indeed have the facilities to do so; when out on the water and boat is in shallows sometimes the OB touches ground and is tilted up possibly raising the OB water intake out of the water or partly so so the ability to still run the engine safely would be a certain plus.

Still maintain that the underlying reason that OB Manufacturers do not appear to solve this situation is that there is no impitus to do so, yet ?

Oh Air Cooled Outboards I have owned a few, they are just great if one wants the reassurance of being able to start the OB out of the water prior to launching, as regards them being Old Hat or something like that, well yes most probably were made then, but Honda have a current model that's Air Cooled, it may be a little Engine but its Air Cooled for sure.

Lets consider that engines used in Lawn Mowers and Tractors etc are Air Cooled and do they generate lots of noise, well they are certainly more noisy than a Water Cooled OB, but are they really noisy ? I think that a Seagull OB is just as noisy and they have been around a long long time, and they are water cooled .

 

[BruceK]

The more pertinent question in my mind is why does the boat engine manufacturers use neoprene or nitrile impellers?

I've had water pumps in many guises from slurry pumps, lay water pumps, irrigation pumps, pond pumps, aquarium pumps etc that pump non stop for years at a time with plastic or metal impellers. Pumping much more water at higher pressures / head lift height and siltier too boot. Why neoprene?

 

[longjohnsilver]

I'd hazard a guess that none the pumps you mention run at vastly variable speeds up to say 10,000 rpm. But still doesn't explain why neoprene as opposed to some other material, maybe more flexible?

 

[BruceK]

There must be a reason granted as the impeller is also completely different in design but what about say Teflon / PTFC etc and other materials that are flexible, hard wearing and heat resistant?

 

[lenten]

boat launched off a beach into waves everyday so engine needed to start first time ----would run engine for a minute or two dry before launching------seagull engine----metal impellor

 

[Bouba]

boat launched off a beach into waves everyday so engine needed to start first time ----would run engine for a minute or two dry before launching------seagull engine----metal impellor

That is exactly why my tender has an air cooled Honda on the back

 

[prv]

I have heard in idle conversation the RNLI use a "non standard" run dry impeller, if true maybe someone can shed some light?

I don't know about that, but their carriage-launched ILBs have a pair of water tanks on the back of the carriage which each feed an engine for a short period so it can be run up before entering the water and ready to immediately power away as soon as the boat floats. The tank is connected to the engine via a hose that pulls off its fitting as the boat leaves.

The tanks are the grey parts:

I believe the Navy have something similar for their seaboats.

Pete

 

[Bouba]

I don't know about that, but their carriage-launched ILBs have a pair of water tanks on the back of the carriage which each feed an engine for a short period so it can be run up before entering the water and ready to immediately power away as soon as the boat floats. The tank is connected to the engine via a hose that pulls off its fitting as the boat leaves.

The tanks are the grey parts:

I believe the Navy have something similar for their seaboats.

Pete

That is the most interesting thing I've read today, thanks Pete

 

[John100156]

I have a 25hp 2001 Mariner 2T motor and use muffs all the time, when I start the motor for the first time after a while, using them before launching the dinghy and again when finished, unless I'm going out again the next day. All very easy to do as long as you can get to a hose...! It only takes a few minutes. I would never run it dry its just asking for trouble.

 

[anoccasionalyachtsman]

On reading this thread it seems that I've been extremely lucky having done this dozens of times, albeit for just a few seconds. I did it recently after a full going over of a new-to-me little Mariner that I'm going to be relying on this week - so there's a new impeller on its way just in case! Thanks for bringing it up.

 

[Capt Popeye]

I have often thought of lubricating the Water Pump housing with a synthetic waterproof grease, prior to assembly, perhaps a silicon type, both to prolong impeller life and efficiency, must try that near the end of this season afloat.

Would be interested to hear from anybody who has tried that ?

 

[John100156]

I reckon a smear of lubricant would be fine to protect at first start-up when after all it would otherwise be dry for a few seconds, after replacing the impeller, but lubricant would soon wash off.

Its madness to chance running the impeller dry for very long though, would you run up an engine for a few seconds without any oil? Unlikely, yet surfaces would likely retain an oil film.

I always use muffs and start the hose then the engine. Change the GB oil and plugs every year and run the carb dry when leaving the boat. The motor is 16 years old, runs sweet and starts every time after one pull.

 

[Capt Popeye]

Humm well re the washing off of the lubricant grease when in contact with water; you are familiar with the well proven stern glands that use grease packed into the revolving joint between the shaft and the stern gland, these glands just require a slight turn on the pressure screw to keep the water from entering the boat; in effect the shaft revolves in a block of water proof grease, there is of course a packing seal of asbestos or similar that also requires to be tightened when required to keep the water out.

 

[John100156]

No - that's a completely different animal - the following gives some idea of how an impeller pump runs, they also confirm they should not be run dry and even for this brief demo Jabsco lubricated their impeller, consider the rotational speed and centrifugal forces at work, I doubt a smear of grease would last very long and you certainly would not want to pack it in :

https://www.youtube.com/watch?v=ECv1VwW6RTo

 

[Bouba]

I would imagine that a dollop of grease finding its way into the raw water cooling channels in the engine block could do some serious damage

 

[John100156]

Its certainly something I wouldn't do.

You normally get a small tube of light lubricant with a new impeller, but if not, I would probably just smear it with a bit of Vaseline of even some fairy liquid, that's what I did IIRC when I changed the impeller on my 25hp mariner the last time. As I say, anything is likely to wash-off/through quickly when pumping sea water.

I would definitely not run it dry though, but acknowledge what's been said above, that this seems to have been done successfully. My thinking is why risk it, assuming you have access to muffs and a hose, it would almost certainly reduce the life of your impeller....