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Do Bravo drives "vacuum up" water?

Old 07-12-2019, 01:44 PM
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Default Do Bravo drives "vacuum up" water?

I understand that it is deadly to the impeller to run an I/O without water for even a very short period of time.
So, when you drop your boat in the water (or get it off its trailer) and the lower unit is in the water at the start of a day of cruising...when you start the motor, does the impeller "self-prime" (essentially vacuum up water) to start pumping? So it starts dry and has enough vacuum/suction to pull water up to the impeller before damage/heat occurs?
Thanks,
Tom
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Old 07-12-2019, 02:32 PM
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that is correct, however, there will nearly always be water sitting on the impeller from the pressure side. That system never entirely drains itself.
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Old 07-12-2019, 04:47 PM
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Once a pump is primed itís never fully dry as it has a head of water sitting on it from the hose to the engine, and the water level on a boat almost primes it as well. Iíve pulled the intake hose off the pump at the lake and water started flowing in.

As I understand it after about 30mph the pump is actually a restriction because the drive is shoving so much water through there.
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Old 07-12-2019, 08:32 PM
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Originally Posted by Baja Rooster View Post
... and the water level on a boat almost primes it as well. Iíve pulled the intake hose off the pump at the lake and water started flowing in.
Are you saying that the boat sitting in the water, displaces enough water so that it is low enough to almost get the water into the impeller?
So, would it be safe to run the motor (at idle) by lowering the Bravo drive into a tub/bucket of water (re-supplied by a water hose)?
Thanks again!
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Old 07-12-2019, 09:09 PM
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I would that in most boats yes the water level on the hull is above the seawater pump.
BUT even if the engine and pump were completely dry it would still suck water up and into the pump.
My engine is mounted high enough that my pump is higher than the water level outside my hull.
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Old 07-13-2019, 12:15 AM
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I reckon my seawater pump is around about sea level. (Single engine). However, backed down the ramp, I'm sure it's above sea level so it depends on "vacuuming" water from the intakes on the drive. Never had a problem starting on the ramp with the stern of the boat in the water, I get full water flow pretty quickly.

Using ear muffs to flush the engine works fine and I reckon both sides of the impeller are dry if the boat has been sitting for a while. I'm sure evaporation will clear te water out. Running in a big trough, same thing applies.

RR
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Old 07-13-2019, 06:37 AM
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Originally Posted by F14A water jet View Post
So, would it be safe to run the motor (at idle) by lowering the Bravo drive into a tub/bucket of water (re-supplied by a water hose)?
Thanks again!
You will drain the container faster than you can fill it from a garden hose....As stated above, water will find it's own level and that can serve as a "self-prime" scenario as the water line outside you boat will be the waterline level in your hose before the pump - the lower the boat the high up the hose you will find water.....

What are you trying to accomplish that a proper set of muffs can not?

Last edited by speicher lane; 07-13-2019 at 06:40 AM.
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Old 07-13-2019, 08:08 AM
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Short answer to the title of the thread is yes
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Old 07-13-2019, 08:29 AM
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Originally Posted by speicher lane View Post
You will drain the container faster than you can fill it from a garden hose
Running in a container would be no different than running it on muffs. The garden hose will fill the container just as fast it would supply the muffs.

Personally I never had a problem running on muffs, although I do like feeding into the sea strainer better.
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Old 07-13-2019, 08:58 AM
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It only takes a small air leak between the pump and drive pickup to keep the pump from pulling water. Just a loose hose clamp can do it. You would think that you would see a water leak at that point when you are on plane at speed, but the pump pulls enough water that there is almost no pressure to the inlet side of the pump.
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