Westerbeke Video

That's what I thought... but I had been told the genset had to be at or below the level of the water to insure there was always water in the impeller. Wouldn't the impeller burn out quicker if it is constantly having to run drive until it sucks water through?
 
Perhaps, but this is just a test and many gensets are mounted a bit above the water line.
 
Mine is mounted above the water line. Think about this, open a seacock in your boat with the hose off.... Whats going to happen? Water will come rushing in. Same applies to inboard engines.

When the boat is in the water there will always be pressure pushing water upwards.
 
Unless there's a way for air to replace the water in the line, the line will remain primed. Like holding the end of a straw filled with water...it won't release the water until you allow air into the top end of the straw. Hopefully, the onboard installation also has a strainer between the seacock and the impeller.
 
Also note that they are filling a bucket and allowing the generator to draw that which it needs. If you were to attach the water hose (garden hose) directly to the inlet to the generator, you would be at risk of forcing water through the exhaust and into the engine exhaust while it was not running. That would flood the combustion chambers with water and chance wasting the engine. The same holds true of cranking the engine too long while it won't start. The muffler can fill and back water into the cylinders when it is not running or starting.
 
Some more details for further clarification.

The raw water pump on that genset is of the
flexible-impeller design, which has no problem
lifting the water from that level. In fact,
it would lift from a couple of feet more without
any fuzz. Furthermore, 99,9% of all gensets & marine
engines use the flexible impeller design for raw
water pumping.
A turbine-type impeller (like your marine A/C)
pump would have a though time lifting water from
that height, though.
H
 
Actually, if a sea cock is opened the water in the hose will only rise to the level of the water outside the vessel unless the air pressure within the hose is less than atmospheric (water will rise above level outside) or more than atmospheric (water will rise below level outside).

Water pumps are positive displacement devices and will retain water.
 
+1
self bailing sit on top Kayaks have a hole straight into the water.
 
quote:
Originally posted by Rick D

That's what I thought... but I had been told the genset had to be at or below the level of the water to insure there was always water in the impeller. Wouldn't the impeller burn out quicker if it is constantly having to run drive until it sucks water through?

Click to expand...


rick, i think you're confusing this with an air conditioner pump. those are typically vane type pumps that must be below the water line as they are not self priming.
 
quote:
Originally posted by Rick D

That's what I thought... but I had been told the genset had to be at or below the level of the water to insure there was always water in the impeller. Wouldn't the impeller burn out quicker if it is constantly having to run drive until it sucks water through?

Click to expand...


Although it would be ideal to locate the genset raw water pump right at or just below water line to prevent it from getting dry, it is not necessary due to the flexible impeller type pump's ability to lift the water quickly while starting the engine. Below water line installations actually create some other problems so it is best to install the genset slightly above water level to insure the exhaust mixing elbow is over the water line. Even then, an anti-siphoning device is often needed to insure the engine doesn't flood with water by siphoning, which incidentally, is always mounted well above water and exhaust mixing elbow level.
Hope this helps.
H
 
quote:
Originally posted by MIke F

Actually, if a sea cock is opened the water in the hose will only rise to the level of the water outside the vessel unless the air pressure within the hose is less than atmospheric (water will rise above level outside) or more than atmospheric (water will rise below level outside).

Click to expand...


Correct. But there's more.
When you open a sea cock, there is the possibility that water will rush in pushed by pressure which is dependent on sea cock depth below water. This pressure and speed create momentum which can push water above water level and can create the risk of the siphoning effect.
Sometimes even boat pitching or yawing can create sufficient water movement to start the siphoning process. This, if not checked and corrected, can flood gensets or engines and worse, can sink boats.
H
 
Siphon only works when exit side of siphon is at lower pressure than entrance side--for example a siphon cannot be used to transfer water from one bucket to another unless the relative water levels are not equal.
 
quote:
Originally posted by MIke F

Siphon only works when exit side of siphon is at lower pressure than entrance side--for example a siphon cannot be used to transfer water from one bucket to another unless the relative water levels are not equal.

Click to expand...

Relative is the keyword here, my friend.
Don't bet your boat (or life) on that.
H
 
You must log in or register to reply here.
Back
Top