MapisM
Well-Known Member
I really struggle to understand why this seems to give you some sort of satisfaction. Regardless, you must try harder!
There are several points in your reasoning that I'm not sure to have understood, but honestly, what you are saying about the water flow while flushing is beyond a joke. I'll give you the benefit of the doubt that you didn't think about it before writing, because I'm sure you know better, if you try for a moment to understand, before criticizing.
LS already said it all 10 years ago, really: "Leave the seacock open and IF the water flow from the dock is greater than the needs of the engine at an idle (usually is if a good valve/water flow/pressure is at the dock, you have a good hose and 5/8" or bigger plumbing all the way to the "T" in your system,) the engine will only have fresh water in it after a couple of minutes of idling".
Now, it doesn't matter how many Nobel prizes for physics you might have been awarded.
When someone like LS says that on a topic like this, the only sensible thing to do is take note - which is what I did.
But let's assume that you are unaware of who the man is, and you rate his comment as if made by any Sunday boater.
What do we have here?
Firstly, a fresh water hose whose capacity in L/min is enough to feed the engine raw water pump running at idle.
Leaving aside what LS said, this is proved by the fact that jfm uses a normal hose, connected through a smallish (albeit high quality steel, but that's irrelevant in this context) quick coupling connector. And that is enough to supply water to a Cat C32, no less!
My supply chain, so to speak, actually has a higher capacity, because on top of using 3/4" valves and 19mm hoses, my coupling connectors are larger (2.4 times the capacity vs. the standard size).
So, it's no surprise that also in my boat the water supply is more than adequate for my much smaller engines, and I can clearly see that if I flush the engines with the seacock closed.
Secondly, there are different pressures at work.
The hydrostatic pressure of sea water, let's say one meter under the surface, even if the strainer is not that deep, is 0.1 bar.
I mean, ONE TENTH of bar, not a typo. Just look at the manual of your diving course if you don't trust me.
Otoh, the pressure of the dock water supply can be different in any marina, and often it also changes over time, depending on the grid demand, how many folks are washing their boats, etc.
In my marina, most of the times I have a pressure of 2+ bar, with peaks of 4 or even 5 (good thing that I have a pressure limiter on the dockside direct connection!).
Therefore, when the hose is attached to the strainer lid (or to the dedicated pipe in jfm setup, which makes absolutely no difference in this respect) leaving the seacock open, what happens is that you have two concurrent water supplies, salt and fresh.
The fact that the first comes from a 3" passage and the latter from a 3/4" hose is irrelevant, because with the engine at idle BOTH these supplies have enough capacity to supply water in excess of the impeller demand.
As a consequence, the only difference is the pressure of the respective supplies.
And I hope you'll agree that it doesn't take a lot of science to know who wins, between 2+ bar and 0.1 bar...!?!
) .
