GL: Boat plumbing

[Ken Bloomfield]

 Hello from Tellico Lake, TN.  You recently wrote "

"A mechanic told us the other day that we were incorrectly hosed, and we could
easily sink.  A scary thought indeed.  But mechanics have been wrong in the
past and our boat has been plumbed like this since coming from the factory, so
before we commit to change, we want your opinions.

Raw water comes into the boat as follows:
    Raw water strainer to engine water pump through engine to after
cooler to transmission and oil cooler to venturi tube to wet exhaust to
out."

And I would like to help if I can, but need a bit more info.  My boat is plumbed as follows:  

  * Raw water into the strainer

  * Strainer to the raw water (sea-water) pump. (Normally, the term
    "engine water pump refers to the internal circulating pump that is
    circulating the anti-freeze/water mixture in the engine and through
    the engine-side of the engine heat-exchanger.)

  * Raw water pump to the dual transmission oil and engine oil heat
    exchanger (one heat exchanger, with two paths, one for tranny oil and
    one for engine oil.)

  * Transmission/engine-oil cooler/heat exchanger to the main engine heat
    exchanger (which takes the heat away from the hot anti-freeze/water
    mixture circulating in the engine.)

  * From the main engine heat exchanger to the water-cooled exhaust
    manifold, and finally

  * From the water cooled exhaust manifold to the exhaust water injection
    point for the wet exhaust.

Of course, there is some differences in installations.  Depends whether
or not your engine and especially the injection elbow is above or below
the water line.  Also, the arrangement of coolers can vary a bit, and so
on.  However, I could not tell from your post whether or not the mechanic
was referring to which of the following possibilities:

  * He was worried about you siphoning back sea-water when stopped, or

  * He thought there was not adequate materials in the plumbing (i.e.
    somebody used PVC pipe or fitting somewhere). Or

  * He thought the sequence of plumbing was wrong for some reason
    (unlikely if factory original).  Or

  * He thought the plumbing was not properly clamped.  Or

  * ???

You refer to the water going "through engine" and I assume you mean
through the engine heat exchanger (i.e. a boat's equivalent to a
radiator), is that correct?

You refer to a "venturi tube" and while I know what a venturi tube is, it
is most unusual (in fact I have never seen one) to find it in an engine
cooling system.  Could you be referring instead to an "anti-siphon loop"
prior to the exhaust injection elbow?

To make a long story short, if you could give a bit of context to the
discussion that you had with the mechanic, I might be able to help you
decide what, if anything needs to be done.  Perhaps nothing, or perhaps
some minor thing that you can do yourself.

All the best,
Ken Bloomfield,
M/V Tellico Lady, 50' Marine Trader
AGLCA #3529
MTOA #2062