keep up with the class, dougies. for your homework for the next three weeks
you are assigned the job of learning what a wet exhaust system is.

JAXAshby wrote:
the term sealed was used in the context of water ingress. keep up with the
class, dougies, or be left behind.

But if it is sealed then how can water get into it?

Seems to me that a sealed exhaust system would not be able to siphon
water back in now matter how much the boat rocked...

DSK

nav babbles incoherently:

The point is that it is never perfectly sealed. Piston engines work
because they run fast enough that gas leakage past the piston is not a
problem. A similar issue exists in turbo seal leakage in t-charged
marine engines. Then there's the water injection point ...

Cheers

DSK wrote:

JAXAshby wrote:

the term sealed was used in the context of water ingress. keep up
with the
class, dougies, or be left behind.


But if it is sealed then how can water get into it?

Seems to me that a sealed exhaust system would not be able to siphon
water back in now matter how much the boat rocked...

DSK

A properly installed system will have a syphon break.

not true at all, except in the land of crackerboxes.

nav? did you slip over into the land of crackerboxes to be close to oxxy?
yuk.

Don't forget gas leaking past the piston to the sump -especially on
older engines!

Cheers

OzOne wrote:

On 07 Jun 2004 11:39:46 GMT, (JAXAshby) scribbled
thusly:


First an exhaust is a sealed system

???

If it's sealed, then how does exhaust get into and/or out of it?

the term sealed was used in the context of water ingress. keep up with the
class, dougies, or be left behind.


But it's not sealed Jocks.
It's open from the carb inlet to the exhaust outlet sometimes.
So guess what, it's protected against syphonage.
Do you know how high you can lift water with a syphon before allowing
it to fall again?


Oz1...of the 3 twins.

I welcome you to crackerbox palace,We've been expecting you.

only happens in the voodoo land of crackerboxes.

What about the hot engine cooling and sucking water in?

Cheers

JAXAshby wrote:

Then you try and tell me that water can only get into the exhaust when
the boat is "seriously rocking for some time".
What is this "seriously rocking"?


that is rocking through an angle fore and aft to the point that water in
the
exhaust thru-hull is tipped and rolled forward enough to rise above the
high
point of the exhaust outlet hose coming from the water lift muffler. It is
also rocking enough times to fill the water lift muffler from reverse and
then
fill the outlet hose to more or less its high point to push the water in
the
water lift muffler back into the engine exhaust manifold and push the air
in
any cylinder with an open exhaust valve past that cylinder's rings and then
fill the cylinder with water. On most boats with a properly installed
exhaust
outlet hose this is not a problem as the boats are normally used. In some
special cases the installation does also need to prevent water ingress due
to
rocking.


Got anything to do with being on an ocean?


not really, through rocking conditions sufficient to water ingress are more
likely on the ocean that fresh water, ocean water is not necessary.

Are you sure?

In this universer, yes. in the voodoo land of crackerboxes who knows what
happened yesterday.

Think about it. Take you time.

Cheers

JAXAshby wrote:
through the exhaust thru-hull. This last only happens when the
engine is not running and the boat is seriously rocking for some time.
This
last condition in no way is mitigated by any anti-siphon valve placed
anywhere
in the system.

rickie sluggs tells us he has visited the voodoo land of crackerboxes and he
finds some salvation in that.


Yeah, isn't it great! There are a couple of technical threads going on
and not a single word!

I guess he got his ass kicked so badly on the others that his attendants
had to restrain him or increase his meds.

Rick

nav? English is your fourth attempt at learning to read?

well, that happens in the voodoo land of crackerboxes.

So now you are saying an anti siphon valve is essential for some
installations. Holy backpeddle!!!

Now think about this: Exhaust outlet below water and and hot air in the
engine cooling and sucking water up over the top of the ubend and down.
What happens next?

Cheers

JAXAshby wrote:

Let's walk things through here, as there seems to be some confusion
regarding
wet exhaust system installation, confusion caused by people looking at line
drawings from advertising brochures.

Let's take a hull with a seacock below the waterline. Just the seacock.
Open
it and water flows into the hull, right? Close it and water stops. Why?
The
outlet is below the waterline. Everybody agrees on that, right.

Now, let's put a length of hose on the seacock. (We called it a "hose",
but
that "hose" could be the entire engine raw water cooling system. Still, we
will call it "hose".) Now, open the seacock and what happens. If the hose
outlet is below the waterline, water flows into the hull. Of course,
everybody
says, the outlet is below the water line. Now, make the hose stop right at
the
waterline, water stops at the top but doesn't flow into the hull (unless
the
boat rocks or heels). Now, make the hose (remember, "hose" can mean the
entire
engine raw water cooling system) **at least** six inches above the water
line.
No water flows into the hull (of course) while the boat is level and there
is
little chance water will flow into the hull under most happenstances of
rocking
or heeling. Great.

Now, let's take that "hose" that opens **at least** six inches above the
water
line and turn on its pump (i.e. start the engine and running its raw water
pump). What happens? Of course the engine pumps water out the top of the
hose
and water flows into the hull. This water must be removed from the hull
(or in
this case, the wet exhaust system), and is removed by the pressure of the
burned exhaust gases from the engine. Hence, a "wet exhaust". Notice that
when the engine stops running the water stops flowing because the outlet of
the
hose is above the waterline.

"But wait a minute," somebody says, "what happens if we place a u-shaped
end on
the hose and put an anti-siphon valve in it?".

Same, same **as along** the outlet of the hose is above the water line.
The
engine stops the water flow stops because the outlet is higher than the
water
line, the anti-siphon adds nothing but expense.

This time lets make the end of the u-shape below the water line (dumb,
dumb,
dumb but let's address that in a minute). *IF* the top of the u-shape is
below
the waterline the whole thing acts as if the hose were straight up. In
other
words the entire hose is below the water line and if the seacock is open
water
flows into the hull and/or exhaust system. Note that any anti-siphon valve
installed anywhere in this system is useless, for there is no siphon just a
hose that starts below the water line, always stays below the water line
and
ends below the water line. Open the seacock water flows in and MUST be
pumped
out by the running engine. This is a forbidden installation. Dumb, dumb,
dumb.

Now, let's make the **top** of the u-shape above the waterline but the
outlet
below. What happens when you open the seacock? Not much, the water flows
into
the hose and up until it equalizes and then stops flowing. But, turn on
the
engine to a pump water and fill the entire hose with water -- from the
seacock
to the top of the u-shape and down to the outlet which is below the water
line
and open to the inside of the hull and/or exhaust system. Water flows and
must
be pumped out (by engine exhaust pressure).

Here comes the potential for trouble.

First, when the pump stops there is in fact a siphoning effect (because
while
the top of the u-shape is above the water line, the outlet is below).
Under
these conditions (should the exhaust installer fail in his job, AND the
boat
designer put the engine very low in the boat) there is a need to "break
siphon"
by installing an anti-siphon valve. Note that this **requires** the
anti-siphon valve to be above the waterline under all potential boat
heeling
positions.

Second, anti-siphon valves fail due to crud in the water. They always do
eventually. The solution for this is regular preventive maintenance.
(There
is another solution to avoid anti-siphon crudding up but I have never seen
it
but once.)

In other words, an engine with its water injection point of its wet exhaust
below the water line is in danger of at some point filling the exhaust
system
with salt water with the engine shut off. A competent surveyor would fail
a
boat with such an installation. If there was no way in hell the water
injection point could be moved higher (due to stupidity or deliberate
choice by
the boat designer) then the insurance company could decline coverage or
increase its premiums to cover the greater potential for boat loss. Sooner
or
later the wet exhaust is going to flood unless the boat owner is deligent
about
keeping the anti-siphon clean AND is damned lucky nothing flukey happens
between maintenance events.

The solution is to mount the water injection outlet **at least** six inches
above any potential water line.

It is in the installation instruction that come with a water injection
elbow.
RTFM, guys. RTFM