Here's a photo for you...

[DDO]

The camera is astern pointing forward. Yikes, this gate valve is somewhat in the middle of the run and yet the hoses etc. look to be in great condition, as did the hot section I had off recently when I did the manifold / valve replacement. So, what should replace the connection between the two hoses and should it include a valve? I never used the valve and didn't even find it for a few years. Of course from my access view it looked fine. (Photo uploaded upside down!)

[sastanley]

DDO, Get rid of that sucker. What are at the other ends of the hoses?

If you have never used it as a valve, you could simply put a type of union there. (close nipple or similar), but even a brass 90 deg. ball valve would be better.

[ndutton]

Once upon a time, somewhere around the late 1960's, it was popular to put a gate valve in the exhaust line to protect against following seas. If a skipper found himself sailing in such conditions he would close the valve, engine off of course. All it took was one time forgetting the valve was closed and starting the engine to blow the exhaust system apart.

Builders realized it was a bad idea by the early 1970's, about the time waterlifts became popular. Some builders still wanted following sea protection but learned their lesson regarding relying on the skipper's memory so external exhaust flappers were fitted and one particular builder put a big swing check valve at the high point of the exhaust line. It works but makes a Helluva racket.

My 1977 boat has both the flapper and check valve.

edit: I think the exhaust gate valve qualified as a solution in search of a problem. That is, a short sighted solution protecting against a theoretical problem. Shawn's advisement is eloquent and to the point: get rid of it.

[DDO]

I'm getting it out of there -- as soon as I can find a proper connector: ABYC may not allow for nipple threads, but what is used for straight connections? Can't find anything for this 2 inch size hose.
My photo allowed us to recall the '70s; I'm always nostalgic around my Atomic4.

[ronstory]

It there is slack in the hoses so you can pull them together without too much tension, just look for a hose repair coupling (not plastic) with the correct inside diameter. That said, I would look at just replacing the entire hose, the hose on the inlet side looks a bit aged.

Normally the pipe fitting on the exhaust is 1.25" pipe, which the outside diameter corresponds to 1.625" exhaust hose, but every boat is different. Last I checked non-wire 1.625 exhaust hose at WM is about $10 a foot. Expensive, but IMO for peace-of-mind... priceless.

That said you can alway spend more and get the wire version of exhaust hose.

[DDO]

back pressure gauge kit question...

I have the pressure gauge kit from Moyer, which came with a long copper tube... is there any reason I must use that length? I'd like it much shorter but wondered if the length had any function in the measurement. I did find fiberglass tube connectors for the two hose lengths, about 2" diameter, nothing else in that size.

[sastanley]

Ah...that reminds me. Centek makes spun fiberglass unions for this type of stuff. When I removed my flapper that Neil mentioned (because the pin broke and the flapper was not flapping) I used a Centek elbow.

If I am sailing in following seas so rough I have to worry about back filling the exhaust, I didn't check the forecast close enough and should stay anchored or tied to the dock.
https://www.centekindustries.com/ - but you can buy it at Defender, Amazon, etc.

[roadnsky]

I have the pressure gauge kit from Moyer, which came with a long copper tube... is there any reason I must use that length? I'd like it much shorter but wondered if the length had any function in the measurement.

I'd think the length can certainly be shorter.
Since the gauge comes with a "Snubbing" Valve attached.
That snubbing valve adjusts how much gas (pressure) gets to the gauge.

NOTE that the gauge is normally not permanently installed tho.
"This kit is designed to periodically measure the total exhaust back pressure down stream of the exhaust manifold flange (every couple years unless symptoms of excessive back pressure develop sooner). The kit is normally removed between tests."

[roadnsky]

If I am sailing in following seas so rough I have to worry about back filling the exhaust, I didn't check the forecast close enough and should stay anchored or tied to the dock.

Don't tell Mo that!

[Al Schober]

Replacement is easy, just a stainless pipe nipple. Size to fit the hose, length to allow you to saw off the threaded ends.
Alternate is a rubber plug where the exhaust exits the transom. Shut off the engine, put in the plug. Start the engine, the plug pops out. Put a cord on it and you can reuse it.