Single Exhaust Plumbing – a good idea or not?

I’m a considering how to plumb the drains on my 46’ motorsailer, (currently under construction) and would appreciate some input.

Steve Dashew recommends using a single exhaust standpipe, with all of the various plumbing fixtures and pumps emptying into it. I certainly like the idea of eliminating a number of thru-hull fittings. Of course there is the complexity of routing everything back to the standpipe. Dashew says, “ We’ve used this solution on all our yachts for years.”

On the other hand, Dave Gerr (Boat Mechanical Systems Handbook) states, “This doesn’t mean you shouldn’t ever use an outlet sea chest, but it hasn’t worked out as advantageous in any of my design work to date.”

Ok, there’s the opinion of two pretty knowledgeable individuals, what say you forum members?

Regards,

SeaJay

 

Some folks fear through hull fittings, likely a bad experience during an impressionable age. There was a time when these fittings were less reliable then they are now, but it's more often then not a mater of maintenance then the actual thru hull fitting.

In this vain I know some that have no below the LWL thru hulls. Their wives never cuss them and their children always get good grades too. In reality, if you use quality pieces, inspect them regularly, use proven practices (double clamps, etc.) you'll never have issue with them.

Does this mean you'll never have a leak, who knows, things do happen, but in all honesty after many decades of working on them, living with them, sleeping next to one, I can resoundingly say, none failed because they "just gave up the ghost". All the failures, except for impact damage, could have been prevented with reasonable inspection or maintenance.

So, there you have it, the live in fear crowd or the have faith in modern machining camp. For what it's worth, I wouldn't go off shore with plastic under water thru hulls. Call me old school, but I've seen more failures with these then the hefty bronze babies. So, if I'm farther from shore then I can swim back to, I want bronze thru hulls and a tapered plug hanging next to each one.

 

I, initially was averse to the concept of putting holes in a perfectly good watertight boat... Why the great effort to make a dry boat, only to poke several holes through the underwater area - - In the end simplicity and common sense indicated life would be easier with a few carefully placed holes to get water (for engine cooling, potable water via RO watermaker, salt deckwash/remove mud from anchor chain)... To dispose of 'black-water' (from toilet holding tank) or get rid of 'white-water' in holding tanks from the shower/handbasin/galley liquid wastes...

It is therefore a necessary evil, (absolved by maintenance and regular inspections), - I am using quality stainless steel through-hull fittings supported by stainless steel ball-valves one each for each function before connecting to the necessary parts and services, bearing in mind that drawing in black water via your engine coolant - (dirty out aft of clean water in), or, RO watermaker supply, is not good, as filters will need cleaning/replacing more often, and the smell could not be recommended... Engine exhaust is above the waterline - (easier to set up if each engine is separately done), - and is a "wet exhaust"... On starting, a quick check of the exhaust indicates coolant is coming through the system and clean exhaust is usually a healthy sign too... but I am no engineer, just accepting reasonable advice and suggestions...

Just another view in support of Par...

 

Oh Lordy Par, now you've opened up the plastic vs. bronze debate!

In looking at my layout options, I'm coming around to Gerr's point of view ( and I suppose, yours as well). It's difficult enough to keep everything flowing down hill on tierra firma, but when you factor in 30 deg. of heel, I see a lot of trouble spots. I suppose with a larger boat and perhaps a deeper bilge you could make it work, but with what I have it seems like a lot of effort and potential problems for, as you've pointed out, a perhaps relatively small gain. Thanks for weighing in.

SeaJay

 

Yea, well I'm known for starting crap flowing around here, I guess.

For what it's worth, no one is using the crapper when the boat has 30 degrees of heel on.

A single outlet system requires a spaghetti like manifold, which seems just a problematic way of doing things, but more importantly, you have no "fail safe" with a single outlet. What happens if you have a small problem with one of the systems, you shut down all of them, until it's addressed? Now this is truly silly and potentially dangerous.

 

We use sea chests with big sized bronce fittings since ages in the commercial world, why should we go a different way in our yachts? Because Mama fears water inside the hull? Leave her at home.
I have never seen a sea chest failing when proper serviced as PAR mentioned, and I have seen some.............

Regards
Richard

 

Richard,

I am using a sea chest / maniford for intake, but my question has to do with a similar setup for drainage. Both Gerrs and Dashew take the time to discuss this matter but arrive at different conclusions. In the intake situation, you have pumps moving the water where required, but on the drainage (exhaust) side of things, if you rely on gravity (as you can do for individual drains with a dedicated seacock) things don't seem to work out as nicely...at least not in my particular situation. BTW, I am not discussing discharge from the head as my crusing grounds include a lot of "no discharge" zones so I have to deal with that in a different manner. What is at issue is the discharge from sinks, showers, bilge pumps, etc.

Thanks for your input.

SeaJay