The Steamboating Forum

We've had some discussions about sizing a keep condenser. It occurred to me while in the shower, surrounded by clouds of steam that the easiest thing to do is to simply use a feed-water heater. What we do is this:

• Provide an ample sized keep condenser. For my (so far theoretical) big boat this would be sufficient to cool 300 lbs steam/hr from 170F to about 60F, a few degrees above water temp.
• Pull the water out of the keel condenser with an air pump at 60F and then run it through a feed water heater in the exhaust stream. Since the vast majority of the energy is the change of vapor to liquid, the exhaust will stay essentially at 170F and heat that cold water right back up to nearly that temperature.

So we don't care how big the condenser is, so long as it's big enough. The feed-water heater will bring the hot-well temperature close to exhaust temp.

So long as the exhaust temperature doesn't reach too high, this will work w/o any moving parts. If the engine exhausts at above 200 F for any length of time. some sort of temperature control will be needed; a simple 180F automotive thermostat can clearly be used for this purpose.

The neat thing is this lets us bolt a nice shiny brass/copper heat exchanger on the engine w/o the need for additional pumps, risk of flooding, etc. that a raw water cooling system raises on the inside of the boat. And the hot well is always the right temperature, regardless of the outside water temperature.

Just make the keel condenser big enough.

- Bart

Hey Bart

You end up with two holes in the hull anyway whether you have a condenser inboard or out. If it was mounted inboard all the pipes would be shorter and easier to get too and the raw water ports could be right there close at hand to shut off in case of a leak. I do like the thermostat idea, those new double plated ones Chevy uses would work well for a bypass setup. As far as pumps go I have one mounted on an old ford engine with more miles on it than the pope has gold and it is still running leak free under pressure and to my knowledge going on 32 years now. I am leaning towards an inboard condenser for the "bling". I have a nice copper condenser all TIG welded together and polished in mind that would look really nifty along side all the other bronze, brass and copper doodads already in the boat. Plus it gives me something else to tinker with.

But alas, you are making a good point... Less moving parts and more steam bling. But what am I going to use to power the water cannon? You know, for when we be boarded by Pirates!

Yes I should have gone to bed hours ago.

Cheers,
Scott

You end up with two holes in the hull anyway whether you have a condenser inboard or out.

It is not holes in the boat that worry me. It is the need for piping & pumps carrying sea water in the boat.
Make sure to use proper through hulls w/ ball valves/sea cocks to keep the ocean out should a pipe, pump
or fitting fail somewhere, and use 'em - when leaving the boat when she's in the water, close them.

- Bart

Hey Bart

If I decide to go that route I will use the proper safety gear. So what metal should I make the pipes out of? Since I have never run any steam gear on the ocean what would be a good alloy to use for the cooling system?

I had this idea to combine a fluid clutch with an automotive thermostat bulb to vary the water flow through the condenser. The hotter the output water from the condenser the faster the water flows in.

Will see what happens.

Cheers,
Scott

Back when the "evil empire" fell, Titanium was available, and was used in some condensers, but now the price is just too high, it is the first choice for sea water cooling tubes, followed by Monel, also very good, and very very expensive. Sea water cooled condensers use Copper-Nickel Tubes, 70-30 is the best choice, followed by 90-10, Admiralty Brass (actually a bronze) is good, but ordinary brass should be avoided. Stainless steel (types 304, 316) is not recommended for this service in salt water. There are plenty of more rare alloys that will do nicely, but usually high price.

For the amount of service most of us see with small steam launches, ordinary copper tubing works just fine (for heat exchanger tubes, as well as sea water piping), is readily available in small quantities, and easy for many of us to work with. If using soldered joints, lead free solder is recommended, as the tin solders (now mandatory in USA plumbing) have less potential to form corrosion on the copper due to electrolysis.

So what metal should I make the pipes out of? Since I have never run any steam gear on the ocean what would be a good alloy to use for the cooling system?

Fred is right, as usual.

I used type either K or L 3/4" copper water 'pipe' and have had no issues. Copper is the right choice for keel condensers for trailered boats. For our big boat which will spend months in salt water either heavier copper or better yet, 90/10 cu-ni (prob 2-2.5 x cost of copper) is indicated. As is well known, the British Navy routinely covered the bottoms of their ships with copper sheet for both anti-fouling and protection from ship-worm.

http://www.copper.org/applications/mari ... ction.html has some interesting bits on alloy selection. In particular, flow rates in copper tubing determine corrosion rates; be quite careful pumping salt water through regular copper pipe as it's subject to sometimes rapid impingement attack above about .75 meters/sec velocity; this is particularly a problem in elbows, valves, etc. where extra turbulence occurs. Copper on the outside of the hull has an better environment than internal piping since the salt water is always fresh. For seldom used boats copper inside and out should work just fine - but keep an eye on things, and pressure test your raw water system when you hydro that boiler.

Don't use brass fittings on any lines carrying saltwater; they will quickly dezincify and fail. Boats are lost every year to a combination of an unclosed sea cock and a small brass fitting in the raw water cooling line.

- Bart

Hey Fred

Thank ya for the info; as it happens I was also looking at corrosion tables and charts last night and about fell off my seat when I priced a few small pieces of Monel tubing. I found myself thinking that gold would be cheaper!

As far as Titanium goes that stuff is easy enough to weld so long as ya have the right tools but still very expensive. I built some parts for a friend of mine for his racing quad. I thought 6061 would do the job just fine be he insisted on titanium.

I have spent a lot of time TIG welding copper for the stills I make because large lap joints for silver soldering are not very pretty. I had in mind to do all the copper plumbing in modules with bolt flanges for ease of dis-assembly.

Admiralty brass? As in copper tin alloy 90-10? If so that would not be too hard to make after I get the smelting furnace built. I could cast the bolt flanges and valve bodies. Do you have any idea how well that stuff would TIG weld given the low tin content?

I like the idea of using copper for the seawater plumbing. All polished up with admiralty brass flanges would make for a very good-looking bit of machinery!

Cheers,
Scott