Designing a new engine for a big(ger) boat...

[barts]

I'm working on a design for the engine in our next steam boat, which is to be a 35' (or so) cruiser suitable for the Pacific Northwest with about 8 to 10,000 lbs displacement. I'd like to be able to steam with wood rather than just oil, and want to keep fuel costs in check. In addition, the boat will have a cabin and pilot house, with both the engine and boiler inside the accommodations. I want to be able to single hand her w/o drama as well.

As a result, I'm looking at the following:

* twin cylinder inline double acting simple uniflow; cylinders are
cut-down Detroit Die*l 53 CID liners. Steam powered vacuum eductor
for ease of starting. 3.875" bore x 4.25" stroke, jacketed head, entire
cylinder well insulated. Built-up hollow piston to cut down on weight.

* poppet valves configured so that excessive cylinder pressure
will lift them; very low clearance volume (2 %).

* Operating pressure 200-300 psi, 600 F steam temperature.

* variable cut-off from 2.5 % to 10%, w/ a bump for starting...

Since the engine is in the cabin, I'm considering a roller crosshead to
cut down on the hot oil smell; perhaps I should finder a better smelling
oil . The mains are likely to be babbit in bronze or iron sleeves;
the crank will be built up w/ a pinch bolt design ala Rolly Evans' designs. I'm considering
pressure lubrication of the mains and crankpins (via drilled passages); I'd likely include
scavenging passages as well to help cut down on oil flying about. The wrist pin
bearings will be greased needle bearings.

For valve gear, I'm inclined to go with Skinner's dual cam setup so that valve
timing is completely variable; two shifting cams would be simpler but offer
limited adjustment and are operationally less sure.

Calculations suggest 6 - 19 IHP over with 35 - 150 lbs/hr steam consumption;
actual HP realized is likely 2/3s of these values.

So far, it appears this design can be made to work as a series of machined weldments
and chucks of cast iron.

- Bart

[Chris W]

Bart,
Chad O'Conner had a 2 cylinder uniflow engine of his own design in "Well Stacked". If I remember correctly it was fully enclosed and a really neat installation. You might be able to find someone who knows more of the details of the design so you don't have to reinvent the wheel. I've lost track of the boat and have been trying to find what happened to it.
Chris

[SL Ethel]

Hello Bart,

Both the engine and boat sound fantastic. I have been noodling around (without much success) with a design for a similarly laid out but smaller engine for my open launch. I am curious about your planned cutoff. Both on the steamer Elpenor and in Johannes Stumpf's book on the uniflows, I seem to remember cutoffs more in the range of 20-25%. Can you really get usable power with a 3% cutoff at those pressures? And even with some sort of cam, how do you get under 3% cutoff?

I (very selfishly) hope you'll share your choices in valve design as you build your engine. Are the DD series 53 cylinder liners for 2-stroke operation with a ring of exhaust holes around the middle?

Cheers,
Scott

[barts]

O'Conner engineering built three cylinder uniflow engines for Disney.

Here's some info on those engines: http://kimmelsteam.com/oconnor.html

There are prints there as well; note the engine used piston valves which made them very sensitive to condensation, and they were used in stop and go service - a misfeature.

Roger (seen in photos) has several of these engines, I believe.

I really think poppet valves are the way to go on these engines, particularly since one needs low clearance volumes for efficiency's sake.
The use of mild (200F) superheat should also significantly reduce condensation as well. I'll also really insulate the cylinders.

I'm opting for a two cylinder engine to smooth out the torque rather than a large single, although the latter would be simpler.

- Bart

[barts]

Hello Bart,

Both the engine and boat sound fantastic. I have been noodling around (without much success) with a design for a similarly laid out but smaller engine for my open launch. I am curious about your planned cutoff. Both on the steamer Elpenor and in Johannes Stumpf's book on the uniflows, I seem to remember cutoffs more in the range of 20-25%. Can you really get usable power with a 3% cutoff at those pressures? And even with some sort of cam, how do you get under 3% cutoff?

I (very selfishly) hope you'll share your choices in valve design as you build your engine. Are the DD series 53 cylinder liners for 2-stroke operation with a ring of exhaust holes around the middle?

Cheers,
Scott

The trick is to get useable brake mean effective pressures... I've looked up commercial uniflow engines; these delivered rated power at 50 - 60 PSI BMEP, and were capable of 175% overloads (e.g. w/ more cut-off) w/o major drop in efficiency. This occurs w/ 300 psia input steam at about 5% cut-off (20 expansions); in marine practice 10% cut-off was used for full rated power, and the valve gears often afforded very high maximum cut-offs to make maneuvering easier. %5 cut-off was commonly used as described in Stumpf's book.

What Skinner did was to use two (rather abrupt) cams whose overlap could be adjusted; both were required to be up to open the valves, and by adjusting the phase between the two cams, a wide continuous range of cut-offs were possible. This is one area that I've still got more work to do in terms of what's possible... Stumpf describes near the end of his book running one layshaft at 2x engine speed to allow the cams an easier time lifting the valves; of course, my engine will be a fraction of the sizes he's talking about so this is less necessary.

If it turns out I cannot get below 5%, I'll simply throttle down or reduce boiler pressure when we need to just poke along. We'll see how things work out; I've not seen any small engines built like this so this is an experiment.

Later Skinner engines resorted to compounding as boiler pressures & superheats climbed higher; a small high pressure multi-flow cylinder would be used in conjunction with a uniflow low pressure cylinder, with both cylinders single acting and the solitary piston valve situated directly between them.

Given the relatively moderate steam conditions, I don't think such measures are needed.


Those cylinder liners are indeed for two strokes as you describe:



I have an old one'; they're readily available new for less than $100 ($50 on EBAY).

I will be definitely keeping the forum apprised of any and all progress here.

- Bart

[DetroiTug]

Bart,

Sounds like a great project. As far as oil smells go, that's not much of an issue. The engine room is going to require ample ventilation to maintain comfortable temps and that provides a lot of fresh air.

Regarding the engine, I would hook up with Gary Hadden, I can get you his email address. He's been designing and running small multi-cylinder Uniflows for many years. He uses poppet valves (Briggs & Stratton) and a linear sliding camshaft. The camshaft is machined with opposing lobes that transition between. They provide forward/reverse and infinite cut-off.

These engines run very smooth, but they are a different animal. They like high RPM.

Here are some pics of one of his engines. I have one of these casting sets in my shop.

[87gn@tahoe]

I was wondering when you were going to begin a thread on that Bart. That is a very interesting project.

Unless Roger sold some recently, he has ALL of the 6 O'Conners. A couple complete and running, and the rest in pieces. He used to bring one to Todd Guldenbrein's house for steam ups. Very smooth, but very ugly. I think aesthetics had as much to do with Disney getting rid of them as did the operation difficulties.

I'm sure roger would be happy to take you to the barn so you can pick over them.

Have you talked to Jim Tangeman at all?

Are you going with a 90* crank?

[barts]

I was wondering when you were going to begin a thread on that Bart. That is a very interesting project.

I'm recovering from a wisdom tooth extraction this morning, so this afternoon was spent having fun as an antidote . I decided I wanted to make some progress on the big boat this year. I keep collecting pieces (a 28"x28" prop, USN bronze destroyer wheel, etc) but that's no substitute for real progress. My brother is noodling on the hull design....

Unless Roger sold some recently, he has ALL of the 6 O'Conners. A couple complete and running, and the rest in pieces. He used to bring one to Todd Guldenbrein's house for steam ups. Very smooth, but very ugly. I think aesthetics had as much to do with Disney getting rid of them as did the operation difficulties.

I saw these engines at B & W, and am of the same opinion.... but I'm not at all sure my engine will look at all graceful. I'd settle for stout and workman-like - like some of the steam tug engines I saw in Dordrecht in 2000.

Have you talked to Jim Tangeman at all?

Yes, during meets at B & W. I hope to discuss this at the SACA meet in Sacramento in March. I'll likely bring the Otter for show and tell.

Are you going with a 90* crank?

That's the plan. If I don't make it self-starting on steam, I'd need to rig a bi-directional starter motor - doable, but less than elegant.
There's a post by Rolly on this thread talking about his method for pinching cranks together. http://steamautomobile.com/phorum5214/r ... 0657,20673

- Bart

[barts]

DetroiTug,

I'd definitely be interested in Gary Hadden's email address. This looks like a small steam car engine...

http://opensourceecology.org/wiki/Hadden_Engine

Sure enough...

- Bart

[DetroiTug]

He has a marine base for it also. He has one in a 22' sailboat hull. Sounds like a 4 cyl flat head running.

I'll PM his email address.