Uniflow Engines

[Cyruscosmo]

Hey All

I have been reading up on steam engines trying to work out what size I need/want for my SL. The hull specs say 15-20 IHP steam/25 hp diesel. I have been looking through the Steamboat Register and am finding that the information is clear as mud.

Most of the hulls with around 28 feet on the water line have engines that are smaller than I would assume for 15-20IHP. Paul at Selway Fisher said that a 3+3x3 would be a good size engine but nowhere do I find a 3+3x3 engine rated at the 15-25 IHP suggested.

I have a background in muscle cars and trucks so my thinking tends to be along those lines for HP ratings and what a given HP number means in what a truck can do.

I realize that a smaller ingine in a boat means I just go slower and cruising in an SL is the point but in the event I do have to outrun the rain or get out of the way of a tanker I would like to have an engine that can push her to hull speed at least.

So after much reading and poking about I will be going with some form of Uniflow arrangement with a mono tube boiler. And if Bart reads this I know I was thinking of a Lamont type boiler but the more info I get on mono tubes the more I like the idea. Lopez Mike might say I should go simple and enjoy the ride but I have never found a ride I could enjoy unless I was poking around under the hood first.

So my main question is what do I need engine/boiler wise to get the 15-20 IHP to push this hull?

Cyruscosmo

[fredrosse]

Have you looked in the FAQ section for hull power requirements, determining engine power capability, steam consumption, and boiler sizing? Anything more than 2 horsepower per ton of displacement is out of the reasonable realm for typical launches. Engine sizing statements for IC engines are typically far above actual requirements, and much of the power is wasted with a small inefficient propellers. Look at fast launches on Windemere, and see what a good design can bring with low horsepower.

15 to 25 horsepower or more would best be met with the engine developed for the Whitecliffs Solar Power Project, this machine is a 3 cylinder single acting uniflow engine. I am currently building a 15 horsepower steam plant for a fast launch, also with a flash boiler, oil fired.

[Cyruscosmo]

Hey Fred

Yes I have read through the FAQs and spent a couple months between work and building my shop reading all the specs of any SL I could find that was close to mine and am still a bit confused. When they did list the IHP number for a particular steam plant the numbers were not consistant. Most being listed at around 6 to 9 IHP even in some cases were the steam engines were the same bore and stroke.

Paul at Selway Fisher wrote in an email to me quote
"For a 30 footer you would be looking at aroound 15-20 IHP. Annabelle has
the following steam plant - Engine: 2005, Roger Mallinson, Model: Roger
Mallinson, Twin, 3" + 3" x 3" @ 12IHP
Boiler: 2003, TRS Boiler Makers, Locomotive type"

Do these boats just typically run under powered?

I am currently building a 15 horsepower steam plant for a fast launch, also with a flash boiler, oil fired.

I am very much interested in your project. Do you have the particulars listed somewhere already? I would like to take a look if I may.

Cyruscosmo

[Mike Rometer]

It should be remembered that when making IHP calculations people seldom agree on the % of boiler pressure they call 'Mean', so two calculations from different places for engines of the same bore and stroke can be different. The other main variables of course are RPM and full boiler pressure.

[Cyruscosmo]

Hey Mike

Ok so making the assumption that these ratings are all based on a standard is a mistake. I kinda figured something like that was going on because the more I read the less I understood.

So the 3+3x3 that Paul told me about could very well put out 25 IHP if I were to push it over the edge with say 1000 PSI steam. Of coarse the engine would be screaming and in danger of becoming an angry grenade. Yes that was an exaggeration. I was thinking more like a few hundred pounds monotube ish...

Is there a chart somewhere that has some general comparisons of displacement plus stroke plus steam pressure equals around X IHP at whatever RPM?

What I would really like to end up with is an engine that is a bit on the large side so for most of its life it would lope right along peacefully and quiet. And when the situation was grim we could get the hell outta dodge if needed. "So to speak"

There are some places on the Sound that can get pretty interesting when the tide is coming in or going out.

Maybe the best question I could ask of you experienced steamers out there would be: If you had a hull that was 30' LOA 28' LOW, Schooner bow, Counter stern, 6'10" beam, 2' draft, displacement 4410lbs. What engine, boiler, prop pitch/dia combination would you use and why?

Cyruscosmo

[fredrosse]

"Maybe the best question I could ask of you experienced steamers out there would be: If you had a hull that was 30' LOA 28' LOW, Schooner bow, Counter stern, 6'10" beam, 2' draft, displacement 4410lbs. What engine, boiler, prop pitch/dia combination would you use and why?"

An approximation from the FAQ section of this forum:

LWL = 28 feet, so nominal hull speed is 1.34 X LWL^0.5 = 7 knots, use this as the design basis.

Displacement 4410 Pounds, say 2 tons, to me this seems like a low displacement but can be? Allowing 2 horsepower per ton = 4 horsepower required to make hull speed.

Your listed displacement is so low that I think the 4410 number is for kilograms, that would be 4.3 tons displacement for a 30 foot boat. Please check this. I am assuming 4.3 tons, and at 7 knots the power requirement would be about 7 to 10 horsepower as the design basis.

Decent propulsion efficiency requires a large, slow turning propeller. For this launch I am assuming 450 RPM engine speed, and at 25% slip you need 25 inches propeller pitch. A common thumb-rule is that steam props should have P/D (Pitch to Diameter) ratio of one or larger, so that equates to a 24 inch diameter prop, with 25 inch pitch. Three blade, and right handed of course!

If you cannot fit this propeller diameter, then a smaller diameter might be used, with four blades, retaining the 25 inch pitch for 450 RPM.

Another workable option might be 500 RPM with a 20 x 22 prop, I mention this because I happen to have a new 20 x 22 RH in my living room, military surplus.

OK, now for an engine of about 7 to 10 horsepower, 450 to 500 RPM. I have revised the FAQ section on engine power, which shows the 3 x 3 twin only puts out about 6 horsepower, a bit too small. For a conventional and popular engine, perhaps the Tiny Power 3 x 4 in twin cylinder configuration. Also note the 15 horsepower engine described there.

I would recommend a 150 PSIG main steam pressure, with cruising at 125 PSIG. It is usually not a good idea to think you will be able to operate right at the maximum steam pressure while cruising, so some margin is prudent. A double acting twin engine, 3 inch bore x 4 inch stroke will work ok here, at 450 to 500 RPM, producing 7 to 10 horsepower depending on cutoff. Note, from the Tiny Power Website, they describe the M Twin engine (3 x 4 twin cylinder double acting simple engine) as follows:

“A twin version of the "M" engine, rated at about 10 h.p. This engine should do a good job in boats from 23' to 30' with a 24" propellor.” OK, so they spell propeller incorrectly, but their conclusion is almost the same as the FAQ evaluation gives!

From the FAQ engine steam consumption section, about 330 PPH (Pounds Per Hour) steam flow is needed at 10 horsepower output. At 7 HP about 240 PPH. So lets assume 300 PPH for a design basis.

Again from the FAQ boiler sizing section, with a watertube boiler you need 50 square feet of heat transfer surface area to generate 300 PPH steam flow. That sizes the basic coil outside surface area.

[racerfrank]

It should be remembered that when making IHP calculations people seldom agree on the % of boiler pressure they call 'Mean', so two calculations from different places for engines of the same bore and stroke can be different. The other main variables of course are RPM and full boiler pressure.

Is it possible to get an accurate psi reading at the valve chest? I would assume that the pressure fluctuates quickly as to make a gauge needle "flutter".

Frank

[Mike Rometer]

It should be remembered that when making IHP calculations people seldom agree on the % of boiler pressure they call 'Mean', so two calculations from different places for engines of the same bore and stroke can be different. The other main variables of course are RPM and full boiler pressure.

Is it possible to get an accurate psi reading at the valve chest? I would assume that the pressure fluctuates quickly as to make a gauge needle "flutter".

Frank

Any I've seen with a gauge fitted certainly do . . . . . wildly!

I think that's where the 'mean' bit comes in again. Top and bottom readings, and split the difference.

To be fair, doing that on a marine should give a better result as the load should be fairly constant, which it never is on a locomotive, road or rail.

[Cyruscosmo]

Thank you Fred

I really appreciate you sharing your experience and knowledge. I have a few more dots connected now and feel I can go ahead with finalizing some build numbers and start collecting parts for an engine and boiler.

I have about 700# of iron ready for the furnace, which should be more than enough for engine parts. The 3D printer is ready to go for some weekend lost PLA casting.

Yes the displacement is listed as 4410#/2000kg but the plans are for a 26' LOA, which can also have the moulds spaced out up to 36' x 8' and as a result the displacement number is not accurate. 30' LOA is what I am shooting for as that is about all the room I have in the shop. I will finalize the length/beam when I figure out what engine and boiler combo I will use. Then I will know better what kid of legroom I will have.

Another workable option might be 500 RPM with a 20 x 22 prop, I mention this because I happen to have a new 20 x 22 RH in my living room, military surplus.

So about the Prop you have in the living room. Is that something you are looking for a new home for? Paul said a 20" prop would fit if I dropped the skeg a bit.

Fred, do those SQF specs apply to a monotube boiler as well? We have what amounts to mono tube heating units where I work and there have been a few coil failures at 2200PSI. The damage is very minimal compared to the pictures I have seen of water tube boiler failures. Usually we pop a burst disk at 3500PSI, and I can trace the failure back to a stuck flow switch. Plus it is something I know how to build use and tune. 125PSIG should be easy compared to 2200#, 4.5 GPM at around 300 degrees.

Nothin removes graffiti from a rose granite wall like heat and pressure!

[fredrosse]

"Yes the displacement is listed as 4410#/2000kg but the plans are for a 26' LOA" Note when scaling a hull, the displacement changes as the cube of the scaling factor, so 30/26 = 1.154, 1.154^3 = 1.536 4410 x 1.536 = 6775 pounds, plus we all tend to gain some weight as time moves forward.

"So about the Prop you have in the living room. Is that something you are looking for a new home for? Paul said a 20" prop would fit if I dropped the skeg a bit. " I would be willing to part with it for a steamer. I also have a new 36 x 24, ex-presidential yacht spare prop (Jimmy Carter Days), but Iunderstand that has some collector's value.

"do those SQF specs apply to a monotube boiler as well?" Yes, unless the tubing is an unusual size or the design varies from the normal practice significantly.

"We have what amounts to mono tube heating units" Perhaps we can make a trade deal, what are the details of the coils you are mentioning?

"125PSIG should be easy compared to 2200#, 4.5 GPM at around 300 degrees." Always shopping for steam rated equipment, 125 and 150 PSI rated valves are common, 200, 250, 300 etc is relatively rare. This makes for a practical consideration of 150 PSI use on the launch, and is not going to scare away the steam meet organizers. I work all day long with steam plants running at 2500 to 3500 PSI, but 600 PSI is about as high as I would be willing to use on a launch.