Upscaling a Hasbrouck engine

[NorwegianOlav]

Hello

First time posting, new to this forum and to steam boats all in all.

I am in the process of making my first own steam boat. Sadly, I do not know any other in Norway with the same interest. Hopefully someone here can help me out a bit here and there..

Lots of things are undecided regarding the boat I am building. 18 – 20 ft. Maybe.
My biggest question now revolves around the engine. My long time plan is to maybe build an Stuart 6A engine.

But for now I am thinking of building Ray Hasbroucks engine # 10. Single cylinder vertical, 2 ¼ inch bore and 3 inch stroke.
However, I want to upscale the #10 a bit. And here is were I need help.

The boiler I have is made by the Swedish company Mora Marineteknikk and is a B2 VFT boiler with 25 KW. It produces around 32 kg steam per hour and has 42 tubes I think.
Mora Marineteknikk also produces steam ready engines. I however want to make my own engine. ( Hasbroucks). The engine Mora recommends for the boiler I have, is a single cylinder 90 mm Bore and 82 mm stroke. 5 HP (Or a compound variant of this).

How much should I upscale the Hasbroucks #10 engine to better match the recommended engine by Mora? I don’t want to completely match the size, just approach it. The Hasbroucks #10 is 2 HP (some say 3 HP)
I have never scaled a steam engine before and are unsure if all pars scale linear. Is it okay to scale the whole thing x% since its a small engine? Or should something be compensated for regarding physics.

I work with 3D application on a daily basis, and are planning on making the whole thing in 3D CAD software before fabricating the engine. Ill figure out all fasteners and those things myself. What I need is a scaling factor for the cylinder.

If anyone have any input on this, thanks!

Olav

[barts]

Power will scale linearly with displacement, thus it will vary as the cube of the linear dimension.

So if you double all the dimension, the engine will produce 8 times as much power.

In this particular case, you have a 2 hp engine and you want 5 hp, a factor of 2.5. So take the cube root of 2.5, and scale the linear dimensions by that.

The cube root of 2.5 is about 1.36. Scaling the Hasbrouk engine by 1.36 and rounding a bit, a simple engine of 3" bore and 4" stroke would produce 5 hp. This is exactly the dimensions of the 5 hp Semple engine, built many years ago.

Hope this helps.

- Bart

[cyberbadger]

a simple engine of 3" bore and 4" stroke would produce 5 hp. This is exactly the dimensions of the 5 hp Semple engine, built many years ago.

Somehow I don't know how that calculation can come out to 5.

I have an engine of exactly 3" bore x 4" stroke, two identical cylinders and that is 6HP. (Both sold as 6HP/6.25HP and the PLAN comes out to the same result as you can see below)

The unit of power is a "horsepower" and is defined as the amount of power necessary to raise 33,000 lbs. one foot in one minute. The horsepower of an engine is equal to the total pressure on the piston multiplied by the number of feet it travels per minute and divided by 33,000.

The total pressure on the piston is equal to the area in square inches multiplied by the pressure per square inch, and this pressure is not constant but varies, being nearest boiler pressure during the early part of the stroke and decreasing after the point of cut-off is reached, as the steam expands to fill the space back of the piston, until the end of the stroke.

This pressure can be measured only by means of the steam engine indicator but we can assume a value which approximates the correct one. This we will take to be 50% of the boiler pressure. If we have a boiler pressure of 130 lbs., our average pressure per square inch, or "mean effective pressure," (MEP) as it is called, will be 50% of 130 lbs., or 65 lbs. This multiplied by the area of the piston will give the total average pressure on the piston in pounds. The area of a circle is equal to its diameter multiplied by itself and the product by .7854.

The travel of the piston is equal to twice the stroke, there being two strokes for each revolution, multiplied by the number of revolutions per minute. As the length of the stroke is usually given in inches this product must be divided by 12 to reduce the result to feet per minute.

The basic formula is PLAN/33000 which gives the theoretical horsepower, ignoring friction losses.

Where:
P=Mean Effective Pressure in Cylinder (MEP) (is equal to boiler pressure psi/2)
L=Length of Stroke in FEET (add times 2 for Double acting engine)
A=Area of Piston in Inches
N=Revolutions per minute

Here is an actual example of a PLAN calculation of a 2 cylinder double acting engine (1902 Toledo)
RPM = 220
200 PSI Boiler Pressure
3" Bore
4" Stroke

2 * 4 * 220 / 12 = 146.666 (travel of piston in feet per minute.) (2 is for a double acting engine)
3 x 3 x 0.7854 = 7.0686 (area of piston in square inches.)
7.0686 x 100 = 706.86 (total pounds pressure on piston) (MEP is 1/2 boiler pressure)
P*L*A*N/33000 = 706.86*146.66/33000 = 3.14HP

3.14 * 2 cylinders = 6.28HP

-CB

* Quote from this thread on smokstak: https://www.smokstak.com/forum/threads/ ... ion.72483/

P.S. In regards to the original poster's question: If somebody asked me how many HP half of my engine was I would say around 3HP. You can play with the inputs to the PLAN equation and alter the result - but unless the inputs are plausible, you will never see that HP.

You could try to increase the RPM for example, but depending on the size of the propeller and any gearing you might have in between, a large propeller (18"-21" diameter) will limit your max rpm. The faster I spin my prop, the bigger the load on the engine. I am not able to run my engine as high as 400rpm, so putting 400rpm into PLAN will yield an implausible result.

There are other schools of thought on this - there are other steamboaters out there who use smaller diameter modern style of propeller at higher steam engine rpm.

You can definitely use PLAN to help you design your engine.

More important than the HP I would recommend considering a decent reversing valve gear. I really don't recommend a slip eccentric reversing gear. The idea behind this is after the engine is warmed up, it should be able to respond quickly to a change at any engine angle. I find my two cylinder simple double acting Toledo to be very response with the Stephenson valve gear and 90 degree out of phase pistons. Remember you'll be in a boat and may need to maneuver. Using your hand to reverse the flywheel on a slip eccentric can easily mash and abraid that hand, with enough HP it may be a more severe injury.

[dampfspieler]

Hello Olav,

before you start working with the engine, please first determine the main dimensions of the planned boat, because its movement is the main purpose of the engine.
When that is done, determine the amount of power required to reach the boat's hull speed. As a rule of thumb you can assume 2.2 kW / 1,000 kg water displacement.

The thoughts are somewhat obsolete given the fact that you already have the boiler. It must be able to supply the engine with sufficient steam at full power and I see a problem there.
In my experience, a STUART 6 that is operated according to the specifications given by STUARTMODELS requires 60 kg of steam/hour. Your boiler would then be too small for the engine.

To broaden your knowledge of a HASBROUK #10 you can check out this thread where I show my modifications to the design to come up with a smooth running and low steam consuming engine.

Best wishes
Dietrich

[barts]

a simple engine of 3" bore and 4" stroke would produce 5 hp. This is exactly the dimensions of the 5 hp Semple engine, built many years ago.

Somehow I don't know how that calculation can come out to 5.

If you disagree with Ray's rating of the engine, say so. My scaling calculations are correct for his rating as given.

More important than the HP I would recommend considering a decent reversing valve gear. I really don't recommend a slip eccentric reversing gear. The idea behind this is after the engine is warmed up, it should be able to respond quickly to a change at any engine angle. I find my two cylinder simple double acting Toledo to be very response with the Stephenson valve gear and 90 degree out of phase pistons. Remember you'll be in a boat and may need to maneuver. Using your hand to reverse the flywheel on a slip eccentric can easily mash and abraid that hand, with enough HP it may be a more severe injury.

I used a slip eccentric reversing gear for many years on a 2 x 2.5" single cylinder w/o any injuries. Note that a single cylinder engine w/ a Stephenson link will get stuck on TDC and require manual reversing; simply throwing the link won't always work.

The safe way to reverse with a slip eccentric is to shut the throttle, reverse the engine rotation by hand and just crack the throttle. If you need to, rotate the engine slightly in the desired direction of rotation. Given the need for manual reversing, of course avoid creating a situation w/ a pinch point on the flywheel.

Cyberbadger, have you ever steamed a single cylinder boat w/ a slip eccentric?

- Bart

[cyberbadger]

Cyberbadger, have you ever steamed a single cylinder boat w/ a slip eccentric?

- Bart

I have not.

I have jammed my hand enough to draw blood testing a 3HP single cylinder slip eccentric engine. That was enough for my testing that that engine wasn't suitable for my purposes. (It's a great little engine for stationary unidirectional work like with a DC generator.)

I prefer my engine to be able to change direction without having to fully stop the engine regardless of the current engine angle. The only advantage I can think of for a slip eccentric engine is that it is easier to machine. Why wouldn't you want the most responsive you can get? This directly contributes to maneuverability.

-CB

[cyberbadger]

Olav,

Here are calculations based on the B2 boiler you have.

This is assuming the B2 boiler has the same MAWP as the B2 35KW, 9bar.

B2 MAWP = 9bar = 130.5psi

MEP = MAWP/2
MEP = 4.5bar or 65.25psi

15.7kg/hr steam = 1 horsepower
B2 25KW horsepower = 2.0382 HP =~2HP

Hasbrouck #10
2.25" bore x 3" stroke
Assume 250rpm

2 * 3 * 250 / 12 = 125 (travel of piston in feet per minute.) (2 is for a double acting engine)
2.25 x 2.25 x 0.7854 = 3.9760 (area of piston in square inches.)
3.9760 x 65.25 = 259.4340 (total pounds pressure on piston) (MEP is 1/2 boiler pressure)
P*L*A*N/33000 = 125*259.447/33000 = 0.98275 HP ~= 1HP

If you could marry two Hasbrouck #10's together your boiler HP and your engine HP will be almost the same, 2HP.

For reference I have ~10HP Boiler HP based on kg steam/hr at 200psi(14bar) and a 6HP engine.

I would definitely look at Dietrich's work for inspiration and ideas.

-CB

[TahoeSteam]

Semple made the v-compounds with slip-eccentric reverse and the ones I've seen and run reversed well. The key is on the compounds they installed a reversing lever. Much safer. A friend of Bart's and mine has converted at least one Semple 5hp that I know of.... Another factor is the conventional d-slide valves that tend to drag or even try to seize up when full boiler pressure is shoving then against the valve face.

Balanced slide valves or piston valves are great for reversing at any speed and nearly any pressure.

Our Doty compound (5+10x6") and Claparde compound (6+11x7") both have Stevenson link and conventional slide valves. Both have evidence of being damaged in the past from attempts to reverse with the throttle open, at full pressure. The Doty's 3' long reversing lever is bent ever so slightly, and the Claparede had at least one valve stem break and the reversing lever bent in it's past.

[fredrosse]

Your proposed launch can get by with about 2 horsepower, and 5 horsepower is a bit overpowered, but still OK

From the FAQ Section of this Forum;

TYPICAL STEAM LAUNCH HULLS - Propulsion Power Required.

Hull design can (and has) occupied entire large textbooks, but for typical Steam Launch practice, some simple relationships are useful for rough quantification of propulsion requirements.

The basic rules of thumb state that a well streamlined displacement type hull will have a maximum hull speed as a function of the waterline length:

Maximum Hull Speed (Knots) = 1.34 x Square root of Waterline Length (feet)

Some slender hulls can do slightly better, and a more box-like hull will do worse, but this approximation is reasonable.

To drive the boat at “Hull Speed”, requires 1.25 to 1.75 horsepower per ton (2240 pounds) of displacement. In general this relationship requires a propeller of good efficiency, which translates to a large diameter slow turning propeller. Launch propellers should have a diameter equal to 10% of the boat’s waterline length, and have a pitch equal to, or slightly larger than the diameter.

The relationship between speed and power, up to the maximum hull speed, is a cubic function, which means low power does not hurt boat speed as much as one might think. An example here illustrates this phenomenon:

Steam Launch, 19 feet long, waterline length = 16 feet, Displacement = 1 ton with all supplies and passengers aboard. Hull speed = 5.3 knots, Horsepower required = 1.75 HP.

Speed, 5.3 Knots HP = 1.75
Speed, 5.0 Knots HP = 1.47
Speed, 4.5 Knots HP = 1.07
Speed, 4.0 Knots HP = 0.75

Conversely, driving the hull above maximum “hull speed” becomes a fifth power function, and is not a practical option:

Speed, 6.0 Knots HP = 3.25
Speed, 7.0 Knots HP = 7.03

These approximations are for pure displacement hulls, which covers the great majority of steam launch hulls. Other types of faster pleasure boats have entirely different functions.

[fredrosse]

The Hasbrouck #10 can be expected to give about 1 horsepower with the parameters shown below The "2HP" published would need about double the steam BMEP, which is not reasonable, or about double the speed (RPM), which is also a little too fast for this engine.

To "Scale Up" the Hasbrouck # 10 to about 2.5x its nominal power, the information provided in Barts first reply is correct, and direct scaling, with the same input parameters of pressures and speed (RPM). This scaling will also result in engine structural parts as well as bearing load pressures increasing as the square of the new engine scaling factor, as well as the bearing areas and structural parts increasing in area also as a squared function, so the bearing loads and part stresses all remain the same as the original engine, with the same input parameters of pressures and speed (RPM).

From the FAQ Section of this Forum;

TYPICAL STEAM LAUNCH ENGINES - OUTPUT POWER of the Engine

Output Horsepower, "Brake Horsepower", BHP = P L A N / 33,000

P is defined as the Brake Mean Effective Pressure (BMEP), in Pounds per Square Inch.

This number could theoretically be as high as the main steam pressure minus the engine exhaust pressure, but using this quantity, while giving the maximum theoretical power of the engine, would give a very uneconomical engine.

Typically for small launches the BMEP is about 40% to 50% of the main steam pressure, the lower fraction tending to the more efficient engines.

L is the length of steam piston stroke, in Feet

A is the Area of the cylinder bore, in Square Inches, equal to (3.14 / 4) x Cylinder Bore Squared.

N is the number of power strokes per minute, generally equal to the engine RPM x Number of Cylinders x 1 (for a single acting engine) or 2 (double acting engine)

For example, taking a 2.25 x 3 Double Acting Single Cylinder Engine, with 130 PSIG Steam (9 BARG), run at 250 RPM, with reasonable economy:

P = BMEP = 9 BARG x 50% x 14.503 PSI/BAR = 65.26 PSI BMEP (Atmospheric Exhaust Pressure Assumed)
L = Stroke in Feet = 3 inches x 1 ft/12 in = 0.25 Feet
A = Bore Area = (3.14 / 4) x 2.25 x 2.25 = 3.98 square inches
N = Power Strokes per Minute = 250 x 2 = 500 Power strokes per minute

BHP = PLAN/33,000 = 0.98 Horsepower