The Steamboating Forum

Hello steamboaters,

My name is Kees Hellinga, 21 years old and I live in the Netherlands. In my spare time I’m volunteer on the steampumpingstation “Hertog Reijnout” (1882) in Nijkerk.

Together with a friend of my, we’re building a steamlaunch c.q. little steamtug called ‘Johannes,’ named after the oldest volunteer of the steampumpingstation.

We bought a secondhand steel hull, a ‘Lelievlet’ of 5,6 metres long and 1,8 metres wide. Last november, I bought a Stuart Turner 6A from Graham Towle (steamlaunch Sarah Jane). That engine is at this moment in parts, to paint it in her new colours blue/red, fitting gaskets etcetera. Also we have to make a enginedriven feedpump, lubricationsystem, insulation and a flywheel with flange to drive the shaft. The plan is to make the system as a puffer with a feedwaterheater.

I have two questions and I hope someone can answer.

Does some owners of a Stuart 6A know the practical steam consumption of the engine in a specific situation to design a steamboiler, feedpump and steampipes. When I calculate the theoretical steam consumtion (all factors included but without condensation loss in the engine) it’s much lower as what the Stuart catalog says.

Two weeks ago ik bought for a “nice price” an old, wooden sailboat hull with in that a Semple engine set. It’s the Semple VFT40 boiler with all the fittings and a Semple V 3+5x4 compound engine. The hull was bad, the interior too, but I thought the engine was suitable. The boiler looks horrible because there was a lot of rust (a half bucket) at the tubeplate and in the firebox. There are no certificates with the boiler and I think it has never had any maintenance. Now the boiler stands without insulation and fittings and I have a few times boiled with soda. Most rust came out of the smokebox and chimney, they are very bad. I think, also because the old owner used the boiler at his full working pressure, maybe the boiler is good enough to use in us own steamboat. To get boilercertificates I need drawings and other paperwork specific for the Semple VFT40 boiler before the first inspection. If someone have the same boiler, could you send me some information about it please?

Thanks in advance,

Best regards, Kees Hellinga

"When I calculate the theoretical steam consumtion (all factors included but without condensation loss in the engine) it’s much lower as what the Stuart catalog says. "

Steam engines have a great efficiency loss due to condensation of the steam admitted into the working cylinder. For small engines the actual steam consumption is about two times the calculated amount of steam theoretically required during steam admission into a cylinder. The 2x number can vary by wide margins depending on several variables.

Factors influencing initial condensation in the engine cylinder include:
a. Single valve (steam admission and exhaust thru the same passages) vs. multi-valve engines, using separate ports for admission and exhaust. Multi-valve is better.
b. Cylinder size, bigger cylinders are better, less heat transfer surface for condensation per volume of steam admitted.
c. Engine RPM, higher speed is better, less time of heat transfer for condensation.
d. Superheated Steam Admission is better, lower heat transfer coefficient for condensation.
e. Counterflow engine vs. uniflow engine, uniflow has better temperature distribution to reduce condensation in the cylinder.
f. Temperature range between admission steam and exhaust steam within a cylinder. Smaller temperature range is better, lower heat transfer due to lower temperature differentials. Temperature differentials fundamentally drive heat transfer. This is the advantage provided by compound engines.

Hi Kees,

Have a look at my post in the section Members Websites and Boats / S/S Martha - and see photos in the SBA boat register.

I have done different calculations and looked at data from other boats I have travelled, as well as got information from Funnel magazine articles from the last 17 years. I all boils down to the specifikations below for my project currently being build:

Hull:
LOA: 18' 0", Beam: 5' 4", Draft: 2' 0", Displacement: 1800 lbs.

Boiler:
Fuel: Coal. Max. pressure: 130 psi. Heating surface (wetted): 18 sqft. Steam output: 90 lbs/hr.
Main dimensions: 20" dia X 31" high steel barrel. 68 X 0.8" dia steel tubes.

Engine:
Compound of own construction. Cyl. dimensions: 2.5" + 4" X 3" (Stuart 6A cylinder casting)
Piston valve on HP, slide valve on LP. SLRG valve gear.
Vacuum pump directly crosshead driven. Feed water pump driven from crankshaft by a cogwheel gearing 1:2. The engine design estimates 2,6 IHP / 2,1 BHP @ 300 RPM and 120 PSI steam pressure. Mechanical efficiency estimated to 80%. Estimatet steam consumption is 35 kg/hr at 300 RPM

Propeller:
Bronze, 3 blades, Right Hand, 19.5" X 31", DAR: 0,35
Shaft: 1,25" Stainless Steel

Calc's shows a hull speed of around 5 knots at 300 RPM corresponding to a power requirement of 2,1 BHP. At 4 knots hull speed and 230 RPM power consumption is 1 BHP.

Thanks for both posts.

The information you give, mister Rosse, I can only agree. My engine is a compound with on the high and low pressure cylinder a slidevalve. The engine works with expansion and compounding, it's some better as a single, but it could be much better for efficiency, haha!

Maybe someone can tell what's the steamconsumption of a Stuart 6A in practice?

Mister Hansen, I understand your specifications. When I'm sure about the boiler, I can post the specifications of my own boatproject. But, one question. Your engine has a vacuümpump, so it has a vacuümcondenser. A condensing compound steam engine has often a bigger cylinder ratio of 1:1.75 - 1:2, depending on the working pressure. Is it effective for efficiency to drive the Stuart, who has a ratio of 1:1,6 (a ratio more suitable for a puffer), produce the engine more power as without the condensor and vacuümpump?

Kees Hellinga

Hi Kees,

As I am still building on the engine, I haven't had the opportunity to test it yet. But I'm pretty sure that the engine will produce more power when vacuum is applied to the LP cylinder. With a 80% vacuum, - 0,8 bar, that will be about 10 procent of the total pressure drop over the engine, with a steam supply pressure of 8,5 bar. The mechanical work delivered by the engine to be consumed by the vacuum pump is mainly associated with the diff. pressure over the piston. A small amount of work will be associated with friction and lifting the condensate. You must know that the "vacuum" pump is not creating any vacuum, but serves as a "lock" between the condenser and the atmosphere - as well as a pump to lift the water out of the condenser and to the hotwell. I will guess that using vacuum will add some 8-10% to the total power of the engine. I will test it and let you know - but you will have to wait a few years on the result.

But, for all practical reasons there is no need for running vacuum-condensing with an engine of that size. For bigger plants it is a case of fuel economy and boiler size, but if you built the plant to be puffing the boiler will procuce much more steam and you will use ½ a kg of coal extra per hour. I am going to operate my boat in salt water, so I need the condenser anyway and I think the vacuum pump is a nice addition to look at.

Best regards Lars