Sisson Triple

[Scotty]

Hallo,
a friend of mine has got an old Sisson triple in his launch and we are all a bit surprised about the steam consumption.

the engine is marked: W. Sisson & Co. Ltd - Gloucester - 1906 - #727
size: 4 + 6 + 8 1/2 x 8

It was declared as 25 HP at 300 rpm, seems to be at least 32 HP at 250 rpm (both at appr. 200 psi).

My questions are:
- is there any information about preferred direction of rotation for ahead (might be lefthanded)?
- which HP cutoff did Sisson use on these engines (if they had a standard)?
- could anyone point me in a direction for further searching?

Up to now I have found the Gloucestershire Archives, anybody know another place?

Thank you
Scotty

[fredrosse]

" seems to be at least 32 HP at 250 rpm "

Just wondering, what is the basis for this conclusion??

" any information about preferred direction of rotation for ahead?"

As far as I have ever known, the loading of the crosshead slipper should be optimized with compression on the guide whist going ahead.

[Scotty]

Speed was measured by GPS at exactly 10 knots,
displacement was 5050 kg,
effective length of waterline 11.5 m,
with Dave Gerr's propeller formula (adjusted to higher propeller efficiency)
this gives a required engine power of 32,0 HP (+/- 1 HP).

Unfortunately the crosshead slippers are symmetrical on the Sisson,
so this gives no indication of preferred rotation.

Scotty

[barts]

How many lbs/hour water at 200 psi saturated is the engine using? How many expansions?

- Bart

[Scotty]

At 180 psi and 20 °C superheat the consumption was in the order of 250 to 280 kg/hr (550 - 620 lbs).
The boiler is designed for 200 kg/hr (200 psi, 220 °C) and is limited by the amount of wood you can
put through the furnace, at this test it was appr. 40-45 kg/hr of wood (we use hardwood - beech).

The engine is a triple expansion.

Scotty

[gondolier88]

Scotty,

Please could you post a photo of the engine in question please? Would help greatly to know what sort of Sissons we are talking about.

Thanks,

Greg

[Scotty]

Here are some pictures:







W. Sisson & Co. Ltd - Gloucester - 1906 - #727
size: 4 + 6 + 8 1/2 x 8

Scotty

[barts]

At 20 lbs/hp-hr, you're definitely using a lot of steam for a triple this size. Full size you'd expect about 11-13 lbs/hp-hr; you should be getting 15 or so. PLAN/33000 says to make 32 hp in a cylinder 8.5 x 8 takes a BMEP of 56 psi - about twice what was typical for a full size triple, which was usually rated at ~25 psi for a full load rating.

If I didn't get my numbers wrong, you need to link up - you're going racing.

Data from Kent's Mechanical Engineer's Handbook circa 1939.

- Bart

[DetroiTug]

Beautiful engine.

I think right hand rotation is the norm, reason being when coming into the dock on the port side the stern is pulled to the dock when reversing.

If the engine will support either rotation and you have no preference, left hand props are generally cheaper second hand.

The steam consumption sounds about right, that is a big heavy hull and running at ten knots it's going to consume a lot of fuel and steam to do it. My tug is a wide heavy hull and it burns a lot more wood than a small launch as we have to make a lot steam to run at hull speed.

About to get her out for the year. Annual hydro and few maintenance things, nothing like past springs.

-Ron

[Scotty]

Hallo Ron,
the design was 9 knots, with a reqired power of 24-25 HP.
Speeding and racing was never the intention.
I was very surprised at the 10 knots.

The engine shows a definite tendency to prefer left hand rotation
(much easier starting), and Sisson built around this time (1906) some
engines for the Windermere Saloon Launches where left-hand is the norm -
as far as I know, I could be wrong.

The steam consumption does also not fit with my calculations,
that was the reason to go for 9 knots.

Scotty