Two-cycle engines use few moving parts compared to many parts used for construction of four-cycle engines where sequence is controlled by
valves opening and closing by the action of a rotating cam shaft. The simple two-cycle construction is one reason for their popularity early
1900. Two-cycle engines are dependable and easy to repair. From about 1900 to 1920, many organizations manufactured two cycle marine
engines. By 1950 most small marine engines were outboard style. Now because of environmental concern, almost all small marine engines use
the four stroke cycle. St Lawrence Engine Company manufactured two-cycle marine engines from 1905 to about 1949 at a facility located in
Canada at Brockville, Ontario. Only minor improvements occurred during the period, notably changing to aluminium pistons about 1935.
Typical two cylinder St
marine engine Circa
1935 Bore 3 1/4",
Stroke 3/1/2' x 2
Flywheel is 14"
diameter 6 HP @ 850
Typical single cylinder
St Lawrence two-cycle
marine engine Circa
1949 Bore 3 1/4",
Stroke 3 1/2'" Flywheel
is 12" diameter 3 HP @
The advancement of gas engine use occurred as a result of understanding the advantage of compression prior to ignition. This occurred in
1876 in Germany by Nikolaus Otto. Otto's engine used a four-stroke cycle where combustion occurred once during two engine revolutions. Even
now the four-stroke cycle is referred to as the Otto cycle.
During 1890 a Scottish engineer, Sir Dugald Clerk, introduced an engine where combustion occurred each engine revolution. This is referred to as
the two-stroke cycle. Clerk's engine used a separate chamber for taking in the combustible charge and transferring it to the power cylinder. In
1892, Frederic Caswell Cock, an Englishman, patented the two-cycle method where combustible charge entered the crankcase before transfer
to the combustion chamber via an integral transfer port.
The content in this site is for information purposes only. The author assumes no liability for inaccurate or
incomplete information in this site or contained in any links that are provided solely as a convenience.
Old two stroke marine engines - their construction and operation
BuildingGertrude - Swampscott Dory powered by vintage 3HP 2 cycle engine
Owner built using techniques developed for single handed construction
Buy these and other rebuilt St Lawrence engines- contact goslowboat
Kitchen Rudder, invented 1914 reinvented 2003 to steer and maneuver Gertrudea
goslowboat powered by a vintage 3 HP St Lawrence two-cycle engine. This old two-stroke is
direct connect to propeller. The owner built Kitchen Rudder uses Clam Shell deflectors that provide
superior boat control compared to an ordinary transmission. Be sure to view the video to experience
this amazing 100 year old boat rudder and ancient one lunger.
Gertrude's two cycle engine is directly connected to propeller. This was
typical during the early 1900s. Transmissions were heavy,costly and not
To provide maneuverability Gertrude is fitted with an owner designed/built
Using Kitchen Rudder engine always operates at preset speed, always in
Kitchen's 1914 British Patent #869,051 ( USA patent #1,186,210) described a
clever mechanism consisting of two clamshell like deflectors that encircled a
boat's propeller. These can be opened or closed in unison. When closed, all of
the propeller stream is reversed and then acts in a forward direction causing
the boat to move backwards. Although this reversing capability was the main
objective of the invention, it was soon discovered that a boat fitted with a
Kitchen Rudder can be maneuvered at least equal to a vessel with twin
screws. This unprecedented maneuverability encouraged the British Admiralty
to install Kitchen Rudders on open vessels used for rescue missions where
ability to maneuver was crucial.
Operation is seamless. Engine manipulation or speed change is unnecessary.
Clamshells are manipulated by
a tiller mounted mechanism
Concentric shafts connect to
Coxswain rotates tiller
mounted crank to open and
At same time Coxswain
moves tiller from side to side
for steering and to control
How a Kitchen Rudder works
Kitchen Rudder, invented 1914 in England by John Aulesbrook Kitchen
Two-cycle engine sequence during one revolution
Reversing capability is only one feature of a Kitchen Rudder.
Maneuverability including speed control, direction control, stern thrust etc provided by the device is much better than provided by a
standard transmission. The video at www.goslowboat.com is intended to display this maneuverability.
When viewing the video, focus on all Kitchen Rudder features, clam shell position , tiller manipulation, then how the boat behaves particularly
directional control when clam shells are closed or almost closed and when stern thrust is applied.
As an example at minute 2 in the video, the boat is stationary. If this were a standard transmission propeller would be detached from engine.
Boat would float without control until transmission is engaged. When using Kitchen Rudder engine and propeller remain connected, thus very
subtle moment of tiller and clam shell crank provides instant control of boat position, direction and speed.
Kitchen Rudder Video
Building Gertrude Information at bottom of this page
click white arrow to play video - to pause video click double bars ll - best viewed full screen