PROPELLERS vs HIGH SPEED PADDLE WHEELS
SEA FROG ™ Pty Ltd is researching the efficiency and advantages of using high speed paddle wheels as an alternative to propellers for marine propulsion
HISTORY
In 1848 the British Admiralty connected a propeller driven ship “Rattler” to a paddle wheel driven ship “Alecto” and they pulled against each other. The propeller ship outpulled the paddle wheeler by 5 km / hour and the demise of paddle propulsion began.
In 1954 to 1957 tests were carried out in Scotland to study the effect of “feathering”the blades on paddle wheels (feathering is changing the angle of entry and withdrawal of the blades at the water). After three years full time work only minimum improvements in efficiency were realized. The tests did not include any shaping of the blades, different sized blades, only one immersion depth of the blades and the equipment was limited to 100 revolutions per minute and variations in horsepower input at different revolutions could not be read.
We believe the time is right to carry out further testing on paddle wheel propulsion with the aim of rebirthing this propulsion system as high speed Sea Wheels ™
DISCUSSION FORUM No 1
We have built a 1:10 scale model of a 10 metre long cruiser and fitted it with various sized paddle wheels to compare high speed paddle wheel propulsion to propeller propulsion.
The paddlewheels are powered by a 14.4 volt battery drawing from 0 to 10 amps, with the wheels rotating at 50 to 500 rpm.
We have decided to initially graph amp (A) draw down against bollard pull forcce in newtons (N) and our best result to date is 7.5 N bollard pull force @ 2.0 A and 14.4 Volts (V) at a rotational speed of 80 revolutions per minute (rpm). The bollard pull force is increased to 9.0N at 4.0 A at 125 rpm and 11.0 N @ 6.0 A at 150 rpm
As a basis for comparison to propellers we have searched the Internet for propeller bollard pull test results, to find values vary from 15 to 30 pounds per horsepower (lbs / HP) and this range covers all boat sizes from small electrically operated models through to outboard motors on dinghys and large cruisers through to inboard motors on massive tugs and ships of many thousands of horsepower.
Our test result of 7.5 N @ 2.0 A is equivalent to 44 lbs/HP and at 9.0 N @ 4.0 A is 28 lbs/HP and 11.0N @ 6.0 A is 21lbs / HP
Our testing so far has raised the following questions.
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Is bollard pull a realistic testing means to compare the propulsive efficiency of
propellers vs paddle wheels ?
We figure it this way:
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A well designed tug boat (all sizes) produces a bollard pull of 25 – 30 lbs / HP
using low propeller rpm and a large propeller i.e. similar to low / 1st gear in a car
A well designed speed boat (all sizes) also produces a bollard pull of 25 – 30 lbs
/ HP using higher propeller rpm and smaller propeller i.e. similar to high / 3rd or
4th gear in a car.
Obviously in the above example of tug boats and speed boats they use
different gearing ratios and rpm to produce different amounts of torque and
speed and they use different hull shapes and boat weights, however the
common start point for the design of power (tug boat) and speed (speed boat)
is propulsive efficiency of lbs / HP, which can be determined by bollard pull.
Therefore we have assummed a boat fitted with a propulsion system rated at 44
lbs / HP will produce higher speeds and fuel efficiency than a boat fitted with a
30 lbs / HP system (both boats with the same hull shape and weight and the
same motor)
1.2 Is it likely that the 44 lbs / HP propulsive efficiency of our 7.5N, 2.0A, 14.4V test
will remain constant if the boat size, paddle wheel dimensions and power input
is scaled up appropriately, to full sized dinghys, cruisers and container ships ?
DISCUSSION FORUM No 2
In our research on the comparison of propellers vs high speed paddle wheels we have found many other advantages in addition to propulsive efficiency. They are:-
2.1 One paddle wheel at the rear of the boat could be used to eliminate the need
for a trailer. Two road wheels, attached one at each end of the blades could be
raised and lowered for road or water engagement. A separate single jockey
wheel at the front for steering and weight support during launching and road
travel may be needed depending on boat weight distribution.
2.2 If the wheels in 2.1 above were powered and geared the boat would be
amphibious and able to launch and land without the need of boat ramps, jetties
and dinghy's.
2.3 Being able to land between ports in an approaching storm improves safety.
2.4 Accessability to shallow waters by riding over the bottom on the wheels
2.5 Damage to sea life with much slower, less sharp blades will be far less than
using propellers.
2.6 Weed entanglement and eco damage will be less.
We look forward to discussion on the above. We would also particularly like to hear from
(a) Boat builders using light weight materials
(b) Marine propulsion test facilities
(c) Naval architects, hydrodynamic engineers and boat designers
(d) Model boat makers
(e) Investors seeking world wide returns
Garry Hart
Managing Director
Sea Frog Pty Ltd
P (07) 3356 9065
E This e-mail address is being protected from spambots. You need JavaScript enabled to view it
