At planing speeds approximately 90% of the weight of a Dynaplane boat is carried by the
cambered region of the forebody, which is near the center of gravity. The remainder of the
weight is carried by the adjustable Vee hydrofoil at the stern. (The location of the CG is,
typically, near the mid-length point of the hull.) The adjustable hydrofoil at the stern makes it
possible to trim the boat to the optimum angle for different speeds and loads, and also to
adapt advantageously to various water-surface conditions. When running in relatively smooth
water, for example, the boat can be trimmed to the angle giving minimum drag; when running in
a head sea the trim angle can be lowered to reduce the impact accelerations; and when
running in a following sea the trim angle can be increased to avoid burying the bow in the
backs of the waves.
The trim-control feature is important in connection with the vital factor of marketing. The
famous American management consultant, Peter Drucker, explains in Reference 1 that the
most important attribute a product can have for marketing success is that it will give the owner
a feeling of satisfaction when using it. The Dynaplane design provides a gratifying new
dimension to the experience of operating a motorboat. The feature of being able to adjust the
running trim angle to the optimum for different speeds and different payloads (as well as for
different water-surface conditions) is outstanding fun! This is in marked contrast to the case
for conventional planing boats, even if they are equipped with adjustable transom flaps. The
flaps in that case are only helpful for getting over the low-speed hump. At high speeds
conventional planing motorboats tend to run at a low, and inefficient, trim angle, and activation
of transom flaps has the effect of reducing the running trim angle even further, and making the
craft even more inefficient. Therefore, at high speeds those flaps are ordinarily kept retracted
clear of the water.
The amidships planing region of the Dynaplane (the region which carries approximately 90% of
the weight) is optimized for minimum drag by incorporating longitudinal camber-curvature of
the type that has been developed for the lower surfaces of efficient supercavitating hydrofoils.
Theoretical equations defining those optimum hydrodynamic camber shapes were developed
by an outstanding expert in hydrodynamics (Virgil Johnson), and published in Reference 2. At
the David Taylor Model Basin Johnson’s equations were solved for the case of zero depth at
the leading edge (which is the planing case), and the results were used to prepare graphs
applicable for designing optimum camber shapes for the planing surfaces of Dynaplane-type
motorboats. Those graphs are given in Reference 3. The applicability of the theoretical
equations, for the planing case, was also verified at DTMB by testing models of planing
surfaces having camber
The Vee hydrofoil at the stern of the Dynaplane provides inherent stabilization underway when
fixed in position. However, a feature of the design is that the position of the foil is vertically
adjustable so that the running trim angle of the boat can be controlled. The vertical adjustment
can be provided by mounting the hydrofoil, together with the rudder, on a power-actuated
transom jack of the type presently being utilized for adjusting the heights of outboard motors.
Results from towing-tank tests of a Vee foil of the type being utilized were given in Reference
4. The tests showed that a foil of the configuration proposed (with the NACA 16-509 section
shape) will give a Lift/Drag ratio of 16, over a range of trim angles, and for speeds up to more
than 50 mph.
A complete design method for Dynaplane-type boats has been developed, and has been
published in Reference 5.
Desired speed for a planing motorboat will usually correspond to a value of the speed
coefficient (volumetric Froude number) of about 5, or higher. Figure 2 shows that at a speed
coefficient of 5, hull resistance for a craft of the Dynaplane type would be less than half as
much as it would be for a hull of contemporary design for a planing motorboat. This
comparison indicates that, with the drag of appendages also taken into consideration, the
horsepower required for a Dynaplane-type of boat, of a given weight, would be approximately
one-half that required for a conventional boat of the same weight. However, a more realistic
view would be to compare the two types on the basis of equal payload (and equal speed),
rather than on the basis of equal weight. Since the Dynaplane type of boat requires much less
horsepower, it will have much lower weights of engine and of fuel, and therefore a considerably
lower total weight, than a conventional boat capable of the same speed. (The trim-control
hardware will add some weight to the Dynaplane design, but this will be much less than the
weight reductions resulting from the lower weights of engine and of fuel.) Accordingly, with all
of the factors taken into consideration, it will be found that, for carrying a given payload at a
given speed, the horsepower required for a Dynaplane boat will be less than half that required
for a conventional planing boat.
All of the surfaces of a Dynaplane hull are developable, so the skin can be made inexpensively
from sheets of plywood or sheets of aluminum. A highly satisfactory and relatively inexpensive
way of making suitable Vee-hydrofoils has been previously developed by major aluminum
companies. Their method is to produce straight lengths of hydrofoils, having the desired
section shape, by extruding the material through a die. The straight lengths are then bent to
the required Vee shape. Dies are presently available for a variety of hydrofoil section shapes
of various chord lengths. The incorporation of an adjustable stern hydrofoil involves a not
inconsiderable item of cost. However, this will be more than offset by the fact that engine power
(and therefore engine cost) will be approximately halved The net result is that a Dynaplane
type of boat would cost less to produce than a conventional boat having the same top speed
and the same payload capacity. The Dynaplane design will, of course, cost very much less to
operate, since its fuel consumption rate will be approximately one half as much as it will be for
a corresponding conventional design.
References
1. Drucker, P.F., “Managing for Results,” London: Pan Books, 1967.
2. Johnson, V.E., Jr., "Theoretical and Experimental Investigation of Supercavitating Hydrofoils
Operating Near the Free Water Surface," NASA Technical Report R-93, 1961.
3. Clement, E.P., "Graphs for Designing Cambered Planing Surfaces Having the Johnson
Three-Term Camber Section, Rectangular Planform, and Zero Deadrise," Naval Ship
Research and Development Center Report 3147, Oct, 1969.
4. Benson, J.M., and Land, N.S., “An Investigation of Hydrofoils in the NACA Tank, I - Effect of
Dihedral and Depth of Submersion,” NACA Wartime Report L-758, Sept, 1942.
5. Clement, E.P., “A Configuration for a Stepped Planing Boat Having Minimum Drag
(Dynaplane Boat).” This publication is available on the web site of the International Hydrofoil
Society: www.foils.org.
The above figure shows the wetted areas when running for a conventional planing
boat and a Dynaplane boat. Each sketch is of a boat 32 ft. long, weighing
13,500 lbs., and traveling at 45 mph. Deadrise angle for both cases is 12 ½ degrees.
The running wetted area for the Dynaplane boat (including the Vee-hydrofoil
stabilizer) is 40 ft.² and for the conventional boat it is 136 ft.². That is, running wetted
area for the conventional design is more than 3 times as much as it is for the Dynaplane
design. This means that when running at the same speed and the same weight the
conventional design will have more than 3 times as much frictional resistance as the
Dynaplane design. The other components of the total resistance (pressure drag,
appendage drag, and air drag) will be similar for the two cases. The net result is that, at
planing speeds, the Dynaplane design will have one-half as much resistance as the
conventional design, and therefore will require one-half as much horsepower and will
consume gasoline at only one-half the rate. Furthermore, the feature of having a control
over the running trim angle of the boat provides greatly enhanced boating fun for both
pilot and passengers.
boat and a Dynaplane boat. Each sketch is of a boat 32 ft. long, weighing
13,500 lbs., and traveling at 45 mph. Deadrise angle for both cases is 12 ½ degrees.
The running wetted area for the Dynaplane boat (including the Vee-hydrofoil
stabilizer) is 40 ft.² and for the conventional boat it is 136 ft.². That is, running wetted
area for the conventional design is more than 3 times as much as it is for the Dynaplane
design. This means that when running at the same speed and the same weight the
conventional design will have more than 3 times as much frictional resistance as the
Dynaplane design. The other components of the total resistance (pressure drag,
appendage drag, and air drag) will be similar for the two cases. The net result is that, at
planing speeds, the Dynaplane design will have one-half as much resistance as the
conventional design, and therefore will require one-half as much horsepower and will
consume gasoline at only one-half the rate. Furthermore, the feature of having a control
over the running trim angle of the boat provides greatly enhanced boating fun for both
pilot and passengers.
The low resistance of the Dynaplane design has been verified by model tests in the U.S. Navy's David
Taylor Model Basin and in the towing tank at Stevens Institute of Technology. The above figure
compares hull resistances, from model tests, for conventional and Dynaplane motorboat designs. For
this graph the resistance values have been corrected to a boat weight of 10,000 lbs. The speed
coefficient used, volume Froude number, is particularly appropriate for comparing the performances of
different types of boats. It realistically uses gross weight rather than length as the significant index of
size, and compares different boats on the basis of equal weight and equal speed. Results from the tests
of two models of the Dynaplane type (DTMB Models 5115 and 5115A) are included in the figure. Both
had the basic Dynaplane features of a swept-back step (of small depth), a cambered planing surface,
and an adjustable stabilizer at the stern. Model 5115 utilized a Plum-type planing stabilizer, and Model
5115A had a V-hydrofoil stabilizer. Photographs of Model 5115A are shown below.
Taylor Model Basin and in the towing tank at Stevens Institute of Technology. The above figure
compares hull resistances, from model tests, for conventional and Dynaplane motorboat designs. For
this graph the resistance values have been corrected to a boat weight of 10,000 lbs. The speed
coefficient used, volume Froude number, is particularly appropriate for comparing the performances of
different types of boats. It realistically uses gross weight rather than length as the significant index of
size, and compares different boats on the basis of equal weight and equal speed. Results from the tests
of two models of the Dynaplane type (DTMB Models 5115 and 5115A) are included in the figure. Both
had the basic Dynaplane features of a swept-back step (of small depth), a cambered planing surface,
and an adjustable stabilizer at the stern. Model 5115 utilized a Plum-type planing stabilizer, and Model
5115A had a V-hydrofoil stabilizer. Photographs of Model 5115A are shown below.
Figure 3 - Values of Resistance/Weight Ratio, Versus Speed Coefficient,
for Conventional and Dynaplane-Type Boats.
for Conventional and Dynaplane-Type Boats.
Model 5115A Ready for Testing in the Towing Tank at Stevens Institute of Technology
The above Diesel-powered runabout had a sweptback step, a cambered planing surface,
and an adjustable planing-type stabilizer at the stern for trim-control.
and an adjustable planing-type stabilizer at the stern for trim-control.
The following two Dynaplane-type boats were built in England.
Both boats performed in a highly satisfactory manner.
Both boats performed in a highly satisfactory manner.
The above craft was a 40 ft research boat that was built for the British Petroleum
Company. Top speed of this boat was 87 mph.
Company. Top speed of this boat was 87 mph.
Underwater photo of Model 5115A when it was running at close to "design speed"
(the speed at which the wetted region of the forebody coincides with the cambered
region). Volume Froude Number equaled 4.68.
(the speed at which the wetted region of the forebody coincides with the cambered
region). Volume Froude Number equaled 4.68.
| The Dynaplane Boat |
| The Dynaplane Boat |
| Site by Eugene P. Clement (Revised December, 2009) For information contact: Eclement5@aol.com or jgh3@aol.com |
Added note, December, 2009:
I have in PDF form my 2006, 65-page booklet, "How to Design an Efficient Stepped
Planing Boat (Dynaplane Boat)." If a copy is desired I can send one that is in metric units
or one that is in English units, whichever is preferred. Send an e-mail to the address
above if you would like to have a copy sent (without obligation) to you. The download time
is approximately 8 minutes.
Eugene Clement
I have in PDF form my 2006, 65-page booklet, "How to Design an Efficient Stepped
Planing Boat (Dynaplane Boat)." If a copy is desired I can send one that is in metric units
or one that is in English units, whichever is preferred. Send an e-mail to the address
above if you would like to have a copy sent (without obligation) to you. The download time
is approximately 8 minutes.
Eugene Clement