Boston
06-07-2009, 02:01 AM
in an effort to establish design criteria for the most fuel efficient mono hull form over 45' and specifically for a 60' build
I would like to consider the possibility of bow wave cancellation appendage forms for a speed cruise range of approx 12~15 knots, 60' length, 13.5 beam, 4.5 depth, in a semi-displacement hull of aprox 42000lbs, 250 hp, bilge keels
I would reference the following two articles
one considering a classic bow bulb
a passive system
the other considering a active lifting body bow appendage originally designed to augment a foil system
but capable of a passive configuration without rest of the foil system
thing is that the lifting body system if made passive would still illicit a wave cancellation effect while offering some advantage to a typical bow bulb by also lending some lift
there is less wetted surface area but I think it would have more drag per sq/ft so the drag should be a wash in the end but the wetted surface area be reduced while canceling some portion of the bow wave
question is since I dont have a computer modeling program
if I removed the active components of the lifting body
its still a lifting body it just doesn't adjust for wave action
but its still got the hydrodynamics of a leading wave front who's trough could be engineered to cancel some portion of the primary bow wave
I think
unless Im missing something
any ideas for me
The bulbous bow, a standard feature of most large, modern ships with displacement hulls, is a protruding bulb at the bow (or front) below the waterline. The bulb modifies the way water flows around the hull, reducing drag and increasing speed, range, fuel efficiency, and stability. Ships with bulbous bows generally have 12 to 15 percent better fuel efficiency than similar vessels without them; thus, it is rare to see a large transport ship without one.
Bulbous bows have been most effective as applied to hulls of at least 45' and especially to those greater than 60'. They have been used to greatest effect on large ships with long, narrow hulls such as freighters, navy vessels and various passenger ships. They are much less common on short, wide hulls and recreational boats designed for wide speed ranges and planing. The gains of the bulbous bow generally increase as a function of speed; highest return is near the top end of semi-displacement speed range. At low speed (e.g., 6 knots), they can increase drag due to their greater wetted area.
How they work
The fluid dynamics of bulbous bows can be calculated.
Long waves are faster, so a ship that wants to go fast has to excite long waves and not short ones. In a conventionally shaped bow, a bow wave forms immediately before the bow. When a bulb is placed below the water ahead of this wave, water is forced to flow up over the bulb. If the trough formed by water flowing off of the bulb coincides with the bow wave, the two partially cancel out and reduce the vessel's wake. While inducing another wave stream saps energy from the ship, canceling out the second wave stream at the bow changes the pressure distribution along the hull, thereby reducing wave resistance. The effect that pressure distribution has on a surface is known as the form effect.
Some explanations note that water flowing over the bulb depresses the ship's bow and keeps it trimmed better. Since many of the bulbous bows are symmetrical or even angled upwards which would tend to raise the bow further, the improved trim is likely a by product of the reduced wave action as the vessel approaches hull speed, rather than direct action of waterflow over the bulb.
A sharp bow on a conventional hull form would produce waves and low drag like a bulbous bow, but waves coming from the side would strike it harder. Also, in heavy seas, water flowing around the bulb dampens pitching movements like a squiggle keel. The blunt bulbous bow also produces higher pressure in a large region in front, making the bow wave start earlier.
It is unclear when bulbous bows were conclusively first examined by western researchers, but scientific papers on the subject were first published in the 1950s. Engineers began experimenting with bulbous bows after discovering that ships fitted with a ram bow were exhibiting substantially lower drag characteristics than predicted, and eventually found that they could reduce drag by about 5%. Experimentation and refinement slowly improved the geometry of bulbous bows, but they were not widely exploited until computer modelling techniques enabled researchers at the University of British Columbia to increase their performance to a practical level in the 1980s.and this next
SUMMARY OF THE INVENTION
In accordance with an aspect of the present invention, an underwater lifting body is provided that meets these objectives. In particular a lifting body of the general type described in U.S. Pat. No. 6,263,819 is secured to the bow of a watercraft hull below the vessel's design water line for improved efficiency and motions in a seaway. Such bow attached lifting bodies are referred to herein as a Bow Lifting Body or BLB.
It has been found that a BLB applied at the bow of a ship can introduce numerous positive attributes.
A BLB provides all the positive attributes of a traditional bulbous bow. However, wave cancellation similar to a traditional bulbous bow is provided by a BLB, in an even larger speed range. Also, because of its volume, a BLB can be used for ballast or as a sonar dome, similar to traditional bulbous bows.
In the early 20 th century, D. W. Taylor developed the bulbous bow which has become a standard feature on modern ships. The battleship USS Delaware exhibited the first such bulbous bow in 1907. These bulbous protrusions are typically mounted at or slightly below the vessel's design waterline and various shapes have been developed over the years. These shapes are generally a cylindrical bulbous torpedo shape as shown in FIG. 3, conical as shown in FIG. 4, teardrop as shown in FIG. 5 or hybrid as shown in FIG. 6.
After Taylor discovered the bulbous bow and its potential to reduce a ship's drag at a specific speed, in 1935–36 Wigley performed calculations to quantify the resistance benefits of bulbous bows due to wave cancellation.
At high speeds, the reduction in wave resistance due to the interference between the wave systems of the hull and bulb, if properly located, is more than sufficient to overcome the frictional and form drag of the bulb, and the net result is a reduction in total resistance.
J D Van Manen and P Van Oossaney, Chapter 5, Volume II, Principles of Naval Architecture
As seen in FIGS. 3–6, traditional bulbous bows exhibit a shape that is symmetric about a longitudinal axis. Because of this symmetric shape, bulbous bows offer no dynamic lift at speed and increase drag and decrease efficiency over a range of speeds due to the fact that bulbous bows exhibit a certain amount of sinkage at speed. However conventional bulbous bows do have the positive attribute of wave cancellation which occurs in a specific speed range that is dependent on the length and beam of the hull as well as the length, size and location of the bulbous bow. This phenomenon is shown in FIGS. 1 and 2, FIG. 1 demonstrates the separate wave patterns 10 , 12 on the free water surface generated by a conventional hull and a schematically illustrated conventional bulbous bow structure 13 operating below the surface. The hull produces a wave peak 14 aft of bow 16 while the bulbous bow 18 creates a wave peak 20 immediately above it followed by a trough 22 . The trough 22 cancels wave peak 14 so a wave 24 of reduced height is formed. (FIG. 1) The size and placement of the bulbous bow is crucial to optimizing the ship's performance at a desired speed. However, because this increased efficiency with a bulbous bow is for one specific speed, generally cruise speed, all other speed ranges exhibit an increase in amount of drag and reduction in efficiency.
Because lifting bodies have a higher lift to drag ratio (L/D, efficiency) than that of a hull alone, most noticeably at high speeds, by adding a BLB component with a higher L/D ratio than that of the original system without such an addition, it is intuitive that the L/D ratio of the entire system increases.
In addition, a typical lifting body can lift as much as five (5) times its own displacement at speed. By adding a lifting body at the bow of a ship, this dynamic lift increases the payload capacity of the ship. A BLB with a high L/D ratio can introduce such possibilities as the option to shift the longitudinal center of gravity (LCG) toward the bow of the ship by means of adding fuel, payload, ballast tanks or similar. This shift in LCG can be desirable in certain seaways to reduce pitching motions.
Furthermore, by the introduction of an underwater body with a large platform area at the bow of a ship, the added mass in the vertical direction is increased, which significantly reduces unwanted motion.
Moreover, the motions of the ship in a seaway can be additionally reduced if the underwater body has active control surfaces which are linked to an Active Ride Control System (ARCS). A BLB offers the option of either being a passive, or active ride control device.
The above, and other objects, features and advantages of this invention will be apparent to those skilled in the art from the following detailed description of illustrative embodiments of the invention which is to be read in connection with the accompanying drawings wherein:http://www.freepatentsonline.com/7191725-0-display.jpg
I would like to consider the possibility of bow wave cancellation appendage forms for a speed cruise range of approx 12~15 knots, 60' length, 13.5 beam, 4.5 depth, in a semi-displacement hull of aprox 42000lbs, 250 hp, bilge keels
I would reference the following two articles
one considering a classic bow bulb
a passive system
the other considering a active lifting body bow appendage originally designed to augment a foil system
but capable of a passive configuration without rest of the foil system
thing is that the lifting body system if made passive would still illicit a wave cancellation effect while offering some advantage to a typical bow bulb by also lending some lift
there is less wetted surface area but I think it would have more drag per sq/ft so the drag should be a wash in the end but the wetted surface area be reduced while canceling some portion of the bow wave
question is since I dont have a computer modeling program
if I removed the active components of the lifting body
its still a lifting body it just doesn't adjust for wave action
but its still got the hydrodynamics of a leading wave front who's trough could be engineered to cancel some portion of the primary bow wave
I think
unless Im missing something
any ideas for me
The bulbous bow, a standard feature of most large, modern ships with displacement hulls, is a protruding bulb at the bow (or front) below the waterline. The bulb modifies the way water flows around the hull, reducing drag and increasing speed, range, fuel efficiency, and stability. Ships with bulbous bows generally have 12 to 15 percent better fuel efficiency than similar vessels without them; thus, it is rare to see a large transport ship without one.
Bulbous bows have been most effective as applied to hulls of at least 45' and especially to those greater than 60'. They have been used to greatest effect on large ships with long, narrow hulls such as freighters, navy vessels and various passenger ships. They are much less common on short, wide hulls and recreational boats designed for wide speed ranges and planing. The gains of the bulbous bow generally increase as a function of speed; highest return is near the top end of semi-displacement speed range. At low speed (e.g., 6 knots), they can increase drag due to their greater wetted area.
How they work
The fluid dynamics of bulbous bows can be calculated.
Long waves are faster, so a ship that wants to go fast has to excite long waves and not short ones. In a conventionally shaped bow, a bow wave forms immediately before the bow. When a bulb is placed below the water ahead of this wave, water is forced to flow up over the bulb. If the trough formed by water flowing off of the bulb coincides with the bow wave, the two partially cancel out and reduce the vessel's wake. While inducing another wave stream saps energy from the ship, canceling out the second wave stream at the bow changes the pressure distribution along the hull, thereby reducing wave resistance. The effect that pressure distribution has on a surface is known as the form effect.
Some explanations note that water flowing over the bulb depresses the ship's bow and keeps it trimmed better. Since many of the bulbous bows are symmetrical or even angled upwards which would tend to raise the bow further, the improved trim is likely a by product of the reduced wave action as the vessel approaches hull speed, rather than direct action of waterflow over the bulb.
A sharp bow on a conventional hull form would produce waves and low drag like a bulbous bow, but waves coming from the side would strike it harder. Also, in heavy seas, water flowing around the bulb dampens pitching movements like a squiggle keel. The blunt bulbous bow also produces higher pressure in a large region in front, making the bow wave start earlier.
It is unclear when bulbous bows were conclusively first examined by western researchers, but scientific papers on the subject were first published in the 1950s. Engineers began experimenting with bulbous bows after discovering that ships fitted with a ram bow were exhibiting substantially lower drag characteristics than predicted, and eventually found that they could reduce drag by about 5%. Experimentation and refinement slowly improved the geometry of bulbous bows, but they were not widely exploited until computer modelling techniques enabled researchers at the University of British Columbia to increase their performance to a practical level in the 1980s.and this next
SUMMARY OF THE INVENTION
In accordance with an aspect of the present invention, an underwater lifting body is provided that meets these objectives. In particular a lifting body of the general type described in U.S. Pat. No. 6,263,819 is secured to the bow of a watercraft hull below the vessel's design water line for improved efficiency and motions in a seaway. Such bow attached lifting bodies are referred to herein as a Bow Lifting Body or BLB.
It has been found that a BLB applied at the bow of a ship can introduce numerous positive attributes.
A BLB provides all the positive attributes of a traditional bulbous bow. However, wave cancellation similar to a traditional bulbous bow is provided by a BLB, in an even larger speed range. Also, because of its volume, a BLB can be used for ballast or as a sonar dome, similar to traditional bulbous bows.
In the early 20 th century, D. W. Taylor developed the bulbous bow which has become a standard feature on modern ships. The battleship USS Delaware exhibited the first such bulbous bow in 1907. These bulbous protrusions are typically mounted at or slightly below the vessel's design waterline and various shapes have been developed over the years. These shapes are generally a cylindrical bulbous torpedo shape as shown in FIG. 3, conical as shown in FIG. 4, teardrop as shown in FIG. 5 or hybrid as shown in FIG. 6.
After Taylor discovered the bulbous bow and its potential to reduce a ship's drag at a specific speed, in 1935–36 Wigley performed calculations to quantify the resistance benefits of bulbous bows due to wave cancellation.
At high speeds, the reduction in wave resistance due to the interference between the wave systems of the hull and bulb, if properly located, is more than sufficient to overcome the frictional and form drag of the bulb, and the net result is a reduction in total resistance.
J D Van Manen and P Van Oossaney, Chapter 5, Volume II, Principles of Naval Architecture
As seen in FIGS. 3–6, traditional bulbous bows exhibit a shape that is symmetric about a longitudinal axis. Because of this symmetric shape, bulbous bows offer no dynamic lift at speed and increase drag and decrease efficiency over a range of speeds due to the fact that bulbous bows exhibit a certain amount of sinkage at speed. However conventional bulbous bows do have the positive attribute of wave cancellation which occurs in a specific speed range that is dependent on the length and beam of the hull as well as the length, size and location of the bulbous bow. This phenomenon is shown in FIGS. 1 and 2, FIG. 1 demonstrates the separate wave patterns 10 , 12 on the free water surface generated by a conventional hull and a schematically illustrated conventional bulbous bow structure 13 operating below the surface. The hull produces a wave peak 14 aft of bow 16 while the bulbous bow 18 creates a wave peak 20 immediately above it followed by a trough 22 . The trough 22 cancels wave peak 14 so a wave 24 of reduced height is formed. (FIG. 1) The size and placement of the bulbous bow is crucial to optimizing the ship's performance at a desired speed. However, because this increased efficiency with a bulbous bow is for one specific speed, generally cruise speed, all other speed ranges exhibit an increase in amount of drag and reduction in efficiency.
Because lifting bodies have a higher lift to drag ratio (L/D, efficiency) than that of a hull alone, most noticeably at high speeds, by adding a BLB component with a higher L/D ratio than that of the original system without such an addition, it is intuitive that the L/D ratio of the entire system increases.
In addition, a typical lifting body can lift as much as five (5) times its own displacement at speed. By adding a lifting body at the bow of a ship, this dynamic lift increases the payload capacity of the ship. A BLB with a high L/D ratio can introduce such possibilities as the option to shift the longitudinal center of gravity (LCG) toward the bow of the ship by means of adding fuel, payload, ballast tanks or similar. This shift in LCG can be desirable in certain seaways to reduce pitching motions.
Furthermore, by the introduction of an underwater body with a large platform area at the bow of a ship, the added mass in the vertical direction is increased, which significantly reduces unwanted motion.
Moreover, the motions of the ship in a seaway can be additionally reduced if the underwater body has active control surfaces which are linked to an Active Ride Control System (ARCS). A BLB offers the option of either being a passive, or active ride control device.
The above, and other objects, features and advantages of this invention will be apparent to those skilled in the art from the following detailed description of illustrative embodiments of the invention which is to be read in connection with the accompanying drawings wherein:http://www.freepatentsonline.com/7191725-0-display.jpg