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The Ship Escalator - A new concept for the lockage of ships-

Marcel A. Hermans

Port of Portland P.O. Box 3529 Portland, OR 97208 U.S.A.

Phone + 1 503-944-7305 Fax +1 503-944-7313 E-mail: hermam@portptld.com (or shipescalator@yahoo.com) Web page: www.geocities.com/shipescalator

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Summary The concept of the ship escalator was introduced in 1996. It provides a new alternative to existing lockage systems like conventional shiplocks, sloping planes, cascade-locks and ship elevators. The characteristics of the ship escalator make this concept very advantageous in situations with very high traffic volumes, not too much elevation difference, and no extreme variation in vessel dimensions. This concept is based on equilibrium, combining the lockage process for vessels transiting in both directions in one system. Vessels that transit through the ship escalator typically don’t need to stop or wait, but can proceed in their travel direction at a slow pace. Serving every vessel individually, as opposed to combining traffic in clusters, contributes to the very low transit times that are possible with the ship escalator. This aspect, combined with the very high capacity, forms the main strength of this concept. Developments in supporting technologies over the last several years have done a great deal in reducing and eliminating the disadvantage or weakness that would normally be linked to the mechanical system with its moving parts. This paper addresses the performance potential of a ship escalator as well as several of its technical details. Since the idea of a ship escalator is a very recent one, the studies that have been performed so far mainly covered the conceptual level. 1 Introduction The ship escalator is a completely new concept for the lockage of ships. Shiplocks have been used for centuries to transport ships from one water basin to another. Throughout the years several mutants of the basic concept of a shiplock have been designed (cascade locks, pente d’eau, ship elevator, sloping lock, etc.). Most of these concepts were designed for a specific field application, or were at least specially fitted for certain circumstances. In the last few decades, developments in navigation have justified the introduction of a totally new concept for a shiplock once again. As commercial navigation has faced enlargement of scale in seagoing as well as inland vessels, there has also been a real boom in pleasure navigation. This development has resulted in sharply increased numbers of recreational vessels in many popular water-recreation areas around the world. The concept of the ship escalator might be very useful in specific situations. In situations where large numbers of quite uniformly sized vessels (such as yachts) pass a lock system transiting from one water basin to another, the ship escalator can prove to be a superior concept, especially when the differences in water elevations are minimal. The ship escalator is a continuously moving transportation medium that allows boats to join in upon demand and be transported to the adjacent water basin. The concept of the ship escalator is a very simple and basic one. It is based on a complete equilibrium of forces by combining up- and downstream traffic flows in one and the same system. Even the loss of water is close to zero. Perhaps the most astonishing aspect of all is that ships passing to the next water basin can do so while maintaining a sailing speed just slightly slower than normal in the direction they’re traveling in.

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Figure 1: The ship escalator facilitating vessel traffic between two lakes

After presenting the conceptual design of the ship escalator in 1996 (see M. Hermans, 1996), a reconnaissance study was performed in 1999. This study focussed on some of the essential technical details of the ship escalator to determine if the concept is feasible from a technical perspective. Although the study wasn’t set up to result in a complete design of the ship escalator, the findings of this study were interesting and promising on this same conceptual level. 2 What it is and how it works The ship escalator is a construction that enables ships to ascend or descend to another water basin. Unlike a conventional shiplock, the ship escalator is able to handle vessels in a continuous process. This allows for the traffic flow to maintain its general character of a flow as opposed to the disruption of a discrete element in case of a shiplock. The ship escalator consists of a central island functioning as the pivot for door movement and two canals on either side of this longitudinal island. The bottom of the complete construction is level without slope in any direction. The doors move slowly around the central island. All doors are connected to some sort of a chain that goes around the island, near the top edge. The force to move the doors is applied through this same chain by the operating mechanism located on the island. The chain assures that all doors move at the same speed and thus stay the same distance from each other. A simple guide rail for the doors is constructed around the island near the bottom of the doors and at the outer edge of the doors in the floor.

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Figure 2: Plan view of ship escalator with main items The doors divide the canals on both sides of the island into several cells, each bordered by the island on the inside, the outer-wall on the outside, and the two doors on the front and back end. Since the cells in both canals are completely closed in, the water level in each of these separate cells can be maintained and adjusted individually as needed. Since the doors (and therefore the cells) move around the central island, one canal has its cells always moving from the upper basin to the lower basin, while the cells in the other canal automatically move from the lower basin to the upper basin. (Note that the floor of the ship escalator over which the doors move is level and that all doors have the same dimensions!) Without a water-control-system, the cells would maintain the same waterlevel as the lower or upper basin until its front door reaches the other basin at the end of the canal. At that moment, the door would start its rotation movement, would open, and water would suddenly flow in (or out) of the cell and bring the cell to the same level as the basin it just reached. Obviously, this will not accomplish the lockage of ships. The actual solution for the water-control system is both simple and effective and undoubtedly adds charm to the concept of the ship escalator. Since the cells moving to the upper basin need water added, and the cells moving to the lower basin need water drained, the solution is to drain the water from the cells moving in the direction of the lower basin to the cells moving in the opposite direction (in the other canal). And again, a simple and effective way to do this is by adding several pipes in the lower part of the central island connecting both canals with each other. With the right control of the flow through these pipes, the water level of each cell can be adjusted in a steady constant pace, just as the cells themselves proceed to the next basin at a constant pace. As will be further demonstrated in section 6.1, because the concept of the ship escalator is based on equilibrium, this water-control process is fairly simple to accomplish. Consequently, the water elevation of each cell starting from the lower basin gets raised in a slow and constant manner so that it is at the same elevation as the upper basin by the time it reaches this basin, and vice-versa for cells starting from the upper basin.

Cell lengthMooring slot

Mooring slot

Central island

Cell length

Total length of construction

Doors

Water basin 2Water basin 1

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Figure 3: Main elements of the ship escalator During any given moment of operation of the ship escalator, the lift height between the upper and lower basin is divided equally over the several cells in the canal, which of course holds true for both the canals. One of the advantages of this is that the hydraulic forces caused by the head (traditionally very significant at lock doors), are evenly distributed over multiple doors as well. Although small, there will still be a differential head between both sides of the door, resulting in water pressure pushing the door forward while traveling to the lower basin, and pushing it backward while traveling in the opposite canal. The door, while being moved forward in a linear direction through the canal, is locked in on its other top corner by a similar chain moving around the outside wall. This serves a constructional purpose by ensuring that the door is supported on both sides at any given moment during which there’s a hydrostatic force (differential head) on the door. Another advantage of this feature is that it gives the opportunity for a better seal along that side of the door, but the main purpose is to help navigation. The outside walls stretch out several ship lengths beyond the island, as does the chain moving around this wall. The spots where the doors (which are mounted at the chain around the island at equal distances from each other) will lock into the chain around the outside wall are clearly marked. To make sure that ships can only moor at the proper location (i.e. between and far enough away from the spots where the doors will lock in), mooring cleats are attached to that same chain at designated spots. Because there will be several doors locked in at any given moment during operation, the movement of the two outside chains is at exactly the same speed as the doors and the chain moving around the island. And more important: since the ships are moored on the outside chain, their speed will be exactly the same as the speed of the doors, which are also attached to that chain. 3 The live experience: Through the eyes of the shipper The boat operator or shipper who travels through a ship escalator, after arriving in the lock approach, steers his vessel closer to the side. There it’s time to slow down the vessel, making its speed equal to one of the mooring slots that are slowly moving forward parallel to the vessel. The shipper then directs the vessel to the mooring slot and will moor it while still slowly proceeding in a forward direction. The vessel can keep its motor running but its speed is now completely controlled and regulated by the movement of the mooring slot. Not too long afterwards, the vessel will automatically enter the canal of the ship escalator and the door will close behind the vessel. The vessel is now in its own individual cell, where the water elevation will be raised or lowered at a constant pace through pipes near the bottom of the construction. Only a few minutes

Movement direction

Sidewalls

Canals

Central islandDoors

Cell

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later the door in front of the vessel will open and the vessel has arrived in the other basin. The mooring slot keeps proceeding forward in a linear motion along the side wall of the escalator in the basin that was just entered. The boat operator now has a few minutes to de-moor the vessel and increase the speed to its normal navigation speed again. The system is set up so that the cleat will automatically fold away in case the boat operator does not de-moor before the mooring slot reaches the end (or turning point) of the side wall, so that any mooring line will be released before the mooring slot makes the turn. 4 Concrete numerical example for a yacht escalator This section describes the main dimensions and design parameters for a specific ship escalator. This ship escalator was designed specifically for use by yachts and other small boats. This specific design was tailored for the location Krabbersgat in The Netherlands, where the connection between two lakes faces very high yearly volumes of recreational vessels. (The prognosis is for almost 100,000 yachts in the year 2010, most of those passing during the few summer months.) The yacht escalator would be built as an addition to the existing conventional shiplock at this location, which would remain in operation. Therefore, oversized yachts and other types of vessels could still pass through the conventional lock. The purpose of this specific example is to get a better understanding of the concept of a ship escalator and the kinds of processes and subsystems that are involved. This example is just a potential version of the ship escalator. Since most design parameters are not limited to a close range, many different kinds of modifications are possible for this example. For this specific case, the design vessel/yacht was set as:

• Length: 20 meters • Width: 6 meters • Draft: 2.7 meters

The dimensions of a cell were determined as follows: • Length: 26 meters • Width: 7.5 meters • Depth: 4.5 meters (below the low-water elevation)

Other dimensions:

• Elevation difference between basins: 1.5 meters • Length of central island: 99.7 meters • Width of central island: 7.5 meters • Length of sidewalls: 245 meters

Motion

• Velocity (doors, vessels): 0.27 meter/second • Transit time to other basin: 5:40 minutes

Hydraulics:

• Pipe diameter: 0.35 meter • Number of pipes per cell length: 20 (equals 1 pipe per 1.3 meter) • Maximum flow velocity in pipe: 1.88 m/s • Maximum discharge from/into a cell: 1.43 m3/s (total of the connecting pipes) • Maximum rate of change in water elevation: 0.015 m/s • Maximum induced wave-height in cell: 0.043 meter

Note: The rotation speed for this particular example of the yacht escalator was based on the limited capacity it needed to achieve for the comparison study. Since the ship escalator under normal conditions can achieve a very high capacity, the necessary (minimum) speed to achieve that limited capacity turned

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out very low (which indeed shows the strength of the concept). Although the maximum limits of the design parameter “rotation speed” have not officially been explored in this exercise, it became clear that a speed of twice the used value (0.54 m/s) wouldn’t pose any limitations or require any significant modifications of the other design parameters. (For more information, see Poelmans and Van Het Hof, 1999) 5 Conceptual comparison with conventional shiplock There are many different kinds of structures in use throughout the world to enable ships to be lifted or lowered from one water basin to another. The conventional shiplock is the most commonly used structure, but certain situations justify different systems (e.g. a ship elevator, cascade locks, a pente d’eau or a sloping lock). In a situation with a high elevation difference, it’s likely that a ship elevator or cascade-locks will be a better option than a conventional shiplock. In situations where large vessels need to be accommodated it’s very likely that a conventional shiplock is the better option. To fully appreciate the great merit a ship escalator can have for vessel traffic, it’s important to understand the effect that the specific characteristics of this concept has on vessel traffic. There will be situations where the ship escalator can be the perfect solution, while in other situations another type of structure will prove to be the better alternative. An analysis of advantages and disadvantages of the ship escalator should therefore have an emphasis on the situations in which application of the ship escalator can be considered. On a rather conceptual level, the comparison of an escalator and an elevator offers a useful and perfect analogy for comparing the ship escalator with a conventional shiplock. You’ll find escalators in places like train stations and department stores where large numbers of people travel from one floor to the next. You’ll find elevators in places like office and apartment buildings and high-rise buildings, where the number of people to be transported at the same time is typically much lower and the number of floors they travel is typically much greater. Just like a normal escalator, the ship escalator is able to handle a quite heavy and steady flow of traffic without any significant increase of the transit time needed to get to the other basin. Basically every vessel gets almost individual treatment with only a very small chance of having to wait for another vessel. Not only does this eliminate the need to wait during any stage of the process, the vessel can even maintain most of its speed in the direction that it is traveling. In situations where a high difference in elevation needs to be accommodated, the primary advantages of the ship escalator will be lost. To make the concept work, the ship escalator either needs to be very long with many cells in both the canals, or needs to move/turn very slowly. In both cases the time it takes for a vessel to pass will increase accordingly, thus eliminating one of the important advantages of the escalator. (See section 7 for additional information.) Based on the two parameters “elevation difference” and “traffic volume”, the ship escalator and other alternatives for “locking” ships can be positioned as follows:

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Figure 4: Positioning the ship escalator based on the parameters “traffic volume” and “elevation difference” and compared to other locking alternatives But elevation difference and traffic intensity are not the only two relevant factors. The ship escalator handles vessels on an individual basis. Since transporting each vessel in its own separate cell is an important condition of the process, rather uniform characteristics of traffic in regards to vessel type and size are preferable. The cell dimensions have to be based on the dimensions of the design vessel. If a high percentage of vessel traffic has dimensions in the same order of magnitude as this maximum-sized vessel that needs to pass the ship escalator, a very effective use of the cells can be accomplished. If however, the design vessel is considerably larger than the majority of traffic, some efficiency will be lost (for information on yacht dimensions see PIANC, Report of Working Group 8 (2000). One of the additional advantages of the ship escalator is that cross-traffic can be avoided completely in the lock approaches. Especially in situations where introduction of the ship escalator can be expected (high traffic volumes), this can be an important advantage. The use of parallel shiplocks in situations of high traffic volumes would almost automatically introduce such cross-traffic, which is often acknowledged as a safety concern. The ship escalator, on the other hand, enables all vessel traffic to stay on its normal side of the waterway throughout the entire process. The fact that the whole process of the ship escalator is based on equilibrium is an advantage for the mechanics as well as the hydraulics. Forces on the construction parts stay quite low, energy consumption is very low, and the ship escalator operates while hardly losing any water! 6 Some technical details Although engineering and design have not been finalized on all construction details, there are several technical features of the ship escalator that are interesting enough to justify a closer look.

6.1 Water-control system The technical “heart” of the ship escalator is its hydraulic system. This can be considered the most essential part of the escalator and yet it demonstrates simplicity, which is a real important advantage. Just like the whole concept, the operation of the water-control system is based on balance. The flow of water needed to fill the cells that are moving to the higher elevation equals the amount of water that needs to be drained from the cells moving to the lower elevation. Therefore, the easiest and most effective way to obtain the

Traffic - volume

Elevation - differenceLow

Low

High

High

Ship escalator

Shiplock Ship elevator or Cascade-locks

Parallel cascade-locks or Parallel elevators

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right level in all the cells is by allowing the water from one canal to flow to the other canal. This is achieved by connecting the two canals by pipes constructed in the center island. There are two essential details that need to be addressed. It is important that at any moment during the operation cycle each cell in one canal is connected to only one cell in the other canal. If this does not occur, there will be moments that a continuous flow-path (direct connection) will exist between the upper basin and the lower basin. To avoid this situation, a simple one-way valve will be installed in each of the connecting pipes so that water can only flow in one direction; namely, from the canal that lowers water elevations and vessels to the canal where water elevations and vessels get raised. The hydraulic process is illustrated in Figures 5 and 6 below. Starting from position A, cells 1 and 8 are both in connection with the lower basin and are therefore at elevation 0. The backdoor of cell 1 is closing and cell 1 slowly moves in the direction of the upper basin (situation B). From now on, the elevation in cell 1 needs to be raised. This is achieved by allowing water to flow from cell 7 into cell 1. At this moment, the one-way valves in the pipes between cells 1 and 8 are closed so that water can’t flow out from cell 1 to the lower basin. (At stage B, the only connections between cells are: cell 5 draining into cell 3, cell 6 draining into cell 2, and cell 7 draining into cell 1; all other pipe connections are closed.)

Figure 5: The process of water control (1/2) Since cell 7 was previously at elevation 0.5 and cell 1 was at elevation 0, the elevation of both these cells will now level out at 0.25. Since all the doors keep moving forward at a constant pace, soon thereafter situation D will occur. Cells 1 and 7 are now exactly opposite from each other and they have both established their new 0.25 elevation. Since this stage of the leveling process is completed, the connection between cells 1 and 7 can now be closed, which is accomplished automatically by the simple one-way valve that’s installed in every pipe. Since the doors continue moving at a constant pace, situation E will occur next (see Figure 5). Cell 1 reaches a position partly opposite cell 6, and the valves between those two cells will automatically open. Cell 6 will now be lowered from its previous level 0.75 to elevation 0.5, while cell 1 gets raised from elevation 0.25 to 0.5 at the same time. At this stage the same leveling process occurs between cells 5 and 2. Cell 3 now gets connected to cell 4 that is in open connection with the upper basin. Therefore, the water elevation in cell 3 gets raised to elevation 1.5, the elevation of the upper basin. In the same way, cell 7 gets

Water elevation in Cell

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connected to cell 8, which is in open connection with the lower basin, and therefore cell 7 will now establish elevation 0.

Figure 6: The process of water control (2/2) This leveling process is a very smooth and constant process, which is of course a very important advantage from a hydraulics point of view. A closer look at the hydraulics will illustrate this. In stage B of the example above, cell 1 just starts to get connected to cell 7. This is when the differential head between those two cells is still at its maximum level of 0.5 meter. Since this differential head makes the water flow from cell 7 to cell 1, this maximum head difference generates a high velocity through the first connecting pipes that open up. On the other hand, since the two cells are only connected by a low number of pipes at this moment, the rate of flow between the cells stays very moderate. While both cells move forward in their own direction, the total cross section of their connection keeps increasing since more pipes open up, and at the same time the difference in water elevations between the two cells keeps decreasing. As a result of this, the flow rate between the two cells –which is a product of the available cross section and the head- remains quite constant throughout the whole process. This effect is illustrated in Figures 7 and 8, which show the results of the hydraulic calculations for the yacht escalator (see Section 4).

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Figure 7: The total flow into (or out of) a cell as a function of time Figure 7 shows the total flow between the two cells as a function of time. The flow starts with a sharp increase when the first pipes open. Every next opening of extra pipes results in a smaller increase, since the difference in water elevations between the cells keeps decreasing. The result of this flow characteristic for the change in elevation over time is illustrated in Figure 8. This figure clearly illustrates that the change in elevation is a very smooth and constant process. Conventional shiplocks have special procedures to open the piping system, either as an instruction to the operator or built in as part of the operating system, and in some cases even by a special shape of the valves. Those features are needed to accomplish a leveling process that’s similar to the one of the ship escalator. The ship escalator automatically accomplishes this without the need for those special measures. (For comparison, the typical shape of an “ideal flow-characteristic” is depicted in the same figure.)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1 9 18 25 33 42

Time [s]

Flow

[m3/

s]

Ship Escalator (calculated) Ideal curve

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Figure 8: Elevation difference between connecting cells as a function of time The basic hydraulic equations describing the water flow from a cell in the lowering canal to a cell in the raising canal are:

(1)

(2)

(3)

(4)

(5)

(6)

(7)

Elevation difference

0

0.1

0.2

0.3

0.4

0.5

0.6

1 9 18 25 33 42

Time [s]

Ele

vatio

n di

ffere

nce

[m]

Elevation difference

Dh h hN

cellupperba in lowerba in

=-

-s s

( / )2 1

Q A hdt

cell cell

proceeding cell length=

´ D1

dt lv

proceeding cell lengthcell

door movement1 =

A n At t p= ´

Q A g ht t t= ´ ´ ´ ´x 2 2

dhQA

tt

t= ´2

vQA

p tt

t, =

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With:

total footprint of a cell = cell width x cell length

total cross section of open pipes between two cells at moment t

cross section of a connecting pipe

time needed for the doors to proceed a distance of 1 cell length

water elevation of the upper basin

number of open pipes between two cells at moment t

total number of cells of the ship escalator = total number of doors of the ship escalator

average flow rate into or out of a cell that’s progressing 1 position/cell length in a canal

total flow to/from cell at moment t

velocity of the movement of the doors

velocity of flow in pipe at moment t

change in differential head between two connecting cells at moment t

maximum difference in water elevation on both sides of any door in the canal = maximum difference in water elevation between two connecting cells

6.2 Mooring system Another very interesting application in the ship escalator is its mooring system. The mooring system is essential for a safe and comfortable passage of the vessels traveling through the ship escalator. Each canal has a separate mooring system. The basic mooring system consists of chain-linked carriages that move around on the outside wall. This system stretches several vessel lengths into both lock approaches and has clearly marked cleats attached to the carriages at which the vessels can moor. This extra length in the lock approach gives vessels the opportunity to come slowly alongside the mooring system and moor at one of the dedicated spots while maintaining a slow forward motion. As soon as the vessel is moored to the mooring slot, its position and motion are completely controlled by the motion of the mooring system. The controlled position of the vessel assures that the vessel won’t come into contact with the doors that close in front of and behind the vessel when it enters the canal. Just like the dedicated spots for the vessel to moor, there are also dedicated slots on the chain where the closing doors will lock in. Since several doors are in a closed and locked position at any time during operation in both canals, the velocity of the door-chain around the central island will always be exactly the same as those of the two mooring chains.

Acell =

At =

Ap =

dtproceeding celllength1 =

hupperbasin =

nt =

N =

Q =

Qt =

vdoor movement =

vp t, =

dht =

Dhcell =

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Figure 9: Cross section of sidewall with mooring system carriages (first-generation design) The second-generation design has an improved and more sophisticated mooring system. Based on the same principle, extra security is added to assure that each vessel is moored correctly before proceeding into the escalator. This application is based on the more familiar ski lift. The essence of it is that a certain slot only proceeds into the actual canal of the escalator after it has been confirmed by the boat operator (and checked by the automated detection system) that its vessel is moored properly in the right spot. If the vessel is moored properly, the process is exactly the same as in the first generation design described above. If proper mooring of the vessel takes more time than anticipated, however, it won’t be necessary to stop or slow down the whole operation of the ship escalator. Only troubled vessels (and any potential subsequent vessels) have to wait before proceeding into the canal until they are moored properly. The mooring chain keeps moving at its usual velocity and the cleat-carriage of the troubled vessel hooks onto the chain again in an approved slot as soon as the vessel is moored.

6.3 Doors The use and type of doors in the ship escalator are definitely quite different than in conventional locks. A ship escalator needs multiple doors (a minimum of six are required, a higher (even) number can be desirable depending upon other design parameters) to operate. The doors are not just opening and closing in one dedicated location as in a conventional lock, but actually move around the central island. Although this might seem to be a weak aspect from a technical point of view, it actually creates some clear advantages. The door is only slightly wider than the design vessel, since only one vessel will be allowed in each cell. The only times the door has to withstand head or water pressure is when it’s moving through one of the

Ä

Floating cleat

Mooring carriage in return position

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canals, since that’s the only situation in which there’s an elevation difference between both sides of the door. What keeps the forces on the door moderate is not just the fact that the total elevation difference will be equally split over multiple doors in the canal, but also that the door in this situation is supported on both sides! This allows the doors in the ship escalator to be fairly light, as opposed to the heavy-duty doors required in a conventional lock. An extra option that can be considered is the addition of valves in the doors that open automatically when a door reaches the end of the canal. At that moment the door is no longer required to maintain a difference in elevation between two cells. While only being supported on one side, it has to push its way around the corner of the island. The holes in the door which automatically open when it starts turning (and close again when the door enters the other canal) will not only reduce the resistance and the forces on the door, but also appear to improve the flow pattern in the lock approach.

6.4 Low resistance coating Presenting a system like the ship escalator with moving parts in a marine environment automatically raises the question of how it deals with aspects like sealing, friction, and wear. The impressive progress that has been made in recent years in the technology dealing with those issues contributes largely to the viability of the ship escalator. The material called UMHWPE (Ultra High Molecular Poly-Etheen) appears to be the perfect solution for the specific requirements and application of the ship escalator. After an analysis of alternatives, the following system has been determined to meet the high requirements that were set for this part of the design. • Tips of the doors are equipped with a seal construction consisting of rubber strips with a stainless steel

strip on the edge. The seal construction will automatically be kept closed by using the differential head over the door (see Figure 10 below).

• Bottoms of the doors are equipped with a stainless steel profile (see Figure 11 below). • The bottoms as well as the sidewalls of the canals are coated with UMHWPE coating. Calculations show that the wear of the coating on the bottom would be only 1.3 mm in a 100-year lifetime with moderate use. The wear of the coating on the sidewalls, where the pressure between steel and coating will be lower, would be even less, with only 0.34 mm in a 100-year period.

Figure 10: Horizontal cross section of seal between the tip of the door and the coated sidewall.

DPwater

2

1 DPwater

Concretesidewall

Door

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Figure 11: Vertical cross section of the seal between the door and the coated floor 7 Actual comparison of performance To illustrate the strength of the ship escalator on performance-criteria for vessel traffic like “lockage capacity” and “transit time” it’s useful to refer to the basic theory of lock capacity and traffic resistance (see Kooman and De Bruijn, 1975). tt = tl + tw + td (8) The transit time tt of a vessel passing through a lock system is the sum of:

• tl, lockage time (time of the actual locking process for that vessel)

• tw, waiting time (time a vessel has to wait (typically because the shiplock is in a not-ready position due to other traffic) before it can start its actual locking process)

• td, delay time (time a vessel has to wait if there is no room in the next one or more locking cycle(s) that take place after the vessel arrived at the lock)

The average waiting time for any vessel at a one-chamber conventional lock is: tw = ½ Tc (with Tc = cycle time) (9) The general form of this equation is : tw = Tc/( Nl +1) (with Nl = the number of parallel locks) (10) This simple equation is the mathematical way to say that a vessel can be expected to arrive at the lock at a random moment in the locking cycle. Therefore, the average waiting time for any vessel (in case of one lock-chamber) is half the locking cycle, which can still be quite substantial. A common way to present the traffic resistance of a lock is by transit time as a function of traffic volume. The traffic volume can be made dimensionless by presenting it as a percentage of the lock capacity (see Figure 12).

Stainless Steel Profile UHMWPEcoating

Concrete floor

Door

17

Figure 12: Typical shape of lock resistance curve With increasing traffic volume, more and more vessels will be influenced by other vessels passing through the same lock and the average transit time will go up. If the traffic volume is so high that it is quite common that vessels have to wait one or more lockage-cycles, average transit time will typically increase sharply. The traffic-resistance curve for a ship escalator looks completely different. The ship escalator in motion has a mooring slot available in each direction approximately every 1 minute (depending on turning speed). Since the doors and cells move at a constant speed, every vessel (once it moors) is basically guaranteed a certain fixed transit time. And more important, as long as there will be no more than one vessel arriving per minute, there will be no waiting time at all! And this is true for low traffic volumes as well as for the quite high traffic volumes. In other words, the resistance curve remains completely flat! This phenomenon is shown in Figure 13 below. The only situation in which waiting times will occur at all is if a fairly high traffic volume (close to the escalator’s capacity) is combined with a very irregular arrival pattern.

Lock resistance

0.0 0.3 0.5 0.7 0.9

Traffic volume (volume/capacity)

Tran

sit t

ime

18

Figure 13: Comparison of lock resistance for conventional lock and the ship escalator The following numerical example (Section 7.1) will illustrate this essential characteristic of the ship escalator that in fact is the key to its superior performance. This example will be based on the yacht escalator with dimensions as described previously in Section 4.

7.1 The ship escalator With a canal length of almost 100 meters (three full cells of 26 meters each plus turning cells) and a moving speed of 0.54 m/s, the transit time trough the canal from one basin to the other would be 100 / 0.54 = 185 seconds = 3.1 minutes. With three “cells” stretching into the lock approach as mooring-slots and a maximum use of that available mooring time (2½ minutes), the total time for passage would be approximately 6½ minutes (including 1 minute for de-mooring). A cell length of 26 meters in combination with a turning speed of 0.54 m/s means that 1 mooring slot or cell is available every 48 seconds, resulting in a maximum capacity of 75 vessels per hour in each direction!

7.2 A conventional shiplock A single lock chamber with dimensions of 12 x 120 meters, would be able to hold a maximum of about 2 x 6 = 12 yachts of similar dimensions as considered for the r. Assume: • Total entry time: 5 minutes (=25 seconds per yacht) • Door opening and closing times: 1½ minutes each • Time to raise or lower water in lock: 2 minutes • Total sail-out time: 3 minutes (=15 seconds per yacht) This results in a cycle time of 2 x 13 = 26 minutes, which can accommodate 12 yachts in each direction. That means that the capacity of this lock is 27 yachts per hour in each direction. The average transit time for a vessel passing this lock would be close to 26 minutes (tl + ½ tc » 13 + 13 minutes; see Equations 8 and 9).

Lock resistance comparison

0.1 0.3 0.5 0.7 0.9

Traffic volume (volume/capacity) à

Tran

sit t

ime

à Conventional lock

Ship Escalator

1.0

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7.3 Comparison Comparing the performance of these two alternatives shows that the ship escalator is absolutely superior to the conventional shiplock in regards to both transit times and capacity. It allows vessels to pass in 6½ minutes compared to about 26 minutes for a conventional lock, and can handle 75 yachts per hour and direction versus 26 for the conventional shiplock. So while it can handle almost three times as many vessels as the conventional lock, the transit time for vessels can be reduced by as much as 75 percent compared to the conventional lock! 8 Challenges on the way to implementation of the first ship escalator One of the main challenges that should be anticipated in getting the first ship escalator in operation is potential skepticism from others in the field of waterway construction. Since this is a field that traditionally has to deal with and operate in an environment with a strong emphasis on long-term use, opportunities for innovations are quite scarce. What is even more complicating is that innovations normally focus on a specific part of the structure, and therefore can be considered and tested rather independently, as opposed to the introduction of a completely new concept, like the ship escalator. Therefore, lessons learned from the introduction of innovations that are a modification to an existing product might not be very applicable to this new concept. It should be not too hard to demonstrate a solid answer to concerns about issues like the sealing, friction, and the sensibility of a mechanical system in a marine environment. Basically all real mechanical parts are applied above water elevation, and are therefore not subject to a very severe environment. (This is really comparable to a conventional shiplock.) The under water part of the structure is a simple guiding structure that doesn’t require any vulnerable moving parts. Recent developments in highly resistant, low-friction materials offer perfect (and even quite cost effective) opportunities in that respect. Safety is an important requirement for navigation and for the ship escalator. A realistic comparison of the mooring system of the ship escalator with the well-known concept of a ski-lift should place this issue in the right perspective. Although those two systems are of course very different, there are also some useful similarities that can be used to address the real safety issues. Implementation of semi-automatic shiplocks and bridges (see PIANC, Report of Working Group 18, PTC 1 (1996)) should also add to this perspective. Looking back to the introduction of escalators for transporting people might be hard and will probably provide mostly irrelevant information. Referring to constructions that are more similar and that have dimensions on the same order as the ship escalator will be a more successful approach. A lot of similarities can actually be found in the hundreds of automated parking garages that have been installed worldwide in the last few decades. Those fully automated parking garages (“automated car-storage systems” might be a better term) look and operate a lot like the ship escalator. A car can be placed in a cell that’s connected to other cells and can then be moved around by a mechanical operation system. If a car needs to be parked in or retrieved from the garage, the system maneuvers that specific cell in front of the only door, on the street level. These structures and mechanical systems are similar to those of the ship escalator. 9 Conclusions • At a conceptual level, some very clear and specific advantages of the ship escalator over a

conventional shiplock can be identified. These advantages pertain to application of the ship escalator in situations where traffic volumes are high, the variation in vessel dimensions are minimal, and the difference in water elevations is not extremely high.

• The progress that has been made in certain supporting technologies over the last several years proves

to be an important positive factor in the feasibility of the ship escalator. Potential concerns that could be raised about certain aspects of the ship escalator are not significantly different from concerns that the introduction of similar kinds of new concepts and technologic innovations had to face.

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• There are currently locations and situations in the world that are well-suited for the introduction of the ship escalator. Introduction of the ship escalator will most likely be in an application for yachts. It’s very likely that the number of locations where use of a ship escalator is advantageous for navigation will further increase over the next decades, driven by the increase in traffic volumes.

• In circumstances as specified above, the ship escalator can be a very attractive alternative, combining

very low transit times for vessels with an extremely high lockage capacity. The continuous process matches well with the general characteristics of vessel traffic, and it also avoids cross-traffic which can be a navigational hazard in busier lock approaches with parallel conventional shiplocks.

Reference listing: M. Hermans, June 1996: Document in Dutch “De Scheepscarrousel –Snel schutten, met hoge capaciteit-“; translated title “The Ship Escalator – Fast lockage, high capacity-“ J.H. POELMANS, A. VAN HET HOF, June 1999: Thesis, Document in Dutch “De Scheepscarrousel –technisch haalbaarheidsonderzoek-”, translated title: “The Ship Escalator – technical feasibility study-“, Technische Hogeschool Brabant, Tilburg C. KOOMAN, P.A. DE BRUIJN, 1975: “Lock capacity and traffic resistance of locks” Rijkswaterstaat Communications No. 22 PIANC, 1996: ”Advanced and automated operation of locks and bridges” report of working group 18, PTC1 PIANC, 2000: ”Standards for the use of inland waterways by recreational craft” report of working group 8