PROJECT CRAB FARMER Part II Tests of the Prototype
Prepared by: Grzegorz Skawiński
Table of Contents.
Table of Contents
Construction of the Crab Farmer prototype.
The purpose of constructing the prototype is to present the idea and conduct tests under conditions that the device is suppose, to work under. If the tests reveal any errors, it will be possible to make corrections so that the final version of the device will be able to work faultlessly.
The CF prototype is almost completely made of carbon steel since this material is easily accessible on the market.
The environment of sea water that the device is supposed to work in is a large problem.
Thus, the choice of material for large-scale production of the device should be made by experts.
The material used in the production process will have influence on the period for which the farmers will be able to use the devices, as well as it will influence the production costs.
Before starting to read this chapter, it is advised to watch the short video “1 How does CF works” in which one will become familiar with the way how individual elements of the prototype work.
The prototype was built according to the dimensions specified in Picture no. 22 in the first part of the description in Chapter no. 7 “The Crab Farmer dimensions
Rods with a diameter of 16 mm form compartments of the basket. The rods with a diameter of 10 mm secure the containers from falling out from the compartments. On the 40X5mm flat bar, there is a mounted bolt used to close the door of the basket.
The flat bar is mounted 5 cm below the joining of rods of section walls. Such a solution facilitates inserting and removal of containers from the compartments.
The short rod in the red circle (Picture no. 4) placed just below the rotation axis of the basket is used for attaching the rope to secure lifting the prototype.
The method used in the prototype for fixation of the lock to the stand (Picture no. 6 in the yellow circle) prevents accumulation of sand in the joint. Sand could disrupt correct operation of the lock.
The lock protection (Picture no. 7) consists of two pipes joined together. One pipe is permanently put onto the basket rod while the second pipe is put onto the part of the lock that protrudes from the handle In Picture no. 8, in the red circle one can see that the basket lock is not secured and we can move it to the bottom position.
In Picture no. 8, in the yellow circle we can see the basket lock position limiter fixed to the basket. The limiter determines the position of the lock in relation to the basket. Picture no. 9 shows four movable supports made of 3 mm aluminum sheet fixed to the tripod. The counterweight of the movable support is made from several steel rods that are connected with each other (Picture no. 10). In this way, the created connection (Picture no. 10) of the movable support with the tripod prevents accumulation of sand in the connection.
Sand could disrupt the correct operation of movable supports of the prototype. Picture no. 11 presents the tripod of the CF prototype. Elements of the tripod marked with yellow lines are made from rods with a diameter of 25 mm.
In Picture no. 11, anchors within the red circle are made from rods with a diameter of 25 mm and length of 25 cm.
The remaining elements of the construction of the stand are made from rods with a diameter of 20 mm.
Model of the device for CF basket rotating
A basket filled with large oysters can be too heavy to be easily rotated by one worker.
At some point, almost every driver had to replace a punctured tire during a trip. In order to replace the tire, the driver must lift the heavy car first.
Every car is equipped with a simple device that allows anyone lift the car with ease.
Rotating a CF basket is an analogous situation. There is a simple mechanism thanks to which anyone can easily rotate a basket filled with oysters.
The diagram of the device for turning the CF basket has been presented in the first part of the project description in chapter no. 8. Summary – “Turning bags. The possibility of rapid mixing of mollusks in the containers”.
Due to my low budget, I could built only a model of that device. It is however sufficient for the purpose of presenting the idea for an efficient solution for rotating the CF basket.
The version of the device used for large-scale production should be constructed as a two-stage gear.
The model of the device for rotating the CF basket has been presented in this video “Video Turn the Basket”.
The device is light and easy to use. It can be carried by one worker without any effort.
After the work is done, the worker takes the device to the tool storage room.
The Crab Farmer prototype after five months at sea.
The prototype was set at sea in the second half of May 2017.
The prototype was set up far away from trestles, so that it could be exposed to direct effect of sea waves (Picture no. 16).
This will allow you to check if the prototype design is stable enough so that storms cannot overturn the prototype or move it.
Pictures no.17 and no. 18 were taken on 11.10.17. Five months after setting up the prototype at sea and one week before the Hurricane OPHELIA.
In Picture no. 17, one may see the bottom rod of the tripod support (parallel to yellow line). Parallel to the red line, one can see the counterweight of the movable support.
Although the prototype was made entirely of steel (i.e. in the heaviest version possible, with included burden of the oysters) it does not immerse into the seabed.
Water also did not wash out a hole under the prototype.
Based on Pictures no. 17 and no. 18, we can conclude that the prototype performs perfectly under the conditions in the Dungarvan bay.
In the period of those five months, there were no strong storms.
The Hurricane "OPHELIA", the Storm "BRIAN" and the later series of storms in winter 2017-2018.
On 16.10.17, Ireland was struck by the Hurricane “OPHELIA”. Wind speed of the hurricane reached up to 190km/h.
Then, on 27.10.2017, Ireland was struck by the Storm “BRIAN” and the wind speed was up to 90km/h.
Despite such heavy weather conditions, the prototype passed the test regarding stormy weather. Waves did not manage tip the device over.
It was a very important test for the CF.
Farmers do not have to worry about incurring losses due to hurricanes or storms.
As a result of the Hurricane “OPHELIA” and the Storm “BRIAN”, the prototype immersed into the seabed at a depth of about 10 cm (Picture no.19). As one can see in Picture no. 19, rods of the stand located at level of movable supports are already invisible
Picture no. 20 presents a small dip that was created around the prototype as a result of the Hurricane Ophelia and the Storm Brian.
Despite such a high wind speed (190 km/h), water did not wash out a deep hole under the prototype. The prototype was set up far away from structures that could suppress the energy of sea waves.
The hurricane did not cause any significant damage.
Lifting the prototype after the Hurricane "OPHELIA" and the Storm "BRIAN"
The place in the bay where the prototype was set up in May 2017 was assigned to a farmer who had been farming oysters in the Dungarvan bay for many years. That is why on 10.02.18 the prototype was moved to a new location, about 100 m from the previous one. It was a good occasion to check the performance of movable supports during extraction of the prototype from the seabed. As a result of the hurricane
(wind speed of 190 km/h), rods of the stand located at level of movable supports immersed into the seabed at a depth of about 10 cm.
As one can see in Picture no. 21, despite the fact that movable supports tilted to a vertical position, the material that the seabed consists of did not slide down completely from the supports. The layer of that material got stuck to the surface of movable supports, making it difficult for them to return to the horizontal position.
In front of Picture no. 21, one can see that a lump of the material stopped on rods of the construction of the tripod.
After a short while of keeping the prototype above the surface of water, some of the material slid down from the supports.
However, as one can see in Picture no. 22, only two supports worked correctly.
The correct position was reached by the back right and front left support of the prototype.
The two remaining supports were stopped by the wet material of the seabed that got stuck to them.
Lifting the CF prototype from the seabed on 10.02.18 was recorded in the video “Taking out a prototype of the seabed”.
After the prototype was moved to a new place, a whole series of storms took place. Such weather persisted until the end of winter.
Pictures nos. 23 and 24 were taken on 30.06.18.
In Picture no. 23, parallel to yellow lines, one can see rods of the stand that rest on the seabed. Parallel to the red line, one can see the counterweight of the movable support. On the other side, the prototype immersed into the seabed at a depth of 5 cm.
Storms that occurred in the Dungarvan bay in the period from February to June 2018 did not cause any damage.
Picture no. 24 presents a small dip that water washed out around the prototype.
Taking out a prototype of the seabed
The prototype after a year at sea
After a year of observations, we know that the prototype performs perfectly under conditions in the Dungarvan Co Waterford bay.
The hurricane and the series storms that struck the Dungarvan bay in winter 2017-2018 did not have a significant impact on the prototype.
We know that the construction is stable and the farmers do not have to worry about incurring losses at their farms due to bad weather conditions.
However, there are two aspects that must be taken into consideration when planning the final version of the device.
When lifting the prototype from the seabed, it appeared that the aluminum sheet is an unsuitable material for the movable supports.
There are two important reasons:
– the material that the seabed consists of sticks to the surface of the aluminum support, making its return to vertical position difficult.
– mechanical properties of aluminum sheet are too weak. During extraction from the seabed, the aluminum support can be damaged easily.
It is very important that the construction of the movable support is strong enough to avoid deformations while being extracted from the seabed.
During extraction of the prototype from the seabed, a lump of wet sand stuck to the rods of the stand (Picture no. 21). In the prototype, the rods form a shape of letter H (in Picture no. 25a, in the yellow circle).
In order to avoid that, the rods that determine the position of movable support can be arranged differently.
It is also possible to use flat bars instead of round rods (Figure no. 25b).
The longer side of the flat bar (B), which is positioned vertically (Fig. no. 25b) has a significantly smaller area that can serve as support for the block of wet sand.
The free space for bags in compartments of the basket should not be too large. During the tide, sea waves cause the containers hit against the rods of basket compartments. The reason for that is to prevent the containers from gaining too high momentum before the impact.
When the energy with which the containers hit the rods of the basket is too high, it may kill the oysters. It is especially unfavorable during summer, when temperatures are high. That is why it is important that the size of containers matches properly the size of compartment of the CF basket.
It will be safe to have the free space in the compartment big enough to allow inserting and taking out the oysters in a convenient way.
Defects of oysters that are formed during the farming process
An oyster shell consists of three elements (Picture no. 26)
1 – convex part of the shell
2 – flat part of the shell
3 – ligament
The convex part of the shell (1) forms space that holds the internal organs of the oyster (the meat we eat). The flat part of the shell (2) closes the convex part tightly. The ligament (3) connects both those parts and works like a door hinge.
When the convex part of the oyster shell keeps growing except for the part with the ligament, a new shell will start growing. This is how the convex part of the shell grows. The newly grown part of the shell of pearl color (Picture no. 27). The flat part of the oyster shell, when becoming larger, adjusts its shape to the newly grown convex part of the shell, closing it tightly.
The bags that oysters are placed usually do not have too much free space. Oysters grow in the direction in which there is free space for them. If a new oyster shell meets an obstacle (another oyster) when growing, it stops growing in that direction. Oysters left in a bag for a long period may take very complex shapes.
In order to obtain good quality oysters, the farmers mix the oysters in the bags several times in a year. This action (called turning) is performed in the period of intensive growth of the oysters.
Turning involves shaking the bag vigorously several times. During this process, oysters pound against each other and, as a result, their newly grown shells are removed. After the process, the oyster shell starts growing anew within its whole perimeter. It is very advantageous for the final shape of oyster shells.
What is more, due to that process, the growth of the shells is stopped for some time. In that period, internal organs of the oyster do not stop growing. The shell fills with meat.
It is the second advantage of performing that process.
Turning is of key significance for obtaining high-quality oysters.
From the point of view of farmers and restaurant owners, oysters may have three defects.
-the first defect is when the shell is not filled enough with meat.
Picture no. 28a presents an oyster that contains very little meat.
Picture no. 28b presents an oyster of the highest quality.
The reason for slow growth of internal organs of an oyster is insufficient amount of food. Places with a lot of food for oysters include river estuaries and their close surroundings.
If the farmer has no access to such places, he or she should frequently perform oyster turning. Such a process will extend the time needed for oysters to reach a proper size, but it will increase the amount of meet in their shells.
– the second defect is improper shape of oyster shells, Picture 29 presents examples of oysters that, in the farmers’ and restaurant owners’ opinion, are of improper shape.
The reason that oysters are shaped like that is that they have been left for a long period without being turned
– the third defect is when oysters grow together
Connected to each other oysters is a natural phenomenon in the case of those mollusks. However, it is an undesired condition in the case of farming. Oysters grow together when they are already very small. The trick is to not let new connections to be formed during the farming process.
Connections between oysters during farming are formed when oysters are in contact with each other in the same place for a long period of time.
The same reason makes the oysters grow into walls of the bags (Picture 39, 40).
In order to avoid it, it is necessary to frequently perform oyster turning.
Oysters placed in the CF prototype.
The containers used for testing are plastic boxes with holes (Picture no. 31). The dimensions of one box are 80X45X8 cm. The containers were placed in compartments of a CF basket with dimensions of 90X60X20 cm. Each compartment of the CF basket had two containers placed in it. The containers were not attached to the rods of the compartments. Sea waves cause the containers hit the rods of, which moves the oysters against each other.
In the further part of this chapter, the pictures present the quality of oysters placed in the prototype after a period of five months and of one year.
Oysters were placed in the prototype, while each oyster weighed about 20 grams.
– oysters after five months in the prototype
Pictures nos. 32, 33 and 34 show oysters after five months in the prototype. The pictures were taken on 05.01.18. As we can see in Pictures nos. 32, 33 and 34, the oysters placed in the prototype reached the highest quality already after five months. Their shells are of beautiful shape and are full of meat.
Pictures nos. 35, 36 and 37 were taken about two weeks after the Storm Brian. In the pictures, one can see the contents of three containers placed in the prototype.
Oysters in the containers that are visible in the pictures do not differ greatly in terms of size and are of correct shape
– oysters after a year in the prototype
Pictures nos. 38, 39, 40 and 41 were taken on 23.05.18.
Each of Pictures nos. 38, 39 and 40 presents the contents of one container.
In the top part of those photos, one can see empty shells that were in the container. The left side in the pictures shows oysters with the same size of shells. The right side shows oysters the shells of which are smaller than the rest.
As one can see in Pictures nos. 38, 39 and 40, over 90% of oysters has a shell of correct shape.
The oysters had never been segregated before.
Shells of oysters from the prototype do not differ greatly from each other in terms of size and they are full of meat.
Adaptation of standard bags to be used in the CF device
In order to obtain high quality of oysters, it is necessary to provide them with proper conditions for growth. Oysters should have sufficient space for growing.
Containers used for testing of the prototype served their role perfectly.
However, it is possible to adapt regular bags to be used with the CF device.
In the case of currently used bags, the most dangerous spots for oysters are the corners of the bags and the spots near joints of the walls (Picture no. 42). Pictures no. 42 and no. 43 show oysters that grew into the walls of the bag. The reason that oysters might grew into the walls of the bags is that they have been left for too long without turning. The shape of oysters that grew into the wall of the bag becomes incorrect and the oysters very often die.
There is a simple solution to adapt the bags to be used in the CF device (Image no. 44).
When designing bags to be used in the CF device, one must remember that several bags will be placed in one basket compartment and that they will be stacked on each other.
Plastic elements, for examples in shape of a cube (4), can be attached to one of the walls inside the bag (Image no. 44). Such elements will separate walls of the bag from each other (2). Space will be formed between the walls so that the oysters can be placed in it.
Bags should be designed in such a way that when placed in compartment of the basket they always rest on the elements that separate walls from each other (4) (Fig. no.45). Thanks to such a solution, the oysters in the lower container (6) will not be pressed by oysters in the container (5).
Picture no. 45 shows two bags in extreme positions that lie on each other in the basket compartment. The bags lean on their wall separating elements (4)
Designations in Figure no. 44.
2- bag wall
3- place of fixation of the element that separates walls of the bag from each other
4- element that separates walls of the bag from each other
Designations in Figure no. 45
1- basket section of the CF
2- container walls
3- fixation of elements that separate walls of containers from each other
4- elements that separate walls of containers from each other
5- container with oysters
6- container with oysters
By using this method for small oysters, bags can be prepared in such a way that one compartment of the CF basket may hold four containers.
The walls of the bag must be rigid so that the bag does not deform when the basket is being rotated.
If bags are prepared according to the method described in this chapter, there is no need to separate the compartments of CF basket.
Division of the basket compartment has been described in the first part of the description “7. The Crab Farmer dimensions”
Fourteen reasons that the use of the CF is beneficial
Trestles have currently been the most efficient method of oyster farming in the world. This method had been developed by farmers throughout the period of several generations. Farmers who use trestles have a very good access to oysters. As a result, the are able to inspect their growth as well as perform actions that allow obtaining high-quality oysters. Good access to means of transport allows efficient carriage of oysters.
Project Crab Farmer significantly improves that method. Thanks to the CF, it is possible to produce three times more oysters of the highest quality while using the same area of seabed, with much less extensive workload.
The chapter has been devoted to a comparison of both these methods and constitutes a supplementation to Chapter no. 8. „Summary” from the first part of the description.
The supplementation is based on observations regarding the prototype and oysters placed in it for the period of one year at sea.
1/14. Three times more oysters within the same area of the seabed.
When using the CF, farmers will place three times more containers with oysters within the same area of the seabed. The CF basket can hold sixteen containers, while in the case of trestles – five.
CF 16 – trestle 5
The farmer who wants to expand the farm and applies this CF system in order to do that will avoid the costs connected with establishing a new farm at a different place.
Such costs include:
– new place at sea
– new place for a farm
– new buildings
– new machines
– new devices
– new tools
– a new team of people
When using the CF, we use the place that is rich in food for the oysters more effectively.
2/14. At the beginning of the farming cycle, when the oysters are very small.
If we use properly prepared containers for placing small oysters (chapter no. 9), then we are able to fit thirty-two containers in the CF basket. Within the same area of the seabed that is occupied by a trestle.
CF32 – Trestle5
3/14. Improvement of growth conditions of oysters.
The containers placed in the CF are not attached to the rods of the basket. They have free space in the compartments in which they can move around due to sea waves.
During the tide, sea waves cause the bags hit the rods of the compartments. As a result of that impact, the oysters placed in the containers change their position against each other. That is why are not formed new connections between oysters and the oysters will not grow into the bags.
If the energy of sea waves is high enough, then the outcome of such hitting will also lead to removal of newly grown oyster shells. That is why oyster shells become of correct shape since being placed in the CF basket (Picture no. 47 and no. 48).
In Pictures no. 47 and no. 48, one can see the shape of an oyster shell after five months in the prototype. It requires a lot of work to achieve such an effect at a farm at which bags with oysters are placed on traditional trestles.
4/14. Quality of oysters.
Pictures nos. 32, 33, 34, 35, 36, 37, 38, 39, 40 and 41 present oysters that, upon reaching a weight of 20g, were placed in the prototype.
Over 90% of oysters is of similar size, they have beautiful shape, and their shells are full of meat.
If 30% of oysters placed on trestles during the first selection meets those conditions, it is a good score.a
CF90% – Trestle30%
Each of the pictures nos. 35, 36, 37, 38, 39, 40 presents the contents of a randomly picked container from a CF basket.
5/14. Profitability of usage of the Crab Farmer system in oyster farming.
The calculations were made with regard to costs of construction of the prototype and by using the knowledge acquired during the tests at sea. The calculation refers to a single CF device and to a single trestle.
The calculations do not cover the purchase price of oysters for farming nor the prices of containers.
Their costs of purchase are low compared to the generated revenue.
The calculations show the revenue that can be generated from both farming systems.
When oysters reach weight of 20g, they are placed in bags so that each bag contains 140 oysters. In the case of CF, the oysters were placed in containers.
– calculations for the CF
The CF basket can hold 16 containers. In each container, we place 140 oysters. Thus, one CF device holds 2240 oysters.
Assuming that 20 oysters will die in each container throughout the whole cycle, there will still be 120 oysters for sale in each container.
This means that the CF device will have 1920 oysters at the time of sale.
120 X 16 = 1920
As one can see in Pictures nos. 38, 39, 40, 41 that were taken one year after placing the oysters in the prototype, over 90% of the oysters is of the highest quality. When the pictures were taken, the oysters reached size N°3 and N°2, i.e. they were ready for sale.
90% of 1920 equals 1728
The prototype holds 1728 oysters ready for sale.
Assuming that one oyster will be sold only for 1€, then all oysters in the prototype will sell for 1728€.
The cost of production of the prototype is 600€.
1728€ – 600€ = 1128€
After deduction of costs of purchase/manufacture of the CF device, the profit is 1128€ already after the first year.
In the case of a large-scale production, the cost of one device will most certainly be lower.
In subsequent years, the profit gained from each CF device will be 1728€.
The calculations do not include the cost of turning because when oysters reach size no. 3, the process is achieved through sea waves.
– calculations for trestles
One trestle can hold 5 bags. Each bag contains 140 oysters, which means that one trestle holds 700 oysters.
140 X 5 = 700
Assuming that 20 oysters will die in each bag throughout the whole cycle, at the end of the farming cycle there will still be 120 oysters in one bag.
This means that the trestle will have 600 oysters at the time of sale.
120 X 5 = 600
Usually, only 30% of oysters placed on trestles will be of the highest quality during the first selection.
Let us assume, however, that 90% of oysters in the bag are of the highest quality and that one oyster will be sold for 1€.
Then, all oysters on the trestle will sell for 540€.
90% of 600 equals 540
The amount of 540€ must be lowered by costs of turning for two seasons.
CF 1728€ – Trestle 540€
The above are the amounts achieved for the same area of the seabed.
6/14. Time spent on attaching containers to the trestles.
In order to attach containers on trestles or to remove those protection, the workers must spend about 40% of the time that is dedicated to working at sea during the outflow.
This happens when the bags are attached to trestles facilitated with rods for fixation of bags (The first part of the description, chapter no. 2. Mollusks farms in the world.).
When the bags are fixated to trestles with bands and hooks, it consumes far more time.
In the case of the CF device, workers will need not more than 5% of the time dedicated to work at sea during the whole outflow.
Cf 5% – Trestle 40%
It is a great time-saver.
7/14. Turning (Oyster mixing).
Turning is the most important operation that farmers must perform in order to obtain high quality oysters. It involves shaking the bag vigorously several times. When the bag is being shaken, oysters pound against each other which removes their newly grown shells. Each bag must undergo the turning process at least four times during one season. Usually, one bag weighs 8-14kg. If farmer has on the sea several hundred thousand bags, it is quite a challenge. Turning of oysters placed on trestles is hard manual labor.
The time that the worker needs to turn sixteen containers placed in a CF basket can be compared to the time that the employee needs for turning one bag placed on trestles.
Cf 16 – Trestles 1
The worker who uses a Crab Farmer basket rotating device will turn sixteen times more bags and will put much less energy into it than the worker at a farm at which bags are placed on trestles.
The CF basket rotating device is a simple gear with a crank. It is easy-to-use and most certainly cheap.
Workers who operate the CF during the turning will not even touch the bags.
Heavy physical labor turns into a walk on the beach.
If the energy of sea waves is sufficiently strong and until the oysters reach N°3 size, the turning will be achieved through sea waves.
8/14. Places poor in food for oysters.
It is possible to obtain high-quality oysters even at places that have scarce food resources. Thanks to turning of oysters, their shells grow at a slower pace. Meanwhile, the internal organs of the oyster do not stop growing and they fill the space inside the shell. In order to obtain high-quality oysters, they must be turned often.
By using the CF, it is easier to achieve that goal.
Obtaining high-quality oysters will take more time, but it is possible.
9/14. Stable construction (Dungarvan bay).
The CF prototype has been set up far away from trestles so that it can be exposed to direct effect of sea waves.
After five months from being set up at seat, the prototype does not immerse into the seabed. Rods of the stand that are located at level of movable supports still rest on the seabed.
There were no storms during that period.
On 16.10.17, Ireland was struck by the Hurricane “OPHELIA”. Wind speed of the hurricane reached up to 190km/h.
Then, on 27.10.2017, Ireland was struck by the Storm “BRIAN” and the wind speed was up to 90km/h.
Huge waves did not tip the prototype over.
As a result of the hurricane and the storm, the prototype immersed into the seabed at a depth of about 10 cm.
After the prototype was set up in a new place (09.02.2018), by the end of winter, there had been a whole series of storms weaker than Brian. The prototype, as a result of those storms, immersed on one side at a depth of 5cm.
Farmers who will use the CF does not need to be afraid of losses caused by storms.
10/14. Extracting the CF from the seabed.
From time to time, the CF must be taken out from the seabed.
In case of the CF system, it is very convenient because the containers with oysters can be left in the basket during lifting. That is why the work can be performed at any spare moment and ceased at any time. Without any consequences for the organization of work at the farm.
Extraction of the CF requires only three people. One person operates the extracting machine (a tractor or a boat with a crane) while the other two attach the pulling rope and position the device during the operation of lowering to a designated spot.
If necessary, those employees will be able to clean the movable supports from sand before the device is lowered.
The farmer who extract the trestles from the seabed must perform three operations:
– remove bags from trestles
– extract trestles from the seabed
– set up trestles again
In the case of a CF system, the farmer sets the device by doing one operation:
– pull out from the seabed and when lowering immediately put the device in the right place.
Only three people are needed to perform this work.
11/14. The Crab Farmer in deep water.
Every farmer knows how important it is that the oysters have sufficient amount of food.
There are many places with plenty of food for oysters, but the water there is too deep for a trestle system.
The CF, which is adapted to operate in deep water, will make it possible to use such places for farming.
In order to secure the CF device that was set up in deep water against effects of storms, it must be clustered in a group.
For instance, by setting up four devices in one group. Devices should stand next to each other in two rows, two devices per each row (Figure 49b).
Description of Figure 49b.
1- CF device
2- element joining CF devices
3- element joining CF devices
Next, to join them with each other so that they form one rigid block. This way, we will efficiently secure them against effects of storms.
12/14. By using the CF system, we improve working conditions and safety
People working in
a heavily bent posture (Picture no. 50) are a pretty common sight at oyster
farms. Bags with mollusks are usually at height of 40 cm above the seabed.
Workers spend from
several minutes to several hours in that posture, almost every day. The posture
they work in may lead to spine injuries.
The CF ensures
working in a standing posture. The containers with oysters are 80 cm above the
Another hazard to health and
life of people working at the farm is posed by short vertical rods used for
fixation of containers.
Falling onto a vertically protruding steel rod can be fatal to the employee.
13/14. Lighter work.
Due to the fact that the Crab Farmer system will greatly facilitate work at an oyster farm, it will be easier to find people eager to work there.
14/14. Environment pollution.
Containers placed on standard trestles generate a great amount of contamination. Since the containers are frequently skewed onto protruding rods, they will eventually become damaged. Weakened structure of the bag is also exposed to damage caused by weather conditions, storms.
Rubber bands used to secure the bags are another problem. When damaged or improperly fixed, they slip from the rods. In such cases, water carries away the bag and the rubber band and contaminates the sea and beaches.
The beaches are
periodically cleaned from trash.
The trash that is carried to
the depths of the sea will be collected by whales
The trash from oyster farms is collected on beaches within several kilometers from the farms.
Picture no. 55 shows rubber bands used to fix the bags on trestles that have been collected within 5 km from the oyster farms.
When the Hurricane OPHELIA struck, water in the Dungarvan bay washed away about 6000 bags from trestles. It is difficult to assess the number of bands and to what location they were washed away.
This problem is non-existent in the CF system because containers are in closed compartments of the basket.
On 01 December 2018, a new batch of oysters was placed in the prototype for another test.
When the oysters were inspected on 10.06.19, it appeared that some elements of the structure of the prototype were bent.
11.1 The mechanism of prototype damage
Picture no. 56 shows bent rods of the stand. The bent sections of stand rods have been marked with short red lines.
The direction of bending of the rods proves that the prototype was pushed parallelly to the seabed. In Picture no. 56 – from left to right.
The anchors immersed in the seabed worked like a lever and, due to the pushing movement of the prototype, they bent the steel rods of the stand. The bent rods have a diameter of 25mm. It requires great force to bend such thick rods within such a short section.
In the Dungarvan bay, it could only be caused by a large vessel or tractor.
The movable supports were bent as well.
– the movable support on the left side in Picture no. 56.
The support got bent because the surface of that support was being immersed in the seabed while being pushed (in the picture, from left to right).
– the movable support on the right side in Picture no. 56.The support got bent because the
of that support was being immersed in the seabed while being pushed (in the picture, from left to right).
The bent movable supports in Picture no. 56 have been marked with short yellow lines.
The other side of the prototype is visible in Picture no. 57. Rod of the stand and the movable support are bent only on one side. The bending angle on this side of the stand is much lower than on the other side of the prototype.
The direction of bending of all rods suggests that the force that pushed the prototype was not distributed on the whole surface of the prototype, but only one side of it. The force was applied on the side of the prototype where the rods bent at a greater angle. In Figure no. 58, the arrow marked with number (5) shows the probable place of application and direction of the force that pushed the prototype.
When pushed, the prototype was rotating around anchor (1). That is why the anchor did not bend.
Anchors no. 3 and no. 4 (Picture no. 56) bent at a greater angle compared to anchor no. 2 since they traveled a greater distance when pushed.
Designations for Figure no. 59.
1- Anchors fixed in the prototype.
Bent elements of the stand are in this case made of round rods with a diameter of 25mm. The rods bent within a section of 20cm. The anchors that are stuck into the seabed are 25 cm long. The seabed at the place where the prototype was set up consists of sand
Anchors were arranged in the prototype of the stand according to Figure no. 59.
Red color represents sections of stand rods that got bent.
11.2 What did cause the bending of the rods?
were the rods of the prototype bent by sea waves?
Picture no. 60 was taken just after the Hurricane Ophelia and the Storm Brian. There have been no stronger storms since then. Despite such a great energy of sea waves, they did not bend the rods.
– a collision with a vessel or a tractor?
This scenario is the most probable one. It requires a great force to bent steel rods with a diameter of 25mm within such a short section.
There is no visible damage in other parts of the prototype
11.3 Reinforcement of the construction of the tripod and movable supports.
Accidents happen everywhere and it is impossible to avoid them. In order to protect the CF device against damage in such situations, we can reinforce the construction of damaged elements.
– construction of the tripod
In the current version, the construction of the stand in the CF is strong enough. A hurricane (190km/h) did not damage the prototype in any way. That is why reinforcement of the construction of the stand does not seem necessary.
Fixation of two additional anchors on each side of the stand will distribute the force pushing the device onto more points of support, from four to eight such points.
Such a solution should be applied in the CF devices set up in deep water. Additional anchors will ensure better stability of the device against the seabed. Thus, it will be safe to attach a boat to CF devices during loading operations of oysters or during performance of other activities.
Designations for Figure no. 61.
1- Anchors fixed in the prototype.
2- Additional anchors that can be fixed optionally
– movable supports
The construction of movable supports in the prototype (Figure no. 10) is too weak and of improper shape!!!
The movable support should have a shape that allows staying on the surface of the seabed instead of immersing into it. If the movable support is already under the surface of the seabed, its shape should allow the support, when pushed, push the device towards the surface of the seabed.
Thanks to the plain (A) (Fig. no. 62), the counterweight (1) will not cause immersion in the seabed when pushed (in Figure no. 62, from left to right). The counterweight will behave like a ski on snow.
When pushed in the opposite direction, the task is performed by element (5) in Figure no. 62.
Element (5) is also to reinforce the construction of the movable support and will not allow it to bend when pulling out from the seabed.
During extracted from the seabed, the movable supports are bent by wet and heavy sand. Construction of the supports should be sturdy enough to prevent deformation or breaking of supports during the extraction from the seabed.
The method applied in the prototype (Picture no. 10) and presented in Figure no. 62 for fixation of movable supports to the stand guarantees correct operation of the movable support. Sand will not interrupt the rotation of the support around the rod of the stand.
Designations for Figure no. 60.
2- rod around which the movable support rotates
3- element that all elements of the support are fixed to
4- plane of the movable support
5- elements reinforcing the construction of the movable support
6- lock attached to the support element no. 3 defines the maximum inclination of the support during cleaning
7- lock attached to the stand rod no. 2 defines the maximum inclination of the movable support during cleaning
A short description of videos and pictures that can be found on our gallery
Videos and pictures uploaded onto the drive are grouped in eight folders.
Folder 1 – Principle of operation of the Crab Farmer.
The first folder contains five videos that show how individual elements of the prototype work.
1- How the CF works
The video shows the construction and the general principle of operation of the CF.
2- Placing of the containers in the CF.
The video shows how to place containers in the CF basket.
3- Rotation of 16 containers
Turning of sixteen containers placed in the CF basket.
4- The CF under sand
Extraction of the prototype from sand or sludge.
Weight of the counterweight should be higher. After slipping from sand, the movable supports should return to horizontal position.
5- The CF after extraction from sand.
The movable supports returned to horizontal position after removal of sand that got stuck to them.
Folder 2 – Details on construction of the CF prototype.
Movable supports and anchors.
Fixation of the basket to the stand.
Lock to the basket door (closed door).
Lock to the basket door (unlocked door).
Protection of the basket lock (secured lock before lowering).
Protection of the basket lock (lock unlocked).
Basket lock (unlocking of the basket).
Such fixation of the movable supports will prevent the mechanism from being jammed because of sand.
The fixation point for extraction of device from sand or for loading onto means of transport.
The first Crab Farmer at sea.
Folder 3 – Model of the CF basket rotating device.
The third folder contains pictures of the model of the device used to rotate the CF basket, as well as a video about its usage.
The basket rotating device should be constructed as a two-stage gear.
Folder 4 – Pictures of the prototype and oysters taken on 11.10.17.
Pictures were taken five months after setting up the prototype in the Dungarvan bay.
The oysters are of correct shape, with shells full of meat.
During that period, the prototype is not immersed into the seabed. Rods at the level of movable supports still lie on sand.
There were no strong storms during that period.
Folder 5 – Pictures of the prototype, taken after Hurricane OPHELIA and Storm BRIAN.
Pictures c1, c2, and c3 in the fifth folder show oysters from three containers placed in the prototype. In each of the containers, over 90% oysters have a correct shape.
Pictures d1 and d2 show that the prototype was immersed into the seabed at a depth of about 10 cm due to the hurricane.
Folder 6 – Extraction of the prototype from the seabed.
The sixth folder contains a movie recorded during the extraction of the prototype from the seabed.
Folder 7 – Photos of oysters, March 2018.
The pictures show the quality of oysters. Over 90% of oysters is of correct shape and their shells are full of meat.
Folder 8 – Pictures of the prototype taken on 30.06.2018.
In February 2018, the prototype was moved to a new place. Since then, there has been a series of storms. The prototype was set up far away from trestles, so it was exposed to direct effect of sea waves.
Pictures taken on 30.06.2018 show that storms that took place from February to June 2018 did not cause any damage.