Table of Contents

1. Admission

All over the world oysters are considered as a luxury commodity.

Meals prepared in the restaurants of these mollusks achieve very high prices. Breeding these mollusks requires a lot of knowledge and appropriate conditions for their growth.

Oyster farmers most often set up their farms in estuaries or their close proximity.

These places bring in large amounts of food which feed on oysters. 

Such places are most prized by farmers. Not always, however, these places can be used.


The two most important conditions for a high-quality oyster is a full shell of meat, and the second condition is the correct shape of the oyster shell.


To fulfill the first requirement farmed oysters should be put in place where there is plenty of food.

Fulfillment of the second condition requires that farmers perform a range of treatments that are aimed at ensuring that the correct shape of an oyster shell.


By joining the work on the project Crab Farmer my goal was to put as much as possible oysters in the smallest area of the seabed. Ensuring a convenient access to them. This will allow better use of places rich in large amounts of food.


Very often farmers increase their breeding renting a space in the sea from people who are not engaged in farming.

Many farmers have their farms all over Europe and is still looking for new places to set up new farms there.

This indicates that the market is in still need of more oysters.


And this is the result of my work. 

2. Mollusks farms in the world

The Internet is a rich source of information for farming mollusks.  I have visited many companies and engaged in the production of mollusks all over the world. Online breeders give summarized information and visual description so that we can understand the methods of their work.

 The sea conditions affects the way of breeding. 



In locations where tractors can’t reach, their work is taken by boats

Many farmers use this system of plastic bags or boxes with holes. Such a solution makes easier to perform many tasks associated with breeding.


On the picture from left plastic bags and boxes on the right

Containers shown in the pictures above are mounted on trestles, set in the column at the bottom of the sea.

On the picture single trestle
Trestles set in the column on the bottom of the sea

In practice, there are two ways to attach containers to the trestles:


      The first way:  the containers attached to trestles with the rubber bands with two hooks. 

This method consists in wrapping rubber bands around the rod and connecting two adjoining containers. 

On the picture rubber band with two hooks
Attaching containers to trestles using the rubber bands with two hooks
Containers attached to trestles with the rubber bands with two hooks.
  • The second way: containers mounted on trestles using rubber bands wrapped around short rods protruding from the trestle.

 First, the containers are placed on rods projecting from trestles and then the rubber band is wrapped around the rods tightly and stretched to prevent the container from slipping off the rod. 

Trestle with rods for attaching bags.
Attaching containers with rubber bands and rods projecting from trestles

There are other ways how to place the mollusks at sea: 

boxes filled with mollusks hung on ropes attached to poles driven into the bottom of the sea
containers stacked on the bottom of the sea
mollusks in cages are lowered to bottom of the sea by a crane mounted on a boat
oysters are hung on wooden structures

In conclusion it is usually the conditions of the place selected for breeding, determine the choice of the appropriate method.

3. Description and principle of operation of Crab Farmer (CF).

Placing oysters in plastic containers during their growth at sea facilitates work on the farm.

It makes it easier to observe the growth of oysters, transport them as well as perform a number of operations necessary for ensuring their suitable growth conditions.


I chose the dimensions of CF in such a way to be able to use the containers already used by farmers.


Dimensions of the presently used containers:

   bags 100x50cm

   boxes 8x50x86cm


1” (inch) = 2.54cm


Explaining the principle of operation of CF, I will use simplified design drawings. In the figures, each of the basic elements was marked with a different colour

Fig. 1 Crab Farmer.

CF is a simple device which consists
of three cooperating elements: 

tripod, basket, lock

3.1 Tripod.


Tripod is a simple steel structure connecting all elements of CF design (marked blue in figures).  

Fig. 2 Tripod.

Anchors mounted to the tripod (marked red in Fig. 2), will help CF maintain the set position in stormy weather. They might be steel bars with the
same section as tripod elements. The length of anchors should be approx. 25cm.

To eliminate fully or at least limit
considerably CF’s sinking in the seabed under the influence of its own weight and the weight of the oysters placed in basket compartments, that weight needs
to be spread over a suitably large area. It can be done by mounting supports to
the tripod (marked orange in fig. 2).
The structure of supports should be adjusted to the material of the seabed. If it is sand, the supports can be made of steel sheets secured against corrosion
and reinforced with steel bars. The steel sheets can be replaced with plastic
elements. If the seabed is made of muddy or clayey sludge, we can try to build the supports as rounded floats made of
light plastic and filled with air. The supports should be mounted symmetrically on both sides of the tripod as close the outer edge as possible (fig. 2). 

Their size should be adjustedto weight and the material of the seabed.

The supports mounted to the tripod will protect the seabed under CF basket against erosion. The flowing water will change its course bypassing the encountered obstacle.

If the speed of the water stream will be so big that the flow between the obstacle (CF basket) and the
seabed will be turbulent, the sand from under the obstacle will be hollowed out. Water will hollow out a hole under the obstacle.The supports mounted to the tripod will constitute a barrier for the water stream which will flow under CF basket and prevent hollowing out the hole.

The supports mounted to the tripod will constitute a barrier for the water stream which will flow under CF basket and prevent hollowing out the hole.

Fig. 3 Erosion of the seabed under CF basket.
Fig. 4 Protection against erosion of the seabed under CF basket.

Smooth surface of supports will make it difficult for the sand carried by water to accumulate under CF basket

3.2 Basket.


Two-level basket (red in the figure) mounted to the tripod has the possibility of full rotation (360°) around its axis in both directions (fig. 5). 

Fig. 5 Mounting the basket on the tripod.

On each level the basket has four compartments. On upper level compartments I, II, III, IV and on lower level compartments V, VI, VII, VIII (fig. 5). 


In order for the compartments to accommodate both types of containers described at the beginning of chapter 3, I assumed that space inside a compartment will have the dimensions of 23x60x105cm. 


The containers placed in compartments will be marked yellow in figures. 


Each compartment can accommodate stacked one upon the other two boxes with dimensions 8x50x86cm (picture 6). 

Fig. 6 Arrangement of boxes in basket compartments.

Stacked, they are 7cm lower, 10cm narrower and 19cm shorter than the compartment. Free space will enable putting the boxes in and out of compartments.

The walls of plastic boxes should be rigid to such an extent that the stacked boxes filled with oysters only slightly changed their shape. In this way the necessary space for oyster growth will be ensured

Fig. 7 Stacked plastic boxes filled with oysters.

It is very similar in the case of bags (100x50cm).If there is approx. 20kg of oysters in a bag, the compartment will accommodate only one bag.However, if the weight of oysters in the bag is not too big, then we can place several bags in one compartment. 

If necessary, each compartment may be divided into two parts so that containers would not be stacked one on the other. This should however be considered in the final version of basket structure.

Crab Farmer enables quick and convenient access to containers (bags or boxes) placed in its compartments.  

All compartments located at one level have one common closing mechanism.  When opening, we make available all upper-level compartments at the same time.

I propose two solutions of basket closing mechanisms (closing mechanisms will be marked grey on consecutive figures).

Solution one gate valve

We open a basket by pulling back the gate valve. (Fig. 8, 9, 10).

Fig. 8 The basket gate valve in closed position – view from above.
Fig. 9 Pulling back the gate valve. Side view.
Fig. 10 The basket gate valve in open position – view from above.

Solution two flap gate

Compartments are opened by lifting the flap gate (fig. 11).

Fig. 11 Basket closed with a flap gate.

In order to make available the bottom-level compartments now, we close the upper compartments and lower the lock to the lower position (fig. 15). 

The basket is unblocked. We rotate the basket around its axis by 180° (fig. 12).  

Fig. 12 Change of compartments location.

Next, we block the basket by lifting the lock to its vertical position. Now the compartments which were at the bottom of the basket are in the upper position and we can open them.

When rotating the basket, oysters will slide down accumulating in the lower part of containers (fig. 13).

Fig. 13 Dislocation of oysters in a container during the rotation of the basket.

Basket rotation is possible only after
lowering the lock to its lower

position (fig. 15).

In order to spread oysters evenly in containers located in the basket, slowly rotate the basket till achieving the expected result. 

It is also possible if we want to do that separately with each container.  If a compartment in the upper location is empty, there is an easy access to the compartment located directly under it.



3.3 Lock


The lock (marked green in fig. 14) is hinge-mounted to the tripod. It can be made and mounted as a separate element or it can be mounted permanently and constitute a moving part of the tripod.

The function of the lock is to determine basket location in relation to the tripod as well as take over static and dynamic basket loads caused by external water pressure and the weight of oysters.


Fig. 14 Lock in the position blocking the basket.

Basket rotation is possible only after lowering the lock to its lowerposition (fig. 15).

Fig. 15 Lock in the position: basket unblocked

4. Installation of the Crab Farmer at sea

When mounting CF at sea, first tripods with already mounted supports and a lock must be set up. Basket is the last element to be mounted.


CF will work in the already tried-and-tested arrangements at sea. 

Fig. 16 and 17 show the place, indicated with a green line, from which workers can operate CF.


Installing CR in deep water, where access in only possible from a boat, one needs to remember about the direction of water flow during the low tide and rising tide. 

Fig. 16 Two-column arrangement.
Fig. 17 Four-column arrangement

5. Destruction by corrosion

The choice of materials with which The Crab Farmer will be made is a complex issue. You have to take into account the mechanical properties, weight and corrosion resistance of the material.

Crab Farmer contains elements of different cross-sections because of the rapidly progressive corrosion of carbon steel in the marine environment, elements with small cross sections should be made of materials that are resistant to corrosion.

A good solution is the use of plastics.

With a wide variety of plastics, you can choose a material with suitable mechanical properties satisfying the demands of working in an environment of seawater.

Another advantage of plastic compared to the steel is its low weight.

To make the right choice you should seek advice from experts in the plastics.

In the case of using carbon steel rods you should avoid bending the material. Without going into much detail:  bent sections will cause internal stresses and small cracks. As a result it will corrode much faster than the rest of the rod. The lifespan of a bent carbon steel rod at sea can be half as long as the same cross-section not subjected to bending.

6. Sinking into the bottom of the sea

Trestles loaded with containers sink into the bottom of the sea. This is because they are based on a very small area (trestle bent leg). On the figure no.18 the bent, part is marked by a red circle.


1” inch = 2.54 cm

1 (lb) pound = 0.45 kg 

Fig.18 Traditional trestle loaded by containers

The length of bent leg on which the trestles stands is 20cm and the diameter of the rod trestle is made of is 2cm. The total area of the four legs on which trestle lean against the bottom of the sea is:


2cm x 20cm x 4 = 160cm².


Trestle weighs about 30kg. We assume that in one container is 12kg of mollusks. So, five containers that trestle can hold, weighs 60kg. The total weight trestle and five containers is 90kg.


For trestle emphasis on 1cm² of seabed is 0.5625 kg / cm ².

The same calculation for CF.


The CF weight depends on the material from which it is made.

I assume that the weight of the CF (in case of use carbon steel) will be about 110kg. Its compartments can accommodate 16 containers of mollusks. Assuming, as in the previous case, that one container weighs 12kg, a total weight of 16 containers is 192kg.

So the weight of CF and 16 containers will be 302kg.


This weight will be based on two surfaces of supports, mounted to a stand with a total area of 5600cm ² and on the surface of the lower rods from stand structure which is 1660cm ². 

Dimensions to calculate the surface area on which CF construction is based (lower rods from stand construction) are referred in chapter No. 9. 


For CF emphasis on 1cm² of seabed is 0.0416 kg / cm ².



                    0.5625 kg / cm ²  :  0.0416 kg / cm ²  =  13,5


Pressure device CF on 1 cm² area of the seabed is 13.5 times smaller than the pressure trestles.


The larger the supports, the better protection against the sinking the CF into the bottom of the sea.

The streamlined shape of the supports will reduce the effect of erosive action of water.


However, the problem of erosion of the seabed does not cease to exist. Sand detached from the seabed and transported downstream can overwhelm the CF. Sand moved by water can prevent rotation of the basket.

I planned that the distance from the lowest point of the basket rotation track to the level of upper horizontal bars of tripod construction will be 5cm (Fig. 19). 

Fig.19 Stand in the section of the seabed

In Figure 19 the dotted line circle tracks the distance of the basket axis rotation. The horizontal dashed line is the lowest position that the basket is during the rotation along the tripod.


Gray rectangle is the level of the seabed where the Crab Farmer has been assembled. Orange rectangle is the sand that can be applied by the water as a result of erosion of the bottom of the sea.



So, if the CF sinks to the bottom of the sea or erosion, the seabed reaches the upper rod in stand structure (Fig. 19) means that only 5cm is left to be able to rotate the basket.


If the rotation of the basket is already impossible it is time to lift CF from the sand.

Fig. 20 Pulling out Crab Farmer from the seabed.

For this purpose, we use a lifting device mounted to a tractor or boat.

When pulling, force must be applied to the stand alternately on both sides in the place of the mounting basket. During the lifting process the supports attached to the stand will carry the sand that is on the surface of the structure and hollow pits. The pits should be filled back in.


When removing the CF from seabed the compartments can be filled with the bags.




When pulling CF out from the seabed, the biggest resistance will come from the material located directly on the device support. There is an easy way of solving this problem

Fig. 21 Structure of the CF support mechanism. Cross-section

Fig. 21 shows the cross-section of CF support mechanism.

a material deposited by water due to erosion of the seabed (orange colour) b bars preventing full rotation of both parts of support around a bar (e) c two parts of CF support d counter-weight (each of both parts of support has a counter-weight) e bars to which both parts of the support are mounted rotationally f structural bar of the tripod to which bars are mounted (b)

Fig. 22 Structure of the CF support mechanism. View from above

The plane of CF device support (blue rectangle in fig. 22) should be divided into two parts (c). Each of those parts should be mounted rotationally on lower bars (e) of tripod structure running along the CF device (fig. 21).  

In external parts of both halves of supports (c) a counter-weight has to be mounted (fig. 22 shows a narrow rectangle (d) on the edge of a support). When the surface of a support is empty, the counter-weight (d) maintains the plane of both parts of the support (c) parallel to the plane outlined by the bars (e) of the CF tripod structure. 

The counter-weight may have the form of a concrete block.

The principle of operation of CF support is very simple

Fig. 23 Operation of support mechanism when pulling CF from the seabed

When pulling CF out, both parts of the support rotate around bars (e) under the influence of material deposited by water. The material slides down from the surface of both parts of the support. The surfaces of supports are already empty.

Now, the counter-weight mounted to both parts of the support operates with greater force and rotates the support in the opposite direction. Both parts of the support are based on bars (b).

This solution will be particularly useful in deep water.

If you use movable support during the pulling out of sand, the force shall be applied on both sides of the basket while simultaneously.

6. The Crab Farmer dimensions

As I said in the third chapter, I assumed that to place the mollusks in the sea, we can use containers with dimensions:

– Boxes 8x50x86cm       

– Bags 100x50cm.

This will facilitate the comparison of CF with systems currently used on mollusks farms.

I calculated the compartment dimensions 23x60x105cm (fig. 21).

The height of compartment is23cm.

This height of compartment is sufficient for containing a bag in which is about 25kg mollusks or two boxes which is the total height of 16cm.

The width of compartment is 60cm.

Width of both types of containers is 50cm. 10cm of free space will facilitate removing and inserting of containers into the compartment.

The length of compartment is 105cm.

Length of bag is 100cm and length of box is 86cm.

CF compartments allow farmers to use both traditional bags or boxes as well as completely new containers.

The shape and dimensions of the containers can be modified and adapted for new opportunities offered by the device CF.

In the figure no.21, the dotted line indicates a track which the CF’s basket circles while rotating around its axis.

The distance from the plane defined by the upper horizontal bars of the stand structure, the lowest point of the basket rotation track is 5cm. If the bottom of the sea does not exceed the level of this plane rotation of the basket is possible (fig. 21). Thus, the upper tripod’s horizontal bars are the indicator of the CF if a basket rotation is still possible.

Fig.24 The CF dimensions

By changing the dimensions of the CF, it can be adapted to the needs of the farm (for example adjusting the compartments for types of used containers). For farms that only use the system of boxes with dimensions 8x50x86cm, you can customize the design of CF so that compartments had dimensions of 20x60x90cm (Fig.25).

Other parts of the CF structure remain unchanged. The height CF in this case will be 102cm

Fig.22 The dimensions of CF on the assumption that in the compartments will be placed boxes measuring 8x50x86cm

I will present a simple way of how to divide CF basket compartments. 

Division of CF basket compartments may be done with a plastic string mesh. Plastic string is a light material, very strong and resistant to the destructive impact of salt water

Fig. 26 A mesh separating CF basket

Fig. 26 shows black lines which signify the arrangement of strings making up a mesh. The yellow rectangle is the outline of the oyster container. 

One end of the mesh must be mounted permanently on the rear wall of the compartment in point A shown in fig. 27.

We place the first container in the compartment. 

Then fasten the loose end of the mesh to the basket door in point B shown in fig. 27 for the time of placing the container in the compartment. Thanks to that the mesh will not be in way when placing a container in the compartment.

Fig. 27 Placing the first container in CF basket compartment

When the first container is already in the compartment, the loose end of the mesh is fastened to the opposite rear wall of the compartment in point C shown in fig. 28. And now, we place the second container in the compartment

Containers in the compartment are separated with a mesh from one another and do not pressure one another

Fig. 28 Placing the second container in CF basket compartment

7. Summary

CF allows to increasing cultivation, three times without the need of
development additional area of the seabed


Compare the CF to trestles currently used by many companies.


Fig. 29 Traditional trestle with containers

Traditional trestles are about 270cm in length and can accommodate 5 containers

Fig. 30 The CF basket filled in containers

The CF 268cm length can accommodate 16 containers.

CF 16   –  Trestle  5


Until now as large increases in cultivation was only possible through the development of new areas of the seabed. Hence the need to seek new suitable sites on the sea and obtaining of necessary permits for the establishment of a new farm. With the foundation of the new farm, it was necessary to purchase or the rent of new land for workshops and warehouses, equipment, employment and training of new employees.

Using the CF, farms increase breeding three times, avoiding most of these problems and expenses. 

Through the use of CF many places so far unprofitable due to too small area can be developed for the benefit of farmers and consumers.



 Improving the conditions for growth of mollusks.


With Crab Farmer you can put less mollusks to containers. In this way we provide them more space to grow. At the same time, we are not reducing the size of the breeding. 

The sea current moves loosely placed containers in compartments. This way mollusks are mixed by water in containers.

The CF will reduce significantly their tendency to grow together as they attach to each other. This will prevent a decline in the market value of breeding oyster



 Saving time. 


The use of rubber bands or hooks to attach containers filled with oysters to trestles takes employees around 40% of their total working time during a single outflow.


In the case of CF, it will take no more than 5% of the time.



CF 5%   –  Trestle 40%


 It’s a big time saver.

Turning bags. The possibility of rapid mixing of mollusks in the containers. 


The possibility of rotating the basket of the CF allows to mix mollusks without having to remove the containers from the basket. By means of a simple device (Fig. 31) one person without much effort can rotate the basket.  

Fig. 31 The device for rotating the CF basket

The torque is transmitted from the crank (a) by the gear arrangement (c) to the basket (b).

The device is mounting to a tripod CF using the grip (e).


Rotating the basket, you can mix sixteen containers at the same time. So, one worker supports CF at the same time does the work of sixteen people turning bags placed on traditional trestles. 

 The Crab Farmer in deep water


CF can be used effectively not only during low tide where people can work walking on the bottom of the sea.

This is also possible when the access is possible only by the boat.When the CF is set in a column, the staff can go through the entire length of the column by the platform (Fig. 32). 


Fig.32 The CF in deep water

Platform for staff should be at a distance of about 1 meter above the lowest water level (0.0 meters) at low tide (distance X Fig. 26).

Then the time to work on the sea will be longer.

By the use of the CF we improve conditions and safety of working 


By the use of the CF we improve conditions and safety of working
People working in a bending position (photo above) is a very common position for mollusks farmers. Containers with mollusks are typically located at a height of 40cm from the ground.
Workers spend nearly every day in bend position from several minutes to several hours. Position in which they work is the cause of spine damage.
CF provides work in an upright position. Containers of mollusks are at a height of 80cm from the ground.
Another threat to the health and life of the people working on the farm are wrestles with short rods for fastening containers.

 If the worker fall, on protruding vertically from the trestle steel rods it can be fatal. 

With CF we avoid destroying containers and environmental pollution


Containers mounted to traditional trestles, generates a large amount of impurities. A natural consequence of frequent sticking containers on protruding rods is their tearing. Weakened structure of the container is additionally exposed to damage by weather conditions, for example storms.

Rubber bands used to secure the bags are another problem. Improperly attached or damaged, slide off the bars. In such a situation container devoid of security is lifted with the flow of water, polluting the sea and beaches.


Problems of this type do not relate to the CF because the containers are in the closed compartments. 

8. Orthographic View CF

View from above

Front View

Side view