Table of Contents

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

– licenses

– 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).

Picture no. 47
Picture 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.

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.

140 X 16 = 2240

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€.

CF 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€.


CF 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


Trestle 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 labour 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.

Fig. 49a The CF in deep water.

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.

Picture no. 50

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.

Picture no. 52 Trash from an oyster farm. This is a common view on beaches near oyster farms.
Picture no. 53 Trash from an oyster farm
Picture no. 54 Trash from an oyster farm
Picture no. 55 Trash from an oyster farm

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.