So it was brought to my attention that although many people know we specialize in making plankton nets, not everyone knows exactly what specifications they need for their nets. So I decided to write an article on the subject in the hope of clarifying a few things.
First of all, it's very important to know whether you're conducting a brand-new study or whether your research is based on a previous study with defined parameters.
If you're doing a study based on a previous study, it's extremely important that the net you order has the same specifications as the one used in the previous study.
On the other hand, if you are starting a new study, the actual specifications of your net will be based on the flow of water through the net, the size of the organisms you want to catch, your towing speed and the type of tow you will be doing.
Here is the list of specifications we will need in order to offer you the right net for your needs:
- Measurement units
Since nets are used for scientific research, it is common practice to use the metric system. Most measurements are given in centimeters, meters and microns.
- Mouth opening
Most standard plankton nets have a circular mouth, so we need the diameter you need. The diameter will determine the surface area of the mouth, and therefore the flow of water through the net at your given towing speed.
- Net length
Most plankton nets follow a standard rule based on the mouth diameter: 1:3, 1:4 and 1:5. That said, we can build any ratio that suits your needs. The length of the net affects the volume of water inside the net at any given time. Combined with the mesh size, its percentage of open area and your towing speed, it will tell you whether the water flow is sufficient to pass properly through the net and through the cod end bucket.
- Mesh size
Mesh size is directly correlated to the size of the organism you're trying to catch.
As a general rule, your mesh size should be 10 % smaller than the average size of the organism you're trying to capture.
- Towing speed
Towing speed will generally be related to net dimensions, mesh size and mesh opening percentage. Speed generally varies between 1 and 3 knots. Any faster and the net may burst; any slower and the water flow will not be sufficient to pass through the cod end bucket.
- Towing type
There are 3 types of tows: horizontal, vertical and oblique. When towing from a moving vessel, you will mostly be doing horizontal and oblique tows.
No additional equipment is required for horizontal tows.
For oblique tows, you will usually need extra weight. Please mention it so that we can adapt the net to support that weight.
For vertical tows, we recommend adding a small weight in the cod end bucket to add ballast and help it sink below the net.
Here are a few bonus questions to ask yourself before going ahead with the purchase:
- How many units do you need?
Most people tend to order the minimum number of nets they need, but this can cause problems. It's not uncommon for customers to contact us during their field survey indicating that they have damaged or lost a net and need a new kit as soon as possible.
For this reason, we recommend that you always order at least one additional net, and ideally 2. This way, you can carry out your study whatever happens.
- Is there a high risk of damage between uses?
Depending on where you're conducting your survey, there may be several ways to damage your nets. On seagoing vessels, many objects on deck can be very sharp, which can easily damage your research equipment. That's why we recommend you buy a protective carrying bag to reduce the risk of damage between surveys.
- You already have parts
Most researchers tend to study the same organisms year after year, which is why they buy the same equipment again and again. All our nets, buckets and rings are of standard design. So if your net and bucket are lost or damaged but you still have your ring with bridle, you don’t need a new ring with bridle and can order just the replacement net and bucket.
- Can you easily make repairs during your study?
Damage often occurs during field research. It's unfortunate, but a reality of the situation. Now, the question that remains to be answered is: can you or can you not carry out repairs during your field survey?
Most of our metal parts are made of stainless steel, but for certain nets and situations where overall weight is an issue, we sometimes use aluminum.
Stainless steel is fairly easy to repair on a ship, most of which are equipped with the appropriate equipment to carry out repairs at sea.
Aluminum, on the other hand, is a little more complicated, and most ships are not equipped to carry out these repairs at sea.
This is very important to know before ordering your equipment.
I know this article isn't a detailed guide to using plankton nets, but it is a quick guide to the most common questions I get from buyers.
I hope this helps some of you, and please don't hesitate to contact me directly at info@filmarnets.com if you have any questions or would like to place an order!
Have a great day
Francis Brisebois
