Introduction

Being able to anticipate the instrument’s weight in water is crucial for deployment purposes. Designing underwater rigs and buoys is an important part of the deployment and is depending on the instrument’s weight in and out of water.

At sea, where oceanographic instruments are often used, buoyancy is a well-known force.
Buoyancy is the upwards acting force exerted by a fluid (water), following Archimedes’ Principle this force is equal to the weight of the displaced fluid.
Giving us:

Apparent immersed weight = weight of object – weight of displaced fluid,

Where the weight of displaced fluid is dependent on the displacement volume.
Meaning it is constant when the object remains the same, no matter what is inside the object (batteries in our case).

However, the weight of the object naturally has changed. So, now it is just a simple question of addition and subtraction.

Calculating for your instrument

You can find bouncy data on our website. Under “products” you can find your specific instrument and under “technical documents” “technical drawings” you can find a general assembly drawing containing the information needed to calculate the buoyancy.
If there are no weight details on the drawing please contact Nortek Support and we will get you sorted.

Because of the many battery combinations available, we only state the weight of the instrument itself and as mentioned the additional weight is simple addition.
Weight information of the different batteries can be found on our websites under products and spare parts.

Examples
Following are a couple of buoyancy examples:

We want to find the weight in air and water for the Signature 500, both using standard canister with the standard 180Wh battery and with the extended canister using the 540Wh battery.

Data for the Signature 500 (kg):

• Weight in air/water with standard canister (no battery): 6,4/-0,3
• Weight in air/water with extended canister (no battery): 8,6/-2,5

Data for 180Wh/540Wh battery (kg):

• Weight in air: 1,8/5,1

Giving us:

Signature 500 standard canister w/ 180Wh battery:

• Air: 6,4 + 1,8 = 8,2 kg
• Water: -0,3 + 1,8 = 1,5 kg

Signature 500 extended canister w/ 540Wh battery:

• Air: 8,6 + 5,1 = 13,7 kg
• Water: -2,5 + 5,1 = 2,6 kg