Yes you need to be stationary. The weight on the disk needs to be sufficient to make the disk sink vertically, and so the weight will vary depending upon the matarial you make the disk from and the strength of the current
. We suggest 200g as a minimum, but it may need to be more. The weight can be anything to hand and it can be added to as circumstances dictate.
Our intention is for sailors to measure the Secchi Depth
whenever and wherever they can do so conveniently - We don't want the project to be a burden. We want it to be interesting and enjoyable. Over the years a database will develop with readings taken by many different sailors in many different places, and in time we will get regional overlap from year to year.
That said, there are likely to be two categories of measurement:
i) random in location and time - likely to be taken by cruisers (oceanic + coastal) or day sailors (coastal) and,
ii) at the same place at regular intervals - more likely to be taken by day sailors in coastal waters - you may set up a 'monitoring station'. For example, a Secchi Depth taken at the same place every week throughout the year can be a quite interesting way to observe and understand your local environment
. Do this over the years and you will detect changes and be able to predict when you may see certain marine life appear that feeds upon plankton.
The database will be accessible to all who contribute. At the moment, if you click on a location marker on the map you can see the Secchi Depth recorded. We will be adding more functionality for users, such as graphing, as the project develops.
In time we may also make calls for paticular areas of ocean to be studied. For example, there is a Northern Hemisphere bias at the moment suggesting that we need to find better ways make southern sailors aware of the project.
In that respect, I welcome suggestions of ways to communicate this project to sailors.
Very happy to keep answering questions.