Use your jugement of the situation. To adapt to the environment. Where to do the S-drill? 

if you use your brain to judge the situation and adapt the protocol accordingly, you might get more out of the protocol. And make it easier to apply.
In this case the S-drill.
Let the environment dictate where you do this.
Don't forcefully do it in rough conditions that either stress you or make you skip it entirety. In stead get all your stuff in place and do it on the shore.

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