Friends and family are able to contact you at Sea by using the free SMS message service provided by Iridium.
Here is the link to the site, https://www.predictwind.com/iridium-free-sms/
All they will need is your Iridium phone number.
It is important to remember that all SMS messages sent to you are limited to only 160 characters. This is regardless of whether they are sent to you from a phone or the service above. Any message greater than 160 characters will be cut short.