Go to the 2016 SHTP site and look for "Race Documents". One of them is entitled "Communications Plan", and it spells out the requirements for a daily check in with a manual activation of the DeLorme satellite tracker each racer was required to carry. Manual activation, rather than automatic, is required "as a sign of life aboard." I don't know if the 2018 race will require the same equipment, but it seems logical that they will want everyone on the same system to facilitate posting everyone's position on the tracking page during the race.
Lee
s/v Morning Star
Valiant 32