Safety First
Alongside all the normal safety considerations in watersports, downwinding comes with its own set of considerations.
In the Netherlands one of the biggest factors to consider is exposure (crossing lakes, foiling far offshore) and water temperature (down to 4 degrees Celcius in winter). One thing people sometimes forget is that there is a lag in the water temp. The water stays warm into October / November, but it also stays cold into March / April even. Its also worth noting that the lakes get colder than the North Sea.
Personal Safety
When it comes to personal safety, the most important thing is to know your limits. Don't put yourself in a position you can't paddle out of (too far out to sea, or crossings with big exposure).
Equipment wise, ensure you have a leash (your board is your best flotation), a PFD, phone or means of communication (EPIRB or PLBs are good to have as well as SafeTRX watches). Having your phone in a case to stop it drowning is a good idea. I also like to foil with Shokz headphones. It's nice to listen to music, but it also easily allows you to use siri, or hear if someone is calling you (see below regarding the local emergency services)
As mentioned above, it gets cold. It's better to be dressed too warm than dressed too cold. Consider what the maximum exposure / paddle time you are comfortable with when considering how warm of a wetsuit to wear.
Group Safety
Always share location with the rest of your group. You can easily do this with Whatsapp, Garmin, Waterspeed, the list is endless. It's important that if you split up (happens a lot) that you, or the rest of the group can keep an eye on where the others are.
Have back up options. This may mean dropping a car halfway, or agreeing with someone who may not be as good, that if things don't go well, they can exit elsewhere and you pick them up. If things don't go to plan, communicate clearly with each other.
Have the keys to the finish car accessible to all. This may mean using a lockbox on the car at the finish, or having enough dumb copies of the keys to that car so that everyone doing the run is able to get into that vehicle in the event they need to collect you or anyone else in the group. Make sure everyone has a dry set of clothes in the car at the finish too to make sure that no one ends up getting cold whilst waiting.
Local Rescue Services
In the Netherlands the rescue services are made up of the Reddingsbrigade, KNRM and the Kustwacht (Coast guard). If anyone calls 112 because they think you are in distress. Then they will be routed to the Kustwatch Control room, who then deploys the relevant parties to go out.
When doing downwind runs in The Netherlands, especially on the lakes where the runs are more in the public eye (along dijks and motorways). It is recommended to contact the Kustwacht control room (email: ccc@kustwacht.nl , Tel: 0889584000) with your plans (group size, run start and finish, start time finish time, contact numbers), and also to email them after your run to confirm everyone is off the water. It's also advisable to ask them to call you in the event that a member of the public does call thinking there are people in danger on the water. This way any false alarms can be de-escalated, saving time and resources. It is therefore critical, that if called, you answer the phone.
In addition to this, there is a "KNRM Helpt" app that you can use as tracking device in the event of an emergency (see picture on the right). It even has the option for you to provide a trip plan. Unfortunately, as this is linked to the KNRM, if someone calls 112, using this app doesn't automatically let them check that you are ok as the call goes to the Kustwacht control room not the KNRM (effectively they are decoupled, unless the Kustwatcht mobilizes the KNRM, but even then they don't check). The app functions more as a "User to KNRM" communication path. Using this app lets you basically just unlock your screen and then click on the "call for help" button. So minimal faffing around trying to call specific numbers.
Its also worth saving your buddies numbers and the coast guars numbers in your phone as emergy contatct. Water and touchscreens don't work well. But if you lock yourself out of your phone, you can always still access the emergency contacts.