Water sports specific GPS Tracking devices with 4 live data on screen at all times. Standard and Metric (Km/Miles)  support with bluetooth  connection for your heart rate monitor support allow you to train with your interval training.
Product direction link 
NK Speedcoach for SUP     -Option for with or without training pack.
NK Speedcoach for OC       -Option for with or without training pack.
Tips:
If you own smart watches and would like to connect two device together  do not  order  HR monitor from NK Training pack is upgradeable with firmware.
Heart Rate Monitor  ANT+/Bluetooth options
Scosche Rhythm 24  -Re-chargeable device.  placement forearm/biceps
Garmin Dual HR  -CR coin battery device.  Chest strap monitor style
Wahoo Tickr – CR coin battery device.  Chest strap monitor style.  Lowest model is only you need for dual setups.
NK How to use example videos