I'm currently using a slightly different patrolling technique.
Ahead 1/3, half an hour submerged, half an hour on the surface.
I know that it's unlikely that within 30 minutes a sound contact would pass into and then out of my hydrophone range, but surfacing every half hour keeps the batteries charged between 75% and 100% at any time.
Not only does this mean I patrol at a faster speed, but I also have enough battery charge left to turn off recharge mode if I need those extra few knots to catch a contact.
