I recently bought (from Steve) a White's Sierra Pulse Pro (SPP) PI detector which is effectively a TDI/SL without a delay adjust (locked at 10 microseconds) and without a conductivity switch (locked in the 'All' position).  When I took it down to the creek with the Minor John 5in X 9 in folded mono coil I was disappointed when it floated.  Apparently most coils are either for dry land use (thus lightweight) or for underwater use (heavy).  I've been spoiled by my Fisher Gold Bug Pro 5 inch round