o ys . ▁The ▁bars ▁are ▁of ▁sufficient ▁weight ▁and ▁the ▁bu o ys ▁of ▁sufficient ▁bu oy ancy ▁that ▁the ▁tra pe ze ▁will ▁not ▁easily ▁change ▁depth ▁in ▁tur bul ent ▁water ▁or ▁if ▁the ▁divers ▁experience ▁bu oy ancy ▁control ▁problems . ▁A ▁decom pression ▁tra pe ze ▁can ▁be ▁t ether ed ▁to ▁a ▁shot line , ▁or ▁to ▁the ▁d ive ▁boat , ▁or ▁allowed ▁to ▁dr ift ▁with ▁the ▁divers . ▁It ▁is ▁effective ▁for ▁keeping ▁the ▁divers ▁together ▁during ▁long ▁stops . ▁ ▁A ▁surface ▁marker ▁bu oy ▁( S MB ) ▁with ▁a ▁re el ▁and ▁line ▁is ▁often ▁used ▁by ▁a ▁d ive ▁leader ▁to ▁allow ▁the ▁boat ▁to ▁monitor ▁progress ▁of ▁the ▁d ive ▁group . ▁This ▁can ▁provide ▁the ▁operator ▁with ▁a ▁positive ▁control ▁of ▁depth , ▁by ▁remaining ▁slightly ▁negative ▁and ▁using ▁the ▁bu oy ancy ▁of ▁the ▁float ▁to ▁support ▁this ▁slight ▁over - weight ing . ▁This ▁allows ▁the ▁line ▁to ▁be ▁kept ▁under ▁slight ▁t ension ▁which ▁reduces ▁the ▁risk ▁of ▁ent ang lement . ▁The ▁re el ▁or ▁sp ool ▁used ▁to ▁store ▁and ▁roll ▁up ▁the ▁line ▁usually ▁has ▁slightly ▁negative ▁bu oy ancy , ▁so ▁that ▁if ▁released ▁it ▁will ▁hang ▁down ▁and ▁not ▁float ▁away . ▁ ▁A ▁delayed ▁or ▁deploy able ▁surface ▁marker ▁bu oy ▁( DS MB ) ▁is ▁a ▁soft ▁infl atable ▁t ube ▁which ▁is ▁attached ▁to ▁a ▁re el ▁or ▁sp ool ▁line ▁at ▁one ▁end , ▁and ▁is