Self Tensioning Drums
The RMG self tensioning drums allow for the elimination of tensioning devices in the sheeting system such as shock cord, rubber band material, hat elastic, springs etc. The spring loaded return spool in these drums takes up any slack and maintains a positive tension in the sheeting system.
32 mm and 42 mm ST Drums are available in Left and Right hand versions. If the winch drum turns clockwise (viewed from top of drum) to sheet OUT, the Right hand ST drum should be used. When the winch turns anticlockwise to sheet OUT the Left hand ST drums is used.
The 45zs4st and 55zs4st are right hand only.
How To Use
At right is an example layout for a right hand ST drum. Note that the load bearing line (pink) comes from the bottom spool and the return line (light blue) goes back to the top spool. This is essential for any ST drum.
The 32stR/L and 42stR/L have only a small difference in travel between the fixed spool and the return spool so the majority of the spring travel can be used to generate tension. Ensure that there is always at least a small amount of travel left in the spring at any position from full in to full out.
For the 45zs4st there is a difference of about 3/4 of a turn and for the and 55zs4st there is about 1 turn difference between the travel of the spiral and the return spool. The point of maximum differential occurs about 100 mm travel distance out from the spiral fully loaded (close hauled) position. So when the drum is at close hauled or at full out, the return spool should have about one full turn left in the spring. If less than 3/4 for 45zs4st or 1 turn for 55zs4st is left in the spring, then the spring will bind and damage is possible.
Start by loading the bottom (load) spool with enough line plus a couple of turns for the required travel and with jib and main lines connected, set the booms to close hauled. Then attach the return line to the top spool. Put a couple of turns on that spool then feed it through the splitter ring as per the above drawing. Once the return line is fed through the splitter, pull on the line to tension the return spool spring. Take it to the point where there’s no more travel in the spring then back off about ¼ turn or so then tie the line off at the splitter.