Jared
 
I use the ABS rules for underwater vehicles as the starting place for shipboard load handling.  Those rules say to add an additional .75g for dynamic loading to the static load or unmanned loads.  So multiply the static weight by 1.75 to get the actual load.  This general number doesn’t account for unusual hydrodynamic loading.  For example, if I’m handling a large flat plate like structure (like the MARS node) I’ll do some more calculations to estimate the additional in-water load due to drag when the ship is heaving to see how significant it is.  I also worry about snap loading which is a much harder calculation.  The drag of the cable isn’t usually significant so I don’t think you need to worry about that.  However towing is a whole different story, particularly if you run the tow line up high (like off the Paragon davit) and may require some more calculations.
 
At first glance, lowering a CTD rosette vertically doesn’t seem to present any unusual factors.  For general work on the Paragon, I think you can use the following:  working backward from a 2400 lbf break strength cable and using a 5:1 factor of safety (ABS rules for synthetic line say 7.0 for running rigging and 5.0 for standing rigging but I use 5 also) you get 2400/5/1.75 = 275 lbf for the maximum static weight of the gizmo you’re trying to lift.  Usually the in-air weight is the limiting factor unless you have unusual hydrodynamic loads like I mentioned above.  Also it would be nice to hang a 500 lbf load on the end of the davit at full extensions and see how much the Paragon heels (if you haven’t already)
 
For lawerly reasons I have to say that it is the captain’s responsibility to make sure loads are handled safely and this quick description is no substitute for a comprehensive load line analysis.
 
There are a lot more gory details we can talk about if you like but that is a rough description
 
Hope this helps.  Let me know if you have any other questions.

Gene Massion Monterey Bay Aquarium Research Institute (MBARI) 7700 Sandholdt Road Moss Landing, CA 95039 831 7751922 (tel) 831 7751646 (fax) http://www.mbari.org
From: Jared Figurski [mailto:jared@mbari.org]  Sent: Thursday, December 04, 2014 10:30 AM To: Gene Massion Subject: Winch loading
 
Gene, 
   Lots of options and concerns are popping up around the winch acquisition.  Are you able to give me a rough idea of the loading we can expect on a deployed cable (cable weight + drag) in moderate conditions.  How does this increase with a small CTD rosette.  Of concern is whether a cable with breaking strength of 2400 lb is even adequate for this application given a 5:1 rigging safety margin.
 
any thoughts appreciated.
 
jared