Hi Dean. I think an 1/8 inch is way too small. We discussed this last 
    year and it's a good idea to have the ability to pull the sub up, but 
    carrying a spool/cable assembly on board will require a pretty heavy 
    set-up.         
         One idea tossed around back then was a float 
    and cable like you had planned, but the cable is used as a guide 
    for lowering a "clamp" that would be capable of attaching to the sub to pull 
    it up. That way the heavy "clamp" is carried on board the surface craft 
    where it's not exposed to sea water, doesn't add any weight to the top of 
    the sub, and can have a thick cable strong enough to pull the sub free from 
    mud or minor entanglement. Just lifting the sub alone may not be enough if 
    it's in the mud or hung up on something.
        It should be pretty easy to fabricate some type of 
    "hook and latch " device that the clamp can drop onto ( guided by the 
    float/cable ) and then be able to pull really hard if the sub got stuck. An 
    1/8th inch cable would then be enough if used as a guide.  Frank 
    D.