Working solo on the packing materials while in the water...that could have a high pucker factor (HPF) as there's just no easy way to stop things once you are committed. And while there are "safe" ways to do it (i.e. packing wax or putty around the shaft from the outside, which isn't hard to do in warm water) there's still a HPF because you know that if you haven't repacked properly...you've got to keep working till you get it right and tight, or else get hauled ASAP.
But replacing a transducer? Heck, I pull the speed log every time I secure the boat, and reinstall it every time I get on the boat. (Unless I'm being lazy and leave it out.) Fire hose? No way, the process of swapping a transducer for the dummy plug (shipped with it, to replace it at these times) should take all of about 5 seconds, which only feels like ten, and the quart or water that comes in only spurts a foot high.
Threading the cap down, sure, takes a bit longer and needs more care, but once the dummy plug is in...no big deal, there's no water coming in. Too many folks are scared at the prospect, but it really is no big deal. Best to let someone else demonstrate it, hands on, to get rid of the HPF before you do it for the first time.
Of course, both are good reminders why we all have damage control plugs tied on next to every hole in the hull. Right?