Boat US reviewed some re-boarding ladders last year and the C-level got a pretty good rating so I have one of these strap-type ladders tied to a rear cleat that I can reach from the water in my Jon boat. I must admit I have not tested it personally though.
I think it’s a good idea as getting back in from cold water or wearing waders would be challenging.
PJM
The site below has a discussion and some other options.
Boarding ladders
There are two times you will need to get back onto your boat from the water. First when you are swimming i.e. intentionally going into the water, and secondly when you fall overboard. The problem when you fall overboard, is that in most cases boats do not have a though out process, for getting you back onboard.
I have had two incidents of a MOB and both were in calm waters. I can tell you its much more difficult than you think to get a person back onboard. In one case the MOB was so tired by the time he got back to the boat, that he did not have the energy to pull himself up. We tried to help him but were having difficulty time in grabbing him as there was not much to grab onto.
Had we a boarding ladder or a plan, getting the MOB back aboard would have been much easier.
The RNLI says that people falling overboard (MOB or COB) is on the rise, with numbers almost doubling in the last year. In the US 2/3 of boating deaths are from drowning and 90% were not wearing a PFD.
http://www.myboatsgear.com/newsletter/2009212.asp
C Level: This simple and cheap and space saving strap is an easy addition and does work. Its a bit harder to climb up into the boat with a strap rather than a step as the strap moves around.