Peter wrote:
Take the loaded weight and subtract 1kg for every litre fuel tank capacity. I am sure it won’t float.
I think you probably mean take the engine weight. The rest of the plane likely has a density not too dissimilar from the one of water.
I did the trip to Corsica on 3 occasions so far in an Aerospool Dynamic WT9, Le Castellet – Calvi and Calvi – Le Castellet in 2012 and last summer from Calvi to Saint Rambert. I always followed the VFR routes and cruised around 6000-7000ft. I carried life jackets (since a life raft is too heavy to carry in an ultralight) and a PLB (attached to my life jacket). The flight is very easy. If I would have a engine failure above the sea I would use the balastic parachute I have instead of trying the water landing. Mainly because I have a fixed gear and the parachute reduces the risk of flipping over.
Engine+prop at some 150-200kg is the biggest bit which definitely won’t float, but there is also avionics, all sorts of metal bits, the fuel tank lining (unless rubber in wood ??!!) etc.
Density of wood is c. 0.75 so you are getting only 25% of its weight as a floation aid. And there isn’t much of it. It is just a skeleton. The rest of the hull will fill up with water.
But the main thing is not whether the plane will float but whether it will float with the occupants inside. It certainly won’t do that.
A modern raft is not big. We have a long thread on rafts here and the Survival products one comes in at around 8kg.
I think a Jodel will do well in a calm sea landing tough with gear it may flip over but will float for hours, also going to Calvi from Cannes you may get back a cruise ship assuming summer/sunny days not now 
https://www.marinetraffic.com/en/ais/home/centerx:8.5/centery:43.1/zoom:7
On rafts, I don’t think there is a legal requirement for it irrespective of distance? PLB/Life jackets it is the minimum you need when “out of glide range” over water?
Tough personally, I don’t see raft usefulness unless you know how to use it and actually have used it before with some passengers, if not you are probably better with proper flight planning and some risk mitigants (e.g. fuel/engine management, hot summer days crossings in vmc only…), I expect 4h waiting list for S&R to find me in a 100NM square in CAVOK days, they are based at Hyeres btw 
VFR flightplan and following the VFR routes from STP (LONSU for Propriano and MERLU for Calvi). Next to MERLU is OMARD: I kept calling it l’homard but no one else found it funny maybe Nice Info get it all the time.
FL95 and FL85 depending on direction. One of the other planes went at FL105, but with full fuel and a lot of Pietra baggage it took a while to get there in the August temperatures
Homard:
Pietra:
I checked the report on the C210, I guess if they would have had a PLB they could have been picked up within the hour. I think they were lucky this occured very close to the coastline, imagine 20min later over open sea?
https://www.bea.aero/docspa/2009/n-sf091012/pdf/n-sf091012.pdf
update: Found this 7kg liferaft, could be good to use in an ultralight: https://www.oceansafety.com/product-range/liferafts/product/aero-compact-2-man-liferaft#details (Price +/- 1000 USD)
Peter wrote:
It makes no sense to fly out of glide range anywhere without a raft, because life jackets will just enable the corpse to float. Especially in these southern european areas, where nobody will get to you really fast.
The C210 referred to above didn’t have a lifeboat and everyone on board survived. But I agree it is stupid not to carry one.
Zorg wrote:
Obviously I agree that a raft would make a lot of sense for my planned route, but I’m not sure whether I could fit one in my Jodel …
Our posts crossed each other. The Survival Inc rafts are not the worst, not the best, but are quite lightweight and compact (5.5 kg and 10 × 30 × 36 cm without the emergency rations). Winslow has better reputation. In the absolute, all these rafts are not cheap.
Survival Inc ones are sold e.g. at
https://friebe.aero/aviation-equipment/emergency-equipment/life-raft/?language=en and they also have a rental service https://friebe.aero/rental-service/ (and I might take the opportunity of you buying mine to upgrade to a Winslow one; Survival Inc Model 1400-1 raft plus model 1500-1 survival gear pack; increases depth and weight by something like 60%-80%).
Peter wrote:
It makes no sense to fly out of glide range anywhere without a raft, because life jackets will just enable the corpse to float. Especially in these southern european areas, where nobody will get to you really fast.
I know it makes little sense to argue these things as people will camp on their positions – usually – (not a dig at you Peter) but I see little value in carrying a life raft in a single engine plane with limited load capacity (which all our tin cans really are) across the Mediterranean. I will carry one to go cross Atlantic next summer – for the first time ever – more for reassurance than for firm believe it will actually save my life. I see more value in a PLB and potentially a SatPhone than trying to pull a life raft from the luggage compartment or back seat in a plane that has 1 small door and potentially 4 – 6 passengers. I might look at this (potentially) different if I were flying a Cirrus with 2 huge doors, or a Robin with a huge canopy (which one can throw off in the air before “landing”).
Personally my first priority would be to get the f**k out of the plane… (hopefully with the life jacket not inflated already on me). Now, I have not done an “airplane” crash in the sea course" where one spends 2 days splashing around in a swimming pool (again sorry if I offend anyone) in order to prepare for a potential ditching. I do however have a career as an Olympic kayaker behind me to know a thing or 2 about rescue situations in and around the water to make me very sceptical about the whole raft thing… Again – it is just me, and I don’t even know why I am arguing (maybe too much coffee :-))
“It makes no sense to fly out of glide range anywhere without a raft, because life jackets will just enable the corpse to float”
Again I disagree. Wear a lifejacket. How many boats are there in the area?
What’s your gliding range to near a boat? Survival time in cold water varies greatly from person to person.
I believe a Jodel which ditched somewhere floated long after the occupants had been rescued. ( Hours after. Baltic area??)
PS. Maybe better to have your documents on you, in case you’re “returned” to North Africa after being rescued.
PPS Agree with LFHN. But wouldn’t hurry to get out of a Jodel. Also canoeing background, but sea/river cruising. Have got into capsized canoe, fitted spraydeck, and rolled up as practice in spring in the Moray Firth.
