I am the owner of a 2001 DL530 with a Yamaha 115 four stroke. If your thinking about buying a Novurania, which by the way is an excellent RIB with great sea handling ability, you should consider several things about Novuranias' or other RIBs coming off of a Yacht.
First if the boat is over 5-10 years old you need to know that Novurania gas tanks which are aluminum are notorious for developing leaks. The tanks are installed in a supposedly sealed compartment surrounded by foam. My Novurania which is 9 years old has had two tanks and I am now putting a third in.
I recently purchased my Novurania from the Novurania company which had accepted it on a trade-in and after having a shop thoroughly go through the boat with a number of engine and tube issues found and repaired by the previous owner, five months later I found a leaking tank. The cost of having the tank replaced is $1600, however since the fore deck was laid with teak, that had to be removed and replaced which was an additional cost. If you buy a RIB with a foamed in tank, have your shop pressure test the tank as well as check the condition of the filters for any clue as to how the tank was maintained.
The tank I just removed was a stainless steel tank and due to what I believe to be poor tank maintenance a hole was eaten into the bottom of the tank by electrolysis. When I received the boat the filters were half full of water. the tank had obviously been replace as Novurania does not install Stainless Steel tanks.
The moral of this story is to understand that a RIB coming off of a mega yacht has spent a lot of time with fuel in it's tanks sitting on the deck of the yacht. Of course the key is to make sure that phase separation does not occur in the tank, that the gas is kept fresh,
and that the gas tank compartment is kept dry.
I was fortunate to have purchased the boat well below market at around 10 grand with a good Yamaha four stroke, and I had a good cushion against any repairs that may have been found such as the gas tank problem. Any RIB with a foamed in aluminum tank will in all probably have similar problems if not meticulously maintained.
If you have any other questions do not hesitate to contact me.