Hi Manos - well for a start the Atlantic 75 does not have a transom (rather like a ZapCat!) which obviously facilitates evacuation of water when it's stuffed in big seas. It also has the facility to take on (or dump) water ballast in (out of) the hull which greatly assists its seakeeping capabilities and enables it to maintain much higher speeds in rough water than it would otherwise be able to do.
I expect you're aware that the engines are equipped with mercury tilt switches which cut them out instantly in the event of a capsize and incorporate a number of other modifications which allow the engines to be fired up once the boat has been righted by the air bag. I understand that's one of the reasons why the RNLI don't use 4-strokes. Incidentally, the replacement RIB for the Atlantic 75, which is currently being phased in throughout the UK, is slightly longer and has a bigger beam and I understand will be fitted with twin Tohatsu 110hp (?) engines.
Oh, and it's got a flashing blue light on the A frame and a bloody big winch for'd which Jono would kill to have fitted to his Land Rover
It's also got a stretcher which has proved useful in Anglesey for carting away rock climbers who regularly fall off the cliffs at South Stack. None of which is much help to you, Manos, with regard to your 5m safety RIB, unless you take a power saw to the transom or fancy fitting a trap door in the hull to let the water ballast in
And I forgot to mention it costs £85K.
Daniel - Yep, it's the same engine as yours, a Mariner 40hp, with a few mods of course to make it immersion proof. They're currently replacing the current D-class inflatables with a slightly larger boat and these are fitted with a 50hp Mariner and a fancy composite hull I believe. You can actually buy reconditioned RNLI engines off the D-class boats, and I'm told they're quite good value. Never raced or rallied and serviced to the hilt.
Steedthrust - The trailer is reversible. The boat is recovered bow first, it's not reversed on. For launching the engines are started and warmed up by means of a dedicated water supply from a tank on the trailer. In the last photo you can actually see the water pipes attached to the side of the trailer cage. On entering the sea these pipes are automatically disconnected from the engines' water inlet ports and off she goes. All clever stuff.