I don't think this is practical. Small craft, very small craft, can be run up a stern ramp, and launched the same way. However an MTB/MGB is a vessel weighing some tons, and when you get that much weight moving at speed, ANY mistake means its done. You also have very lightly built vessels going out to attack submarines, all well and good, if you have a good sonar (I may be wrong but don't think they are very good) and as long as they stay submerged. If they don't then you will be facing a deck gun, probably multiple machine guns and auto cannon up to 37mm. Your also going to need to take into account your heading and the sea state in launch or recovery, as it will need to be directly into the seas. Or, you can build 10 or 11 Flower Class corvettes on the tonnage of your vessel, that can operate in any sea state.