The RNLI is a serious organisation, whose role is saving lives at sea. Its purpose is not to entertain people who want to get a "log flume kick".
If you really want to experience a lifeboat launch, get in touch with your nearest lifeboat coxswain and ask him how you should go about training to be a genuine, dedicated crew member. It will probably be too much like hard work for your liking.
Thanks for your reply but I must say I don't see the need for your judgemental tone! I happen to know this IS something they have done in the past as a way of raising much needed funds!