Good advise from the others above, I've done both by rib and from Calshot spit. Right at the end of Calshot you are almost as close as you'll get by Rib , so if weather is poor and you don't want to launch it is a good option.
Either way it's good fun.
Make sure you get the people on the ship to take a flag or something similar to make identifying them easy..... It's a big ship to find your friend/relatives
(Pictures bellow taken with iPhone from Calshot so u can see how close they pass)