How do i make the rocket go?  I've got 3389 (White Whale) and its a really nice boat to sail.  Unfortunately i can't make her go, i'm positive its something that i'm not doing but i can't think of what it might be.  We seem to go well in a good blow but up until that the boat seems a bit sluggish and doesn't pickup on the gusts as i'd expect.  

Part of my thinking is that at 25/26 stone we are heavier than recommended and that with the majority of the weight being me at the back i need to move my weight a good distance forward.  Also the older sails seem very flat, is this normal for a merlin rocket?  I've just purchased a new suit from Norths and i'm hoping this should sort the possible power issues.  Is there anything else with the way i should be sailing it or tricks to get the boat powered up more?

2 things come to mind.  Check the front tank isn't full of water (silly maybe but been there done that) have a look at your mast rake, in case what you think is your upright powered up setting is in fact 2 ft of rake.  A flat main if you are on the heavy side is unhelpful.

Even though I'm a dog here's my thoughts

You got to keep a merlin moving and not stuff her up to make sure  the foils are all working , always remember mike McNamara saying the wind had to go over the sails like the sails weren't there and the water had to flow past the hull as though the hull wasn't there

So re the sails make sure top batten is parallel to the boom and never hooked , make sure jib isnt too tight so wind can get through the slot,  ease kicker and shrouds downwind

Re the hull ad u say keep your weight forward  very easy to hang around too long at the back of the boat when you are tacking gybing hoisting kite, the boat just had to be flat

Twitchy devils are merlins again just concentrate on keeping speed up

You can tell from the wake if you need to move forward, it should leave the transom cleanly without a lot of bubbling and turbulence.  Incidentally, the thwart in a Merlin may look like a nice seat for the crew but in lighter conditions you have to be a lot further forward than that, if there's not enough wind to both be on the side deck I helm from in front of it, move back downwind once the boat is actually planing and the bow wants to lift.

Thwart position varies on Merlins, some of the nose diving designs are further back,Wine vis Cant. 5ins.(to keep the helm back). We sail with 25st.so I lengthen and work on the spreaders.

You could also try lifting the c/board and check the rudder for weed...a very effective brake, especially in light airs.