I've just bought my first Merlin and am having a problem with the mainsheet. The rope goes through a ratchet block on the back of the centreboard case and then though a cam cleat. Is this a common arrangement? I find that it cleats automatically when sheeted in, which means that every time I want to ease the sheet I have to jerk it upwards out of the cleat. This makes balancing the boat a lot less smooth upwind. My previous boat (a N12) had an aft mainsheet with no cleat which is why this in new to me. Should I remove the cleat or am I just using it wrong?

Thanks in advance

Yes this is the common arrangement.  Your cleat is too high/block too low if you cannot easily uncleat the main with a straight pull from the hiked position.  A lot of the arms the cleat is held on are adjustable for height but if yours is not try using a longer shackle on the block.

If the mainsheet is runs out of the mainsheet block too close to the cleat then it can jam itself. This can be sorted by getting a smaller ratchet block. 

An alternate option is to get rid of the ratchet block and put a 4:1 purchase on the mainsheet. If you then use a slightly thinner mainsheet it will run as easy as the 3:1 purchase with a ratchet.

I should think you would need the cleat to cleat the main sheet off when hoisting the spinnaker.

Hope that will help.

I will see if I can adjust it next time I sail then. I hadn't thought about the spinnaker hoist, it's a good point.