Originally Posted by slimtim
So MAM is the max mass that can be towed (I assume its this) or the max gross mass of car and trailer?!
MAM is the maximum gross weight of the car. i.e the car, fuel, people and whatever the design expected to get crammed in the boot and should be on a plate on the car (usually under the bonnet or on driver's door/post.
The trailer will also have a plate with its maximum laden weight on it. Beware that if you tow a 2000kg trailer with a 1500kg MAM car (on a post 97 cat B only licence) you will be illegal even if the trailer was empty and only weighed 300 kg. Its the authorised limit that matters rather than the actual weight.
The combined limits for the car and trailer must also not exceed 3.5 tonnes for your current license.
In terms of width - I don't think you need to worry if you are looking at 6.5m boats. The max width is the same for everyone regarless of license.