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Size? are you towing-limited? or do you have something which can tow 2.5 tonnes and up? Exercise gets expensive when you have to change your vehicle as well. Most stuff around 5.5 m will come in around 1500kg. Weights go up rapidly as you go up in size, add a metre to that and you likely add a tonne, fully fuelled with all gear on board. If you are buying new, salesman will try to sell you a package which likely has a trailer which is marginal, at best, to keep the package price down. Industry is rife with it, unfortunately. If he tries to say " dry hull weight is such and such, motor weighs xx, add a hundred kg for gear, you only need this trailer' he will be WAY out. Weighbridges don't lie, and neither do the Mermaids' scales. Over-ride brakes are not allowed on trailer of over 2000kg GTM. GTM is the weight of the trailer/boat, weighed when hooked upo to the vehicle. ATM is that weight plus downforce on towball--in other words, weighed on the jockey wheel, not hooked up. So many peoiple are in contravention of this, it is just not funny. The silly part is, once you have actually used the EOH systems required on the larger trailers, you'd never go back to over-ride. People will try to tell you that ali boats are a lot lighter than glass--they will be lighter than glass up to a certain point, then the gap narrows right down, as the thickness of material needed in the larger ali boats grows exponentially with length, get over 6.5 metres, or thereabouts, not much in it.
There's a lot to take in with the intial purchase, get it right. HTH, and may you have many years of happy boating