JF your ok with a long wheelbase Landi
You can pull 4ton with a long wheelbase Landi on the rd legal including trailer with mecanical brakes max weight but not a shorti.
With tractor you can pull 8.25 for the complete rig inc tractor on a normal licence Trailer needs Hydroulic brakes if combined weight is over 4 ton.
Never use red and if tractor is used on the rd and if over 8.25 ton for the lot then its HGv with Trailer endorsement on your liscence to be legal and speciel vehicle tax and insurance and Hydroulic brakes not mecanical as they are only good for 4 ton max trailer and boat.
This ins and tax is used for any none Agri use of a tractor £40 if towing less than 3/4 mile normal car tax if more + speciel vehicle insurance.You can get away with more beam with this unit if needed up to aprox 2.9 mtrs and overall length of aprox 18 mtrs for whole unit inc tractor.
Its a bit of a ball ache as the one thing drivers hate more than a tractor,is a man who is pulling his boat and a tractor.
We weigh 3.5 ton so the question is can we get a strong trailer that doesnt weigh more than 500kg for towing?that will last?
Or a lounching trolley that will be sited at the boats base and if needs to be shifted then it can be lounched and recovered with this leagally but not towed on rd.
I am going to sell the Tractor as I dont think its feasable.With all the extra costs of being legal.I will then get a louncher built and bite the bullit when it needs shipping down south for a swoiree on the back of a waggon or motor down over the weekend.
Thats my take on it after buying a Tractor and a RNLI louncher Trolley.