The lighting board shown in this picture is attached to the rear protection system of the trailer. This protection system is both adjustable and demountable, the latter being essential if you intend to launch your boat from the trailer and not use a crane. The Road Vehicle Lighting Regulations 1989 stipulate that any rearward overhang from a trailer lighting system must not exceed 1Metre. Therefore if the rear protection system , with lighting board attached, cannot be adjusted to meet that stipulation then a lighting board will require to be fitted on the transom of the towed boat, or bow if it is being towed t’other way about.
David Hume
The Flying Fifteen Blog 