1st what is a bigger boat?
And will it be duel axle?
Duel axle is a pig to turn, be it front or real mounted hitch.
We had similar issues at our last home..a 7 point turn IF hit each of the markers dead right...
Markers are paint marks on drive and on the grass a weed killer line couple inches wide you can follow with the trailer on the side easiest to see.
Get wrong and got messy.
Current home, there is no way to clear fences decks house.
Last home we hung on the little digger, put a hitch on the bobcat.. eventually picked up a little 14hp (?) yamma tractor for $150 on trademe.
Now to get a duel axle to turn well, we increased the height of the hitch on the yamma so the front wheels where just touching.. this effectively made it a single axle, and with weight further back manover around tight cnrs rather easy.
Also since a well balance duel axle trailer will have a little more weight on the front axle.. this will have a slight wheel alignment tow in to steer straight
The rear axle will have a slight tow out.. (tow in in reverse)which makes the trailer steer well in reverse.
We have tried several 4x motor bikes.. they just dont quite have the tyre grip, even messing with pressures water etc once getting gross weight up around 1000kg plus
End of the day thu.. its a matter of giving it a go...
We found when looking at boats..( and new tow vehicles, demos) we where quite welcome to give it a go.
So to your initial question
Is there a simple way to estimate the turning circle of a boat when attached to a car or not?
I believe there is , sorta.. but given the parameters of
1/ distance on tow vehicle rear axle to hitch.. and it is dead square
2/ height of the hitch
3/ distance from trailer hitch to axles(s)
The distance between trailer wheels
4/ the distance between the axles.
5/ the over hang behind the rear axle to tip of motor clearance
6/the tow in on each of the axles
7/That the axles are exactly square.. set up right and NEVER hit a big pot hole or clipped a curb
Ours (7/) when unloaded bloody hooks to the right in reverse down the ramp.. bloody pain... and slightly when loaded reversing up a long drive.. but easy controlled.