in reality small fishing crafts use tires that were from scrap yards or could be 'picked up' as a cost free solution to stop the boat getting damaged by rubbing against others or the pier wall. although you should get the 'best fitting' tires to to scale, to be honest it shouldn't matter what size they are as long as they are in reasonable proportion to the boat as well as a scale person.
if the tires bigger then 5'9" in scale then its likely its a monster truck tire, or worse, making it look daft.
its a bit of a trial and error approach to what looks best for your boat, you could be very pedantic and buy 1/18 scale tires designed for the job but it would look to 'clinical' where as a range of small and med sized tires would look the part better.
as for bollards these should be to scale as its part of the boat if there to big they will look over powering for such a vessel, too small and well to feeble to use!
there are many sections within mayhem that have gone through 'bollard builds'.
if your working from a plan , the bollards should be marked up on the plan with there dimensions, or you can measure them (if plans full size to scale) and just use brass rod, or tube in the right diameter to create them. if your not working from a plan then i suggest you use your judgement to a scale person.
