(taken out of context)On the current trailer, I have full contact of the bunks for about 8ft, which I estimate at about 576 square inches of contact, for less than a 1.5 lbs per square inch.
Dave, you are correct, and my explaination maybe too general, and to use a displacement hull is a poor example. A planing hull that has a long straight section, and bunks properly fitted and supported along that length is the best situation for the hull. Another point that I think gets missed for many folks when fitting a trailer properly is how the bunks or rollers support the transom, or where the loads are on the hull. I see many boats trailered with the bunks ending short of the transom, sometimes by more than a couple inches. I like the bunk supports to align with the transom and have the bunks extend a few inches (makes a great step!). And then I add a transom saver too! But that is the engineer in me... I tend to over think and over build!Dave,
In my experience "full contact" does not usually equate to "full support". In an earlier post you mentioned that your bunks were supported near each end and that the board flexed to conform to the hull.
In theory, the board will continue to flex until either;
(a) the wood will not flex any more due to the strength of the board (at which time the center of the board may be carrying more load than the ends)
(b) the boat comes into contact with the board at the point that the board is supported to the trailer (at this time the load may be concentrated on the support points and not much carried by the flexed board in the middle)
I will concede that the bunks, even if not equally supporting along it's entire length, tend to spread the contact points over a longer/larger area than the rollers. A lot of roller trailers are using more numbers of rollers to address that concern.