there really is nothing mush to see other than bunk boards like any other swing keel boat.. or water ballasted boat.
I have the original trailer, as originally set up by macgregor under my 25 (except for the re-positioned axle), and there is nothing complex or scientific about it. very simple.
there is a cross member in the trailer almost directly below the front edge of the forward window.. the trailer frame ends about a foot behind where the cabin trunk meets the cockpit... so another cross member there.
the front x members have 3"high risers from it, 20" out from centerline of the trailer... the rear xmember has 10" risers (to allow for the keel), but you could get by with 7.5 or 8 though.. these are also 10" out from centerline.
there are over sized holes drilled in the top of the risers, and angle irons with over sized holes in them also (these points mate together and allows for some adjustment of the bunk angle as it fits to the boat)....
then a carpeted 2x6 is bolted to the top of the angle irons.... on each side.
in time, the weight of the boat will form the boards to the hull...
macgregor had the axle under the 25's, much too far forward.
when the boat is loaded "normally" with the gear we usually carry for daysailing, it can cause minor swaying in the tow vehicle. you will need to move and keep all the loaded gear into the v-berth to keep some tongue weight.
if you are going to load the boat for cruising, the axle will definitely have to be moved rearward.
with the axle under the trailer and positioned just a few inches forward of the rear part of the rear window is a perfect balance no matter how the boat is loaded.
the Mac 25's are nice comfortable boats to cruise, sail and relax in when they are set up right... good luck
