depending on the kind of riggers you got.how long are the booms?i have a magna19 series boat with a full splashrail,and i mounted a pair of cannon unitroll hp's on there.they have 5 ft booms so they clear the motors.take a 3" long stainless screw and screw them down through the wood and aluminum rail.they will hold good enough to break the base before pulling out.
if they are short booms,you might try mounting them to the gunnels,bolt them through with either a wood spacer block under the rail,or a aluminum plate there.use lock washers,nylock nuts and loctite on them also.trust me on that.i had a pair of walkers stolen off my boat and they had locwashers on them,they turned the bolts out and left the nuts there.
im going to be mounting a pair of big jon captain packs this coming month,im leaning twards a rail i am making out of aluminum channel with 4" high posts off the transom and all 4 riggers mounted to it.
i have pictures if you like to see how mine were mounted.let me know.
