There should be a hole on the inside of each hull.... right under the beam that has a plug in it. Take the plug out and that will give you access to the nut.
And don't lose that plug, they aren't being made anymore as are a lot of Prindle parts...
That's only on the rear beam not the front. Also Murrays has plastic caps to fill the holes of you lose the plugs but they are a very tight fit and might need some sanding around the holes to get them in. Also the plug is not there to keep water from filling your hulls. The small section the hole goes into is only access for the recessed screw in the rear beam track. it can only hold about a cup or so of water so even without the plugs it is not big deal.
