I keep my bolts, all eight, TIGHT. I really crank them down. However, I do this on the water. If you do this on the ground, the hulls can not tilt, or cant as I refer to it in this post:
I use this method to set up the "chassis" on my boat and I end up having to retighten the bolts after about two regattas. I have learned the hard way that you can not get the bolts as tight as they need to be on land. Actually, you stand a good chance of cross threading the bolts if you try it on land. It is a real bear if you completely disassemble the boat and go back together with it and cross thread a bolt.
The inboard bolts screw into a casting that is riveted to the crossbars. If you crossthread a bolt and are lucky enough that the bolt breaks off flush with the hull, consider yourself really lucky. Normally the bolt threads will get trashed and the threads in the casting will stay good. I still run a tap through the casting to clean up the threads before installing the new bolt though.
If you are a poor soul that has the crossthreaded bolt break off flush with the interior casting, good luck. I had to drill out the rivets for the end castings, drill out the rivets for the interior casting, and fight for four hours to remove the remaining piece of bolt. Then rivet it all back together. NOT FUN!
Hobie Nick, be careful with that 12" SCH40 pipe. If you break the bolt, you might be in the same situation as mentioned above. AND IT SUCKS!!
I use a 3/8" ratchet that is about 10" long and tighten until I can't tighten anymore. I would rather the bolt fall out than break off. Much easier to replace.
Also, the lock washer idea is a must have. Only problem is that you must use the Hobie supplied washers or find a place to find thin walled lock washers. If everything is installed correctly, the lock washers you find at most hardware stores will be too wide when installed. I found out the hard way.
One more thing. I run a bead of silicone sealant on the threads of the bolts before I install them on my non race boat. It helps keep them in place, seals areas around the through hull connection, and helps to fight off corrosion.
Hope this helps, just DON'T BREAK THE INBOARD BOLTS OFF!