When sailing my H16 I noticed that the hulls were "flexing". What I mean is that you could see that the leeward hull would "rotate" in relation to the windward hull, the one I was sitting on.
Back on land I would put the boat on the grass and push up one of the hulls. It came up for quite a bit (say, 10 inches) before the other hull would follow.
Now, as I know from this forum, and also from an article in "On the Wire", this is not a new problem, and there is also a solution: glue the frame and the pylons together. But, I like taking the boat apart for winter storage. Glueing, therefore, is an option I don't want to consider. So, I investigated the cause for the flex first before trying to think about a different solution.
I started out easy and checked the tramp - I know from many posts in this forum that it needs to be really tight. Which it was.
Then I took a closer look at the pylon/corner casting joint. Interesting: if you looked at the rear corner from under the tramp, and somebody pushed up the hull, you could see the casting and the rear cross bar move like a clapper around the pylon.
I took the boat apart and checked if the pylons were loose. No such thing. I then noticed that the bolt holes in the pylons weren't circular anymore, and rather worn out. This must be it: the worn pylon holes allow the bolts movement, and thus the boat flexes when the hulls are under different loads.
So, I need a solution which reduces the bolts' movement. Again, glueing comes to mind. But here's another idea - let me know what you think:
1) Get four short aluminium tubes; inner diameter == bolt diameter, length == pylon inner width at bolt holes.
2) Get epoxy and high-density filler.
3) Start with the boat taken apart. Fill the four pylons with epoxy (HD filler mixed in) until it starts oozing out of the bolt holes. Keep breather tubes in the forward pylons.
4) Put one aluminium tube into each pylon such that the bolts will go through them after boat re-assembly.
5) Add more epoxy, about as much as used in step (3).
6) Re-assemble boat and tighten tramp. Take care that the hulls are aligned correctly (just like when glueing the frame). Let epoxy cure.
I believe the alum tubes, with sufficiently small inner diameter, would restrain the movement of the bolts. Hence, stiffer boat. The epoxy again, should take the load of the tube inserts.
Does this make sense? Might the epoxy break when under load? Any other problems that you see? Do you think it'll WORK? 
Regards,
H77
H77
You didn't mention if this looseness was evident when you were rigged to sail. That is, are you finding this hull slop (10 inches) when your jib is up and you've hauled down on your jib halyard to tighted the rig. I suspect it will be much less than 10 inches when tight and what difference remains you'd have to consider whether it affects the boats performance.
While the looseness is inherent to the H16, it usually isn't great and doesn't really affect the performance for the averge to above average sailor. Probably, like most of us H16 sailors, it just kinda bugs you 'cause it shouldn't move like that. But in reality, the H16 does fine with what little movement you have between the hulls when rigged and tight.
With the jib down, you always have much more movement between the hulls
Cheers
Ron
H16 '82
Ron,
thanks! I did check the slop without the jib hoisted. I'll also check if there's as much movement when the jib is up and the rig is tight.
On the other hand, I started thinking about stiffening the boat when I noticed the slop while out on the water 
You're probably right that it doesn't have a huge impact on performance - it does bug me, though. And it feels kind of squishy when hopping those waves.
Regards,
H77
H77,
I must admit I rarely think about it and I almost always sail in big wind often with big waves. The H16 is so great in waves - maybe partly due to this "give". I've read that many people feel it may be the best all 'round cat in waves, surfing, etc.
I must say I've never been in a situation that I noticed it on the water nor found that it hindered anything. I'm usually trapped out and holding on for dear life. In these situations, hull slop is low on my priority list!
Cheers again and good luck
Ron
I would look into not filling the pylons wiht epoxy to support an aluminum tube as a way to stiffen the boat. If you decide to continue on teh route of making the holes in teh pylon round again, may I suggest an alternative method.
1)Attach (with an appropriate adhesive) an aluminum plate on the inside of the pylons that will cover each hole. The plate should match the curvature of the inside of the pylon wall.
2)Reinsert the pylon into the casting. Using hte hole inteh casting a a guide, drill a hole through the newly affixed plate on one side. Move to the other side of the casting and repeat.
3)To help prevent slop in the future, which will prevent the holes from elongating again, put a shim in between teh pylons and the castings. This will take out the slop, but you still can disassemble for storage.
Even if you don't fix the elongated holes, shimming will make teh pylon/casting joint tighter.
Guys,
thank you for your posts. I'll do some more thinking about Nick's aluminium plate solution. Or live with the slop, as Ron suggested 
Best regards,
H77
While everyone is on the subject....what adhesive is recommended to glue the frame to the pylons? I'll probably glue mine before next summer.
Short answer - epoxy.
Sunvista,
check
http:/
for Gary Willcox' article on his frame epoxy project.
Regards,
H77
Some caveats on that article:
It's unneccessary to glue the front corner castings to the front crossbar - the dolphin striker and rivets hold it together just fine. (This means you don't have to disassemble the front crossbar, either.)
DO NOT glue the sidebars in. They are non-structural and really serve only as a place to hold the trampoline (and to sit on). They need to "float" in the corner castings to allow for thermal expansion/contraction differences between them and the hulls.