TAMUmpower wrote:
No, glue wont work. A big enough plate riveted over the location would help but be super ghetto. Just weld it, a decent shop can handle that even if they have to put a thin plate on. It's gonna affect the dolphin rod angle since the striker rod wouldnt go as far through the beam with the step sitting on a reinforcement plate but it should still be fine.
Welding the crossbar won't work. The crossbars are made from 6061-T6 aluminum, which is a tempered (heat treated) aluminum. Welding on it compromises the heat treatment in the area of the weld, and the aluminum will likely crack again right along the weld. Standard 6061 aluminum has a yield strength of 8,000 psi and tensile strength of 18,000 psi, while T6 aluminum has a yield strength of 35,000 psi and tensile strength of 42,000 psi. If it's cracking, it's either been stressed close to 42,000 psi, or frequently stressed/fatigued at >17,500 psi. If you weld on it, you reduce the strength of the welded aluminum to as low as 11,000 psi. No epoxy is going to build that kind of strength back. The only means of repairing the crossbar are a mechanical means, like srm suggested, with a riveted reinforcement plate, or to weld and then heat treat the entire crossbar, which involves putting the crossbar in an "annealing" oven and heating the aluminum to about 775 degrees for several hours, and then going through a slow, controlled cool down to relieve the built in stress from welding. (
https://en.wikipedia.org/wiki/6061_aluminium_alloy)
Note that mechanically joining two plates together is a very imperfect means of transferring stress. In the days of riveted ships, a single row of rivets was expected to transfer just 21% of the stress on the adjoined plates, while even a quadruple row of rivets was only good for 67% of the stress. This is why riveted ships had such thick hulls, the steel was greatly oversized to account for the imperfect method of joining plates. I'd honestly be weary of the riveted doubler plate approach to repair a cracked crossbar, as four rivets aren't a very seamless means of transferring stress from the doubler plate to the crossbar.
As I mentioned in the posts about the mast step, the forward crossbar right under the mast step is the point that is under the most load/force on the entire boat. If you increase the tension in the tension rod, you can relieve some of the stress on the crossbar (that is the purpose of the tension rod, to help share the load of the crossbar), but you'll never relieve enough stress to be able to sail safely with cracks in the crossbar. I'd look for a replacement. Hobie does sell them for $572, currently. There are also a handful of ebay users that collect spare parts like crossbars and tend to sell them for around $300-$400.