Modern Cruising Under Sail the author reports successfully carrying bikes on a rack while off-shore. In another post describes the use of an unmodified rack (Narrow boat rack) on a British narrow boat.
I picked up this rack at a thrift store for a few dollars, cut away the parts that weren't needed, added a pair of Starboard hooks to fit around the rail, creating a simple rack. It's light, out of the way, allows easy unloading to a dock on the side, and easy lowering into the tender. I can use the bikes I have, and if one were to disappear or rust up, I can find cheap replacement bikes anywhere. Salt is a factor, no doubt, but ample use of oil helps and I don't cruise full time. A simple solution for most cats, at least.
I apologize for not offering more detail, but every rack and rail combination will present different possibilities. I will share this; most racks come with hooks that are meant to hold the edges of the trunk, but this will not work well on a boat, at least not on the PDQs. We tried it; the strain on the hatches looked scary and it makes opening the hatches awkward. As on a car, dedicated attachment points are much better, stronger, simpler, and cleaner.
When this one fails, I will make a permanent folding attachment to the rail, I think, only because I'm a tinkerer. (Note 9-22-2016: 6 years later it's still going strong)
- Bikes are secured to the stern rail in additional spots if bad weather is expected. Then, they won't move a bit. In ordinary weather and small craft advisories, we have found a single strap to be enough to prevent all motion.
- The rack simply hooks over the rail. A pair of straps to the base of the stern rail holds it down. Much simpler than mounting to a car. No new holes were required--I used climbing bolt hangers under existing stanchion bolts.
- Throw a towel across the tender before loading the bikes; they have many sharp bits.
Maybe it's a catamaran thing. But I don't think so.