Just finished making and installing hardwood treads to make it (much) more comfortable to climb the swim ladder on my 27. The Admiral had complained that the original 1" tubular stainless steel is really hard on the feet. This was a fun project for a cold, rainy winter weekend at home. Here's the finished ladder:
The treads can be made of any hard, durable wood. I like oily tropical hardwoods since they are very weather resistant. I used Ipe (sometimes called Brazilian Walnut) because I had a spare board left over from a home deck project. Ipe looks like mahogany, but is much harder - very fine grained, hard as a rock, incredibly resistant to weathering. For my ladder, I cut a 3/4" thick board into 2.25" wide strips.
I drilled 1" dia. holes spaced 15.75" on center (measure your ladder to confirm), then cut through the center of each hole to form half-circle notches that fit around the vertical tubes. I used a router table with 1/8" straight bit to cut two 1/8" wide by 1/8" deep grooves, each one centered 5/8" from the edge of the board, for drainage slots. Finally all sides were rounded using a 3/8" radius roundover bit.
On the bottom of each tread, I used a 1" diameter round nosed bit on the router table to cut a 1/4" deep groove or "saddle" to fit over the stainless tube.
Attaching of the treads was done with #10 x 2" flat head stainless bolts, cut down to 1.75" length, with #10 nylock lock nuts. I used a #10 countersink bit on the drill press to drill the treads, then clamped them in place and drilled through the stainless tube with a (new, sharp) 3/16" bit.
Finally, I finished the treads with Watco teak oil. Finishes that form a surface film (varnishes, polyurethane, translucent stains like Cetol etc.) do very poorly on Ipe. Oil finishes are good, or just leave the wood unfinished and it will weather to a beautiful silver gray color like cedar.
Tip for CP-19 owners: you can do exactly the same project, but since your ladder is made from 7/8" tube rather than 1", use a 7/8" spade bit to drill the large holes, and a 7/8" round nose router bit to cut the bottom saddle. I would downsize the width of the treads to 2" for the smaller ladder. Have fun!