Hull 215 Rudder Dissected
Camelot (sistership to Ursa Minor #178)
By Nick Wigen

 

Camelot and Ursa Minor are identical fin keel, 3-cabin MkI boats built in 1990 that share adjacent slips in Portland, Oregon. A couple of years ago Bob Teeter upgraded his rudder to the newer elliptical design while Ursa Minor is still blessed with the old barn door slab. The new rudder has beneficial effects on boat handling but any improvement in boat speed is small enough to get lost in variations in sail trim, luck and sailor attention. We’ve found when racing head to head we both generally lose about the same number of causal races. Our plan for Ursa Minor is to upgrade the rudder fairly soon.

Camelot’s rudder sat in Bob’s garage gathering dust and getting in the way. Recently the planets lined up just right where I had my utility trailer at the moorage and he wanted to get rid of the old rudder. There may have been beer involved… Anyway, I ended up with the rudder in my carport with a vague idea of stripping off the fiberglass, reinforcing the stock and building a new rudder. Here is a story of those events.

I cut around perimeter to a depth of about 1” with a carbide blade in a Skilsaw. I expected the rudder to be made of a fairly soft foam core and a thick fiberglass shell so it would split in half fairly easily. Instead, the construction method appeared to be to form the shell with a fairly thin layer of woven glass cloth and resin and then inject a mixture of resin, glass fibers and some light weight foamed resin beads. Here is a close-up of the edge showing cut and split areas. The core material was fairly hard and dense. A small portion would just barely float in water. The core could only be taken apart by cutting, chiseling and chopping.

It appears that the fiberglass shells were molded and a layer of honeycomb type cloth and glass fibers was layered into the uncured resin. The outer skin could be peeled with some difficulty but came off cleanly. Here is the core after the cloth and gelcoat skin was removed. You can see the honeycomb layer. There are some voids between the shell and this honeycomb layer. Although these voids were fairly large there was no evidence of any water intrusion. While not especially impressive, I would not think these voids were a structural problem on this rudder..

The rudder stock was a piece of 2 ½” schedule 80 (Double Strength) stainless steel pipe. I was quite shocked to find out that the web was only 3/16” mild steel plate! Below is a picture of the stock with the plate welded to it. The 3 round holes were so the core material would tie the 2 sides together.

Here is a close up of the weld between the mild steel plate and stainless steel pipe near the bottom of the pipe rudder stock. The weld area was cleaned with a wire brush on a heavy duty angle grinder. Notice there is some loss of steel due to corrosion – perhaps 5-10% of the plate thickness.

The bottom end of the pipe rudder stock is closed by a steel plate but not seal-welded. This is a good path for water to come directly into the rudder interior. Evidence of water intrusion was seen – the surface between the mild steel plate and the cast core was wet. Water was also found where the pipe entered the top of the fiberglass rudder body. The gap between the core and the rudder stock seen here was caused by blunt force trauma during the dissection and was originally found to be tight

Conclusions: The general method of forming the shell and injecting the resin/fiber mix appeared to provide a solid structure. Two things do concern me about the way this rudder was built. The use of plain carbon steel below the waterline seems to be foolish economy. Camelot has spent all but a few months in fresh water. It would be interesting to see what a rudder with full-time saltwater immersion would look like. The other concern is the compete lack of bracing or reinforcement against the torque transmitted to the rudder which is carried only by the single plate. My company uses heavy duty air control dampers in our equipment and we have seen failures of the weld between the blade and shaft when this method is used. We would never accept this configuration. Before buying a replacement  rudder from Catalina I would need proof that they have changed to a proper design.

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