Thursday, June 14, 2018

Rudder Rebuild and Adding a Fence

Why a fence? Because occasionally when bearing off hard at speeds over 12 knots and frequently at over 15 knots, the rudder will ventilate, compromising control. Air sucks down from the top, releasing the water on the lee side and reducing rudder force by about 1/2 just when you need it most. Better sail balance and gentle, preemptive steering help, but sometimes gusty conditions require a firm hand. Once the bow starts to dig in the under water center of effort moves way forward and gentle isn't enough.

Adding the fence is a simple project. Hack out a U from a bit of1/8-inch fiberglass scrap and bond it in place with a filet.

 Scaled from Ians design, printed, and traced onto 1/8-inch fiberglass. Should work.

The rudder itself was in good condition. A little fairing here and there, some sealing around the rudder shaft just to be sure, and she's good to go.

The problem is the rest of the rudder system:

  • The PO used a flat head bolt in the tiller pivot. This acted as a wedge, cracking the head of the wooden tiller. Fortunately we caught that early, and with a new bolt and a plate on each side, it will be fine. 
  • The bolt was all-thread. NEVER EVER use an all thread bolt for a pivot. They don't fit well and the threads are like a file inside the hole, cutting the hole larger, in this case about 1/8-inch larger. I filled the hole with epoxy and chopped glass cloth (cut 1/2-inch wide strips and stuff them in the hole after filling with epoxy--it really helps) and re-drilled. Good as new.
  • Never use fender washers where there is real load. They bend too easily. Both were bent into cones and had crushed the wood. Fill, sand, and install 1/8-inch aluminum plates. 
  • It was also just do for sanding and varnish.
Tiller to cassette fittings:
  • The PO used a galvanized bolt in the upper. That took some time. Others were seized with time. ALWAYS use Tefgel or Locktite Marine Anti-Seize.  
The cassette. These are the serious problems. The lower portion is shattered and the lower rudder bearing is just floating around. The PO attempted some repairs with Bondo. Good grief.

  •  The upper pivot was broken loose and worn oversized. The carbon bushing was just floating in the core foam. Fill and re-drill. And add some fresh fiberglass to replace damaged laminate.
  • Add some glass to reinforce the top. The cassette was molded in two parts that were just glued together, and they are thinking about separating. A few layers of 6-ounce cloth should be enough to discourage movement.
  • The lower bearing area was a complete rebuild. Grind out everything that is bad, replace with more glass, including multiple layers of unidirectional on the sides. Mostly 17-ounce triax and unidirectional instead of 6-ounce cloth, since real strnegth is needed. Also filling cracks in foam with epoxy.
So how is it coming?

 I ground off the junk and replaced it with 3 layers of 12-ounce unidirectional and 2 layers of 17-ounce biax, with 6-ounce cloth over everything. Strong.

 A thick filet holds the fence in place.

 Pivot holes in the cassette and tiller had to filled with epoxy+glass and redrilled. I also replace the worn surface glass with 2 layers of 17-ound biax. Should be better than new.

All that remains for the rudder and cassette is a final sanding and 2-3 layers of paint. The tiller needs ~ 3 layers of varnish. The anchor well cover is still drying in the sun. One more day, and then I can fit the core and cover it up, plus 2 coats of paint. 
Repairs like this are expensive, not because they are difficult per se, but because the many steps are time consuming.

Zoom! Not my boat, but a sister F-24.


  1. I really enjoy your articles in Practical Sailor...probably my most favorite part of the magazine. Sorry that I just recently found this blog! I especially like your methodical approach and detailed explanations. As a novice fiberglass hobbyist, this article got me wondering - when doing repairs, how do you choose between unidirectional, biaxial, and cloth?

  2. I'm glad my writing helps. I try.

    As for picking cloth, in general I will use 6-ounce finish cloth on the surface, just to make it smooth. However, even though it is light it does not conform as well as you would hope. I like 17/3 ounce biax (3-ounce mat on the back) for building general strength. It gets nice and floppy when wet and builds glass fast, with minimal resin. Then us unidirectional when you KNOW the direction of the stress, like a stringer, for example. However, I tend to alternate uni with either cloth or biax; there is always some force the other way and it hold the uni in place.

    I prefer uni over carbon for most things, because it's stiffness is similar to the rest of the fiberglass. The problem with carbon is that it is so stiff, it will try to carry the whole load by itself, often introducing stresses you did not intend. It's sort of like reinforcing wood with steel; the steel carries the load.

    If you want a direct response, the e-mail tab at the right is faster.

  3. That makes a lot of sense. Sure is nice that you can utilize multiple layers, each with its own unique properties to get a customized repair or new build. Thanks for the reply.