Hobie 16 Rudder Blade Drilling Jig

This is a jig I use to drill (or re-drill) Hobie 16 rudders with precise control over the rudder rake. The rake of the rudders influences how much or how little helm your boat has. Raking the rudders further under the boat reduces weather helm (tendency to pull into the wind). Ideally you want enough rake so that you have little or no helm when sailing to windward. 

The standard measurement for rake is to measure the leading edge of the rudder relative to the rudder pin axis (a line extending down through the center of the pin). At a point 12 inches below the bottom of the casting, the leading edge of the rudder should be between 1-1/4" and 1-3/4" forward of the pin axis. Here is the jig:

It's basically just a flat sheet of plywood big enough for the rudder, with a 2x4 "transom" and gudgeons mounted on it. The gudgeons are positioned such that when the casting is mounted, it lies perfectly flat on the plywood. The pencil line running from the gudgeons is the center of the rudder pin. In the bottom of the photo there is a "fence" with an adjustment screw that lets you set the rake relative to that line.

Here the casting is mounted in the gudgeons, and the blade is inserted in the casting. The clamps keep the front of the blade firmly seated against the casting. Ignore the bolt through the casting and rudder -- this rudder is already drilled so I'm "cheating" a bit for the photo session!

The block in the foreground keeps the blade level. You can check this by going around at various points on the blade and measuring from the plywood surface to the center of the blade, adjusting the block or adding shims as needed to level the blade.

This table shows how to set the adjustment pin for the desired rake. The line in the center is the rudder pin axis. The fence is 50mm forward of that. So the rake is the difference between 50mm and the amount of protrusion of the pin. More protrusion = less rake.

In my case I wanted about 1-7/16 inches of rake, or about 36mm. So I set the pin at 14mm (=50-36). I have found that EPO3s need a little less rake than the older rudders. This may be because the rubber pad where it inserts into the casting pushes the head of the rudder aft a bit, which has the effect of pre-raking the blade in a way.

Before inserting the rudder to drill it we set the drill press up to align the bit with the holes in the casting, as in this video:

(Ideally you would do this before clamping the blade in place; I took the photos in the wrong sequence.)

Then simply insert the blade, clamp it in place, install a 5/16" bit, and drill baby drill!

If you do not have a drill press you could do this carefully with a hand drill. A block with a guide hole drilled through it would be helpful in this case.

I do not have pictures of drilling the hole for the upper casting. Once the rudder is bolted into the lower casting, position the upper casting in place with the cam locked down. Mark the rudder through the hole in the upper casting and drill at that spot. If you have adjustable upper casting, put the adjustment plate roughly in the center to mark the rudder. After drilling you can nudge the plate forward to tighten up the cam engagement so the tiller arms are snug when the cam is closed.