Rudder Chaos

Last we left the Macgregor rudder, I was in the planning phases. We took a trip to Woodcraft not far from the house. This is an outfit that caters to woodworkers, from turners to carvers to form/function guys like myself. I like visiting that store because they have a good selection of exotic hardwoods that are rarely found in person. Marblewood, for example, and Bubinga and Wenge and of course, Padauk.

We settled on a board of Mahogany. Not sure if it's African or whatever, but it was really nice. Good lines, mostly flat, vibrant grain, and just the right size. The price was reasonable, so we hauled it over to the counter. The cashier who ran the card asked what I was going to do with it. Why, build a rudder of course. His eyebrows raised: a rudder? That should be fun, and he was serious.

We got it home where it sat in the family room for a couple days as I finished up some PocketShip parts (trimming the 'glass off the cockpit decking) and got the area ready for some work.

The board - it is 1x15x75 solid Mahogany.

I also needed to plan out the strategy. There's a wide range of rudders out there. A 2x4 can act as a rudder, just not a very good one. And the Macgregor is not known as a performance boat, so it needs every bit of finesse it can get. I did some research and found an outfit that sells the tiller-block-rudder assembly in high end plastic (though with a laminated tiller) for about $900. That's more than the boat cost. But what was nice about that site is I also got the specs. It turns out the existing rudder is very close to spec except for the foiling.

I don't know when foiling came into vogue for rudders, but the old one definitely was not foiled. There's a little bit of rounding, but nothing near the specs called for in the NACA 012 tables I pulled down for it.

If you want to use this, just input the right two columns under "NACA 012 Ratios" and then calculate the rest.

Graphic representation of the table, minus the German.

NACA 012 are industry-standard foil specs for foils. The table works very much like offset tables when lofting a boat. The table is given in percentages against both the Y and X axes. Apply the percentages against the length and width of the block (or chord), and you've got how far from the centerline it should be. I entered the percentages into Excel, input the size of the chord (11 9/16") and it spit out the specs. Nice!

NACA 012 is the one used by the third party rudder maker, so if it's good enough to cost $900, it's good enough for me, too.

Tracing the pattern. I went a little wide to give some room for error.

It was planed, rough cut, and sanded, waiting for next steps. Everything was cut a little larger than the actual spec for a few reasons. First, it's of course much easier to cut a tree than grow a tree. If I make a mistake over, I can always sand back. Second, epoxy ooze can muck up the finish. The less finished area that has epoxy on it, the better it will look. Third, I was lazy and didn't feel like following the lines as much as I did. It's all close, but maybe 1/4" larger all around than it will be when done.

Old rudder where the kick up line is. Looks like a shark took a bite out of it.

Tables and drawings and rough cuts.

Trimmed and rough cut with table saw and jigsaw.

Taking a page from the PocketShip centerboard build, except without the table saw madness, I cut a nice little dado into the blanks which will become the trench for the leading edge epoxy. I almost made a cardinal mistake by cutting non-mirror images of each other, but thankfully I dry fit it first and realized the near mistake. I also cut dados instead of rabbets because rabbets are easier to cut for me, and I knew I'd be filling in this trench so I wanted any squeeze out to fall in here.

Cut dados for epoxy trench.

Hole all the way through. Two dados = hole. The left 1/4" or so will be cut away.

I wanted to increase shear strength, reducing the ability of the boards to slide past one another. Water moving past the rudder faster along one side will put more shear force on that board. Probably way too over-thinking and over-engineering, but I wanted to be sure the rudder would hold up to those forces. And since I'm not cutting "blocks" and re-installing them grain-against-grain, I fast tracked it and installed dowels. The dowels, though small, will provide added strength and stability, plus also allow contraction and expansion in these smaller joints. When the rudder gets shaped, some of these are likely to be visible, but only barely.

Added dowels.

Three batches of thickened epoxy made for a nice bit of lather. I'll probably need to order some more epoxy for PocketShip but my wife said she'd help pay for that since I'm using a good amount on "her" rudder and tiller.

Lathered on thickened epoxy.

I brought out the clamps again and set the planer on top (with a small board under it to even the pressure and not muck up the surface).

Clamped and planed. Sort of.

This will sit for a couple hours before I scrape off the epoxy ooze. If all goes well, I'll cut it to spec and start shaping tomorrow. It's going to take a lot more effort than the centerboard as this is 1.5" thick. The air foil goes down to nearly a point at the trailing edge, meaning at least 1 1/4" is going to be sloughed off. In the meantime, I ordered a quick release cleat for the kick up which will go a long way towards rudder life. Progress is slow, but progress is good.