Sailing is Fun, But is Heeling Fun?

My theory on why some people love their monohulls is that speed is fun, and if you have grown up on monohulls speed is associated with heeling.  The only catamaran sailing I've done has been on beach cats.  A few times I've had nice windy days where I got to drop off the kids and get some actual speed (between them all their weight adds up), I didn't miss heeling one bit.  Since I'm on the subject of heeling, here is a picture of me and the kids heeling over a J-70 on a breezy afternoon.

A Plan Made in Haste.....

I cleared my boat stuff out of my boat shed to make room for my son's birthday party (see "Boat-Life Balance" 9/21/15). I thought I if I gathered the materials I could work on rudders in the garage until I get my boat shed back. I was wrong. I forgot to account for where all the boat materials would be stored.

As you can see I won't be doing anything in there in the near future. One good thing that did come from this is that I did think through how to make the rudders and I will still do that next. Somewhat simultaneously with setting up the level frame on which to build the first Ama.

Found Alaskan Yellow Cedar for Rudder Spars

So I'm in gather materials mode for the rudders. The rudder drawings call for spruce for the rudder spars, but the only spruce I could find near the house was a bit too thin 3/4 inch instead of 20mm. So I drove across town and found Sitka Spruce that would work, but for the same price they also had Alaskan Yellow Cedar. So I went with the AYC. Its really amazing how much this lumber does not weigh.

Next problem will be how to cut very accurately. Thinking I will rough cut it on the table saw and then work it down to size with a power planer.

Paper Scaling Vs Trig

So I used the scale printout for the rudder section to find the half angle for the rudder construction jig. At first I just took measurements and used trigonometry to find the angle. I got 31.6 degrees. I then laid out an extension line on the printout and measured it on paper with a protractor. Fully expecting my trig to be verified. It wasn't. By laying it out on paper I got 34 degrees. Then I looked at my measurements again and realized that very small difference in what you read off the scale make a huge differences in the angle calculated.  So I printed out a scaled up version and repeated, this time I calculated an angle of 32.6 and measured 33. I'm going to go with 33.

Using Draftsight for Templates (Scaling)

So Bernd's instructions for rudder construction call for you to print out the drawing at 1:1 scale and use that to find some dimensions.  Having had no end of problems with this sort of thing in the past I was all set to send this to a print shop and deal with the hassle of having to go out to pick up the paper. For giggles I tried to print it out at home. Sure enough I measured the rudder as printed at 17cm when it should have been 22. But as I was poking around the print interface in Draftsight I noticed the print scale is in the form of a ratio. So I plugged in 22:17 as the ratio and it came out perfect.  Not a huge deal but it saved me some hassle.

Why I chose a DUO 660

Start with the understanding that there is no better all around boat. Certain boats may be better for certain uses, so the place to begin in choosing a boat design is to be honest about how you intend to use the boat. Not so easy since sailing for me is aspirational and spiritual so how can more not be better.

So here are my considerations:
My family likes boats if they can jump in the water and play. They will tolerate me simply enjoying to relative silence and peace for awhile (not long).
We like to go crabbing in the summer, but don't like hauling the inflatable and rowing to the crabbing grounds.
Puget Sound is always cold to the touch.
My wife is prone to seasickness, although she is getting better.
I harbor a deep and abiding animosity for convention.
We still have to pay for three college educations so the bank must not be broken
Need to carry the family and hopefully a guest (6 persons although many are small)

So going from considerations to requirements I came up with the following:
Seasickness: Means it needs to either be a catamaran or a trimaran.
Capacity: Trimarans are not much better than monos for people carrying so it pretty much needs to be a catamaran.
$:Besides the build cost the truly scary cost to consider is moorage. In Seattle the sailing season is relatively short. So to avoid paying for moorage in the winter, the boat must be trailerable. That way I can store it either in the driveway or in a much less costly storage yard.
$: Building the boat myself saves money in two ways. First the labor is "free" but also commercially available catamarans seem to be either not trailerable or beach cats. It seems the only way to get the boat I want in the first place is to build it.  Also building myself also has the benefit of spreading the cost over time.
Convention: I really like the bi-plane rig. It puts the structural loads in the place that makes the most sense and is apparently easy to sail with no jib to mess around with when turning.  Ease of sailing is also of great benefit when sailing with only mildly alert kids.

Going from requirements to design selection:
I tried to treat the bi-plane rig as a bonus rather than a requirement since that would have severely limited the choices. Actually it came down to selecting either a Richard Woods or Bernd Kohler design.  I chose Bernd for a few reasons; his designs seemed to weight ease of build more than the Woods designs, he has an easy to detect reputation for after sale support of his designs, and his designs are more unconventional. He has Gunther, Biplane and even "A" frame mast rigs in his stable. With Bernd I could get the right sized, trailerable, easier to build, Bi-plane rigged catamaran and get awesome support.

Other notes:
The 660 uses anti-vortex panels instead of a centerboard or daggerboard.  I read Bernd's paper on them and everything I could find online.  The physics make sense and I think the trade off is that you are accepting a bit more wetted surface area (vs board up) for alot more simplicity. Given that this light catamaran should already be plenty fast I think it is a good trade.

Biplane rig. The reason this is so cool (besides the  easier structure on the boat) is that it allows for a lower heeling moment on the boat for the same sail area.  Basically more of the force on your sails can be put to work propelling the boat instead of tipping it over.

Radical Bay: Schionning Designs of Australia has a Biplane Rig design. While I like the thing I think there are issues. It is too beamy, its been thousands of years of testing that has shown a 2:1 length to beam ratio works for a sea-kindly catamaran.  Not sure why they chucked that out the window.  That is my main complaint, as for my build it is too long for me to build at home and uses strip plank construction. Stip planking while not impossible, is more difficult than I want to deal with now.

So here is a picture of what the finished catamaran should look like. This is taken from Bernd Kohler's website: http://www.ikarus342000.com/CATpage.htm .  His site has many designs for various needs.