Hi Chris,

I like where you are going with your concept. Can you give us a hand full of data about it?

I think as a beach cruiser you should stay with the side mounted rudders. The Newick daggerrudders, which áre so brilliant in deep water, will make a lot of trouble when it gets undeep. If you still want to use them, it may bee a to good idea to design them to maximum efficiency “offshore” and if you sail in flat waters lift them both and steer with an oar.

Don’t care too much about ventilation of the surface piercing foils. It’s more a theoretical problem than a real one. In the real world ventilation starts at around 15 knot if your rudder is swept a little forward . I sailed on a Kellsall Cat with air mounted rudder and board and we had no problems with ventilation until 16 or 17 knots and thats pretty fast.

Even if your boat is faster than 15, wich is unlikely with the small sail of 97sqf. you are planning, there are some tricks to delay this problem even further. Special profiles or a special form of the leading edge will help. But for this I have to dive deep into the windsurfers trickbox and make some research first. One option mentioned was to have a sharp leading edge at the area where the foil meets the surface of the water. I think this will help. But there are other details on the market.

Best Regards, Michel

One of the techniques to handle ventilation is to have “fences” parallel to the waterline which help shed the air that starts to travel down the foil. I’ve wondered if doing the reverse and cutting grooves in the foil surface would work as well and could be done on dagger type foils like Gary D is using. Kinda moot at the moment, don’t have anything that’s going to be hitting those 15 knot + speeds, 10 to 12 is plenty, especially if you can maintain those kind of speeds in most conditions.

cheers,
Skip

I really like Gary’s rudder design.  That’s the way I’m going with the 16’ Wa’apa my daughter and I built (but have only paddled so far).  Being able to vary the depth of the rudder would be a nice tuning trick. Ventilation is not my only concern.  Having all that stuff hanging off the side where the water can hit it feels inelegant.  But the simplicity and kick-up-ability are terrific.  Are Newick dagger-rudders inappropriate for a beach cruiser?  My Nacra 5.8 had deep daggerboards that did not kick up or have crash blocks, and I never had a problem with them—including beaching.  There was the time we hit a sea lion though.  Poor guy.  The daggerboards and cases did fine.

There’s some part of me that wants to reinvent the steering paddle.  Or maybe fan shaped centerboards in either end like Michael’s monoproa.  I’ve tried imagining a trim tab on a pivoting centerboard, but then the tab would prevent kick up.  Or maybe when they kick up there’s some sort of linkage that straightens out the tab real quick when it detects the urge to kick up.  Sounds complicated and fallible.

The beach cruiser is just a thought experiment and exercise in proportion.  But there is a little thinking behind it. 

The sharp keeled, 3 plank, asymetric Walap-esque vaka is to resist leeway and get the unstayed mast windward of the keel.  Also I like the way it looks.  LOA is 20’, 18’ish on the waterline.  He’s about 12:1 L:B at the waterline.  The beam overall, center to center, is about 10’.

I want it to be the simplest, smallest practical proa I could imagine.  Practicality, in this case, means that it can daysail 2 or cruise with 1. 

If the vaka split in two, you might be able to get it on a roof rack (maybe..) or stuffed in the back of a pick up.  It sure would make it easier to drag out to the beach in two pieces.  Perfect for the walk from the parking lot to the beach in Hanalei. One piece construction would be lighter and simpler.

Chris

For the rudders have you considered a system similar to Harmen Hielkema’s boats? He uses asymmetric daggerboards. Raising and lowering steers the boat. Apparently the lift effect you get is as good as turning a rudder.
-Thomas