Subject: Re: [harryproa] Survey/build/feature discussion - Rudders/foils
From: Gardner Pomper
Date: 1/20/2013, 4:57 PM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Mike,



AUTOPILOT. 

  As for an autopilot, I'd use a Raymarine ST-4000 tiller pilot.  The control goes inside, or at least at the cockpit, and just the mechanical portion sits out, the base connected to the leeward hull, the end connected to the tiller (not the extension).  I use one of these on my catamaran with great success.  If patched into the nmea system, you can even have it steer to GPS waypoints, or to the average wind direction of the last minute. 

So, would you just have 2 autopilots? One for each tiller? I guess that would be simplest, and somewhat affordable, since we are saving so much money on the boat <grin>. 


12' FOLDED BEAM. 

  I hear you about not being able to fit in a full-sized permanent cockpit in to a 12' width while folded.  I've tried, and if everything is just so, it might be possible, but only if I skimp on the interior, the cockpit, or both.  Given that I'm shooting for a table inside, and a 6' cockpit, there may be no way it can happen unless there's a funky system like your Contrarry where the cockpit overhangs the leeward hull when folded.

  Going along with your idea of a removable cockpit (or Dennis' flip/folding one), how about a 14' width to 16' width while folded, going down to a 10' or even 8' width while trailering? 

My current drawing gives a 14' beam while folded on the water. That is is with an interior table (4' width) plus a 4 1/2' wide removable cockpit. Since the table, galley and cockpit are all on the same level, I think that the cockpit is large enough. I can send you my drawings, if you like. I don't want to bother posting them to the group before Rob is finished with them.


FOILS.

  Could you point me to an image of Todd's design with a fixed vertical steering board?  I think you mean the one here: http://www.youtube.com/watch?v=Jn8fr0PaUqg , but want to check 

  If you went with this, how would you incorporate raising and lowering the foils?  Or would you just count on your hull design to counter leeway, and have the foils raked way back for sailing in skinny water?  And how would that work with the hull profile you're planning on? 

That video does show the basic structure of Todd's rudder design. I don't have any drawings of my ideas right now, but I better get on that (if I want to convince Rob) . For now, just imagine that instead of just having a rudder attached to one of Todd's steering boards, you have a rudder case, like Rob's. That case allows the rudder to be raised and lowered, so if your blade is 8' long, it can go from a 2' draft to a 6' draft (or so). If the rudder hits something, the case pivots with the rudder, but the steering board stays vertical. That would also allow the rudder to cant 20 degrees or so in order to stabilize the symmetric rudder. I have a mechanism in mind that would make that canting operation automatic during a shunt (it is tied in with the mainsheet).

Overall, I am pretty happy with the layout. Hopefully I can get some builders quotes, which will give me a better idea if I am ever going to be able to turn the plans into a boat.


        - Mike





Gardner Pomper wrote:
 
Mike,

Just a couple of comments:


  BD has special draft requirements, as does Gardiner's plan to sail in the Chesepeake, and both could be nonoptimal with low-draft beam-mounted rudders.  Without enough foil in the water, it's easy to go from laminar to non-laminar flow, and then the foils become a lot less effective.  But such is the challenge with a 48' boat designed to sail in 3' water, and yet somehow be expected to hit 20 knots (by observers, not by the owner).

I don't want to sail at max speed (15 knots will do for me!) in 3' of water! I just want to be able to sail at 5-6 kts in shallow water. I want to sail at 15+ kts in deep water (> 30'). I even want to ghost along at a couple knots in 1-2' of water (with a soft bottom, like  mud or sand) for anchoring. It is very important to me that the rudders raise, but it is also important that they lower to 5' or so.

  Just as important, rudders on the beam would permit simple tiller extensions all the way to the cockpit, which is something I'd definitely like to try.  It's a simple system that wouldn't care one way or the other if the boat were folded or unfolded, won't stretch out of shape, and will be more fun than using a wheel.  At least for me -- I much prefer tillers.

I am not clear on the tiller idea. I would be happy enough with a single tiller, but I am having a hard time seeing the use to two tillers; sometimes one at a time (having to stow the other partway through the shunt) and sometimes both (to be able to use both rudders). Am I just missing some simple way to do this? Plus, I am not willing to give up on autopilots when cursing, so how will that work?

Because of these questions, I am trying to move forward with the idea of using a wheel. As much as I love how clean Rob's new rudder desgn is, I don't see how to make the steering simple. Instead, I think that Todd got it right with his rudder design, where the steering board is fixed vertically, and the rudder case is pinned to that board and kicks up independently. That allows the steering system to work regardless of the cant of the rudder, or to impact.

Btw, I have also hired Rob to try to help put a design to paper with all my weird-ass requirements (on water folding, fit in a shipping container, etc). I think I may have had to give up on the 12' beam for trailerability (sorry, I tried to put that one in just for you!) but for now, there would be (minor) disassembly to make that happen (have to remove the removable cockpit). When Rob has beaten some sense into me and come up with drawings, I would also be happy to share with the group (with Rob's permission).

        - Mike





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