<<Now that they are working, we are looking at various fuses.  Any suggestions, much appreciated.>>

Rob,

  Have you looked at an auto-release cam cleat? 

  Check out the video of a guy running his beach cat aground 2/3 of the way down this page:

    http://www.clamcleat.com/cleats/cleat_details.asp?theid2=78

  Dragonfy trimarans use a beefier version of this style for their kick-up centerboards and rudders.  I don't think they'd work on the original rudder design, but if you're moving towards shaft rudders, this might do the trick: one fore and one aft on a diagonal to the shaft.. 

  With some blocks and fairleads, you could even run both "downhaul" lines to near the center of the lw hull, making it quick and easy to recover after a kick-up.  Running the lines below deck would be quite slick, though would make it harder to observe them.

  There can't be too much more fore/aft loading on a single rudder than a Dragonfly 1200 sees on its centerboard at 20 knots, particularly with 94 m2 of windward sail area and a 5-ton empty weight.

  I imagine you could also tune larger versions of the cleat for general release forces +/- 10-20 kg or so, but that's just a guess. 

  Even if you can't adjust the cleats, you could always get a cleat that requires more release force than you want, and then mount it with the line entering at an angle that will pop the cleat earlier.  Every 0.6 degrees, give or take, would increase the vertical component by 1%, allowing some pretty fine tuning.

  In any case, I can't think of much that would be simpler, more likely to release when needed, or easier to reset.

        - Mike

 
   
Rob Denney wrote:

On Wed, Sep 14, 2011 at 2:18 AM, Gardner Pomper <gardner@networknow.org> wrote:

I have watched all the available videos from Rare Bird and Blind Date and I have a few questions on the rudders (Rob's version, not the replacements that didn't work out).

The current ones are not specifically "my version". My version did not work on Rare Bird when first launched. Mark (builder) then redesigned them and after a couple of alterations, they work well on RB. The beam mounted ones on BD were scaled up versions of the ones that work on El. The current BD ones are beefed up (mostly the X bracing on the cassettes) versions of BD's. If this is faired, the spray will reduce considerably.

Can the rudder blades be lifted for shallow water sailing?

Yes, but too far and shunting/sailing gets tricky. As shunting experience increases, the sailable draft will drop. The blades are raked forward to keep the coe in line with the rotation axis. As they are lifted, this gets out of line, so loads increase. High speeds in shallow water will not be possible.

I believe they kick up. Am I correct?

No. They were designed to fall out the back of the case in an impact, which they do very well on BD. I don't like this system as the loads on the case as the board exits get large. The back of the case was closed off when the X went on BD and a sacrificial tip put on the boards, which is a partial remedy. Now that they are working, we are looking at various fuses. Any suggestions, much appreciated.

Other than the excessive amount of spray, these seem to be a very solid and reasonable way to install the rudders on a HarryProa. However, since Rob has been trying alternatives, and Blind Date replaced them completely for a while, there must be some problems with them. Can I get an explanation of why these rudders aren't a good idea? Most of the alternatives seem to lose the support down near the waterline, which would reduce the spray issue, but require stronger, heavier and more expensive rudders.

I don't like the drag, even when faired. It is also connected to the hull, albeit above the waterline. Hence the beam rudders, which are far less drag, not attached to the hull but need more support. This is a small price to pay for the other benefits, if they work. I still prefer the side mounted rudders to in hull rudders for safety.

My leading alternative right now is the asymettrical rudders that Todd has been using, but they also have a support near the waterline, so if the Rare Bird style of rudder works, it seems like less risk. Related to this, there was a comment about it being possible to reduce the spray from the rudders by sharpening something... I wasn't clear on what. Might it be possible to reduce spray significantly? I am not seeing how to do that. Related to that, have either boat ever run in heavy seas? Doesn't the rudder mount get submerged? Is that a problem?

Fairing the boxes will reduce the spray. Presumably Aroha was run in large seas at some stage, but no issues reported. The rudder mount will be submerged, but is not a problem per se unless it hits something.

My criteria are the ability to lift for shallow water and drop for deep water. Ideally, it would be easy enough to lift that I could just pull the forward rudder up and reduce the spray when on a steady course. I also want kick up protection and wheel steering.

Impossibilities on the spot, miracles take a little longer! I have high hopes for telescoping beam mounted rudders, but have not built one yet. Your requirements are met fairly easily, except for the wheel steering, which is very difficult. Nol, Sorry for the overlap, wrote this before I read yours. Looking forward to the next edition. When does the boat come out of the water? rob rob

Thanks, - Gardner