Please visit our home site at www.TRILOBOATS.com.

Anke and I are building our next boat, and writing about it at ABargeInTheMaking.blogspot.com. Access to the net comes and goes, so I'll be writing in fits and spurts.

Please feel free to browse the archives, leave comments where you will and write, and I'll respond as I can.

Fair winds!

Dave and Anke
triloboats swirl gmail daughter com

Thursday, February 2, 2012

Travelling OffCenterBoards




Board in stowed position.


We love Big Windows, and we love OffCenterBoards (OCBs, in our case, are like leeboards prevented from winging out on the windward tack... this lets them stay down and effective on both, with no tending between tacks).

But this presents a problem. When stowed, OCBs go more or less horizontal, and pretty well eliminate our view.

What to do? What to do??

After considerable head scratching and a false start or three, we came up with the following system...

Approximate component locations, Position Line not shown... see schematic for close-up.

Schematic for components above and aft of Window.


The general idea is that the board hangs by the Lanyard, from a block running along an SS Cable, high on the hull.

The Board's position is controlled  via the running Position Line, which is a loop through the EyeBolt and a shackle at the forward Bracket, with both ends fixed at the shackle of the inverted, Running Block. Pull aft on the upper portion of the loop, and the Board rolls forward, and visa versa. To fix position, jam upper portion of Position Line in the Clam Cleat. This is oriented to prevent the line from slipping forward, and therefore preventing the board slipping aft; no forces make it slip forward.

Additionally (as seen in profile in the first schematic) a second SS Cable forms a slot between itself and the Board Guard. The Board fits in this slot during daily use, and is prevented by the cable from winging out on the windward side. Leeway presses the board tight against the guard on the leeward side, in the manner normal for LeeBoards.

To stow, release the Position Line. Using the Board Retrieval Line, raise the Board clear of its slot, and roll aft. Pull up to lodge the stopper knot in the Board Retrieval Line in the crotch of the Pinch Cleat, then make the fall fast around the Horn Cleat.

To deploy, reverse the procedure... Raise the end of the Board and angle the Board Retrieval Line aft to clear the Pinch Cleat. Roll forward until over the slot, and lower. Position with Position Line, and fix in Clam Cleat. Trim Board Retrieval Line to desired Board angle, and make fast on Horn Cleat.

While this was intended to be a prototype, it has worked astoundingly well. It takes about 15 seconds to stow or deploy, per board.

We used available 1/4 inch SS Cable, which looked a tad light. We have heavier backups, but sofar, no problems in high end of gale conditions. The brackets for both cables absorb a huge amount of stress. They should be very well built and strongly bolted to adequate structures. We used aluminum T-channel, bolting the cross-bar of the T to the hull, and shackling to a hole drilled in the post of the T.

The boards are pretty heavy for dead-lifting. I'd like to build lighter, surfboard style. For larger installations, the upper cable could be carried aft, and the Board Retrieval Line mounted on rolling blocks to provide purchase and full movement.

One of the fringe benefits of this system is that we can really bring the Center of Lateral Resistance aft. When running, for example, the boards can be set aft in the slot for improved directional stability (not needed on square boats, particularly, but ya never know).

For a fixit solution, the whole thing worked out pretty well!

Board in use position, cocked up by dryout... we used it to keep the boat from drifting as tide went out.


PS. I apologize for the poor photo qualities... turns out we didn't have any great pictures... come spring I'll reload with better shots.

6 comments:

  1. John Wrote:

    Dave,
    If you're writing a book, based in part on what you're writing here, I might mention my confusion regarding the post you wrote on Traveling Off-Center Boards. In particular the diagram labeled "Schematic for components above and aft of Window" I found confusing. I'm not sure how that diagram fits into the previous diagram. I also wish you could draw more lines from caption to item. For instance, I'm puzzled what item "Eye Bolt" and "Horn Cleat" and "CLAM?? cleat" etc,refer to.
    John

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    Replies
    1. Hi John,

      Thanks for your feedback. Good points. For the book, hopefully comments like yours will have 'debugged' the presentation. I hope to have better pictures, by then, and larger and better technical drawings.

      I can see that I should have a view from top, as well as the side!

      The first diagram shows the entire side... starting from aft, the components are Pinch Cleat, Horn Cleat, EyeBolt, Clam cleat, Bracket, SS Cable, Bracket.


      The SCHEMATIC is a close-up of the portion between horn cleat and the forward bracket. It repeats the order above, starting with the Horn Cleat. Additionally, it shows the endless loop which is fixed at the Running Block, led through the EyeBolt (which we see from its top... from above, we'd see the hole), forward through a shackle or block (not shown) at the forward bracket, and back to be fixed again at the Running Block.

      CAM cleats have the two little swinging sides (cams) that bite down on a line and hold it fast against pull from one direction.

      CLAM cleats are similar, but have no moving parts... lines are drawn down into a toothy valley full of blunt teeth that also resist pull from one direction. In the SCHEMATIC, it's figure with little, slanted, artistically rendered teeth. 8)

      Yeesh. In highschool, we had a hilarious exercise in trying to write directions for tying one's shoe. You can imagine the results!

      Hope this helped,

      Dave

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  2. Dave,
    Thanks for the clarification. I can imagine the shoe-tying exercise would be a challenge! Your descriptions are pretty good; I'm just a bit slow at times.
    John

    ReplyDelete
    Replies
    1. John,

      I'll work on that! Part of it is arranging the picture worth 1000 of 'em.

      Frankly, I'm better at BS than tech talk... but practice (and perceptive feedback) makes perfect!

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  3. For your drawings it helps to have several views. Some being a kind of 3D view. Well these are hard to draw but there's a trick that Jim uses to draw knots. You might could take pictures of actual boats or models and use his technique to clarify.

    http://jimknowsknots.blogspot.com/2011/11/how-to-electronically-draw-knot.html

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    Replies
    1. Hi Sam,

      You're right. This is a post I've been meaning to fix, but vanity (waiting for a beeYOOtiful paint job) has held me back. Hopefully I'll be attending to this, soon.

      Thanks for that link... it's a great technique!

      Dave Z

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