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Alan Stewart

Core Sound 20: Hull #103

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The board required about 15 pounds of lead to sink it, so I installed about 18 pounds. It drops with authority. The hoisting lanyard is marked at 1/4, 1/2 and 3/4's down positions, so you know how much board is deployed. These are just magic marker stripes on the lanyard at the cam cleat.

If I was to do it again, I'd move the pivot down, not up. This increases the leverage the case stringers have over the board to resist side loads and the amount of leverage the lanyard has on the board for hoisting. The current setup has 14.75" of leverage over the pivot. By lowering it I could get near 18" for a 20% improvement in the length of the "moment arm". This would also decrease the amount of tension required to haul the board up, which is comfortable, but on the high side at 15 pound of pull (static). I didn't want to go to a gun tackle for the board, which would have required 33% more line to pull up the board. With the whip tackle it presently uses, the total pull length is about 30" from full up to full down.

The pivot pin mounted externally (let into the keel and planking) would also prevent any leaks inside the boat.

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Guest LeeH

Paul R., in your arrangement as drawn, what keep the pennant from trying to "jump the track" on the curve between the centerboard attachment point and the "captured shieve" while the board is down? Seems like, if it worked its way down alongside the top of the board, you might get it in a hell of a pinch.

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I've attached the latest version of the centerboard assembly for CS-17, #196. This is how it was built with one exception. The cheek block used to make a fair lead out of the front of the case wasn't used. A 3/4" hole was drilled a 3/4" dowel of HDPE glued in and a 3/16" hole drilled through it. It acts as a "dumb" sheave, or fair lead with little friction or wear on the line.

Note the location of the weight on the leading edge. It was cast as a plate and glued into the board, before sheathing.

Also note the tackle is revised from the original drawings to get it out of sight and make it less prone to snag anything.

The tackle isn't visible, as it's all under the forward seat or case stringer. The hoisting lanyard, runs through a couple of fair leads, attached to the under side of the case stringer and comes out between the mizzen mast and the case on the centerline of the boat. A cam cleat, under the thwart dogs it down. The only presence of the hoisting tackle is the tail of the line hanging from the cam cleat under the thwart.

The lower section of this image shows what happens if the pivot is lowered. The radius at the top of the boat is much larger, meaning more leverage for the lanyard. The board descends further in the water, for the same length and the pivot pin isn't in the case, but on the bottom of the boat, so no cheek blocks and pin arrangement to leak. This area can't leak, because it's not there any more.

The lanyard sits in a groove, routed into the curved portion of the board. The groove isn't a tight fit and though it can move around, the sides of the case and the board have little clearance, certainly not enough to permit the lanyard to wedge between the board and case sides. The lanyard is always under some level of tension, which will keep the line seated. If it tries to "climb" out of the groove, the steep walls and generous size of the groove, with "walk" it back into the center of the board.

This isn't my idea, I stole it from a famous designer who did something similar on a much larger boat back in the 70's that I use to own an example of. I always thought it was a clever approach, so I've been hijacking it with modifications ever since. He used a winch to move the much heavier board and installed a fairly inventive stuffing box for the lanyard exit.

I can email large, scaled versions of this upgrade to those interested.[attachment=1]

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Paul,

I'd like to be able to study your upgrade.  I already have the case installed in a CS-17, but have not mounted the centerboard yet.  I was toying with the idea of using a weighted board anyway.  Thanks

Larry

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doodles.....

....unweighted CB ....

...  side-by-side tracked uphaul & downhaul (using symmetric whip tackle) both routed to a single winch. 

... The winch has two spools on a single axis:  uphaul comes in as downhaul goes out,    or uphaul goes out as downhaul comes in.

  ..... ? .....

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It might not be clear in the drawing, but the curved portion of the board is the key to making this arrangement rigid, in the case.

The top of the case has two stringers, one on each side. These are locked laterally with framing to the forward portion of the seats and aft by the thwart. Along the middle of the case, they could flex slightly, but they'd first have to start the fasteners in the case cap.

The curved portion of the board never leaves contact with the stringer areas. In other words the forward end out the board doesn't rotate off these bearing areas of the case assembly.

Captured by a low pin (stock configuration or lower) and the stringers at the top of the case, you have plenty of leverage over the torsion loads on the board.

As far as "jumping around" I'm not completely sure what you mean, but the weight keeps the board positively down and allows it to bounce over objects if you're doing some "sounding".

Paul, you've increased the tackle amount 2 times over, likely more then that in line and fair leads. This complexity was the reason I redid the up haul arrangement, plus the client wanted an unobstructed sleeping area in the forward cockpit. You've also reshaped the forward end of the board which makes the rounded portion lose contact wit the stringer area, which will permit the board to bear solely on the case sides, this I suspect would quickly test the joints at the king posts and start a leak.

If I was to rig a down haul, it would be a continuous loop from the up haul.

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Paul,

   

Many thanks!               

       

"jumping around":  I think Tom is probably referring to the fact that the plan (version 2.0) shows only a bare pivot pin   --the plan does not show the hardware (e.g., gudgeons, brackets, whatever) that would hold the two ends of the pivot pin.  Yes?

"increased the tackle amount 2 times over":  on the other hand my current (standard) up haul and down haul  have each have a block or two,  so the doodle is twice as much tackle as in version 1.2 /2.0  but just slightly more than my current. 

"down haul ... as continuous loop from up haul":   Would you care to elaborate on how that would look?

bi-directional winch:  A winch is certainly a complication but for an unweighted CB system it seems like it might be advantageous when trying to make adjustments but the CB is hard to move due to heavy side pressure (e.g., when on a reach).  Sometimes you'd love to not have to round up to relieve the pressure so that the CB can be moved.

"losing contact with the stringers":   I see what you mean.  The standard handle stays in contact with the stringer for lateral stability,  but if it is cut off then the upper part of the CB could bear against the side walls of the trunk   --which currently are not designed for that pressure.   

"new forward kingpost":   lengthening the trunk would be tedious,  but apparently is the price to be paid   --along with building a new CB. 

Any thoughts on dealing with the behaviors of the weighted CB in a knock-down (turtled) ? 

--Paul

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Paul,

One of my objections with a ballasted board is if the boat ever inverts after a capsize. If the board falls down into the trunk, how do you pull it back it up to right the boat?

Southern Skimmer will not invert during a capsize because of the bouyancy of the cabin. Your boat may be the same, you need to test it.

I prefer the uphaul downhaul standard design. The reason that I am going to the ballasted board is because of the lee helm. I can put in a vertical post without too much work. I can't use Pauls uphaul method because it will destroy the cabin.

One of the problems that I see with your downhaul is running it out through the aft post. There is a lot of water pressure back there as anyone who has not sealed the thwart to the trunk can attest.

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Graham,

Thank you for the comments!  Centerboard configuration is a fascinating topic as it involves so many design considerations;  e.g., ergonomics,  shallow-water strategy, foil shape, control line tackle, engineering/physics,  design pros- and cons-,  improving sailing skills to make the most of it.   

Looking forward to seeing what you do (I don't have access to Princess board plans):

  "I am going to try a different board design. Gordie has been urging me to use a ballasted tip instead of a downhaul for years. I hate to add an extra 20# to the boat but it will allow me better access to the cabin and eliminate any possibility of water slopping through the trunk at high speed. It will be like a Princess board. ...  The new board design will move the board forward 6" for the same draft which will help a lot.

...  .... going to the ballasted board is because of the lee helm." 

It's moving the board forward 6" that addresses the lee helm, while the ballast in the board has other advantages.  (Right?) 

--Paul 

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Gordy,

      In theory, a strong bungee in the downhaul tackle does the same thing as weight in the CB (and has better behavior when turtled) but in practice the bungee behaves differently than weight in one situation:  when there is heavy side pressure, pulling on the downhaul just stretches the bungee and the CB does not move so then you have to grab the handle to try to move the board; whereas, with a weighted CB instead of bungee, pulling on the downhaul moves the CB (if it will move).   Of course,  in either case rounding up into the wind reduces the side pressure.

      Interesting point about curving the edge of the CB for shallow-water advantage.       

--Paul

With my boat I sailed in very shallow water with bottoms of mud, weeds, sand, oyster shells, or old chevy engine blocks.

I like the uphaul - downhaul system Graham designed, but I changed it a bit.

In my first Great Race , my friend was continually 'searching' for the bottom using the horn of the centerboard. We would pull it up in shallow water and then not know when it was deep enough to put it down a bit. In light wind, or during a lull the board would float in a position leaving 4-6 inches exposed out the bottom.

I used a hole cutter to cut two 3" holes on the board and, after taping off one side I filled them with epoxy and bird shot. This left the board floating about a foot lower. In this position it was still at quite an angle and basically 'weightless'. When it touched the bottom it pretty much took care of itself and returned to it's position when the water got deeper.

For me, the uphaul-downhaul with the addition of weight worked quite well.

I also changed the shape of the leading edge of the centerboard.  If there's only about 6" under your hull only a small triangle of board will be exposed. If you let the board out a foot and then cut off 6" on a line parallel to the bottom, what's left is a board with much more showing when there's only 6" of water. I didn't actually use an exact number of inches, but that was my thinking and I ended up with a board with a sweeping curve to the leading edge. It helped measurably in very shallow water and I really don't think I gave away anything in deeper water. 

And just for fun, here is one with a "Centerboard Extension Spring" ....

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The cb horn and rigging does interfere a bit with my sleeping space, and (because I routinely leave the starboard floorboard up and store my inflatable under it) also interferes with sitting.  The cb design innovation not only solves these, but also eliminates the open slot in the trunk, which can be a fountain at speed, wetting sleeping bags, etc.  Even so, the possibility of losing my lever in a capsize is a serious thing.

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How we put a 20' sailboat in a 20' garage:

For several months now our CS20 has enjoyed the luxury of a clean, dry, temperate shelter when at rest.   Wow, what a wonderful change from the days of trying to make do with a tarp boat cover to fend off the weather, dampness, temperature extremes, bugs and leaves.  We considered building various kinds of tents and sheds but ultimately decided to saw off the tongue of the trailer and put her in our (unheated) garage.  Good choice!

Having the boat in the garage greatly facilitates work on the boat. The lighting is good, the tools are handy,  the temperatures are moderate.  Much more convenient.  It is now easy to spend a few minutes now and then working on the boat  --much different than when it was outside.   I love it!

Our "two-car" garage is 1" short of being 20' long and the CS20 is indeed 20'.  So even after sawing off the tongue of the trailer,  the "Dawn Patrol" still must be slightly angled to fit inside the garage.  But fit it does.   With the tongue hinged to fold aside, or removed entirely,  the trailer is shorter than the boat.

I ultimately decided that it was most convenient to park the boat in the garage bow-first.  The cockpit is more accessible this way.  And it turned out that this only adds a minute or two to the task of rolling the boat out/in  for  hitching/unhitching to our van. 

And, at ~$100 in costs, putting the boat in the garage was less expensive than building a tent or shed for the boat.  I bought the Fulton Fold-Away Hinge kit from pacifictrailers.com.  This kit appears to be a well-established product that is not hard to find.

Some research was involved; e.g., checking the fit of the boat in the garage, deciding whether to go with a hinge vs. a tongue insert connection,  deciding exactly where to make the cut on the trailer tongue and making sure that placement of the hinge would fall within the load-rating guidelines of the hinge.  The hinge kit included the two halves of the hinge, 16 bolts and lock-nuts, a pivot bolt (with nut and tethered keeper-clip),  and a removable pivot pin.   The bolt and pin turned out to be exactly the same size,  so I subsequently ordered a second pivot pin ($6) (to use in place of the pivot bolt) in order to make it convenient to completely remove the tongue  --instead of just swinging it aside.

Cutting the steel tongue was very easy with a jigsaw and metal-cutting blade. Also cut the electric wires in the tongue and bought a male and female connector kit for rejoining the wires.

The heads of the 16 bolts had the star-shaped impression and required a star bit (torx bit) for the socket wrench.  The installation instructions specified 70 foot-pounds of torque.   I bought the required $4 star bit (or "torx bit" size T55) at an auto-parts store.  I borrowed a torque wrench.

I've posted photos of the hinge installation process and the routine for moving the boat:

http://picasaweb.google.com/danceswithsandybottom/20090712_Trailer_Tongue_Hinge#

Also, here are a few highlight photos below.

So far, the results have been wonderful.  Hinge works great.  Love having the boat in the garage.   Looking at the trailer parking lot at Jordan Lake,  tongue hinges seem to be popular.

--Paul

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With the WaterTribe's 100mile NC Challenge just around the corner (Sept. 25-27, 2009) and late registration still open,  I am posting a detailed report of our trip scouting the course.  We scouted the first 65 miles of the 100 mile course.  I realize that if Southern Skimmer wins this one it will surely be only because of this valuable info I'm posting,  but here it is....    :D  

About 45 photos and 4 charts are posted at

Trip Report: Scouting the WaterTribe

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Great report Paul!

Thanks!

It looks like your garage interior is drywall. If it is, is it possible to remove a small section to give you a few more inches for the boat?

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