Centerboard

For issues common to different models of DaySailer.
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Centerboard

Postby rnlivingston » Fri Sep 10, 2004 2:09 pm

I checked prices on a new centerboard for my Spindrift DS1 and it is not affordable at this time. This winter I will make a new centerboard using mahogeny covered with glass. I'll probably make a new rudder at the same time.
Does anyone have any templates for the centerboard shape ? Any help or advice would be appreciated.

Roger Livingston
DS 11538
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Postby boone » Fri Sep 10, 2004 2:25 pm

Bob Hunkins recently built one, so I'm sure he has some good advice.

http://www.bobhunkins.com/mt-archives/000224.html

Also, see the specs from the DSA Handbook:

http://www.daysailer.org/dsa_handbook_spec.php#Centerboard%20Tip%20Detail
Last edited by boone on Mon Dec 11, 2006 10:48 am, edited 1 time in total.
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Postby Bob Hunkins » Mon Dec 04, 2006 10:00 am

Here's a link to some drawings. They may not be exactly to scale, since I had to cut and paste them into word before PDF'ing them.
Bob Hunkins
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San Leon, Texas
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Postby Bob Damon » Mon Dec 04, 2006 4:49 pm

As noted above, please read the specifications. In additional to profile, the max weight is 25 lbs. This is important if you plan to race and have a legal board. Good luck
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Postby TIM WEBB » Wed Dec 06, 2006 9:58 am

Just for everyone's information, here at work I have access to a 50" plotter. We build parachute equipment, and we use it to plot canopy patterns on .010" manila pattern paper. If anyone would like full scale patterns for a centerboard or rudder or whatever, I'd be happy to plot them and mail them to you. Just send an AutoCad file (preferably) or whatever scale file you have, to tim@jumpshack.com.

- Tim
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Postby Geronimo » Wed Dec 06, 2006 6:15 pm

Question for our class measurer... My centerboard is stock and probably the original. I've weighed my board by standing on a bathroom scale without the board (ouch !!) and then with the board. It seems to weigh between 27 and 28 lbs. Does the class require me to somehow lighten the board to get a measurement certficate? I plan to someday make a trip to an event and I'd like to be class legal.

Thanks,
Andy
Andy from the Jersey Shore
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heavy board

Postby Roger » Wed Dec 06, 2006 9:15 pm

A heavy board (especially an original) may be the result of taking on water over the years. Check for cracks, squeeze the softer cheeks of the board to see if water oozes out. Slosh the board around with your ear to it to hear if water moves from one end to another. The usual place for cracks is the leading edge nearest the water level. That is the place that typically receives the first hit, whether that is coming onto the trailer or hitting floating debris.

There is usually some wear at the bottom tip but not typically enough to allow water in.

If your boat is stored in a freeze thaw zone, then any water that overwinters inside the board, expands as it freezes, typically expanding the sides of the board out. The split will occur in the weakest part of the fg skin, that being the leading edge nearest the waterline, that is subject to greater amounts of abuse.

If this is the case, drill a small 3/16 hole in opposite sides and ends of the board to access the voids. These voids start 2" inside any edge and usually there is a longitudinal solid spacer that is 2" wide running down the middle of the board. So one hole will be at the top of the void on one side, and the bottom of the void on the other side. Use your shop vac to suck out any water, then leave it on of a few hours to move air through the middle of the board. After this, set the board aside for a couple of weeks in a warm dry place to totally dry out, prior to re-epoxying the holes. Re weigh your board. When I did this to mine, it came in at 22 pounds.
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Postby jpclowes » Thu Dec 07, 2006 10:51 am

I can vouch for this!
A spider crack just below where the board comes out of the trunk has allowed my centerboard to completely fill with water for at least the last three summers, despite my best efforts to fill the crack. I even went as far as grinding out most of the gel-coat for a quarter inch on either side of the crack and filling the space with new resin, and a small layer of cloth! I have come to the decision that my board is probably on its last legs, and needs to be replaced. Besides the fact that it is horribly misshaped (the port side of the board was shaped so that it would be more hydrodynamic when placed in backwards!) , I think the cracks are probably also signs that the board will fail some time in the future, probably at the worst possible moment.

I don't really have the skills or tools to build it myself well, and don't have the 600 or so bucks that Phil's Foils wants for a new one. Thank God for skilled people in my Fleet, who are willing to help a guy out!
J .P. Clowes
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DSI 14083
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Postby jpclowes » Thu Dec 07, 2006 9:09 pm

I should probably add that I would guess my board probably weighed 40 lbs or more filled with water. Now since a lot of that was water, it was probably neutral when my board was down, and therefore no advantage when racing.
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The case of the fat foil

Postby Peter McMinn » Mon Feb 12, 2007 7:23 pm

From the DSA Bi-Laws:

6.1. The thickness of blades is not controlled. Tolerances of blade profiles are plus and minus
1/4 inch unless otherwise specified. Leading and trailing edges shall be parallel plus or
minus 1/4 inch.
6.2. CENTERBOARD: The centerboard shall be of built-up or molded fiber-glass and resin
material or of wood covered with fiber-glass and resin. The profile of the centerboard
shall conform to Drawing 6.1 and Drawing 6.2. The centerboard profile shall be a fair
curve between reference points A and B.
6.3. The weight of the centerboard, including any fittings permanently attached, shall not
exceed 25 pounds.


Now my story:

About 15 years ago, a previous owner replaced the stock centerboard on #568 with a custom foil. The owner had wanted as thick a board as possible to maximize lift potential. The new board core is “aircraft grade” spruce. Although fashioned to dimensions within the legal specs, it was glassed up to allow only about 1/32” of space between the trunk wall and the board (1-9/16” at it’s thickest point).

When I bought the boat in 2001, the board was snug but came down with a little effort. As the years passed, it became increasingly difficult to lower, eventually resulting in a broken handle (which had already been damaged/repaired) and several attempts at fairing the board down to bare glass. Now, I have another bent handle, and the board is next to impossible to lower, even with added leverage.

Having read the many comments in this forum on “water in the board”, I think I can say this board is not so affected. There is no “dripping” from cracks, etc., and I can’t believe it’s retaining water, as it has consistently weighed in at 22 pounds. Even now, with the board out of water for almost five months, it’s the same weight and dry as a bone. It's occurred to me that the CB trunk has changed shape somehow, causing the CB to jam; but I don’t see any evidence of this, inside or out. Could the board have swollen due to the elevated level of moisture in Portland, OR relative to where the board was made and custom fit in Fresno, CA? 'tis a mystery.

I took the board out for about the eighth time a couple of days ago (it comes out from below with a certain ratio of leverage and verbage) swearing to rectify this situation once and for all. My plan is to shave a ¼” off the thickest part of the board, about 4” aft of the leading edge, down to where the taper starts. I’ll do this by cutting three to five ¼” deep grooves lengthwise along both sides of the board with a circular saw. This should cut through the fiberglass and into the core about 1/8”. I’ll then chisel out the excess and belt-sand to profile. With a little luck (maybe a lot) I won’t simply replace the thickness as I re-glass/gelcoat the faired section of board.

Before I perform this fat reduction surgery, I thought I’d toss some questions to the crowd:

1. Given the observations above, why would this board be getting too thick for the slot?
2. What is the desired thickness of fiberglass for foil strength (how many layers of matting achieves 1/8” of thickness)?
3. Can you think of anything that might suggest what I’m about to do is sheer folly and will end in wailing and gnashing of teeth?

:roll:

Process pictures to follow.
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wailing and gnashing

Postby Roger » Mon Feb 12, 2007 10:33 pm

Your board may have been reconstructed differently than mine so take that into consideration after reading my comments. My board (original), was repaired (by me) last winter due to taking on water at a crack on the leading edge just below the waterline. I repaired it by removing the 'skin' back about 2.5 inches and about 5 inches long on one side of the crack and about an inch back by 2 inches tall on the other side of the crack. When I peeled off this skin, it exposed a 2" solid (fore to aft) and about a 1" thick rib that was the structural member of the leading edge of the board. Another similar structural member (similar size) ran along the trailing edge of the board, with a similar member running straight down the middle of the board. These members formed a solid tip about 4+" from the tip up. The head of the board was also solid. The 'skin' covered all of these members and in so doing caused two hollow channels in front of and behind the middle member. The important piece that I am telling you here is that the board, (at least my board) was not solid. Water collected in these hollow voids.

I of course drained the water before repairing it, but here is the caution for the procedure that you plan to use. (I can't answer question 1 and 2 as the first depends on how your board is constructed, but certainly water swelling wood, could cause it.) Mine was made of fiberglass members so it was freeze/thaw that cause my cracking with the freezing expansion causing the swelling, then eventual cracking.

To the second question, roving comes in different thicknesses, so you may be able to achieve 1/8" thickness with just one layer, but most likely you will require 4 or 5, if using general duty cloth. My skin was about 3/32" thick, not quite an 1/8".

Finally, your plan to ..."shave a ¼” off the thickest part of the board, about 4” aft of the leading edge, down to where the taper starts. I’ll do this by cutting three to five ¼” deep grooves lengthwise along both sides of the board with a circular saw. This should cut through the fiberglass and into the core about 1/8”. I’ll then chisel out the excess and belt-sand to profile." ... will not only cut into the skin but, if your board is not solid, then you will cut into the hollow channel forward of the trailing structural member. To check to see if you have a solid or hollow board, press on the sides about 3-4" forward of the trailing edge. If there is give, then you have a hollow board, and your skin is mis-shapen. Cutting down with a circular saw will only remove the skin and cut into the structural members. If your board is solid, you will have resistance when you press on the sides behind the middle structural member. If it is solid everywhere, then your procedure should work. ( I have my doubts that you have a solid board, because otherwise, water would have no place to be stored inside) Proceed with caution. If I have failed to give you a good visualization of the structure of your board, please send me a private e-mail roger02@mts.net, and I can draw and scan a sketch for you. Good luck with your project.
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Postby Peter McMinn » Tue Feb 13, 2007 1:34 am

Roger, thanks for the prompt reply. This board is not a "reconstruction" but an entirely new and custom blade. Upon closer inspection this evening--scraping away some loose "skin", I've found moisture. As I also live in a freeze/thaw zone what you describe sounds likely.

I know my board is solid as the construction is diagrammed in the notes that have followed the boat over the last couple of decades.

The interesting thing is that the weight is not 22 but 17 pounds, per fish scale reading. Go figure.

Revised theory: moisture trapped, but how much? Before I embark on above mentioned operation. I'm going to drill some alternating vent holes and dry it out a few days next to the wood stove.

I'll revisit this thread when I discover something. More opinions are welcome.

Meanwhile the sun's out and the water's looking inviting. Arrghh!
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Postby calden » Tue Feb 13, 2007 1:41 pm

Peter:

Interesting mystery about your board.

Is it possible that it's not swelling but rather developing a very slight warp over time? If it's solid wood, it would certainly be susceptible to warp if it takes on moisture. Even a tiny amount of twist, practically imperceptible, would make it stick in the slot with the tight fit you've got.

We're also getting some warmer weather up here in the Far Frozen Frigid Northland. It only gets to freezing at night. Days are up to almost 40 and people are out in their t-shirts. I'm thinking sailing every day.

Carlos
DS I #1653
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Postby Phill » Thu Feb 15, 2007 12:11 am

Hi Peter, and all

It is very difficult to keep moisture out of our CB's and Rudders.
The smallest crack or chip in whatever we coat the wood with, will allow the wood to absorb moisture and swell. I am also into acoustic guitars and just a 10% difference in relative humidity in the house can cause the tops to swell or shrink enough that it can be easily seen with a straight edge laid on the surfaced. The same 10 % shift can cause the Ebony or Rosewood fretboard to swell/shrink enough that there can be a 1/32" measurable difference in the string height. The fretboard is only a small piece of hardwood.

Peter, when/if, you resize your CB, try and find where it is hitting and sticking. You may not have to take off too much material. Our CB trunks are usually not parrallel sided, front to back or top to bottom. They were manufactured with a slight taper top to bottom, and front to middle to back to make getting the trunk off the mold easier. I found with my board, that most of the problem was with the tapers and fitting the head to swing through them. Also I eventullly needed to thin the board near the tip where the rear taper again caused a binding point.

If my ramblings aren't making sense, Wine with dinner tonight, Feel free to give me a call, I'm in the book.

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The plot thickens as the board thins...

Postby Peter McMinn » Thu Feb 15, 2007 1:38 pm

The plan is underway. Thanks for the insight, all.

After cutting five grooves along both sides of the board (1/8" receding to 1/16"), I shaved off the skin, which turned out to be no more than two layers of matting. With more bare wood exposed, I'm fully drying it out inside, near our wood stove.

Having done some research, I think the next steps (prior to re-glassing) are to 1) power plane to depth, and b) fine-tune with an orbital sander (good excuses here to go tool shopping!).

Carlos, after reading your message, I furrowed my brow and went home to look for any warp or twist; the board's straight and flat. Having revealed the wood, I can see that someone really applied some know-how in building this board.

Phill, your note on the CB trunk is right on. I noticed in the current Quarterly a note that some racers "build-up" the interior walls of the trunk, and there's evidence this occurred on #568.

Through forensics and triangulation, I think I understand what was going on with my sticky board. A previous owner had both built-up the interior of the trunk and fabricated a board to a very snug fit. All was done with great skill but not with the forethought that this boat would be sold up to Oregon, where it freezes now and then.

The occasional freeze/thaw has resulted in more moisture in the board, transforming the snug fit to a friction lock.

Again, thanks Roger, JP, Carlos, Phill for your thoughts.

Phill, Carlos: see you on Memorial Day? I'm still looking for crew.

Promised photos still forthcoming...


:wink:
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