CS17 Centerboard

[ecgossett]

Not sure from the plans but what is the centerboard width? 1 1/4" x???? on the ripped boards?? The alternating this is screwing me up because I'm thinking the ripped boards are rectangular shaped...

[Ray Frechette Jr]

I don't have the plans in front of me so I can't quote the thickness of the board.

However the strips are indeed rectangular blanks.

You use plain sawn lumber and cut strips and tip them 90 degrees so the resulting blanks will be quartersawn in orientation to the face of the board.  This reduces warpage.

To further reduce warpage, you alternate the boards so the grain curvature is opposed to one another.

Do you understand the terms quartersawn and plainsawn and what effect moisture content has on grain orientation?

Not meaning to be dismissive or pedantic but many many people have no idea.

In any even, the pieces you cut will rectangular.  The flipping of orientation does not refer to having some pieces thicker than others.  If you look at the ends of the boards you will see there are arcs where the growth rings are.  So two boards will have the arcs of the convex area of the growth rings facing each other and the next board will have the concave areas of the arcs facing each other.

When the board is layed down on it s side and you look at the glued up board form the end,  all of the growth rings should be pretty much oriented up and down,  not front to back .

Geesh this written language thing is proving difficult tonight. A couple of pics would be far handier if I had access to same.

[ecgossett]

The flipping was confusing me.. I was looking at photos on the CD that came with the plan, then back at the description and going how am I going to flip with out making this out of whack size wise..

Thanks,

Edward

[ecgossett]

Is the centerboard supposed to be 3/4" thick or 1 1/4"?

The plans are confusing and looking at photos of others it looks like they are all different.. I have cut about 10 of the pieces I need to far for 1 1./4" thick.

[Designer]

Edward, you are trying to make it more complicated than it is. The finished thickness of the board is 1 1/4".

The reason that I make the board this way is because there is practically no old growth lumber available anymore and it is hard to find it quarter sawn.

I am sure that you have seen plenty of boards that are warped, cupped, bent and twisted. We don't want to put a lot of work into our boards and find that it has changed and jammed in the trunk.

Laminating is the way to solve this problem. For practical reasons I show cutting from 2x6s which is finished at 1 1/2" thick and 5 1/2" wide and it is plain sawn rather than quarter sawn. If we cut that board in 1 5/16" slices (The extra 1/16" will be consumed during cleaning up the glued blank.) and lay them on their side we will have 1 5/16" thick x 1 1/2" wide strips that now become quarter sawn. If we end for end every other strip length wise we cancel any grown in stress in the wood that is released when cut.

Why do we want quarter sawn boards anyway? It gets its name from slicing the log in to quarters and cutting boards off the quarters alternating so that one edge of the board is near the heart and the other edge is near the bark and the growth rings are running vertically across the board when it is viewed laying flat. This is necessary for stability as the greatest shrinkage is in the newer growth which is near the bark. Our quarter sawn board will shrink along the long axis but remain flat. The plain sawn board, cut with one side toward the heart and one side toward the bark will shrink more toward the bark side causing the board to cup. There are other reasons why wood changes shape but when the board is made this way they are canceled out.

It does not matter what size our laminations are, we could glue up our boards from toothpicks but that would be highly impractical. 2x4s, 2x6s, 2x8s etc. are readily available and cheap and with a little care we can have a board that we can install in the trunk and forget about it and it will never give us any trouble.

[wkisting]

Edward, it is simpler than you are thinking, but I realize it can feel confusing to think through if you aren't comfortable with ideas like grain orientation or terms such as "quartersawn." Once you start doing it, it should become clear quite quickly.

Here is the most visually accessible way I can think to describe the process:

1. Mark the 2x6 boards you wish to use with a permanent marker. Draw a line on ONE FACE and another line on ONE END of each 2x6 board. Both lines should be drawn so they span the WIDTH of the board. This will help you preserve (or restore) the original grain orientation of the board once you cut it into strips.

2. Set your table saw fence to 1-5/16" thickness and rip your 2x6 boards into the required number of strips. This will yield strips which are 1-5/16" wide (per the fence setting) and 1-1/2" thick (the actual thickness of the 2x6).

3. Lay out your strips on a table, using the reference lines from Step 1 to make sure you have the faces and ends arranged as they were before you ripped the board into strips. You will be looking down on the 1-5/16" thick strips, and they will be rising 1-1/2" off the table.

4. Rotate each strip 90 degrees to the left. Now you are looking down on the 1-1/2" thickness, rising 1-5/16" off the table. The reference line you originally made on the FACE of the board has now disappeared; however, you should still see a reference line (now rotated to look like a series of vertical lines) on the ENDS of each strip.

5. Flip EVERY OTHER STRIP end-for-end (i.e., flip the strip LENGTHWISE so that the reference line on one end moves to the opposite end -- bottom to top or top to bottom). This will result in reference lines on both ends of the stack, alternating every other board. Now you have canceled out the stresses in the wood and, if you glue them together in this orientation, it will yield a very strong, stable blank for the centerboard.

6. Once you have them in this orientation, I would number or mark them for quick reference so that you can keep them in the same order/orientation during the glue up process.

Hope that helps! That was how I made sense of the process and it worked well.

[ecgossett]

I am a IDIOT!! I was ripping 1x8's to 1.25"......

I guess I could keep on doing this and laminate more boards in.

[Designer]

It won't hurt, you will just have twice as many glue joints. As I said, "you could glue up a lot of toothpicks".

[ecgossett]

Someone should take you up on the tooth pick idea! It would be fun to see a toothpick laminated rudder handle or something

[PAR]

Or Viking long boat . . .

[ecgossett]

What kind of wood do you use for the top part of the centerboard?? The photos and plans make is loot like a single piece and I am thinking I need to laminate something then plane it down to 1.25" for it.

[wkisting]

To make the head (or "lever arm" or whatever you want to call it) at the top of the centerboard, I ran a 2x4 through the table saw and cut the thickness down to about 1-5/16" (leaving a little sacrificial extra to allow for the glue up and final shaping down to 1-1/4" thickness). Then I glued it on top, cut the correct profile shape with a jigsaw, and planed its thickness down to match and blend into the rest of the board. To reinforce the glue joint, I embedded four long screws down through the top of the head into the laminated blank. I drove the screws deep and then filled over the heads with epoxy. That way, the head is held on by screws as well as epoxy. To finish, I sanded the entire CB to its finished shape and covered it with a layer of 6 oz. fiberglass, plus some kevlar felt for additional abrasion protection on the leading edge. (If you do this, make sure you allow for the thickness of the cloth/epoxy when building your CB case.)

[Docpal]

Ed,

This is what mine looked like at the assembly point. If you follow Wes's instructions, you'll get exactly what you need.

PS- the white thing under the rudder is a "spar clamp"I made up of HDPE. It worked great for clamping the stepped scarfs, as well as leveling out all of the rudder pieces...

[ecgossett]

Thanks,  the resolution on this photo is decent..

[ecgossett]

On the centerboard plans for corners it has a 5" on one, and another that is 3" or something.. Is this referring to radius or diameter to make the corner?

[Hirilonde]

A rounded corner is only part of a circle, therefore it doesn't have a diameter. 

Radius is virtually always used in all kinds of plans for an arc or circle.

[ecgossett]

[ecgossett]

I'm almost 4 1/4" inches short on the centerboard in the trunk.. However, I've checked measurements and everything is correct on both trunk and centerboard.

Do other people have this issue?? I have looked at the photos on the cd and it shows the centerboards fitting exactly.

V/R, Edward

[wkisting]

Do you have a picture? Short where? Width? Length? Need more info.

[ecgossett]

Length, but the measurements all match properly... The photo above pretty much explains it...