CB foil project

[Lil Maggie]

Hey,
I am in the process of building a CB foil for Lil' Maggie and I have a few visuals to share with you all. I am using Dave Misunas's instructions, but I had some good quality, fairly knott-free 2"x12"x16' board that had some sections of 1/4 sawn wood. I cut those off into roughly 3-1/2" x 50" strips (yes, I made a boo-boo and my board is right now 1=3/4" too short compared to my stock board: MEASURE TWICE, CUT ONCE; I will spline in a piece to the pivot end to make up the diff.)



After what seemed like an insane amount of routing and planing the rough shape of the foil came out, though still too thick


It appears my CB trunk only will take a 1-3/8" board which is what I had after all that planing..so I had to take off an additional 1/16"...not realizing my board was not only 1-3/4" short but also 1/2" too narrow (which is not necessarily bad and is within class spec...a slightly narrower board would increase the relative thickness ratio of the chord, which is good, right? for light to moderate speeds, anyway)


Continued...

[Lil Maggie]

Continued...

Once the profile was cut out, there was (is) still more planing and sanding to taper off the trailing edge from the tip of the board aft, and on the leading edge as well. I plan to achieve a 3/8" radiused leading edge all the way down to the tip, then taper off the trailing edge to a squared off 1/8"...which is where I'm at presently.




Any thoughts? advice? do's don'ts?
cheers,
Mike

p.s. GL I realize this topic might belong under repair and improvement...feel free to move it if so...

[Cavofficer6]

I guess I don’t understand, I thought the DS centerboard was fiberglass? Am I wrong with, and/or are many made of wood?

[Lil Maggie]

DS stock boards are indeed fiberglass with rebar...however, class rules allow for other materials as long as it's within the weight limit, is not to exceed 39" in length (depth) and it can be any thickness as long as it fits in the CB trunk. What is more tightly restricted is the lateral profile of the board

Mike

[GreenLake]

Continued...

Once the profile was cut out, there was (is) still more planing and sanding to taper off the trailing edge from the tip of the board aft, and on the leading edge as well. I plan to achieve a 3/8" radiused leading edge all the way down to the tip, then taper off the trailing edge to a squared off 1/8"...which is where I'm at presently.

Any thoughts? advice? do's don'ts?

p.s. GL I realize this topic might belong under repair and improvement...feel free to move it if so...

There's various descriptions of jigs people used to make sure that sanding reproduces the intended foil shape. One I like works with a layer of epoxy putty (e.g. QuickFair from System Three).
You use a notched trowel to make ridges. Then you sand those down to fair. Then fill grooves with putty for a smooth surface.

Whether I'll move the thread would depend on the performance you get from your new foil, wouldn't it.

[kokko]

Is there a reason you are starting from lumber rather than adding shape to the existing board?

[GreenLake]

Is there a reason you are starting from lumber rather than adding shape to the existing board?

Final shaping and finishing will take the majority of the effort. Starting from scratch with wood doesn't make the project that much harder, but may have some benefits.

1) the stock CB uses rebar, which can rust (and from rust expand, causing cracks) - conceivably this can happen after you spent a week refinishing it.
2) the stock CB has a profile that does not fit within the theoretical best foil shape (in the rear 2/3 of the profile, it's too thick). That limits how good you can make a stock CB. If you sand into it, you might cause issues, among them exacerbating item 1

I did refinish my CB, accepting the limitations. It seems to have made a positive difference (and I was not confident that I could build something from wood that I can't inspect every trip - unlike the rudder, which I did from scratch). In essence, having done one foil in each technique, there are pros and cons. For the rudder, I did have some problems after the first season, which, since it is "inspected" when taking it off the boat after every use, I was able to detect and fix. So I'm happy to have merely faired the existing CB and not replaced it - my own techniques for creating foil blanks could benefit from more experience.

[jdoorly]

Hi Mike, I was contemplating doing a similar project this winter and was wondering where to find 'Dave Misunas's instructions'? Also, what do you figure is the widest the foil can be to not jam in the trunk?

[Lil Maggie]

Hi Mike, I was contemplating doing a similar project this winter and was wondering where to find 'Dave Misunas's instructions'? Also, what do you figure is the widest the foil can be to not jam in the trunk?

Why...right here:http://forum.daysailer.org/pdf/qtr_buildcb.pdf

the how to figure what thickness board can you make involves measuring at various points of the CB trunk on the opening and 12" up

GL, the board will not be just wood...the final product will be wrapped in f/g cloth and epoxy resin...not nick proof but pretty tough in my experience. Also, depending on how heavy your stock board is, one runs the chance of putting the board over the weight limit. The main concern for me was to obtain as perfect a foil shape as possible; having studied a bit of hydrodynamics in my time would not let me sleep at night knowing that I could have had jut a bit more lift off the board if I did it from scratch. Once I finish the CB I'll be doing a new rudder too. The scratch method takes not so much skill as some equipment (planes, router, clamps, table saw...). Both take a LOT of "elbow grease"

[kokko]

Although both foils of my DS1 should be faired to NACA shape, I might start with the kickup rudder for my Catalina. Several years ago I bought a straight blade Idasailer (Ruddercraft) rudder. I was amazed at the perfromance difference. There were two things different - it had a NACA shape and the leading edge was just forward of the pintles. I had more lift and a balanced helm. No more weather helm.
THe lake where I sail the Catalina is weedy and the straight blade grabs at them. I have to motor to a non-weedy area, back the boat up to clear the weeds from the keel, then knock the weeds of the rudder. A kickup, like the DS1 would make life easier. If only all the foils were as nice as my Idasailer.

[GreenLake]

@LilMaggie the day may DS ever gets measured to class rules, that'll be the day. (What "racing" I've done is in a mixed fleet with a "free-for-all" attitude, otherwise I might care about DS class rules differently).

When I did my rudder, I found it difficult to get the glass layer to be the outer most layer and still get a really fair shape. Hence the filler.

[Lil Maggie]

well I am pleased to announce that the foil is ready for test fitting...I just need to shake off this nasty cold so I can careen the boat again. The CB un treated is weighing in at 14 lbs! Pictures coming soon

GL, I will probably never have the time or the $$ to compete in class, but if it comes the time to sell it, I want be able to tell the new owner that the boat is still "class legal"...more of a marketing thing

Cheers (snif!)
Mike

[GreenLake]

Congrats on getting your foil to this point. Hope your cold gets better.

On selling, it depends on your area, but around here, I figure most prospective buyers are facing the same reality. However, when it comes to foils, keeping the stock ones around would be insurance enough. If anything doesn't measure up, the buyer could simply revert.

[Lil Maggie]

Good point..yeah, I don't plan to get rid of the stock CB just yet, but I also want to make a (slight) effort to stay within class rules

M

[Lil Maggie]

Progress report:
- The board was finally fitted to the boat, after what felt like forever planing the taper in the head of the board for it to fit (and pivot)...and what took "long" was also drilling and filing the handle hole.

-the board now is curing its first coat of west system epoxy

Pictures will come soon

Cheers
M