Hi there,
while still trying to shape daggerboards, I "heard" that I could use the Nacra F18 daggerboards on my Sol Cat 18.

As I don't have any of those available near me, I would appreciate any expertise on this.

I made a "sample" for my Sol Cat out of foam, that at least fits into the pontoon slots.
Its a little less then 12.1/2 inches at the top, a little less then 11 1/2 on the bottom, 39 inches long (I looked at some pictures to get that length. The daggerboard at many cats seem to "stick out" on the bottom the same length as the rudders going down.) Its a little less than 3/4 inch at the thickest part, only 1/4 at the small end (back).

The sample fits in "snuggly", so could obviuosly be a little smaller in size.

How's that in comparison the Nacra F18 ?

I had the cat in the water today for the 1. time, but without daggerboards I was just drifting to leeward

Thanks and have a great holiday.

Michael

From your dimensions, the Sol Cat boards are wider than the F18.

If you are going to make the boards, do yourself a favor, buy the foam core from a RC airplane company. It will already be shaped and smooth. All you will have to do is cover it with Expoxy/glass or carbon.

Vaccuum bagging will give you a stronger lighter board but a hand layup with peel ply works fine.

As a guess, a NACA 0006 foil will work. Tell them you want a 1/8" skin.

If the foam core is stock, it will cost $US 30-40 for a pair of wings (boards). Custom will cost more.

I have ground foils out by hand and covered pro built ones. Buying one is worth every penny


If you want you can build a hot wire cutter and cut your own cores. Do an internet search.


Carl

Thanks carlbohannon.
that was quite a journey thru the RC airplane world.
Seems that more links are dead there than in cat sailing ?
Now I know how to build a foam cutter in 4 days from HomeDepot parts, sanding, vac bagging with a 40$ pump, getting stringer in with an iron etc.

But I rather prefer to use a somekind smaller daggerboard
if I can get one ready made, before I start that adventure.
At this moment, I just try to plane and sand down some plywood and put some epoxy around it.

But anyway, thanks for the insight into the foam wing world.
May come in handy later.
What was that part of you making those things ?

Michael

I have built a couple of foils. Rudders and daggerboards. Let see planed ceder, vaccum formed plywood and foam core. I have sanded out one foam core and purchased one. The easiest, strongest, and best foil is carbon over purchased foam core. 3 evenings and it was done and ready for the boat

Carl,

As Michael has said, the RC world seems to have more dead links than even catsailing. Could you offer some suggestions as to where to find the prefabricated foam foil sections?

Thanks,

GARY

I recall seeing a nice "descriptive site" w/pics on daggerboard fabrication - you can view it @ http://www.jaimezx.com/Boating/Hobie/part3.html

He does a great job detailing the steps involved in working with foam & glass...

I did this with a G-Cat rudder, pretty simple.

Rudders 101

Dave Mosley

Great work Dave!

I remember seeing some photos on Phill Branders site where he shaped and made some foam/carbon foils for a F-16. Photos are gone now, unfortunately. But it looked easier to shape than working with wood.

How did you ensure that you got the proper shape on the foil, and identical on both sides, any tips to share? I have made four rudders (plywood/glass) and one set of centerboards in strips, and found the hardest part was getting proper and consistent shape..

Did you come around to building the foam/glass foils? Eventually, what kind of glass layup did you use?

Sorry Rolf, I sold the G-Cat, never glassed the board, and never got to the foam board. I did get uniformity(close) by using calipers, but that was still only close. Pretty sad huh?
Had I laid up the board with glass, it may have been totally different. But it worked well to get a decent shape.
David

Very good pictures pitchpole, thanks for the link
And thanks Dave for the tip with the router, haven't thought about that.

One question do I have still:

If you use foam and put a layer of fiberglass on that,
isn't that too weak ? Aren't you supposed to stand on those
daggerboards with all your weight if you want to right the cat after capsizing ???

Michael

couldn't let go with these foam cutter pages,

In case you are looking for some cheap model just to make
ONE foam, this is what I found. Looks very easy:

http://www.vatsaas.org/rtv/construction/hotwirecutter.aspx

Oh well, Dave, I bet you had fun building the foil anyway. If the surface was not 100% after glassing.. thats what bog and elbow grease is for.

If I am to build another set of rudders, I want to try foam/glass. But I am not competent to calculate the glass layup. "Guesstimating" the layup will be costly in the long run, as some sets are bound to break..

It's tempting to do a female 'pirate mould' off some fabricated rudders I have, but that avenue is also full of problems (getting the mould flange correct, internal flange for joining, layup, legal/moral issues etc.). I guess most production foils have their foam CNC cut like Phil's foils does, or uses CNC'ed female forms.


Michael, you are correct in assuming that just one layer of glass is not enough. How much glass, weight of glass and orientation are issues you need to calculate before building. You also have to calculate how thick the glass will become after laminating, so you can get an exact fit. That is one of the reasons female moulds are so much easier to work with in a production environment.
You probably will get a better result with spruce strip planking and a thin layer of glass for abrasion resistance, wood is so much nicer to work with as compared to fiberglass and epoxy (probably cheaper also).

Using hot wire technique to make the foam core is pretty much standard today for homebuilders.

Perhaps some of the really experienced homebuilders (or pro's) here will share some experience on layups for foils.

I think what Carl says about buying what you can is good advice if you want to get on the water fast, with a good result. The seller of the core can probably spec out the glass layout and weight for you to achieve the 1/8" skin Carl mentions.

I would forget plywood without serious glass reinforcement. We have personally broken two centerboards of plywood without glass reinforcement.. Strip planking is much stronger than plywood, as half the wood fibers in plywood lies in the wrong direction and does not add to strength/stiffness.

Nils,

you guys keep me working.
Looking for "strip planking" (of course I had no idea what it is) I now found letter to the journal "Watercraft", saying that strip planking is "Time consuming and hard to repair" . Anyway, I think it's beyond my capabilities and time. Thanks for the insight concerning plywood.

Slowly but steadily, I start to think about throwing the cat away and buying a sailboat with everything on it

before I spend more nights on the PC and days with planer
and sander

Hello,
to hand shape foils...
draw a center line all the way around. also draw a line on both sides where you want the max thickness. Make a few templates of the foil you want at different spots up the length of the blade. this is to check your progress.
i once got the foil in jpeg form off the internet. next i redrew the foil in a vector program and outputted it. use your "eye" when shaping.
styro core foils for a cat are a pipedream in my opinion. once you get enough material on for the skins, the foil will have changed too much. that's if you could get enough material on there. also you need solid glass or carbon in the center for the tip, leading edge, and trailing edge. then there are somtimes holes in the blade to deal with as well.
you can layup a nice blank on a sheet of glass just using tape or weights without using clamps. clamping strips, normal wood working style is good too. especially if you have a planner.
cheers

I was wondering since foam board is used in some places, if it could be substituted with balsa wood in the non-structural areas?
For me it would be easiest to shape balsa covered with carbon fibre then 1/2 oz. cloth for sanding.

Most foils on production cats(NACRA's and Hobies) are foam core. Marstrom carbon foils are foam core (Tornado's are hollow core), Mine are are foam core.

The techniques used to determine the shape and size of the core is very similiar to the techniques used to calculate ribs for aircraft wings, it dates to 1910-1920

You do have to taper the trailing edge

jUST A WORD OF ENCOURAGEMENT:
I think it needs be said that a lot of production dinghys use centerboards - literally. they round the frontand rear edge. Yet without the board, the boat simply will not sail upwind. Cats with some weight on (leeward hull) board to make the hulls bite, can sail poorly upwind without boards. Chrysler made a cat with board boards. (no foil shape) One presumed it sailed.
Point is, however badly built,whatever the profile, if it is strong enough it will work OK.
A bunch of 3/32 plywood glued together makes a "contour map" as the glue lines expose as you sand. By eye, you will do a nice looking job.
Cutting a profile out of plywood and using it to check as you sand, will get you right on.
Two layers of 6 oz and you should be strong enough. The lateral force will be about 200 lb so if you laid your boat on its side and cn stand on the tip of your newly made board, it should be plenty strong enough. Or support the board by a brick under each end, and two of you stand in the middle....

well,
i wrote styro core not foam core. they were talking about hotwiring stro like they do with remote control glider wings for a solcat daggerboard.
regular styro soaks water. extruded styro is very hard to bond to with any longevity.
Most all of the strength would be in the skin so you would have to calculate that thickness and subtract that from the shape of the core. you would end up with a pretty thin core which would leave alot of leaway for the shape to change as the blade got laminated.
the foam that is inside of molded blades is pretty strong and doesn't soak up water. Also it can be difficult to obtian, and use effectively. Maybe that's why some are hollow. hollow blades have to be molded because you wouldn't be able to laminate a foil made of air like you could with wood.
if you are making you own foil in your garage, shaping it in wood as perfect as possible and putting a very thin coating to seal out the water is the way to go.

While we are talking about hollow foils buildt in moulds.

How do they go about joining the two shells? I imagine they add a a stringer at 30% to take large loads, and the aft part can be routed flat while it is in the mould. But what do they do to make a bonding surface able to take the load at the forward part (front glue line/seam)?

A word about styrofoam. I have seen it used as partial bulkheads and distance material in different boats.
Ref:
http://homepages.paradise.net.nz/garyd/quikama.html
http://thebeachcats.com/modules.php?op=modload&name=News&file=article&sid=49

According to the builder of the A class referenced above, the polystyrene foam bulkheads was quite OK.
I tought styrofoam was a closed cell structure, that did not draw moisture?


Michael: Dont worry about the stripping process, that is easy. Just glue spruce staves together parallel before you begin to shape it. Look at Dave Mosley's page again, the whole process is documented very nicely there. Just get to it, and get on the water.
Buying a new cat just becouse you miss the centerboards sounds expensive. Dont listen to the us technophiles, wood is a perfectly good material, and very nice to work with.

There are companies around that have computer controlled hot wire foam cutters, they are relativley cheap to use, and can give some fantastic results. If you are clever you can get some quite complicated shapes out of them.

We used one to build a hull plug. See picture below.



All the best

Gareth
www.fourhulls.com