hi all,
am idly thinking of sometime in the future reshaping the daggers and rudders on my old nacra 5.2 to a more modern profile, (round out the forward lower corner of the daggers and removing some of the width of the rudder blades)

but to do so i need to know what they cored with
heavy enough to either be ply or solid glass!

or maybe safer to copy them in shaped ply and then wrap with glass, anyone guess what weight of cloth and how many layers would be needed to provide enough strength?

Most are foam core with glass or carbon skin. Oftentimes, the builder will use some sort of stringer for stiffness. The H Tigers have 3 G10 stringers running the length. The old 18's didn't have stringers. They are usually built in two halves and glued together.
Not sure about the 5.2.

G10 stringers??

Hi SurfCity and all,

Old tornados used wooden rudders. Is there any true reason, why todays rudders are from class or CFRP? The rudders of my Dart are of glass and heavy, and I see no point that wooden rudders could not resist the loads acting on it. Having a straight leading edge, a aluminium or glass or kevlar leading edge cover would be easly applicable.

Cheers,

Kolja

One off would be expesive, but a set of polished aluminum blades and rudders would look super cool. Or worse yet in the finance department what about titanium?

Those boards are fiberglass with a sort of solid resin core. I'm not certain exactly what they use in the core on those but you can sand to it, shape it, and cover it a little with some glass with no problem.

I built a set of rudders and daggers for a viva 27. The rudders were 1 3/4 in thick, by I think 38 long and were very heavy solid mahogany. I used the originals as cores planed them down about 3/8 3/16 from each side and then cut off the leading and trailing edge leaving a top w/ a tapered stringer. I then glued on 1 lb styren foam. A few templates and and using my old surfboard shaping skills. 1 layer of of uni-knitted "rutan" glass "highly recommened" about 2/3 lenth and then 1 layer of 4oz glass. a little micro light. the new rudders were approx 48 in long an extra 8 in. with the last 12 in or so just, an egg shell. skin. new rudders were about 1/3 the wieght. With an much improved foil. I used a naca 12 foil. If I did it again I use the resource "here" to get a better foil. As for daggers, I used www.flyingfoam.com had Bob cut the cores with a cnc machine. again glassed w/ approx 10 layers of the Rutan uni-knitted glass. 1 layer of 4 oz glass. a little micro light. new boards were great I got close to a naca 12 foil but was restricted by the slot. new daggers were 8 ft 4 in long. and wieghed about 30 lbs each about 50 lbs lighter than the originals. In my opinion, the wieght savings vs strenth vs cost I would look at the new cloths being developed by the airplane composite company's. The foils I built were with in 10-15% of the wieght of a full carbon foil. But approx 1/3 the price. These are my opinons based upon 20+ years "part time" of fiberglass and water craft production and airplane restoration. PM if you want or need an opinion. Question has anybody out there built a set of aluminum boards I'm considering it for my new project "C-class" if so I would like to see how they were built.

Guy at the Texas city dike where I use to sail had a SWEET set of wooden rudders on his Hobie 21. Even LONG spin run of hours her had no problem. Light tan and dark mahogany color. They looked REALLY good.

Doug

They don't have to be high tech. I've heard that there was a company that made wooden rudders for the H14 and 16 back in the day. Anyone know about that?

I don't know anything about this really, but my friends at Elkhorn Composites were building hollow surfboards out of aluminum honeycomb core and carbon. They were super stiff and very light. I thought it would be a cool way to make rudders. It would be expensive though! Billet aluminum on a CNC would be cool Karl. Titanium??? Ouch, my wallet.<img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />



You can make daggers out of a lot of materials and each method has pluses and minuses.

When I used to race quads you could buy a steel axle for about $400, the Ti ones were close to a thousand. Just a reference. Aluminum would be plenty strong and light. Plus you can polish it to a mirror shine. I wonder what it would actually cost? Might be cheaper than one would think.

weighed my daggers today and they came in at 5kg or 11lb each, which must be much heavier than newer foam cored daggers

i think solid alloy would weigh about the same, however an aerospace alloy honeycomb core, like the old usa ski maker hexcel used, wrapped and sealed in riveted duralinium skins would be pretty cool

pity i'm no longer working as an aircraft mechanic with access to all that cool stuff



well shaped ply would look pretty good too as the different colored laminates would show up like contour lines in the leading and trailing edge tapers

maybe if they are well soaked in resin they wouldn't even need a cloth sheath. doing without the cloth would make them easier to build and lighter

might cut out some bits and start flex comparisons, i know the glass ones can support my weight after my last 2 capsizes and that old nacra daggers can break when being used all the way down in heavy air. perhaps they aren't flexible enough

Flexible is bad when you are trying to go fast.

lateral twists in the dagger cases would be bad but if others are snapping 5.2 boards in heavy air it seems to me they don't give enough

those long high aspect daggers on boats like the inter17 and A cats at half the width and twice the length must bend more than 5.2 boards

if 2 daggers weigh 10kg, 22lbs, together, then the 2 rudder blades probably weigh another 5kg, 11lbs. that's 10% of the boats 150kg, 325lbs

I have seen "ally" skinned plates and rudders for a serious contender for Cherub skiff class....

They had a backbone stringer made of wood and the plate ally was folded. The backbone then formed the max depth. The issue is sealing the trailing edge and keeping the plate ends at the trailing edge together. They solves it by riveting the two edges and silicon sealing. It worked.. At that stage one couldnt weld easily thin plate end to plate end. The other issue is the temp to weld would warp the plate near to the trailing edge and thus create uneven flow.. High speed and uneaven flow isnt much fun..
I dont think much was gained over a conventional plate.

I think you would have to do it billet. Cut it from one piece of aluminum. I'm sure there are places you could ship a rudder to and they would be able to scan it and be able to make a 3D CAD image for a cnc

if your asking me..
I would get access to a cnc machine.
Then laminate up alternative strips of foam and wood (western red cedar or similar) alternatively balsa strips with carbon running between each strip and a central strip of western red.. I have used both techniques. Here I will say having a semi-dense wood core, like western red, at the tips and edges helps when impact happens! So the blank profile is 2 cm of western red 10cm light foam 10 cm western red 10 light foam 2 cm wester red. For a total width of 340 mm. One can use smaller and more strips if one wishes but try and keep the max width with the denser core as well as the tip being totally dense core.

Then glassing skins to the cnc form. Glass or carbon as your mech engineer requires to handle the loads.

I would not use a foam only form unless your really sure of the skin thickness!! Even then the point loading when righting the boat or sailing under hard conditions can be very interesting!!

hope that helps




<img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

doubtful that you should take a grinder to your foils.
wood is a perfectly good material to make new ones. you will need to glass them. they need to be quite strong so stringers are great. put one at max camber for easy shaping.

foils for the foilboards are cut from aluminum billet on a cnc. some big windsurf fins are made that way. heavy and accurate. g10 on a cnc is a good way to make a windsurf fin. heavy, accurate, expensive, right amount of flex for a board.
when H16 first came out we were forced into making rudders because the abs ruuders couldn't handel the loads.it was a while before lexan rudders were invented, so a whole market sprang up to supply usable rudders. the molded ones were glass with mysterious fillers, and the custom ones were wood. there was lead in the wood blades because rudders had to be 7 or 10 pounds(whatever the rule is). i always thought my wood ones were a speed advantage. the best tornado blades were custom wood with glass in those days.

The Tornado class dont allow carbon in the foils, so the best rudders around are still wood. Not hand shaped, but veneers put into a mould and laminated. I have tried finding out how Marstrøm do this, but no success so far.

What is g10? Some kind of alu?

I would probably not go down the path of cnc'ing a block of "ally"..
While it sounds great "ally" does not float!! So if for some reason it comes out of the case the whole thing sinks!! At least with wood you have a chance the plate/rudder can be retrieved.
Even though its old read the chapter in Frank Bethwaite's book.

For those classes which have a no carbon rule.. Very thin veneer or ultrathin ply is the natural carbon substitute.. One can steam veneer and epoxy together to make a side of plate.. then put in the backbone stringer epoxy the side together and glass.. should be very strong and light

Had a friend of mine snap two 5.2 boards in heavy air quite recently with two big guys on the wire in 30+. When you experience that type of wind it is better to raise the boards about 1/3 of the way to help depower the boat along with droping the traveler. Without a reef point that's a good way to reduce the chance of inadvertant swimming.