I think I've asked this before.

Would a billet aluminium blades and boards work?
Would they be stronger?
Would they be lighter?

I'm gonna go out on a limb and say they'd be definitely cheaper. Once you've got the file, load up a blank in a 4 axis cnc mill and basically walk away. Plus polished boards would be frickin' cool. Or even anodized. Might want to make the top removable, a bent board could be trouble if you couldn't pull it out the top......

Snipes use aluminum dagger boards.

the amount of machining and polishing required to get a real foil shape would be massive. Otherwise, the molds they use for foils would be frequently machined from aluminum...but they use more cost effective processes even for the molds. It would still be pretty weighty too.

Yes.
No. More ductile, for sure, but not as stiff.
No. Aluminum is about 165 lb / cu ft. Carbon fiber/epoxy composite is only about 97 lbs / cu ft., but since it's almost 3 times as strong, the middle can be replaced by foam, which has a density of ~4 to 8 lbs / cu ft.

Aluminum foils are easy to make, but they're heavy and bend easily (not just flex, but bend plastically - permanently deform)

Of course, you could have figured this out on your own, but you're a lazy bastard.

Matt, you don't reach this station in life by not being a lazy bastard. It takes training, practice, and a whole mess of luck. I was actually going to figure the volume of a board by dunking it something, but then I realized I didn't have anything big enough. Then weigh it.



The machining would be nothing if it were essentially one piece. Making a female mild is a whole mess more complicated as far as machining goes.

Magnesium. 112lb per cu/ft.

Magnesium and water don't mix well. Kinda like sodium and water, if you've ever done that prank.

The Sprint 750 trimarans had aluminum extrusion boards/rudders, and there's a fair number of owners that are ridding themselves of them and going with carbon fibre

Magnesium is non-reactive in water (certainly not like sodium that will literally explode). It will corrode quickly in salt water, though. Very low on the galvanic series.

Get magnesium hot enough and it will burn with an intense white light. And you can't put the fire out. (Actually, aluminum will do the same, but you've got to get it really hot.

This is what happens when aluminum burns:

Is that on carpet?

Don't worry, Jake - the carpet won't be an issue in the next frame.

I am not sure they would be much cheaper. Your talking big and expensive pieces of aluminum, plus mucho machining time. A 1" sheet for 1 60" x8" board would cost about $300 I bet, that's before you touched it with a machine.

I'm just kicking around ideas. Its what happens when I get bored. It just seems re-goddamn-diculous what a set of daggers cost nowadays.

I wouldn't put foam in the middle. Pointless, just make them hollow, bolt the two halves together with a flat surface around the edge that can be gasket'd, or sealed, then just put a drain bolt at the top should they leak.


If you're into cars, and into building weird stuff, this is an awesome read. Larry Ellison had these guys build him a AC Cobra replica with a billet aluminum chassis. Frickin' cool stuff. The Art of Engineering


There's all sorts of strange projects I'd take on for fun if I had the means. I want to make a set of billet aluminum rudder stocks, with the.... (I can't think of the word)..... where the rudder arms are bent inwards. Its the same name as a punctuation. Anyway, make them so you can use just a straight carbon tube. It'd have to be three pieces, two halves that hold the rudder that are bolted to a piece that slides over the pintles. Maybe press in a brass bushing there too.

Then there's my want to make a carbon fibre RC flying wing. That might actually happen soon. I need to buy a new one, and make a mold of it. We'll see how horrible that goes. I know it won't survive the crashes, but it should be unreal compared to a solid foam one.

A 1" x 10" by 72" slab is about $400, (that's what it would take to get a 1st gen C2 dagger out of it.), if you're buying it retail. Which who the hell buys anything retail. Probably be cheaper if you're getting it in a 20' stick too, and you'd be able to recoup a small percentage recycling the waste.

I'm curious what the machining would cost, or more importantly how long it would take. If the machine is $100/hr, would it take six hours to do it? I kinda doubt it in a CNC, and that's what it'd take to get it up to the cost of a C2 dagger board.

I like these discussions. Way more than WtheF are we going to do with the Alter Cup.

I can't help but think about the incredible things they are doing with 3D printers nowadays. What will happen when these machines become commonplace any each boat owner can design and "print" his own boards?

6 hours is probably reasonable - it all depends on the finish you are after...how many steps the machine needs to make. I had a mold made from two chunks of aluminum for a 5lb lead bulb for r/c sailboats. The mold was about 12 inches long and it took 18 hours of machining for the two halves (I don't think the programmer really approached it correctly though).

Karl,

Aluminum foils do not survive long in salt water - no matter what the core. When the Corsair Sprint 750 appeared on the waterfront, Bob Hodges pointed out that they were subject to corrosion and fatigue.

During the 38 mile offshore race we had in 2009 for the Trimaran Nationals there were foil failures; however, they were due to the head design.

In the background, it was discovered that the rivets used in seaming the halves were becoming weak from wear, and the surface area was becoming contaminated via water absorption. The ultimate 'Fix' was to go composite, and that is what the top sailors did.

Now, let's go to curved foils for discussion... how many sailors are able to afford the cost of maintaining/replacing curved foils for an entire sailing year?

Convex machining vs concave though? I don't know for sure though. Just a wag from watching wood cnc's go at it. The feed rates in wood are faster, but there are some crazy fast metal machines too.

Our boards are never in the water though. Couple hours here and there, that's it.

Most of the boards on the Sprints are not in the water 24/7. When fully retracted they are dry inside of the daggerboard trunk.

Its hard to say, there would be a rather large amount of metal removed and that means many many passes.

Trying to build a foil from sheet metal with well designed and stout spars would be lighter and I could imagine them being strong enough, still not sure about it being much cheaper though.

Wood CNC's..

If you are going to go to the trouble, why not machine a foil out of a block of laminated wood/composite. I don't remember anyone trying that.

Build your block out of wood or foam laminated with fiberglass, carbon, Kevlar, foam, aluminum... You could leave appropriate volumes hollow and except for your reference points, the finish could be sloppy.

Machine out the foil then machine out the skin(wood, carbon prepreg...) and glue them together

Or use a reinforced paper for the skin. Print it out on a large printer with little cutouts to make it lay flat. You could print whatever graphics you like. You could have a foil with your face on

I don't think this has been tried with a foil. I have heard of similar methods used for architectural pieces or high price furniture. You could be the first and lead the way if it shows promise.

Phil's foils...he's been machining wood core foils for some time. I think he's since merged operations with CCI.

http://fastcomposites.ca/publications/TankTalkPhilsFoils.pdf

http://www.fastcomposites.ca/site/marine/design-tips-fabrication-overview/care-of-wood-cored-foil/

Hey Jake >

I was just gonna say Phil's Foils or maybe mention Jim Bauman, from Recreational Composites. JB has done a few cat and tri foils as you know. He is about finished with restoring the C 24 and is willing to work for food

Bauman is great - I had him clean up a pair of Nacra 20 foils for me once and he became standard to clean up our foils from then on. There's nothing worse than 500 miles on a boat that speed warbles a song through the water all day and night. A little touch up from Jim and they are silent!

Karl with all this time you have spend the Weekend and Build yourself a DN.With all your carpentry skills you would have it built in no timeI am coming down this summer to Build some Planks with A few guys.

DN is on the short list.

Jim's retired from epoxy work. Too much exposure. Sad to see a master retire.

What I was thinking about is a little different from machining a wood core and then vacuum bagging or molding a skin over it.

The idea started years ago when I saw an exotic piece of furniture built like this. With this method the structure was built into the "block". First the skeleton was bonded to gather in a jig. Long, short, and little blocks of wood, composite and even steel was joined to form the structure. Then the outer wood that will be seen was bonded to the structure so that it formed a rough blocky equivilent to the final shape. Then the furniture was carved out and finished. The advantage was you could build "solid" wood in shapes that are not structurally possible with plain wood.

When I saw this, my first thought was you could build a hollow wood rudder by laminating strips of wood and composite for strength. You would not need the jigs and molds normally needed. Just build the rough shape around a hollow core and cut the outside to the final shape.

While this might not be as light as say a hollow core carbon, as long as you have access to a way of cutting out the final shape, the tools needed are simpler. Also since molds are not needed, it would be easier to build rudders with different foil profiles or even shapes.

I don't think this will revolutinize the world, but if you want to CNC a set of foils, its probably better and cheaper than starting with a block of aluminum.

For straight foils, you can get by with CNC cut foam cores (high density foam) and laminating carbon over them (lots of carbon). If people are interesting, I can cut 100 PSI foam on my CNC for reasonable prices.

The issue is when you go longer or curved; in these cases you need a CNC router machined core and a PVC based foam or wood core. Finding someone that will machine cores or molds for reasonable prices is not a trivial task, I have a few sources and may evaluate designing and building some curved A-Cat foils if the business case is justifiable.

As far as aluminum is concerned, built properly you can approach composites in weight and strength, but time wise it would take longer than the methods proposed above (unless you are THE metal guy). The corrosion issues posted above have never really been solved, take a look at any aluminum vessels (boats or seaplanes come to mind) after 10 years. Foils would not hold up very well to this abuse!

I believe you could have used him on your 18 at Tradewinds. According to the Vid, those things were pretty dang loud!

Jim is still in the foil business. He is finishing the C 24 as his final tribute to boatwork. He is hoping to mount the ama this week and begin installing the nets.

Once this boat project is complete he will be devoted to his windsurfing fin business, sailcraft foil design, fabrication, and repair.

There are many alloys available, some are very strong, some not some have excellent corrosion behaviour, some not, and so on. But fact is that the right alloy is resistent to salt water and strong (as proven by thounds of masts). It has similar strength to hand layed up glasfibre, but less than carbon. Best production process would be extruding (if you can live with a straight board), not machining. Topcats use extrude alu rudders since ever. They have decent quality and are unkaputtbar (undestructable). At all the whole rudder system is a nice one on the Topcats.
Not cheaper than some glass boards though. http://www.topcat.de/shop/index_e.htm . The rest of the boat is fairly outdated...
Alu rudders wouldn't be particular heavy, about the same or a bit more than glass fibre boards of the same strength and size and maintenance free by the way.

Cheers,

Klaus