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Boat Forum / Building / September 2005How to shape a dagger board?
My mahogany dagger board was damaged when I bought the boat used. I glued it with epoxy and put some fiberglass around it and it has held up for a few years, but I don't think it will last. I bought some 8/4 white oak on ebay for almost nothing (100bf for $1.25), and figured I will build a new daggerboard while I had something intact to copy. The blank is 44" long, 2" thick, and 15" wide. It weights 35 pounds. I originally intended to cut the corners off on my table saw, but it is so heavy that it doesn't seem particularly safe. So, I have been going at it with my 3" belt sander and my 2" power planer. Both would work, but they would take hours and hours of work. Any suggestions for a good way to shape my blank into an airfoil shape? I am thinking of buying a better planer, but hope someone here will be resourceful. ><snip> >Any suggestions for a good way to shape my blank into an airfoil shape? >I am thinking of buying a better planer, but hope someone here will be >resourceful. Google for "naca airfoils" Regards, Bruce Nichol Talon Computer Services ALBURY NSW Australia http://www.taloncs.com.au If it ain't broke, fix it until it is.... I assume you have the old board to use for a pattern of the cross section. I know that white oak would be difficult to shape by hand plane or any of the power tools you mention. For my 3" thick plywood rudder, I use a 4" disk grinder fitted with a special wood carving wheel. This is a steel disk with chain saw teeth on it's edge. Very aggressive cutting, so go slow and careful.. The PacNW wood carvers use these along with their regular chainsaw tip to carve detailed statues. Just rough out your board shape and finish with the plane or belt sander.  SignatureMy experience and opinion, FWIW -- Steve s/v Good Intentions > The blank is 44" long, 2" thick, and 15" wide. It weights 35 pounds. > I originally intended to cut the corners off on my table saw, but it is so [quoted text clipped - 5 lines] > I am thinking of buying a better planer, but hope someone here will be > resourceful. I'd go for the power planer. A good one can take away 1.5mm (1/16") in one stroke, which means you can take away half of the thinkness of your blank in 16 strokes. Meindert > My mahogany dagger board was damaged when I bought the boat used. I glued > it with epoxy and put some fiberglass around it and it has held up for a few [quoted text clipped - 13 lines] > I am thinking of buying a better planer, but hope someone here will be > resourceful. Use your table saw as a shaper by sliding the blank sideways over the blade. It will leave concavities, a hollow ground shape you can refine more easily. A well made slide jig should provide a reagulare shape and remove most of the unwanted material. Don't be afraid to drill a few bolt holes in your saw top to hold special jigs, or use eccentrics to hold in guide slides. Cut strips to sit in grooves able to slide, lay ply on top, pin with brads, screw together from other side. with saw, route grooves the other way, make side slider jig. Screw on a fence to enable milling. Terry K You can make transverse saw cuts and take out the wood with a chisel. Then clean up with a plane or whatever. Dont' go all the way in with the saw because the wood will not cut out smoothly. Practice on scrap first. If you can figure out some way to do it with a power saw it allows you to set the depth of cut. -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-FreeNet email must have "notspam" in subject or it's returned > You can make transverse saw cuts and take out the wood with a chisel. Then > clean up with a plane or whatever. That's an interesting idea that none of the woodworker I spoke to thought of. I will try it out on some scrap. <snip> > I bought some 8/4 white oak on ebay for almost nothing (100bf for $1.25), > and figured I will build a new daggerboard while I had something intact to > copy. > > The blank is 44" long, 2" thick, and 15" wide. It weights 35 pounds. Question: Is this a massive plank or quarter-sawn strips glued together? If it is a massive plank you should count on it warping. > I originally intended to cut the corners off on my table saw, but it is so > heavy that it doesn't seem particularly safe. [quoted text clipped - 4 lines] > I am thinking of buying a better planer, but hope someone here will be > resourceful. This is probably the wrong answer but I actually mean this: Use the oak for something else. Buy some light wood like Western Red Cedar and shape a board. Add unidirectional carbon for bending stiffness and strenght. Sheat in glass-epoxy and paint. A WRC blank should be light enough to handle on the table saw. Cut grooves to a depth that just 'touches' the future profile. Use a power plane to remove material almost down to the future profile and then continue with a hand plane and long board sanding. Have someone calculate how much carbon you need and then use a router to cut out some material from the WRC board so you can add the carbon without ruining your profile. More on boards at: http://hem.bredband.net/b262106/Boat/dagger.html Signature======================================================================== Martin Schöön <Martin.Schoon@gmail.com> "Problems worthy of attack prove their worth by hitting back" Piet Hein ======================================================================== I'd go with Martin's recommendation of materials. A white oak board, while maybe stable, will be too heavy to handle. Google for a NACA foil design program. For shaping it, I'd use a router as the shaping tool. Make a slotted 'bridge' which will guide a router over the victim. The bridge can run either the long way or cross-ways. If the bridge runs the long way, it can be straight but rest on curved templates at the ends of the board. If the short way, the bridge must be curved, but it will run on straight guides at the edge of the board. I'd favor the short curved bridge, which will flex less. > <snip> > > [quoted text clipped - 32 lines] > More on boards at: > http://hem.bredband.net/b262106/Boat/dagger.html > Question: Is this a massive plank or quarter-sawn strips glued together? > If it is a massive plank you should count on it warping. It is two pieces (both 2" thick) glued together. I don't need it until next spring. I can get it close, leave it for a few months, and then finish it. Would that help? > This is probably the wrong answer but I actually mean this: > Use the oak for something else. Buy some light wood like Western Red > Cedar and shape a board. Add unidirectional carbon for bending > stiffness and strenght. Sheat in glass-epoxy and paint. Oak is about 50% heavier than mahogany, but I actually want the weight, so that is not a problem. Besides, it is free and the cedar would be about $50. > Oak is about 50% heavier than mahogany, but I actually want the weight, so > that is not a problem. Besides, it is free and the cedar would be about > $50. What you are describing is a disaster guarenteed to happen. As someone suggested, use the oak for something else. Might even barter it for some good foam, but these days, good white oak, even 8/4 is cheap compared to foam, even Divinycell. Cover the foam with some 17 oz double bias and epoxy. SFWIW, the above describes how my rudder will be built. Lew > What you are describing is a disaster guarenteed to happen. Why? The mahogany board weighs 15 pounds. The oak board should weight about 23. Even if I hadn't just lost 7 pounds, what severe problems will the 8 pounds cause? I am not being argumentative; I concede I don't know anything about boat building, and little more about sailing. But I have sailed this with my 95 pound son in it, and it is fine (if a little sluggish); why would 8 pounds of board matter? >>What you are describing is a disaster guarenteed to happen. > [quoted text clipped - 7 lines] > pound son in it, and it is fine (if a little sluggish); why would 8 pounds > of board matter? It is not the added 8 lbs although rudders are designed to be as light as possible. It is that this is not a good application for white oak. Now if you quarter saw that 8/4 stock, you can make some very nifty trim for tha boat. Lew >> What you are describing is a disaster guarenteed to happen. >> [quoted text clipped - 8 lines] > 95 pound son in it, and it is fine (if a little sluggish); why would 8 > pounds of board matter? Without looking at the board and reading the grain, it is near impossible to tell what it will do. Not knowing how old it is and how it was dried muddles things further. I don't think the weight is a concern. I would think warping, bending, settling, etc. of the board is the potential (big word there) cause for concern. A guaranteed disaster? I hardly think so. A likely disaster? Nah. It is yours, the board is free. The penalty will be to redo it. Go for it, it might just work! Ed > > Question: Is this a massive plank or quarter-sawn strips glued together? > > If it is a massive plank you should count on it warping. > > It is two pieces (both 2" thick) glued together. I don't need it until next > spring. I can get it close, leave it for a few months, and then finish it. > Would that help? Some but I think it will warp sooner or later anyway. A good epoxy seal helps slow the process. But as someone else stated: Without being able to see your blank and how the grain looks it is very hard to be anything but rather vague about this. > > This is probably the wrong answer but I actually mean this: > > Use the oak for something else. Buy some light wood like Western Red [quoted text clipped - 4 lines] > that is not a problem. Besides, it is free and the cedar would be about > $50. I would say your troubles with the white oak is more about handling and working on it in your workshop than all-up weight on your boat. You will spend a lot more time shaping your oak than it takes to shape cedar. Oh, I almost forgot. It is my experience that oak and epoxy coats don't always work well together. Signature======================================================================== Martin Schöön <Martin.Schoon@gmail.com> "Problems worthy of attack prove their worth by hitting back" Piet Hein ======================================================================== There is no need to worry about making a daggerboard, centreboard, or rudder out of solid wood. Visit your nearest sailing facility and look at all the centreboards, daggerboards, and rudders made of solid wood. The fact that your board is glued up means it will not warp. You can look at the end grain to see which way the two pieces are oriented. Put a couple coats of polyurethane varnish on it and refinish it every few years. I've never put epoxy resin on oak but peope who have say it's only necessary to sand the surface of teh wood to roughen it up a bit. Oak contains tannin, and acid, and acids dilute epoxy rdeucing its bonding strength. One way to clean up epoxy resin that has not cured is to use vinegar, lemon juice, or some other mild acid. -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-FreeNet email must have "notspam" in subject or it's returned > There is no need to worry about making a daggerboard, centreboard, or > rudder out of solid wood. Visit your nearest sailing facility and look at > all the centreboards, daggerboards, and rudders made of solid wood. The > fact that your board is glued up means it will not warp. You can look at Well, it depends on the level of knowledge of the guy/gal who did the job. That's why asked if it was a massive slab or built from quarter-saw pieces. Signature======================================================================== Martin Schöön <Martin.Schoon@gmail.com> "Problems worthy of attack prove their worth by hitting back" Piet Hein ======================================================================== toller, I have been watching this thread, but did not have time to write until today. There seems to be a a multple of questions here and some interesting thoughts among the responses. First, If you glued the damaged board with epoxy and glassed also with epoxy, there is no reason it will not last as long as the mohogan holds out - that may be quite some time. Mohogany is a relatively light wood, but not that light. You will pick up probably 10-12 pounds. It was probably choosen for it's rot resistance and the ease of working. It is a very dimensionally stable wood which is why it is so valued by pattern makers. By "cut the corners off" I am guessing that you mean the long edges. If that is the case, we need to ask more questions here. Are you going to make this cut the entire length of the blank? If yes, just be sure you have pusher sticks handy and a friend to catch the plank and trim as they come out of the saw. The second cut will be much more exciting the than the first because of the small support area left on the trailing edge. If no, you still need the friend, but not the pusher sticks. Plus now the operation has a new twist because sawblades only cant one way. In one direction, you will have to start the cut as a pocket cut and saw out of the blank, and the other you have to stop in the blank. There is only one safe way to do this. Shut the saw down and then retract the blade. You will have to finsh the cut by hand. As to the actual section, yes, you can get there with the power plane and belt sander (look up supergrit belts - effective prices). If the boat is a class of any kind, the class site probably has the section available. If not, you probably want a modified four digit. I own code for this, but I do not know if it is available on the web - search. Cutting guide reference slots is not a bad idea, you will have a lot of wood to hack off before you get close to the sand-to-shape phase. You might consider doing that before you even "cut the corners off" because it will be easier to handle the blank then. Thinking is the Cheap thing to do. Matt Colie (I have been at this way too long) > My mahogany dagger board was damaged when I bought the boat used. I glued > it with epoxy and put some fiberglass around it and it has held up for a few [quoted text clipped - 13 lines] > I am thinking of buying a better planer, but hope someone here will be > resourceful. <snip> > Cutting guide reference slots is not a bad idea, you will have a lot of > wood to hack off before you get close to the sand-to-shape phase. You > might consider doing that before you even "cut the corners off" because > it will be easier to handle the blank then. Well put. This was what I intended to describe but your command of the English language is clearly superior. I recommend Western Red Cedar (or similar light wood) for two reasons: 1) Easier to handle both while building and on the boat. 2) Easier to work on than oak. I have shaped plugs out of MDF-blanks this way. A plug for a rudder 1.8 m long and with a 30 cm cord took only one evening to shape. Painting, wet sanding, rubbing and polishing took much longer. > Thinking is the Cheap thing to do. Indeed :-) Here are some more ideas on shaping foils if you don't want to make molds. * Strip planking using 6-8 mm thick WRC strips. Use external frames. Glass+epoxy inside, join halves and don't forget that you need a good structural member running down the middle of the foil. The exterior will need some final shaping, then add carbon as needed and wrap in glass and epoxy. Potentially lighter than the massive board for big boards but more work and less robust. * Central structural member made from WRC+carbon laminate. Foil shaped from foam cut by hot wire. Cover in glass+epoxy laminate. Note, this time the laminate is structural. My current boards were build like this some ten years ago. They are 2.5+ m long and has a 44 cm cord. New they weighed 12 kg each. /Martin [snip] > * Central structural member made from WRC+carbon laminate. Foil > shaped from foam cut by hot wire. If you go this route, consider having the core cut by the folks at flyingfoam.com. They are in business to cut wings for RC gliders and airplanes, but a core is a core. > Cover in glass+epoxy laminate. > Note, this time the laminate is structural. [quoted text clipped - 3 lines] > > /Martin --Mac [snip] > If you go this route, consider having the core cut by the folks at > flyingfoam.com. They are in business to cut wings for RC gliders and > airplanes, but a core is a core. > --Mac http://philsfoils.com/ is reported to do this sort of thing for dinghies and multihulls. Probably cost-justified only if you're serious about racing >> If you go this route, consider having the core cut by the folks at >> flyingfoam.com. They are in business to cut wings for RC gliders and [quoted text clipped - 5 lines] > and multihulls. Probably cost-justified only if you're serious about > racing. [snipped HTML] Cool, I didn't know about philsfoils. But I don't think that flyingfoam is very expensive. I got a quote from them once, but I don't remember the details. Then again, I don't have a lot of free time, so what seems reasonable to me might seem expensive to others. --Mac >My mahogany dagger board was damaged when I bought the boat used. I glued >it with epoxy and put some fiberglass around it and it has held up for a few [quoted text clipped - 13 lines] >I am thinking of buying a better planer, but hope someone here will be >resourceful. I congratulate you on eliciting a wonderfully practical, innovative, and helpful thread. Even the most radical contributions ("Don't use oak!") were well-meant. Notice that suggestion of using a wood carve blade in a circular saw? Wow! Wood propeller carvers use a router in a kind of copier frame, profiling an existing fair copy of the blade. I notice the respect given to mahogany on the traditional end, but also the foam core glass or carbon approach at the leading edge end. Iobserve in passing that the center board on the SouthCoast 22 I am preparing, is a hefty chunk of iron - its weight so low down is of course desirable - but that has a wind up hoist. Brian Whatcott Altus OK > My mahogany dagger board was damaged when I bought the boat used. I glued > it with epoxy and put some fiberglass around it and it has held up for a few [quoted text clipped - 13 lines] > I am thinking of buying a better planer, but hope someone here will be > resourceful. Several people have suggested finding NACA foil software. If you don't want to do that, I would be happy to calculate the coordinates for you and post them here. I would need to know the desired thickness of the foil (at its thickest point), and the chord length (fore and aft extent of the daggerboard). I am assuming that the daggerboard is basically rectangular when viewed from the side. --Mac > Several people have suggested finding NACA foil software. If you don't > want to do that, I would be happy to calculate the coordinates for you and > post them here. I would need to know the desired thickness of the foil > (at its thickest point), and the chord length (fore and aft extent of the > daggerboard). Or go here: http://www.ae.uiuc.edu/m-selig/ads.html for free section coordinates. /Martin I bought a good 3.5" power planer and cut it down in 30 minutes. I used a belt sander to smooth the lines out, and a router table to radius the front and back. Tomorrow I will see if it fits. (the boat is 30 miles away, with no electricity) Since oak is 40% heavier than mahogany and the finished oak board is only 20% heavier than the mahogany board, I must have made it thinner than I intended; but since oak is also 50% stronger than mahogany, that shouldn't matter. It may not be a perfect mathematical airfoil, but it is pretty close to the (unpracticed) eye. >.. I must have made it > thinner than I intended; but since oak is also 50% stronger than mahogany, > that shouldn't matter. maybe, maybe not. if it's too thin for the slot it can vibrate while sailing. you can always build it up with a fibreglass coating to make it fit better. with wood you can always take more off, but you can't put it back on. that's what fibreglass is for, although it makes the product heavier. -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-FreeNet email must have "notspam" in subject or it's returned > with wood you can always take more off, but you can't put it > back on. A carpenter is a whittler who knows when to quit. Ed > > with wood you can always take more off, but you can't put it > > back on. > > A carpenter is a whittler who knows when to quit. > > Ed a "journeyman" is a guy who knows how to fix his fux ups. if wood is going near water, it needs several coats of epoxy. read directions about application and secondary bonding. fiberglass cloth is imbedded in wet epoxy using paint brush and squeegee. see directions for weight of cloth and radius of corners glassed over. second and third coats of epoxy/filler yield smooth surface and built up(squared) corners. good luck. >> > with wood you can always take more off, but you can't put it >> > back on. [quoted text clipped - 11 lines] > coats of epoxy/filler yield smooth surface and built up(squared) corners. > good luck. Hmmm.... in a word... bullhockey. There is a chance that a bit less maintainance will be needed but epoxy is hardly a necessity. Epoxy is no guarantee of seaworthiness or durability. Ed > >> > with wood you can always take more off, but you can't put it > >> > back on. [quoted text clipped - 17 lines] > > Ed well, give it a couple of coats of primer and then a coat of your favorite anti-fouling. (personally, the only things I use wood for is interior trim and of course, the fireplace. if I was building yet another daggerboard, I'd use foam core and fiberglass/epoxy. different tech. for different folks, huh?) >> Hmmm.... in a word... bullhockey. There is a chance that a bit less >> maintainance will be needed but epoxy is hardly a necessity. Epoxy is no [quoted text clipped - 7 lines] > another daggerboard, I'd use foam core and fiberglass/epoxy. different > tech. for different folks, huh?) I guess I should have thrown in a smiley or a (grin).... Different strokes, not only for different folks, but for different applications. I had a Luders L-16 many years back. A 26' loa cold molded plywood boat. It was made with mahogany and resourcinol glue which I used to match up the repairs it needed when I got it. It seems to me that that would be the "perfect" material (only sub'ing epoxy for the glue) for a larger boat. All the best points of both wood and plastic. For a simple daggerboard (and again, depending on the application) the simple method described by the OP seems fine to me. The last dagger I made was 1/2" plywood. I rough cut it with a bandsaw, sanded the profile with various power and hand sanders, filled the voids with a glue sawdust mix and it has about 12 coats of polyurethane on it. It works great and has lasted (with no new coating) for about 3 years so far. It was for a Snark (the styrofoam covered with plastic sheathing boat). As is, it was more work than the boat is worth. But "worth" rarely fits in a discussion of boat building or repair. If it were a boat I was racing (not likely, another "not my bag") I'd have probably put more into it. (grin) Ed >... The last dagger I made > was 1/2" plywood. I rough cut it with a bandsaw, sanded the profile with > various power and hand sanders, filled the voids with a glue sawdust mix and > it has about 12 coats of polyurethane on it. It works great and has lasted > (with no new coating) for about 3 years so far. I'm a great beliver in economy. I have one 1/2" plywood daggerboard which serves all three of my home made sailboats. After all, a person can only sail one boat at a time. It was rounded off on the leqding edge and tapered on the trailing edge with a sanding disk on an electric drill. The edges were then give a couple of coats of tinted polyester resin the the whole thing was painted with exterior latex house paint from a garage sale. The plywood was made of some sort of dark wood, salvaged from a packing case, possibly some sort of mahogony. When it got wedged under one of the boats in shallow water and cracked it was repaired by pumping PL Premium into the crack and weighting it down with bricks over night. It's been well used and looks beat up but is still functioning fine. Photos on my website under "Boats". Come to think of it the rudder on a 20 footer I once owned was also made from plywood. I broke the cheeks on it surfing downwind under full sail in a blow and had to replace them. The cheeks were plywood. -- ------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage: www.ncf.ca/~ag384/top.htm warning: non-FreeNet email must have "notspam" in subject or it's returned > >> Hmmm.... in a word... bullhockey. There is a chance that a bit less > >> maintainance will be needed but epoxy is hardly a necessity. Epoxy is no [quoted text clipped - 29 lines] > > Ed L-16 is still on my list of most beautiful boats. OK, I'll admit it, I had a snark too. >>.. I must have made it >> thinner than I intended; but since oak is also 50% stronger than [quoted text clipped - 6 lines] > back on. that's what fibreglass is for, although it makes the product > heavier. I was thinking that myself, but I am unsure about the technique. I have done fiberglassing, but not on something like that. Would it be reasonable to staple the glass in place, and then apply the epoxy; while working on waxed paper? |
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