bill1111 Posted March 4, 2010 Report Share Posted March 4, 2010 Are these as strong as metal masts? Lighter ? cheaper? look better? If none of the above why? Bill Quote Link to comment Share on other sites More sharing options...
hokeyhydro Posted March 4, 2010 Report Share Posted March 4, 2010 Hmmm . . . Carbon is very strong. Not sure what size mast you want, but for a small sailboat you could shape blue foam to the size, wrap that sucker in carbon, maybe use the Chinese Finger Trap style carbon tube socks, let `er cure, and in a safer no smoking zone, dribble gasoline inside which will dissolve the foam. If you do birdsmouth the wood weight remains. But I guess you could do an ultra thin-wall birdsmouth core. Quote Link to comment Share on other sites More sharing options...
Tom Lathrop Posted March 4, 2010 Report Share Posted March 4, 2010 Hmmm . . . Carbon is very strong. Not sure what size mast you want, but for a small sailboat you could shape blue foam to the size, wrap that sucker in carbon, maybe use the Chinese Finger Trap style carbon tube socks, let `er cure, and in a safer no smoking zone, dribble gasoline inside which will dissolve the foam. If you do birdsmouth the wood weight remains. But I guess you could do an ultra thin-wall birdsmouth core. Sure, you can do that. What you will wind up with is a nice tube with no useful utility that I can think of. The carbon Chinese sock offers very little stiffness in such a form. Quote Link to comment Share on other sites More sharing options...
bill1111 Posted March 4, 2010 Author Report Share Posted March 4, 2010 somewhere in surfing the core sound info I saw a picture of a thin wall birdsmouth that GB was doing for maybe the ec22 so must be of some use the wood then is only for a form? Bill Quote Link to comment Share on other sites More sharing options...
bill1111 Posted March 4, 2010 Author Report Share Posted March 4, 2010 Sorry was looking at mast for core sound 17 Bill Quote Link to comment Share on other sites More sharing options...
Tom Lathrop Posted March 5, 2010 Report Share Posted March 5, 2010 somewhere in surfing the core sound info I saw a picture of a thin wall birdsmouth that GB was doing for maybe the ec22 so must be of some use the wood then is only for a form? Bill The carbon sock on the top mast sections of the EC22 only offers hoop strength and the mast stiffness is from the birdsmouth fir core. Quote Link to comment Share on other sites More sharing options...
John Turpin Posted March 5, 2010 Report Share Posted March 5, 2010 All I know is that I unintendedly added weight to my mast top sections by glassing them. I didn't use carbon, but rather 9 oz tape and epoxy. I was shocked at how much weight it added to the tops of the masts. I sought to add some strength up there, but am now concerned that the extra weight that the epoxy added will ultimately hurt me. I'm not sure that I did the right thing. Quote Link to comment Share on other sites More sharing options...
hokeyhydro Posted March 5, 2010 Report Share Posted March 5, 2010 Hmmm . . . Carbon is very strong. Not sure what size mast you want, but for a small sailboat you could shape blue foam to the size, wrap that sucker in carbon, maybe use the Chinese Finger Trap style carbon tube socks, let `er cure, and in a safer no smoking zone, dribble gasoline inside which will dissolve the foam. If you do birdsmouth the wood weight remains. But I guess you could do an ultra thin-wall birdsmouth core. Sure, you can do that. What you will wind up with is a nice tube with no useful utility that I can think of. The carbon Chinese sock offers very little stiffness in such a form. You are most likely right, Tom. I've never used carbon sock tube, just strips. And then there would be the problem, either material, of a BLACK mast, and a toasty sun heating that bugger up and possibly degrading the epoxy. Reckon one could paint it white, or . . . Back in the day of airplanes made of sticks and fabric, the prime coat on the fabric to prevent sun damage was aluminum paint. Yes, even colored paint is translucent, but the aluminum paint did a great job of keeping the underlying material in the dark. Aluminum paint base, and then the color of your choice. Sounds like work. I'll stick to a wood only mast. I have two birdsmouth spars built for the Cat - a 22' mast, and a 7'+ boom. finish: 2 coats of 105/207 WEST and several coats of spar varnish. If the Carolina sun starts to eat the finish I'll paint it. Quote Link to comment Share on other sites More sharing options...
Palolo Hawaii Posted May 8, 2010 Report Share Posted May 8, 2010 WB214 (May/June 2010, page 46ish) has a small piece on a catboat mast with carbon tapes & rods laminated to the inner face of the staves. Seemed to be successful in their comparison test with uncarbon'ed birdsmouth masts. Quote Link to comment Share on other sites More sharing options...
Tom Lathrop Posted May 8, 2010 Report Share Posted May 8, 2010 WB214 (May/June 2010, page 46ish) has a small piece on a catboat mast with carbon tapes & rods laminated to the inner face of the staves. Seemed to be successful in their comparison test with uncarbon'ed birdsmouth masts. If properly designed and constructed, this would be an ideal combination of the two materials. Uni directional carbon fiber has lower elongation than wood fiber and should be used toward the center of the bending axis to balance the characteristics of the wood. How far from the surface to place the carbon? You'd really have to know the tensile strength of each material to do it accurately and that would be hard to come by (impossible) for the particular section of wood. I'd think they just winged it in the WB example. I proposed this exact layout to Graham last year as a possible better use of carbon in birds mouth masts. I might make such a mast for Lapwing if I have confidence that it can be done at the same diameter of the aluminum so it would fit the boat as built. Haven't really studied the problem enough to determine that yet. Quote Link to comment Share on other sites More sharing options...
Howard Posted May 9, 2010 Report Share Posted May 9, 2010 On a related theoretical note, I've wondered about making the following modification to a birdsmouth mast: In this case, you would put a "cross" of some light wood.....say 1/8" baltic birch plywood.....inside the mast. This would be shaped to fit loosely, but close enough that there would be enough epoxy to hold it firmly in place inside the mast. The thought being this is similar to how cardboard is built. The triangle providing substantial stiffness to the layup. Perhaps enough to really lighten the thickness of each stave? Yes, I have wondered.....but not enough to build the thing to try it. Quote Link to comment Share on other sites More sharing options...
Tom Lathrop Posted May 9, 2010 Report Share Posted May 9, 2010 Howard, such a structure would add very little to the stiffness of a mast since it is located near the center of the bending axis where the stress is minimal. It would not pay its way in weight vs added stiffness. At the center of a mast, there is zero stress. Stress varies exponentially with distance from the central axis. That is why a hollow mast is the most effective in weight vs stiffness. Its also why a thin wall aluminum tube is so difficult to beat for a mast. Quote Link to comment Share on other sites More sharing options...
Howard Posted May 10, 2010 Report Share Posted May 10, 2010 Thus another idea by a non engineer goes down in flames. My thought was each of those crosses would act as miniture I-beams or a truss to resist bending. Like taking a thin yardstick and bending it on edge vs. on it's side. The other cross would stabilize it in the column. Oriented at 45 degrees to the centerline of the boat, each I-beam would be in line with the sail hard on the wind, which is probably the only place it matters much. And it would probably only need to be in the upper 1/3 rd or so of the mast where most of the bending occurs. Aside from this, to a certain degree, the birdsmouth masts already have the I-beams in them. For nearly any direction of bend, you have two staves that are shaped as rectangles opposing the bend, and each acting as an I-beam. Along these lines, for those with access to scantling details for these masts, which is stronger: a relatively small diameter mast, with thick staves, or a larger diameter mast with thinner walls? Somewhere in one of my resources I seem to recall someone saying that all things being equal, more staves (say a 12 stave mast) is stronger than less. Perhaps that is because less of the wood is planed off to make it round? If you offset your birdsmouth joint closer to the middle to move the corner joint inwards, doesn't that require less wood to be planed off to make it round, thus adding strength? Quote Link to comment Share on other sites More sharing options...
Dogdad Posted May 10, 2010 Report Share Posted May 10, 2010 A large-diameter thin-wall tube is much stiffer per unit weight than a small-diameter heavy-wall tube because there's more material working in the area of highest stress. The downside is that a thin-wall tube is more vulnerable to buckling. http://aluminium.matter.org.uk/content/html/eng/default.asp?catid=213&pageid=2144417026 My favorite book on structures for non-engineers is J.E. Gordon's "Structures: Or why things don't fall down". It's a bit dated, but it reads as if you're sitting in a pub with an enthusiastic retired professor. http://www.amazon.com/Structures-Things-Dont-Fall-Down/dp/0306812835 Among other things, it lead me to Kipling's engineering short story "The ship who found herself" http://www.readbookonline.net/readOnLine/2414/ Quote Link to comment Share on other sites More sharing options...
Tom Lathrop Posted May 10, 2010 Report Share Posted May 10, 2010 My favorite book on structures for non-engineers is J.E. Gordon's "Structures: Or why things don't fall down". It's a bit dated, but it reads as if you're sitting in a pub with an enthusiastic retired professor. http://www.amazon.com/Structures-Things-Dont-Fall-Down/dp/0306812835 Among other things, it lead me to Kipling's engineering short story "The ship who found herself" http://www.readbookonline.net/readOnLine/2414/ I have Gordon's book and you are right. It reads like a novel and offers a lot of knowledge in an interesting and simple format. Quote Link to comment Share on other sites More sharing options...
hokeyhydro Posted May 10, 2010 Report Share Posted May 10, 2010 Thus another idea by a non engineer goes down in flames. If you offset your birdsmouth joint closer to the middle to move the corner joint inwards, doesn't that require less wood to be planed off to make it round, thus adding strength? I did that. By adjusting the height of the router bit I made staves that had no overhang. The inside and outside corners were perfectly mated when glued up. I did not round the mast, just knocked the sharp corner edge off with a plane. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.