infusing with contour balsa

Hi Groper - I'll put the basic numbers/process down for you this evening. If you don't have a CAD program to calculate the I for the wing use an ellipse "I" as an estimate. This also allows you to do it in a spreadsheet for initial design purposes. Peter

 

mast compression

Hi groper - I tried to put the puzzle together but there are some numbers missing, so could you fill out the numbers please? I'll write up the maths when I get them. ta peter s

 

Your numbers are correct. P1 and P2 are whatever we want to make them... same goes for the unsupported top, how to work out ideal?

If we assume the top of the stays to be at 12m above mast step, we have a forestay length of ~14.5m due to the mast step being ~1m higher than the forebeam. Mast step is over the cabin roof. Same goes for the shroud chainplates, they are about 1.2m lower than the mast step.

At this point, assume ideal ratios for ideal panel lengths? Factor in mast taper? It all gets a bit complicated once we go beyond a straight section... Any idea how much saving in terms of weight and materials between a tapered and straight section?

I appreciate there is a bit of work in optimizing a design - should we choose to go down this route, im happy to pay for a complete engineering design. Just looking for some rough figures at this point to determine if the time, money, man hours is worth it compared to a conventional aluminium rig....

EDIT:- Forestay tack is 6.3m forward of mast step - 1m lower vertical plane. Shrouds dimensions are good, but 1.2m lower vertical plane.

If we assume a configuration similar to that described here - http://www.boatdesign.net/forums/multihulls/carbon-fiber-wing-mast-my-cat-25444.html

Im not sure how he assumed the panel lengths and hounds position of 29 feet and 41 feet. Works for him... The main difference between his rig and the one im thinking of, is the fact that our mast step and aft chainplates are around 2m further aft. So a shorter main sail boom, and larger headsail. Everything else is basically identical...

 

Added pic; Doesnt show possible increased mast height above hounds...

 

Hi Groper - To design the "ideal" rig first start with the sail plan. If it is to be a jib and main then you need to think about the overlap? If the jib is to be self tacking it needs to have no overlap (use a jib track or a jib boom) Then work with the sail maker to decide on overall sail area, or the engineer to calculate the required sail area for the use. Once you know the SA and mast height the rest falls out. Then you decide how to hold it up. The forestay is determined by the jib geometry, the rest is laid out using conventional angles. The simple inner and upper shroud is the simplest arrangement (other then free standing) cheers Peter

 

Sail plan is as shown above... Only potential difference, is increasing the main sail height with a ~2m taller mast which then overhangs the forestay and upper shrouds attachment. Already have quotes for the above sails from the sail maker...

 

so Groper - Heres the skinny, very back of the envelope stuff for you. You need to get a grip about the various partial safety factors or load factors and I have used a circular mast as an example but you can play with the numbers to get an understanding. Your sailplan can't lift the hull until 35 or 40 knots so its good for a cruiser, depending on what weight you are aiming for with the mast sets a few things but a carbon Dia130x3 is 1.85kg/m (12m 22kg??) which is light for this boat I'd expect?? Any clues from aluminium sections on weight?

From the statics and aero loads the boat mass gives a basic SF=2.0 and if you include forestay tension and a couple of gust factors this would come down to about 1.5. Its usual to design at 2 or 3 for this type of thing unless you go quite deep in the engineering ie develop a sailplan including spinnakers and reefing, then develop loadcases for each downwind and upwind set etc find out the worse conditions etc then make better decisions on design factors. Hope all this helps.

You can find the equation for an ellipse and redo the section size, build a spreadsheet and your away!! The only thing you can't do is figure the local buckling out but if you keep to a dia/t ratio of >50 it will be close. eg if the mast 100mm dia then don't go under 2mm thick. cheers peter s