Carbon Fibre Masts

[CTMD]

There is no reason why you couldn't use a foam core, the trick would be to pre-laminate is with some uni each side before ripping it up for stripping. Alternately you could put some of the external laminate on flat sheets and then kurf cut the inside until it sat happily in the mould.

[Eric Sponberg]

Without knowing all the details, I would not comment on the suitability of one mast design over another.

Righting moment is always the same and does not change. Heeling moment changes with conditions.

It is OK to reduce safety factor, so long as you understand the implications of what you are doing. In America's Cup competition, safety factors are a little more than 1.0.

On a multihull, an unstayed rig is not the most efficient form of rig where cost and weight are concerned. A stayed rig is a much better solution.

On a free-standing rig, a cored carbon laminate will be heavier, harder to make, and more expensive than a solid carbon laminate. This is because a cored laminate achieves it's advantages when the load acts normal (perpendicular) to the skins. In a mast, whether free-standing or stayed, the load acts parallel to (within the plane of) the laminate. So core adds little to no effect in a mast.

Eric

[terhohalme]

Eric and Alan,

my catamaran parameters include now righting moment for rig design. It is somehow different from my previous post, but it is done according ISO/DIS 12215-9.

Terho

[Archim]

From WD_12215-9__E_-2004-03-02.pdf (which is not the latest DIS document), one can read :

9.2.2 Design heeling moment for sailing multihulls
For large sailing multihulls, the righting moment is so huge that it would not be realistic to assess the load on rig by equating heeling and righting moment. Therefore for multihulls, the design heeling moment is taken when the fist reef is taken, as calculated in ISO 12217-3, unless the boat is stated by its manufacturer to be designed to "fly a hull". [To be implemented]

and

9.4 Distribution of heeling moment between several masts
For multiple mast rigs the maximum heeling moment of each mast is to be determined on basis of the sail area moment, SAM, of each mast

Terho, is it the same in the DIS document ?

[rob denney]

[quote=Eric W. Sponberg;198884]


On a multihull, an unstayed rig is not the most efficient form of rig where cost and weight are concerned. A stayed rig is a much better solution.

G'day.

While I agree with pretty much everything Eric says on carbon and unstayed masts, I disagree about their suitability for multihulls.

As you can see from the video at http://www.youtube.com/watch?v=8chR6DAFjGA some multis do really well with unstayed masts. This boat is an overweight cruising 15m/50'ter with less than wonderful sails, on it's maiden voyage yet it is doing wind speed with ease. A lighter version with a stiffer mast goes in the water next month, it will be interesting to see how it performs.

We have also built unstayed masts on 12m and 7.5m versions and one for an 11m bridgedeck cat. The bury between the bearings was 750mm on a 12m/40' mast. All work well.

The boat in the video has the same righting moment as a 12m cat. The professionally built carbon mast is cheaper and lighter than an alloy/ss rigging mast for the cat. Add on all the extras for the stayed rig plus the inconveniences and unstayed rigs are definitely the way to go for multis, and monos.

We are now selling plans (and low cost materials) for amateur built carbon masts as well as building them professionally.


regards,

Rob