rotating aluminum wingmast

[Doug Carlson]

A friend asked me about the feasability of retrofitting his 45', sloop rigged, catamaran from a conventional mast to a rotating aluminum wingmast. I believe he would be willing to surrender some sail area to go unstayed. This boat is used for cruising.

A quick review says most of these larger rigs are carbon fiber.

Cat ketch seems most reasonable if unstayed, though that doesn't seem practical on a cat.

The larger aluminum rotating rigs seem to be stayed and that obviously messes with mast rotation off the wind and doesn't get rid of the stays.

Any thoughts or suggestions?

[dionysis]

45 ft cruising cat, sounds heavy.

If the mast is free standing, you need adequate "bury" (mast step to partners) of cantilever mast - this will require substantial reinforcement in these areas. Heavy boat means quite heavy scantlings for mast - would be better in carbon fibre (approximately half the weight of an aluminium mast).

While wingmast will allow you to design for smaller sail area, you still have to take into account downwind sail -spinnaker - asymmetric etc.

Bottom line : wingmast good idea for easily driven boat (light). For heavy boat it is marginal : at best you need to figure out how strong and big the mast will need to be and then compromise.

Hope this helps, cheers.

[betelgeuserdude]

Hey Doug. You may want to crack a copy of , "The Cruising Multihull" by Chris White. It is considered the best reference for multihulls, and I highly recommend it.

DC

[Doug Carlson]

Dionysis,

Thanks for your input.

Do you know if a wood epoxy structure might also be used?

Assuming that wood epoxy is a viable alternative, and that all three structures are correctly engineered, would you have an idea of the relative costs of manufacture based on materials and labor?

I'm not so much asking what they would cost but rather if the weight/performance to cost trade off might favor one construction method over another in a non-competition environment.

Doug Carlson

[Doug Carlson]

b-dude,

Thanks, I'll check it out.

Doug Carlson

[dionysis]

Wood epoxy, check Gougeon Brothers book. For noncompetive use I would get serious about wood. Excellent fatigue resistance-like carbon). If I was worried about weight: wood will be a little heavier than aluminium. Again the final decision will come down to juggling fatigue, weight, strength, stiffness in light of righting moment and cost. Of course, carbon is ideal- no question.

cheers Doug.

[dionysis]

I didn't answer your question Doug.

Weight performance to cost >> wood

[Doug Carlson]

Are 45' rotating wingmasts off the shelf, custom built, or is diy the only way to go? I've done a lot of looking on the internet but haven't found any suppliers.

[dionysis]

Wingmasts are usually custom designed and built for a particular boat. No off the shelf. There are boatbuilder wingmast manufacturers that will do this for you. You can of course, build your own, after your mast is designed and engineered for diy building by a wingmast design office.

Designing and engineering your own mast, is a complicated process. You will need finite-element analysis capabilities to do this properly, and you have to know about enginnering and aerodynamics etc.

Check out some yacht designers that do wingmasts, and try composite yacht builders as well.

You need to do quite a bit of research to be confident you are making the right decisions.

Good idea is to find comparable boats with wingmasts and size the dimensions, so you know ballpark size and weight. They are more complicated to use efficiently. More expensive etc.

cheers

[dionysis]

Check out freedom yachts, and Professional Boat Builder Magazine has had several articles on wing masts
and carbun fiber masts.

[dionysis]

By the way, Eric Sponberg has designed several free-
standing cat ketch rigs, using rotating wing masts.

http://www.sponbergyachtdesign.com

[Doug Carlson]

Dionysis,

Thanks again!

What is the perceived wingmast advantage in a cruiser?

For background; my brother is used to wing masts, having won titles in a wing-masted dinghy, won races in the Tornado nationals, and spent years cruising a tri with an alloy wing mast.

His fast cruising cat has a fixed mast. The aerodynamic advantages of the wing mast just weren't enough for the hassle in his opinion, and he's a keen competitive sailor with a light 38' non-bridgedeck cat.

I race wingmasted cats and dinghies, the wingmast advantage is very significant when racing, but it's only a fraction; you only need a 1% advantage in boatspeed in racing and you're in clover.

But how much use are a few % of speed to a typical cruiser? And will your friend play the rotation in and out, depending on wind strength and angle? Will they mind the slamming of the mast, or tending to the roation device?

It may be significant that while wing masts have been tried in many dinghy classes, they have been accepted as faster only in two or three (Australian NS14, Tasar, MG14) - all boats with fairly small high-aspect rigs where the extra power is vital. In unrestricted monos it's faster to just chuck more sail on than to worry about the wing. I love 'em but they are a pain in some ways.

Also, it's hard to bend a wing mast of cruising cat dimensions enough to flatten the mainsail. Having a nice leading edge is no use if there's a full bag behind it. It's like big-roach main, they're great if you are prepared to trim them continually, but if you aren't, the roach closes up too much in the lulls or hangs open too much in the gusts.

Just my unskilled throughts.

[Doug Carlson]

Thanks. I appreciate your insights.

[tspeer]

There are some advantages to a wingmast for a cruiser. For example, Gold Coast Catamarans uses rotating elliptical-sectioned masts for their charter boats and have developed an inexpensive design for composite masts. Contact Roger Hatfield (questions@goldcoastyachts.com ) for more info. I'd think you could do the same thing with an aluminum extrusion.

One advantage of a rotating mast is the boat doesn't have to be head to wind to raise and lower the main. Being able to rotate the mast into the wind makes for less friction when reefing or dousing, and when off the wind can be the difference in being able to reef or not.

Another advantage of the wingmast is low windage. This could make a difference when riding out a storm at anchor.

The rigging of a rotating mast is often simpler than that of a fixed mast, consisting of just cap shrouds and diamonds. The tension of the cap shrouds is not all that important, since the bending of the mast is controlled by the diamonds.

The shorter spreaders of the diamonds also make it possible the sheet the jib closer for good windward performance.