Monohull wing mast

How many degrees does a wing mast need to rotate on a masthead sloop with a 110% jib for max upwind efficiency? What is the penalty if the boom is fixed to the mast? For a 45' fast cruising sailboat. 16 degrees of articulation is about the max possible w this design.

Also, does anyone have a feel for the tradeoff between a 3 spreader rig in which the mast can rotate 150 degrees relative to the fixed spreaders, vs a conventional wing mast setup, with single upper / fixed lowers / jumpers / spreaders? 12' beam at the chainplates, 75' mast height.

 

You might want to check the Kuka-Light thread here and on SA(under Ocean Racing). The boat is one of the very few keelboats designed with a wing mast.
It was designed by Doug Schickler-you can find his site url in one of the threads and just send him an e-mail-he's first class and will likely answer you. Another person to talk to is Eric Sponberg-he's a regular here and a very innovative naval architect.

http://www.sponbergyachtdesign.com/

 

Dear Doug,

Thank you. I have read all of Eric's posts on wing masts as I can find, and they are very interesting. However, he is focused on freestanding rigs, which are a different animal. I can not find the Kuka-Light thread - a search leads to the endless posts on DSS.

I will email Doug Schickler.

 

Dear Lightship, don't write Eric off so easily.

1) http://www.boatdesign.net/forums/sa...eelboats-not-dss-kuka-light-others-45947.html

2) SA- http://forums.sailinganarchy.com/index.php?showtopic=141464

 

Ligthtship,

I seriously doubt that 16degrees is the limit for a masthead rig.
The setup will be essentially the same as a daysailing cat, I have easily rotated the mast 90 degrees, although it does not typically need that.

Don't even fix the boom, you need to rotate the boom relative to the mast, so the mast and the sail have a relatively transition at the sail luff or you just wasted your effort.

 

Thank you Up. 16 degree's (8 degree's per side) is the relative angle of the boom to the mast. When you say 90 degree's what angle are you speaking about?

There were several comments in (much) older wing mast posts that with a larger jib the relative angle will be less than with a free standing cat rig, but no numbers.

Doug - the Kuka Light site was very impressive. In the video, her mast looks like it might be as much as 15 degree's to the boom. I assume they have played w different angles. Wonder if they have a polar / target graph for the ideal angles. Because the cruising nature of this rig, our angle has to be limited and will be automatic.

I am astonished and very thankful at how much effort you put into this and how you champion new technologies.

 

Thank you-I wish you good luck. I'm going to use an A Class Cat carbon wing mast on my "Crossbow fl" singlehanded dinghy(in this forum) when I finally get to build it . I'll be interested in what your research yields.
Good Luck!

 

lightship,

The 90 degrees I was referring to was the mast centerline to the boat centerline.

 

On Tasar dinghies, probably the most popular mono wing-masted sloop in existence, the wing mast is set at something like 35 degrees to the boom upwind, at a guess. The nature of the rotation lever means that we don't have infinite control and therefore don't really look at the angle, so this is a pretty rough guess.

Downwind the mast rotates to around 80 degrees against the boom, at a guess - again there are only about four different angles to choose from and we almost always go for the same one, so I've never really looked at the angle.

I have a bunch of extended luff pocket masts and two wing masts and have sailed with a bunch of other wing masts, but while I like them, it seems that their performance attributes are often waaaay over-rated.

 

CT, sorry to spoil your fun but the Tasar mast is hardly a wing mast, in fact it is perhaps half a step up (no make that a quarter) from a conventional fixed mast in cross section shape with its very ugly chopped off and un-aerodynamic trailing edge shape ... in fact a fixed oval mast section is probably a better performer ... so all your figures about mast rotation and mast performance have to be taken with the proverbial ??
For interest sake, what are the two other wing? masts you are referring to?

 

Yeah, Gary, because it's not as if Bethwaite had made any other wing masts to test it against...... apart from scores of them, in at least four classes of which three would have had active fleets of about 200-300 at the time.

I did not say that the Tasar section was the best aerodynamically. The theory of the chopped off trailing edge is explained in his books and is off course followed by other aero-shaped devices from cars to 2011 pushbikes. I'm not meaning to put words in Tom Speer's mouth, but here on BDF he wrote "Frank Bethwaite found that it was good to have a blunt, flat base to a wingmast, which you can see in his section for the Tasar dinghy. I think it depends on the thickness ratio of the mast" which does not sound like a denunciation of the Tasar style!

Frank had wing masts of conventional shape about 9" chord even in boats as small as Flying Ants before he got into the Tasar style IIRC, and the NS14s had other wing masts available for years, but Frank's section stayed at the top level against deeper conventional wing sections for some time. Even today the Tasar (with its larger rig) is very competitive against the much finer and more modern NS14 with their conventional wing masts, so the Tasar wing can't be too far out.

Where are your test figures comparing the Tasar section. that enable you to come to such conclusions? How many wing masted dinghies are there in NZ that allow you to come to such conclusions?

Both my current wing masts are Tasar ones. Before that we had the deep "Superwing" section used on Taipan (and Capricorn) cats. I have also used wing masts on Tornadoes, a Twiggy, a Super Shockwave 37, windsurfers, etc.

As late as about '88 or even later, even some of the Irens 60' tris were winning with carbon tubes against wing masted boats. As Lock said, the aero efficiency of the rig was often beaten by the light weight and gust response of the tubes. Yes, these days in multis wing masts are superior but they are dealing with very different ratios, dimensions and dynamics to a mono.

I suppose you are going to say that Alex Vallings doesn't know how to make wings either? His experiments on the 12s didn't go far. Nor did the ones as far back as the '30s or as late as the '80s/'90s in ICs, the '50s and '80s ones in 18s, the '90s one in Merlin Rockets, the '50s one in Rs, the ones in the Gwens in the '70s, the Cherub ones, the windsurfer ones, etc etc etc. The Finns have improved in speed since they went to wings, apparently, but not by much according to what I read in class publications.

All of these classes tried wings and almost all of them found that they did not give an advantage. Either those who tried them were fools, or wing masts don't give advantages as significant as sometimes claimed for them, which is what I said.

 

CT, there's no denying that you know about dinghy history and rigs ... but on small monohulls, weight, as Lock said, is a very important factor in the boat/rigs performance, no argument there. A wing is heavier and on small boats, this is a disadvantage.
However, in my experience with wing masts on monohulls (true wing masts, not some fractionally larger conventional mast that can rotate a bit) the wing/wings in the 5.5m CB Skimmer's case, work superbly, outpointing other designs, also faster offwind, especially reaching where you can over rotate the masts to create large power.
However this boat is very unconventional and is not a true indication of similar sized dinghies, so we'll leave it.
But where I do have more knowledge, true wing mast carrying multihulls, (no luff gaps, large chord, clean aerodynamics) there is no comparison ... wing masts are superior, everyone recognises this, history reveals it is so ... end of story.

 

Yes, I never claimed that wing masts don't work in multis because they certainly do in that application. But as we both agree, different factors dominate in different craft and therefore different rigs work better.

 

excuse my probably stupid question...

but how are the halyards and all the other lines going up the mast and boom directed back into the cockpit?
i mean - how is it compensated for that the mast rotates by more than 180°?
i have never been on a boat with a rotating wingmast, so i simply do not know and have right now absolutely no clue, how this is achieved...

 

All halyards have to exit and be cleated at and on the mast; that means you can't run lines from turning blocks attached to deck back to cockpit, like on a fixed mast, instead everything has to be attached to the mast itself ... so it can rotate.