Unstayed carbon fiber mast on cruising catamaran?

The builder of the Wyliecat 30' states: "The 46-foot carbon-fiber mast was designed to bend, allowing the top of the sail to "depower" as the wind increases. The result is a simple and effective self-reefing system."

Wyliecat Performance Yachts: Wyliecat 30 http://wyliecat.com/models/wylie_30.html

I've been interested in this design for quite some time and when I was asked to transport such a boat from Long Beach CA to San Diego I readily accepted. I won't take up the air here by going into details but let me just say that I came away very impressed. The rig lived up to the builder's talk and then some.

My question is A: if there is a catamaran in the ~40ft range with a similar rig and B: is such a rig desirable on a catamaran where the primary requirement is ease of handling when singlehanding over long stretches.

 

The 60 foot catamaran I am presently designing will have unstayed wing masts but as a bi rig with one mast in each hull. Check Harry Proa boats by Rob Denny, his are all unstayed and they design and build for all boats. Not only ease of sailing, there are so many benefits if the boat is build with that intention from the start. Im sure RD will chime in

 

Many thanks. Is there a website where your designs can be viewed? I can see the case for the biplane rig but in my case the single mast would be quite sufficient.
One would think that the design of the mast structure is dependent on the sail's shape and area as well as the expected heeling angles of the hull, correct? It took me a while to trust that the flex of the upper mast section would provide sufficient wind spillage and continue to do so in sudden wind gusts. Then it was a great game.

 

Nico, I am not a designer, just doing the pre-design before I send it off to the NA. I'm glad to hear of your experience was good with the unstayed mast!

I also was going with a single mast but it's a bit harder on a catamaran because you need about 1 foot of bury for every 7 foot of mast height. That means using the salon roof for the top bearing but I only have a hard bimini. My thread is in MultiHulls-CNC Plans, there is a pic on this page but it's still a work in progress. - CNC Plans not Included https://www.boatdesign.net/threads/cnc-plans-not-included.56453/page-60

 

Thanks for mentioning Harryproa, I've never imagined anything like this:

 

Yeah they are pretty cool ))

 

All freestanding masts, if properly designed are intended to spill wind as strengths increase.

 

Gday Jorge

Preface this withe the fact that I haven't sailed a bi rig cat but I would like to check out one really important fact first. Generating apparent.

On a normal cat you sail downwind fastest in many modes by getting the apparent breeze at exactly 90 degrees. It is pretty much a concrete rule of thumb on our cat. If I sail at this angle with the reacher up I can do windspeed on our cruising cat and sail nice deep angles.

My worry with the biplane rig is that you can't do this. I know that there have been a few biplane rig cats sailed but I would like to know how the go for VMG downwind when other cats can sail 90 degrees apparent. The leeward sail would be totally useless in this situation. There may be a work around but this may be a large flaw in good downwind technique.

cheers

Phil

 

The Wiliecat 30 isn't a catamaran, but you asked about catamarans, so I assume that is what you are interested in.

Yes, it is highly desirable in a shorthanded boat of any size. Properly done, a single set will have more range in terms of gust response than a stiff setup. But the Marconi rig is not the easiest to sort out in this respect. And a fixed mast begs for a roundish section for this to work over a wide range of headings. Oddly, cruising cats seem to have undervalued the ease of handling aspects, figuring (I guess) that with the huge available RM, dynamic gust response wasn't as important in a cat as in a cruising mono. But nobody wants to sail poorly, and they don't want to sit there and wear themselves out trimming either. The vast majority of historical craft exploited bendy masts and anisotropic woven sailcloth. The real fun part is getting this to work when reefed. You have to establish fixed reef heights and get the mast to work at each one. Arguably, it is more important for dynamic response to work well when reefed.

This is a pretty fundamental decision that needs to be sorted early in the design cycle. To simplify it into two choices, you can choose a rig where you can change the area of both main and jib infinitely using modern reefing/furling gear and expect to do this often while sailing, or choose a rig where sails are swapped out occasionally, taking maybe 20 minutes in good conditions and twice that in crap conditions, but then having a setup that can be sailed decently with less need for adjustment until the next sail change is needed. The former seems to win hands down in the showroom <shrug>. Cruisers have long shortened sails at sunset and shaken them out at sunrise as a matter of habit. It's a good habit. Set the sails for best dynamic response at night.

One other issue - on a 40' catamaran, the mast really wants to be taller than the ICW bridge clearance. This creates additional constraints when you try to put the necessary sail area on a bendy, ICW-friendly mast. I figure max is about 38' LOA for normal cruising cat proportions.

@catsketcher - to a first approximation, it doesn't matter. If you keep the load divided equally on the two sails, there will be almost no difference in theoretical performance as apparent wind angle changes. The ideal spanwise lift distribution on the masts changes a bit as a function of AWA to minimize induced drag, but induced drag is not the biggest worry sailing with wind on the beam.

 

Phil,

I have zero experience with them but I have read that would be one example of a sheltered sail. This is my fav bi rig video

 

Thanks for the response philSweet. Correct, it is called a cat due to its cat rig. Indeed I am interested in this kind of rig on a catamaran or a trimaran since a rotating free standing mast would be easier accommodated on the tri. Ideally it would be a production boat in the 40-45ft range that can be sailed prior to purchase.
Since I sailed the Wylie I've been doing deep searches but so far no luck.

BTW about AICW Bridge Clearances, all the non-opening bridges have a project height of 65 feet. The one exception is a fixed 56-foot bridge at Mile 1087 between Fort Lauderdale and Miami.

 

Phil

I am not worried about induced drag but the blanketing of the leeward sail by the windward one at a really important apparent wind angle - 90 degrees. Sailing the boat at 90 degrees apparent is rudimentary apparent wind sailing technique. It provides the fastest VMG for deep angles much of the time.

So for me the interesting facet of biplane rig sailing is "What do you do with 90 degree apparent sailing?" I guess you would have to get the apparent further forward so the leeward rig does not get blanketed. I expect this would be detrimental to VMG.

cheers

Phil

 

Blanketing issues aside the main problem I see is having enough strength and depth in the crossbeam to handle the mast loads, every load is going through the mast base ?
Perhaps on a Bridgedeck boat this isn't an issue ? I guess wether its fixed or rotating is going to make a difference, either way getting enough mast bury in the beam is surely going to be an issue ?

 

Nico,
Thanks for the Wylie cat feedback. I for one would love to hear more about it, please.
There are numerous unstayed mast threads on this and other forums. Lots of heat and negativity, not much light. An example is Single main sail with unstayed mast on cruising catamaran? https://www.boatdesign.net/threads/single-main-sail-with-unstayed-mast-on-cruising-catamaran.57033/ which I mention as post #26 explains the benefits of the unstayed rig for cruising.

We have been building and sailing them for 20+ years, I'm happy to answer any questions. I do not know of any production cats with unstayed masts, but as long as the rig is sized for the boat weight, the sailing characteristics will not be very different. What will be different is the inconvenience and hassle which always comes as a surprise when you sail a stayed rig after an unstayed one.

The harry video is a group of visually impaired people sailing for the first time on a 15m/50' harry in Holland. Only the skipper had been on the boat before. A better video for seeing the mast and rig working is a cruising version of the dutch boat

The first part is sailing at 10 knots in 10 knots of breeze, the second 15 in 15. The boat weighs just over 3 tonnes/tons but due to 60% of the weight being in the windward hull and it's wide boa, has the same righting moment as a 12m cruising cat. ie, it could use the same rig. The mast weighs 120 kgs. It would be a bit less using the build methods we now use, which also make it easy for a home builder to construct. The materials in the mast cost about $Aus3,500/$Aus2,700.

There are numerous biplane rigs sailing and racing, they alter course by 10 degrees or so when the apparent is at 90. I would be amazed if any of them, apart from the large dedicated racers (Hydraplaneur, Jaz, 50/50) sail downwind at these apparent wind angles quicker than they would with the sails at 90 degrees, equally amazed (based on a fair bit of large multihull racing experience) if any cruising cats do so faster than they would if they could also get their sails eased out enough.

My argument against biplanes is that they are not far off twice the price and weight of a same size single unstayed rig in one hull.

 

Hi Rob.
Thank you for the link to that earlier thread, had I found it I wouldn't have started mine.
Your posts #26 and #28 in that thread address and answer most everything that can be said on this topic.
I made two omissions in my OP. One about the type of hull which should have read "multihull" instead of catamaran -I prefer Tris for cruising but Cats are more common- and another about failing to mention that part of the simplicity and beauty of the Wylie is its wishbone rig. Quoting you, if I may:

" Wishbone booms are almost as much of a boon to cruisers as unstayed masts. No traveller, multipart mainsheets, lazy jacks or struggling with too small boom bags. Plus the main sheet loads are reduced by about 90%. "
All true!

One doesn't expect people who haven't sailed this rig to be able to understand the advantages of it but after my own experience it is now my #1 choice for easy and safe singlehanded cruising hence my search for a multi with this kind of rig.

The mast's ability to bend and depower in sudden gusts has to be experienced to be appreciated and I don't begrudge the traditionalists for being so supportive of the traditional rigs with their innumerable, expensive and failure prone bits of harware. It is much like the initial opposition to multihulls from the monohull camp.

Thanks again Rob.