Aftmast rigs???

Fanie, I do noy say that aft mast will not work, I just say that there some problems involved. For sure those can be solved but prototype needs to be built and tested. Your experience is really valuable because is based on building and testing real boat.

 

The 'problems' involved are only there because nobody ever took the time to figure them out. Common sail types have had more than their share of attention, if the same is done with aft masts there would be even less problems.

Personally I favour them for their ease of operation and simplicity to use.

I'm going to try and find someone who will be interested in this to sponsor a decent cat with such a sail setup. I'm too friggin poor to get this done in an acceptable time span.

Will post if I have somehing more on these sails.

 

Brian:
Than trimaran windsurfer picture is a really poor photo montage. If you are going to post fake ****, please take the time to make it more credible.

 

Gonzo, what trimaran windsurfer are you taking about??

Ohhhh, now I remember, you are talking about that posting I did back a few pages ago:
http://www.wiebel-sailing.com/index.html

I don't believe I represented it as anything other than what it was, a group of Dutch fellows, technical types, looking to break some speed records with a craft that happens to have an aft mast concept:
http://www.wiebel-sailing.com/Theteam.html

Sorry if you get offended by futuristic concepts...keep an OPEN MIND

 

Very interesting Brian, like all those pictures, they show how he approaced and solved some problems.
I think the airfoil masts are not the best shape because they would only be effective at anchor; anytime sailing they would increase windage comparing with a round mast.
I have been thinking about it for a while: the bent whishbone mast with its internal bracing, is going to be very strong and will not bend or buckle from side to side, but is not so strong fore-aft, so an elongated section fore-aft would make it stonger, I am thinking a slightly elliptical shape could be the best.
I am getting the help of an engineering group to give me the best shape and will report back on their finding.

 

Mast Sections for your A-frame Rig

You definitely do not want to use round mast...just too much drag. I'm unsure as to you definition of 'airfoil mast' as apposed to 'elliptical mast'??

Peter Wormwood came up with an interesting mast section for the Stiletto 23 catamaran (rotating mast) that emphasized the leading edge of the section to be most optimal for a variety of wind incident angles. It consisted of several different radius's on the front of a modified elliptical section. I chose this same mast section for my Firefly trimaran. Don't know if I can find a sample now or not.

What I'm getting at is I feel that elongated section would be best aerodynamically and strength wise. In many cases your headsail(s) are going to be redirecting the airflow to a somewhat fore-to-aft direction by the time the flow reaches the mast.

Pay close attention to the joint where the two legs come together. There are some unusual twisting forces here that can be detrimental. Procyon experienced this as well. And if you build in carbon fiber remember it doesn't like some of these 'off-center' twisting loads.

As a secondary thought, maybe you could construct the A-rig with round sections and add fairings. But this might only make sense if you were using alum, not hand building carbon fiber.??

Did you get that private message I sent you about another gentleman there in Aus looking for a similar size vessel with the same requirements to get under a bridge??

What did they do 'Downunder', bridge all your inlets.

 

So that's where the 'down under' part comes from... down under the bridge

 

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Interesting 'sea trial' that has just today been reported on another forum...excerpts:

"I spent the weekend test sailing the Dolphin 46 my sister purchased. It was her first sail on the boat (her second on a Dolphin). This was my first sail on a Dolphin, but I have chartered a half dozen slightly smaller cats over the years. The boat is docked in Ft. Lauderdale way up river.

The winds were from the east at 12-18 both Saturday and Sunday which made for some rough waters (6 - 7 ft confused) , but a good test for the boat(and our stomachs).

There was a slightly off axis swell mixed with the wind driven swell that keep all but a handful of boaters in their slips. On Saturday we counted 3 other sailboats boats within 12 miles of the Ft. Lauderdale entrance and Sunday there were 8 (3 of them cats). Obviously, the ocean state wasn't what South Florida sailors consider a "fun weekend", but we were happy to have the adverse conditions to test the boat.

With a single reef in the main and full jib the GPS averaged 8.8 knots hard on the wind. We ran on NE and SE tacks to take the current out of the equation. On a beam reach the boat averaged 11.5 knots going north and south with a wind speed of 15-16 mph. Not too bad for the sea state. The tell tales were laying down only about 30% of the time and it wasn't because the sails weren't trimmed correctly.

One of the ways we tested the Dolphin's sailing ability was by going close hauled with a single reefed main and no jib. I told my sister if the boat could tack with the main only in this sea state and wind I would be impressed.** With only the single reefed main, boat the speed dropped to 4 knots, but we completed a tack! Sure we had to ease the main and fall off to 90 degrees on the new tack to get the rudders working, but the boat did it. The same maneuver with jib alone was much easier of course."

** Note by BE: The Dolphin cat is a daggerboard vessel, and that surely contributed to this ability to tack under mainsail alone.

 

Brian keep posting his guesses, weblinks and other 'valuable proofs' from forums. Really tired to read this multi-page rubbish...

Brian, SHOW REAL BOAT WITH YOUR RIG TO PUBLIC!

 

Brian, I'm all for new ideas and experiments but your mast aft rig is ....... a no exit street IMO. This talk of round masts too, is also no way; if there would be anything that you really need, it would an airfoil mast section that rotates so as to reduce drag behind your large (and sagging luff) headsail. Presumably you are having a furling arrangement up front - because dragging differing sized sails up there on a pitching deck is awkward and dangerous. This is one of the main reasons that NZ racing designs went against the accepted grain of large headsail/small mainsail and pioneered the opposite, almost going to una rig proportions - plus of course the bendy mast and feathering rig; this almost four decades ago. Your theory on tacking a large headsail is also suspect: unless you have your keel, dagger, centreboard well forward, that rig wants to bare away - you would be more comfortable grannying around than tacking, an oxymoron (so to speak) when beating to windward.
There is a headsail rig that functions reasonably well and that is the Pacific lateen .... but that is on a proa and they end for end the assembly when they shunt, and to do so they at first bare away. And to sail to windward on those craft, they sail letting off the sheet, if sheeted in hard, they want to bare off - how frustrating must that be?
Once, on my light 32 foot catamaran, the clew ripped from the wing mast luff track which damaged it and so we had to sail with just a headsail, an unpleasant experience with huge amounts of lee helm and, being unable to tack while beating up a channel in fresh wind, (the boat would lock itself in irons, and we had the area of the wing mast to help us round too) so we had to gybe around - resulting in large and precious distances to windward lost. You can have it mate.

 

badly balanced boat?

 

Do you realize that I was NOT talking of using round mast sections on my particular version of the aftmast concept?? But rather I was addressing the A-frame rig that Stefano is building in order to lower his mast to clear bridge obstructions. Two different situations, and in both cases I have suggested NOT using any round sections. I believe he plans to build the mast himself, and that was the only reason for suggesting the possibility of a round section with fairings added afterward.

Of course I have furling on all three sails...no sail changes. Perhaps you should have looked here:
http://www.runningtideyachts.com/sail/
...and balance is obtained by the selection offered by a ketch rig layout.

Any sailboat seeks to have 'balance' whether its rig is located forward on the vessel or rearward. We taylor our CLR/CE relationship accordingly. One item less understood by monohull sailors about multihull boats is the lack of a need for the 'lead' of the CE over the CLR. Since the multihull does not heel over this lead distance is virtually zero

I'm not familar with that craft, but my first question would be, 'does it have a board??'. I rather doubt it, in which case I could understand the lee helm.

Did your 32 footer have a board or a very shallow, long keel??
Did you consider purposefully backing the jib to push your bow thru the tack??


You seem to want to thrash big headsails as leeway inducers, or old style, or etc. Yet we see a lot of use of CODE Zeros these days

 

You might look back at the illustrations in posting #98
http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-7.html#post198605

That fractional rigged cat with a 90 foot wingmast carries about the same sail area of my mast aft rig with a 73 foot mast. And my forestay is just slightly longer than his fractional jib forestay. My sail area is balanced over the pivoting centerboard.

 

Brian, quite correct, it wasn't you advocating a round mast but others posting here. And thanks for the Running Tide link. And to be honest I have only briefly followed this thread, but realize your mizzen is very important for the cat's balance, and there is nothing wrong with having balancing boards forward to counter bare away effect once the mizzen is down - do you have them?. However, to be honest again, the rig looks very clumsy and holding those forestays tight with their furlers looks problematical.
My lightweight 32foot cat had deep daggerboards and when I say light, I mean a platform that doesn't carry weigh on once head to wind. That plus the lee helm (and admittedly the boat was not set up (CLR too far aft) to sail in that configuration) tacking was almost impossible in a fresh wind. There is a lot of nonsense spouted about backing headsails - that is guaranteed to stop a lightweight multihull dead in its tracks - maybe okay for a loaded down, plodding cruising version. Equally, tacking una rigs on light multis, as long as the traveller and main sheet are eased as you pass through the eye of the wind, then you can make it across, tricky, yes, requires timing, but way better than holding a headsail against the wind.
Yes, code zeroes are carried high to windward in light conditions - but if you're caught in a decent gust, lee helm goes way up (unless balancing foils forward are carried).
Oh, the Micronesian proa, of course the traditional ones did not carry boards, just a large, angled aft rudder steered by a skillful foot and strong arm by canting the foil- check out "East is a Big Bird" - Thomas Gladwin.

 

Gary, I developed this rig concept long ago (1973-4), and primarily because of those big sectioned mast we had in those days that just destroyed the drive from the first foot, foot and a half, of mainsail area. And I personally owned a 47 wood staysail ketch at that time. Those two factors drove this design. I laid it aside for many years. Procyon's development rekindled the interest.

Granted the mast sections these days are much smaller and more aerodynamic, so my reasoning for eliminating the mainsail is less applicable. but I still defend the aerodynamics of this configuration, and the ease of use in the ketch configuration. Regrettably the forces involved in trying to maintain a 'tight rig' add considerably to the mast compression and loading on the hull structure. So these factors are the real limiting ones, not the aerodynamics.

I'm actually more interested in the Dynarig and Kite-Assisted Multihull at the moment