I call your bluff. The naked mast drag. A myth?

Discussion in 'Sailboats' started by pbmaise, Nov 17, 2013.

  1. messabout
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    messabout Senior Member

    Hoerner has shown that a round column with a trailing flap can diminish the Cd by a meaningful amount.

    To benefit the case of constant tinkerers, here is a scenario.

    Consider the lowly Sunfish with its lateen rig. The mast is 2 inches in diameter and rises above the deck about ten feet. The tack of the sail is positioned ahead of the mast such that there is some interference in clean air flow. On one tack, usually starboard, the sail moves away from the mast a short distance. On the other tack, part of the sail lays against the mast.

    There are other problems of course because the yard is necessarily, progressively, closer to the mast as it is traced up toward the halyard attachment at the mast head.

    Suppose we fashion a mast cover sort of thing that resembles a sleeve luff. We will let a bit of sailcloth protrude behind the sleeve for a few inches, something like Hoerners drawings. The sleeve thing will not touch the sail on starboard but it might help smooth the flow on the port tack. Maybe or maybe not. Is this worth thinking about as a possibility for a small improvement? Opinions ???
  2. PAR
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    PAR Yacht Designer/Builder

    I disagree about racing high dollar machines with similar budgets produces rotating Bermudian rigs as the ultimate way to go. Racing isn't about the best, but is about the best at staying just this side of the rules, which often doesn't consider serious innovation, but conformity, to help level the playing field.

    Elongated sock luffs have been tried in a number of fashions and they do preform to various degrees, depending on how it's done. If you can keep the windward side inflated as the luff falls to leeward, to keep flow attached to a higher degree, you'd have something. I tried this with a semi rigid luff foil a couple of summers ago, with mixed results and a lot more convolution and complication. Basically, I needed to have the option to over rotate, for any big gains, which tested the limits of the encased mast and semi rigid nature of the luff. A better approach would be a rigid luff (wing mast), but unlike my semi rigid setup, this can't be reefed (the sail can of course) and brings a lot of weight and other issues to the table. Pneumatics are an option, but here we go again on convolution and complexity.
  3. groper
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    groper Senior Member

    I never insinuated that because something hasn't been done, it can't be done - don't know where you got that from upchurch?

    PAR, there are many boats built to simply break records, hydroptere, BP5 or now spindrift 2, boats like these are not bound by any rules... The designers had free choice of any rig... The rotating wing mast Bermudan always seems to hold and break the records... Others tried some things like parliers hydroplaneur and its twin biplane rig, but it wasn't successful to any large extent and its records fallen to bermudan again... None of the other strange ideas have shown any real performance advancements. If someone nails it, we will see all the new record breakers following suit.

    Rigid multi element wings are the next level, but these can't be considered or compared alongside a reefable soft sail rig for obvious reasons... These rigid wings are almost identical to a Boeing jet liner with flaps deployed... We won't see much improvement beyond these until we see some form of revolution in the aerospace industry which would allow our sails to follow their discoveries... Any advancement from where we already are will be only small percentile refinements, until some form of undiscovered knowledge allows the next giant leap...
  4. mij
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    mij Junior Member

    I think that we are currently watching the next big leap. Over the next few years records will break to foiling wing sail multis. With respect to sails, I think that the development of solid wings for sailing purposes is only in its infancy. There will be a lot more to see with wing sails.
  5. daiquiri
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    daiquiri Engineering and Design

    Only when the problems of:
    1) cost
    2) de-powering (i.e. reefing or similar)
    of the wing sail have been effectively resolved, will their widespread use be possible.
  6. mij
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    mij Junior Member

    I completely agree. The current wings are clearly expensive and relatively unintelligent. But there seems to be huge potential. Improvements in materials and construction could make wing sails more accessible, while at the high end the coupling of sensors with realtime computing and wings that have more flexibility to change shape could produce remarkable advances in speed and safety.
  7. michael pierzga
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    michael pierzga Senior Member

    Wings on boats ? Say it aint so........you must be kidding.....
  8. mij
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    mij Junior Member

    I think that you miss my point (if you are responding to my posts). What I am suggesting is that in terms of the evolution of technology I think that solid wings are still early in the cycle and that there are still some technological challenges. Once these are overcome there are still significant advances to be made.

    I haven't yet seen a cheap wing sail that changes shape (profile, slots, twist, aspect ratio etc) in response to wind conditions and course, and automatically initiates a de-powering procedure in an emergency. I don't see why these aren't all possible.
  9. michael pierzga
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    michael pierzga Senior Member

    Im sure that anyone with really deep pockets can go wing sail right now.

    But since they are so complex , , expensive, with a maze of moving parts and controls you wont see them on a normal boat

    A soft foil may work, but even those look complex.
  10. mij
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    mij Junior Member

    I agree, for wing sails to become common on normal boats they will need to be quite a different beast. But the incentive is there, someone will work it out.
  11. mij
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    mij Junior Member

    Back (almost) to the topic of the thread, something that hasn't been addressed yet is the drag associated with the rigging for an aft mast rig. In terms of drag, the rigging its self is significant.

    Having said this, I agree that the aft mast rig has lots of things going for it that have nothing to do with its drag compared to a conventional rig.
  12. pbmaise
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    pbmaise Senior Member

    Aloha All

    There are two separate issues within this thread.

    1. What items (masts, sails, rigging), when placed aloft, in which sequence, will provide the lowest drag. I'm objecting to a claim that a naked mast overall placed in the back increases drag.

    2. Which configuration provides the best performance when in action. I.E. More drag with a mast in the back is okay in my book, if overall the boat performs better since sails are more effective as shown in wind tunnel testing.

    mij Thank you for the link to that research. I attached the paper below. I follow and read what everyone says. You said that research:

    Perhaps supports the suggestion that the overall effect of the aft mast rig can be positive, despite the drag associated with the "naked mast".

    That is an understatement. The conclusion of the paper specifically states that after making a detailed review of a Bermuda rig in wind tunnel testing and comparing it to "unconventional" aft-mast rigs with A frame support that:

    Both experimental tests and VPP calculations show that the double jib configuration (with aft-mast A frame) with overlap gives the best performance and also the same configuration without overlap gives better results in comparison to the standard sloop solution (Bermuda rig).

    This is encouraging scientific research. Unlike the A frame mast, my mast is a rotating wing mast, and I use a traditional lifting sail. So I expect my own rig tested in that same manner would outperform both the aft-mast rig tested and the Bermuda rig too.

    What I don't see is scientific research papers backing up the Bermuda rig. Perhaps I am only hearing from one side. I've heard again and again C.A. Marchaj's research showed lifting sails were 190% more efficient that a Bermuda rig.

    Perhaps I may be one of the first lowly cruising sailors to put all this to a live test racing a full size boat. I'm considering the 2015 King's Cup in Thailand. However, racing is not priority and to enter that race I might have to make modifications to my rig to meet rules. I looked at their website and found really big difficulties about entering. There is one rule that read. Working roller furling with sail attached to swivel and above deck drum are required. That isn't how a lifting sail reduces area. So I will need a special review. I reviewed the requirement for OMR Certification. They come measure your sails. Hmm..I have no sails like a main, jib, genoa, or spinnaker. In short yes racing rules are set around Bermuda rigs. Entering the race would be really difficult.

    It is interesting how many sailors firmly close ranks around the Bermuda rig. Many defend it as the cat's meow with lines like you have posted. Millions in research, years of refinement etc. How could something be better?

    This reminds me of something I read on Wikipedia. Yes ggg I am a fan of Wikipedia. I contribute to Wikipedia as an editor.

    Nathanael Herreshoff, began to build catamaran boats of his own design in 1877 (US Pat. No. 189,459), namely 'Amaryllis', which immediately showed her superior performance capabilities, at her maiden regatta (The Centennial Regatta held on June 22, 1876, off the New York Yacht Club's Staten Island station[1]). It was this same event, after being protested by the losers, where catamarans, as a design, were barred from all the regular classes[1] and they remained barred until the 1970s.

    Monohull sailors back then closed ranks on the monohull sailboat and pushed a superior performing type of sailboat out into the street.

    I am fine with Bermuda rig sailors closing ranks on their design. However, I am not fine with attacks that are not backed up with scientific proof.


    This is a forum. It gives a chance to voice our opinions, display our findings, showoff our new designs, and ask others questions.

    Is it my opinion that the rig I designed is the best thing in the world? Absolutely not. My particular rig was designed to solve some very real problems:
    ....Safe for big sailboat and a small novice crew.
    ....Quickly and safely reef without leaving cockpit.
    ....Stand in extreme winds... Super-typhoon winds

    I agree with everything in last post. BTW where in S.E. Michigan? I'm from Detroit. This is probably why I reference cars so much. It is my dream to get my boat home to Michigan and up to Charlevoix.

    I concede. Yes a lot of what I talk about is irrelevant or beside the point. Gets lonely out here in aft-mast world. When we talk to each other we keep pointing back again and again to the same scientific research. Oh, I didn't mention the testing in France where a crab claw rig placed first.

    You wrote:
    The fastest yachts in the world all use a rotating wing mast Bermudan rig.

    I think that is better rephrased that the most dangerous cruising yachties all around the world risk their lives crossing oceans using overpowered Bermuda rigs that they can't handle. Sorry I am not into racing. I'm into safe cruising and 99% of talk of racing and performance is irrelevant to me.


    Thank you. I expect to get flack one side down and up the other. You might just imagine what I get in person when I pull into the marina and every sailor asks what happened to my main mast. They all say I can fix by boat by adding a second 100 foot plus main mast. Right. I've been there done that.

    Again, yes, putting anything behind a round mast will decrease the drag. You mention work trying to get a sleeve luff to help decrease the amount of distance it takes the sail to change from the flat shape forced upon it by a rigid mast, to the correct shape of the sail. Well, that is my whole quest in part. By putting the mast in the back there is zero issue about the mast shaping the sail. There is no need to put any sleeve on the leading edge of an aft-mast sail. The leading edge is nothing but the bolt rope within the sail. This makes the entire sail area effective.

    PAR gropher mij
    Perhaps advances in wing and ridged applies to racing. However, I don't think it is the next level for cruising sailboats. I know, I know, my type of boring sailing is irrelevant. Sorry they don't interest me. I don't have the budget to find out.

    Thank you for back on track. The drag on my particular rigging lines is much higher than the drag on a typical multi-hull rigged Bermuda style. I designed my rigging to do some really neat things. Low low compression was my goal and never having a lee/weather side. See separate thread called:


    I am willing to accept having more rigging lines aloft, and the increased drag to solve a problem specific to my trimaran. I was unable to put a rear side stay far back on the two ama. That would have required too much reinforcement along the length of the ama. If I had put a chainplate on the back of my two ama, I think I would now be talking about my former sailboat.

    Philip Maise

    p.s. I'm anxiously awaiting a crew member of mine and the catamaran he sailed on to deliver relief aid to a small island here in the Philippines. We loaded that cat with 8 to 10 tons and they were due back 12 hours ago. Sorry irrelevant again.
    Last edited: Nov 23, 2013
  13. Mikko Brummer
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    Mikko Brummer Senior Member

    In my opinion, you should look at the mast as part of the sail area, rather than as a drag creating device. Rather than discussing the lift and drag, I prefer to discuss DRIVE and HEEL (or heeling moment), when it comes to sailboat performance. Drive defined as the force in the direction of the motion of the boat, heel as a force perpendicular the the centerline, turning the boat over.

    We have found through computer analysis that the mast is actually the most efficient part of the sail area. It can provide up to 10% of the sailboat drive (a Finn-dinghy with a rotating mast). For a sloop rig with main & jib the percentage is more like 2,5-5% of the total drive, with an area which is less than 3% of the total sail area (in case of the Star shown here). Per sqare meter the mast is far more efficient than the mainsail behind it, when it comes to driving the boat forward.

    We have also tested the mast alone, without the sails... while with the mainsail the mast positive drive in 12 kn of wind is around 1 kgf (2 lbs), without the sail behind it, the drive goes negative by the same amount, or -1 kgf. You can study the illustrations below - X-component represents DRIVE, but note that positive-X is against the boat's motion, so negative-X is positive drive. the Z-component is HEEL. The 3rd illustration shows the flow pattern behind the mast, with vortices forming. The view from above with the heavily bent Star mast makes it look a bit odd.

    Why is this so? Daiquiri's fence-illustration from Hoerner is one explanation, but also the mast is simply so well placed at the front of the mainsail that it takes full benefit of this. There is also considerable positive interaction between th top of the jib and the mast.

    Attached Files:

  14. groper
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    groper Senior Member

    Another issue ive had a practical belief in, from experience using different types of sails - kitesurfing kites in particular - is the separation bubble along the windward side of the leading edge having little negative effect.

    Ive flown single skin inflatable leading edge kites and also twin skinned ram air kites - the leading edge inflatable kites suffer no noticeable performance disadvantage despite the large round tube acting as the leading edge and first part of the camber in the sail. The separation bubble in this location obviously contributes little drag when the surface attached to it follows the correct camber and profile of the desired foil shape on the lee side. This is at odds with a typical fixed mast however, with a central sail track as you have a separation bubble on the lee side aswell - which has a huge negative effect.

    I actually think the LEI kites perform better, but likely due to other design features...

    Some pics to illustrate what im referring to;

    A leading edge inflatable kite - [​IMG]

    And a twin skinned ram air kite;

    The Leading edge inflatable kite is basically the same as a rotating wingmasted mainsail - they are very powerful and effective wings. They operate at much higher apparent wind however, frequently in the range of +50kts in a 15-20kt true wind speed. Therefore drag minimization is a very important consideration for traction kites considering drag is proportional to apparent wind speed ^2.

  15. CT 249
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    CT 249 Senior Member

    Sorry, but your presentation IS dismissive of the bermudan rig and by inference, those who prefer it. If you are going to dish it out, you'll have to take it.

    By the way, I grew up in an area where the conventional short-batten bermuda was an oddity on small boats, so people like me are NOT conservatives when we adopt it; it was not the usual choice for most craft there and then. My family has had wishbone rigs, rotating wing masts, mast-aft rigs, unstayed cat rigs, freesailing rigs, etc. However, even when not bound by a conventional background one can see that the standard bermudan rig does work and it works very well.

    No one is dissing you for choosing to put whatever rig you want on your boat, as far as I can see. We are just defending other people who prefer other rigs for damn good reasons for their own boats. They are NOT closed-minded ******. Different rigs work for different people in different situations, it's no big deal.

    By the way, I put on a modern short-overlap bermudan rig about two years ago. With the exception of one massive blast that had me down to a No 4 headsail and nothing else, I've never used anything but the main, number 1 headsail and spinnaker. As in other modern boats, one good film headsail and a good set of barber haulers and bendy mast can get you from 0 to almost 30 knots in a boat that is easy to tack, high winded and fast.
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