10 meter proa sail rig options

Discussion in 'Multihulls' started by Forecaddie, Oct 18, 2023.

  1. Forecaddie
    Joined: Apr 2023
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    Forecaddie Junior Member

    wharram.jpg Puke3drb2.jpg Südseeabteilung_in_Ethnological_Museum_Berlin_34.JPG IMG_8709.jpeg IMG_8708.jpg Building a 7.5m leward hull with cabin and 10m windward hull with 2 sails planned.
    looking for input/ opinion on sail rig option and ease of sailing.
    anyone use 7m tall catamaran masts with cat sail. I think I need 20sm sail area. I want to have option to reef and keep boat in water, so cant take sail mast down after every sail. I want to spend weekends on boat so a cabin is ib the works.

    1. Crab Claws
    2. Fixed wing front section of mast with normal sail cloth
    and wishbone boom for less sheeting tension?
    Last edited: Oct 18, 2023
  2. Robert Biegler
    Joined: Jun 2017
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    Robert Biegler Senior Member

    Most proas have a lee hull as long as or longer than the weather hull, for diagonal stability. The last exception I know of was the Kelsall design Sidewinder, which competed in the 1970 Round Britain and Ireland Race.
    Proafile has a series of articles which covers much of what has been tried. This article comes with links to the rest: Proa File | Proa Rig Options: the Biplane https://proafile.com/multihull-boats/article/proa-rig-options-the-biplane There are some more exotic configurations if you want to experiment, but if you just want something that is likely to work, pick one of those, and ideally find one of the people who used such a rig so you can ask them more questions, in case differences in hull and rudder configuration mean that your boat and that rig will interact differently.

    Probably the most experienced users of those sails are still in the Pacific, but their focus is more on keeping their traditions alive than on exploiting modern materials to enable sailing with smaller crews:

    For reading about a fair bit of practical experience, read this blog from the beginning: Grillabongquixotic's Blog https://grillabongquixotic.wordpress.com/
    Also https://www.youtube.com/@fjordproa6510/videos
    https://www.youtube.com/@BalkanShipyards Rael Dobkins does post here.

    If the rig is also to lee, that generates strong weather helm, and you need to design your lateral plan to deal with that. If the rig is on the windward side, helm balance is easier to achieve, though if you were to lie ahull without sail, the rig's drag on the windward side would tend to turn the bout around.
    Last edited: Oct 19, 2023
  3. Forecaddie
    Joined: Apr 2023
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    Forecaddie Junior Member

    Thank you. Plan on 7.5 ww hull and 10 meter LH. Can you explain more about this windward drag and rounding up? Or a link so I can read it?
    Also, what do you mean lateral plan?
  4. Robert Biegler
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    Robert Biegler Senior Member

    A proa with the rig in the windward hull is called an Atlantic proa. The first one was the Newick design Cheers, which placed third in the 1968 Observer Singlehanded Transatlantic Race:
    Proa File | The relaunch of CHEERS https://proafile.com/multihull-boats/article/the-relaunch-of-cheers#pid=2

    Another was Eterna Royal Quartz:
 REF:YA ETERNA ROYAL QUARTZ 1981 Stock Photo - Alamy https://www.alamy.com/stock-photo-ajax-news-photos-6th-june-1981-plymouth-england-two-handed-transat-111503832.html

    I don't have a single source for a rig to windward getting the boat turned round. You have the tendency for unattended boats to lie parallel to the waves, but if an Atlantic proa ever got turned enough to be before the wind, the rig would provide most of the drive and would tend to turn the boat so that the rig ends up on the lee side.

    Everything that prevents the boat from going sideways: hull, rudder, boards, keels. The narrow and deep hulls of a multihull are much more effective than the shallower and wider hulls of dinghies at preventing the boat from going sideways. The problem is that the centre of pressure of a hull that is moving tends to be at around 25% of the waterline from the bow. For a proa, that translates to well before the midpoint. You have to balance that by one or more of the following:
    1) Move the sails' centre of pressure forward. This is what moving a crab claw to the new bow does. Rael Dobkins moves a junk rig from end to end. Some proas have a sloop rig that sets a jib on the current bow.
    2) Move the sails' centre of pressure to windward. This is what Atlantic proas do, and Rob Zabukovec's biplane rig. Some proas with crab claw rig set up the mast so that it can be leaned to windward for downwind courses and leeward for upwind courses. Fjordproa is an example.
    3) Move the hull's centre of pressure aft by shifting weight aft and immersing the stern more. Small proas, especially with deep V hulls and modest waterplane area can use that method. A boat of the size you plan would need a large crew, or water ballast and a big pump.
    4) Move the foils' centre of pressure aft, usually by dropping a rudder at the current stern and retrieving a rudder at the current bow.

    I have seen a claim that hull asymmetry may help as well, but that may depend on fine details. The report I saw claimed that having one side of the hull fatter than the other but the keel straight didn't help, but curving the keel line did. That is a single report from decades ago. I would suggest testing some models to see whether the claim holds up.
  5. rwatson
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    rwatson Senior Member

    I don't see the obvious references to refer the OP to for a Western Proa, that is HarryProa, whose designs specialise on twin mast, long hull rigs
    These specs will be of direct relevance to the project, including the solving of rig operation, balance effects etc.
    There is certainly no problem with directional control on any point of sail. Some sail areas and designs for the OP to consider.

    Note for Rob Denney - your website http://harryproa.com/?page_id=2762 comes up with "Not Secure". May need some attention when you can relax from your tropical island "holiday" :)
    oldmulti likes this.
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    ALL AT SEA Junior Member

    "Proa sailing and construction" on facebook has some good experience.
    A couple of posters have actually built very similar rigs to what I have doodled over the years that combine modern materials and practicality with ancient concepts. I hope they don't mind me sharing.

    Personally I prefer one mast in a proa, as two mast means having to reef both sails to maintain balance between shunts.


    I should also mention the proa "Sidecar" that I've had the privilege of sailing. Rob has applied a lot of logic after starting with a 'clean sheet' and come up with someting simple and unique.
    Proa File | The Proa Sidecar https://proafile.com/multihull-boats/article/the-proa-sidecar
    The photos don't do the simplicity justice.
    Last edited: Oct 20, 2023
  7. keith66
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    keith66 Senior Member

    Of all the proas I have seen online Fjiord proa's Elliot seems to be the best sorted boat. He has the crab claw sail yard tack running along a rail that runs from end to end, it makes shunting fast & simple, some great video of his proa being driven really hard in windy conditions.
  8. myszek
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    myszek Junior Member

    This proa looks like Reto Brehm's Lili'Uokalani. Is it? I've never seen her with this kind of rig. I wonder, how it works in compare to the classic crab claw.


  9. rob denney
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    rob denney Senior Member

    Thanks for posting. The web page is being replaced as I type, although none of the 'experts' could shed any light on 'Not Secure'.

    Some thoughts:
    Proas, especially ones with low volume windward hulls require rigs that, when caught aback in a breeze, weathercock. ie they align with the wind. Otherwise you may capsize the wrong way. The crab claw option of the rig falling down is an option for smaller sizes.

    Beams and stays should also be sized and supported for this non-weathercocking caught aback load. ie if the beams need the shrouds to support them in normal sailing, they may need waterstays for caught aback in a breeze situations. Fore/backstay angles should also be considered if they are holding up the mast when the breeze is from the wrong side.

    None of which is a problem if you don't sail in a breeze, and/or never get caught aback. The test is to sail with full sail (and max ballast) with the windward hull just flying, then push the helm down and tack. Proa designers who consider this, end up switching to unstayed rigs. The rest sail very cautiously.

    Sails supported only by stays exert huge compression loads on the mast and it's supports and get fuller as the wind increases, the opposite of what is required.

    Wing sails are great, but tricky to trim. Solid ones are fragile and can't be reefed, soft ones lose shape in a breeze if the leading edge dimples.

    Balance is many facetted. In my 25 years plus proa experience rockerless hulls, rudders at around 25% and 75% of the lee hull work well with crab claws, single mainsails, aero rigs (jib on an extension of the main boom, all rotating together) and schooners. The mini cargo proa could be steered by moving one person fore and aft between the masts, the Visionarry steered itself for 20 minutes at a time with the rudders locked fore and aft. Single mainsail versions are easily steered (upwind and reaching) with the front rudder, the aft one acting as a leeway preventer.
    The windward hull water drag does not make a heap of difference unless the boat is really wide or has a draggy windward hull. If it did, when you flew a hull, proas (and cats) would bear away dramatically. They don't.
    I deplore the use of daggerboards on common sense and safety grounds, but even if I didn't, they don't belong in the windward hull if you are concerned about weatherhelm.
    Hulls with rocker don't only have lower top speeds, they pitch more and tend to trim bow down, exacerbating any weather helm issues. Rocker is handy for boats that need to turn sharply to tack, but add to build time and complexity on proas.
    rwatson likes this.
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    Boat Design Net Moderator Moderator

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  11. ALL AT SEA
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    ALL AT SEA Junior Member

    Yes, you picked it. He seems happy with it, there's also a video of it sailing reefed on the page. Looks very effective.
    myszek likes this.
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