Multi-masted sailing cats

Discussion in 'Multihulls' started by marshmat, Jan 3, 2009.

  1. brian eiland
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    brian eiland Senior Member

  2. KSONeill
    Joined: Jan 2009
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    Location: Lake Jackson, TX

    KSONeill Junior Member

    If you're interested in smaller multihulls as well as larger cruising designs with split rigs, I have a 21' proa that has a schooner rig with roller furling jibs, with masts that are 20' from the deck and about 170 ft^2 of sail.

    Compared to a beachcat, for example, it's very easy to sail. Very, very easy. I've taken it on several week long cruises in constant winds of >20 knots and been very happy, it's no stress at all.

    Regarding performance, it's surprisingly good to windward. I had a day of racing with a nicely built proa with very good foils and an A cat rig:

    http://www.youtube.com/watch?v=04H71un6d7A

    http://www.youtube.com/watch?v=UZBnC2tTlxM

    The windward legs were far better for me than downwind. Even with more sail area, dead downwind he killed me just on sail area up high, at least to windward I could do something like keep up.

    I've sailed the boat a good bit in heavy air, beam reaching to running, in the company of moderately fast monohulls (Core Sound 17s and 20s, for example). It's clearly faster than they are. It's certainly slower than a Hobie 18, though, and was slower downwind than the Core Sound 22.

    I think the wide staying base and very skinny masts help the windward performance a lot.

    A bigger proa with a very similar rig is the french proa des Jours Meilleurs

    http://www.youtube.com/watch?v=uqv6taRg6XQ

    http://www.youtube.com/watch?v=xf2pLFC5xCs

    Kevin
     

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  3. Stefan H
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    Stefan H Junior Member

    Thats a big project...76', Maybe not to any help since my boat is like a toy in comparison...Anyway, I use two unsupported spri riggs on my experimental 14' tri. The benefits are that it is easy lower the masts, the healing is less and I reef by simply take down one mast (depending on the wind direction). The downside is that the boat is a little too fast for this old fashioned rigg, ie the apparent wind is almost straight ahead so I cant go fast upwind.

    I am now considering a flatter high aspect rigg. I can only have one tall mast since the forward mast is very close to the bow and there it is difficult to support it without heavy reinforcements due to a very narrow hull. Another thing with taller masts is that you can take advantage of stronger winds higher up which at least partly helps to solve the issue of apparent wind angles.
     
  4. Stefan H
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    Stefan H Junior Member

    Looking at the proa design I just realized that two tall high aspect riggs would be ideal on a tri if you position the masts on the two crossbeams. Just disregard my earlier post about not being able to use 2 tall masts.
     
  5. Fanie
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    Fanie Fanie

    Questions please -

    Why are the sails in tandem and not side by side.

    Which would perform better ? I have seen cats with two sails side by side, it is claimed to work quite well...

    On my own boat I plan to have two aft masts, free standing.
     
  6. Stefan H
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    Stefan H Junior Member

    Because in a "tandem" setup you can balance the boat with the sails, if the sails are side by side it is a little odd but I don´t see why not and the mast could support each other like on the Hobie trifoiler.
     
  7. Fanie
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    Fanie Fanie

    How about these ?
     

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  8. Stefan H
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    Stefan H Junior Member

    It looks like two windsurfing sails that is too small for the boat although it would probably not capsize easily then. Making the masts taller the load on them would be too great for being unstayed. Look at what happened to team philips...Although maybe with som sort of braces between the masts the concept would work..
     
  9. marshmat
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    marshmat Senior Member

    Sails often look a bit small for the boat if they're on a very light boat.

    As for the Team Philips thing.... part of the nature of race boats is that they break. You try to push the envelope, the envelope will thwack you upside the head now and then. Besides, think about how much publicity that team got as a result of the boat snapping a hull in half, then wrecking its mast bearings, and later breaking up mid-Atlantic. Had it finished the race mid-pack without incident, the sponsor's name wouldn't still be flying around every time wavepiercing cats or unstayed masts come up.

    As the aircraft industry figured out in the '30s, it is quite possible and perfectly OK to use unstayed spars for even the largest, most highly stressed applications. We boaters, unfortunately, don't have access to the simulation techniques and engineering teams the aircraft companies use to predict (and correct for) the exact deflection and twist that an unstayed wing or mast will undergo in a particular loading case.
     
  10. Stefan H
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    Stefan H Junior Member


    Yes team philips got attention but it is arguable if that is positive publicity, some people say all publicity is possitive. You are absolutely right that aircraft engineers can calculate deflection and twist. If aircraft builders would have built team philips it would probably be a completely different story...However, for a boatbuilder it is cheaper and safer to look at tested and proven concepts for a big (76'!!) and expensive project rather than experimenting with new and risky designs. Ok for a small and cheap project like on my small 14' boat since I do alot of concept testing. My masts are unstayed, but the force on the base is extreme even with my low aspect riggs. Now, to use unsupported high aspect riggs would prove problematic since I don´t want to add weight by supporting the mastbases further. If I would use alot of carbon though it might be lighter than using shrouds? But why use unsupported masts? reduced windage? lower centre of gravity? But on a cruising boat I think safety should be prioritized.

    You read my thread about controlled flex, right?http://www.boatdesign.net/forums/boat-design/controlled-flex-30754.html.

    I think we will see more aircraft engineers involved in the next record breaking boats...
     

  11. marshmat
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    marshmat Senior Member

    Safety is one of the main arguments put forth in favour of freestanding masts: a conventional rig will collapse if any of about a hundred components fails, and many of these components are hard to inspect on a regular basis. A properly engineered freestanding mast, by comparison, has all its engineering concentrated in three components: a stick strong enough to handle any load the boat is capable of producing, and two highly loaded, but easily inspected, hull-level bearings.

    Of course, there have been many poorly engineered freestanding masts that have failed, in all sorts of boats. So far, though, I've seen no evidence at all to suggest that freestanding rigs fail more frequently than stayed ones.

    There are plenty of good reasons to choose a stayed rig over unstayed, or vice versa- it's not a one-size-fits-all answer.
     
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