Monohull verses Multihull powersailers / motorsailers

Discussion in 'Motorsailers' started by brian eiland, Aug 8, 2004.

  1. brian eiland
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    brian eiland Senior Member

    Trimaran Hull Design for Combat Ships

    I ran across this site, and excerpted this portion of the discussion. This might account for a rejection of the tri-hull concept, even while it looks so advantageous in its operational goals.

    LOTS of illustrations also!
    http://navy-matters.beedall.com/fsc-pre2005.htm

    Future Surface Combatant (FSC) - until late 2004

    One design option for the FSC is a revolutionary trimaran hull concept with a slender main hull and two outriggers. There are numerous theoretical advantages of a trimaran hull form with a slender central hull with outriggers over conventional mono-hulls:

    •Reduced hull resistance at higher speeds resulting in typically 18-20% less installed power for an escort sized vessel required to achieve 28 knots
    •Wide range of propulsion options
    •Greater fuel economy
    •Improved stability and reduced motion.
    •Increased directional stability.
    •Top weight growth margins are greater. There are significant additional stability benefits in the area of growth margins. This will allow equipment upgrades during the life of the ship to be easily accommodated .
    •Increased deck area (up to 40 per cent) on 1 and 2 decks for a given tonnage, offering more space for hangars, helicopter operation and weapons. Some of the greatest advantages for the trimaran comes from the improved effectiveness of the whole ship design afforded by this very large deck area.
    •Improved sea keeping performance at higher speeds, operational in higher sea states.
    •Increased stealth - potential for reductions in radar cross section and infrared signatures. A reduction in heat signature could be gained be exhausting between the side hulls rather than conventional main structure funnelling.
    •The side hulls can be utilised for configuring a multiline towed array sonar.
    The Ministry of Defence has been sponsoring research in to triple hulled ships since the late 1980's. Importantly, work by QinetiQ (formerly DERA), UCL and Vosper Thornycroft has now confirmed that a trimaran hull form does indeed reduce drag by about 20 percent at high speeds compared to a single hull. The lower resistance will permit higher speeds to be achieved, or a reduced machinery fit leading to lower through-life costs.

    Increases in size and to some degree location of the superstructure can be easily accommodated without affecting the ship's stability. This is because of the de-coupling of the main hull beam from the required stability. The required stability can be obtained by adjusting the size and distance from the main hull to the side hulls with little impact on drag and weight. This will allow heavy equipment such as large radars to be fitted more easily than could be achieved with a monohull.

    The outriggers make the ship more stable and give it a larger flight deck, which can be moved away from the stern and nearer amidships, allowing helicopters to operate under a wider range of sea conditions. It is possible that the wide upper deck will lead to the provision of a second hangar which could be used for other service helicopters such as the Apache for land attack, support or relief operations. Optional side-hull propulsion in the outriggers makes the ship more manoeuvrable. And if the ship does take a hit, the outriggers protect the inner hull, where the main power plant is contained. Survivability in general from weapons strikes will potentially be greatly improved.

    However, the trimaran approach does also have several possible disadvantages when compared with a mono-hull approach for FSC:

    •the very long and wide hull will make a trimaran FSC too large to fit in to existing escort refit facilities and dry docks, necessitating expensive redevelopment of these.
    •worldwide, there is no experience with designing, building and operating large steel trimaran ships (other than the small RV Triton).
    •increased and unusual structural stresses may present significant design challenges and technical risks
    •possibly higher construction costs.
    •reduced stealth - radar, noise and wake signatures may actually increase in practice
    •reduced internal hull volume for a given tonnage, so less room for accommodation, VLS cells, fuel and stores, etc.
    •instability if an outrigger is lost or flooded.
    These disadvantages when combined with the risks and doubts inherent with any major revolution in naval design may yet prove too severe, and a mono hull form adopted for FSC.

    Originally a hull displacement of about 5-6,000 tonnes was expected for a trimaran FSC, but this seems to have crept upwards. Concept studies have apparently considered displacements as high as 14,000 tonnes and a 9000 tonnes design was the baseline configuration in early 2003.


    ...further down in the discussions:
    RV TRITON
    A joint report written by senior USN and RN officers in early 2002 on the Triton trials was positively glowing about the results. Apparently all the hoped for trimaran virtues were confirmed – economy, sea-worthiness and comfort, etc. The only downsides highlighted were the predictable impact on berthing and dry-docking. The results will be included in the Staff Requirement submission for the FSC.
     
  2. brian eiland
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    brian eiland Senior Member

    http://www.motorship.com/news101/triton-trials-trimaran-form

    "The result is a main hull having a round bilge shape with underwater sections approaching semi-circular shape amidships. A gentle rise of the bottom lines aft leads to a counter-stern transom with minimal immersion. The side hulls are of multi-chine design on the outboard face with a flat plain inboard face for ease of manufacture.
    The demonstrator was built at two thirds the size of a full-scale warship"


    "The trimaran design is faster and more manoeuvrable than an equivalent sized mono-hulled craft, says QinetiQ. It adds that Triton has proved that the triple-hull design offers a reduction in drag of 20% compared to a conventional mono-hull vessel"


    "The extensive sea trials have been undertaken in a wide range of weather conditions up to a sea state of 7 to 8 with the ship sailing at short notice to stormy sea areas around Ireland, south Iceland and off the Norwegian coast. Using a star trajectory pattern the trimaran was subjected to every conceivable wave pattern. QinetiQ says there were very few instances where it shipped green seas over the bow. Special attention was paid to the slamming effects under the decks linking the hulls. QinetiQ says the vessel?s handling capabilities have validated the designers? claims by confirming the naval architectural performance."


    " Bob Short, QinetiQ?s RV Triton programme manager, says that Triton has already gone a long way to validating earlier research and has demonstrated the considerable benefits associated with triple-hulled vessels. He is also quietly confident that trimarans have a huge potential commercial application worldwide and the agreement with Vosper Thornycroft strengthens the UK?s position as a world leader in trimaran technology.
    Ultimately, however, one has to recognise that a fundamentally conservative industry such as shipping will take some convincing before it will commit hard cash to a new hull type"
     
  3. brian eiland
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    brian eiland Senior Member

  4. Ilan Voyager
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    Ilan Voyager Senior Member

    Briand Thanks for all the very interesting info, a bit outdated as the project has been abandoned. Always the same mix of advertising and impossible to exploit data but the principal assertion remains valid: trimaran is a very interesting configuration.
    That was known at little scale since Nigel Iren's Ilan Voyager and confirmed by the Benchijigua Express. Unhappily the financial crisis did not and won't help for further development.
    Navies have other requirements and with the changes in warfare, small and medium ships are practically expendable. The survival of a frigate (or other small ship tracked by satellites,planes and drones, and shot by missiles, cruising missiles, drones, torpedoes, planes and others) after a few days of a true war is unlikely...So the hard core of small warships are the cheapest possible as the electronics are now the major expense on a warship.
    It seems unlikely that we'll see a new generation of multihull warships, a part a few exceptions.
     
  5. whitepointer23

    whitepointer23 Previous Member

    i thought they were saying 18 knots under power not sail. i welcome these new powersailers brian. they might not be ideal for everyone but i like the multipurpose idea. l like cats too. this powersailer is just a scaled up mac 26 really, which is a boat that does a good job in the role it was designed for. there are heaps of cats which travel fast under power or sail available. pity they are such ugly creations.
     
  6. FAST FRED
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    FAST FRED Senior Member

    only 66' long and carries a 21' beam

    Perhaps she simply sails on her ear.

    The old "sandbaggers" when underway were one hulled really skinny boats if you look at what is left in the water.

    So the fat beam might help spinnaker plaining in huge breezes and the one cat hull style immersed wetted area when sailing to windward or reaching should make a fast boat , with out the usual cat problems.

    Lots of wetted area , so light winds or motoring will be less than sterling.

    FF
     
  7. brian eiland
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    brian eiland Senior Member

    Two Marketable Ideas, Rhodes Discoverer & Domonio Powersailer

    Just this morning I wrote a short note to a gentleman suggesting that if I were a boat dealer looking for product to handle in todays market....

    Speaking as if I were a boat dealer (sales), if I had two models on hand for this near-term boating market, they would both be motorsailers with live-aboard potential. And to satisfy both camps, one would be a monohull, and one a multihull....one would be that Rhodes Discoverer like vessel, and one would be this Domonio powercat like vessel with an added rig. I think I would have two sellable products that could accomodate a fairly broad range of the upscale market.
     

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  8. Ilan Voyager
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    Ilan Voyager Senior Member

    Brian, sorry for being picky but the last pic of the "cat motorsailer" leaves me in stupefaction:

    Let's forget that the Domino's actual hulls are unsuitable for any sailing, it's the rigging that bothers me.
    Not because it's unusual (some of this kind have been tried with very mixed results) but because "as is" this rig is a bunch of problems;

    The rig is awfully complex with as much cables as a WWI biplane. Not easy to tune correctly.
    The compression is enormous as the 2 forestays need a lot of tension to have the genoas/jibs with a decent shape, and the poor mast is posed on a roof. Let's imagine the due reinforcement is done: that's very heavy. Practically a beam only for the mast.
    Where do you put the winches and tracks? On the roof that means that it needs to have the strength to withstand the stresses. Again more weight and high placed. Not good for the center of gravity.
    The very small high aspect mainsail with a wishbone has some utility? Just hidden behind the thick mast it won't receive a good flow.
    Tacking won't be a pleasure...
     
  9. brian eiland
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    brian eiland Senior Member

    First off let me say that this was just a very quick cut and paste job I did by placing a dwg of the mastaft rig (from the HK40 powersailer cat) onto a dwg of the Domino hull profile. It was just a quick job to give two gentleman a general idea of how this Tennant design Domino might appear as a motorsailer.

    HK40-catamaran-project-02.jpg
    HK40-catamaran-charter-version-01.jpg




    I believe this subject likely deserves a lot more discussion, but I would like to hear why you believe these catamaran hulls are unsuitable for sailing?? ...particularly as a combination of motor and sailing...MotorSailer

    The single biggest negative I can find is there deep forefoot that could make tacking more problematic.


    First off let me explain that I very quickly grabbed the rig profile dwg from that existing HK40 vessels and placed it on the Domino hull. I should have taken my mast-aft rig profile and used it instead. I still have some problems with HK40 rigging arrangement, and as I am lead to understand there may be some review going on.

    I believe I have accounted for some of the excessive loading problems that so many naysayers have brought up in the past. Have you had a look HERE
    Rigging Force Review
    I think you will find that it is not an excessive bundle of cables.


    Again I emphasize this was a quick 'cut and paste', and was not meant to be a definitive rendering....notice the mast doesn't even touch the vessel, so no recognition as to where this mast will best be stepped at this time.


    The sail you are referring to is really a mizzen sail, and performs those same duties as does any mizzen sail in a ketch rig.

    Chris White on Ketch Rigged Cat

    Bryon Toss on Mizzens
     
  10. High Tacker
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    High Tacker Junior Member

    High Tacker (www.damsl.com)

    Practical application of proa canted sail geometry on a motorsailer cat

    See details at www.damsl.com

    I think of my Catbird Suite as two proas leaning together so that sails can be canted in either direction, to windward or to leeward, take your pick for the conditions. She has A-frame mast and four sails so far, all on furlers, including mainsail, staysail, and a genoa on each bow. The mainsail and staysail are on soft furlers, so their tacks can be moved easily around to different positions on deck, because with the beam of a cat there are many possible and advantageous sail configurations in addition to the usual straight up and down-fore and aft plan.

    Since I'm a lazy 70-year-old cruiser, and safety conscious, and my cat sails pretty fast anyhow, I usually do the opposite of what the Sailrocket guys do. On a long passage-making tack, I attach the main and staysail tacks to the windward side deck and use those sails and the windward genoa so that I can go from close hauled through reaches to run and have the entire width of the boat to sheet down to, to various tracks and pad eyes, and thus maintain ideal sail shapes with no booms needed. The leeward genoa can be added without a whisker pole when close hauled or with a whisker pole for reaching and running.

    In addition to having no booms bashing about, so that an accidental jibe is a non-event, there are built-in safety factors with sails canted away from the wind. The heeling moment is substantially re-directed downward, and since the sails themselves are "heeled" away from the wind, even though the boat herself is not heeled, there is some spilling of wind in gusts, so that the shock loading that would be experienced on a big cat with vertical sails is somewhat diminished. As cat sailors well know, big cats are very unforgiving in a gust, no heeling, so no shock absorbing and wind spilling effects. So everything about the rig must be much stronger than on a monohull. (Not to mention an A-frame with each leg stepped in a hull, rather than a single big mast in the middle trying to break the boat in two. A monohull rig on a cat just doesn't make sense to me. A cat is two boats in one, so why not take advantage of that. Uh, a proa is one and a half boats in one, LOL.)

    Uh, I don't fly a hull, but if she ever did heel much, with sails already canted away from the wind, the increased spilling would be dramatic before the heeling became dangerous.

    On the other hand, if you don't want to spill any wind, if you want to go faster instead, and with upward lift on the sails and thus upward lift on the boat, a la Sailrocket, then you attach the mainsail and staysail to the leeward side deck and use the genoa on the leeward bow, so that the sails are canted into the wind, like Sailrocket or like a windsurfer leaning into the wind. Sorry I don't have any photos of this configuration. I haven't done it often, and when I did, I was too busy to take photos. In the sailing photos below, all sails in use are attached on the windward side. Hey, as I said, I'm old.

    It is also advantageous in very light airs to have the sails attached to the windward side and thus canted away from the wind so that they set into proper aerodynamic shape by the effect of gravity when there's not enough wind to lift them into shape. You remember when sailing a little dinghy, when there is very little wind you move your butt over to leeward to heel the boat a bit so that the sail will fall into shape. So in very light wind, as soon as I unfurl a sail I'm away, while all those vertically rigged boats have sails hanging like so much laundry, all drag, and going backwards. Also, my sails don't come flopping down in the lulls; they're already down and so maintain their shape, ready for the wind to come back.

    For short tacking, I attach mainsail and staysail on the center line of the boat. The leeward genoa can be added and then, when coming about onto the other tack, that genoa must be furled and the genoa on the other bow unfurled as it becomes the leeward one. The older I get the more often I think about getting electric winches, but then I don't short tack often using a genoa, just use a motor or two if there's that little wind. What the hell, a cat is too fast to be short tacking up a narrow channel anyhow, but if you really want to do it, quite often the mainsail and staysail are enough.

    A monster main could be added, but she does very well to windward without one, and she is superior reaching and running. She's great motorsailing, too, and just motoring. But I shouldn't get too longwinded here. Read all about it at www.damsl.com

    Cheers, Tom Bradshaw
     

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  11. High Tacker
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    High Tacker Junior Member

    High Tacker (www.damsl.com)

    Superyacht monohull motorsailer with A-frame rig & 5 furling sails

    Greenpeace's new Rainbow Warrior, 840 tons, with two 50-meter A-frames, is in the midst of sea trials, so far has sailed in winds of 10 to 25 knots and everything is working fine, huge sails safely handled. Details and more photos on another thread of this forum, see:

    http://www.boatdesign.net/forums/boat-design/wishbone-sailing-rig-1999-14.html

    Scroll down on that page for close-ups of wind tunnel model and the finished mast structure being readied for stepping. The wishbone sailing rig thread contains quite a few interesting bipod rig examples on substantial motorsailers.

    Motor power for Rainbow Warrior III is diesel-electric. The A-frame rig was chosen for efficiency, strength and practicality, according to the designers Dykstra & Partners.
     

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  12. High Tacker
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    High Tacker Junior Member

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  13. High Tacker
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    High Tacker Junior Member

    1 person likes this.
  14. High Tacker
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    High Tacker Junior Member

    High Tacker www.damsl.com

    Perhaps the biggest nuisance on a sailboat, especially when motoring, is that big mast and boom right in your face. Everybody who comes aboard Catbird Suite, with her A-frame mast and boomless main, remarks that there's no mast stuffing up the view from cockpit or saloon, and no boom. That appeals particularly to older sailors who like a 50/50 situation, sail when it's nice, but get inside and motor when it's nasty. And it's great to have an unobstructed view from shelter. See below for photos of the Missus at the wheel sailing and then the Old Man maneuvering, poking his head out for an even better view, and with no danger of getting bashed by a boom. More pics at www.damsl.com
     

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  15. sabahcat
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    sabahcat Senior Member

    LOL, when motoring in a cat you have a section at most probably 200mm wide on the centreline
    You steer from the sides,as shown in your above pictures, so its hardly an issue

    Your A frame still has two furlers in front PLUS a furling main, where a mast would be, so if anything, my view is more inhibited by the A framed setup.
    [​IMG]

    As for the boom, I am yet to be on a cat over 35 ft where the boom interferes with my 6.2 ft height.
    And again, as you steer from the side, how can it possibly be right in your face as you claim?
     
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