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

    The second Hong Kong 40 Powersailer has been launched a few days ago, and there are updated photos on that referenced webpage.

    The builder sent along this note,
    "Yesterday they were sailing to Kho Chang with 6.9 knts speed with only one sail. Top speed is 9.5 knts with 2 x 50 hp"
     

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  2. sabahcat
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    sabahcat Senior Member

    Is it just me or is that bridge deck clearance looks a little lacking there?
     
  3. brian eiland
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    brian eiland Senior Member

    ??. Go to that link and have a look thru the other photos, I only posted a few on the forum......More interior shots there as well, but that is not the real subject matter of this tread.

    The boat does look to be rather nicely finished off.
     
  4. michael pierzga
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    michael pierzga Senior Member

    Why would you use an unbloomed sail for motor sailing ??? , the apparent wind would be s far forward that the sail would be useless as power and roll dampening. The purpose of a main traveller and tight sheeting the main when motoring is to propel the boat , dampen roll and relieve rigging cycle , rudder and autopilot stress.
     
  5. brian eiland
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    brian eiland Senior Member

    I assume you meant to say 'un-boomed'...no boom? There are lots of reasons for using no boom, if you can get away with it...and on the wide sheeting base of a multihull's deck those possibilites greatly increase.

    And we are talking multihull vessels here...they don't tend to roll excessively, or as rhythmically as a monohull.

    I'm not using the sails of a motorsailer as just a steadying device as on a trawler application., I am using them as a propulsion device...either primary or auxillary propulsion.

    Did you note the quote above, "Yesterday they were sailing to Kho Chang with 6.9 knts speed with only one sail". I have confirmed that with the author, that speed was attained under sail only. That is a premise behind the concept of multihull motorsailers. these vessels can make passages under sail alone...think of that when the fuel prices double over the next year or two.
     
  6. michael pierzga
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    michael pierzga Senior Member

    6.9knotes means nothing to me withpout the polar diagrams forthe performace of a fully rigged vessel. I understand that some customers would prefer to sail with un boomed sails. I also view un boomed sails as a serious performance handicap.
     
  7. brian eiland
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    brian eiland Senior Member

    Boomless

    Hey they just got the thing launched a few days ago...I don't think they even have all the sails (one more in this case I believe) for it yet....they are just out sailing around to get a feel for it......

    Polar diagrams don't even exist for the vast majority of boats on the market.

    My boomless Firefly tri certainly didn't suffer from being boomless...nor did the Stiletto 30 Mirage

    Besides how many vessels do you know of that carry booms on their headsails?? You seem to fixated on this boomed-sails idea...and that they are superior for some reason?? I don't understand?

    Maybe have a look thru these subjects:

    http://www.boatdesign.net/forums/sailboats/loose-footed-mains-2595.html

    ....not only boomless, but mainless
    http://www.boatdesign.net/forums/multihulls/main-less-rig-21274.html
     
  8. brian eiland
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    brian eiland Senior Member

    Lee Shore Grounding

    The headline-grabber for the week was undoubtedly the Phuket King's Cup, which ended last Saturday with no less than 12 boats on the beach at Kata after a wild night of westerly wind and swell coming straight in from the ******* Sea. And this after a King's Cup that is more likely to be remembered for indifferent weather than anything else (except the beachings).

    12 grounded boats is quite a big deal, really. The multihulls just got carried up the beach beyond the high water mark to wait for more clement conditions and a re-launching, but the monohulls suffered a lot more. Judging by what we saw, there will likely be some write-offs – what the insurers call TCL, or Total Constructive Loss.

    http://www.sail-world.com/Newsletter_show.cfm?nid=460575
     
  9. Alik
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    Alik Senior Member

    Original vertical clearance of this boat is 720mm, but it is sitting deeper due to extra weights added. On this particular boat, much heaver engines and genset are installed, racks for dive tanks, etc., wooden finishing. For such boat vertical clearance should be 4-6% of length; so above 500mm is still OK.
     
  10. sabahcat
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    sabahcat Senior Member

    Damn those owners wanting it all on short hulls
    Pretty common and it would seem like most owners, they should have got the 10ft longer version to carry the load.

    Thanks for the answer
     
  11. brian eiland
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    brian eiland Senior Member

    "Song Saigon", 80' Custom Trawler Catamaran

    Just ran across this beauty:

    Custom built in 2008, she is probably the only power catamaran intended as an all ocean global cruiser. Some 110,000 man hours were invested in her design and construction and she has demonstrated her sea keeping ability with over 15,000 nautical miles logged under her keel in some of the most notorious oceans in the world without incident or problems. And it is doubtful you will find a greener superyacht; constructed in aluminium, she is incredibly fuel efficient, burning less than 30 litres an hour at her cruising speed of 8 knots.

    Her accommodation consists of a full beam owner’s cabin on the main deck, plus 3 ensuite guest cabins on the lower deck...

    more HERE:
    http://www.song-saigon.com/


    ...and she has had a big price reduction recently:
    the asking price is down from $3.6 million to €2.2 million
     

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  12. sabahcat
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    sabahcat Senior Member

    Damn fine looking passagemaker Brian (better not let apex see it, he'll have a thrombo :D)

    Steps on one side only is an "interesting" thing
    I wonder why?

    [​IMG]
     
  13. Guillermo
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    Guillermo Ingeniero Naval

    It's obvious: Because there is only one lady aboard! :D
     
  14. brian eiland
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    brian eiland Senior Member

    Steadying Sail vs. Get Home Sail

    ...just found this thoughtful anaylsis on another forum...thought it could be appropriate to some of these discussions...brian



    Unlike most of the scholastic arguments on the TWL, I have some
    practical data on this one.

    For a couple of decades I owned an older Willard Horizon motorsailer.
    The Willard had a full keel displacement hull with gently rounded
    chines, a high bow and a rounded stern. The design was similar to that
    of small sail working boats of a century ago with all that that
    implies. Power was supplied by a Perkins 4-107 driving an 18" x 14"
    prop. It was easily driven below hull speeds and had good seakeeping
    qualities but tended to roll in beam seas.

    The boat carried 260 sq. ft. of sail on a low aspect rig, a large
    foresail and a smaller main. This is only about half the sail that a
    cruising sailboat of similar specifications would carry and the Willard
    could be considered to be sailing under perpetually reefed conditions.

    On a calm day and with a clean hull it required 22.6 hp. to drive
    PUFFIN at its 7 kt. hull speed. This estimate was confirmed by careful
    fuel consumption measurements kept over several years. The best speed I
    had ever gotten under sail alone in a beam wind was 5 kts. It took
    approximately 8.2 hp. to move the boat at this speed under power.
    Sailboat designers estimate that sails can produce about 1 hp. for each
    27 sq. ft. of area under good conditions. The 260 sq. ft. of sail on
    the boat should generate about 9.6 hp. of propulsive effect. The 1.4
    hp. difference between the 9.6 hp. generated and the 8.2 hp. required
    to move the boat at a 5 kt. speed is undoubtedly due to the drag of the
    large non-feathering prop. In essence, the prop drag costs 15% of the
    generated sail power.

    To make only 3 kts. in a get home sailing mode, the boat will
    theoretically require approximately 1.8 hp. Allowing for prop drag the
    sails will have to generate about 2 hp. Under good sailing conditions
    this would require 54 sq. ft. of sail, about that of a small sailing
    dinghy or Sunfish. Obviously this is for ideal conditions. To be on
    the safe side, a minimal get home rig for the Willard would require at
    least 100 sq. ft. of sail. And, since get home conditions are likely to
    be in horrible weather, the mast and rigging should be strong and the
    sail made in storm sail weight. A low aspect ratio 12' x 10' standing
    lugsail would suffice.

    Scaling this data up for a 45' LWL, 45,000 lb. displacement boat, 3 kt.
    get home speed, allowing for prop drag, would require 2.75 directly
    applied hp. under ideal conditions. This could be generated by about 75
    sq. ft. of sail area. Using a safety factor of 2, the get home rig
    should carry 150 sq. ft., about that of a small daysailer. This might
    require a 20' mast and a 15' boom. As in the previous case, the rig
    should be suitable for storm conditions. Low aspect ratio rigs, perhaps
    a gaff, spritsail or lugsail would be best for carrying the maximum
    amount of sail on an unballasted boat. This type of sail is more
    efficient in beam and following winds anyway. Even a square sail would
    do but these require more rigging and knowledge than most of us want to
    burden ourselves with.

    I would like to point out that either of these minimal get home rigs
    will have very poor sailing performance by modern standards. They would
    parallel those of ancient Greek and Egyptian vessels. Pointing ability
    would be almost non existent. The boat could make progress only in beam
    or following winds. That's exactly the way the ancient ships sailed.
    They stayed at anchor or rowed until the wind was favorable. Still,
    with patience, a boat could cross oceans with this type of rig.

    Getting back to the main topic. Steadying sails are not for propulsion
    and are effective in stopping roll in beam winds. I have found a reefed
    mainsail minimizes roll when motoring in choppy conditions. For the
    Willard that meant about 50 ft. of sail area. The sail is sheeted in
    tight amidships and offers no propulsion power. The boat takes up a
    slight angle of heel and and the roll is attenuated. It is far more
    effective, of course, to actually sail using the full sail area. In
    that case the roll disappears almost entirely. We did most of our
    cruising along the Atlantic coast in a motorsailing mode, using both
    power and sail whenever the wind was suitable. Fuel consumption dropped
    to low levels and the sails stabilized the boat.

    Again scaling up to bigger boat size, a 75 to 100 sq. ft. sail would be
    effective as a steadying sail. But, if you are going to rig a sail
    anyway, why not go whole hog and make it a get home sail.

    Riding sails are useful for high bowed or forward pilothouse trawlers
    that sheer back and forth at anchor. These are small sails mounted at
    the stern of the boat that serve as feathers on an arrow, keeping the
    bow pointed toward the wind. A small 20 or 30 sq. ft. sail will usually
    suffice. Recent research at MIT shows that a small riding sail will
    substantially reduce anchor loads by minimizing sheering.

    Finally, under the windy conditions in which get home and steadying
    sails are used, there is a lot of stress on the mast and stays. The
    rigging should be sized primarily for the stiffness of the boat not for
    the sail area. While a 150 sq. ft. sail area daysailer may get by with
    1/8" wire rope for mast stays, a trawler using the same sail might need
    to upgrade the stays to 1/4". Most of the force on the sail is
    translated to downward pressure on the mast and upward pull on the
    windward stay. Typically trawlers are not constructed to resist deck
    compression forces and the structure under the mast may have to be
    reinforced or a compression post installed to transfer load to the
    keel. Using sails as roll dampers is even harder on the rig than steady
    sailing and the chainplates, the places where the mast side stays are
    attached, must be firmly fixed to the hull structure and not just the
    cabin sides. The ultimate disclaimer, of course, is to have your get
    home or steadying rig designed by a good naval architect.

    Larry Z
     

  15. brian eiland
    Joined: Jun 2002
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    brian eiland Senior Member

    Still unanswered...the considerable difference in the length of those outer sponsons (hulls). I imagine the longer ones are better in terms of speed, but I wonder how they might contribute to a diagonal stability problem in a heavy following sea (running down big ocean waves)??
     

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