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

    Stability, Comfort, & Capsize Resistance

    Fred, from this posting and several others of yours, you seem to preoccupied with the subject of capsize and subsequent recovery. It appears as though you are of the impression that monohull powercraft will readily recover from a capsize.

    I would like to refer you to Steve Dashew's analysis as he was looking to build his new power craft, "Stability, Comfort, & Capsize Resistance" (very interesting discussion and illustrations). One small paragraph from that discussion, "The powerboat industry must assume that there are no capsize risks, because as far as we can see, 99% of all powerboats - right up to 100,000-ton bulk ore carriers - will capsize and not recover, given the right set of circumstances. One of the facts which startled us when doing research for our book Surviving the Storm, was the calm manner in which the professional seamen we interviewed discussed what would happen if the right wave caught them at a vulnerable angle. The norm for most yachts, ships, and military vessels is a maximum heel angle of 65 to 70 degrees, after which the boat keeps going and does not come back. They accepted that their ships would capsize and everyone would die. One of our former clients told us of a 50-knot gale he weathered, hove to behind a parachute anchor, in a heavy displacement 60-foot steel trawler. He said he felt they would not have survived much worse conditions than this modern storm (after which he sold his trawler and went back to sail)."

    Brian commented:
    It's a shame we could not get ahold of that video Derek Kelsall mentioned in his posting, excerpt... "However, imagining lying ahull to those waves did not fit the picture. A couple of clients have described being in a situation where they expected to capsize from the size of the wave and the angle of heel, but then suddenly found the cat was back on its feet again. One of these clients decribed the waves passing while lying ahull and of the most disturbing part being the fall of the windward hull into the trough as the wave passed. The video demonstrated the situation as I understand it. The tank test was done in Southampton comparing a Lock Crowther catamaran ferry with a comparable mono, in large breaking waves and high wind, with the models lying ahull. As the wave hit the cat, which was still in the water, the windward hull was thrown up into the air, looking like an immediate capsize, but before the angle of heel had gone to 30 - 40 degrees, the wave had passed to the lee hull, lifting it just as rapidly to bring the cat level and then fall as the wave passed. The cat never capsized. The mono rolled every time. This situation actually applies whatever the orientation of the catamaran to the waves.

    I also find the RV Triton hull interesting, look here. But I'll venture to guess she is not self-righting
     
  2. DiverDown
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    DiverDown Junior Member

    There also is a major difference between fixed keel hulled cats (usually 4.5-5' draft) and shallow draft (<2' daggers up,6' draft or so daggers down) daggerboard cats.Apparently keel hulls won't slide sideways as well and may trip up,but it would still take a hell of a lot.

    I spent a lot of time in a large dagger cat in Australia.We were playing around in a cyclone once (daggers up) when everyone else was freaking out and getting extremely beat up.
    Very large swells would come from abeam-she would slide sideways down the hill quite a bit.The weather hull would float up and over the crest,and then the crest would drag the lee hull along for a bit and then we would start the ride all over again.

    You would have to be trying very hard to flip that thing.
     
  3. chandler
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    chandler Senior Member

    What was the draft of the cat? CB up and down?
     
  4. DiverDown
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    DiverDown Junior Member

    It's been 13 years...for sure 18" up and I think 6' or so down, 64' by 31' beam.
    The cat was very similar in design/dimensions to the Shuttleworth 63.

    Fabulous for scooting over the barrier reefs and beaching on a little tropical cay.
     
  5. shoulders
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    shoulders New Member

    lifeboat sale

    After reading your story I was thinking you might know some lifeboats for sale. Im seriously looking for lifeboats.

    Yours sincerely Simon Sluis

    sofian@kth.se
     
  6. Guillermo
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    Guillermo Ingeniero Naval

    Motorsailer definition

    Here you have my definition for monohull motorsailers:

    "Motorsailers should be, in my opinion, hybrids among sailing boats and motor boats, with amplier volumes than those of a pure sailing boat (And to my taste with a nice pilothouse!) to make them more livable and able to carry a generous cargo; have manegeable sails but able to easily develope hull speed under sail alone; have a propeller-engine combination allowing for a fuel efficient motoring and with power enough to reach hull speed, as well as some extra muscle to beat dead to winward in a storm (force 10) in protected waters.
    This means, to me, an SA/D ratio from 13 to 15 and a HP/(D/1000) ratio from 2 to 2.5 (Imperial units)
    D/Lwl ratio may go from 250 for lighter ones as in many modern designs bred in sailing boats, up to 450 for heavy-weigths long keelers bred in fishing boats"


    Now, your criticisms.
     
  7. Vega
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    Vega Senior Member


    Regina, Nordship and the new range of Nauticat seem to fit the description. If you want more power than standard they will provide it.

    http://www.siltala.fi/
    http://www.reginayachts.se/
    http://www.nordship.dk/

    Regarding motorsailing, for me, the best improvement came from a propeller:
    Autoprop, manufactured by Bruntons.

    Suppose I have wind to make 3.5 knots and I want to make 6 knots. With the standard propeller I would have to put the motor at 2000rpm. With an Autoprop, to do the same, I only need 1000rpm. There is almost no noise and the autonomy increases almost twice, not to mention costs and motor life.

    http://www.bruntons-propellers.com/products/variable/autoprop/
     
  8. FAST FRED
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    FAST FRED Senior Member

    "Fred, from this posting and several others of yours, you seem to preoccupied with the subject of capsize and subsequent recovery. It appears as though you are of the impression that monohull powercraft will readily recover from a capsize."


    I was under the assumption that a MOTORSAILOR would have some sails and be as usefull as a std OTS sail boat , where a knockdown is a survivable event.

    Some have had the mast submerged and NOT lost the rig , so with the usual smaller rig installed on Motorsailers expect any Knockdown would be survivable .

    Sure pure motorboats don't come back up , but a real MOTORSAILOR should easily, and with proper hull and deck constriuction remain watertight integrity and stay afloat.

    My concern is many multihulls CANT right themselves and therefore become death traps in the right (perhaps Wrong) conditions.

    Having gone offshore in a Headly Nichols Voyager Tri in the mid 60's I know that low aspect ratio keels will allow the hull to sideslip when caught abeam in the small rough stuff 20ft and under. The ride is rough as the vessel assumes the slope of the waveform , but its survivable .

    The concern is with the NASA finding that 70ft waves are more common (10X) than previously thought, and that the old 24 ft of beam would be really hard to right after meeting a big one.

    Seems silly to me to venture offshore in a vessel that can not take conditions that may be met at times.

    Esp when so many simple small monohull boats have met these conditions and survived to continue their voyage . A proper offshore voyaging M/S should be able to SURVIVE even the rough stuff , why endanger folks lives when OTS designs some 100's of years old do so well?

    A modern Version of Herrishofs Marco Polo with modern construction and engineering (and a modern interior) should be able to survive any conditions met , even the Southern Ocean . Added stability with modern engineering (roll tanks, gyroscope, bilge keels , powered active foils or RV Triton training wheel style amas ) or just good old fully battened sails should bring the ride up to todays standards.

    Anyone got a few tons of Marine Aluminum??

    FAST FRED

    FAST FRED
     
  9. sharpii2
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    sharpii2 Senior Member

    Proposed Motorsailor Labeling System

    Hi Guillermo.

    Not a bad definition.

    But to say it is all encompassing is to do the type a major disservice.

    My definition would be a bit looser.

    I would go by what I call "the 25% or over" rule. If a vessel is either sail or motor powered but intends to use the propulsion method not chosen as its main propulsion exclusively for at least 25% of the time, then it is a motorsailer. Thus, if you are on a, say, 3,000nm voyage and you intend to use the engine, if you are a sailboat, or the sails, if you are a motorboat, for at least 750nm of the trip, you are a motorsailer.

    This definiton, I think, is inclusive enough to include a vast array of hull types and engine/sail combinations. All the way from a kayak with an unbrella on board to serve as a makeshift down wind sail to take advantge of frequent strong favorable winds to a sailboat with an outboard auxiliary that has extra fuel tanks added in exchange for less light air sails stored in the forepeak.

    These two examples are, obviously, at the outer edges of my definition, but I think they definately qualify. And, if that's so, everything else in between qualifies as well.

    This, of course, creates new problems, because some vessels are specifically designed to be motor sailors and others just end up that way. Some of the former are primarily sailboats and others are primarily powerboats.

    To solve this problem, let me suggest a return to the old "century definiton". That is, if the boat can only sail or power well, its label will add up to 100. So if the boat is primarily a Motor boat but can sail in strong winds and, perhaps, make gruding progress upwind without the motor running, it might be called a "30/70p" motorsailor (or, perhaps, a "25/75p" if it can't go upwind at all without the engine running).

    If the vessel can do one really well and the other well enough to consider making an entire voyage (but perhaps a shorter one) using its secondary propulsion system, then its label should add up to more than 100, with the dominate power source having the larger number and the larger number alway being stated last with a single initial signifiying which one it is. So a boat that is primarily a sailboat but can its usual rounds under power alone would be called a: "50/75s motorsailor".

    I would further enhance this system by adding a starting initial which would signify the vessel's heft. How about an "L" for light, for vessels with a D/L of less than 100 to 150, "M" for vessels with a D/L of 151 to 270, and an "H" for vessels from a D/L of 271 on up.

    With this proposed labeling system, I think one can get a pretty good idea of what a proposed vessel is about by reading just its label. A john C. Hanna "Tahiti Ketch", for example, might be labeled an "h35/65s" motorsailor. The exact numbers in the label would be subject to individual judgement and interpretation and, therefore, should be thought of as only a general indication of the vessel's type and, more importantly, it's design objectives.

    Just about every boat I would design would be a "century boat", meaning it's label would only add up to only 100. That being said, I certainly wouldn't fault any one for designing hat I might call a "super-century boat". After all, in the end, it's the client, not the designer, who gets to determine a design a success or failure, or whether its design goals are appropriate or not.

    Bob
     
  10. chandler
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    chandler Senior Member

    Is the threat of a rogue wave going to determine design? I can't believe this is a new phenomenon. Every boat should be designed to withstand the seas it can expect to encounter.
     
  11. Tennant
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    Tennant Malcolm Tennant

  12. Milan
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    Milan Senior Member

    One of the major problems of the motor - sailors are costs. "Traditional" motor - sailors types combine heavy displacement hull with the expensive bermudian rig and strong engine. So, result is slow, expensive boat. It can't sail well especially not to windward (what's the point in wasting money installing bermudian rig on the hull which can't sail against the wind any way). Such a boat isn't very good for motoring either. To be economical she have to motor under the speed 'length ratio of 1, (would be about 6 knots for 36 ft LOA hull). Faster then that just digs deeper hole in water wasting a lot of fuel for marginally faster ride.

    Multihulls offer very interesting possibilities but at the high price I'm afraid. If budget isn't limited that's fine, but unfortunately, for most people costs does meters. If one wants economical, (to build, run, and maintain), motor boat or motor sailer, long, narrow nad low mono hull with a minimum windage and wave making resistance, could be the best answer. Such a hull would move with a respectable speed under engine, burning little fuel. There is no need to sail to windward, so no need to use expensive sail rigs of contemporary sailing boats. For the reaching and running, low aspect sail plan actually works better then high aspect. It's also much cheaper. Perfect sail shape is not so critical so you can make your own sails for very little costs. Masts could be solid wood pole, rigging galvanized wire, winches not needed. FIn (fins) could be a lot smaller, enough to give stability against capsize, but with a less drag than sailboat fin. Such a boat of about 15 m LWL and 3 m beam could heave constant cruising speed of about 8 - 10 knots, giving daily mileage of around 200 miles using very litle fuel and being very easy to sail when the wind is wright. That should apeal to the lots of boaters. George Buhler designed his "trollers" more or less along these lines. Sharpii2, for kayak inspired design look at the Wunderberg, for more affordable size Pilgrim.

    http://dieselducks.com/Wunderberg.html
    http://dieselducks.com/Pilgrim.html

    For the people who would like Dashew non - sail boat but can't afford it, have a look at the simpler, traditional similar concept:

    http://dieselducks.com/ellemaid.html

    Milan
     
  13. Guillermo
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    Guillermo Ingeniero Naval

    Vega:
    I find NORDSHIPS and REGINAS could be better classified into something like a "Pilothouse Sailing Cruisers" category, rather than Motorsailers (under my definition), because models I've checked have a D/L under 250 and SA/D well over 15.
    On the other hand, NAUTICATS fall better into my definition, although I find some models overpowered.
    I agree with you on the autoprop point: That kind of propellers are a great convenience to motorsailers, and not only.
    Regards,
    Guillermo.
     
  14. chandler
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    chandler Senior Member

    I think most motor sailor owners appreciate the silence of sailing without the rigors of sailing.
     

  15. Guillermo
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    Guillermo Ingeniero Naval


    Have a look at the very nice Paul Gartside's Motor Sailors: http://www.gartsideboats.com/catsail6.php

    Regards,
    Guillermo.
     
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