Monohull verses Multihull powersailers / motorsailers

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

  1. fcfc

    fcfc Guest

    Unsinkable and self righting

    The TITANIC was unsinkable.

    About self righting boats, I have mixed opinions.
    Probably on the drawing board, such things exists, but in the real life ?

    Having been on *cruise* sailboats in sustained heavy weather, I can speak you of tons of mess you can find on the cabin floor. From sails to toolboxes to nearly everything.

    In case of a roll down, every thing would roll on the lowest point : the cabin roof. And I dont think stability have been computed this way.

    Of course, I expect an openning drawer, a tool or a winch handle not to fall on a window and break it.

    Per my own little experience, up to 45° heel, nothing move in a sailboat. Up to 60°, you become to have some problems with flying objects. over 60° , you will have serious problems inside. I have never gone beyond than spreaders going near the water, but I have seen the mess inside.

    Race boats are of different kind, because there are not so much flying objects inside.
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    FAST FRED Senior Member

    The OCEAN is where the difference in "cruiser racers" and honest offshore cruisers is most visable .

    Not many Cruiser racers have opening ports that will take much abuse , or in the "New " style, of sailing deck cottages with huge glass windows, that could flood the boat in seconds , just from a heavy wave impact.

    Many of the early voyages in small boats were done with simple monohull boats and simple equippment , and not a few survived multiple knockdowns.

    The old saw , Cats for Costal (where you can swim home) and Tris for Trans ocean , is still rational.

    Having sailed thousands of miles in a 45ft Headly Nichol try , yes the Tropics cruising is great !

    But if I were going around the higher latitudes , a "lead slead " would still be first choice if Storm Survival were any concern.

    Some oceans and some storms are far too big to hide from ,

  3. 249

    249 Guest


    The books I've read (I may be wrong) said that the Titanic was never said to be unsinkable until a legend grew up after it sank. The waterproof bulkheads were too low.

    So she could sink, because she was never designed to be unsinkable.

    I used to know a guy, an engineer by profession, who has a 45'ish alloy cruiser, with foam flotation along the hull sides. I can't recall how it's fixed but I certainly can't see it coming undone. There are many videos of Etaps and Sadlers sailing around with the seacocks open.

    So surely there can be an unsinkable boat?

    That's an interesting point about the mess inside cruisers - I've never got a cruiser down too far.
  4. fcfc

    fcfc Guest

    Unsinkable and self righting

    There are boats who are boths. I don't think there is a *single* heavy weahter rescue craft who is not.

    But that comes at a price.

    Unsinkable boats are possible. But that is a complex thing. Flotation is made by foam. The foam must not be too low (say under the floor) because in that case the boat will float inverted. Nor it can be to high (under deck) because the boat will float too low and will barely be liveable. Nor too in front, or too aft (floating like a diving duck may be fun only a few seconds). So maximum of foam have to be where most of the accomodation is if you want your flooded boat floating uprigth, horizontal, with some remaining stability and some liveability.

    One interesting device I once saw where inflatable cylinders under the berths (firmly fixed) . In "normal" operation, they took nearly no place. But inflated with an automatic bootle, (about 2 ft diam, 6 ft length, texture equiv to inflatable boats), they would provide buoyancy at the correct heigth. One would provide about 1000 lbs of lift when fully submerged.
    I don't think they could make unsinkable a boat not designed for, but they could make more liveable a flooded boat floating too low, or not stable enougth, or with pitch.

    Next thing for unsinkable are waterproof bulkeads. Nearly all regulations requires it. (at least one in the forepeak). If water floods your boat, it must not flood ALL. Again, it is not an easy thing to do. How many aft storage can be made waterproof, but are crossed by an exhaust pipe. With of course a big hole in the bulkhead around the pipe to avoid vibrations and heat.
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    FAST FRED Senior Member

    "So surely there can be an unsinkable boat?"

    I presently own a conversion of a 50ft Navy Untilty Launch that is claimed by the mfg (Uniflite) to be both fire retardant and unsinkable.

    There is a band of foam about 2 ft square that runs all round the boat at gunwhale hight.
    The flotation foam takes a huge amount of room , not a problem when an open launch to carry 150 men , but a pain while converting to a costal cruiser.

    The hull is Hetron FR fire retardant resin that has a burn rate of under 100 (wood is also 100)

    Cheap GRP has a burn rate of 500 , and I wonder how Mfg can sell boats for "offshore" with flame throwing resin.

    The difference in resin cost is only 3c a pound , not much on $400,000++++ "Ocean

  6. tarrysailor
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    tarrysailor Junior Member

    Go to Tahiti for fast multihulls

    If you want a fast multihull, I hear you can go to Tahiti. There are plenty abandoned there, or up for sale for pennies on the dollar.

    You know why? Because after sailing many a snazzy, fast, 21st-century-wonder across an actual ocean for a good while, people got tired of losing the fillings in their teeth from the unending jarring. After going through a storm and finding out for themselves what seaworthiness literally means, they dock, leave their ships behind them, get on a jet and fly home, rather than ever set foot on their awesome wonders again.

    There is good reason why traditional designers like Colin Archer put seaworthiness first, comfort second and speed last. Try to tell this to some thrill junkie before he sails, though. Just try. He will tell you in detail all about technology. But after he's come back on a jet, you will never see a person who has so thoroughly turned one-hundred-eighty degrees about-face in his opinions.

    Myself, I would not set foot on a multihull. No more so than I would put a heavy lead helmet on my head, wrap life perservers on my shins and go swimming in the surf. If you ask me, it's the same thing. I've had friends in the Navy onboard aircraft carriers who tell me about the man standing on deck getting washed overboard by a wave, and the deck is sixty feet above water. It's true. A definite cause of accidents in multihulls is pitchpoling. In other words, some idiot is sailing so damn fast that he rams a big wave, pushes his hull under it and flips. If he's close to shore, you hear about it, if not . . . . well, it must be hard to speak to a radio microphone when you and it are underwater.
  7. Ilan Voyager
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    Ilan Voyager Senior Member

    249, almost all the capsizing of multihulls you show are race accidents or with race boats. The offshore power race boats have also a lot of accidents. All race boat driven hard is subject to a have a big problem. For cruising boats is a different problem.

    About the two times I have been in a capsized sailboat there are a lot of similarities:
    -strong winds around 40 knots, and very strong sea with breaking waves (arriving to the coast the change of depth of the sea may induce breaking waves, and if you had a tidal current against the wind it becomes worse).
    -classic 35 feet monohulls of english design around end of sixties-beginning seventies, heavy displacement, deep keel and suffering of the same defect: instability while going downwind, they can make half-turn at any moment even without main sail. In the two cases we were with swedish main sail and the storm jib.
    The two boats were rolled by the waves and went upright very slowly and full of water. After it has been matter of survival and happily in the 2 cases we were young and strong experimented sailors able to cope with such situations.

    Following these experiences I looked to this kind of boats with a lot of suspicion, and I do not share the "american" opinion that heavy classic sailboats are safer. Lightness and speed in hard following seas are the best security.

    Some years later I and a friend (so only 2 guys) have convoyed a former formula 40 catamaran (design Nigel Irens) very lightly modified (in fact just a kitchen and berths) for fast coastal cruising. With just the mainsail with 3 reefs we crossed at a very fast pace the same place of the second knock down (Raz de Sein) with similar conditions of sea and wind (so 35-40 knots winds and breaking waves around 4-5 meters) ; it has been and exhalariting (and very wet) experience of surfing these waves with a total stability and none fear.

    I have recrossed this same place on a 92 meters warship in the same conditions and it was a very shaking experience (but without any danger)... That gives me good comparison points of seaworthiness and I never put the feet again on a monohull sailboat.

    Over 30 feet it's very hard to make a boat unsinkable, specially sailboats with their ballast. All the Etap (the first was the 22 designed by Van Stadt around 1975) are small boats and lose a lot of interior space, but are very safe boats.

    A multihull must be designed with the event of capsize in mind. All issues must be foreseen (strength of the boat, escape hatches, antiskid surfaces, emergency radios etc...I won't detail all) and I can say after trials we made that in a capzised multihull you can organise quietly your survival.

    First it's a relatively stable platform. Second you have plenty of food and water, electrical energy, radio etc... Third you can rise an antena and a radar reflector with a simple kite and send messages of your position. Fourth you can wait in (very) relatively dry and warm place the rescue.

    Those who have spent only 12 hours (for trials) and vomited of seasickness during this time while being burnt by the sun, wetted by the rain and chilled by the wind in a small rubber lifeboat have understood...

    The most convenient boats in this event are the trimarans as the arms and outriggers keep the boat high on the water. The worst are the cats with the big "saloon" over the hulls as this disgracious appendice is immediatelly flooded.

    The self righting powerboat is an horrible roller (it's getting better with the dynamic stabilizig devices) and I've always admired the very strong stomach of the courageous sailors jumping in the rescue boat after a good diner to save lifes in a force nine gale. A self righting power boat for cruising must be a nightmare.

    Personnally; power or sail trimaran well thought. These boats have the best combination of seaworthiness and dynamic and static safety.

    I agree with you that finally is splitting hairs and the best safety device whatever the boat is a conservative attitude with good marine forecasts. If you have not good forecasts make your best guess.

    After it's matter of fate and/or God's will depending of your religion and life's philosophy. We will all face death, and I share the opinion of late Tabarly : drowned is preferable to cancer. He has been lucky. I hope to have the same luck.
  8. Ilan Voyager
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    Ilan Voyager Senior Member

    I know pretty well the Colin Archers as one of my professors was Michel Presles (naval architect who designed a lot of Archers) in the Arts et Metiers school of engineering at Paris.

    I've met some people who had Archer type boats similar to the Johua of late Moitessier made by the shipyard Meta. Heavy, slow and often frightening in hard following seas. Read Mrs Smeeton book...

    If you reread Moitessier or Vito Dumas (who made around the world by the roaring forties in 1943 on Legh II designed by Manuel Campos, great naval architect of Colin Archer boats) you understand immediately that they were in survival situation (Moitesser with sea anchors etc...) where now guys are racing not surviving on monohulls or multihulls, and a lot cruising to the Antartic.

    Archer (circa 1900) work is very respectable but now obsolete, d'Arcier (1763) works on mathematical hulls of warships is extraordinary and totally obsolete. A Ford T is a great piece of engineering but the Ford Ranger is far better. I can give hundreds of examples.

    Boat design has evolved a lot in all its domains as I've seen myself as naval engineer and I'm always surprised that for sailing boats a lot of people are stuck to antiquated boats. I understand that someone prefers a Chapelle or Herreshof sailboat because of aesthetics but I do not understand when anyone tries to convince me that are a better boats, safer and so on.

    Compare the possibilities of Gypsy Moth IV (16.5m Laurent Giles design for Chichester who had very hard times with this boat) with a modern 50 feet cruiser. No match in speed, strength and seaworthiness.

    In reality Tahiti is full of multis and monos for sale simply because is the final destination of a lot of guys running after a dream of paradisiac lazy life in the tropics. And the dream paradise, no money, no easy job, but boriness followed by alcohol and drugs. We see this kind of guys also here in Mexico, and Belize is full of them.

    I've seen a lot of bad sailors who call mommy with a 25 knots wind even with the best boat as some will be always bad drivers even with a Mercedes at 100 km/h. And there are some bad boats of any kind.

    About seaworthiness of multihulls ask to Mike Birch how he slept quietly and read books in Third Turtle (trimaran 9.15m, 1000 kg only, design Dick Newick) waiting the end of a force 10 storm during the 1976 OSTAR.

    You can go also to Cabo Verde islands to make a passage on Ilan Voyager, or go to Buenos Aire to take the ferry catamaran Juan Patrico for crossing the Rio de Plata at 55 knots with a good pampero of 30 knots blowing.

    I'm old enough to have sailed traditionnal and modern boats, monohulls and multis, racing and cruising in a great variety of conditions so I have a first hand opinion by myself. Well designed after 1985 multis are my choice.

    Boats, ships, warships, carriers, ferries and others have changed and a lot.
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    D'ARTOIS Senior Member


    Reading the discussion mono/vs multi, it's like everything a matter of taste.
    I bought my first 40' sailingboat way back in '80 - a well known Dutch design from Frans Maas, fast & reliable.
    I sailed this boat alone, going to the Dutch Island, England, France till Hebrids and Iceland.
    The general speed I got was something between 7 and 8 knots. Nothing exiting,
    so I became smitten with the designs of Lock Crowther, I bought his book and started dreaming....

    I have had some more boats in between, I have been at many shipyards since, Jongert, Huisman, Abeking and Rasmussen, CNB and many others.
    I have seen famous names to be built - when Von Karajan, the famous German conductor came to launch his new Helisara V, his dolly for the moment stepped with her high heels through the nomex flooring panels (nobody dared to tell her to take her shoes off)- many years later I saw the boat back and not in the best state, the same thing happened with the ex-Flyer from Conny van Rietschoten, I saw her being built and many years later she came into hand of a Dutch broker, so I had an chance to look at her again. My tastes clearly had changed, since I found nothing exceptional at her, looking after so many years again.
    I have now a 100" schooner, an ex-trawler type navyvessel, converted to live aboard floating home annex entirely autonomous pied a terre.
    The powerful new rig by Rondal gives this 100 tons Lady a speed of 8 - 11
    knots, the latter in a stiff breeze. The engine gives sufficient power for 9/10
    knots. Now I don't dream anymore. I can go in reasonable comfort wherever I want to go. With a draft of just 10' I cannot enter too small harbours, but I can always stay outside because, built as a reconaissance vessel, she is strong and can ride out a good swell. I sail her very shorthanded, with just one crew.
    I still like fast ships. I try to follow latest design-topics but my dreaming period is definately over......
  10. Ilan Voyager
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    Ilan Voyager Senior Member

    Mr d'Artois (are you of french huguenot descendance from those who emigrated to Holland because of the persecutions by Louis XIV in the 17th century?) I agree totally with you: the good boat is the boat you like and which fits to your program and needs. It's a matter of personal taste.

    And happily the choice is vaste, so we can (besides money issues) take the kind of boat which incarnates our ideas and dreams.

    But the objective facts remain; there is no comparison between of a 1960 and a 2004 cruising sail boat in matter of materials, hardware, comfort, seaworthiness and speed. Simply evolution as it happened in all domains involving technics from washing machines to rockets.

    I've seen also the boats you evoke...the drama of these racers is they were built for the jauge of the moment (RORC, SORC, IOR, and so on) so they have not future as good cruising boats; a retrofit is too expensive for no guaranteed results. A hull designed for a jauge is generally very far from being the all around best boat, it's often a "slow" boat as we could see while making amical regatta against IOR boats with out of jauge sailboats.

    Also these last 30 years the evolution of naval design has been so improved in all domains that a lot of boats became obsolete and will end in the junkyard if someone does not fall in love with them. And I predict that the evolution will be atonishing. It'll take some time as boats are expensive and long life objects at difference with short life objects as cars.

    While reading Slocum it seems that the Spray was a perfect boat for him, and now who would make a circumnavigation with a Spray replica? Nothing is permanent.
  11. sharpii2
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    sharpii2 Senior Member


    Hi Everybody

    I thought I would just share a little thought experiment that I did a few years ago.

    I have been working on this design concept for years. Its called a 'lola boat'. It is supposed to be the simplest and the cheapest thing I would ever go to sea in. Its basicly a cylandric developed double ender with a moderate 1 to 2 dead rise which makes up most of its bottom. It is propelled by a single ballanced lug rig. It was supposed to be 20ft (6.15m) long by 5ft (1.54m) wide. It was supposed to displace around 3000lbs (1364kg), and have a SA of about 180sft (17sm). In my preliminary thinking, I figured one third displacement for the hull and rig, one third for ballast, and one third for me and my stuff. It was not to have an external ballast keel and the ballast was to be cheap and removable. I originally thought of water ballast (whats cheaper than that). It looked realy good on graph paper.
    Then I did th math.

    I found the water ballast would not work. I would need too much of it (1400lbs). I also found that the rig was too much. It got trimed. first to 160sft (15.2sm) then, finally, to 140sft (13.3sm). For ballast, I ended up with sand (still pretty cheap) and about 800lbs of it. This all started comming together. The boat displacement got trimmed down to around 2800lbs (1273kg) and I ended up with something that could right itself from a 140 deg. knockdown. But it was going to be ...a...slow...boat...
    My guess is that it might make 5kts in ideal conditions. Mostly, though, 3kts was what was more to be expected. This would mean 72mile days and more likely 50mile days.

    Then one day I got an idea. What if I threw all the sand overboard and replaced it with a set of outrigger floats? This of course, would mean crossbeams as well. I guessed that this entire rig may weigh around 300lbs (136kg). Each float would displace around 1000lbs (455kg) when fully submerged. To keep this from becomming too rediculous, I decided to limit the beam to 10ft (3.08m). Not a very good tri, some may say. But I thought about it. 1000lbs at 4.5ft from the centerline = 4500ft/lbs of max righting moment. About 1600 was the best I could get with the sand bags. I could, perhaps, get my 180sft (17sm) sail back. Maybe even go to 200sft (19sm). And I could carry all this in a pretty good breeze. And the boat would be at least 400lbs (182kg) lighter. Maybe it could get 6, maybe 7kts top speed ( relatively beamy center hull would probably preclude higher speeds). And maybe make it to 100 mile days.

    I thought about stability. How hard would this be to capsize?
    I thought about it. In order to roll this boat over, you would have to imerse the lee foat, its two crossbeams, and the 18 inch wide side deck and roll them completely under the main hull. These items, in my opinion, would present an awful lot of dampening force so, it would take quite a sustained breaker to do the job. And since this boat won't have any deep keels or deep fins (it will have two long, shallow, bilge fins), it may dissipate much of the energy by moving sidways. Not only that, but because the main hull is wider than usual (twice as wide as typical in pure tri's) much of my stuff, that used to sit on top of the sand, (remember the sand) would find itself sitting lowerer in the bilge. My guess is the VCG would be raised by about 12 inches to end up about 1.5ft above the water line. This is because the 800lbs of sand have been removed (replaced with 320lbs of FW and about 200lbs of batteries) and the heavy crossbeams and floats have been added (all much above the WL).

    Still. Rolling it in its new configuration compared to its old one would be like rolling a Mercury Town Car as opposed to a Ford Explorer. It can happen and (with terrible luck) it will happen. But this boat was never designed to live on the edge. Carrying a lot of sail in really strong winds would not be attractive because after reaching about 7kts it probably would go no faster anyway. Also, because the main hull will always bear most of the boats displacement, I see pitchpoling (another favorite method of multi capsize) being far less likely.

    An interesting idea, eh? A low performance (and much lower cost) multi.

    Its interesting to note that Captain Cooke observed more than two hundred years ago that the native craft (ouriggers and double canoes that he encountered) were half again as fast as western boats of the same size. And its (even with todays astounding technology) still true today. (The monos go nearly as fast as the multis used to but multis go about half again faster still).

  12. Bob Leask
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    Bob Leask Junior Member


    I'm working on a design concept that might seem a bit eccentric, but here's how the idea germinated:

    I just finished a circumnavigation in a 37' traditional double ender of my own design, but to say that I sailed around the world is to use the word "sailed" a bit loosely. She's a heavy boat, around 30,000 lbs, and when the wind is 15 knots or better she'll make good time, my best 24 hour mileage was a little over 150 and in good sailing conditions I averaged about 125. But when I did a review of my logbook and estimated how many days I had such conditions, I came up with a rough estimate of about 25%. And that's optimistic. I did more or less standard trade wind westabout passages at the right times and latitudes and found that the pilot charts can be very misleading. The pilot charts give average wind strength and direction compiled from observations of deep sea vessels over long periods of time, but the figure they give for probability of calm is way off, from a cruising sailors point of view. If the observer saw any ripple at all on the water, the report would have been Beaufort 1, but anything less than Beaufort 4 for all practical purposes is flat calm, if you're trying to sail in a heavy displacement boat. All full time liveaboard/cruising boats less than 45 feet overall should be considered heavy displacement. If they aren't before you moved aboard, they will be by the time you've moved everything you own onto them, including fuel, water, food, stores, spare parts, tools, books, souvenirs etc. etc.

    Having voyaged over 30,000 miles I have come to the conclusion that idyllic trade wind sailing with steady winds of 15 to 25 knots for 24 hours is a dream, or a myth made up by writers of cruising stories. I've never experienced a single day like that, anywhere.

    However I found out early on, in the calms that prevail on the west coast of the mid-latitude Americas, that low speed motoring is a very good way to make passages in flat calms. Motorsailing is by far the easiest and safest way to cope with highly variable conditions, when the wind is constantly varying from near calm to 25 knots and back again cyclically, which is common. In my experience trade winds were always variable to some extent.

    The days when I had my best passages were not the most pleasant. To make an average speed of near 6 knots meant that some of the time I was overcanvassed and overdriven, which can be exhausting and uncomfortable. It's hard to relax when the boat is heeling and rolling heavily, and at any moment you might have to take in a reef if the wind increases any more. To get into passagemaking and seamanship is too big a subject so I'll leave that now, but just summarize by saying that relying entirely on sail to cross oceans is not as easy as many might think, or hope, or want to believe.

    Early in my voyage I found out that my boat would motor at four knots and burn 1 liter of diesel per hour in flat water. That means 96 miles in 24 hours which is quite an acceptable rate for ocean passagemaking and when you can buy fuel in places where it's cheaper, such as latin america or southeast asia, the cost per mile is very reasonable. When I was in Indonesia the price of diesel fuel was less than 15 cents US per liter. Of course I can throttle up and go faster, but fuel consumption goes up exponentially. At my top speed of 7 knots the consumption is about 3.5/hour, roughly 1 US gallon.

    Here is some very simple math: to go around the world (about 30,000 miles) divided by 4 knots would have cost me a total fuel consumption of 7,500 liters. At the current high prices today of about 60 cents US per liter the voyage would have cost me a total of $4,500 dollars in fuel. Add to that a guesstimate of $1500 for oil and filters etc. and we have a grand total of $6,000. Think you can set up a sailing rig for that price? And you can spend plenty on all the bells and whistles to gain more sailing efficiency, and add to that the cost of larger battery banks and solar and wind charging systems, to cope with electrical requirements when under pure sail for long periods.

    And another hidden cost of offshore sailing: the heavy wear and tear on sails and rigging while trying to sail in very light and variable conditions. One day of flogging your sails in light air and a swell running, quite a normal experience at sea, probably shortens their life more than weeks of hard sailing. When you have lots of wind the sails stay full and are under a constant load, but they aren't wearing much, and the same goes for your standing rigging. When you hear about dismastings at sea they almost always happen in light and variable conditions. When you do the simple math, you can't avoid the conclusion that from a purely economic point of view, it's unlikely that sail propulsion can ever come close to the cost effectiveness of an efficient diesel. Flogging that expensive sailing gear to bits to go very slowly makes no sense at all. The miles I sailed cost me a lot more than the miles I motored, probably by a factor of 3 to 1. By the time I got home all my sails were totally worn out. My engine is still going strong.

    Here's a broadside at the sailing purists: those who haven't lived among the offshore cruising community might be amazed at how often they are sailing "dark ships", with no navigation lights at all, to conserve battery power. A totally idiotic practice but it's shocking how often it's done.

    The sailing purists have already clicked out, those still interested in where I'm going are now thinking that I haven't considered engine breakdowns and rebuilds. I have a simple answer for that, it's a single word: Sabb. After the thousands of hours I've put on my Sabb 30 horse engine from Norway it's running exactly the same as it did when I got it, secondhand. I'm pretty sure that it'll still be running long after I wear out. It may outlast my boat, too. Low speed diesels like the Sabb are designed to run efficiently at low rpms and you can idle them for long periods without damage, unlike modern high speed engines. The bearing surfaces are so large that at such low speeds the wear on them is practically nil. I'm willing to bet that my Sabb would do another circumnavigation without major trouble, just the way it is.

    The high efficiency is for several reasons: One is that I don't have a heat exchanger. I used a Walters keel cooler and dry exhaust which saves much of the energy wasted by running in effect two cooling systems. The low rpm engine design is another, as is the controllable pitch two blade propeller which comes standard with the Sabb 2J. It has a large diameter and is always optimally pitched. And I have no doubt the efficiency could be improved. But it definitely beats any other sailing auxiliary diesel I've heard of so far, by a wide margin.

    Another observation of mine was how much fuel cruising sailors actually do use. When I admit that I motored or motorsailed approximately 50% of the way around the world, I'm simply using the records of my log book. What I am quite sure of is that I used less fuel than the average cruising "sailor". Almost every other cruiser I met in harbour after a long passage had used nearly all their fuel, and most of them carried more than I did, my own fuel capacity being only 210 liters. I would say that on average, those claiming to be "sailors" were using more fuel on passage than I was. The reason for that is that the average sailing auxiliary yacht built these days is abysmally inefficient for motoring. Too small propellers, badly designed propeller apertures, high rpm engines that are inefficient at low speeds, and wasteful heat exchanger/wet exhaust systems are to blame. All of those things are done for the sake of incremental improvements in sailing performance. Fuel efficiency is simply not part of the equation in the design of modern crusing boats.

    Motorsailing offshore is by far the most pleasant way to make passage, most of the time. With the engine barely above idle and a moderate amount of sail set, there is a synergy created by the apparent wind which generates more forward thrust than either one alone, with the bonus that you don't have to set large areas of canvas, which will have to come down in a hurry if the wind increases. The boat rides better, makes a better average speed and the batteries are always full. The beneft of using a much smaller sailplan can only be appreciated by someone who's been caught offguard in a squall with too much sail up. "Adventures" like that might be fun for weekend sailors and short coastal passagemakers, but on a long ocean passage they're something to avoid, even if it means a slower passage.

    Now that I've made my case for the motorsailing offshore cruiser, I'll describe my design which is a work in progress. For a lot of reasons I've chosen a catamaran as the best overall type for long range cruising and living aboard. My main reasons are shallow draft, beachability, visibility from the bridge deck salon and ample deck space. Even the slowest cruising multihulls generally beat monohulls on passage times. However I view that as a bonus, not a primary design objective. With my slow boat I spent about a week in harbour for every day I spent at sea. When you're wandering around the world on a boat, speed is simply not an important issue. Comfort, liveablility, economy and versatility are the things that matter most to a liveaboard/cruiser. If you can have those qualities and go faster too, that's great.

    And now I'm finally coming to the point. After much time spent browsing the offerings of boatbuilders and designers around the world, I've found nothing, zero, zipola about achieving maximum fuel efficiency per mile, with mono or multihull boats. Where fuel consumption graphs can be found, most of them start at five or six knots. It seems that there is not a single professional boat designer working today who is interested in designing boats to be used in the real world, the way offshore cruisers actually use them. The main design objectives are speed speed and more speed, and anything less than 3 gallons an hour is touted as "economical".

    There are a lot of designs I like, in particular at:, but in this case information is lacking as to actual fuel consumption rate, displacement and payload, and fuel capacity. Can such a motorsailing cat carry enough fuel to make a 2000 mile passage? Is the fuel efficiency only relative, compared with other boats at the same speed? In the real world when you might have to motor on one engine at a minimal speed to stretch your fuel out over a long passage, does the efficiency still apply, or is it better/worse than the average cruising monohull?

    In terms of optimal fuel economy per mile for monohulls and multihulls of the same displacement, monohulls have a theoretical advantage. Going strictly by experience because so little data seems to be available on the subject, I believe the most economical speed for a yacht is at around 50% of hull speed where wave making resistance is not important and skin friction will be the major factor, but optimal speed will depend on whether or not the propulsion system is designed to operate at a low power output efficiently, and that for me is one of the most crucial things for a good offshore cruiser, but does not seem to be considered at all in the modern world of boat design. Why not? A little more simple math will tell you that even if you don't mind the cost, it just isn't possible to carry enough fuel for long motorsailing passages in a boat of 40 feet or less, especially a multihull, if your consumption is over a liter or two per hour. You simply can't carry enough fuel to go the distance.

    Which brings me finall to the concept that I've settled on: a catamaran with three engines. Two will be outboard motors mounted on the sterns of each hull. The third will be a small, low speed diesel, preferably air cooled, on the centerline housed in a pod. I expect to pay a penalty in wetted surface higher than a monohull of the same displacement, offset by the fact that a multihull can be a bigger boat with less displacement, which I hope should work out approximately equal. The outboard motors will be lighter weight and cheaper to install, and will provide higher power when high speed is wanted, albeit at a much higher fuel consumption. The high redundancy factor in this design will add to safety, with enough power to get out of bad situations like dragging anchor in a confined area. Outboard motors won't have the service life of inboard diesels but will probably not be used very often, almost never offshore. They're easily serviced or replaced, and it would be possible to carry spares onboard. New ones are available anywhere.

    My most basic question now is what would be the best combination of engine and drive? The belt drive system described on makes a lot of sense, it would virtually eliminate mechanical loss. The best option of all might be a direct drive or longtail system, if the problems of installation on the centerline are solvable. There are some very good gensets on the market that might be easily adaptable to a direct drive with a chain or belt reduction, and voila, you've got an economical auxiliary and a genset all in one, that will work fine while you're beached, too. Yet another option would be installing a genset wherever it pleases you, and using an electric motor for propulsion. That's also a nifty idea, because a fixed magnet electric motor will also serve as a very good water generator while you're sailing. Lots of electric power at all times while underway, eliminating the need for elaborate and expensive solar/wind power systems. And no limit to propeller diameter with either system. Either way it could be made to easily retract out of the water and with the outboards retracted up as well, no propeller drag while sailing at high speeds.

    Has anybody here been thinking along the same lines, or know of anybody who's done anything similar, or have any ideas? I know the idea of a multihull that isn't designed to be a seagoing hot rod is a little radical, but after weighing the pros and cons of every other idea I've thought of, it seems the best one. A monohull designed for low speed economy might be the absolute best motorsailer for long passages, but could not have as shallow a draft as a cat. Shallow draft and beachability are my main design criteria, a little time in the third world with a boat that requires a travelift to haul out will teach you why.

    1 person likes this.
  13. Mark Peiffer
    Joined: Sep 2003
    Posts: 14
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    Location: Colorado

    Mark Peiffer Boat dreamer

    Could'nt agree more

    I too have come to many of the same conclusions. In much the same way - though without the experience I just dream alot. In terms of the motors the need to make speed to avoid a blow is a consideration. Multihulls are faster and could make good use of speed if your anchorage is not to far away. I understand that a cat actually can move well on only one engine - But I prefer the tri design as well. I think the electric would be too ineffecient and I would stear clear of a system that is not widely used ( belt) as parts would not be available. I think a pod on a central position that could be withdrawn might be the best option. I think inboards are often made into outboards in the philipines ( there
    is a thread in this regard.) Perhaps the Z drive that began this thread might be a reasonable alternative. I would like two have the largest prop spinning in the least disturbed water. But mechanicly the angled drive shaft with a universal terminating joint would be the simplest and most effecient. I wonder if this could be mounted in a housing and rotated with the entire pod, like a large outboard. We often use sliding splined shafts - perhaps one above the water line could be detatched and the entire motor would not have to be tilted.
    In addition where would you put the exhaust? Would it make for better motosailing if the exhaust was sent up an elevated stack, perhaps within a mast or radar pylon ?
    Thanks for letting me dream along with real sailors - Mark
  14. sharpii2
    Joined: May 2004
    Posts: 2,092
    Likes: 231, Points: 63, Legacy Rep: 611
    Location: Michigan, USA

    sharpii2 Senior Member

    21st century motorsailor?

    Hi Bob

    I really liked your post. This is a problem I've been working on since the late '70's. It was at that time that my dad told me about some guys he knew that liked to canoe on some Northern Michigan lakes. The canoe worked out good except when the lake breazed up (at about 20 kts or more). Then it was a desperate struggle to make any headway at all against the wind.
    Their solution, of course, was an out board.It had several problems though. First, the engine wasn't light (for a 1 mile portage). Second, it needed fuel (which also had to be portaged) And third, it got in the way to such an extent that it was just simpler to bolt the damned thing to the transom and motor all the time.
    My dad wanted to know if I could come up with an alternative.
    When I thought about it for a while, I realized that what was needed was a small sailing rig that could sail up wind in a good breeze. In anything less, the paddles would most certainly be used either in conjunction or instead of the sail.
    I thought that a rig of maybe 30sft or less would do the trick. Such a cut down rig would be reasonably light, easy to stow, and very easy to work. All it needed was some sort of leeway preventer. I thought of a leeboard or maybe even one of the paddles. The hope was that the entire rig would could go with the canoe during a portage. That would save these ilustrious adventurers one trip for each portage which would add up quick.
    The idea never came to anything. I was too young (still in highschool) and I knew nothing about how to engineer it. Stepping a mast in a boat without a mast step proved to be a bit too much for me at the time (I have since seen how it can be done) and these two men lives took on differnt tacks anyway. However, the idea of a boat with a small but real (capable of going up wind) rig stayed with me. When at THE LANDING SCHOOL OF BOAT BUILDING AND DESIGN, I drew two sailboats. One was what I called my 'Mackinaw Boat'. It's purpose was to be able to make the trip from Port Huron to Mackinaw and back in under a week in all but the very worst conditions. It had an average mast head sail rig, a powerful (36 hp) deisel, and an inefficient folding prop. The 35 footer also had a long fin keel and had a beam of only 9 ft. The hope was to be able to push it at hull speed continueously, so half the average two week vacation could be used for sight seeing and half could be used for the voyaging itself.
    The second boat was to be an ocean going craft for a live aboard. It was just as long as the first one, half again as heavy, and with a diesel with one third as much power. It was, however, to have a three bladed feathering prop intended for much greater efficiency. It was supposed to push the 27ft WL boat at about 4kts, but have some reserve for when things got hairy (sails were expected to be used in survival situations such as beating off a lee shore). The hope was to get good fuel economy during those looong periods of calms and to despense with inventories of light air sails (more room for my stuff). Though serviceable, it was not a good design. The raised deck cleared the boom by a mere 18 inches making it necessary to 'work it from below' and the cockpit was a mere foot well. I jokingly called it a 27 footer crammed into 35 feet.
    A present project is a 12ft scow with a 48sft rig along with short sweeps to propel it through calms. The lake it is intended to sail on has either dead calm or wind shot out of a cannon.
    As for your proposed design, I would suggest that you forget about the outboards and invest their weight ration on better ground tackle. The reason I say this is because it has been my experience that engines don't like long periods of non use (especially in salt water conditons). And you may very well find yourself with one or both of them concked out when you need them most.
    At another thread 'Concept Catamaran Project' A man named Duane is working on a boat that is very similar to your ideas. I keep adding my two cents. why don't you join the fun. A man with your experience could be most helpful.


  15. brian eiland
    Joined: Jun 2002
    Posts: 4,964
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    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    MotorSailing Synergy, Alt CB's, Single Engine

    I was making this same point in my #3 posting above in this thread, "In light airs, running one engine often is all that is needed to bring the apparent wind forward to make the sails work harder, and the combination provides much better results than either motoring or sailing alone…… sailing synergy/harmony, the motor taking over in the lulls and the rig taking over in the puffs"

    And take note from that same posting, "Optional nacelle-mounted centerboard precludes any extra hull penetrations, and permits maintenance without hauling-out."

    I'll come back to a few of your other questions a bit later, but meanwhile I'll post this portion of a previous thread I tried starting with no results. It considers a centerboard mounting that is above the waterline (easy maintanence and repairability without hauling), and a single 'cockpit mounted' engine with steerable outdrive....and the relatively small HP you are considering would be easily compatable with the industrial belts I site.
    "One item of your thought processes caught my attention in particular; your desire for a single centerboard, and real shallow draft capabilities. I'll certainly second that motion, that shallow draft idea. One of the greatest attributes of multihulls is their capability to really go exploring ALL the water areas including those tributaries, lagoons, reefs, etc. That's why I had kick-up CB's in each hull of my design.

    BUT, what you may not have noticed was my alternative to the CB's in each hull. Look at the attached drawing, (or the very bottom profile drwg that denotes "asymmetrical CB's, nacelle mounted". First, imagine a flat plate, on edge, mounted down the centerline on the underside of the bridge deck. This flat plate will act as a rib to strengthen the fore-to-aft rigidity of the vessel, a somewhat weaker characteristic in a catamaran structure vs. a keeled monohull. If a tow bundle (rope, etc) of carbon fiber (kevlar, PBO, etc) was laid along the bottom edge of this flat plate, the rigidity could be even greater (sort of akin to a bottom truss structure, or a flange of an 'I' beam). Now on either side of this flat plate I propose to mount a centerboard, not a single, symmetrical one, but rather two asymmetrical ones; sort of like a single board split in half. The flat sides of these asymmetric boards would fit up against the flat plate nacelle, and rotate on oversize (possibly 1-foot) diameter bearings. The flat fit & big bearings would together supply a great big surface for the large bending moments to bear against. Only one board at a time would be lowered. In fact the two could be linked together such that the act of lifting one automatically lowers (& powers) the other down. And they both could be rigged to 'kick up' upon hitting any solid object and/or for shallow cruising. The control lines (cables) could be routed right up to the cabin top and back to the cockpit.

    There are several advantages to an asymmetrical shaped centerboard. First, it requires less total board area to develop a leeway reducing the board size is reduced. Secondly, since it is asymmetrical, it does not require an angle of attack (does not require the boat itself to be sailed at a skewed angle) to develop the 'board's lift' (leeway reducing force). This actually
    may result in the vessel making less leeway. Plus the drag forces associated with the CB lift forces are on the centerline of the vessel, rather than off in one hull that produces turning moments about the center of the vessel.

    This centerline mounting may also improve the tacking capabilities of the vessel as it allows the 'clean' hulls to slip a little while pivoting about the central board.

    The front of this nacelle/plate could be configured to act as a wave splitter to actually attack, up front, the formation of those peaky waves under the tramp areas that eventually slap at our bridge deck underside. We kind of slice those waves down a bit. A lightweight fairing might also be added to this 'flat plate nacelle' so it appears outwardly much more esthetically pleasing, as well as more curvature to shed those peaky waves.

    And how about the maintenance factor, particularly in remote cruising areas. No need to haul-out the vessel to repair kick-up CB problems, or even bottom painting problems. Everything, including the cables, bearings, and boards is all above the load waterline. The initial building cost should be less by eliminating the trunks in two hulls, and the watertight integrity is much
    better. The twin boards might have to be made a little bit longer as they operate with a 'free-surface' end, but then they are asymmetric so they can be correspondingly shorter. I would further suggest that surplus helicopter blades are prime candidate sources for both CB blades and rudder blades....high tech, extremely strong carbon fiber fabrications that have a
    prescribed limited life span aboard aircraft, but are perfectly happy for our use.

    For rudder designs I would give a cassette system such as the Vara rudder a close look in lieu of a kick-up system. Or maybe even Tony Smith's Gemini cat system. Kick-up rudder systems can get pretty complicated, plus they usually don't steer the boat very well at all when they are kicked up in shallow water. (LOTS of weather helm).

    If I were looking to use my auxiliary engine in a strictly aux manner, rather than in a motor/sailing demand, I would seriously consider a single engine installation. This engine would be conveniently mounted in an enclosure on the cockpit deck and would belt drive a steerable out-drive leg that would be incorporated into the rear portion of the central nacelle structure. Maybe this rear nacelle might appear as on "Earthling's pod" (attached photo and/or This saves the cost and weight of the second engine, trans, shafting, prop, etc, and opens up the rears of the hullsfor a nice master bath, or whatever."
    Last edited: Jan 6, 2005
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