A LIVEABOARD CRUISER FOR THE REAL WORLD
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:
Motor/Sailer Design Expedition Yacht http://www.runningtideyachts.com/motorsailing/, 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
Motor/Sailer Design Expedition Yacht http://www.runningtideyachts.com/motorsailing/ 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.
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