CHOOSING AN AFFORDABLE OFFSHORE CRUISING BOAT
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I'm in a hurry, show me the list of cheap cruisers !
The April 1998 issue of CRUISING WORLD contained an article I wrote titled Crunching Numbers For A Quality Cruiser. In it I presented a process that used fuzzy logic and a data base to select boats with characteristics suitable for offshore cruising. The process sorted out ninety boats that were CLOSE to the fuzzy logic template, and these were listed in a "Best Cruisers" list. The response from readers was very positive, and I would like to thank the many people who took the time to comment, ask questions, and suggest additional boats. Due to this participation, the data base has doubled in size, and now contains over 1100 monohull sail boats. I have also made several improvements to the selection process, including more emphasis on dynamic characteristics and the inclusion of retail prices. With this new price information, it is possible to identify potential bargains in offshore cruisers. Of course many other factors are important in selecting a cruising boat, like passing the survey, but looking at boats that are on the Best Cruisers list and within your price range, is a good place to start.
The Fuzzy Logic process allows boats to be scored on "how close" they come to the optimal values applied to a set of evaluation parameters. To make the Best Cruisers list, a boat must score greater than zero on all the parameters. Miss one, your out. These parameters (see EQUATIONS) include the traditional Disp / LWL and Sail Area / Disp ratios, as well as well as less known ones like Comfort Factor, Capsize Risk,.and Vmax / Vhull. The latest version includes the LOA / BEAM ratio, and a term called Max Acceleration. The Max Acceleration term is particularly interesting in that it introduces dynamic factors such as roll period and the moment of inertia into the evaluation. The acceleration level that the crew experiences as a boat rolls is especially important for safe offshore cruising. Prolonged exposure to high levels of acceleration can promote fatigue through sleep deprivation, which leads to mistakes and accidents. Adding these additional parameters makes the selection process more discriminating, and increases confidence that the selected boats are truly unique.
Once the evaluation parameters have been chosen, the optimal values for these parameters can be selected. In the original article I used my own "best judgement" for selecting the optimum values for the fuzzy logic variables, which was a somewhat subjective process. At the suggestion of my internet friend, Jim Manzari, I modified the way the optimum values are selected, and now calculate them directly from the work of nine well respected cruising boat designers. Average values for each of the seven fuzzy variables are calculated for each designers work, covering a total of 131 boats. The Optimal Value is then calculated by taking the average over all the designers. Figure 1 shows the results of this process
DESIGNER |
S/D |
D/L |
CF |
CR |
Vm/Vh |
L/B |
ACCEL |
ALBERG |
15.94 |
365 |
30.9 |
1.68 |
1.08 |
3.35 |
.055 |
ALDEN |
16.69 |
323 |
41.1 |
1.59 |
1.07 |
3.71 |
.050 |
CREALOCK |
15.71 |
342 |
38.3 |
1.61 |
1.06 |
3.40 |
.049 |
BREWER |
16.13 |
270 |
34.0 |
1.68 |
1.07 |
3.34 |
.065 |
HESS |
15.90 |
320 |
34.2 |
1.60 |
1.07 |
3.34 |
.048 |
HOOD |
15.38 |
335 |
43.5 |
1.59 |
1.03 |
3.49 |
.049 |
MASON |
16.53 |
349 |
41.8 |
1.62 |
1.06 |
3.51 |
.049 |
PAINE |
17.16 |
247 |
33.3 |
1.72 |
1.08 |
3.39 |
.075 |
PERRY |
16.64 |
262 |
35.6 |
1.70 |
1.07 |
3.33 |
.069 |
Optimal Value | 16.24 |
313 |
37.0 |
1.64 |
1.06 |
3.43 |
.057 |
FIG. 1 OPTIMAL VALUES
Figure 2 shows the current and past values for the Fuzzy Variables, along with the average from the entire data base.
FUZZY VARIABLE | NEWEST VERSION |
APRIL 98 VERSION |
AVERAGE OF DATA BASE |
S/D |
16.24 |
16 |
18.8 |
D/L |
313 |
300 |
236 |
CF |
37.0 |
35 |
29 |
CR |
1.64 |
1.8 |
1.82 |
Vm/Vh |
1.06 |
1.07 |
1.11 |
L/B |
3.43 |
Not used |
3.34 |
ACCELERATION |
.057 |
Not used |
.12 |
FIG. 2 COMPARISON OF OPTIMAL VALUES
Fortunately, the new optimal values did not change all that much, but its reassuring that the ones used now are mathematically linked to the actual work of nine well known yacht designers. Its interesting to compare these cruising boat values with the averages over the entire database. Cruising boat designs show a definite trend away from the average boat, with less sail area, more weight, higher comfort factor, lower capsize risk, and half as much acceleration. My interpretation of this data is that it shows that most of today’s boats are designed for high performance and coastal cruising. These are not "bad" designs, they simple reflect what the majority of today’s buyers consider important. It does point out, however, the need for cruising boat purchasers to understand these fundamental differences so that they can make informed decisions based on how they intend to use the boat.
Once the optimal values have been selected, an acceptable region around each (called a HEDGE in fuzzy logic) is calculated. I use the "standard deviation" of each variable ( a term that statistically measures the spread in data) to set the acceptable range for each of three hedges, VERY CLOSE, CLOSE, and SOMEWHAT CLOSE. Using the VERY CLOSE hedge returned only three boats. Going to the CLOSE hedge increased that number to 59, and using the SOMEWHAT CLOSE hedge returned a total of 164 boats, the latter being the hedge level used in this article. Boats in the Best Cruisers list were first scored together, then broken down into length categories. The individual scores are not listed. All the boats are approximately equal, and fully compatible with our best cruisers template.
For the most part, the Best Cruisers list has not changed a great deal, which is reassuring, but many of the smaller boats, like the Catalina 27 and Allegra 25 were eliminated, due to low comfort factor or high acceleration. The comfort factor is closely related to the roll period, as is acceleration, and the smaller boats just don’t have enough weight. For the gentle motions characteristic of a comfortable cruising boat, big is always better. The 164 boats listed are only a few boats more then the 154 found in the previous article, even though the size of the data base has more than doubled. This infers that only a relatively small number of cruising boat designs are needed to satisfy today’s market. Only a few builders target the cruising boat market, since these are low production rate, labor extensive products, with extremely high prices.
The used boat market is the only alternative for many buyers, and quite a few older cruising boats are available, some at bargain prices. Price information is not in my data base due to its changing nature, but realistically it is an extremely important factor in selecting a cruising boat. With some help from Charlotte Schmidt (a local yacht broker who specializes in cruising boats), several internet sources, and some time perusing magazines, I was able to find 36 boats that were both on the Best Cruisers list and priced less than $100,000. The results of this effort, broken into price ranges, are shown in the Best Cruising Boat Values list. The boat listed offer a variety of style, from traditional double enders like the North Sea 27 and Jason 35, to reverse transom ocean racers like the venerable Cal 40. The under $25,000 category are mostly small ( 30 feet and under ) boats, but these are affordable choices for single handers or young couples, and if a larger boat is needed, the Colombia 34 is a lot of boat for the money. The 25 to 50 k group ranges from the traditional styled Jason 35 to the roomy Colombia 43 MK III. Above 50 k the boats seem to settle around the 38 to 40 foot size, and include many well know cruisers like the Cal 40, Corbin 39, Cabo Rico 38, Pacific Seacraft 37, Tayana 37, and the Valiant 40.
When evaluating a used boat purchase, try to collect as many facts about the boat as possible. The most successful transactions are often the result of an informed buyer knowing the basic factors normally associated with a quality cruising boat, and the trade off that result when these factors are missing. My Best Cruisers list is a good place to start but you should let your own requirements influence the final selection. Its not difficult to run through the numbers on your own and find out where a particular boat differs from the Best Cruisers List. If it’s a small factor, like slightly to little or to much sail area, it may not be important. On the other hand, if the Disp / LWL ratio is low and the acceleration level high, and you like a smooth ride, then be cautious. If your not familiar with the design, the rec.boats.cruising news group on the internet is a good source for unfiltered advise. It goes without saying, of course, that any boat purchased for offshore cruising should pass a through survey. Again, the key factor is "make an informed decision" - use every tool available.
Finding a boat within your price range and on the Best Cruisers List is a good start, but these are older boats and many will need extensive rework before an offshore voyage Cosmetic work like varnishing and "remove and replace" tasks are not difficult, and are well within the capabilities of most cruising sailors. The hull can be painted, the mast stripped and coated, rigging and sails replaced, and many interior upgrades completed for a fraction of the cost of a new boat. Be careful to avoid projects involving rotted wooden structural members, really sever blistering (relamination required), or other serious structural problems, unless your ready to spend some serious time and money. Fortunately, many of the older designs, like the CAL 40 and Colombia boats were over designed by today’s standards, and have structures with a lot of life left in them. Even if the structure is sound, be sure to not underestimate the cost involved in bringing one of these boats up to offshore standards. While each case will be different, many spend at least the purchase price of the boat on upgrades. Be sure to include these costs in your final decision.
The boats on the Best Cruisers List mirror the work of well known cruising boat designers. If your thinking about buying a boat for offshore cruising, looking at these boats is a good place to start. Evaluate them based on your own requirements and determine what trade off are acceptable. Once you feel comfortable about the boat, have it inspected by a competent marine surveyor and get estimates for the cost involved in bringing the boat up to blue water standards, before you sign anything. Use all the resources you can to evaluate potential cruising boats. You may still choose to tackle Cape Horn with your Collapso 40, but at least it will be an informed choice.
End
(1) DISP / LENGTH RATIO = disp./2240/(.01*lwl)^3 Dimensionless, if you ignore the constant "2240" that converts displacement from pounds to long tons. ".01" is another constant that scales the result. Probably the most used and best understood evaluation factor. Low numbers (resulting from light weight and long waterlines ) are associated with high performance. Depending on who you ask, cruising designs begin around 200 and can go up to the high 300's. Many racing designs are below 100. The general trend for new designs is towards lower ratios that favor higher performance. The trade off is that a light boat will have more violent motion in storms. This requires constant attention to steering and sail trim, resulting in crew fatigue.
(2) SAIL AREA / DISP RATIO = sail area/(disp/64)^.666 Dimensionless. "64" converts displacement. to cubic feet . This is basically a ratio of power to weight, calculated using a 100% jib. Most monohull designs range between 16 and 18. Racers can be much higher, motor sailors lower. The ratio is independent of boat length.
(3) VELOCITY RATIO = 1.88*lwl^.5*sail area^.333/disp^.25 / (HULL SPEED) Sort of dimensionless (knots/knots). The numerator of the equation calculates potential maximum speed, using an empirical relationship. Boats with a generous sailplan and light displacement will have a velocity ratio greater than 1. Under powered or extra heavy boats will be less than 1. Where HULL SPEED = 1.34*lwl^.5 and has dimensions of velocity (knots). Derived from the speed of a wave under gravity forces, but generally regarded as the highest practical velocity for a displacement boat assuming a reasonable power input (2-3 hp per ton).
(4) LOA / BEAM RATIO = loa/beam Dimensionless. This ratio measures the fineness of the hull. Fine hulls, having ratios of 3.5 - 4.0 and higher, are long and slender which promotes easy motion, high speed (due to low drag), and good balance when heeled. Many newer designs favor wider hulls which have a larger interior volume, sail flatter, and have high reaching and down wind speed potential.
(5) CAPSIZE RISK = beam/(disp/(.9*64))^.333 Dimensionless. An empirical factor derived by the USYRU after an analysis of the 1979 FASTNET Race. The study concluded that boats with values greater than 2 should not compete in ocean races, due to their high inverted stability. The formula penalizes boats with a wide beam (the most important factor in inverted stability), and light weight boats because of their violent response (low roll moment of inertia) to large waves. It does not indicate anything about static stability
(6) COMFORT FACTOR = disp/(.65*(.7*lwl+.3*loa)*beam^1.33) Dimensions of "Length" to the 2/3 power. An empirical term developed by yacht designer Ted Brewer. Large numbers indicate a smoother, more comfortable motion in a sea way. The equation favors heavy boats with some overhang and a narrow beam. These are all factors that slow down the boat's response in violent waves. Racing designs can be less than 20, and a full keel, Colin Archer design, could be as high as 60.
(7) ROLL ACCELERATION = (6.28/T)^2*RADIUS*(ROLL ANGLE*3.14/180)/32.2 Units of G's, where "T" is the ROLL PERIOD. From Marchaj's book, SEAWORTHINESS, THE FORGOTTEN FACTOR, chapter 4, "Boat Motions in a Seaway". The author presents a graph of roll acceleration Vs four physiological states; Imperceptible, Tolerable, Threshold of Malaise, and Intolerable. Malaise starts at .1 G, Intolerable begins at .18 G. Spending much time under these levels of acceleration reduces physical effectiveness and decision making ability through sleep deprivation. The radius term assumes an off center berth located 1.5 feet inboard from the maximum beam. The roll angle is 10 degrees. G levels above .06 are considered undesirable for offshore cruising conditions. Several light weight, large beam designs have G levels above .4, definitely "intolerable" for any length of time. The ROLL PERIOD is calculated from the equation: T = 6.28*( I /(82.43*LWL*(.82*beam)^3))^.5 , and has dimensions of seconds. The roll period is based on the moment of inertia, I, waterline length, and beam. The term (.82*beam) has been substituted for the waterline beam due to lack of data. The general rule of thumb is that boats with periods less than 4 seconds are stiff and periods greater than 8 seconds are tender. The MOMENT OF INERTIA is calculated from the equation: I = (disp^1.744 )/35.5 , and has dimensions of lb.ft.^2. An empirical term used by SNAME for analysis of the 1987 Fastnet race. The moment of inertia is very sensitive to the distance items are from the center of gravity. A heavy rig can greatly increase I, with little impact on displacement.
Less Than $25,000
ERICSON 29 |
14500 |
COLOMBIA 30 | 10000 |
BRISTOL 30 | 19000 |
CAPE DORY 28 |
20000 |
DOUGLAS 32 |
23000 |
COLOMBIA 34 |
24000 |
$25000 - $50,000
NORTH SEA 27 |
37000 |
MARINER 36 |
40000 |
COLOMBIA 43 MK III |
40000 |
ERICSON 39 M |
47000 |
JASON 35 |
49000 |
$50,000 - $75,000
NEWPORTER 40 |
42000 |
HUNTER 37 CUTTER |
56000 |
CAL 40 |
57000 |
CHRIS CRAFT APACHE 37 |
60000 |
ROBERTS 38 |
60000 |
TARTAN 42 |
63000 |
SOUTHERN CROSS 39 |
74000 |
IRWIN 38 |
75000 |
WHITBY 42 |
75000 |
$75,000 - $100,000
HORIZON 39 |
80000 |
BRISTOL CHANNEL CUTTER |
95000 |
HANS CHRISTIANS 38 |
92000 |
PACIFIC SEACRAFT 31 |
80000 |
CAPE DORY 36 |
80000 |
PACIFIC SEACRAFT 34 |
85000 |
MORRIS 28 |
88000 |
CORBIN 39 |
88000 |
CABO RICO 38 |
91000 |
BABA 35 |
95000 |
BRISTOL 40 |
95000 |
PACIFIC SEACRAFT 37 |
95000 |
TAYANA 37 |
97000 |
ENDEAVOUR 42 |
98000 |
VALIANT 40 |
99000 |