Hi everyone, To thank Peter Brennan for his help and invaluable information on this fine boat, I want to share with everyone the following ratios that I have calculated on the boat. We are planning to ours around the world in about 18 month and are in the process of refitting the S/V StarShine to accomplish this (SSB, EPIRB, home made watermaker see the excellent article in good old boat issue 28, liferaft , add a second reef to our full batten main, set up a cutter rig, windlass, etc ...). Many people would not think to undertake such a voyage with this boat but after making all the calculations, I have found our boat to be similar in specification to some fantastic blue-water cruisers even if the boat is a little on the light side (According to John Holtrop's MS Excel vessel database our boat compares to some pretty impressive boats i.e. Valiant 40, Oyster 391, Malo 37, Malo 39, ... via a fuzzy logic selector, but I would take all this with a very large grain of salt!) . Finally before I put the numbers down for you, according to Nigel Calder, most if not all manufacturers use a form of light load when establishing displacement, therefore is would be reasonable to add about 2000 lbs to the 14,000 displacement. I have therefore provided both per spec numbers and adjusted (realistic) numbers for comparaison. Enjoy ! O'day 37 CC (1981 lead keel) Masthead Marconi Sloop LOA: 37 feet Mast: 47 feet, keel steepd LWL: 30'4" Beam: 11'2" Ballast: 6000 lbs Displacment: 14,000 lbs Draft: 5' Sail area: 594 sq feet SA/Displacement ratio: 16.4 Displacement/LWL ratio: 224 LOA/Beam: 3.3 Capsize Risk: 1.8 Ballast Ratio: .42 Hull Speed: 7.4 (According to Nigel, on a boat with a D/LWL of around 200 you can go up to 1.5 X lwl raised to .5) in this case the hull speed could be as high as 8,2 knots Vmax/Vhull (velocity ratio): 1.08 Moment of Inertia: 479,313 Period in seconds: 3.12 Stability Index: 0.92 Comfort Factor (Ted Brewer): 26.7 Period/Beam: 5.26 Roll Acceleration: 0.091 g (in gravitational force) What all this means is that the boat is a little light but because it has a narrow beam compared to new boats, it is very stiff and should provide a fairly seakindly behaviour in a seaway. The only part that I am still researching is the actual manufacturing process of the hull (what kind of glass and how thick) and how the deck is joined to the hull. This will tell me if my hull will withstand the constant pounding of 10-15 meter waves that I could encounter crossing the capes (just joking ;-) ). So here are the modified numbers LOA: 37 feet Mast: 47 feet, keel steepd LWL: 30'4" Beam: 11'2" Ballast: 6000 lbs Displacment: 16,000 lbs (added 2,000 lbs for gear and people) Draft: 5' Sail area: 594 sq feet SA/Displacement ratio: 15.2 Displacement/LWL ratio: 254 LOA/Beam: 3.3 Capsize Risk: 1.72 Ballast Ratio:3.3 Hull Speed: 7.4 Vmax/Vhull (velocity ratio): 1.05 Moment of Inertia: 605,002 Period in seconds: 3.5 sec Stability Index: 1.03 Comfort Factor: 30.6 Period/Beam: 5.93 Roll Acceleration: 0.072 g (in gravitational force) This makes the boat look at lot better. According to Nigel Calder, I am lowballing my weight estimates. Be careful though, we only have 1% of LWL of sinkage available which is 3 inches of play before the boat becomes dangerous. To sink the boat by one inch requires approximately 1143.3 lbs (pounds per inch of immersion=LWL X Beam at waterline X .70 X 5.33). You can read up on the different ratios in Nigel Calder's Cruising Handbook and the excellent site http://www.johnsboatstuff.com/Articles/estimati.htm by John Holtrop. The following is a direct copy from John Holtrop's fantastic web site to help explain some of the value of these ratios: 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 exhibit more violent motion in a heavy seaway or storm. This requires constant attention to steering and sail trim, resulting in crew fatigue. 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. HULL SPEED = 1.34 * lwl^.5 Dimensions of velocity (knots). Derived from the speed of a wave under gravity forces, generally regarded as the highest practical velocity for a displacement boat assuming a reasonable power input (2-3 hp per ton). As a boat's speed increases, the wave it creates becomes longer, creating a trough that moves aft. At hull speed, the trough will be as long as the waterline length, creating a "hole" that the boat just fits. An enormous amount of power (50-100 hp / ton) is required to "climb out" of this hole and transition to higher speeds ( planing ). Boats with lots of "overhang" (the difference between loa and lwl) will appear longer as they settle into the trough, and have slightly higher hull speed than their lwl would indicate. Keel type, underwater shape, heel angle, and wetted surface will effect power requirements for a given speed, but have nothing to do with hull speed itself. 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. BALLAST / DISP = ball / disp Dimensionless. A poor indicator of stability by itself, since details of the center of gravity, center of buoyancy Vs heel angle, and total weight are needed for a complete picture. Values range from a low of .25 to a high of around .5. LOA / BEAM RATIO = loa / beam Dimensionless. This ratio measures the fineness of the hull. Fine hulls, having ratios of 3.0 to 4.0 and higher, are long and slender which promotes easy motion, high speed (low drag), and good balance when heeled. Many newer designs favor wider hulls which have larger interior volume, sail flatter, and have high reaching and down wind speed potential. One note of caution when making comparisons, longer boats tend to be finer then short ones. 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 was funded by the Society of Navel Architects and Marine Engineers (SNAME). They concluded that boats with values greater than 2 should not compete in ocean races. Values less than 2 are "good". The formula penalizes boats with a large beam for their high inverted stability, and light weight boats because of their violent response (low roll moment of inertia) to large waves, which are both very important factors during violent storms. It does not indicate or measure static stability. Some modern coastal cruisers and many racing designs have problems meeting this criteria. An interesting note, the study concluded that static stability was relatively unimportant in predicting dynamic capsize. Beam and weight were much more important factors. Wide boats give waves a longer lever arm to initiate roll and light weight boats require less energy to roll over. 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. This design philosophy is contrary to many modern "racer / cruisers", but it is based on a great deal of real blue water data, not just what looks good in a boat show. A value of 30 - 40 would be an average cruiser. Racing designs can be less than 20, and a full keel, Colin Archer design, could be as high as 60. This factor is related to LOA, longer boats have higher comfort factors, and is linear with respect to the roll period. MOMENT OF INERTIA ("I") = disp^1.744 / 35.5 Dimensions of lb.ft.^2. A rather simplistic empirical term developed by SNAME for the Fasnet race analysis. Large values resist rolling forces. The moment of inertia is very sensitive to the distance items are from the CG. A heavy rig can greatly increase "I" with little impact on displacement. ROLL PERIOD (T) = 6.28 * ((disp^1.744 / 35.5) / (82.43 * LWL * (.82 * beam)^3))^.5 The roll period is based on the moment of inertia, waterline length, and beam. The term (.82*beam) has been substituted for the waterline beam due to lack of data. Using (.82) results in a close match for the few boats with measured periods. Simply stated, a sailboat’s roll period, in seconds, is inversely proportional to its stability. Tender boats have long periods, stiff boats have short periods. The roll period is very easy to determine, you simply grab a shroud and push / pull until the boat is rocking over a few degrees. Then measure the time it takes for ten full cycles , and divide by 10. 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 roll period is related to LOA and strongly related to COMFORT FACTOR. ROLL ACCELERATION = (6.28 / T)^2 * RADIUS * (ROLL ANGLE * 3.14 / 180) / 32.2 ( units of G's) In Marchaj's book, SEAWORTHINESS, THE FORGOTTEN FACTOR, chapter 4, "Boat Motions in a Seaway". The author presents a graph of roll acceleration ( in G's ) 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 assumed to be 10 degrees. G levels above .06 are considered undesirable for offshore cruising conditions. Several light weight, beamy designs have G levels above .4, definitely "intolerable" for any length of time. PERIOD / BEAM = T * (g / beam)^.5 This is a dimensionless expression that is closely related to the disp./lwl ratio, and very closely related to the comfort factor. T is the period (seconds), g is the gravitational constant (32.2 ft/sec^2), and beam is in feet. Have fun !!!
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Wow! Thanks!
Thank you so much for the additional information. I now have all that I need to complete my work. I have started on many of the improvements that you are doing except for the bulkheads. Now that I know that there is a problem with the bulkhead bonding, I will have another look. I am not sure how I will address the issue since I would not want to cut through the inner structure (hull liner) as it provides the required rigidity to the boat. From what I could see, the boat does not have stringers. We are currently planning to go from Montreal, to the carabeean via the ICW and we will hop around there for a while. We will then either go south and cross to the pacific via the magellan straits or via panama if they still accept small boats and the costs haven't gone through the roof. Afterwhich, Galapagos, Fidji, Cook Islands, New Zealand and finally Oz. What about your plans? Merci beaucoup et au plaisir de se rencontrer un jour !
Thank you so much for the additional information. I now have all that I need to complete my work. I have started on many of the improvements that you are doing except for the bulkheads. Now that I know that there is a problem with the bulkhead bonding, I will have another look. I am not sure how I will address the issue since I would not want to cut through the inner structure (hull liner) as it provides the required rigidity to the boat. From what I could see, the boat does not have stringers. We are currently planning to go from Montreal, to the carabeean via the ICW and we will hop around there for a while. We will then either go south and cross to the pacific via the magellan straits or via panama if they still accept small boats and the costs haven't gone through the roof. Afterwhich, Galapagos, Fidji, Cook Islands, New Zealand and finally Oz. What about your plans? Merci beaucoup et au plaisir de se rencontrer un jour !
Hokey smoke! Gentlemen
You guys have really done a lot of digging here, and many thanks for the credit. Glad to help. I have printed out your dissertations and added them to the ship's log. I envy you your plans. Wife refuses to sell everything and move to the boat. Not going to sail off without her because I sort of like having her around. Besides, she's a good sailor. I was amazed at the amount of work you have both done until I reflected on the amount of work I have done and decided we're in the same boat, so to speak. I think I mentioned that breaking up the under settee spaces with little bulkheads greatly imroves storage and adds stiffness to the hull as does the anchor locker bulkhead. The keel is a good thing about this boat. As you know, it is encapsulated lead. It can take a heck of a beating and come back for more. We hit a rock once at full speed (chart said 13 feet) and came to a crashing halt. I was sure we had done serious damage. Had her hauled instantly and found only superficial damage which did not even need repairing on the spot. Had it fixed at the next winter haulout. Friends who have done the same with appendage keels have sustained thousands of dollars in damage and months out of service. It's a big plus for the boat if you are going where the water is thin. Good luck to both of you.
You guys have really done a lot of digging here, and many thanks for the credit. Glad to help. I have printed out your dissertations and added them to the ship's log. I envy you your plans. Wife refuses to sell everything and move to the boat. Not going to sail off without her because I sort of like having her around. Besides, she's a good sailor. I was amazed at the amount of work you have both done until I reflected on the amount of work I have done and decided we're in the same boat, so to speak. I think I mentioned that breaking up the under settee spaces with little bulkheads greatly imroves storage and adds stiffness to the hull as does the anchor locker bulkhead. The keel is a good thing about this boat. As you know, it is encapsulated lead. It can take a heck of a beating and come back for more. We hit a rock once at full speed (chart said 13 feet) and came to a crashing halt. I was sure we had done serious damage. Had her hauled instantly and found only superficial damage which did not even need repairing on the spot. Had it fixed at the next winter haulout. Friends who have done the same with appendage keels have sustained thousands of dollars in damage and months out of service. It's a big plus for the boat if you are going where the water is thin. Good luck to both of you.
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Hi Peter !
Hello Peter, Great to hear from you again! Say, was it you that wrote that article in a sailing magazine a few months back about bringing a Brigantine back to Maine ??? Very cool, if it was the same Peter J. Brennan. I am thinking seriously about holding back on the chain locker. I have done much research on mixed nylon and chain rodes and have come to the conclusion that for now, I will put a 50' length of chain plus 250' of strong three strand nylon, hooked up to either a large danfort or 20+kg Bruce. I am also getting a Fisherman as a secondary and storm anchor. I will try to haul this by hand for a while since I am still rather fit and young (37), possibly using the mast winch to help. If I am going to fit a windlass, it will be manual and horizontal, setup in back of the forepeak well because there is no space in front. I looked at the forepeak, and mine as a great big plastic access port at the tip with a small drain close to it. I suspect that it empties into the bilge. This is all quite wrong for a bluewater sailing vessel. There is going to be big waves coming over the bow many times. I will replace it with a bronze one and make sure that the forpeak drains through a through-hull with a ball seacock, high above the waterline. From what I can see, a lot of water can come in this way. Also will put a 4 inch SS deadlock on the hatch. Hope to talk to you guys again! Thanks for all the help.
Hello Peter, Great to hear from you again! Say, was it you that wrote that article in a sailing magazine a few months back about bringing a Brigantine back to Maine ??? Very cool, if it was the same Peter J. Brennan. I am thinking seriously about holding back on the chain locker. I have done much research on mixed nylon and chain rodes and have come to the conclusion that for now, I will put a 50' length of chain plus 250' of strong three strand nylon, hooked up to either a large danfort or 20+kg Bruce. I am also getting a Fisherman as a secondary and storm anchor. I will try to haul this by hand for a while since I am still rather fit and young (37), possibly using the mast winch to help. If I am going to fit a windlass, it will be manual and horizontal, setup in back of the forepeak well because there is no space in front. I looked at the forepeak, and mine as a great big plastic access port at the tip with a small drain close to it. I suspect that it empties into the bilge. This is all quite wrong for a bluewater sailing vessel. There is going to be big waves coming over the bow many times. I will replace it with a bronze one and make sure that the forpeak drains through a through-hull with a ball seacock, high above the waterline. From what I can see, a lot of water can come in this way. Also will put a 4 inch SS deadlock on the hatch. Hope to talk to you guys again! Thanks for all the help.
Drains overboard
The anchor locker drain goes overboard high up on the bow, not into the bilge. That access port gets you to the bow cleat. If you leave the deck-based anchor locker alone, no water will come into the boat. But if yu make a chain locker below the V-berth, then of course water will come down the hawse hole forward of the V-berth and drain to the bilge. We have not found it to be a problem. The main advantage of having a chain locker is getting the weight of all that chain and rope rode low in the boat. And of course with a windlass you need a free drop for the rode. Have you looked at my windlass installation picures in the photo section? PS. At 71, no way I am going to risk my back hauling a 35 pound Delta and 100 feet of chain. My storm anchor, by the way, is a Fortress 23 with 40 feet of chan and 250 feet of three starnd. I also have a Fortress 12 lunch hook in the deck locker.
The anchor locker drain goes overboard high up on the bow, not into the bilge. That access port gets you to the bow cleat. If you leave the deck-based anchor locker alone, no water will come into the boat. But if yu make a chain locker below the V-berth, then of course water will come down the hawse hole forward of the V-berth and drain to the bilge. We have not found it to be a problem. The main advantage of having a chain locker is getting the weight of all that chain and rope rode low in the boat. And of course with a windlass you need a free drop for the rode. Have you looked at my windlass installation picures in the photo section? PS. At 71, no way I am going to risk my back hauling a 35 pound Delta and 100 feet of chain. My storm anchor, by the way, is a Fortress 23 with 40 feet of chan and 250 feet of three starnd. I also have a Fortress 12 lunch hook in the deck locker.
oh ! oh !
Oh! So that's the small hole in the bow...I was wondering about that. Thank you for the information about the forepeak. it will be useful. I have looked extensively at your setup for the windlass. Is is possible to put it topside after the forepeak instead of cutting the forepeak in two like you did? You have a good setup for the anchors! And I agree, it is not worth putting your back out over it!
Oh! So that's the small hole in the bow...I was wondering about that. Thank you for the information about the forepeak. it will be useful. I have looked extensively at your setup for the windlass. Is is possible to put it topside after the forepeak instead of cutting the forepeak in two like you did? You have a good setup for the anchors! And I agree, it is not worth putting your back out over it!
Well, yeah, but...
I have looked extensively at your setup for the windlass. Is is possible to put it topside after the forepeak instead of cutting the forepeak in two like you did? ...where do you put the hawse hole? The windlass must have a free drop beneath it of about 24 inches (I forget the exact number) otherwise the rode will not self tail. Which is why you can't put the windlass on top of the anchor locker cover unless you always want to hand tail the rode. If you put the windlass aft of the locker, the hawse hole will be over the V-berth. You could use a piece of PVC pipe to make a hawse pipe that goes though the V-berth and into the locker under it but it would be an impediment. A manual windlass won't have the under deck motor but you will still have to beef up the deck where it is situated. I have seen an O'Day 37 with a manual windlass actually inside the anchor locker. But he had to hand tail the rode and it didn't look like a very good arrangement to me.
I have looked extensively at your setup for the windlass. Is is possible to put it topside after the forepeak instead of cutting the forepeak in two like you did? ...where do you put the hawse hole? The windlass must have a free drop beneath it of about 24 inches (I forget the exact number) otherwise the rode will not self tail. Which is why you can't put the windlass on top of the anchor locker cover unless you always want to hand tail the rode. If you put the windlass aft of the locker, the hawse hole will be over the V-berth. You could use a piece of PVC pipe to make a hawse pipe that goes though the V-berth and into the locker under it but it would be an impediment. A manual windlass won't have the under deck motor but you will still have to beef up the deck where it is situated. I have seen an O'Day 37 with a manual windlass actually inside the anchor locker. But he had to hand tail the rode and it didn't look like a very good arrangement to me.
I thought so
Hi Peter, I had thought about the hawse pipe and came to the same conclusion as you did. I will need to think about it so more before I make my mind up on the subject. I am sure that your setup works well. I am just wondering if I can change it a bit for my needs. Thanks!
Hi Peter, I had thought about the hawse pipe and came to the same conclusion as you did. I will need to think about it so more before I make my mind up on the subject. I am sure that your setup works well. I am just wondering if I can change it a bit for my needs. Thanks!
A picture is worth
umpteen thousand words. Here is a sketch that may help you mull it over until the temperature gets high enough to go look.
umpteen thousand words. Here is a sketch that may help you mull it over until the temperature gets high enough to go look.
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