I had some fun over the weekend. I found this page with a lot of calculations for determining the seawothiness and comfort of offshore vessels. Well being a math nut I decided to "run the numbers" on our venerable H37C. I've included what I found out with all my math work shown so you can check my work if you desire. Hopefully I didn't plagarize the site too badly. Enjoy...(I put it in Microsoft Word hopefully the formatting won't be a problem) Hunter 37 Cutter Disp / Length Ratio (D/L) = disp / 2240 / (.01 * lwl)^3 D/L H37C = 17800 / 2240 / (.01 * 30)^3 D/L H37C = 17800 / 2240 / .3^3 D/L H37C = 17800 / 2240 / .027 D/L H37C = 7.95 / .027 D/L H37C = 294.44 Disp / Length Ratio is probably the most used and best understood evaluation factor. Low numbers are associated with high performance, cruising designs generally begin around 200 and can go up to the high 300’s. Light boats (low numbers) will have a more violent motion in storms. Sail Area / Disp Ratio (SA/D) = sail area / (disp / 64)^.666 SA/D H37C = 710 / (17800 / 64)^.666 SA/D H37C = 710 / (17800 / 64)^.666 SA/D H37C = 710 / 278.13^.666 SA/D H37C = 710 / 42.45 SA/D H37C = 16.73 Sail Area / Disp Ratio is basically a ratio of power to weight. Most monohulls range between 16 and 18. Racers can be much higher, motor sailors much lower. Hull Speed (HS) = 1.34 * lwl^.5 HS H37C = 1.34 * 30^.5 HS H37C = 1.34 * 5.48 HS H37C = 7.34 kt Hull Speed is generally regarded as the highest practical velocity for a displacement hull with reasonable power input (2-3 hp per ton). Velocity Ratio (VR) = 1.88 * lwl^.5 * sail area^.333 / disp^.25 / (hull speed) VR H37C = 1.88 * 30^.5 * 710^.333 / 17800^.25 / 7.34 VR H37C = 1.88 * 5.48 * 8.90 / 11.55 / 7.34 VR H37C = 91.69 / 11.55 / 7.34 VR H37C = 91.69 / 11.55 / 7.34 VR H37C = 7.94 / 7.34 VR H37C = 1.08 kt/kt The Velocity Ratio for boats with a generous sail plan and light displacement will be greater than 1, while under powered or extra heavy boats will be less than 1. LOA / Beam Ratio (LOA/B) = loa / beam LOA/B H37C = 37 / 11’-10” LOA/B H37C = 37 / 11.83 LOA/B H37C = 3.13 LOA / Beam Ratio measures the fineness of the hull. Fine hulls, have ratios of 3.5 – 4.0 and higher, are long and slender which promote easy motion, high speed and good balance when heeled. Capsize Risk (CR) = beam / (disp / (.9 * 64))^.333 CR H37C = 11.83 / (17800 / (.9 * 64))^.333 CR H37C = 11.83 / (17800 / 57.6)^.333 CR H37C = 11.83 / 309.03^.333 CR H37C = 11.83 / 6.75 CR H37C = 1.75 Capsize Risk does not indicate anything about static stability. It was derived by 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. Comfort Factor (CF) = disp / (.65 * (.7 * lwl + .3 * loa) * beam^1.33) CF H37C = 17800 / (.65 * (.7 * 30 + .3 * 37) * 11.83^1.33) CF H37C = 17800 / (.65 * (21 + 11.1) * 11.83^1.33) CF H37C = 17800 / (.65 * 32.1 * 11.83^1.33) CF H37C = 17800 / (.65 * 32.1 * 26.73) CF H37C = 17800 / 557.72 CF H37C = 31.92 Large Comfort Factor numbers indicate a smoother, more comfortable motion in a seaway. Racing designs can be less than 20, and a heavy, full keel design could be as high as 60. Moment of Inertia (I) = (disp^1.744) / 35.5 I H37C = (17800^1.744) / 35.5 I H37C = 25866191.23 / 35.5 I H37C = 728625.11 lb/ft^2 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. Roll Period (T) = 6.28 * (I / (82.43 * lwl * (.82 * beam)^3))^.5 T H37C = 6.28 * (728625.11 / (82.43 * 30 * (.82 * 11.83)^3))^.5 T H37C = 6.28 * (728625.11 / (82.43 * 30 * 9.70^3))^.5 T H37C = 6.28 * (728625.11 / (82.43 * 30 * 912.67))^.5 T H37C = 6.28 * (728625.11 / 2256941.64)^.5 T H37C = 6.28 * .32^.5 T H37C = 3.58 seconds Roll Period based on the moment of inertia, I, waterline length, and beam. Boats with periods less than 4 seconds are stiff and periods greater than 8 are tender. Roll Acceleration (RA) = (6.28 / T)^2 * radius * (roll angle * 3.14 / 180) / 32.2 radius is 1.5’ inboard of max beam = (11.83 / 2 ) - 1.5 = 4.42’ roll angle is 10° RA H37C = (6.28 / 3.58)^2 * 4.42 * (10 * 3.14 / 180) / 32.2 RA H37C = (6.28 / 3.58)^2 * 4.42 * (31.4 / 180) / 32.2 RA H37C = (6.28 / 3.58)^2 * 4.42 * .17 / 32.2 RA H37C = 1.75^2 * 4.42 * .17 / 32.2 RA H37C = 3.06 * 4.42 * .17 / 32.2 RA H37C = 13.53 * .17 / 32.2 RA H37C = 2.30 / 32.2 RA H37C = .07 G In Marchaj’s book “Seaworthiness, the Forgotten Factor” the author presents a graph of roll acceleration vs. four physiological states; Imperceptible, Tolerable, Malaise and Intolerable. Malaise begins at .1 G, Intolerable begins at .18 G. G levels above .6 are considered undesirable for offshore cruising conditions. The webpage with more info is below. He rates the H37C as one of the best offshore cruisers for under $100K.
- Status
Too much time John?
You should be sailing!
We tested some of these theories on Saturday. On Lake Erie with 20 knots and higher gusts with no reefs and an oversize yankee. My first mate is starting to get used to watching the rail disappear. I did something similar years ago when I found John's site. I built a spreadsheet and included other boats like Valiants, Tayanas, and Island Packets. The H37C, as you point out, stacks up extemely well. And at 1/3 the cost! Thanks for taking the time to further enlighten us.
You should be sailing!
We tested some of these theories on Saturday. On Lake Erie with 20 knots and higher gusts with no reefs and an oversize yankee. My first mate is starting to get used to watching the rail disappear. I did something similar years ago when I found John's site. I built a spreadsheet and included other boats like Valiants, Tayanas, and Island Packets. The H37C, as you point out, stacks up extemely well. And at 1/3 the cost! Thanks for taking the time to further enlighten us.a quick evaluation
If your interested in comparing numbers look at this site. great way to see how you stack up against other boats. WWW.Image-inovation.com/sailcalc. or just type in sail calculator pro in the google search engine. Great way to compare yours with the other guys toys.
If your interested in comparing numbers look at this site. great way to see how you stack up against other boats. WWW.Image-inovation.com/sailcalc. or just type in sail calculator pro in the google search engine. Great way to compare yours with the other guys toys.
Cherubini designed seaworthy boats!
The 37c and the 33 both do very well. Even more remarkable is that our little Cherubini h27 stacks up pretty well against a lot of other boats! Hi, Ed. We are finally moved to Sandusky. August is busy, but we will stop over sometime in September to meet the two of you, and see your boat! David Lady Lillie
The 37c and the 33 both do very well. Even more remarkable is that our little Cherubini h27 stacks up pretty well against a lot of other boats! Hi, Ed. We are finally moved to Sandusky. August is busy, but we will stop over sometime in September to meet the two of you, and see your boat! David Lady Lillie
- Status