Rodney Johnstone has been adding some cruising boats to the J Boat line. The 40 and the 28 have already taken off, and the newest cruising boat from J Boats is the 37. I am a J Boat fan, I even own a J/24, so it should come as no surprise that I like this new design.
I did not have a drawing showing the underbody of this design, but it doesn't take too much of an imagination to figure out what it looks like. The rudder will be balanced space and the keel a medium-aspect-ratio fin with draft of 7 feet. (That seems like a lot of draft for a 37-footer, perfect for Puget Sound. We tack if the depth sounder gets under 30 feet. I wonder if a more shoal draft version is available for the East Coast.)
The D/L ratio is 183. I have lately had several letters asking me to reexplain that ratio. Divide the displacement in pound by 2,240 and this will give you this displacement in long tons. Divide this by one percent of the waterline cubed and you have the D/L ratio. For the J/37 this number is 183.92. In the normal range of D/L ratios, 100 is low, 250 medium and 400 is high. The J/37 is medium light.
The midsection shows a narrow BWL (9.2 feet) and a deadrise angle of 9.5 percent.
Just for fun I took the area of the midsection — 11.025 square feet — with my trusty digital planimeter and worked out a prismatic coefficient of .59. This is very high for a sailboat. So I assumed a keel fin with an average chord length of 4.2 feet and a span of 5.15 feet. I gave this hypothetical keel fin a thickness ratio of 10 percent and an average foil thickness for the entire fin of 3.825 inches.
According to these calculations, the keel fin displaces 441.25 pounds. If you subtract that from the gross displacement, you can get a canoe body displacement of 13,057 pounds and a new prismatic coefficient of .578. This is still pretty high for a sailboat, but it indicates lots of volume in the ends and a correspondingly high hull speed. Prismatic should be based upon canoe body displacement only.
If you look at the long string of excellent performing yachts that Rod Johnstone has produced, you have to believe that the new 37 will be no exception. The interior is pretty typical. The quarter berth has grown into a double and is enclosed in its own stateroom. The head is tight but adequate. No tricks here, just a good functional layout.
Rod Johnstone has always been the master of balancing a clean hull shape with a well-designed rig. The new 37 has a small foretriangle and a large, relatively low aspect ratio main. The mast is well forward, which produces a rig that can drive the boat reasonably well under main alone.
The mainsheet traveler is at the end of the boom and the traveler bridge bisects the cockpit. I know a lot of people find this objectionable, but it is the best system when it comes to trimming the main. I would guess that there is no mainsheet winch and that there is a four-to-one purchase on the mainsheet with a cam cleat. A good vang is essential with a rig like this. Standard equipment on the 37 includes a tubular Quick Vang.
The SA/D ratio is very healthy at 21.6. You get this number by taking the displacement in pounds and dividing it by 64 to get displacement in cubic feet. Take this number to the two thirds power (square it and then take the cube root) and divide it into the sail area. These numbers will range from 12.5 to 25. Most cruising boats are around 16.5 and most racing boats are around 21.
I like this cockpit. It combines the comfort of big wide coamings forward with the convenience of "ramps" aft. The side decks are wide and the foredeck is uncluttered. This will be a good platform for racing.
The compromises are minimal and there is a balance of comfort and speed and the effective range of use is broad. This is a simple and well-thought-out design.
|Sail Area||752 sq. ft.|
This story originally appeared in Sailing Magazine, and is republished here by permission. Subscribe to Sailing.