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How to Lay Out Spars for a Marconi Rig (Pub. No. 7710)

by Robert M. Steward

Masts are calculated as columns, booms as beams, therefore the load and the length of the longest unsupported span are factors determining the size of the maximum section. The calculated section is required only at the middle of that span, where the greatest load occurs, and this point on a mast is half way from the deck to jib stay, and at the mid-length of a boom. Therefore, a spar can be tapered down smaller each side of the largest section, but to save work most economical builders make masts of constant section from the step to the point described above and then taper to the top, where the saving in weight does the most good. Booms, being shorter and simpler, should always be shaped to both ends.

2 page(s)

Balance of Sailing Boats, The (Pub. No. 7712)

A Rough Method of Determining Proper Location of the Sails in Small Boats

The location of the mast (or masts) in a sailing boat, and the consequent disposition of the areas of sail, must be arranged to suit certain conditions or the boat will very likely not perform properly under canvas. The sail cannot be placed anywhere in the boat. It must be placed so that the center of its area bears a certain relationship to the center of the underwater plane of the hull. When the sail plan is placed in its proper relationship to the underwater body of the boat,  the boat is said to be properly "balanced" and it is to be expected that the boat will sail on her course, on all points of sailing, without the need of much corrective pulling one way or the other on the part of the rudder. A perfectly balanced boat should need no rudder at all, except for alteration of the direction of her progress--in other words, in the perfectly balanced boat one should be able, after settling the boat on the desired course, to take the rudder off entirely, and she should keep on this course, provided the wind were steady and the sea smooth, indefinitely.

2 page(s)

Historical Cat Boat Rigs and Lines (Pub. No. 7713)

3 pp., illus. with lines and rigs of 12 catboats.

Your Propeller (Pub. No. 7714)

by C.H. Van Dusen

An article which describes in the simplest terms the underlying principles of propellers, why they work, slip, and they way they are chosen.

In reality it is very simple to understand. If you screw a nut on a bolt, the distance that the nut travels in each complete revolution is called the pitch. Get this clearly. Now, in the propeller, we have exactly the same thing and the pitch of the propeller (usually given in inches) is the distance that the propeller would travel through the water, in the ahead direction, if it could be screwed through the fluid as the nut is screwed onto the bolt. Since the propeller is turning in water though, it will be at once apparent that it is not possible for the propeller to travel forward or backward without some loss due to the slippage of the water off the blades. The water is not solid enough, in other words. Therefore, we come to a rule which, for the sake of argument, we will term Rule 1: The difference between the actual speed of the boat and the actual pitch speed of the propeller is called “slip.” It is usually expressed in percentages

2 page(s)

Curve Sheet of Rudder Areas (Pub. No. 7715)

by George L. Cary

The area of the rudder must be proportionate to the area of the lateral plane, and in these curves the author has approximated the lateral plane for various classes.

1 page(s)

Method of Determining Balance in Sailing Hulls, A (Pub. No. 7718)

The "Metacentric Shelf" system and how it works.

by Douglas H. C. Birt

The so-called Metacentric Shelf is one of the few systems in yacht design which may claim to have evolved by truly scientific methods. It has developed from step by step experiments first with model yachts and later with the real things. Some years ago Engineer Rear Admiral A. Turner, R.N., originator of the metacentric shelf system of hull balance, designed and built a model he called “Principia,” which embodied the first elements of the theory of balance. Following this came a chain of such experiments carried out by various people under Admiral Turner’s guidance. Gradually the principle of balance was formulated on the evidence of experimental success and failure and amplified by mathematical proof. Today the metacentric shelf has lifted yacht design from the category of a rather nebulous art, and placed it on a scientific basis. It is now possible to ensure, with a fair degree of certainty, in the design stage, that a yacht will be well mannered and docile—will have that peculiar quality known as balance.

4 page(s)

Experimenting with Yacht Lines (Pub. No. 7865)

by S. A. Vincent

A practical article on testing and towing models to determine the bestforms of underwater body. This data should be of interest to every yachtsman

The only sure way of developing the lines of vessels to fulfill all expectations by the amateur is by trial and error. Good judgment is not to be belittled, but even the best of naval architects are not perfect and it is rarely that a design is so fine that it cannot be improved upon. To build a special series of full sized vessels, whether they are motor boats or battleships, each varying slightly in a definite way from the other and so find the best hull form, would be unduly expensive. Fortunately it is possible to build small models at a comparatively moderate cost and from these the exact performance of a full sized vessel can be predicted with mathematical precision. For years, all naval vessels and most merchant vessels, have been designed following extensive model experiments. It is only rarely that yachts or motor boats are designed from such tests and this will be understood when I explain that it costs several hundred dollars for one model to be built and tested.

3 page(s)

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