Yachting: Volume 31, Issue 2 – February 1922

| YACHTING What the Model Yachtsmen Are Doing How to Use the Model Yacht Rating Rule By Joun O. Bere The advent of the American Rating Rule for the classification of model yachts, as adopted by the Model Yacht Racing Association of America and many of the model yacht clubs, has caused considerable comment, and to those yachtsmen who are not familiar with the elements of yacht design the rule appears at first complex and difficuli to apply. The reason for this article is to make clear the application of the rule to those having some knowledge of the art of yacht design. Without that it would be difficult, if : not impossible, to impart sufficient , information to be of value. Un- ) fortunately, many yachtsmen have : ) not had the opportunity to study the art, others do not think the model yacht worthy of so much mental strain. It is from the latter gentlemen that the chief opposition to the change in measurement has been found. They prefer to, build a model by the rule of thumb, and their product is usually as haphazard as the methods they employ. Furthermore, they miss the most interesting part of the work by neglecting to keep pace with the trend in larger vessels and by adhering to the old water line, or Seawanhaka rule, which has been discarded many years ago for large yachts as it produced freak designs and boats with unsatisfactory qualities. The old water line sail area rule : . (i= LWL + VSA) was adopted 2 by the American Model Yacht Club in 1878, and has been in use until recently by most clubs. The reasons for its discontinuance by the more progressive organizations are in part the same as those responsible for the change in rule for large yachts. Particularly in the desire to eliminate freak designs do these reasons coincide, as the model, having a much greater factor of safety, particularly lends itself to unwholesome distortion. It is generally conceded that the model must be treated in some respects as an individual structure, and for that reason some changes have to be made from the Universal Rule for full size yachts in order to govern the proper design’ of a model yacht. These changes have been made, and as the coming In- ternational Race has_ stimulated building so that a large number of boats is being designed and built, we will have, at the season’s end, all the data and information required to correct, if need be, any undesirable feature in the American Model Rating Rule. For the full text of the American Rating Rule (which need not be reprinted here) see YACHTING of July, 1921. The formula in the rule which produces the “rating” of to the (LWL? X so that the restraining influence of the QBL may be noted. This boat has very full lines in the after body, which produce a long Quarter Beam Length and, in consequence, a higher rating than if the after body were developed in harmony with the fore body, which is comparatively sharp. Thus, it will be seen the OBL would produce a very heavy penalty in the scow type of vessel. LXVSA a boat, is .18 _—_——_——, which vWD reads, 18 per cent of the product of the length multiplied by the square root of the sail area, divided by the cube root of the dis- placement. The result of 1.60), and that the draught shall not exceed (.32 &K LWL + 1.56 inches) with a severe penalty for any excess in the two latter factors. To explain the rule we will take an example of a conservative hull developed under the waterline rule this which is the principal purpose for ¢g./ or ee LITER Lite | PEQCENTADE OF £04 USO @ O- VIEL 1 ——” = a anes rave. LOAD WATE be LINE LENETA Pa Vea > £¢8 _ = Me Wf Agary * S00 ~ C44 m FUSE aren nema Fa G9 © IF-2> ~ oem | | FEBRUARY, 1922 —Lwea = a Wl. Biattia ° Aig.s = 08 wLigee\ 4@e” =~ ee : ff What the various terms in the measurement rule mean formula gives the boat’s rating. The rule states, also, that the factor (L) or racing length of the formula shall be tound by first establishing what is called the quarter (QBL) and comparbeam length ing this with a percentage of the load water line length (LWL). This percentage of the LWL required .is equal to one hundred minus the square root of the load water line length (100 — VLWL). Any excess of the QBL over this percentage of the LWL shall be divided by 2 and added to LWL to give the racing length, or factor L. The rule states, further, that the displacement shall be the volume of displacement in cubic inches and that the cubefroot of this figure be used: That the sail area be limited : poet. its existence in the rule. The true scow being a boat lacking in sea- worthy qualities, and not a satisfactory all around type to encourage, the rule works to the disadvantage of that type. It is the writer’s opinion that the model yacht requires fuller lines than would be best for a large yacht, particularly in the fore body, as the model loses somewhat, proportionately, in stability, because of her small size and proximity to the sur. face, where the water is in a more or less broken condition and, there- fore, that the taking of a small penalty in this QB length, not exceeding one inch in class B, would be an advantage rather than a detriment. The dimensions of the assumed craft we illustrate here are as follows: LWL, 42 inches; beam, 12.50 inches; displacement, 30 pounds; sail area, 2,800 square inches. Now let us take each factor separately to find the rating of this model under the rule. To establish factor L we must first know the load water line 76 YACHTING length. As the load water line (LWL) is the line produced on a floating body by the surface or plane of the water, its length is the distance between the furthest forward and the furthest aft intersection of the vessel and the water plane, as in Fig. 1. On a model it is usually measured by floating the boat, when in racing trim, in a measuring tank, the distance apart of the intersections of the hull with the water plane being transferred to the edge of the tank by means of one straight edge and one T square. In this case the LWL measures 42 inches. Other water lines parallel with the LWL are drawn in the plans by the naval architect to aid in fairing up the body and for use in making his calculations. They may be drawn in anywhere above or below the LWL. The rule states that we shall lay in a water line, at a dis- tance equal to one-tenth the load water line beam, above the LWL. I This water line is known as the — 10 beam WL. To do this we must first know the water line beam of the model. The beam as required in the rule is the greatest width of the vessel on the LWL, wherever it may be found. It is taken as shown in Fig. 2. We find it is 12.00 inches in this boat. So, if our beam is 12 inches then our 1/10 beam WL must be drawn in or established 1/10 X 12 inches, or 1.2 inches, above the LWL, as in Fig. 3. A buttock is a line or plane laid in -parallel to the vertical axis or centre line of the boat. It may be placed at any distance outboard of the vertical axis or centre line. FEBRUARY, 1922 — 4 Beare Lewgrn GAL)… gs #2.f0″ QB.L UMTY awe facron Los S59″ 176″ $ 2.00% 43.76″ a OBL above this percentage of the LWL shall be divided by 2 and added to the LWL. OBL % LWL So we have 42.80” 39.27 Excess = 2) 3.53 Penalty = 1.76 This Reon added ps the LWL of 42 inches gives us the racing length or LZ in the equation equal to 43.76 inches. Continuing, we must extract the square root of the sail area quantity, so 1/2800 = 53. (nearly) and we have for our formula .18 43-76 X 53 There remains only the cube root of the volume of displacement to make our problem solvable. The term displacement in naval architecture has reference to the volume or weight of the water pushed aside when a body is put into it. The weight of this volume of water will be exactly the same as the weight of the floating body. Therefore, if we wish to know the weight of displacement of a model being.measured we weigh it in racing trim, and no alterations may be made to it thereafter without the consent of the judges until the race is over. Now, having the weight, say, in pounds, we may find the volume of water it will push aside by dividing the weight of the displacement by the weight.of one cubic inch of water in which the race is to be sailed. Fresh water is computed at .036 pounds per cubic inch, sea water at .037 pounds. We find our model weighs 30 pounds measuring this distance to be 42.80 inches. (See Fig. 4.) Now, the rule states that we must compare the QBL with a percentage of the LWL and_ that that percentage shall be equal to 100 — VLWL, so that V42 = 6.48, and 100 — 6.48 = 93.52, or we may say .935 per cent of 42.00 exactly. inches or 39.27 inches. The rule also states that any excess of the $2 90° _jpsz” ~ 2) a Like water lines, the buttocks are used to fair up the body of the vessel. The rule calls for a buttock laid in at a distance from the centre line outboard, equal to % of the water line beam, which in this case would be 4% X 12 = 3 inches, as shown in Fig. 4. The quarter beam length will be the distance between the forward intersection and the after intersection of the 1/10 beam WL and the 4 beam buttock. It is called the QBL and we find by «+ Blak ~ LXCESS of so short a water line length and is due mainly to the considerable QB length she incurs by her full after body and good sized sail plan, coupled with a normal displacement. Here are the various classes adopted by the association under this rule. Many of the existing boats built under the old rule will be found to rate favorably in some one of these classes when they are measured, particularly if they have a normal, wholesome type of body. 55 inch, Class A. Not over 55 inches and over 46-inch rating. 46 inch, Class B. Not over 46 inches and over 38-inch rating. 38 inch, Class C. Not over 38 inches and over 31-inch rating. 31 inch, Class D. Not over 31 inches and over25-inch rating.. Annual Meeting Montclair Model Y. C. On January 20 the Montclair Model Yacht Club held its first annual dinner at Montclair, N. J., some thirty members and guests being present. After the dinner the manual training shops of the Montclair High School were inspected, as there are unusual facilities here for building both sail and power models and many of the students are taking up the making of models. The club is going to have at least three new boats for the international race next June. Two of these are from designs by Wm. Atkin and the third is for R. Johnson, from his own designs. After the dinner the annual meeting was held and officers were elected for the year 1922. 30 —— = 833-33 cubic inch 036 volume of displacement. The cube root of 833.33 is sought and found as 9.3, and our problem may be solved and the rating of this craft established as .18 43-76 X 53 9-3 a 44.9 rating. This is a high rating for a boat Detroit Model Y. C. Joins Racing Association At the last meeting of the Model Yacht Racing Association of America, the Detroit Model Yacht Club of Detroit, Mich., was elected to membership in the association. A letter from Commodore Bash of the club inferred that this organization might also have a boat in YACHTING FEBRUARY, 1922 Lines of Class B model yacht /ibwanasi, built under the new Model Yacht Rating Rules. Race with England will be sailed this summer the international elimination races next June. The club is “going strong,” with some forty odd members (although less than a.year old) and sailing models on the waters around Detroit is becoming very popular. A Class “B” Model Yacht In order to illustrate the type of boat which may be considered of normal design under the American Model Rating Rule, the lines of Jibwanasi are shown here. These lines will produce a boat which will act satisfactorily for outside work, as well as on lakes and ponds where the winds are somewhat less steady. The calculations are on a salt water hasis, and if the same amount of ballast is put on the keel as is indicated on the plan, then, if the model is used in fresh water, her water line length will be about .75 of an inch longer and her draught about .2 of an inch greater. Her rating, however, will not change sufficiently to be of any importance, so that one who follows these plans with reasonable accuracy may be assured that the model will rate in Class “B” of the Rating Rule. The sail area is moderate and should show up well for general use. It is a trifle large for outside sailing in early spring or late fall, perhaps, when the winds are strong. The jib-headed or “Marconi” rigis shown because of its simplicity and its advantages for model use. A gaff-headed rig may be substituted if desired. Jibwanasi was built and tested to substantiate in the designer’s mind his ideas on the changes from the Universal Rule which have been incorporated in the American Model Rating Rule before this rule was put forward for the consideration of the Rules Committee of the Central Park Model Yacht Club and that of the Model Yacht Racing Association of America. Her dimensions are as follows: Length over all, 70 inches; length, water line, 43% inches; beam, 12%4 inches; draught, 15.3 inches; sail area, 2,865 square inches; displacement, 32.8 pounds. She was designed by J. O. Berg. Prospect Park Model Elects Officers Y. C. The Prospect Park Model Yacht Club; of Brooklyn, N. Y., held its Annual General Meeting on December 5th, 1921, the principal feature of the meeting being the election of officers for the coming ear. The following is the ticket elected : Commodore, E. A. Bull; Vice Commodore, F. P. Wright; Rear Commodore, Captain H. H. Stilling; Measurer, J. L. Wilson; Treasurer, F. Meinertz; Secretary, R. W. Barton. Chairman of Regatta Committee, R. W. Barton. Trustees, Captain H. H. Stilling, F. H. Tucker, J. B. Ketcham. The Secretary’s report gave a complete resumé of the club’s work This is the class in which the International for the past season. One of the important racing events of the year was the winning of the Eagle Trophy by Mr. E. A. Bull with the Wetona at Gravesend Bay on Decoration Day. Eight new members joined the club during the year. The results of the Weekly Point Races and Special Class Races were announced at this meeting. Chey were as follows: Point RAceEs Owner Yacht Points 233 E. A. Bull, Wetona F. Meinertz, Amelia….. 211 C. R. Daniels, Ruth. . F. P. Wright, Arapahoe.. F. Tucker, Dorothy……. Lieut. E. S. Tucker, Yankee Girl .« J. B. Ketcham, Gadfly. . F. F. J. R. 142 140 139 703 7 First Crass Mopets P. Wright, Shawnee Chief…. Tucker, Emerald… B. Ketcham, Gee Whiz… W. Barton, Lorna Doone , ‘ oe: Seconp CLass F. P. Wright, Arapahoe. . J. B. Ketcham, Gadfly | F. Meinertz, Hilma F. Tucker, Dorothy Lieut. E. S. Tucker, Yankee Girl Tuirp Crass F. Meinertz, Amelia….. E. A. Bull, Wetona……. W. Windeiman, [roquoise.. F. C.° Poggenberg, Kelpie y H. P. Taylor, Orienta } . F. C. Poggenberg : { F. P. Wright, Comet Capt. H. Stilling. Vanitie ‘ **TM i for Second 3 “4 I 2 3 Tied ° ; SCHOONERS I. Meinertz, Fairwind.. J. B. Ketcham, E Isie) . 1 2 3 Tied Tied }…. §… H. P. Taylor, Grace H 3 4 5 6 88 C. E. Wauker, Ripple WT Pos. ‘ 2 ot . Tied for Second Tied