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Ref:fusil de aluminio llevado al maximo? - 2009/07/31 18:28
Como ya te han mencionado nadie mejor que tu para tunear, evaluar tu fusil y sobre todo que te sientas comodo y seguro.
Mi experiencia con un beuchat marlin de 85 en aluminio con cabezal abierto y trabajado es asi:
Goma circular de fusil de 90 de latex 19mm roballen ambar por dentro y negra por fuera con obus de hilo y flecha de 6.75mm x 130cm riffe. Con esta configuración hago tiros cortos y algo largitos para un 85, me encanta, no fallo nada. Si notas la flecha es algo grande para el fusil pero asi yo apunto bien.
Por otro lado, la pareja de gomas de latex de 14mm me parecen que tienen mucho que aportar para fusiles de 25-28mm y curiosiando conseguí lo siguiente:
The purpose of this document is to explain the relative power difference between different diameters and combinations of speargun bands/slings.
Most speargun bands are made of natural latex rubber. Why? Because natural latex rubber has the best elasticity or highest modulus. Currently there is no synthetic elastomer that can match the performance of natural rubber.
Obviously, the power of a speargun band is a function of two factors, the diameter or more precisely the crossectional area, and the percentage it is stretched.
If you were to draw the end of piece of band tubing you would basically be drawing a donut, one circle inside another. The outer circle would have the diameter of the outside of the band and the inner circle the diameter of the hole which is 1/8"(3.2mm). The crossectional area is the area of the outer circle, calculated πR² (3.14 x Radius x Radius) minus the area of the inner circle (the hole). Example: For 1/2" diameter tubing the radius is .25" so the overall area is 3.14 x .25 x.25 = aprox. 0.196 square inches. The area of the 1/8" diameter (.0625" Radius) hole is calculated the same way, 3.14 x .0625 x .0625 = aprox. .012 square inches. You then subtract the area of the hole from the overall area 0.196 - 0.012 = 0.184 square inches which is the crossectional area of 1/2" speargun tubing.
When you know the crossectional area, you already know enough to compare different diameters of tubing because the power is directly proportional to the crossectional areas. For example: 1/2" tubing has a crossectional area of 0.184 square inches and 3/4" inch tubing has a crossectional area of 0.429 square inches. Dividing the area of the larger tubing by the area of the smaller tubing you get 0.429 / 0.184 = 2.33. This means that one 3/4" band has more than double the power of a 1/2" band of the same length.
If you want to put a number on power, it is easy to calculate the force in a cocked band if you know the crossectional area. The modulus of natural rubber is 190 pounds per square inch at 300%. This means that if you stretch a straight piece of band with a crossectional area of 1 square inch to 3 times the original length you will be pulling against a peak force of 190 pounds. For a circular speargun band you would have to double this because you are actually pulling back both sides of the band simultaneously.
At this point you are probably saying this is way to much math for spearfishing. We agree, that's why we give you the table below containing the crossectional areas of the most common tubing sizes and the force of a cocked circular band at the optimum 300% stretch. You will notice that we have included numbers for 1 to 4 bands in each diameter. This so you can evaluate the gain or loss from changing the diameter and number of bands. For example: If you are using three 5/8" bands and want to be able to load faster you can see from the chart that you will get almost the same power from two 3/4" bands.
Warning: You should always know and adhere to the speargun manufacturers stated limits for band size and number for a particular gun. Over powering your speargun may result in serious damage to your gun or yourself. "Shaft Whip" (the flexing of the spear shaft when fired) is another consequence of too much power and will actually rob you of some of that hard earned power.
Band/tubing peak force1 cicular bans at 300%
1/2'' (13mm) 70lbs
9/16'' (14mm) 90lbs
5/8'' (16mm) 111lbs
3/4''(3/4mm) 163lbs
Crossectional Area of Circular Band(s)
1band 2bands 3bands 4bands
0.368sq.in. 0.736sq.in. 1.104sq.in. 1.472sq.in.
0.472sq.in. 0.944sq.in. 1.417sq.in. 1.889sq.in.
0.589sq.in. 1.178sq.in. 1.766sq.in. 2.355sq.in.
0.859sq.in. 1.717sq.in. 2.576sq.in. 3.434sq.in.
Lo que quiero decir es que antes de usar 2 gomas de 16mm en un fusil de 25-28mm de tubo, probaría primero con 2 gomas de latex de 14mm y asi las modificaciones no afectarian tan radicalmente el fusil.
Fuente :http://www.spearitco.com/index.php?main_page=page_3
PD: un neumático con reductora ya hace todo el trabajo 
Playa, sol, Arena y unas cuantas nenas! |
