A few words for introduction: I am using a virtual test with models of saltwater rods. There are two 9 foot rods, one for a number 8 line, one for a number 10 line, and I have added a shorter number ten rod, 8 feet long (commercial rods are in the range 8’3 to 11’). These rods belong to the same family (series); their loaded frequency is similar for a given length of their corresponding line in the 20 to 70 feet range of carry (line outside the guides). So the rods once loaded feel as fast.
Number 10 rods have nearly the same small deflection stiffness (a question of fine tuning, I can do better); the stiffness of the three rods is illustrated below with a horizontal rod and an increasing load. The shorter rod is a slightly harder spring by comparison to its longer counterpart, which is normal. To design the rods I used my own scale, the materials used for each piece are the same, and only the mandrels and cloth patterns are changing.
- rod stiffness.JPG (31.16 KiB) Viewed 7955 times
Now let’s see the deflection for a tough condition, where the rod shaft is tilted 30 degrees upwards from horizontal with an imaginary fish pulling vertically. The torque at wrist is a given and you can see the relative difference in “lifting power” (in %).
- rod deflection lift.JPG (23.08 KiB) Viewed 7955 times
If an angler changes its 908 for a 910 he will lose on the fighting playground, even if its casting (fly, line) is more adequate. If he can choose a shorter rod, then he will win on the fighting ground but maybe loose something on casting distance, although this is arguable: the swing weight of the 810 is lower than the one of the 908, so you can expect some compensation in terms of maximum rotation speed.
Incidentally, in terms of stresses, there is a price to pay. Under these lifting conditions, the highest stresses are met for the short rod (810), followed by the 908 and then the 910. Maximum stress level is raised by 25 % (810 versus 908) or reduced by 10% (910 versus 908). We are still far from the limit however.
Now you may have a better view of the pro and cons of rod/ line combinations for salwater fishing. Feel free to ask for information.
Merlin