sms wrote:Hi Bruce,
I have a few questions:
- Why are most cores still so low breaking strength (that you can't really use them for tuna)? I think some dacron/gsp mix braid should get the b/s to around 50lb without much if at all affecting the diameter and the adhesion of the coating to the dacron would still be there.
- Is there some correlation with line diameter, line suppleness and how well the core is centered? For example thick and supple line makes it more likely that the core is on one side. Or does it depend on machinery and or method - like if the line is made in horizontal or vertical direction?
SMS,
Most line fly lines break at 20-40 lbs. because that is all that is needed, most lines are not used for tuna, of course. SA, and other mfgs. do make lines for tuna though, SA's Big Water Tapers have 100 lb. test cores for example. There are lots of exotic materials today that might seem like good fly line cores, but almost all of them have at least one fatal flaw, that's why none are being used... For example, GSP usually has a melting point less than the cure temp of most coatings. It also has no stretch, which is bad. Think what happens when you mix two cores with radically different properties, like GSP and Dacron. Dacron stretches, GSP doesn't. Let's say you've mixed 30 lb. of GSP with 30 lb. of Dacron.. Now pull on it. At 30 lb. of strain the GSP breaks, the Dacron has done little so far. Now all the strain is on the Dacron and its nearly at its breaking strain. It quickly stretches to about 7%, then breaks at 30 lbs. 2 +2 doesn't always equal 4...
How well the core is centered in a line is largely determined by the people making the lines and the machinery. However, some lines are much easier to center than others, depending on a number of variables including diameter, coating material and a few others I can't discuss... But mostly it's the skill of the people operating the machinery, and the machinery itself (precision, maintenance, etc.)....
Good questions..
Bruce
A DT is a great distance line in the right hands and will outperform most 40ft WF lines however for a beginner who can't double haul he will do better with a short WF line, especially one that is one or two line weights heavier! 
