Being a heavy agressive sailor I have a history of breaking every piece of my equipment, a lot! With a combination of buying smaller sails, better technique and full carbon booms I've gone close to 3/4 of a year without a breakage(touch wood), except harness lines.
Weather dependant I get 2-4 sails a week so my gear gets a lot of use. I am finding I am going through a set of harness lines every 2-3 months. Is this normal? I have broken 2 fixed line NP ones, 2 NP adjustables and just recently my first Dakine fixed line (although it did lasted longer). At first I blamed it on NP ones which easily get sand inside, but the Dakine breakage has made me think again. If getting sand inside the tubing causes friction on the rope surely they can make one that doesn't get sand inside.
Any suggestions on a harness line will last longer (love to hear from heavy sailors because I know you light fellas don't break anything 
), also one that seems to resist getting sand in the tubing.
Thanks.
Have you thought about these roller spreader bars - they are credited for increasing harness line life.
www.dakine.com/
I've never used them - I've never had an issue with harness line life.
I tend to work of the opposite way of thinking about harness line strength.
I generally go through about 3-4 sets of lines a year either through wear or breakage.
With catapults, If I don't automatically come unhooked I hope and pray (I have a little mantra going through my head) that the line will go "plink" and snap as I gain forward momentum.
The thing which causes me the most damage is when I stay hooked in and the harness line doesn't snap, that results in all that energy which can throw 90+kg's a considerable distance being used to slam me into the water with painful results.
The roller bar is the go! Like you I used to go through several sets of harness lines a season - changed to the roller bar a few years ago and seriously have not broken a harness line since! They are awesome! SHQ usually have a few in stock - well worth a try!
), 
I'm a 90kg plus sailor and for most of my sailing life have used 2nd hand gear so that I could afford to get out and sail. After smashing up a lot of gear and lots of long swim/walks I started to try different techniques. Whilst unhooking is best for the gear, too often I crash too fast for that. Sailing less of on the edge does work but takes out the fun.
I know it sound counter intuitive but when I get catapulted I sheet in. It means that I take most of the impact of the crash rather than the slack and then bang, smash when My body takes up the slack and brakes another boom or mast.
By sheeting in it seems as though you reduce the radius of the catapult and by absorbing the shock with your body rather than your gear you prolong the life of your gear. Admitedly now that I'm 40+ it does take me longer to shake off the impact and I never sail without a helmet but it seems to work. Give it a go
Exactly nicr- sheet in and it rotates the sail around rather than dead stop, you just need reliable lines so you don't get trapped under the sail.
I don't catapult much, but I purposely go for the pryde lines so that they break rather than the boom but I do keep a set spare.
Leman have a look at the chinook lines, then you can just replace the rope.
At 105kgs, I've broken lines, masts, booms, and flattened the deck on my board, I feel your pain Leman! Although, if you're that hard on your gear, I wouldn't be too worried about your lines, more the technique? If you're putting a lot of weight on the harness when jumping, you're better off breaking harness lines, than getting indestructable ones...and breaking, or bending your boom...lines are cheaper!
I'm currently using North fixed lines, haven't broken one yet.
As for Easty's comment... you're right! The first few breakages I had, I called the suppliers to ask how it happenned, and got the question "how much do you weigh?" Once I tell them my weight, the standard response is "Ohhh, that would explain it then." 
Hi, Leman,
Can you verify that the sand is getting into the NP lines? because the NP lines are sealed where they meet the boom attachment points. I've used them for years and never had a sand penetration problem. I did have the problem umpteeen years ago, using early-model lines, when the outer plastic tube stopped close to the top of the lines, near the boom. The outer tube could move up and down the inner line and when you put the boom down on the sand, sand would find its way between the inner and the outer and erode the inner line as you have suggested.
The other way the lines fail is by external abrasion. Typical DaKine style hooks abrade the outer tube as you inadvertently move back and forth along the boom, trimming the sail whilst under way. If this is the case, I'm with Fletch: the Reactor roller bars are the way to go BUT, during a catapult onto your sail, the sharp edges of the Reactor will punch a hole through the sail, EASILY. You learn very quickly to roll your body away from the sail during a catapult.
Even with Reactors, the external tube will eventually rub through, but after years of use (in my case).
Hope this helps,
),
I had the same thing happpen to me a few weeks ago. I go through some harness lines every few months as well. maybe it's because we are victorians. our wind can be nasty. last week end I went through me sail and cracked the end of me boom all because of a nasty gust at Inverloch.
this is my list of damaged gear this year:
smacked me jp sailboard 3 times in the nose all in the exact same spot
put me knee through me 08 ka koncept
put me hand through me 09 neilpryed alpha sail
cracked me boom
and broke two sets of harness lines
and broke a fin while jumping on a sand bar 100m out from rye
One thing i noticed when i used to have the ends of the harness lines fairly wide apart was that as i sheeted in and out the harness line would move thru the bar to compensate since the shape was a wide U.
now that ive moved the lines really close togeather on the boom the harness lines are more of a T or a very narrow V shape there is very little movement along the line and it acts more as a pivot.
Since this change ive had a lot less wear on the Lines.
I run mine about 2 fist widths apart and have never broken lines in 15 years.
I use a set for about 2 yrs (summer and winter so like 3 good seasons) and then just buy new ones as preventative maintenance
Leman, do you pump the sail with the back hand to get going faster whilst still hooked in? I used to do that a lot and one particular hook on a harness was a little rough and wore out lines very quickly. My most recent harness hook is much smoother and I haven't had an issue.
The only way I break a line now is at the velcro/webbing part.
