kite surfing shoots need help !

[hancor]

Hi just like most I'm been with my great Nikon D90 for about 6 months now and i love it. I'm trying to take pics of kite surfers and not having the greatest of luck.I know the sport inside out as i kite surf myself (for about 5 years). The lens i was using was a Tamron AF18-270mm f/3.5-6.3 Di 11 VC . Dark images ( even when iso was up ) and as you would gather they were quite small. So today i went out after a very hard decision and brought a sigma 150-500 f5-6.3 APO DG OS. Now i don't what any one to tell me i brought the wrong lens it was hard enough with the $$ i think its a great anyway.

I would like to here some tips on sun, shadow, reflection or do the you think i what struggle as much with type of lens ?????? Any tips would help please as the wind is going off all weeked.Great time to kite and take pics.