Tiger charge a sporting goods fee to carry your boards which you pay when you book similar to Air Asia. This fee only covers one leg so if you have multiple stops you cop the fee for each leg, I think this gives you 20kg. It was about $25 a while back but I think Tiger have pushed all there hidden prices up so best check first. I was travelling with boards up to 6'8".

Never used Silk Air but have used most of the other Asia local airlines carrying boards all good, chuck a 20kg bag of rice and a couple of chooks in while your at it, no problems.