To get to Daku island for the gnarliest surf in Siargao, you need to hire a local outrigger boat known as "banca" in the early morning before the tides get low. The banca ride can be pretty rough, so make sure to bring a waterproof bag to keep your belongings dry.
Once you get to Daku, you'll be greeted with some epic waves that are perfect for intermediate to advanced surfers. The swell size ranges from chest to overhead, and the wave shape is a mixture of left and right-hand breaks. There are a few different spots on the island where you can catch waves, but the best ones are on the west side of the island.
The surf on Daku is not recommended for beginners, as the waves can be pretty fast and powerful. However, if you're an experienced surfer, you'll love the challenge of surfing here. Make sure to bring a board with enough volume and a leash, as the water can get pretty shallow on some spots.
The best season to surf on Daku is from September to November, during the peak of the typhoon season. During this time, the waves can get pretty big, and the wind is usually offshore, which makes for some epic surf sessions. However, if you're not a fan of big waves, the surf on Daku can also be pretty good during the dry season from April to June.
Overall, Daku island is a must-visit for any surfer visiting Siargao. The waves are challenging, but the reward is worth it. Just make sure to bring your A-game and respect the local surfers and the environment.