Floating Rock!

Just before our departure from Tonga, the talk among cruisers was of the underwater volcano. 

The active volcano had been puffing out clouds of floating rock.

Floating rock! It sounds so strange, until you realise the rock is pumice. The rock has so much air trapped that it rises to the top of the sea, and spreads out like a giant slick. These brownish floating pumice fields appear on the ocean surface. They dampen the shape of the waves, making the sea look sludgy, they get blown about by the winds, and drift in the currents. 

On a boat you do not want to go near any of this stuff. Although they are light, the rocks are still abrasive. They do break up, but this only presents a bigger problem for boats as the pumice fields become more spread out. In dead calm conditions it would be difficult to steer clear of the pumice. Once you enter a field it can be so spread out that and it leaves you unsure how to escape.

If you are going too fast you could take damage, but too slow and you might not get out. Using an engine is not a good option, as tiny fragments of the rock can get sucked into the engines raw water feed. Just sailing through the pumice can still clog up through holes, damage the waterline finish, and the anitfouling. 

We managed to avoid the Pumice on our passage from Tonga to Fiji, but it caught up with us weeks later in the Yasawa Islands. Luckily we weren't going too fast. By this time the field was already spread out. We managed to navigate through the patches to the next anchorage without taking any damage.

pic. a field of pumice - try not to sail through this