Furling the sail on a Hobie Island is a method used to reduce the power being harnessed by the wind. To understand why we furl you need to understand how the power of the wind is transferred to the Island to create forward momentum. Most of what you are about to read is in relation to sailing upwind.
The first point you need to understand is “Hull Speed”, hull speed is the speed a hull can be pushed through the water. This is limited to a certain speed called “maximum hull speed” and this is the point where the Island can go no faster through the water no matter how much more power you generate from the sail. In fact the exact opposite will occur when you try to over power the Island. Any more energy applied to the Island via the sail is then transferred to the hull which will rather than increase speed, increases drag with that extra power resulting in the boat trying to heel or lean over further away from the wind. This extra heel results on the leeward ama being pushed deeper into the water and thus extra drag is created and the Island will slow down.
This is a very dangerous situation to be in as you are now placing additional stress onto the island which will result in a breakage of some sort. Most likely it will be the plastic shear pins that keep the ama’s locked. If one of these breaks the ama will fold on and the Island is likely to capsize. It is for this reason that many of choose to swap out the plastic sheer pins for stainless steel. This is not recommended by Hobie.
It it is vital that you furl the sail in as the wind strength increases. There are specific signs as to when to do this. When you notice the leeward Ama is digging into the water or you are having to use more rudder control to keep the Island on s straight course , it is time to furl the sail in. Start with one full turn and reduce further as needed. You will see in the video, the wind strength is up around 30 knots yet with just a little bit of sail out, the island is sailing fast and is easy to manage.
To Sum up, more sail does not equal more speed. The purpose of furling the sail is to balance the boat and maintain control. In the video, the wind strength is around 30 knots and the Island is in control at all times.
Reading the Wind
You can see the wind on the water. Stronger wind will be indicated by darker looking water and if you watch the video you can see in the beginning a darker patch of water coming towards me. Because we can see it, we can prepare for it and there are 2 methods to manage a gust, the first is to sail higher into the wind, called feathering and the second is to furl the sail in more. Feathering means to sail higher into the wind than what you would normally sail at. This effectively reduces the amount of wind harnessed by the sail and will allow you to continue in a forward motion without loosing speed or control. If it is a small gust, then you can hold the position till it pasts then return to your course, if the stronger wind is consistent then you can furl the sail in whilst in the position to set the boat up for the new stronger wind.
Down wind is a bit different, when you sail upwind, the sail is acting like a wing and creating a force. When sailing downwind, the sail is acting more like a parachute and you are being pushed along. The rules of furling are still the same but you will find you can carry more sail area down wind than upwind.
Gust control is reversed, when sailing upwind we steer closer to the wind in a gust whereas when sailing downwind we sail even further downwind in a gust.