Von Karman Vortex Street
This same thing happens behind a truck at speed, which you may have observed as the trailer unit of a truck sways from side to side, or you may have even felt the buffeting from side to side when driving close behind the truck.
Sometimes the simple action of removing your spinnaker pole can release a vortex which initiates the Death Roll.
Don’t let the Death Roll take your Soul
On a keel boat – Avoid sailing dead downwind
Everyone likes going fast
In a Dinghy – Sail by the lee
To maintain air flow across your sail in a dinghy learn how to sail by the lee and how to transition into and out of using it.
Sailing by the Lee
Limiting the Roll
If you feel the roll is developing or you are in conditions where it’s more likely than normal for the Death Roll to develop there are some things you can do, and there are some myths which you should not do.
Pull on your main
Sheet that main in more than you think. By pull it in you make it easier for the air to flow across it (from Leech to Luff), and it shuts down the size of any vortices that can be created. Also as mentioned in sailing by the Lee pull on your kicker (Vang).
Spread your weight out
Really this is a bit like being on a merry-go-round. Remember how you go faster when you are closer to the centre, and slow down as you move your weight out. You might also remember that it was harder to push when everyone was at the outside, but easier when they were in the middle. Your boat is the same, if you are near the middle it’ll easily roll, if you spread yourselves out to either site you’ll have a greater moment of inertia and it will be harder for the rolling to develop.
There is no point trying to counter the roll by trying to move quickly to counter it (especially on a keel boat), you’ll need to use all of the boats dynamics to get it under control.
Anchor the Spinnaker Down
If the shoulder of the spinnaker can freely move it makes it an easy target for the vortex street to get to work on rolling the boat. Pull the spinnaker in down and in close by; sheeting in, pull on your barber haulers, and lowering the pole. Also set kite a little fuller than normal (pool forward) to ensure that the flow across it is kept constant and that the luff doesn’t collapse.
You can also set up your main so the air flows from the leech to luff and then into the spinnaker creating a steady air flow.
What to do when you’re in the drink
Smoking the Halyard
On a keel boat, or any other boat with a spinnaker, then one of the best ways to remove the force from the spinnaker trying to pull the boat over, or keep it tipped over is to release the spinnaker halyard, letting it out. Keep hold of the sheets so you can easily retrieve it.
The San Fransisco/Californian Roll
No it’s not a type of sushi, and you can’t eat it, although doing one will feel like you are. As your dinghy has tipped over to windward (in that the boom is up in the air), and to leeward in that it has tipped downwind – you’ll probably find that your mast and sail have sunken in quickly and you are close to upside down almost immediately. Now you can try to pull your boat back up the right way by pulling it up normally with the sail on the downwind side, but you’ll probably find this slow, very slow as the boom is not trailing the mast in this motion, instead it’s probably folding out to one side and thus the main sail is holding up your recovery. instead you can do a San Fransisco Roll where you pull the boat up with the sail to windward, and then expect it to be blown over straight away again, so you keep a hold of the centerboard as this happens, getting pulled under the water and then pop up on the windward side of the boat with the boat now tipped over like normal (mast and sail to leeward), which you can now right like normal.