I guess that AI could easily produce as confusing a reply to a question as we often see on internet forums.
Since I'm mostly a human being, I wondered how I would answer the question here.
The question was: "Where is the draft location on the Severne Blade ?"
The Chat GPT answer was that the draft location is 'variable'. But is that true, or indeed even helpful?
Here's my answer.
The 'draft' or 'draught' in a sail is its belly, so the fuller you set the sail the more draft it has. The draft position or location is where the fullness is deepest, or where the sail point is furthest from an imaginary line drawn along the boom, from mast to the boom end. This draft point often coincides with our harness line positions. The draft point might also be described as the 'point of drive'.
We use this term a lot to determine how powerful as sail is set, and whether the rig then drives forwards, or more side ways. With a wave sail, we often want more 'backhandedness' for down the line sailing, whereas we might prefer a more forward-pulling sail for blasting, jumping, or to help us stay upwind.
The draft location on most sails is about a third of the way back from the mast. If you were able to cut a cross section through the rig then you should get a shape which resembles an aerofoil, like a cross section through an aircraft wing, or showing an elliptical curve.
With a windsurf rig, fullness cut into the sail in front of the draft point helps the sail be forward-pulling, whereas a more flat entry at the luff panels often means the sail is more sideways pulling or more backhanded.
How does this then apply to the Severne Blade?
Of the two Severne wave sails, the Blade and the S-1, the Blade is more forward pulling and that's because it has a bit more shape in the luff panels which is held there by broadseaming. The centre of drive on the S-1 is set a bit further back, with a slightly different cut. At rest, laid on the beach, the Blade may appear to be flat, in terms of sail belly, but it's not - that's just the five battens making it look flat on the beach, and helping the sail depower in transitions.
With any rotational sail, you can flatten the rig with more downhaul and by adding outhaul, and that's one way to control the sail draft and the power created. If you add more downhaul that bends the mast more, which releases the leech at the head whilst also flattening the luff panels as the mast bend takes up the cut of the luff round. Broadseaming, cut in the luff panels, ensures that some fullness remains in the elliptical curve there, and that's what keeps the sail forward pulling. If there were no broad-steamed shape cut there, then the draft point would move aft, and the sail would become more sideways-pulling or more back-handed (and you'd need to shift your harness lines back a bit.).
When you add more downhaul to any sail, it's important to reset the outhaul, because the tension at the clew will have been slackened by the extra mast bend. A slack outhaul allows more belly or shape in the rear section of the sail, which then makes the sails more sideways pulling. Adding outhaul then re-establishes a flatter rear section to the lower leech of the sail, making the rig more forward-pulling again.
So in other words, you can make any wave sail a bit more backhanded by leaving the outhaul slack, and as such it is possible to move the draft point of any sail, using downhaul and outhaul. However, most sails when properly rigged have a consistent and non-moving draft point.
I guess there are so many words written here that my answer may sound as confusing as the Chat bot one. It's a complicated subject which probably needs diagrams to illustrate the explanation. But you can google 'sail draft' to see those.
The Severne Blade is NOT known for its 'adjustable draft position', so the Chat Bot was wrong here.
Sambo #
> 9 months ago, 13 Aug 2023
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