From heuristics to a per-boat sail-force model
One of the next major sailing-system passes is moving from broad heel heuristics toward a more explicit sail-force model, where drive, heel, leeway, reefing, and keel position all interact in a more natural way.
Where the current model stands
The current heel and speed behavior is reasonable in spirit, but still heuristic. It captures the right ideas — more sail pressure means more heel, reefing reduces strain, and too much heel should cost speed and control — but it is not yet fitted to real-world polar data or individualized by hull.
That means the game can feel broadly believable while still being conservative, especially for retractable-keel boats and lighter hulls. The shared curve is useful as a first pass, but it should not be the final answer for every boat in the roster.
The model shift
The better approach is to treat sail force as the source of both speed and heel. Wind creates sail force. That sail force splits into forward drive and sideways force. Side force creates heel and leeway. Heel then feeds back into efficiency, control, and safety. Reefing should reduce sail area, which lowers both drive and heel at the same time, instead of applying a blunt hardcoded speed penalty.
That gives a more sailor-like result: in moderate air, full sail can still win because the extra area adds useful drive; in overpowering wind, a reef may keep or even improve effective speed because less of the force is being wasted on heel, rudder fight, and sideways slip.
Why the model needs to be per boat
Different boats should not tolerate the same heel. A light marsh skiff should feel lively, heel earlier, and slide more sideways. A packet or trader should be able to carry sail longer before feeling overpressed. Retractable-keel boats should also differ from fixed-keel boats, not just in drag but in how much grip and stiffness they lose when the keel is raised.
That is why the next model pass moves toward per-boat heel bands, righting behavior, keel effects, lateral resistance, and displacement damping, rather than relying mostly on one shared stability value.
What changes with the keel
The discussion around retractable keels made one thing clear: the current keel-up versus keel-down difference is probably too modest for a final model. The intended idea is correct — keel down should require more wind load to produce the same heel, while keel up should produce more heel and especially more leeway — but the exact values still feel conservative.
The next pass aims to make that difference stronger and more boat-specific. Some boats may gain only a modest heel penalty when the keel is raised. Others may become dramatically less stable and much more slippery.
What is being specified now
The proposed implementation introduces a shared sail-force structure with boat-specific heel bands and stability profiles. The draft spec includes per-boat values for heeliness, righting force, keel-down and keel-up lateral resistance, drag effects, and target heel bands across the current roster. It also defines target scenario outputs for boats like the Bay Sloop 24, Marsh Skiff 19, Shoal Cutter 28, Bay Packet 32, and Gaff Trader 34.
Why this matters
This is the kind of systems pass that can change the whole feel of the game. It should make reefing smarter, heel more readable, lighter boats slipperier in strong wind, and retractable keels feel like real tradeoffs rather than one slider with a small penalty. It also helps damage modeling, because overpressed sailing and excessive heel can become a more believable source of strain on the boat.