Start from a standard. Each boat class has a reference rig for elite men on a Comp / Smoothie2 blade, inside the ranges Concept2 publishes (sweep spread 83–87 cm with inboard = spread + 29–31 cm; scull span 157–161 cm with 12–20 cm handle overlap). Faster boats carry heavier gearing, as on standard federation charts.

Gearing follows boat speed. Once the blade is locked in the water, the handle moves at roughly boat speed ÷ gearing. A slower crew at the same gearing gets a slower, heavier drive. RigLab estimates boat speed from each rower's individual 2k erg score (their own indoor-rower time, not a boat time), converted to power with Concept2's formula P = 2.80 / pace³. Missing scores are estimated from age, sex, mass and experience. It averages power across the crew and adds the boat's displacement using v ∝ (P / D^2/3)^1/3. It then scales the reference gearing by (v / v_ref)^0.08, which matches the small rig differences real crews of different speeds use.

Gearing ratio here is the actual lever: (outboard − blade centre of pressure) ÷ (inboard − hand position). Blade efficiency is built in as a length offset: Fat2 runs about 5 cm shorter on sweeps, per Concept2's tables.

Wind changes air drag on rowers and oars, which is roughly 8–12% of total drag in still air. A head wind slows the boat, so the rig comes off a little. A tail wind does the opposite.

Current: a uniform stream carries the boat and the water together, so the blade sees exactly the same water speed. Current changes your time over the ground and the apparent wind, but not the load on the blade. Rig for the wind; steer for the current.

Water temperature changes viscosity. At 5 °C, water is about 50% more viscous than at 20 °C, which adds roughly 6% to skin-friction drag. That's worth a couple of seconds over 2k and a slightly lighter gear.

Handle overlap (sculling). Sculling inboard comes from inboard = (span + overlap) ÷ 2. Overlap is how far the handle ends cross when both oars are square. The standard is about 17 cm for elite men, a little less for smaller hands and frames, women, juniors and newer scullers, and auto values stay within 14–20 cm (Concept2: 12–20). In crew boats it is set for the smallest-handed sculler so every pair of sculls matches. Left hand leads over the right through the crossover, so the rower's left gate sits about 1 cm higher. You can override it with Custom.

Erg stroke length. If you enter each rower's average erg stroke length (ErgData or the PM5 Force Curve screen), RigLab uses it instead of height to predict how far their hands travel on the water. Erg travel runs longer than on-water travel along the boat (straight chain, no oar arc), so it's scaled by about 0.83 for sculling and 0.87 for sweep. If no stroke length is entered, one is estimated from height (about 1.42 m for a 190 cm man). Erg travel is converted to on-water travel (about 0.93× for sculling, 0.97× for sweep) to predict the arc. These conversion factors are estimates. The stroke length also feeds the chart engine directly, which is how Purcer's charts use it.

The base rig comes from published charts. Mike Purcer's Notes on Rowing (2024, ch. 3) gives span/spread, oar length and inboard by crew-average erg watts, erg stroke length and crew weight. RigLab fits twelve of those charts (men's single, double, quad, pair, four and eight; women's single, double, quad, pair, coxed four and eight; 1,800 cells). Every chart turns out to be linear in ln(watts), stroke length and weight. The slopes depend only on discipline and sex, and each boat class shifts the level. The fitted model reproduces all twelve charts to within about 0.1 cm on span/spread and inboard and 0.15–0.35 cm on length, and Purcer holds sweep inboard − spread at about 30 cm throughout. Charts added later were first predicted out of sample: within 0.1–0.6 cm for the sculling boats and men's pair, and up to 1 cm for the women's coxed four. Boats still not charted use the same boat from the other sex plus the average men/women difference (men's coxed four, women's coxless four). Otherwise they step by boat speed from the nearest charted boat (coxed pairs from the pair; coxed quad and octuple from the quad). The app notes when a baseline is interpolated. What the charts say: lower power → shorter oar plus wider span/spread and longer inboard; longer erg stroke → more inboard and overlap, the same length in sculls and slightly shorter in sweep; heavier crew → slightly wider, slightly shorter. Women's sculling is less sensitive to power than men's (≈4.4 vs 5.3 cm of length per ln(watts)). "Length only" keeps span/inboard at the class-standard geometry and carries load changes on the oar with the same gearing.

Shaft stiffness. A softer shaft (e.g. Concept2 Skinny) gives a softer loading profile, so it's run about 1 cm longer on sweeps (0.5 cm on sculls) to hold the same load; stiff shafts run a little shorter. Soft is suggested for juniors, masters over 55, novices and lighter crews; stiff for heavy elite crews.

Catch / finish split by boat class. Faster boats row a longer catch and a shorter finish (World Rowing rigging guidance): about 64% of the arc in front of the pin for an eight, 60% for a single. The foot-stretcher slides the arc fore and aft without changing gearing; moving it 1 cm toward the stern adds roughly 1.5–2° at the catch and takes about 1° off the finish. Enter measured catch and finish angles under Current rig to get the stretcher move.

Span & inboard scale gently with rower size, and take a share of any load change while overlap / leverage stays constant. Work height rises for taller rowers, novices and rough water. Stern pitch starts at 4°, with more for novices and rough water.

RigLab gives a well-founded starting rig. Confirm it on the water with angle and feel, change one thing at a time, and re-measure after every adjustment.