Before you start
Gather the appropriate supplies and review the specific equipment manual.
- Accurate sail area
- Displacement figure
- Model variant details
Step-by-step instructions
Confirm the data source
Builders may quote different sail-area conventions, such as 100-percent foretriangle or an overlapping genoa.
Understand what the ratio expresses
The SA/D ratio compares approximate driving sail area with displacement raised to a scaling power. It is not a measured speed test.
Check loading
Tankage, equipment and stores can change actual displacement and therefore the practical meaning of a published ratio.
Include hull and keel design
Waterline shape, wetted surface, rig efficiency and stability can significantly affect performance.
Compare similar configurations
Use the ratio as a starting filter, then inspect real sail plans, polars and owner-reported performance.
Safety note
Do not select a boat for difficult offshore conditions using a single design ratio.
Key takeaway
Ratios aid screening, not certification or precise speed predictions.
Keep this job on your maintenance schedule
Save the topic as a maintenance task, choose a due date or engine-hour target, and record future service. Free and stored on your device.
Add to my maintenance plannerThis guide is for general education. Follow your equipment manufacturer’s instructions, current navigation guidance and applicable marine safety standards. When uncertain, use a qualified marine professional.