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Hms 18
Designer: Herb Stewart  ·  Builder: Hms Marine (Usa)  ·  First built: 1973
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About the Hms 18

Designed by Herb Stewart and built by HMS Marine from 1973 to 1975, this compact 18-footer represents an interesting chapter in American small boat sailing. With only 75 hulls produced during its brief three-year production run, the HMS 18 has become a relatively rare find in today's used boat market. The boat's most distinctive feature is its lifting keel configuration, which provides remarkable versatility for coastal exploration. When fully deployed, the 3.58-foot draft offers solid windward performance and stability, while the ability to raise the keel opens up shallow anchorages and simplified trailering. The fractional sloop rig delivers a well-balanced sail plan that's manageable for small crews. At 1,225 pounds with 370 pounds of ballast, this fiberglass design strikes a reasonable compromise between trailer-ability and seaworthiness. The SA/Displacement ratio of 18.48 suggests spirited performance in moderate conditions, while the comfort ratio of 7.45 indicates this is primarily a coastal day-sailer rather than an offshore passage-maker. The HMS 18 suits sailors seeking an affordable entry into keelboat sailing, weekend coastal cruising, or a capable boat for sailing instruction. Its compact size and lifting keel make it ideal for exploring shallow waters while maintaining the stability advantages of ballasted construction.

Core Dimensions
LOA (Length Overall) 18.75 ft / 5.72 m
LWL (Waterline Length) 16.75 ft / 5.11 m
Beam 7.50 ft / 2.29 m
Max Draft 3.58 ft / 1.09 m
Min Draft 0.50 ft / 0.15 m
Displacement 1,225.00 lb / 556 kg
Ballast 370.00 lb / 168 kg
Sail Area (Reported) 132.00 ft² / 12.26 m²
Design & Construction
Hull Type Lifting Keel
Rigging Type Fractional Sloop
Construction FG
Designer Herb Stewart
Builder HMS Marine (USA)
First Built 1973
Last Built 1975
Number Built 75
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Performance Ratios
SA/Displacement Sail Area to Displacement ratio measures how much sail power a boat has relative to its weight. Higher values mean more performance and speed.
Under 14 — Heavy cruiser, slow14–18 — Cruising sailboat18–22 — Cruiser/racerOver 22 — Performance racer
 18.48
Ballast/Displacement Ballast to Displacement ratio shows what percentage of the boat's total weight is ballast. Higher values generally mean better initial stability and stiffer sail carrying.
30–35% — Typical cruiser35–45% — Stiff performance boatOver 45% — Racing oriented
 30.2
Displacement/Length Displacement to Length ratio measures how heavy a boat is relative to its waterline length. Lower values mean a lighter, faster boat.
Under 100 — Ultralight racer100–200 — Light cruiser/racer200–300 — Moderate cruiser300–400 — Heavy cruiserOver 400 — Very heavy
 116.37
Comfort Ratio Ted Brewer's Comfort Ratio predicts how comfortable a boat will feel in offshore conditions. Higher values mean a steadier, more comfortable motion in a seaway.
Under 20 — Uncomfortably rough20–30 — Acceptable coastal30–40 — Good offshore comfortOver 40 — Very comfortable offshore
 7.45
Capsize Screening Formula The USHS Capsize Screening Formula estimates offshore capsize risk. Lower is safer — values under 2.0 are considered acceptable for offshore sailing.
Under 2.0 — Safe for offshore2.0–2.2 — Borderline offshoreOver 2.2 — Coastal use recommended
 2.81
Hull Speed Hull Speed is the theoretical maximum speed of a displacement hull, calculated from waterline length. Most cruising sailboats reach this speed in moderate conditions. 5.48 kn
Pounds/Inch Immersion Pounds per Inch Immersion (PPI) tells you how much weight is needed to sink the boat one inch. Useful for calculating how additional gear and stores affect waterline. 448.87 pounds/inch
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