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16data points analyzed by Sailpages.com to compile this ROCK 20 buyer’s report
ROCK 20

ROCK 20

Birka Marine🇫🇮· Design: Heinz-Jurgen Sass
1968–1975200 built
$900 – $2.4K est. annual maintenance
Offshore CruisermonoMasthead SloopFin

Specifications

Hull

LOA23.52 ft
LWL19.52 ft
Beam7.38 ft
Draft3.94 ft
Displacement3,858 lb
Ballast1,322.9 lb
Hull speed1.34·√LWL5.9 kn

Rig & Sails

Iforetriangle height25.6 ft
Jforetriangle base9.02 ft
Pmainsail luff23.23 ft
Emainsail foot8.73 ft
FLforestay9 ft
Mainsail225 sq ft
Jib (100%)115.5 sq ft
Spinnaker196.3 sq ft

About the ROCK 20

Another version called the ROCK 24 is probably based on the same hull but with a different sail plan.

Performance

Comfort20.1
Capsize1.88
SA/Disp14.2
Disp/Len232
Bal/Disp34.3

ORC Performance Data(2 certificates)

Measured performance data from ORC (Offshore Racing Congress) certificates.

Polar Diagram

24680°30°60°90°120°150°180°WIND
6kn8kn10kn12kn14kn16kn20knbeat VMGrun VMG

Boat speed (kn) vs. true wind angle. Source: ORC

Racing Ratings

GPH863.3 s/miOSN795.9

Triple Number

LowMedHighOffshore0.62430.82900.9362Inshore0.48160.66770.7759

ORC Measured

Displacement1586 kg (3496 lb)Wetted surface13.0 m² (140 ft²)Stability index125.9

Sail Areas (ORC)

Main10.9 m² (117 ft²)Genoa12.7 m² (137 ft²)Spinnaker16.6 m² (179 ft²)

Speed Table (kn)

TWA \ TWS681012141620
52°3.84.55.15.45.65.75.7
60°4.04.85.35.65.85.95.9
75°4.25.05.55.86.06.16.3
90°4.35.25.76.06.16.36.6
110°4.45.35.86.16.56.77.0
120°4.25.25.86.16.46.87.4
135°3.84.85.55.96.26.57.3
150°3.34.25.05.65.96.26.9
Beat VMG2.42.93.33.63.83.93.8
Run VMG2.93.74.35.05.55.86.4

Pricing

We don't have market pricing data for the ROCK 20 yet. If you own one, help other buyers — what did you pay for it? Reports build a community price estimate over time.

Estimated Cost of Ownership

Based on 23.52ft LOA. Actual costs vary by condition, usage, and local rates.

$/ft/mo
Annual Maintenance
$900 – $2.4K
Hull, rigging, sails, engine service
Annual Docking
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Annual Insurance
N/A
No price data available

Known Issues & Pre-Purchase Inspection

We don't have enough data on the ROCK 20yet to publish model-specific findings we'd stand behind — but here's a free general inspection checklist, built from our research into what actually goes wrong on boats of this kind.

Drawn from 7,029 documented issues across 2,391 models, ordered so the areas that most often turn up problems come first.

1Structural & Bulkheads9732Standing Rigging6403Deck & Topsides6404Keel & Keel Bolts5535Rudder & Steering5086Hull & Bottom377
Free general pre-purchase checklist
25 survey areas — hull, keel, rig, engine, electrical and more. Take it aboard when you view any boat.

Own a ROCK 20? Reports from owners are what turn this into a model-specific checklist — and they're the reason the boats above it have one.

Similar Sailboats

Which engine powers your ROCK 20?

We haven't confirmed the engine for this model yet. If you own or know one, tell us — as owners report in, we build an accurate picture over time.

Already know your engine? Search all engines → to find its exact parts.

Used sails that fit the ROCK 20

Checking eBay for sails sized to this boat's rig…