The Cnb 78 is aggressively canvassed for its weight, with a gentle bluewater motion.
Hull Speed
The theoretical displacement-mode speed limit — determined by waterline length, not engine or sail power.
A displacement hull pushes a bow wave whose speed is limited by the waterline length.
With a waterline of 72.8′, the Cnb 78 tops out around 11.4 knots in displacement mode — after that, the bow wave outruns the hull and resistance climbs steeply.
1.34 × √72.8′ LWL = 11.4 kts
Performance Ratios
Racing handicap, sail-carrying power, stability and comfort — and what each one actually tells you about a day on the water.
SA / Displacement
23.6
Performance-oriented — carries a lot of canvas for its weight.
Ballast / Displacement
26.3%
Light ballast — tends to be tender; reef earlier than the numbers suggest.
Displacement / Length
122
Ultralight — responsive and fast, but carries less stores.
Comfort Ratio
40.5
Very comfortable in a seaway — a genuine bluewater motion.
Capsize Screening
1.70
Below the 2.0 offshore threshold — acceptable for ocean passages.
SA/Disp (Calculated)
21.3
Computed from measured I/J/P/E rather than reported sail area.
Pounds/Inch Immersion
5lbs
Weight needed to sink the hull one inch — loading sensitivity.
Motion & Offshore Suitability
Two ratios that matter most when you're planning passages — how the boat feels in a seaway, and whether the hull geometry is suitable for open ocean.
Comfort Ratio
40.5
Very comfortable in a seaway — a genuine bluewater motion.
Under 20 — Snappy, racing motion
20–30 — Acceptable coastal
30–40 — Good offshore comfort
Over 40 — Very comfortable offshore
Capsize Screening Formula
1.70
Below the 2.0 offshore threshold — acceptable for ocean passages.
Under 2.0 — Acceptable for offshore
Over 2.0 — Coastal / protected waters
Estimated Speed by Wind
Rough boat speed estimates at different true wind speeds and points of sail — derived from hull speed, SA/D, and displacement, not measured polars.
| Point of Sail |
6 kts TWS |
10 kts TWS |
15 kts TWS |
20 kts TWS |
| Close-hauled40–50° |
5.4 |
6.8 |
7.6 |
7.9 |
| Close Reach60° |
6.5 |
8.2 |
9.2 |
9.6 |
| Beam Reach90° |
8.0 |
10.1 |
11.3 |
12.2 |
| Broad Reach120–135° |
7.4 |
9.3 |
10.4 |
11.3 |
| Run150–180° |
5.9 |
7.5 |
8.3 |
8.7 |
These are simplified estimates based on hull speed (11.4 kts),
SA/D (23.6), and empirical efficiency curves — not instrument-measured
polars. Real-world speed varies with sea state, bottom condition, sail trim, and current.
Speeds in gold approach hull speed;
bold gold means near or at hull speed.
Wind Range & Comfort Envelope
Estimated wind ranges for comfortable sailing on the Cnb 78 — based on sail area, ballast, and displacement characteristics.
Ghost
Sweet Spot
Reef
Heavy
0–5 kts
5–14 kts
14–22 kts
22+ kts
Ghosting
0–5 kts
Light air, motor-sailing likely. Need patience and a light genoa.
Sweet Spot
5–14 kts
Comfortable under full sail. Best speed-to-comfort ratio.
Time to Reef
14–22 kts
Time to shorten sail. Reef the main, swap to a working jib.
Heavy Weather
22+ kts
Storm conditions. Storm jib or bare poles. Seek shelter if coastal.
How It Compares
Side-by-side with the boats most often cross-shopped against the Cnb 78.
|
Cnb 78 |
Baltic 73 |
Hallberg Rassy 69 |
Oyster 745 |
Swan 77 |
Swan 80 2 S |
| Dimensions |
| LOA |
78.5 |
73.2 |
72.9 |
74.6 |
78.8 |
82.3 |
| LWL |
72.8 |
60.7 |
64.6 |
65.7 |
60.3 |
72.8 |
| Beam |
20.0 |
18.0 |
19.3 |
19.4 |
19.7 |
20.0 |
| Displacement |
105 |
77 |
102 |
118 |
112 |
79 |
| Ballast |
27 |
29 |
39 |
— |
39 |
39 |
| Sail Area |
3 |
2 |
2 |
3 |
— |
3 |
| Performance |
| SA/Disp |
23.6 |
22.0 |
17.7 |
19.9 |
— |
28.9 |
| Bal/Disp |
26.3 |
38.6 |
38.9 |
— |
35.3 |
— |
| Comfort |
40.5 |
39.3 |
45.8 |
51.9 |
— |
30.1 |
| Capsize |
1.70 |
1.70 |
1.66 |
1.58 |
— |
1.86 |
| Hull Speed |
11.4 |
10.4 |
10.8 |
10.9 |
— |
11.4 |