The Jollyboat is aggressively canvassed for its weight, with a quick, snappy motion best suited to day sailing.
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 17.5′, the Jollyboat tops out around 5.6 knots in displacement mode — after that, the bow wave outruns the hull and resistance climbs steeply.
1.34 × √17.5′ LWL = 5.6 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
57.2
Performance-oriented — carries a lot of canvas for its weight.
Comfort Ratio
3.1
Quick, snappy motion — better for day sails and racing than long passages.
Capsize Screening
2.99
Above the 2.0 offshore threshold — best suited for coastal and protected waters.
Pounds/Inch Immersion
313lbs
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
3.1
Quick, snappy motion — better for day sails and racing than long passages.
Under 20 — Snappy, racing motion
20–30 — Acceptable coastal
30–40 — Good offshore comfort
Over 40 — Very comfortable offshore
Capsize Screening Formula
2.99
Above the 2.0 offshore threshold — best suited for coastal and protected waters.
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° |
2.6 |
3.3 |
3.7 |
3.9 |
| Close Reach60° |
3.2 |
4.0 |
4.5 |
4.7 |
| Beam Reach90° |
3.9 |
5.0 |
5.5 |
5.6 |
| Broad Reach120–135° |
3.6 |
4.6 |
5.1 |
5.3 |
| Run150–180° |
2.9 |
3.7 |
4.1 |
4.3 |
These are simplified estimates based on hull speed (5.6 kts),
SA/D (57.2), 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 Jollyboat — based on sail area, ballast, and displacement characteristics.
Ghost
Sweet Spot
Reef
Heavy
0–5 kts
5–16 kts
16–24 kts
24+ kts
Ghosting
0–5 kts
Light air, motor-sailing likely. Need patience and a light genoa.
Sweet Spot
5–16 kts
Comfortable under full sail. Best speed-to-comfort ratio.
Time to Reef
16–24 kts
Time to shorten sail. Reef the main, swap to a working jib.
Heavy Weather
24+ 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 Jollyboat.
|
Jollyboat |
Cape Cod Knockabout |
Duxbury Duck |
Interlake |
Mercury 18 |
Rhodes 18 |
| Dimensions |
| LOA |
18.0 |
18.0 |
18.0 |
18.0 |
18.0 |
18.0 |
| LWL |
17.5 |
15.5 |
15.1 |
— |
13.0 |
17.0 |
| Beam |
5.0 |
6.0 |
6.3 |
6.3 |
5.3 |
6.3 |
| Displacement |
300 |
650 |
700 |
650 |
1 |
1 |
| Ballast |
— |
— |
— |
— |
635 |
— |
| Sail Area |
160 |
165 |
342 |
175 |
— |
162 |
| Performance |
| SA/Disp |
57.2 |
35.2 |
69.5 |
— |
— |
25.1 |
| Bal/Disp |
— |
— |
— |
— |
57.7 |
— |
| Comfort |
3.1 |
5.7 |
5.8 |
5.4 |
— |
8.2 |
| Capsize |
2.99 |
2.77 |
2.85 |
— |
— |
2.46 |
| Hull Speed |
5.6 |
5.3 |
5.2 |
5.2 |
— |
5.5 |