The Impulse 21 is aggressively canvassed for its weight, with a quick, snappy motion best suited to day sailing, designed for cruising comfort rather than racing.
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 18.5′, the Impulse 21 tops out around 5.8 knots in displacement mode — after that, the bow wave outruns the hull and resistance climbs steeply.
1.34 × √18.5′ LWL = 5.8 kts
Performance Ratios
Racing handicap, sail-carrying power, stability and comfort — and what each one actually tells you about a day on the water.
PHRF Rating
183s/nm
Typical cruiser — designed for comfort and ease, not podium finishes.
SA / Displacement
28.0
Performance-oriented — carries a lot of canvas for its weight.
Ballast / Displacement
46.2%
Race-oriented ballast ratio — very stiff and powerful.
Displacement / Length
92
Ultralight — responsive and fast, but carries less stores.
Comfort Ratio
6.5
Quick, snappy motion — better for day sails and racing than long passages.
Capsize Screening
2.93
Above the 2.0 offshore threshold — best suited for coastal and protected waters.
Pounds/Inch Immersion
529lbs
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
6.5
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
2.93
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
PHRF Fleet Position
Where the Impulse 21 sits on the PHRF handicap spectrum — lower numbers mean faster boats.
Cruiser/Racer 90–150
Cruiser 150–210
Heavy Cruiser 210–300
Impulse 21
183s/nm
Typical cruiser — designed for comfort and ease, not podium finishes.
Irwin 21 Free Spirit
215s/nm
Hunter 212
216s/nm
Macgregor 21
263s/nm
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° |
2.7 |
3.4 |
3.8 |
4.0 |
| Close Reach60° |
3.3 |
4.1 |
4.6 |
4.8 |
| Beam Reach90° |
4.0 |
5.1 |
5.7 |
6.2 |
| Broad Reach120–135° |
3.7 |
4.7 |
5.3 |
5.7 |
| Run150–180° |
3.0 |
3.8 |
4.2 |
4.4 |
These are simplified estimates based on hull speed (5.8 kts),
SA/D (28.0), 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 Impulse 21 — based on sail area, ballast, and displacement characteristics.
Ghost
Sweet Spot
Reef
Heavy
0–5 kts
5–18 kts
18–28 kts
28+ kts
Ghosting
0–5 kts
Light air, motor-sailing likely. Need patience and a light genoa.
Sweet Spot
5–18 kts
Comfortable under full sail. Best speed-to-comfort ratio.
Time to Reef
18–28 kts
Time to shorten sail. Reef the main, swap to a working jib.
Heavy Weather
28+ 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 Impulse 21.
|
Impulse 21 |
Hunter 212 |
Irwin 21 Free Spirit |
Macgregor 21 |
Nimble 20 |
Parker 21 Trailer Sailer 21 |
| Dimensions |
| LOA |
21.0 |
21.0 |
21.0 |
21.0 |
20.9 |
21.0 |
| LWL |
18.5 |
18.0 |
16.5 |
18.5 |
19.8 |
18.8 |
| Beam |
8.0 |
9.2 |
8.0 |
6.8 |
7.8 |
8.2 |
| Displacement |
1 |
1 |
1 |
1 |
1 |
1 |
| Ballast |
600 |
140 |
750 |
400 |
400 |
800 |
| Sail Area |
208 |
202 |
202 |
— |
207 |
220 |
| Performance |
| PHRF |
183 |
216 |
215 |
263 |
— |
— |
| SA/Disp |
28.0 |
21.9 |
21.9 |
— |
22.0 |
22.6 |
| Bal/Disp |
46.2 |
7.8 |
41.7 |
34.0 |
21.6 |
41.0 |
| Comfort |
6.5 |
7.7 |
9.8 |
— |
9.3 |
9.5 |
| Capsize |
2.93 |
3.02 |
2.63 |
— |
2.53 |
2.62 |
| Hull Speed |
5.8 |
5.7 |
5.4 |
— |
6.0 |
5.8 |