The Mobjack 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 16.8′, the Mobjack tops out around 5.5 knots in displacement mode — after that, the bow wave outruns the hull and resistance climbs steeply.
1.34 × √16.8′ LWL = 5.5 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
49.1
Performance-oriented — carries a lot of canvas for its weight.
Displacement / Length
43
Ultralight — responsive and fast, but carries less stores.
Comfort Ratio
3.4
Quick, snappy motion — better for day sails and racing than long passages.
Capsize Screening
3.40
Above the 2.0 offshore threshold — best suited for coastal and protected waters.
Pounds/Inch Immersion
389lbs
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
3.4
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
3.40
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 Mobjack sits on the PHRF handicap spectrum — lower numbers mean faster boats.
Cruiser/Racer 90–150
Cruiser 150–210
Heavy Cruiser 210–300
Thistle
186s/nm
Montgomery 17
264s/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° |
2.6 |
3.3 |
3.6 |
3.8 |
| Close Reach60° |
3.1 |
3.9 |
4.4 |
4.6 |
| Beam Reach90° |
3.8 |
4.8 |
5.4 |
5.9 |
| Broad Reach120–135° |
3.5 |
4.5 |
5.0 |
5.4 |
| Run150–180° |
2.8 |
3.6 |
4.0 |
4.2 |
These are simplified estimates based on hull speed (5.5 kts),
SA/D (49.1), 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 Mobjack — 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 Mobjack.
|
Mobjack |
Holder 17 |
Leisure 17 |
Montgomery 17 |
Siren 17 |
Thistle |
| Dimensions |
| LOA |
17.0 |
17.0 |
17.0 |
17.1 |
17.2 |
17.0 |
| LWL |
16.8 |
15.0 |
14.0 |
15.8 |
15.0 |
17.0 |
| Beam |
6.5 |
7.3 |
7.0 |
7.3 |
6.7 |
6.0 |
| Displacement |
450 |
950 |
1 |
1 |
750 |
515 |
| Ballast |
— |
345 |
550 |
550 |
130 |
— |
| Sail Area |
180 |
147 |
148 |
154 |
139 |
— |
| Performance |
| PHRF |
— |
— |
— |
264 |
— |
186 |
| SA/Disp |
49.1 |
24.4 |
18.3 |
19.7 |
27.0 |
— |
| Bal/Disp |
— |
— |
— |
39.3 |
17.3 |
— |
| Comfort |
3.4 |
6.7 |
11.5 |
9.4 |
5.9 |
— |
| Capsize |
3.40 |
2.95 |
2.46 |
2.62 |
2.94 |
— |
| Hull Speed |
5.5 |
5.2 |
5.0 |
5.3 |
5.2 |
— |