Feb 20 • ⚓ Quarterdeck (General)
Hull Speed Example for C350 -16m Trawler
HULL SPEED FOR A ~16 M (52.49') TRAWLER (RULE-OF-THUMB)
Hull speed (knots) ≈ 1.34 × √(LWL in feet)
(LWL = length at waterline, not LOA.)
If your boat is “16 m” by LOA, typical LWL-based hull-speed range
Because LWL is usually a bit shorter than LOA, here’s a practical bracket:
- LWL 14.0 m (45.9 ft) → hull speed ≈ 9.1 kn
- LWL 15.0 m (49.2 ft) → hull speed ≈ 9.4 kn
- LWL 16.0 m (52.5 ft) → hull speed ≈ 9.7 kn
That 9–10 knots number is the point where wave-making resistance starts climbing fast for a displacement hull (not a brick wall, just “now you’re paying a lot for each extra tenth”).
WHAT THIS MEANS FOR A TRAWLER CONVERSION IN REAL LIFE
- Comfortable cruising target: often ~70–85% of hull speed, so very roughly 6.5–8.5 kn depending on hull, load, sea state, prop, and power.
- If you’re consistently trying to cruise 10+ kn on a true displacement hull, fuel burn tends to jump sharply and engines/props need to be matched very carefully.
CONVERSION “SPEED SANITY CHECKS” (WORTH DOING EARLY)
1) Get the real LWL at your loaded waterline (fuel/water/gear aboard). Hull speed tracks LWL, not the brochure LOA.
2) Confirm hull type: true displacement vs semi-displacement. Semi-displacement can live a bit above “hull speed” with enough power; true displacement usually hates it.
3) Prop/gear/engine match: a conversion often gains weight (interior, tanks, house systems). That can pull RPM down and make the boat feel “stuck” below where you expected.
4) Pick a “happy cruise” goal: many owners love a trawler at 7–8 kn because it’s quiet, efficient, and easy on machinery—then accept that 9–10 kn is “push mode.”
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Hull Speed Example for C350 -16m Trawler
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