Navalt · Ship Resistance & Propulsion Calculator

Ship Resistance & Propulsion Calculator
Resistance · propeller design · powering

Vessel particulars ▸

Ship type

Hull family

Hull input

Propulsion

Length waterline, L_wlm

Length b.p., L_ppm

Beam, Bm

Draft, Tm

Displ. volume, ∇m³→ C_b 0.595

Prismatic, C_p–→ C_m 0.980

LCB (%L, +fwd)%

Half-entrance, i_E°

Speed range ▸

Speeds

Design speedkn

Comma-separated, in knots. The design speed is the propeller design point — shown as a dashed line on the charts.

Holtrop parameters ▸

Waterplane, C_wp–

Forward draft, T_Fm

Bulb area, A_BTm²

Bulb centroid, h_Bm

Transom area, A_Tm²

Stern form, C_stern–

C_stern: −25 pram · −10 V · 0 normal · +10 U. Set A_BT/A_T = 0 if none.

Planing — Savitsky ▸

Deadrise, β°

Chine beam, bm

LCG fwd of transomm

Prismatic planing hull; weight W = ρ·g·∇. Valid only when fully planing (Fn∇ ≳ 1, λ ≤ ~4).

Michell — thin-ship ▸

Wave resistance from Michell's integral; bare-hull total = wave + ITTC friction. Best for slender, low-block hulls and multihull components. The hull form follows the global Hull input mode (Vessel particulars): a Wigley body from the particulars, or the imported offset table.

Hollenbach (1998) ▸

Length o. surface, L_osm

Propeller dia., D_pm

No. rudders, N_rud–

No. brackets, N_brk–

No. bossings, N_bos–

No. side thrusters, N_thr–

Screw count comes from Vessel particulars → Propulsion; bulb from Holtrop A_BT>0. Even keel assumed (T_A=T_F=T). L_os ≈ L_wl (slightly longer for transom sterns). For single-screw the rudder is built into the formula, so the appendage counts apply to twin-screw only (set N_brk=2 or N_bos=2). Reference area for C_R is 0.10·B·T, not wetted surface.

Appendages (Holtrop) ▸

Appendage	On	S (m²)	1+k₂

Bow thruster tunnel

Present
Tunnels · d (m) · C_D

Add this appendage drag to every method (van Oortmerssen, Hollenbach, Savitsky, Michell) so the comparison charts are on a common hull + appendages basis. The same ½ρV²·C_F·ΣS(1+k₂) + thruster term Holtrop uses is applied to each.

Air resistance ▸

Include in total

Air drag, C_DA–

Frontal area, A_VTm²

Air density, ρ_airkg/m³

Head windkn

ITTC still-air drag R_air = ½·ρ_air·C_DA·A_VT·V². C_DA ≈ 0.5–1.0 (0.8 default). A_VT = transverse projected area above the waterline (hull + superstructure) — set for your vessel. Head wind adds to relative air speed (0 = still air; negative = following). Enters the Holtrop total only.

Sea margin (wind & waves) ▸

Sea margin%

Service allowance on the calm-water Holtrop total for added resistance in wind and waves (and conventionally hull/propeller fouling over the docking cycle). Typical 15–25%. Gives “PE service” — the power to size the drivetrain against. If you also set a head wind under Air resistance, that steady head-wind drag is already counted there; keep this margin for the seaway/fouling allowance to avoid double-counting wind.

Propeller ▸

Open-water, η_O

Hull eff, η_H–

Rel. rotative, η_R–

Propeller open-water efficiency η_O is shown as a per-speed row — it varies with speed. Enter one value (applied to every speed) or a comma-separated list matching the speed list. The propeller-design module will populate this row when added. QPC η_D = η_O·η_H·η_R; η_H and η_R default to 1.0 (set them, or let the module compute them from wake & thrust).

Motor — direct drive ▸

Drivetrain

Envelope

Rated power, P_ratedkW

Base rpm, n_baserpm

Max rpm, n_maxrpm

Design rpm, n_designrpm

Shaft/seal, η_S–

Motor, η_m–

Inverter, η_inv–

Choose direct drive (motor on the propeller shaft, motor rpm = propeller rpm) or geared (motor rpm = propeller rpm × gear ratio, with gearbox loss η_GB). n_base, n_max and the envelope are motor-side rpm; n_design is the propeller shaft rpm used for optimum-diameter design. The parametric envelope is constant torque up to n_base, then constant power P_rated to n_max; switch Envelope to rpm–power table to enter a measured curve (one “rpm, kW” point per line) and the check interpolates it instead. Chain: P_B = P_D/(η_S·η_GB), motor input = P_B/(η_m·η_inv).

Water properties ▸

Density, ρkg/m³

Kin. visc, νm²/s

Gravity, gm/s²

Roughness, ΔC_a–

Derived

Hull coefficients

Resistance

Propeller

Propulsion

Selection

Method suitability vs speed

geometry + Froude gate

OK recommended · OK* fits but different hull family · SPD Froude out of range · — geometry out of range. Computed resistance below is shown for every method; trust it only where the row reads OK.

Output

Resistance & power tables

Holtrop–Mennen

van Oortmerssen

Savitsky (planing)

Michell (thin-ship)

Hollenbach

Resistance vs Speed

Effective power vs Speed

Propeller design

Propeller design (Wageningen B-series)

Resistance source

η_O method

Methodical-series propeller design — active when η_O method = series design Series Design mode D m Z A_E/A₀ P/D wake w thrust-ded. t Cavitation — Keller minimum blade-area criterion (Ghose & Gokarn Eq 6.16) shaft immersion h m k

Step 1 — Powering

Effective → delivered → brake → motor

Propulsion power chain — shaft line

Each marker is a power level in the Holtrop propulsion zone of the powering table below; each η is an input from the Propeller, Transmission and Electric-drive sections.

Step 2 — Speed–power

Power vs speed — selected method & propeller