ShipForm is a free, browser-based parametric ship hull designer with integrated resistance estimation. It provides a 4-panel CAD viewport for visualizing hull geometry and computes hydrodynamic resistance using established naval architecture methods.
Hull Types & Methods
Displacement Vessels
Uses the Holtrop-Mennen (1982) method with ITTC 1957 friction line. Applicable to cargo ships, tankers, and bulk carriers at Froude numbers below 0.4. Includes form factor (1+k₁), wave resistance, and correlation allowance.
Semi-Displacement Vessels
Uses the van Oortmerssen (1971) regression method with ITTC 1957 friction. Suitable for ferries, patrol boats, and trawlers operating at Fn 0.3–0.6. Accounts for higher-speed form effects and residuary resistance.
Planing Hulls
Uses the Savitsky (1964) empirical method for hard-chine planing craft. Computes lift, trim, wetted area, friction drag, and pressure drag. Includes deadrise angle (β) and LCG position effects. Applicable above Fn ≈ 0.5 (beam Froude number Cv > 1).
Resistance Components
- Frictional Resistance (Rf) — skin friction from fluid viscosity, computed via ITTC 1957 correlation line based on Reynolds number.
- Residuary/Wave Resistance (Rw) — energy lost creating waves. Dominant at higher speeds. Strongly depends on hull form and Froude number.
- Form Factor (1+k₁) — accounts for the difference between flat plate friction and actual 3D hull friction due to pressure gradients.
- Correlation Allowance (Ca) — empirical correction for model-to-ship scaling effects and hull roughness.
Key Parameters
- Froude Number (Fn) = V / √(gL) — ratio of ship speed to wave speed. Determines the resistance regime.
- Block Coefficient (Cb) = ∇ / (L×B×T) — fullness of the hull. Higher = fuller (tanker ~0.85), lower = finer (yacht ~0.35).
- EHP (Effective Horsepower) = Rt × V — power needed to tow the hull at speed, before propulsive efficiency losses.
- Deadrise (β) — transverse bottom angle for planing hulls. Higher deadrise = softer ride but more resistance.
Limitations
This tool provides preliminary estimates for early-stage design. Results should not replace model testing or CFD analysis. The parametric hull form is simplified and does not capture all geometric features (bulbous bow, transom stern immersion, appendages, etc.).
References
- Holtrop, J. & Mennen, G.G.J. (1982). "An approximate power prediction method." International Shipbuilding Progress, 29(335).
- van Oortmerssen, G. (1971). "A power prediction method and its application." International Shipbuilding Progress, 18(207).
- Savitsky, D. (1964). "Hydrodynamic design of planing hulls." Marine Technology, 1(1).
- ITTC (1957). "Skin friction correlation line." 8th International Towing Tank Conference.