What is wetted surface area (WSA)?

Wetted surface area is the area of the underwater hull in contact with water when the vessel is floating at its design waterline. It is the primary driver of frictional resistance — the dominant resistance component at low to moderate Froude numbers — and directly affects fuel consumption and required power.

What is the Denny formula?

The Denny formula (also written as the Taylor–Denny approximation) estimates WSA as 1.7 × LWL × T + ∇ / T, where LWL is the waterline length, T is mean draft, and ∇ is the displaced volume. It was developed from systematic series data and is accurate to within a few percent for conventional ship forms.

What is the Mumford formula?

The Mumford formula estimates WSA as LWL × (1.36 × T + 0.45 × B), where B is the molded beam. It was derived from a different dataset and gives comparable accuracy. When the two formulas agree closely, the estimate is reliable; a large spread suggests an unusual hull form.

Which formula is more accurate?

Neither formula is universally superior. For conventional displacement hulls (Cb 0.50–0.85) both are accurate to roughly 2–5%. For fine-form yachts or unusual multi-hull vessels, purpose-built methods or direct computation from the hull offsets are more reliable. Averaging the two is a common practice in preliminary design.

Does WSA change with loading?

Yes. As a vessel loads down, draft increases and more hull surface is submerged, increasing WSA. The formulas here use the design draft; if you need WSA at a different loading, enter the actual mean draft and displacement at that condition.

Wetted Surface Area

Name: Wetted Surface Area
Availability: InStock
Author: Nham Vu

Enter hull dimensions and displacement to estimate wetted surface area using the Denny and Mumford formulas.

Hull Dimensions

Waterline Length (LWL) (m)

Molded Beam (B) (m)

Mean Draft (T) (m)

Displaced Volume (∇) (m³)

If unknown, enter LWL × B × T × Cb (e.g. 150 × 25 × 9 × 0.74 ≈ 24 975 m³)

Enter dimensions and click Calculate WSA

Typical WSA for Common Vessel Types

Vessel	WSA (m²)
10 m sailing yacht	~20 – 35
25 m motor yacht	~150 – 250
60 m offshore supply vessel	~900 – 1 400
150 m general cargo ship	~4 000 – 6 500
300 m container ship	~15 000 – 22 000
350 m VLCC tanker	~27 000 – 35 000

Summary

Enter hull dimensions and displacement to estimate wetted surface area using the Denny and Mumford formulas.

How it works

Enter the vessel's waterline length (LWL), molded beam (B), and mean draft (T).
Enter the displacement volume (∇) in cubic meters or cubic feet.
The Denny formula computes WSA = 1.7 × LWL × T + ∇ / T.
The Mumford formula computes WSA = LWL × (1.36 × T + 0.45 × B).
Both results are displayed side by side so you can compare or average them.
Switch between metric (m, m³) and imperial (ft, ft³) with the unit toggle.

Use cases

Estimate frictional resistance during early ship design.
Calculate paint area for hull coatings and antifouling budget.
Compare Denny vs. Mumford estimates to bracket the likely true WSA.
Support preliminary powering calculations and speed-power curves.
Validate hydrostatic software output against simple closed-form formulas.
Naval architecture coursework and self-study exercises.

Frequently Asked Questions

Last updated: 2026-07-22 · Reviewed by Nham Vu