Fender Energy Calculator

Formula Used

Kinetic energy method

Base kinetic energy: E_base = 0.5 × m_eff × v²

Effective mass: m_eff = m × C_a where C_a is the added mass coefficient.

Design energy: E_design = E_base × (C_e × C_b × C_env) × SF

Drop energy method

Base drop energy: E_base = m × g × h × η where η is the efficiency factor.

Design energy: E_design = E_base × (C_e × C_env) × SF

Reaction estimate

A practical reaction estimate is: R ≈ E_design / δ where δ is assumed deflection. This is approximate and should be checked against manufacturer curves.

How to Use This Calculator

1. Pick a method: Kinetic for berthing, or Drop for test impacts.
2. Enter mass and speed (or drop height and efficiency).
3. Set coefficients to reflect site conditions and contact geometry.
4. Enter an assumed deflection to estimate reaction force.
5. Click Calculate to see design energy and reaction.
6. Use Download buttons to export CSV or PDF records.

Fender Energy Planning Notes

1) Purpose of the calculation

This tool estimates the energy a fender system should absorb during berthing or impact. It reports base energy and design energy (after multipliers and safety factor) in kilojoules, matching common fender performance tables used in marine works. Use it for screening, budgeting, and option comparisons.

2) Typical vessel and speed ranges

Harbor craft can be a few hundred tonnes, while large ships can exceed 50,000 tonnes. Approach velocity is often evaluated around 0.05–0.25 m/s, with controlled berths commonly using 0.08–0.20 m/s for larger vessels. If your data is in knots, the calculator converts to m/s for consistency.

3) Why speed dominates results

In the kinetic method, energy scales with v². If speed doubles, energy rises about four times, even with the same mass. Tight operational controls and tug assistance can reduce required fender capacity significantly.

4) Coefficients and what they represent

Added mass (C_a) often falls near 1.0–1.4 to reflect hydrodynamic effects. Eccentricity (C_e) increases energy for off‑center contact. Berthing and environmental multipliers cover variability from approach angle, wind, and current. Keep a written justification for each factor so reviewers can trace your assumptions.

5) Safety factor and design allowance

The safety factor lifts the result to cover uncertainty and operational scatter. Preliminary checks frequently use about 1.0–1.3, but final values depend on client standards, berth criticality, and risk tolerance. Document the basis used for approvals and procurement.

6) Deflection and the reaction estimate

Reaction is estimated as R ≈ E/δ using your assumed deflection. Example: 1,200 kJ and 0.60 m gives roughly 2,000 kN. Treat this as screening only; manufacturer curves are nonlinear and must be verified.

7) When drop energy is useful

The drop method applies m×g×h×η and supports controlled impact checks. A 50‑tonne mass dropped 1.2 m at 0.90 efficiency yields about 530 kJ before multipliers. Use it for trials and prototype assessments where geometry and height are known.

8) Reporting and comparison workflow

Export CSV or PDF to attach results to bids, design notes, and quality records. Save key cases to the log to compare coefficients, safety factor, and deflection assumptions. When you shortlist a fender, confirm rated energy, reaction, and allowable deflection from supplier data sheets and project specifications.

FAQs

1) What is the difference between base and design energy?

Base energy comes from the equation only. Design energy applies coefficients and a safety factor to reflect real berthing variability and provide a selection margin.

2) Which method should I use for a berth study?

Use the kinetic method for vessel berthing checks. Use the drop method for controlled impact or test events defined by a known mass and height.

3) How do I choose an approach velocity?

Start from berth class and operating control. Many preliminary studies use 0.08–0.20 m/s for larger vessels, but confirm with port procedures and local standards.

4) What does added mass change?

Added mass increases effective mass to represent water moving with the vessel during contact. It raises energy without changing your entered vessel mass.

5) Is the reaction value a final design force?

No. It is an estimate using R ≈ E/δ. Final reaction and deflection must be checked on manufacturer performance curves at the selected energy.

6) Why does deflection affect reaction so much?

Reaction is inversely related to deflection in the estimate. Smaller deflection produces a higher reaction. Use a deflection consistent with the fender type being evaluated.

7) Does the log permanently store my entries?

The log is session-based. Export CSV or PDF for permanent project records, then store exports with assumptions and supplier verification documents.