Donut Fender Guide: Benefits, Sizing & Applications for Marine Berths

Donut Fender Guide: Benefits, Sizing & Applications for Marine Berths

 

Description:

Discover why donut fenders are ideal for marine berths. Learn sizing formulas, installation tips, and saltwater durability. Get a free donut fender selection consult today!

When it comes to absorbing vessel impact in tight spaces, donut fenders (also called doughnut or annular fenders) outperform many traditional designs. Their circular, hollow-core shape distributes load evenly around the berthing line—making them the go-to choice for dolphins, jetty corners, and narrow quay walls.

Yet 41% of port engineers still opt for rectangular fenders in situations where donut fenders would offer 30% better energy absorption and 50% longer lifespan (Marine Structures International, 2025). This guide explains why donut fenders belong in your harbor’s safety toolkit—and how to choose the right one.

 

What Is a Donut Fender?

A donut fender is a circular rubber unit with a central hole, designed to fit onto piles, bollards, or fixed structures. Unlike flat panel fenders, its geometry allows 360° load dispersion, reducing stress concentrations on both the fender and the berthing vessel.

Key characteristics:

①Shape: Torus (ring with hole)

②Materials: Natural rubber blend, EPDM, or polyurethane (for extreme abrasion)

③Mounting: Slide onto cylindrical pile or bolt through reinforced eyelets

 

Benefits of Donut Fenders for Marine Berths 

①Uniform Load Distribution

Absorbs impact forces equally around the circumference—ideal for vessels with uneven approach angles.

②Space-Saving Design

Fits snugly around piles or dolphins without protruding into navigation channels.

③Easy Installation & Replacement

Slide-on design reduces labor time by 40% compared to bolting large panel fenders

④Superior Energy Absorption

Lab tests show 25–35% higher deflection efficiency than square fenders of equal cross-section.

⑤Corrosion & Abrasion Resistant

Marine-grade EPDM or PU coatings resist saltwater, UV, and fender-to-hull abrasion.

 

How to Size a Donut Fender for Your Berth 

Step 1: Determine Vessel Parameters

LOA, beam, DWT, and max berthing velocity (m/s)

Use 1.5x safety factor for dynamic loads

Step 2: Calculate Energy Absorption Requirement

E=0.5×m×v²×ρ_salt/ρ_fresh

m= vessel mass (kg)

v= berthing velocity

ρ_salt= 1025 kg/m³

Step 3: Select Donut Dimensions

Match outside diameter (OD) to pile/bitt size; wall thickness determines load capacity.

OD range: 300 mm – 2400 mm

Wall thickness: 50 mm – 300 mm

Step 4: Verify Deflection Limits

Ensure deflection under max load stays within manufacturer’s recommended 40–60% compression range.

 

Best Applications for Donut Fenders

Dolphin mooring points

Jetty corners & curved berths

Narrow quay walls

Floating pontoon edges

Ship-to-ship transfer zones

 

FAQ

Q1: Can donut fenders be used in freshwater ports?

A: Yes—simply omit the saltwater density multiplier in calculations.

Q2: How long do donut fenders last in saltwater?

A: 12–18 years with EPDM or PU covers; 8–12 years with natural rubber.

Q3: Are donut fenders suitable for large container ships?

A: Yes—specify larger OD and thicker walls; pair with mooring bollards for heavy loads.

 

Conclusion

Donut fenders deliver unmatched performance where space and uniform load control matter. Choosing the right size and material ensures decades of reliable protection for your harbor and vessels.

Need help sizing a donut fender for your berth?Our marine engineers offer a free selection consult—including load calculations, material recommendations, and supplier quotes. Click here to schedule now!