How to choose the right mooring lines for your boat

Mooring lines are your boat's first line of defense: they secure it to the dock, pontoon, or locker, absorb shocks, and protect your deck hardware. Recycling an old sheet may seem economical, but it's the quickest way to weaken your mooring. Here's a comprehensive guide to selecting, sizing, and equipping your mooring lines with complete peace of mind.

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1. Basic principles

An effective mooring line must:

• Cushion movements (controlled elasticity).

• Resist breakage despite wear (scuffing, UV, salt).

• Keep it handy to make knots or handling easier.

• Survive the chemical and mechanical attacks of the port.

2. What makes a rope a good mooring line?

Criteria	Why it matters
Elasticity	Absorbs shocks from wind, chop and waves; protects cleats and fairleads
Breaking strength	Secures the boat in bad weather; allow for wear and tear
Flexibility	Makes knots easier, prevents hulls
UV/abrasion resistance	The moorings often remain in place

Remember: the heavier or more exposed the boat, the more elastic and oversized the rope is required.

3. Adapted constructions

Construction	+	–
Twisted	High elongation; economical; easy splicing	Torsions (shells); stiffening over time
Square line braid	Flexible, non-squeezing, good cushioning	Propensity to fray
Double braid	Very robust, good flexibility, controlled wear	Less stretch, higher price

4. Materials

4.1 Polyester

• Advantages : excellent UV & abrasion resistance, low water absorption, reasonable price, easy to handle.

• Limit : lower elasticity; provide shock absorbers or generous lengths.

• Ideal for : long-term main moorings, well-sheltered ports.

OUR MOORINGS

4.2 Polyamide (Nylon)

• Advantages : elasticity ≈ 10% better than polyester; absorbs shocks.

• Limitations : hardens with age, water absorption (→ loss of flexibility), UV less good than polyester.

• Ideal for : points or crossings dedicated to gusts, anchor lines.

OUR MOORINGS

4.3 Polypropylene

• Advantages : floats (zero risk of propeller); very light; resistant to chemicals.

• Limitations : low UV/abrasion resistance; lower breakage.

• Ideal for : occasional use, very sheltered ports, temporary trailers.

OUR MOORINGS

5. Dimensions

5.1 Recommended diameter

Boat length	Ø Polyester	Ø Polyamide	Ø Polypropylene
≤ 6 m	10 mm	8 mm	14 mm
8 m	12 mm	10 mm	16 mm
10 m	14 mm	12 mm	20 mm
12 m	16 mm	14 mm	22 mm
14 m	18 mm	16 mm	26 mm
16 m	22 mm	18 mm	28 mm
18 m	24 mm	20 mm	28 mm
20 m	26 mm	22 mm	32 mm

Tip : in exposed areas (wind/current) or heavy boats, go up a size.

5.2 Recommended length

• Always have four standard mooring lines :

  • 2 × boat length (tips)

  • 2 × 2 × boat length (main or long)

• Add 1–2 long lines (≥ 2 lengths) for trailers, side-by-side mooring or lock.

Example 10 m boat : 2 × 10 m + 2 × 20 m + 1 25 m long.

6. Use & accessories

6.1 Why splice?

• Strength : a splice retains ~90% of the breaking load (a knot ≈ 50%).

• Durability : no protruding parts that rub or age.

• Ready to use : stainless steel thimble + shackle → instant installation on the pontoon.

6.2 Useful accessories

Accessory	Main use
Stainless steel lugs	Protect the mooring eye from chafing
Shock absorbers	Polyurethane or rubber, absorbs shocks
Leather covering	Limits abrasion on bits & fairleads
Shackles	Quick attachment to ring or trunk

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Conclusion

Choosing a good mooring line means combining material , construction , diameter and length to absorb energy without weakening. Be generous with your dimensions and favor quality spliced finishes. You will increase the lifespan of your rope, the safety of your boat and the comfort of the entire crew.

Need a custom installation? Gorilla Ropes can make your spliced mooring lines with thimbles.

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Tags: moorings, ropes, polyester, polyamide, polypropylene, splice, anchoring, boat safety, Gorilla Ropes