Introduction / Preamble:I decided to look into pilot ladder strength and intermediate securing arrangements after MNZ put out what I felt was a confusing and unclear document about securing of pilot ladders.
Looking for information about why lashings were preferred got me nowhere; all sources just said they were best.
The discussions went along the line of the following:
Me – “So a piece of rope is not going to damage another piece of rope, but shackles are?”
Expert – “No the shackles put load on the step fixtures, lashings do not”
Me – “But the rope lashings do put load onto the step fixtures”
Expert - “No they do not”
Me – “look at these images”
Some say traditional seamanship skills are disappearing / gone,
Or is it crew have found a “quicker” way of doing the job with other gear?
How to test?
Load / destruction test.
Where / how can I do that? In the Barn, certified load cell + hydraulic pulling ram system + testbed
structure + assorted shackles + time + rope + ladders…. As another pilot says “Easy peasy”.
Onto investigating intermediate securing methods and strengths of ladders.
Methods investigated included the rolling hitch lashing, choking shackles, shackles between sideropes, endless slings, and “deck tongues”.
Testing Intermediate Securing of Pilot Ladders:
To determine the actual strength of ladders top end securing was tested as well.
The investigation into methods started with assessing the traditional method – rope lashings using rolling hitches.
Tests were also done with thinner higher strength synthetics – all results were lower but further testing could be done.
Average breaking strength of Manila rope used for lashings = 2516kg (24.67kN), samples were taken at random from the different parcels received from the supplier. Eyes were spliced in each end then tested to destruction.
Rolling hitch and other assorted knots
First step was to determine if lashings, in particular the rolling hitch, place any load on the crimps / step fixtures.
To determine if lashings would put load onto the fixtures a number of knots where tested on a mock siderope;
- The knots were tied and firmed up manually with block and tackle,
- Then a single 200mm pull using a hydraulic pulling ram was applied,
- The peak reading was taken to determine the best performing knot.
As a pilot climbs a ladder the load on either side of the ladder will alternate depending upon the climbing technique, so100kg of force a side is not hard to achieve when including the ladder weight.
Chaff damage - Chaff on the mock side ropes ranged from minor to moderate or worse.
Four different makes of ladder were tested, two new, two old.
Testing On Ladders:
As it only takes the failure of one side of a ladder for a pilot to fall the majority of tests were carried out on one side only.
The following may affect the results:
- Less distortion occurs when one side gets loaded than both (results possibly higher)
- Testing was inline versus uneven setups onboard ship ( results possibly higher)
- Testing has no deck edge feature (results possibly lower)
Side rope strength testing:
Side rope with no fittings
Thimbles were used to allow for a better D/d1.
Single part of line
New crimped avg result = 3269kg Removing crimps possible damage to the rope.
Sideropes with steps crimp / seizings and chocks/widgets
- a section of ladder was modified to have two tops so that the side ropes would be loadedand no load placed on any steps, chocks or crimps except by the sideropes
One side of a ladder loaded
Failure occurred at 2600kg
Stopped test at 4800kg, after removing shackles noted that the holes had elongation of approx 1mm in all four side rope holes
Failure occurred at 1730kg
Result Test 2:
Failure occurred at 1760kg
Result Test 3:
Failure occurred at 2910kg
Test 1 shows the likely strength of a wooden step if a pilot boat were to come down on one.
Test 3 shows the timber step strength when use on a deck tongue - see results for deck tongue.
I hear people talk about strength of pilot ladders, they refer to the rules which state 24kN for the side rope material, the rules do not state the strength for pilot ladders it is the strength of the material for the side ropes.
Strength of Pilot ladders
You may think this means little, but…. A pilot ladder is proof tested to 8.8kN, which means that the load you should safely put on a pilot ladder in use will be less than 8.8kN.
From the testing carried out we can see that the actual strength of pilot ladders is not 48kN and nowhere near 96kN. Testing so far as an average of 40.3kN
SWL / WLL
Looking at safety factors and proof testing to determine a SWL for a pilot ladder with manila sideropes:
Manila rope SF of 12,
48kN = 4kN,
96kn = 8kN
What proof load is required, looking back I found pilot hoists had to have an overload test of 2.2, below is some of the text from the old MNZ Part 53. Dutch rules are similar.
Test load / proof load factor = 8.8kN/2.2 = 4kN = 407kg force
Perhaps this is the SWL / WLL of a pilot ladder.
Being practical is a 407kg SWL / WWL acceptable for a pilot ladder:
What weight does a pilot ladder have to carry?
- itself…. (a 15m long pilot ladder weighs in at 100kg.)
- a pilot 150kg to allow for wallet (with pilots licence in), radio, small bag, wet weather gear (may be fitted with pockets to carry PPU), PPE (Incl Covid-19 gear).
250kg/407kg = 61% of the SWL adequate?
- New crimped - 2 – New: 1506* crimps slid at ~1000kg, load increased, ladder badly distorted
THE FOLLOWING TESTS WERE CONDUCTED ON ONE SIDE OF A LADDER
Rolling hitch lashing:
- Old Crimped ladder -857kg
- Old Seized – 1280kg
- New crimped - 1s – 1043kg
- New crimped - 2n – 1145kg
- Old Crimped ladder - 898kg – crimps kept sliding
- Old Seized – 1469kg
- New crimped - 1s – 1091kg
- New crimped - 2n – 1422kg
Choking Shackle 20mm pin dia D shackle:
- Old Crimped ladder -692kg – crimps kept sliding
- Old Seized – 1857kg
- New crimped - 1s – 1492kg
- New crimped - 2n – 1421kg
Choking Shackle 15mm pin dia D shackle:
- Old Crimped ladder -1000kg
- Old Seized – 1822kg
- New crimped - 1s – 1480kg
- New crimped - 2n – 1522kg
Choking Shackle – all types tested:
- Old Crimped ladder -888kg
- Old Seized – 1827kg
- New crimped - 1s – 1481kg
- New crimped - 2n – 1472kg
- Old Crimped ladder - 1025kg
- Old Seized – 2184kg
- New crimped - 1s – 2094kg
- New crimped - 2n – 1925kg
Results so far…
Summary, Comments & Observations
The following graph uses a factor of 1.49 to convert one side results (light blue), into a calculated failure load for both sides (Purple), it also shows the avg for tests conducted with both sides at the same time (Grey).
The 1.49 comes from the ratios found with testing.
side ropes failed before the securing gear did.
The lashing either cut itself or it caused the side ropes to fail.
Currently the strongest intermediate securing arrangement available that I have tested is to use soft round endless slings cow-hitched to the sideropes and shackled to strong points using tested shackles. See last page for photos.
2T WLL slings(14T MBL) with 6.5T WLL (MBL over 30T) green pin shackles were used in testing. The strength of these exceeds the strength requirements under the rules.
Average strength of ladders tested – 4110kg / 40.3kN
Would having a SWL make a difference?
Perhaps - it might mean that after a pilot boat snags a ladder it would have to be thoroughly inspected or tested?
Or maybe if ladders had a SWL of 407kg ship’s crew might take better care, pilot transfer vessels might just might get designed and driven with that in mind, after all a ladder is tested to 8.8kN, whatinsurance company would pay out on an equipment failure that occurs at a load beyond that whichthe equipment has been tested to?
There is presently a device under development, initial tests show that it is as strong as using slings, but it has the added benefit that it leaves a mark on the side ropes to show that over half a tonne has been applied to the side of the ladder it is securing – in other words if the side ropes have both got the marks then the ladder has been subjected to more than it has been tested to (8.8kN).
Last sayWith limited resources and limited testing carried out, less than 300tests on 4 different makes of ladders, further testing may show differences.
Very early testing showed choking shackles and lashings to be similar in strength, yet with further testing this has been found to be false.
Fatigue testing should be carried out – I currently do not have the time or resources to do this though I do intend to continue testing methods that are currently in use and investigate alternatives, any assistance is appreciated.
Gear used for the intermediate securing of pilot ladders should be tested and certified.
Random knots tied with random offcuts of line - you would not secure cargo with them.