An investigation into actual strength of ladders and intermediate securing methods used
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.Update from 30.11.2020:
"I have reissued my report due to hearing that some are justifying their use of deck tongues with the results.
The report did not cover regular use and damage caused.
In my opinion, deck tongues are not a good method due to how the load is placed onto just the two crimps, whereas with lashing, the correct shackles for the ladder type or soft round endless slings all place load on the sideropes and 4 crimps.
The reason the deck tongue got a reasonable failure load is to do with inline transfer of load. Recent testing has shown distortion of ladders due to deck tongue securing at relatively low loads. Loose steps and lost wedges / widgets result. Would be interesting to see how often ships replace ladders and how they were secured."
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”
Expert –“…….”
As you can see in the images the lashings are on the step fixtures.
As you can see in the images the lashings are on the step fixtures.
So Rolling hitch lashings versus …. Choking shackles and other methods, and along with that the strength of ladders – are they as strong as some people think?
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.
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.
Testing Intermediate Securing of Pilot Ladders:
Methods investigated included the rolling hitch lashing, choking shackles, shackles between sideropes, endless slings, and “deck tongues”
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.
Rope Lashings
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.
All the knots shifted more than 150mm with the manual load placed on them - this mean the knots would have slid onto the step fixtures.
All the knots shifted more than 150mm with the manual load placed on them - this mean the knots would have slid onto the step fixtures.
To make it clear - If the knots were tied onto a pilot ladder rather than a mock side rope with no step fixtures every single knot would have come up on the fixtures with less than 200kg load, nearly all with less than 100kg. In all tests using knots on actual ladders this was found to be true..
As a pilot climbs a ladder the load on either side of the ladder will alternate depending upon the climbing technique, so 100kg 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.
As a pilot climbs a ladder the load on either side of the ladder will alternate depending upon the climbing technique, so 100kg 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.
Testing On Ladders:
Testing On Ladders:
4 different makes of ladder were tested, 2new, 2 old
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
Single part of line
Single part of line
Old Seized avg result = 1970kg
New crimped avg result = 2002kg Removing crimps possible damage to the rope.
Doubled part of line
Doubled part of line
Doubled 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
One side of a ladder loaded
One side of a ladder loaded
New crimped avg result = 2755kg
Both sides were loaded
Both sides were loaded
Both sides were loaded
- 3 makes of ladder were tested
Results:
Old Seized = 3020
New crimped =4110
Ratios:
Step testing - wood only:
Strength of timber steps.
Longitudinal pull -
Remove side ropes from step.
Strength of timber steps.
Longitudinal pull -
Remove side ropes from step.
Test 1 - Fit shackles to side rope holes - one shackle at each end
Test 1 - Fit shackles to side rope holes - one shackle at each end
Test 2 - Fit shackles to side rope holes - Two shackles at each end
Test 2 - Fit shackles to side rope holes - Two shackles at each end
Result Test 1:
Failure occurred at 2600kg
ResultTest 2:
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 2600kg
ResultTest 2:
Stopped test at 4800kg, after removing shackles noted that the holes had elongation of approx 1mm in all four side rope holes
Step strength – transverse - loading on tread
Remove side ropes from 2 steps - upper step is there as a spreader.
Fit synthetic line in place of sideropes.
Remove side ropes from 2 steps - upper step is there as a spreader.
Fit synthetic line in place of sideropes.
Test 1 - Sling in centre of step - no spreading of load
Test 1 - Sling in centre of step - no spreading of load
Test 2 - Sling in centre of step - timber fitted cross grain to avoid crush damage
Test 2 - Sling in centre of step - timber fitted cross grain to avoid crush damage
Test 3 - Block fitted to place load closer to side rope holes
Test 3 - Block fitted to place load closer to side rope holes
Result Test 1:
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 the step is used to secure the ladder - see results for deck tongue as these results cannot be used to justify a deck tongue setup due to the test not including conventional side ropes.
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 the step is used to secure the ladder - see results for deck tongue as these results cannot be used to justify a deck tongue setup due to the test not including conventional side ropes.
Strength of Pilot ladders
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.
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.
So applying the 2.2 to what Pilot ladders are currently tested to.
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?
But the ladder strength is 24kN x 4….
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?
Intermediate Securing Methods
Methods tested:
Deck tongue
Deck tongue
Deck tongue
Rolling Hitch lashing
Rolling Hitch lashing
Rolling Hitch lashing
Shackles between siderope parts
Shackles between siderope parts
Shackles between siderope parts
Choking shackles – D shackles
Choking shackles – D shackles
- 20mm pin diameter – more common size
- 15mm pin diameter
- 20mm pin diameter – more common size
- 15mm pin diameter
Choking shackles – D shackles
- 20mm pin diameter – more common size
- 15mm pin diameter
- 20mm pin diameter – more common size
- 15mm pin diameter
Endless soft sling
Endless soft sling
Endless soft sling
Deck Tongue
Tests were conducted inline without a deck edge turn
- Old crimped: 815kg
- Old Seized: 2669kg, note between 300 - 1000kg seizings slid
Tests were conducted inline without a deck edge turn
- Old crimped: 815kg
- Old Seized: 2669kg, note between 300 - 1000kg seizings slid
- New crimped – 1 - New: 2316 crimps slid at ~900kg, load increased until failure
- 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
- 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
Shackle between the side ropes:
- Old Crimped ladder - 898kg – crimps kept sliding
- Old Seized – 1469kg
- New crimped - 1s – 1091kg
- New crimped - 2n – 1422kg
- Old Crimped ladder - 898kg – crimps kept sliding
- Old Seized – 1469kg
- New crimped - 1s – 1091kg
- New crimped - 2n – 1422kg
Choking Shackles:
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
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
Endless Soft Round Sling 2T WLL and Shackle 6.5T WLL:
- Old Crimped ladder - 1025kg
- Old Seized – 2184kg
- New crimped - 1s – 2094kg
- New crimped - 2n – 1925kg
- Old Crimped ladder - 1025kg
- Old Seized – 2184kg
- New crimped - 1s – 2094kg
- New crimped - 2n – 1925kg
Summary, Comments & Observations
Results so far…
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.
Note 1: have added calculated failure one side for deck tongue and double ended.
Note 2: In the case of the deck tongue tests the ladders would have been damaged beyond repair well before side rope failure occurred.
Note 2: In the case of the deck tongue tests the ladders would have been damaged beyond repair well before side rope failure occurred.
Note 1: have added calculated failure one side for deck tongue and double ended.
Note 2: In the case of the deck tongue tests the ladders would have been damaged beyond repair well before side rope failure occurred.
Note 2: In the case of the deck tongue tests the ladders would have been damaged beyond repair well before side rope failure occurred.
Sometimes the lashings using rolling hitches failed before the ladder did. All the other methods the
side ropes failed before the securing gear did.
The lashing either cut itself or it caused the side ropes to fail.
Strongest method?
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.
side ropes failed before the securing gear did.
The lashing either cut itself or it caused the side ropes to fail.
Strongest method?
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.
Strength of ladders
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?
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?
Another possible intermediate securing method
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).
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 say - Revised
With 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.Different shackles with different ladders brought different results – check with the ladder manufacturer.
Deck tongues – The use of deck tongues – note that the test results show seizings / crimps started to shift at loads as low as 300kg for older ladders and at around 1000kg for new. It appears deck tongues are practically guaranteed to shorten ladder life.
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.
Slings cow-hitched to sideropes:
Sling cow-hitched to siderope with turns taken around shackle to shorten the sling:
Capt. Troy Evans, October 2020
