Blockline and crown loads - Audit

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Blockline Loadings, release 5, issued 24 April 2008. AUDIT version.

The current release of this worksheet exists in different versions. They are identical apart from the way they are formatted. The Work version hides intermediate calculations and allows the user to see the results just below the inputs. This is useful for quick “what-if” games, changing various inputs to see what works best. The Audit version displays all intermediate calculations. The PDA version removes all text and formats the input and output fields for optimum viewing on a mobile, small-screen device.

This Audit version of the worksheet shows the formulae and intermediate results to allow auditing.

User input


1″ 6×19 IPS IWRC1″ 6×19 EIPS IWRC1.125″ 6×19 IPS IWRC1.125″ 6×19 EIPS IWRC1.25″ 6×19 IPS IWRC1.25″ 6×19 EIPS IWRC1.375″ 6×19 IPS IWRC1.375″ 6×19 EIPS IWRC1.5″ 6×19 IPS IWRC1.5″ 6×19 EIPS IWRC1.625″ 6×19 IPS IWRC1.625″ 6×19 EIPS IWRC1.75″ 6×19 IPS IWRC1.75″ 6×19 EIPS IWRC1.875″ 6×19 IPS IWRC1.875″ 6×19 EIPS IWRC2″ 6×19 IPS IWRC2″ 6×19 EIPS IWRC





Either; select a blockline

OR, enter wire breaking strength



Number of lines strung. Nbl =



Safety factor required for the blockline. SFbl =



Select a block bearing type to determine API friction factor





What is the maximum crown load (eg derrick limit)? Fcllimit =





Travelling block weight. mtb =





Desired load carried under the travelling block. Fhlbb =


Click here when any values are modified to update the result.


First calculate the limiting loads within the capacity of the line and the crown/derrick.

Reeving efficiency;

Max fast line tension;

Max hook load;

Dead line tension at max hook load;

Load on the crown at maximum hook load;

Now compare the limiting crown load with the crown load at the maximum hook load and return the lowest value;

Using the lower of the two, work out the hook load, fast line and dead line loads.

Calculate the maximum useable load below the block

Actual safety factor on the fast line at the maximum (limiting) hook load.

Second calculate the actual loads arising from the desired load under the hook.

Total hook load = load under the hook plus the travelling block.

Fast line load and dead line loads.

Actual safety factor on the fast line at the desired hook load.

Actual load on the crown.

Desired hook load as a percentage of maximum.


1 – limits of the line and derrick; the limiting 

Wire rope strength

Maximum hook load (including travelling block)

Maximum useable hook load (accounting for block)

2 – loads arising from the desired load under the travelling block,   or 

Fast line load

Dead line load

Crown load

Safety factor on the fast line

Specified hook load as % of maximum

Worksheet references

Institut Francais du Petrole. “Drilling Data Handbook” 6th Edition.

Release 1 of this worksheet was issued on 18 April 2008

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