Marine Crane Reach Calculator

Calculator Inputs

Unit system

All computations are performed in meters internally.

Boom length

Main boom length (m or ft).

Tip extension

Optional tip extension (m or ft).

Boom angle (degrees)

Angle measured from horizontal.

Slew angle (degrees)

Used for X/Y plan projection.

Pivot height above deck

Boom pivot height from deck (m or ft).

Slew center to pivot offset

Horizontal offset from rotation center (m or ft).

Horizontal hook offset

Sheave/reeving offset from boom tip (m or ft).

Hook drop below tip

Distance from tip to hook (m or ft).

Boom deflection (%)

Reduces effective reach and height (0–10%).

Deck height above water

Freeboard or deck elevation (m or ft).

Tide correction

Positive means higher water reduces clearance (m or ft).

Wave heave allowance

Vertical allowance for vessel motion (m or ft).

Sway allowance factor

Adds a fraction of radius for drift/sway (0–0.2).

Target radius (optional)

Compare against radius with allowances (m or ft).

Target height above water (optional)

Compare against vertical above water (m or ft).

Results appear above after submission.

Example Data Table

Scenario	Boom (m)	Angle (deg)	Offset (m)	Hook drop (m)	Radius (m)	Height above water (m)
Deck lift near vessel side	30	60	1.0	1.2	16.6	32.0
Longer radius transfer	40	45	1.0	1.5	29.0	29.3
High pick for clearance	28	75	1.0	1.0	8.2	34.6

Example values are illustrative and should not replace certified crane documentation.

Formula Used

This calculator uses a geometric reach model based on boom length and boom angle. A small deflection factor can be applied to reduce the effective length.

Effective length: L_eff = L_boom + L_ext
Deflection factor: f = 1 − (deflection% / 100)

Horizontal reach from pivot: H = (L_eff · cos(θ) · f) − H_hook
Working radius from slew center: R = H + O_pivot
Allowance radius: R_allow = R · (1 + s)

Vertical above deck: V_deck = H_pivot + (L_eff · sin(θ) · f) − V_hook
Vertical above water: V_water = V_deck + H_deck − tide − heave

θ is the boom angle from horizontal, s is the sway allowance factor, O_pivot is the slew-center-to-pivot offset, and hook offsets approximate reeving geometry.

How to Use This Calculator

Select your unit system and enter the boom length and angle.
Add tip extension if installed, then set pivot height and pivot offset.
Enter hook offsets to better match your reeving and block geometry.
Set deck height above water and allowances for tide and wave heave.
Optionally add a sway allowance factor to build conservative radius margins.
Enter target radius and height to get a quick pass/fail envelope check.
Download CSV or PDF to attach to lift planning documentation.

Professional Guide

1) Why reach planning matters offshore

Marine lifts combine construction tolerances with vessel motion, so a quick reach check helps confirm that the hook can reach the set point without exceeding the planned working radius. Small differences in boom angle can change radius by several meters, which directly affects lift capacity on the load chart.

2) Interpreting working radius

Working radius is the horizontal distance from the crane’s rotation center to the hook line. For a 30 m boom at 60°, the geometric horizontal component is about 15 m before offsets. Adding a 1 m pivot offset and small hook geometry adjustments can move the radius into the 16–18 m range.

3) Boom angle sensitivity

Angle is the strongest driver of reach. Holding boom length constant, shifting from 45° to 60° reduces horizontal reach by roughly 13% while increasing vertical height by about 22%. Use angle sweeps during planning to find a safe envelope that also supports the required capacity.

4) Allowances for deflection, sway, and drift

A practical deflection allowance of 0–3% is common for preliminary geometry checks. Sway factors around 0.01–0.05 can be used to add conservative radius margin for wind, tag line dynamics, and operator control. Increase the allowance for long radii or high wind exposure.

5) Heave and tide in vertical clearance

Clearance to water and structures should include vessel heave and tide. For moderate sea states, a 0.3–1.5 m heave allowance is often used in lift plans, depending on the motion criteria. A positive tide correction reduces the available height above water, so treat it as a conservative subtraction.

6) Using plan X/Y for deck layouts

The plan projection converts radius and slew angle into X/Y offsets, useful for plotting laydown areas, avoiding handrails, and checking exclusion zones. If your lift point is defined by coordinates, compare it directly to the computed X/Y to validate alignment before execution.

7) Envelope checks with target values

Enter a target radius and target height above water to get a quick pass/fail check. A positive radius margin means your planned configuration can reach the point even after allowances. A negative height margin indicates insufficient clearance, prompting a higher boom angle, shorter hook drop, or revised set point.

8) Field verification and documentation

Use the CSV and PDF exports to capture assumptions and results for toolbox talks and lift plan packages. This estimator supports planning, but it does not replace certified charts, rigging calculations, or competent-person review. Confirm actual boom length, reeving, and offsets during pre-lift checks.

FAQs

1) Does this calculator replace a crane load chart?

No. It estimates geometry only. Always confirm capacity, configuration limits, and operating conditions using the certified load chart and the manufacturer’s instructions.

2) What boom angle definition is used here?

The boom angle is measured from horizontal. A higher angle increases vertical height and usually reduces horizontal radius for the same boom length.

3) How should I choose the sway allowance factor?

Use a small factor for calm conditions and short radii (0.01–0.02). Increase it for long radii, wind exposure, and dynamic lifts (0.03–0.05). Keep it conservative.

4) Why is height above water reduced by tide and heave?

Tide and heave can raise the effective water level relative to the hook. Subtracting them provides conservative clearance when planning lifts near the waterline.

5) What should I enter for hook offsets?

Enter horizontal and vertical distances that represent the reeving block geometry between the boom tip and hook. If unknown, use small values and verify during rigging checks.

6) Can I use imperial units and still get consistent results?

Yes. Inputs can be in feet when imperial is selected. The tool converts internally and reports results in meters for consistency in calculations and downloads.

7) Why do my results differ from a site plan?

Real lifts include crane pedestal geometry, slew center definitions, vessel trim, and structural clearances. Treat this as a planning baseline, then refine using certified drawings and surveys.