A&CE — Deepwater Mudmat Installation

Methodology

This analysis screens deepwater mudmat installations across a parametric matrix of vessels, water depths, structure sizes, and sea states. Each case evaluates five installation phases per DNV-RP-H103 and DNV-ST-N001 methodology.

Phase 1: Lift-off

Hook load = mass_air × g × DAF_lift (1.10). Checked against crane SWL at operating radius via interpolation of the crane capacity curve.

Phase 2: In-air Transit

Tilt check for 4-point lift with spreader beam. CoG offset / hook height gives tilt angle, checked against 5° limit. Symmetric mudmats always pass.

Phase 3: Splash Zone (Critical)

Slamming force: F_slam = 0.5 × ρ × C_s × A_p × v_rel², where v_rel = v_lowering + v_wave. Additional varying buoyancy and drag forces. DAF_splash = 1.30. This phase typically governs for large mudmats in higher sea states.

Phase 4: Lowering through Water Column

Cable tension = W_sub + W_cable(depth) + snap load. Snap load from dynamic cable response using vessel heave RAO. Checked against 85% of wire MBL. Becomes critical at extreme depths due to cable self-weight.

Phase 5: Landing

Bearing pressure = W_sub / A_base. Checked against 50 kPa soft clay bearing capacity. Rarely governs for typical mudmat proportions.

Go/No-Go Criteria

GO: All phases pass AND max utilisation < 0.85
MARGINAL: All phases pass AND max utilisation in [0.85, 1.00]
NO-GO: Any phase fails (utilisation > 1.00)

Applicable Codes & Standards

DNV-RP-H103 (2011) — Modelling and Analysis of Marine Operations
DNV-ST-N001 (2021) — Marine Operations and Marine Warranty
DNV-RP-C205 (2010) — Environmental Conditions and Environmental Loads

Installation Screening Summary

All cases at Hs = 2.0 m reference sea state

Vessel	Structure	Depth (m)	Max Util.	Governing Phase	Status
Large CSV	Mudmat-S-50te	500	24.7%	Landing	GO
Large CSV	Mudmat-M-100te	500	21.5%	Landing	GO
Large CSV	Mudmat-L-200te	500	20.6%	Splash zone	GO
Large CSV	Mudmat-S-50te	1000	24.7%	Landing	GO
Large CSV	Mudmat-M-100te	1000	21.5%	Landing	GO
Large CSV	Mudmat-L-200te	1000	20.6%	Splash zone	GO
Large CSV	Mudmat-S-50te	1500	24.7%	Landing	GO
Large CSV	Mudmat-M-100te	1500	21.5%	Landing	GO
Large CSV	Mudmat-L-200te	1500	20.6%	Splash zone	GO
Large CSV	Mudmat-S-50te	2000	24.7%	Landing	GO
Large CSV	Mudmat-M-100te	2000	21.5%	Landing	GO
Large CSV	Mudmat-L-200te	2000	20.6%	Splash zone	GO
Large CSV	Mudmat-S-50te	2500	24.7%	Landing	GO
Large CSV	Mudmat-M-100te	2500	21.5%	Landing	GO
Large CSV	Mudmat-L-200te	2500	20.6%	Splash zone	GO
Large CSV	Mudmat-S-50te	3000	24.7%	Landing	GO
Large CSV	Mudmat-M-100te	3000	21.5%	Landing	GO
Large CSV	Mudmat-L-200te	3000	20.6%	Splash zone	GO
Medium CSV	Mudmat-S-50te	500	24.7%	Landing	GO
Medium CSV	Mudmat-M-100te	500	34.8%	Splash zone	GO
Medium CSV	Mudmat-L-200te	500	71.5%	Splash zone	GO
Medium CSV	Mudmat-S-50te	1000	24.7%	Landing	GO
Medium CSV	Mudmat-M-100te	1000	34.8%	Splash zone	GO
Medium CSV	Mudmat-L-200te	1000	71.5%	Splash zone	GO
Medium CSV	Mudmat-S-50te	1500	24.7%	Landing	GO
Medium CSV	Mudmat-M-100te	1500	34.8%	Splash zone	GO
Medium CSV	Mudmat-L-200te	1500	71.5%	Splash zone	GO
Medium CSV	Mudmat-S-50te	2000	24.7%	Landing	GO
Medium CSV	Mudmat-M-100te	2000	34.8%	Splash zone	GO
Medium CSV	Mudmat-L-200te	2000	71.5%	Splash zone	GO
Medium CSV	Mudmat-S-50te	2500	24.7%	Landing	GO
Medium CSV	Mudmat-M-100te	2500	34.8%	Splash zone	GO
Medium CSV	Mudmat-L-200te	2500	71.5%	Splash zone	GO
Medium CSV	Mudmat-S-50te	3000	24.7%	Landing	GO
Medium CSV	Mudmat-M-100te	3000	34.8%	Splash zone	GO
Medium CSV	Mudmat-L-200te	3000	71.5%	Splash zone	GO

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Assumptions & Limitations

Crane SWL evaluated at maximum capacity radius (most favourable position)
DAF lift-off = 1.10, DAF splash zone = 1.30 per DNV-ST-N001
JONSWAP peak period approximation: Tp = 4 * sqrt(Hs)
Slamming coefficient Cs = 5.0 for flat-bottom structures per DNV-RP-H103 Table 4-1
Added mass coefficient Ca = 1.0, drag coefficient Cd = 2.0 for flat plate geometry
Wire rope MBL safety factor = 0.85 (max tension / MBL)
Bearing capacity limit = 50 kPa (soft clay, undrained)
Vessel heave at crane tip uses simplified single-frequency RAO peak
No current loads or wind loads on structure during lowering
Rigging weight excluded from hook load calculations
Seabed assumed flat — no slope corrections for landing
Seawater density = 1025 kg/m3 throughout water column

Chart 1: Go/No-Go Installation Matrix

Side-by-side vessel comparison at Hs = 2.0 m reference sea state.

Chart 2: Crane Utilisation vs Water Depth

Max utilisation across all phases. Solid = Large CSV, dashed = Medium CSV.

Chart 3: Phase Utilisation vs Water Depth — Splash & Lowering

Shows how splash zone dominates shallow cases while lowering governs at depth.

Chart 4: Operability Envelope — Max Hs vs Structure Weight

Maximum sea state where all depths pass. Defines weather window requirements.

Chart 5: Vessel Head-to-Head — Structures Installable per Depth

Number of mudmat sizes (out of 3) each vessel can install at Hs = 2.0 m.

Deepwater Mudmat Installation Analysis