Project Overview
This case study documents the complete design process of a 15-meter high-speed patrol boat for coastal
surveillance and interception duties. The project demonstrates real-world application of naval architecture
principles, from initial requirements through final specifications.
🎯 Project Objectives:
- Design a 15m patrol boat capable of 35+ knots
- Maximum range of 400 nautical miles
- Crew capacity of 6 personnel
- Seaworthy for coastal and offshore operations
- Cost-effective construction using aluminum
1. Requirements Analysis
1.1 Operational Requirements
| Parameter |
Requirement |
Justification |
| Length Overall |
15m ± 0.5m |
Trailerable, marina constraints |
| Maximum Speed |
≥ 35 knots |
Interception capability |
| Cruising Speed |
25 knots |
Fuel efficiency balance |
| Range |
400 nm @ 25 kn |
Extended patrol endurance |
| Crew |
6 persons |
Standard patrol team |
| Seakeeping |
Sea State 4 |
Coastal operations capability |
| Construction |
Aluminum |
Weight, corrosion, durability |
1.2 Mission Profile
Primary Missions:
- Coastal surveillance and law enforcement
- Search and rescue (SAR) operations
- Interdiction and boarding operations
- Maritime security patrols
Secondary Missions:
- Emergency medical evacuation
- Environmental monitoring
- Training exercises
2. Design Process
2.1 Hull Type Selection
Decision: Deep-V planing hull with variable deadrise
Rationale:
- Speed requirement (35+ knots) demands planing configuration
- Deep-V (20-24° deadrise) provides good rough-water capability
- Variable deadrise (higher forward, lower aft) balances ride quality and planing efficiency
2.2 Principal Dimensions
Initial Dimension Calculations:
Given: LOA = 15m
Calculate:
• LWL = LOA × 0.90 = 15 × 0.90 = 13.5m
• Beam = LOA / 4.3 = 15 / 4.3 = 3.49m (use 3.5m)
• Draft = LOA / 28 = 15 / 28 = 0.54m
• Depth = LOA × 0.105 = 15 × 0.105 = 1.58m
• Deadrise (transom) = 20°
• Deadrise (bow) = 45° (for seakeeping)
• LCG = 29% LOA = 4.35m from stern
2.3 Displacement Estimation
Weight Budget:
Target Displacement: ~12 tonnes
Breakdown:
• Structure (aluminum hull): 4,200 kg (35%)
• Machinery (2x diesel engines): 2,400 kg (20%)
• Fuel (2,000 liters): 1,700 kg (14%)
• Equipment & Systems: 1,800 kg (15%)
• Outfit & Furnishings: 900 kg (7.5%)
• Crew & Gear: 600 kg (5%)
• Margins & Misc: 400 kg (3.5%)
Total: 12,000 kg (12 tonnes)
3. Calculations & Results
3.1 Resistance Calculation (Calibrated Savitsky)
Speed: 35 knots
Input Parameters:
LOA = 15m, LWL = 13.5m, B = 3.5m
Δ = 12,000 kg, Deadrise = 20°
Speed = 35 kn = 18.0 m/s
Results:
• Froude Number = 3.08 (full planing)
• Total Resistance = 28.7 kN
• Effective Power = 517 kW
• Required Power (η=0.65) = 795 kW
→ 1,065 HP required
3.2 Power Selection
Engine Configuration: Twin diesel engines
Per Engine:
Power = 1,065 / 2 = 532 HP
Selected: 2x 600 HP diesel engines
Total Installed: 1,200 HP
Margin: 12.7% (adequate for rough conditions)
Propulsion:
• Surface-piercing propellers
• 2:1 reduction gears
• 14" diameter × 18" pitch (estimated)
3.3 Speed-Power Curve
| Speed (kn) |
Resistance (kN) |
Power (HP) |
Fuel Burn (L/hr) |
| 15 |
8.2 |
165 |
35 |
| 20 |
12.5 |
285 |
55 |
| 25 |
18.1 |
465 |
85 |
| 30 |
24.8 |
720 |
125 |
| 35 |
32.7 |
1,065 |
175 |
| 38 |
38.5 |
1,350 |
220 |
3.4 Range Calculation
Fuel Capacity: 2,000 liters (530 US gallons)
Cruising Speed: 25 knots
Fuel Consumption: 85 L/hr @ 25 kn
Endurance: 2,000 / 85 = 23.5 hours
Range: 23.5 × 25 = 588 nm
Add 20% reserve: 588 × 0.80 = 470 nm
✅ Requirement met (400 nm target)
3.5 Stability Analysis
Static Stability:
- GM (Metacentric height): 1.25m (good initial stability)
- Righting arm (GZ) at 20° heel: 0.68m
- Maximum GZ: 0.82m at 45° heel
- Range of stability: 0-70° (excellent)
Dynamic Stability:
- Roll period: 3.2 seconds (acceptable)
- Damage stability: 1-compartment flooding standard
4. Challenges Faced
Challenge #1: Speed vs. Range Trade-off
Problem: High speed (35 kn) requires large engines, which consume fuel rapidly.
This conflicts with range requirement (400 nm).
Solution:
- Optimized hull for cruising speed (25 kn) rather than max speed
- Selected fuel-efficient common-rail diesel engines
- Increase fuel capacity to 2,000L
- Used surface drives for improved propulsive efficiency
Challenge #2: Seakeeping vs. Speed
Problem: Deep-V needed for rough water, but increases resistance and reduces
planing efficiency.
Solution:
- Variable deadrise: 45° forward → 20° aft
- Optimized LCG at 29% LOA for proper trim
- Added longitudinal strakes for lift and spray reduction
Challenge #3: Weight Control
Problem: Aluminum hull still heavier than expected due to scantling requirements
for offshore service.
Solution:
- Used high-strength 5083 aluminum alloy
- Optimized frame spacing based on structural analysis
- Finite element analysis (FEA) to minimize material while maintaining strength
5. Final Specifications
| Parameter |
Value |
| Principal Dimensions |
|
| LOA |
15.00 m |
| LWL |
13.50 m |
| Beam |
3.50 m |
| Draft |
0.54 m |
| Depth |
1.58 m |
| Deadrise (transom) |
20° |
| Displacement |
12.0 tonnes |
| Performance |
|
| Max Speed |
38 knots |
| Cruising Speed |
25 knots |
| Range @ 25 kn |
470 nm (with reserve) |
| Propulsion |
|
| Engines |
2x 600 HP Diesel |
| Total Power |
1,200 HP |
| Drives |
Surface-piercing propellers |
| Capacity |
|
| Fuel |
2,000 liters |
| Water |
200 liters |
| Crew |
6 persons |
| Construction |
|
| Material |
Aluminum 5083-H116 |
| Class |
ABS High-Speed Craft |
6. Lessons Learned
💡 Key Takeaways:
- LCG Position is Critical: Initially designed at 35% LOA, but resistance
calculations showed this was too far forward. Moved to 29% LOA, reducing resistance by 12%.
- Weight Budgeting: Early weight estimates were optimistic. Detailed weight
accounting revealed 15% higher displacement. Always add 15-20% margin!
- Calibrated Savitsky Accuracy: Resistance predictions were within 5% of
model tests, validating the Calibrated Savitsky method for this application.
- Surface Drives: Surface-piercing propellers provided 8% efficiency gain
compared to submerged propellers, justifying their complexity.
- Iterative Design: The design went through 5 major iterations. Each iteration
refined the balance between speed, range, seakeeping, and cost.
7. Conclusion
This 15m patrol boat design successfully meets all operational requirements. The Calibrated Savitsky
method proved accurate for resistance prediction, and proper LCG optimization was crucial for performance.
The vessel balances speed, range, and seakeeping while remaining cost-effective to build and operate.