2025 Professional Boat Floating Calculator
Comprehensive tool for calculating boat buoyancy, flotation needs, stability, center of gravity, displacement, and capacity. Add dimensions, components, customize parameters, and export detailed reports.
Boat Dimensions & Type
Customize Parameters
Add Component
Add Flotation Foam
Material Specific Gravity & K Factors
| Material | Specific Gravity (SG) | K Factor (Submerged) | Notes |
|---|---|---|---|
| Aluminum | 2.6 | 0.63 | Common for hulls |
| Fiberglass | 1.5-1.8 | 0.33 | Average 1.65 SG |
| Wood (Douglas Fir) | 0.5 | -0.81 | Buoyant material |
| Steel | 7.8 | 0.87 | Heavy, for large vessels |
| Plastic (ABS) | 1.1 | 0.11 | Lightweight |
| Gasoline | 0.72 | N/A | For fuel tanks |
| Lead | 11.0 | N/A | For ballasts |
ABYC & USCG Standards
| Standard | Component | Formula | Notes |
|---|---|---|---|
| Boat Flotation (Fb) | Hull/Deck | (W × K + Dry Weight) / Foam Support | W: Weight, K: Material factor |
| Engine Flotation (Fm) | Engine | Swamped Weight / Foam Support | For outboard/inboard |
| Passenger Flotation (Fp) | Persons | If Wp > 550: (0.5 × 550 + 0.125 × (Wp - 550)) / 60.4; Else 0.25 × Wp / 60.4 | Wp: Passenger weight |
| Total Flotation (Ft) | All | Fb + Fm + Fp × Safety Factor | Apply 1.33 safety |
| Capacity | Persons | (Length × Beam) / 15 | For <20ft boats |
| Horsepower | Engine | Based on Length × Transom Width table | Max HP for small boats |
Factors & Formulas
| Factor | Description | Impact | Formula |
|---|---|---|---|
| Displacement | Volume of water displaced | Buoyancy = Displacement × Water Density | Length × Beam × Draft × Block Coefficient (approx 0.5-0.7) |
| Center of Gravity (CG) | Balance point | Affects stability; low VCG better | Sum (Weight × Position) / Total Weight |
| Stability (GM) | Metacentric height | Positive GM for stability | Approx: KM - KG; KM = Beam² / (12 × Draft) |
| Reserve Buoyancy | Extra flotation | Safety margin | (Freeboard / Draft) × 100% |
Frequently Asked Questions
How to calculate displacement?
Use hull dimensions and block coefficient (0.5 for fine hulls, 0.7 for full).
What is a good GM value?
>1 ft for small boats; consult ABYC for specifics.
How to place foam?
Bilges for low CG, gunwales for upright stability, transom for engine weight.
Why safety factor?
1.33 accounts for uncertainties in weights and conditions.
Tips for Professional Use
- Measure actual weights for accuracy; use scales for components.
- Apply 20% reserve buoyancy for waves/weather.
- For catamarans, distribute foam in hulls for balance.
- Verify with software like DELFTship or Orca3D for complex designs.
- Always test in water; adjust based on trim.
Disclaimer: This is an estimation tool based on 2025 standards. Consult certified marine engineers for final designs.
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