| Item | Value used | Notes |
|---|---|---|
| Float geometry | 20 ft long × 4 ft diameter cylinder | Internal volume (idealized): ~251 ft³ (~7.1 m³, ~7110 L) |
| Wall thickness | 1/4 inch duplex stainless | Strength is not the limiting factor in the leak calculations; it matters for whether a hole forms at all. |
| Internal pressure (initial) | 10 psig (≈24.7 psia) | Assumed gauge pressure relative to atmosphere. |
| Hole size | 0.5 inch diameter | Area A ≈ 0.196 in² ≈ 1.27×10-4 m² |
| Hole depth below outside water surface | 4 ft (≈1.22 m) | Hydrostatic pressure ≈ 0.433 psi/ft ⇒ ~1.73 psig at 4 ft. |
| Discharge coefficient | Cd ≈ 0.6 | Typical for a sharp-edged orifice. A jagged tear, partial blockage, or a long “tube-like” path changes this a lot. |
| Thermodynamics | Approximately isothermal | Good enough for minute-to-hour scale estimates in a metal tank exchanging heat with seawater. |
Water is held out as long as the internal gas pressure at the hole is higher than the outside water pressure at the hole. At 4 ft depth, outside pressure is about 1.7 psig. So the float can blow air out (no water ingress) until internal pressure falls from 10 psig → ~1.7 psig.
Using ideal gas behavior at constant temperature, the mass of air in the float is proportional to absolute pressure.
For a 1/2" orifice, the initial air jet is vigorous and then slows as pressure drops. With the assumptions above, the time to blow down from 10 psig to ~1.7 psig is on the order of:
~2 to 5 minutes
With a single opening to the sea, and assuming air can escape as bubbles out the same opening, flooding generally continues until the internal water level matches the outside water level (same hydrostatic head).
So, measured from the hole upward, the water can rise by approximately the hole’s depth below the outside surface:
Maximum rise above the hole ≈ 4 ft (until internal water surface is at outside sea level)
What that means in terms of “fraction of the float flooded” depends on where the sea level cuts the 4-ft diameter cylinder in actual operation. If the hole is near the very bottom of a 4-ft diameter float and that bottom is ~4 ft below the surface, then “4 ft above the hole” is near the top of the cylinder and the float can become nearly completely flooded. If, instead, the float normally sits higher (less draft), then the final flooded volume is less.
Once internal pressure is near atmospheric, water inflow through a 1/2" hole driven by ~4 ft of head is not instantaneous. A simple orifice estimate gives an initial inflow around:
Because the driving head reduces as the internal water level rises, the average inflow is lower than the initial value. For a full 7.1 m³ (7110 L) cylinder, a crude estimate puts “mostly flooded” times on the order of:
Several hours (roughly 4–10 hours)
If the equilibrium flooded volume is only half the cylinder (because the float normally rides high), then the time is correspondingly shorter, still typically hours, not minutes, for a clean 1/2" hole.
To prevent water ingress at a 4 ft deep opening, you need the internal pressure to be at least the outside water pressure at that depth:
Required internal pressure ≈ 1.7 psig (and practically a bit higher to provide margin against wave/pressure fluctuations)
If you can maintain internal pressure at (say) 2–3 psig continuously, then the leak becomes “air out” rather than “water in.” That can indeed arrest further flooding, but only if:
A 2 hp (≈1.5 kW) compressor might be in the right ballpark for a 1/2" hole at a few psi, but it’s close enough that real-world details matter a lot (compressor type, efficiency, actual discharge pressure, duty rating, restrictions in hoses, etc.).
Practical takeaway: Yes, an onboard air system can be a very useful “damage control” tool here, but design it as a real emergency subsystem (with known delivered CFM at 2–3 psig and 10 psig, proper check valves, isolation valves, and procedures).
Air escaping through a submerged 1/2" hole generally creates a loud bubbling/roaring sound in the water and can transmit vibration through the metal structure. However, predicting audibility onboard depends on hull/structure transmission paths and ambient noise (wind, waves, generators, HVAC).
From a safety standpoint, it’s good that you also have pressure-drop alarms and bilge/water detectors—those should be treated as the primary alerting mechanism, not human hearing.
On the specific failure mode “small hole below waterline causes progressive flooding,” your concept has several risk-reducing features:
However, “overall risk” also includes other credible failure modes that are different from yachts:
So: yes, this can plausibly be much more tolerant of “bump” damage than a typical fiberglass yacht—especially at 1 mph and with no through-hulls— but you should validate the new dominant risks (attachments, fatigue, corrosion, stability-after-damage) with engineering and testing.
Many people choose metal-hulled expedition sailboats because they perceive them as more collision/ice/debris tolerant, and watertight compartments can increase survivability. That said:
Your seastead’s combination of slow speed, no below-waterline through-hulls, and buoyancy redundancy should reduce “sudden sinking from an unseen object” as a top anxiety—if the system is engineered so that a damaged float does not lead to loss of the entire platform (progressive failure) and alarms are reliable.
It could, if done carefully and honestly. It demonstrates two important points: low-speed impact behavior and damage tolerance. To make it credible (and not backfire), consider:
A good demo can reduce fear—just make sure it matches realistic hazards (sharp container corner vs rounded log is very different).
If you share (even approximate) values for:
then I can give a tighter flooding-volume estimate (how many liters enter before equilibrium) and a more defensible time-to-alarm/time-to-action timeline.
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