Important: this is a first-pass, order-of-magnitude comparison.
Real heave/roll/pitch response requires hydrostatics + added-mass/damping + RAOs versus wave spectrum and heading. Your concept is not a typical hull; it behaves more like a small semi-sub / spar-like structure where drag and added mass dominate. The numbers below should be treated as illustrative ranges, not design values.
If you want tighter estimates, the minimum extra inputs are: float geometry at depth, draft, CG height, metacentric heights (GMt, GMl), displacement volume, projected areas for drag by direction, and intended wave headings (beam/bow/quartering).
| Metric | 40×16 Seastead (semi-sub-like) | 50 ft Catamaran (sailing) | 60 ft Monohull (sailing) | 45 ft Trawler + Active Fins |
|---|---|---|---|---|
| Assumed displacement (loaded) | 36,000 lb | ~32,000 lb (typical 28–35k) | ~55,000 lb (typical 45–70k) | ~50,000 lb (typical 40–60k) |
| “Liveliness” (qualitative) |
Low (slow, damped motions if designed like a semi-sub). Can feel “platform-like” rather than “boat-like.” |
Medium–High. Typically stiff in roll (quick), can hobbyhorse in pitch. |
Medium. Slower roll than cats but often larger roll angles. |
Low–Medium. Fins reduce roll strongly, but heave/pitch remain. |
| Waterplane area (very approximate) |
~70–150 ft² (dominated by 4 oblique ~4 ft dia columns at the waterline; underwater floats contribute little if fully submerged) |
~250–450 ft² (two slender hulls) | ~500–700 ft² (broad monohull waterplane) | ~350–500 ft² (fuller displacement hull) |
| Heave natural period (typical range) |
~10–18 s (small waterplane + high added mass can lengthen period) |
~4–6 s | ~4–7 s | ~5–8 s |
| Roll natural period (typical range) |
~10–25 s (if corner mass + wide underwater stance + strong damping) |
~3–5 s (stiff/quick; lower angles but “snappy”) |
~5–8 s (often comfortable period, but can be large angles) | ~6–10 s (fins add damping/reduce angle; period itself changes less) |
| Roll inertia (relative, qualitative) |
High Heavy corners + large lever arms to roll axis. |
High Mass distributed across wide beam (two hulls). |
Medium More centralized mass than cat. |
Medium–High Heavy machinery low; moderate beam. |
| Roll damping (what controls roll amplitude) |
Potentially very high Drag of multiple deep members moving sideways; added mass; any appendage plates help a lot. |
Low–Medium Slender hulls: low viscous damping; relies on stiffness (GM) more than damping. |
Medium Keel + hull shape give damping. |
Very high (with fins active) Fins add controllable damping/anti-roll moments. |
Interpretation in plain terms
These are typical ranges assuming the vessels are not actively seeking the worst heading. Numbers can be much worse in bad headings (e.g., beam seas for roll, head seas for pitch/heave) and can improve with good heading management.
| Sea (Hs) | Vessel | Heave amplitude (ft) | Pitch (deg) | Roll (deg) | Peak vertical accel on living deck (g) | Peak “jerk” (g/s) |
|---|---|---|---|---|---|---|
| 3 ft | Seastead | ~0.3–0.6 | ~0.5–1.5 | ~0.5–1.5 | ~0.02–0.05 | ~0.01–0.03 |
| 50 ft Cat | ~0.7–1.2 | ~1–3 | ~1–4 | ~0.05–0.10 | ~0.04–0.09 | |
| 60 ft Monohull | ~0.8–1.4 | ~1–3 | ~2–6 | ~0.06–0.12 | ~0.05–0.10 | |
| 45 ft Trawler + fins | ~0.7–1.3 | ~0.8–2.5 | ~0.5–2 | ~0.04–0.09 | ~0.03–0.07 | |
| 5 ft | Seastead | ~0.6–1.0 | ~1–2.5 | ~1–3 | ~0.04–0.08 | ~0.02–0.05 |
| 50 ft Cat | ~1.2–2.0 | ~2–5 | ~3–8 | ~0.10–0.18 | ~0.07–0.15 | |
| 60 ft Monohull | ~1.3–2.2 | ~2–5 | ~6–15 | ~0.12–0.22 | ~0.09–0.18 | |
| 45 ft Trawler + fins | ~1.1–2.0 | ~1.5–4 | ~1–4 | ~0.08–0.15 | ~0.06–0.12 | |
| 8 ft | Seastead | ~1.0–1.8 | ~2–4 | ~2–5 | ~0.07–0.12 | ~0.03–0.07 |
| 50 ft Cat | ~2.0–3.5 | ~4–9 | ~5–12 | ~0.18–0.30 | ~0.12–0.25 | |
| 60 ft Monohull | ~2.2–3.8 | ~3–8 | ~12–25 | ~0.20–0.35 | ~0.14–0.30 | |
| 45 ft Trawler + fins | ~2.0–3.5 | ~2.5–6 | ~2–8 | ~0.15–0.25 | ~0.10–0.20 |
How to read the “jerk” column
Jerk is the rate of change of acceleration. People often tolerate a given acceleration better when it changes slowly. Longer-period, well-damped platforms tend to have lower jerk, which can feel “less violent” even if the motion amplitude isn’t zero.
| Activity | Seastead (semi-sub-like) | 50 ft Catamaran | 60 ft Monohull | 45 ft Trawler + fins |
|---|---|---|---|---|
| Walking / moving around |
Often best in moderate seas if roll/pitch are low and slow. Risk is “slow but persistent” motion; you may still brace, but less sudden. |
Can be tricky because roll is often quick (short period). Even at smaller angles, it can feel “snappy” underfoot. |
Usually needs “sea legs” in 5–8 ft seas; roll can be large. Walking becomes a timing/bracing task. |
Usually good because fins cut roll; still some pitch/heave. Feels like a heavy vehicle: stable but not motionless. |
| Eating / sitting at table |
Often very good if accelerations are low. Drinks/plates slide mainly if you have steady heel/roll; use non-skid. |
Generally okay in 3–5 ft; in 8 ft may be annoying due to pitch + quick roll impulses. | Can be uncomfortable in beam seas (roll). More “sloshing” and bracing. | Usually best among conventional boats when stabilizers are working. |
| Cooking (knives, hot liquids) |
Potentially safer if motion is slower and less jerky. Still design for sea: gimbaled stove not typical on platforms; consider deep fiddles and restraints. |
Requires good galley design; quick motions can surprise you. | Traditional monohulls often have good “at sea” galley layouts, but motion can be larger. | Good if fins powered and conditions allow; still watch pitch in head seas. |
| Sleeping |
Often best if roll is low and long-period. Many people sleep well with slow motion. If you hit resonance with long swell, sleep quality can drop sharply. |
Some people dislike quick roll/pitch; others adapt. Bridge-deck slamming (some cats) can wake you. | Can be okay if roll period is not too short, but larger angles can wake/light sleepers. | Often very good when stabilized; without fins (power loss) can become more “trawler-rolly.” |
Send any sketches or the following numbers and I can tighten waterplane area, GM estimates, and compute approximate natural periods: