I fell down a rabbit hole watching videos of 70-80 ft patrol boats and big carbon sport yachts running 50+ knots and now I can’t stop thinking: how big can a “speed boat” really get before physics, structure, or systems say “enough”? I don’t mean fast ferries with commercial hulls-I mean a boat that still accelerates, trims, and turns like a hot rod, just… big.
If you’ve designed, driven, or maintained 60-100 ft high-speed boats (ex-military/SAR, large performance yachts, foil-assist cats, etc.), I’d love your real-world take:
- Hull form: At this size/power, what’s actually working-deep-V mono, stepped mono, foil-assist cat, wave-piercer, even a pentamaran? Where do stepped hulls stop scaling well (re-attachment in rough water, porpoising, chine-walk)?
- Structure and slamming: What fails first at sustained 40-60 knots-bottom panels, stringer bonds, bulkhead joints, deckhouse? Are ISO 12215/HSLC rules conservative enough for repeated 2-3 g impacts? Any fatigue life data you trust?
- Ride control: Interceptors vs. tabs vs. active T-foils-how much can these tame pitch/heave on a big planing hull without killing efficiency? Do gyros still matter above 35-40 knots or does dynamic lift make them redundant?
- Propulsion: Waterjets vs. surface drives vs. conventional shafts with supercavitating or cleaver props-where’s the crossover on efficiency, cavitation margin, crash-stop, and low-speed control? Any gotchas with jet inlets in steep chop?
- Power density and weight: Is carbon/foam core the only path, or can aluminum still hang at 50+ knots without a maintenance nightmare? How are you managing tank placement/CG as fuel burns off to avoid trim sensitivity?
- Tricks that actually moved the needle: Air lubrication, foil-assist on the bow or transom, interceptor automation-snake oil or legit at this scale?
- Operations: What sea states are realistically comfortable at speed for crew safety (with shock seats)? Any insurance or classification hurdles once LOA and Vmax cross a certain line?
- Dockside realities: Are big surface-drive boats miserable to dock compared to jets? Anything clever you’ve seen to make them civilized in marinas?
Bonus points for war stories: what broke, what you’d spec differently, and the one upgrade that turned a sketchy rocket into a usable machine.