How leaks really start here

Most “mystery” flooding I see started with below‑waterline fittings—split sanitation hose, a failed seacock, or a shaft log hose that nobody touched since the boat changed hands last spring at Coconut Grove. Structural hits are the other bucket: a coral rub on the reef edge, a drift into a rock pile after a late squall, or a punt from floating lumber after storms roll through Biscayne Bay. The trick is not to romanticize it—first pass is always penetrations and machinery, then the hull shell, and you move fast because water pressure gets worse as levels rise. If you grounded near Stiltsville and the boat shudders, start your search where physics says the hurt is, not where it’s convenient to open a hatch.

What actually stops water

I carry tapered softwood plugs on lanyards for every thru‑hull, and they’ve saved more weekends than any “miracle” epoxy because they conform and bite under pressure when you’re kneeling in a cold bilge. A rubber‑wrapped plug or a wedge plus a couple of hose clamps will tame a fractured barb or a popped seacock faster than anything that needs a surface prep you don’t have time for in a seaway. For jagged holes you can reach from inside, a thin plywood square bedded in sealant and braced with a short 2×4 turns “firehose” into “annoying leak” while your pump actually wins for once. Outside covers like collision mats or a small spare sail can help, but they’re fussy in swell and they need tension and coverage—wrinkles are little rivers straight into your boat.

The math, pumps, and stability

Flooding doesn’t care about optimism; double the hole diameter and your inflow climbs roughly fourfold, and depth below the waterline stacks the deck against you every minute you hesitate. That’s why even “good” bilge pumps can lose to a one‑inch breach a couple feet under when you’re bouncing in inlet chop between Haulover and Government Cut. On top of that, free‑surface effect from sloshing bilge water kicks your stability in the teeth, raising your center of gravity and making the boat feel drunk when you can least afford it. Keep compartments isolated, keep pumps running, and don’t let downflooding through open lockers or ragged hatch seals make a bad day worse.

Fix or call: the real thresholds

If you’ve knocked the flow down so pumps are gaining, trim is predictable, and your temporary structure isn’t walking with every wave, you can jog home slow along the inside and keep eyes on the patch the whole way. If ingress still beats pump capacity, access is unsafe, or you see the boat start to loll with water moving underfoot, stop kidding yourself and start talking on the radio like you mean it. Give position, people aboard, damage type, and what you actually need—more pumps, an escort, or a tow—because clarity moves help faster than panic. This is where emergency boat hull damage either becomes a controlled transit or an avoidable mayday, and choosing early is grown‑up seamanship.

Miami cases from the dock

Last June at Dinner Key Marina, Javier brought in a Sea Ray 230 after tagging submerged debris off Stiltsville, and a rubber‑wrapped soft plug plus braced plywood got his leak from scary to manageable in ten minutes flat while we staged a slow run to the yard by sunset. In August near Bahia Mar, Sofia’s crew called about a failed toilet intake hose on a Boston Whaler, and two clamps plus self‑fusing tape put that fire out before we even finished checking the other hoses for age cracks. A Key Biscayne buddy with a Yamaha 200 on a center console swore a “fast epoxy” would cure the world, but the water beat his prep until we jammed a proper wedge and shore, then he admitted the truth with a laugh that sounded like relief. Last fall a family near Government Cut braced a cushion into a split panel with a boat hook and a scrap of 1×2, and I’ve never been happier to see ugly woodwork in my life. Every one of these wins started with simple tools reached in seconds, not minutes, and with someone actually looking where the water came from, not where they wished it did.

I put this table together from South Florida jobs

Scenario	Temporary method	Tools carried	Pros	Limits
Split intake hose below WL	Rubber wrap plus twin hose clamps	Self‑fusing tape, clamps, knife	Fast, conforms, holds pressure	Needs cleanish access; may creep
Failed seacock/thru‑hull	Tapered softwood plug on lanyard	Plug kit, mallet	Seats under pressure, instant	Not for jagged cracks; can loosen
Jagged hull puncture inside reach	Thin plywood patch bedded and braced	Plywood, sealant, screws, 2×4	Tames flow so pumps win	Needs structure to brace against
Large or hidden exterior breach	Collision mat or small sail outside	Pre‑rigged mat, lines	Buys time if tensioned well	Wrinkles and sea state defeat seal
Unknown source, rising bilge	Compartment isolation and pump focus	Temporary dams, pump routing	Controls free‑surface, buys stability	Only slows if inflow still high

Quick FAQ and field notes

Closing, without the sugar

Emergency boat hull damage is solved by speed, simplicity, and honesty about physics—get the flow down, keep the boat upright, and choose help early if the numbers don’t add up. If a plug, a patch, and one good pump buy you a slow, boring ride to a friendly dock in Coconut Grove, that’s a win you’ll brag about over coffee at the dockside café tomorrow.