Maintenance, Corrosion & Winter
Should You Leave the Drain Plug In or Out on a Boat Lift?
Quick answer
Out, for a boat raised clear of the water on a lift, with the bow up and a reminder on the helm to put it back before launching. Every inch of rain on 100 sq ft of open boat is about 62 gallons and 520 lb, and a common once-a-year storm drops 2.3 to 3.8 inches in 24 hours across US lake country; with the plug out it drains with no power, with it in you are betting the lift on a pump, a float switch and a battery. Keep it in only when water can reach the hull.
On this page
- How much rain actually lands in a boat
- Why that weight matters on a lift
- Why "plug in, pump on auto" fails more often than it sounds
- The real case for keeping it in, and what to do about it
- When to keep the plug in on a lift
- Help the water reach the drain
- Snow counts too
- Where this answer stops applying
- Frequently asked questions
- Sources and further reading
Take the drain plug out when the boat is raised on the lift and the hull is clear of the water. Rain that falls into an open boat with the plug in stays there until a pump removes it, and every gallon is weight hanging on the lift. With the plug out, the same rain runs out the transom by gravity, with no battery, float switch or pump involved. Put the plug in only when water can reach the hull: the boat is lowered, the lift sits low in a surge or a big tide, or the boat is about to go in.
The other answer on every boating forum sounds more careful: "plug in, bilge pump on auto, treat it like it is floating." It guards against one rare event, the lift dropping the boat, by relying every rainy night on parts that fail more often.
- Rain load: 1 inch over 100 sq ft is about 62 gal and 520 lb
- Typical yearly storm (24 h): 2.3 to 3.8 in at five US lake and coastal locations (NOAA Atlas 14)
- Dockside sinkings: rain and snow caused 47 percent in BoatUS Marine Insurance outboard claims
- Default on a raised lift: plug out, bow up, plug stored at the helm
- Keep it in: whenever water can reach the drain, and always before lowering
Safety: Pulling or setting a transom plug means reaching under or behind a raised boat. Do it from the swim platform, from inside the boat if your hull has an interior-accessible plug, or with the cradle lowered and the boat floating. Never stand in the water or on the cradle under a raised hull, and do not rely on the lift's brake to hold while you work beneath it.
How much rain actually lands in a boat
Water weighs 62.4 lb per cubic foot, or about 8.3 lb per gallon. One inch of rain is 1/12 of a foot deep, so every square foot of open boat collects 5.2 lb and about 0.62 gal per inch. Scale it to the boat:
- Per 100 sq ft of open area: 62 gal and 520 lb for each inch of rain.
- Open area is everything that drains into the hull: cockpit, bow seating, swim platform wells, open hatches. Multiply interior length by width. A 20 to 22 ft bowrider with the cover off is roughly 120 sq ft.
What matters is how much rain falls between your visits. NOAA's Atlas 14 estimates give that for any US location: below, the 24-hour depth expected about once a year, the 24-hour depth expected about once in 10 years, and the 7-day total expected about once in 10 years (a wet week while you are away), each converted for 120 sq ft of open boat.
| Location | 24 h, about yearly | 24 h, about once in 10 years | 7 days, about once in 10 years |
|---|---|---|---|
| Orlando, FL | 3.80 in: 284 gal, 2,370 lb | 6.10 in: 456 gal, 3,810 lb | 9.61 in: 719 gal, 6,000 lb |
| Charleston, SC | 3.49 in: 261 gal, 2,180 lb | 6.50 in: 486 gal, 4,060 lb | 9.40 in: 703 gal, 5,870 lb |
| Lake of the Ozarks, MO | 3.13 in: 234 gal, 1,950 lb | 4.98 in: 373 gal, 3,110 lb | 7.86 in: 588 gal, 4,900 lb |
| Minneapolis, MN | 2.48 in: 186 gal, 1,550 lb | 4.27 in: 319 gal, 2,660 lb | 6.03 in: 451 gal, 3,760 lb |
| Lake George, NY | 2.34 in: 175 gal, 1,460 lb | 3.85 in: 288 gal, 2,400 lb | 5.82 in: 435 gal, 3,630 lb |
Even the driest column, an ordinary yearly storm in upstate New York, puts more than 1,400 lb into a plugged open boat. For your own dock, enter its coordinates in NOAA's Precipitation Frequency Data Server and multiply the depth by 5.2 lb per square foot of open area.
Why that weight matters on a lift
A lift is sized for the boat's loaded weight plus a margin, and the usual rule is a lift rated 15 to 25 percent above loaded weight (see boat lift capacity sizing). That margin exists for gear creep, off-center loading and wear. Rain spends it.
Worked example: how many inches of rain use up the margin
A 21 ft bowrider weighs 4,000 lb loaded with fuel, battery and gear, and sits on a 5,000 lb lift: 1,000 lb of margin, a 25 percent cushion. Its open area with the cover off is 120 sq ft, so each inch of rain adds 624 lb.
1,000 / 624 = 1.6 inches of rain uses up the whole margin. The Orlando yearly storm of 3.80 in adds 2,370 lb, putting 6,370 lb on a 5,000 lb lift, 27 percent over its rating. The same storm at Lake George adds 1,460 lb: 5,460 lb, still over.
With the plug out and the bow raised, the bilge holds only what sits below the drain. The lift sees the boat it was sized for.
Rated capacity is not the point where a lift collapses, but the extra load lands on parts that already wear (cables, sheaves, brake, gearing), and it collects at the hull's low end, usually over the stern cables. HydroHoist's troubleshooting table for one of its floating lifts lists "water or equipment in boat creating additional weight" as a cause of a lift that will not fully raise the boat or leaves the stern low; its fix is "remove water or equipment." A lift that creeps down after rain is diagnosed in boat lift slipping or not holding; on davits the margin is thinner still.
Why "plug in, pump on auto" fails more often than it sounds
The pump is not the weak point; everything around it is. A Rule 500 GPH bilge pump draws 1.6 A at 12 V. The Orlando 10-year storm, 456 gallons, is under an hour of pumping at rated flow, about 1.5 amp-hours, and even its wettest hour (2.91 in, about 218 gal) is within one working pump's reach. Rain does not drain a good battery. The strategy fails when one link is not working on the night it rains:
- A float switch that sticks on. The pump runs dry at 1.6 A, which is 38 amp-hours a day. An Optima BlueTop 34M starting battery is listed at 50 Ah, so a stuck switch can flatten it in little more than a day, and the next storm finds no pump at all.
- A clogged pickup: leaves, pine needles or a wrapper on the pump screen.
- An auto circuit that is not live. If the automatic bilge circuit is wired through the battery switch, turning the switch off for storage disables the pump. Check yours: switch off, lift the float, and listen.
- A battery already low from standing loads or a disconnected charger (lift batteries too: see solar and battery problems).
This is the same pattern BoatUS Marine Insurance found in its claims. Outboard boats sank at the dock four times as often as under way, and rain or snow caused 47 percent of the dockside sinkings, "although almost all had 'self-bailing' cockpits." Those boats were floating, not on lifts, but the lesson carries over: drainage that depends on something staying clear and working fails in the storms that matter. A plug left out needs nothing.
The real case for keeping it in, and what to do about it
The lift could drop the boat
If cables part or a brake lets go, a plugged hull floats; an unplugged one starts taking water through the drain. It is a rare failure on a maintained lift, and extra weight makes it likelier. The answer is the inspection routine in the maintenance checklist, not a heavier boat.
Someone launches without the plug
In the same BoatUS research, the drain plug caused 16 percent of sinkings while under way. Taking the plug out on the lift moves that risk to launch time, so build the habit that defeats it:
- Store the plug on the key ring, clipped to the steering wheel, or in a cup holder at the helm, never in a dock box.
- Hang a tag on the lift remote or the switch: "PLUG?"
- Lower until the hull just touches, check the plug is in and tight, then float off.
Self-draining plugs try to solve both problems. U.S. Patent 7,434,528 describes a buoyant valve that seals the drain when submerged and drops open when the boat is above the water or running at speed. Confirm one fits your drain fitting, and inspect it as you would a pump.
When to keep the plug in on a lift
| Situation | Plug | Why |
|---|---|---|
| Raised clear of water, open boat, no canopy | Out | Rain drains by gravity, lift stays within its rating |
| Raised under a canopy or in a boathouse | Out is still better | Wind-driven rain and wash-down water still collect; nothing to lose |
| Raised, but waves or tide can reach the transom | In | Water can enter through the drain; raise the lift higher if it can go |
| Storm surge forecast near the hull | In, or remove the boat | See hurricane preparation |
| Lowered, floating in the slip | In | It is a floating boat |
| Self-bailing cockpit, sealed bilge | Out | Scuppers clog, as the BoatUS claims show |
| Winter storage on the lift in ice country | Out | Meltwater drains instead of freezing in the bilge; see winterizing |
How high is high enough? The hull bottom at the transom needs to clear the highest water you expect plus waves, typically 12 to 24 inches above high water on a lake and more on exposed or surge-prone water; the geometry is in water depth requirements. If your lift cannot get the drain that high, the plug stays in and the pump and battery become essential, so check them before every absence.
Help the water reach the drain
A plug that is out only helps if water can get to it. Set the boat slightly bow-high so rain runs aft and out; a boat sitting level or bow-down holds water forward. Bunk height is the adjustment (see why a boat sits crooked on the lift). Clear limber holes of debris so each compartment can reach the drain. A canopy is the best complement, because it keeps most rain out of the boat in the first place (see boat lift canopies); snap-on covers pond water and blow loose in exactly the storms that matter.
Snow counts too
Snow is lighter per inch, but it piles up on a boat on a lift and on its cover, and it all melts into the hull. UCAR describes a typical ratio of about 12 inches of snow to 1 inch of water, dropping to 10 to 1 or even 5 to 1 for wet snow near freezing. A foot of wet snow at 5 to 1 is 2.4 inches of water: about 1,500 lb in 120 sq ft of open boat, before the next storm. Leave the plug out and clear heavy snow off the boat, or take the boat off the lift for the season.
Where this answer stops applying
- Pontoons and tritoons do not collect rain in a hull: the deck drains through. Their tube plugs stay in; they are not drain plugs in this sense. See pontoon boat lifts.
- Engine block and cooling drains are a winterizing question, not a rain question. Follow the engine maker's procedure.
Frequently asked questions
Should I leave my boat drain plug out when it is on the lift?
Yes, when the boat is raised clear of the water. Rain then drains by gravity instead of adding weight to the lift; one inch over 100 sq ft of open boat weighs about 520 lb. Set the boat slightly bow-high, store the plug at the helm, and put it back before lowering. Keep it in only if waves, tide or surge can reach the drain.
Can rain water overload a boat lift?
Yes. An open 20 to 22 ft boat collects about 624 lb per inch of rain with the plug in. A routine yearly storm of 2.3 to 3.8 inches, per NOAA estimates for US lake regions, adds 1,460 to 2,370 lb. For a 4,000 lb boat, the usual 15 to 25 percent capacity margin is only 600 to 1,000 lb. Use the capacity calculator to see your margin.
Is it better to rely on the bilge pump while the boat is on the lift?
Only if water can reach the hull and the plug must stay in. A working pump easily keeps up with rain, but the strategy depends on the float switch, the pickup, the auto circuit and the battery all working on the night it rains. A stuck float switch on a 1.6 A pump uses 38 amp-hours a day and can flatten a 50 Ah battery in little more than a day.
How do I remember to put the drain plug back in?
Keep the plug on the key ring or clipped to the steering wheel, hang a "PLUG?" tag on the lift remote or switch, and make "lower until the hull touches, check the plug" a fixed step every launch. BoatUS research found drain plugs caused 16 percent of sinkings under way, so the habit matters as much as the decision.
Sources and further reading
- Soundings, "Publication researches causes of sinkings," reporting BoatUS Marine Insurance Seaworthy claims research on outboard boats (dockside sinkings outnumber under way 4 to 1; rain/snow 47 percent at the dock; drain plug 16 percent under way) (https://soundingsonline.com/news/publication-researches-causes-of-sinkings/)
- NOAA National Weather Service, Hydrometeorological Design Studies Center, Precipitation Frequency Data Server, NOAA Atlas 14 Volumes 2, 8, 9 and 10, partial duration point estimates for Orlando FL, Charleston SC, Lake Ozark MO, Minneapolis MN and Lake George NY, queried October 8, 2026 (https://hdsc.nws.noaa.gov/pfds/)
- Rule (Xylem), Rule Bilge Pumps 360-1100 GPH Submersible Bilge Pumps data sheet (model 25DA, 500 GPH, 1.6 A at 12 V; ISO 8849) (https://www.lindemann-kg.de/images/produkte/pdf/JPR20DA.pdf)
- HydroHoist International, Side-Tie "B" Model 7500B Installation Manual, publication 8/1/04, Trouble Shooting section (https://cdn.shopify.com/s/files/1/0509/5174/9813/files/HydroHoist_Side_Tie_B-_7500_Manual.pdf)
- Hamilton Marine, Optima BlueTop 34M AGM starting battery listing (50 Ah, reserve capacity 100 minutes at 25 A) (https://shop.hamiltonmarine.com/products/battery-agm-starting-optima-14815.html)
- U.S. Patent 7,434,528, Self draining boat plug, L. G. McKibben, filed January 20, 2006 (https://patents.google.com/patent/US7434528)
- UCAR, "Accumulated wisdom: How to measure snow" (snow-to-liquid ratios) (https://news.ucar.edu/5823/accumulated-wisdom-how-measure-snow)