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Dock flotation calculator
One 8′ × 20′ aluminum-frame floating section on the residential basis needs 4,571 lb of catalog buoyancy — 10 drums of 500 lb. This calculator shows all three criteria the dock engine sizes against, which one governed, and the source behind every number — down to the published frame and decking weights the dead load is built from.
Your dock's flotation
Your dock
Floats on drums — the only type with flotation to size.
Sections run end to end. Each can be up to 20 ft wide and 60 ft long.
Frame, decking and section size set the dead load: the heaviest published decking, the largest published frame that fits under each section (the smallest published one where none fits), and never less than a whole-dock figure derived from a published one where it covers the frame.
20 psf deck live load and a 28 psf flotation floor. Live load: Ameren Lake of the Ozarks Permit Requirements, Appendix B §7.7.1, permit-mandated on that lake only (Tier 2 — published guideline).
Sized in 24"×48"×16" foam-filled float drums, rated 500 lb at full submersion.
Site conditions are held neutral — 4 ft of water at seasonal low and high, a sand bottom, sheltered exposure, no jurisdiction recorded — because flotation never reads them. They drive the dock studio's site checks, not this number.
10 float drums · 4,571 lb
Set by reserve buoyancy at full live load
Required flotation · residential basis
10 float drums
4,571 lb of catalog buoyancy — 28.6 psf over 160 sq ft, set by reserve buoyancy at full live load.
Required buoyancy
4,571 lb
160 sq ft × 28.6 psf of catalog (full-submersion) buoyancy — counted in the ratings, never loaded to them.
Tier 2 — published guideline UFC 4-152-07, Design: Small Craft Berthing Facilities §6-3.3.2
Float drums
10
24"×48"×16" foam-filled float drums rated 500 lb each — whole drums, an even count per section so they pair across the width.
Tier 3 — documented practice Published full-submersion ratings for 24"×48"×16" drums — 526 to 598 lb (Formex FF 2416-FM 526, Eagle Floats 2 x 4 x 16 530, Formex FF 2416-TM 580, PermaFloat BD2448-16 598); held at 500 lb, the round conservative figure below each of them; Eagle Floats 2x4x16F publishes 480 lb, below this figure, so the catalog does not offer it
Live load
20 psf
The residential basis, carried at full value into the reserve-buoyancy case.
Tier 2 — published guideline Ameren Lake of the Ozarks Permit Requirements, Appendix B §7.7.1, permit-mandated on that lake only
Dead load
800 lb
1.62 psf frame (8 × 16 ft) + 2.51 psf decking = 4.13 psf, under the 5 psf whole-dock figure DeckPro derives from the TechniDock float drum guide's published 800–1,200 lb for a typical 8' × 20' aluminum section (800 lb ÷ (8 ft × 20 ft)), which governs: 5 psf.
Tier 3 — documented practice TechniDock float drum guide — an 8' x 20' aluminum section might weigh 800–1,200 lb, depending on the decking; DeckPro derives 5 psf from its low end, 800 lb ÷ (8 ft × 20 ft), the only figure the page applies to every decking. It governs over the heaviest published frame figure for this dock's sections and the heaviest published decking figure, Hewitt 8'X16' Custom Floating Dock Aluminum-No Deck 1.62 psf + Tommy Docks ALUMINUM DECKING PANEL REPLACEMENT 47 3/4 X 5 1/2 X 1 (TD-30070), laid at Patriot Docks' 1/2 in board spacing (derived) 2.51 psf = 4.13 psf
The three criteria — the worst one governs
Dead load at design submergence
11.1 psf
The dock at rest rides no deeper than 45% of the drum’s height — the middle of Dock Builders Supply’s published practice: design near 40% submergence, never past 50%.
5 psf dead ÷ 0.45 = 11.1 psf
Tier 3 — documented practice Dock Builders Supply published flotation method — the dock at rest rides no deeper than the design submergence
Reserve buoyancy at full live load
28.6 psfgoverns
At dead load plus the full 20 psf live load, at least 2 in of the 16 in drum stays above water.
(5 dead + 20 live) ÷ 0.875 = 28.6 psf
Tier 2 — published guideline UFC 4-152-07, Design: Small Craft Berthing Facilities §6-3.3.2
Published total-flotation floor
28 psf
The residential basis never drops below its published total, even when the loads ask for less.
28 psf floor
Tier 3 — documented practice Dock Builders Supply — the floor of its published residential total-flotation band
What the count delivers: 10 × 500 lb = 5,000 lb, or 31.3 psf of deck. At rest the drums ride 16% submerged (the limit is 45%); at dead plus full live load 3.2 in of drum stays above water (the minimum is 2 in).
Catalog buoyancy is a full-submersion figure, so the load is never compared with the rating directly. Deck freeboard, anchoring, wind and wave are not checked here — see every source and gap.
How the number is sized
A float drum's catalog rating is measured fully underwater, so a flotation number is only honest if it says how deep the drums ride. The dock engine sizes against three criteria and takes the worst. For the 8′ × 20′ section the calculator opens with:
Dead load at design submergence
11.1 psfThe dock at rest rides no deeper than 45% of the drum’s height — the middle of Dock Builders Supply’s published practice: design near 40% submergence, never past 50%.
5 psf dead ÷ 0.45 = 11.1 psf
Tier 3 — documented practice Dock Builders Supply published flotation method — the dock at rest rides no deeper than the design submergence
Reserve buoyancy at full live load
28.6 psf · governsAt dead load plus the full 20 psf live load, at least 2 in of the 16 in drum stays above water.
(5 dead + 20 live) ÷ 0.875 = 28.6 psf
Tier 2 — published guideline UFC 4-152-07, Design: Small Craft Berthing Facilities §6-3.3.2
Published total-flotation floor
28 psfThe residential basis never drops below its published total, even when the loads ask for less.
28 psf floor
Tier 3 — documented practice Dock Builders Supply — the floor of its published residential total-flotation band
160 sq ft at 28.6 psf is 4,571 lb, which takes 10 drums once the count is rounded to whole drums and paired across the width. Make the same section pressure-treated wood and the dead load climbs to 13.36 psf, which raises what the reserve-buoyancy rule asks, from 28.6 to 38.1 psf, and the count becomes 14.
What it refuses to estimate
Two docks get no number, on purpose. A piling or pipe dock stands on the bottom — nothing on it floats, so there is nothing to size. And round or pipe pontoons load non-linearly, which the rectangular-drum math cannot describe; rather than stretch it over them, the engine stops and says why:
Circular / pipe pontoons load NON-LINEARLY (Tier 2, CA DBW 2005 §C6.8.2: the lower half of the diameter gives disproportionally greater buoyant uplift and the upper half disproportionally less), while this engine sizes flotation with the linear rectangular-pontoon relationship of §C6.8.1 against a rectangular-drum catalog rating. UFC 4-152-07 §6-3.3.2 adds that where pontoon width varies with submergence the reserve freeboard must be INCREASED by an amount it does not quantify. No float count was produced — the engine will not extrapolate its rectangular model onto a shape it does not describe.
What to do: Size pipe/circular flotation from the manufacturer's own displacement curve or a marine engineer's calculation, or set Float shape to rectangular drums to get a takeoff from this engine.
Common questions
How many float drums does an 8x20 floating dock need?
10 drums rated 500 lb each, for one 8′ × 20′ aluminum-frame, aluminum panel-deck section on the residential basis — 4,571 lb of catalog buoyancy, which is 160 sq ft at 28.6 psf, set by the reserve buoyancy at full live load. The count rounds up to whole drums and then to an even number per section, so the drums pair across the width. The same section in pressure-treated wood needs 14 drums, because its heavier dead load raises what the reserve-buoyancy rule asks, from 28.6 to 38.1 psf.
How much flotation does a floating dock need per square foot?
The worst of three published criteria, not one rule of thumb. Dead load alone may sink the drums no deeper than 45% of their height, the middle of the Dock Builders Supply published flotation method: design near 40% submergence, never past 50% (Tier 3 — documented practice). At dead load plus full live load, the reserve-buoyancy rule keeps at least 2 in of a 16 in drum above water (Tier 2 — published guideline: UFC 4-152-07, Design: Small Craft Berthing Facilities §6-3.3.2). And there is a published floor — 28 psf residential, 40 psf marina (Tier 3 — documented practice). A light aluminum dock sits at 28.6 psf; a pressure-treated wood one asks 38.1 psf.
Why not divide the dock’s weight by the drum’s buoyancy rating?
Because catalog buoyancy is a full-submersion figure: a 500 lb drum delivers 500 lb only when it is completely underwater, with the dock awash. Formex prints that caveat on its own specification page. So the rating is never compared with the load directly — the dead load is held to 45% submergence and the full live load to the reserve line. On the 8′ × 20′ section above, the 10 counted drums leave the dock 16% submerged at rest, with 3.2 in of drum still above water at full load.
Residential or marina load basis — which should I use?
Whichever your dock actually is, and never one for the other. Residential designs to 20 psf of deck live load (Ameren Lake of the Ozarks Permit Requirements, Appendix B §7.7.1, permit-mandated on that lake only; Tier 2 — published guideline) with a 28 psf flotation floor. Marina designs to 25 psf (CA DBW, Layout and Design Guidelines for Marina Berthing Facilities, 2005, §C2.2; Tier 2 — published guideline) with a 40 psf floor. The same 8′ × 20′ section needs 10 drums residential and 14 marina.
Can it size round or pipe pontoons?
No, and it says so instead of estimating. Every number here describes a rectangular drum, whose waterline area stays the same as it sinks; a round pontoon's does not, so it loads non-linearly. Choose round pontoons and the engine returns no float count and raises DOCK-BP-FLOAT-SHAPE, with this remedy: Size pipe/circular flotation from the manufacturer's own displacement curve or a marine engineer's calculation, or set Float shape to rectangular drums to get a takeoff from this engine.
Is there a code for dock flotation?
There is no national dock code. Nothing national sets how much flotation a dock carries. What exists is a ladder: your waterway authority — typically the U.S. Army Corps of Engineers district, then your state waterway agency, then local shoreline zoning — decides what you may build; published design guidelines sit below that; documented manufacturer practice below that. This calculator names the rung of every number it uses, and the dock source register publishes the documents, with their checksums where they have one, and the gaps.
What does this calculator not check?
It does not weigh your dock. The dead load is the heaviest published decking weight for the option you pick, plus the largest published frame that fits under each section — the widest, then the longest; a smaller frame weighs more per square foot — or, where no published frame fits under a section, the smallest published one, with the heaviest section's figure used for the whole dock, and never less than a whole-dock figure where one covers the frame: for a pressure-treated wood frame, 13.36 psf, which DeckPro derives from the published 10–15 psf (15 − 28 × 35 ÷ 598; Tier 3 — documented practice: Dock Builders Supply flotation method). DeckPro sizes its "HDPE panels" option on the heaviest published solid HDPE panel, Hewitt 4' x 4' Classic Weardeck Gray Decking at 76.00 lb, 4.75 psf (Tier 3), which its maker describes as "HDPE reinforced with fiberglass" (Tier 3); the light-passing grated panels (ThruFlow, Titan Deck, SunWalk), which their listings describe as reinforced polypropylene, glass-reinforced plastic, HDPE or a plastic composite, are lighter than a solid panel, 1.35–2.33 psf (Tier 3); American Plastic Lumber's solid HDPE planks — the 14 boards 2 in nominal or thinner with a 5-1/2 in face that are not tongue-and-groove, from the TI-grade HDPE 1 x 6 plank to the BS-grade HDPE 2 x 6 plank — run 2.47–6.54 psf at the 3/8 in dock gap (Tier 3). What is not yet in it depends on what governs: on a dock sized on its frame and decking figures, pile guides or anchoring hardware, the gangway's reaction on the dock, water the flotation absorbs, connection hardware on a metal frame, and cleats and other attached equipment; where a whole-dock figure governs, only pile guides or anchoring hardware, the gangway's reaction on the dock, and water the flotation absorbs, because that figure already counts connections and attached equipment by its own page's words. The drums' own weight is not added because the ratings are already net of it. Deck freeboard is not checked against the published bands, and anchoring, wind, wave and ice are site questions this tool does not ask: the site is held neutral (4 ft of water at seasonal low and high, a sand bottom, sheltered exposure, no jurisdiction recorded) because flotation never reads it. A dock carrying a crowd, a vehicle or a boat lift belongs with a marine engineer.
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Source & limits
There is no national dock code.
Every number above names its rung on the authority ladder — rules with legal force, published design guidelines, documented manufacturer practice — or says plainly that no published source exists. The documents, with their checksums where they have one, and every gap are in the dock source register.
Estimate only — not an engineered design. THERE IS NO NATIONAL DOCK CODE: these quantities are sized to documented industry practice and published design guidance — flotation counted in catalog full-submersion ratings but never loaded to them, with a design submergence and reserve freeboard — and not to a prescriptive code table. Each line states the basis it was sized on. Your waterway authority governs: typically the U.S. Army Corps of Engineers district, then your state waterway agency, then local shoreline zoning, each setting its own dimensional limits. Verify everything with your permitting authority and a licensed marine contractor or engineer before ordering or building.