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newSchoolWorks.com › VoTechWorks › Manufacturing & Marine › Shipbuilding / Marine Fabrication › Marine Outfitting: Systems Installation and Interior Fabrication › Lesson 7
MFG-SHIP13-06 · Lesson 7 · 18 clock hours · lab

Deck Equipment Foundations: Bitts, Cleats, and Fairleads

Objective. The student lays out, fabricates, and welds a deck cleat foundation pad to a structural drawing, with the pad located within ±1/8 inch of the drawing dimension, flat within 1/16 inch across the bolt-hole pattern, and all welds meeting visual inspection criteria.

Why Deck Equipment Foundations Matter

Bitts, cleats, and fairleads are the anchor points that transfer mooring and towing loads from lines and cables into the ship's structure. When a vessel is secured to a pier or under tow, these fittings can see forces measured in tens of thousands of pounds. If the foundation pad beneath a cleat is undersized, poorly located, or inadequately welded, the fitting can tear free — a catastrophic failure that endangers crew, vessel, and the dock. Fabricating and installing these foundations correctly is therefore one of the highest-stakes tasks in marine outfitting.

Reading the Foundation Drawing

Every deck equipment foundation job begins at the drawing. A deck equipment arrangement drawing shows where each fitting sits on the deck in plan view, with X-Y dimensions referenced to a baseline or frame line. A foundation detail drawing shows the pad plate dimensions, plate thickness, stiffener gusset geometry, bolt-hole pattern (diameter, spacing, and edge distance), and all welding symbols.

Work through the drawing in a specific order:

1. Identify the load path. Trace how the cleat load travels from the fitting, through the bolts, into the pad plate, through the welds, into the deck plating, and finally into the underlying frame or girder. Stiffener gussets are placed to transfer load directly to those structural members.

2. Read the welding symbols. Foundation-to-deck welds are typically fillet welds called out with leg size and length. Gusset welds may differ from pad-to-deck welds — check each symbol separately.

3. Record the bolt-hole pattern. Note hole diameter, center-to-center spacing, and edge distances. These must be held to tight tolerances because the hardware supplier's bolt pattern is fixed.

4. Mark up your drawing copy. Circle every dimension you will verify in the field. Draw arrows showing the load path. This marked-up copy stays with you at the work site.

Fabricating the Foundation Plate and Gussets

Cut the pad plate and stiffener gussets from mild steel flat bar or plate to the dimensions on the cut list. Use a combination square and steel rule to lay out cut lines; scribe clearly. After cutting, deburr all edges with a file or angle grinder so mating surfaces are clean and flat — a gap under a gusset compromises the weld and the load transfer.

Drill the bolt-hole pattern on the drill press using a drill jig to ensure repeatability. Clamp the jig firmly before drilling; never hold small plate stock by hand against a drill press. Use the correct jobber drill for the specified hole diameter, and verify the first hole location before drilling the full pattern. After drilling, check center-to-center spacing with a steel rule; the tolerance is tight (±1/32 inch is typical for a bolt pattern).

Assemble the gussets to the pad plate with tack welds — small, evenly spaced tacks that hold position without introducing excessive distortion. Stop and call your instructor for a check before final welding. Once final welds are laid, rework is costly and time-consuming.

Installing the Foundation on the Deck Panel

On the mock deck panel, the deck surface has been scribed with the X-Y location lines for the foundation. Position the pad over those lines. Use a level across the top of the pad and a straightedge across the bolt-hole pattern to confirm the pad is not rocking or twisted. Clamp firmly before welding.

Weld in the sequence shown on the drawing or, if none is specified, use a balanced sequence — weld opposite sides alternately — to minimize distortion. Weld size, length, and placement must match the weld symbols exactly.

Dimensional Inspection

After welding, complete the inspection record:

If any single criterion is out of tolerance, the foundation is reworked before the inspection record is signed off.

Safety

Key terms10

BittA pair of vertical posts (bollards) mounted on a strong foundation on deck, used to secure mooring or towing lines by taking multiple turns around the posts.
FairleadA deck fitting — roller or closed chock — that guides a line or cable in a specific direction, reducing wear and controlling the lead angle to a bitt or winch.
Foundation pad plateA steel plate welded to the deck beneath a deck fitting that spreads the fitting's load over a larger area of deck plating and provides a flat, level bolting surface.
Stiffener gussetA triangular or rectangular plate welded between the pad plate and a deck frame or girder to transfer vertical and horizontal loads directly into primary structure.
Load pathThe route by which force travels from the point of application — in this case the fitting — through bolts, pad plate, welds, and stiffeners into the ship's primary structure.
Drill jigA hardened template clamped over the workpiece that guides drill bits to produce a repeatable hole pattern at the correct spacing and location.
Flatness toleranceThe maximum allowable deviation of a surface from a true plane, measured with a straightedge and feeler gauge; for bolt-hole patterns in this lab the limit is 1/16 inch.
AWS D1.1 visual acceptance criteriaThe minimum visual weld quality standards defined in AWS D1.1 Structural Welding Code — Steel, covering allowable undercut, porosity, cracks, weld size, and profile.
Edge distanceThe minimum distance from the center of a bolt hole to the nearest edge of the plate, specified on the drawing to prevent tear-out under load.
Tack weldA short, small weld used to hold components in position during assembly before final welding; must be sound or ground out before final welds are applied.

Worked examples4

1. The foundation detail drawing calls for four bolt holes in a rectangular pattern: 6 inches center-to-center in the longitudinal direction and 4 inches center-to-center in the transverse direction. The pad plate is 10 inches × 8 inches. What is the edge distance in each direction, and does it meet a minimum edge distance of 1-1/4 inches?
  1. Longitudinal direction: plate length = 10 in, bolt spacing = 6 in. Remaining length = 10 − 6 = 4 in. Edge distance each end = 4 ÷ 2 = 2.00 in.
  2. Transverse direction: plate width = 8 in, bolt spacing = 4 in. Remaining width = 8 − 4 = 4 in. Edge distance each side = 4 ÷ 2 = 2.00 in.
  3. Compare both computed edge distances (2.00 in) to the minimum (1.25 in): 2.00 > 1.25 in both directions.
Answer: Edge distance is 2 inches in both directions. Both exceed the 1-1/4-inch minimum, so the pattern is acceptable.
2. After welding, you measure the X-location of the forward bolt-hole center from the frame baseline. The drawing calls for 14-3/8 inches. Your steel rule reads 14-1/4 inches. Is this within the ±1/8-inch location tolerance?
  1. Convert everything to decimal inches for easy comparison: 14-3/8 in = 14.375 in (drawing). Measured = 14-1/4 in = 14.250 in.
  2. Calculate the deviation: 14.375 − 14.250 = 0.125 in.
  3. The tolerance is ±1/8 in = ±0.125 in. The deviation equals exactly 0.125 in, which is at the boundary of the tolerance.
Answer: The deviation is 1/8 inch, which is exactly at the tolerance limit. The foundation is at the edge of acceptable. In practice, document the measurement exactly on the inspection record and discuss with the instructor, since any additional measurement error could push it out of tolerance; a small adjustment before final acceptance is advisable.
3. You drill a four-hole bolt pattern. The drawing specifies hole centers at 4.000 inches apart transversely. You measure the following center-to-center distances on the finished plate: 4-1/32 inches, 3-31/32 inches, and 4-1/32 inches across three pairs. Are any measurements outside the ±1/32-inch bolt-hole spacing tolerance?
  1. Convert tolerance to decimal: ±1/32 in = ±0.03125 in. Acceptable range: 4.000 − 0.03125 = 3.96875 in to 4.000 + 0.03125 = 4.03125 in.
  2. Convert measurements: 4-1/32 = 4.03125 in; 3-31/32 = 3.96875 in; 4-1/32 = 4.03125 in.
  3. Compare each to the range [3.96875, 4.03125]: 4.03125 is exactly at upper limit — acceptable. 3.96875 is exactly at lower limit — acceptable. 4.03125 — acceptable.
Answer: All three measurements fall exactly on the tolerance boundaries and are therefore acceptable. Document the actual values on the inspection record.
4. The drawing calls for a 5/16-inch fillet weld on the pad-to-deck joint, 4 inches long, on both sides of the pad. The pad has two parallel sides to be welded, each 10 inches long. The weld symbol shows intermittent welds: 4-inch welds spaced at 8-inch pitch. How many individual weld segments are required on one side of the pad, and what is the total weld length on that side?
  1. Pitch means center-to-center spacing of repeating welds. Pad side = 10 inches long. Number of segments: starting at the first weld center, subsequent centers at 8-inch intervals. Centers at approximately 0 in, 8 in — that gives 2 weld segments (the second starts near the far end within the 10-inch length).
  2. Actually, for intermittent welds, the number of segments along a 10-inch joint at 8-inch pitch: first weld placed at start, second placed 8 inches from the start of the first weld. Since 8 < 10, a second segment fits. A third center would be at 16 inches, beyond the joint length. So 2 segments per side.
  3. Total weld length one side: 2 segments × 4 inches each = 8 inches.
Answer: Two 4-inch weld segments per side, totaling 8 inches of weld on each side of the pad.

The math in this lesson2

Learners compute the diagonal of a 6 by 4 inch bolt pattern to check squareness.
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Brush up in the math halls at newSchoolWorks.com:
In class: Instructor-led drawing interpretation session: reading a deck equipment arrangement drawing and a foundation detail, identifying load path, welding symbols for foundation-to-deck and stiffener welds, and required bolt-hole pattern; students mark up their own drawing copies. · Foundation fabrication in shop: each student cuts foundation plate and stiffener gussets from mild steel flat bar to cut list, drills the bolt-hole pattern using a drill press and jig, and assembles components with tack welds for instructor check before final welding. · Installation simulation on a mock deck panel: students position their foundation to scribed lines, clamp in place, check with a level and straight edge, weld per weld symbol requirements, and complete a dimensional inspection record recording X-Y location, flatness, and bolt-hole spacing.
Materials: Mild steel plate and flat bar stock, drill press, jobber drill set, drill jig, MIG welder, angle grinder, combination square, steel rule, level, straight edge, scribe, tap and die set, weld gauge, foundation arrangement and detail drawings, inspection record forms, full welding PPE
Check: Instructor verifies location within ±1/8 inch, flatness within 1/16 inch, bolt-hole spacing to drawing ±1/32 inch, and visual weld quality to AWS D1.1; completed signed inspection record is required; any single criterion failure requires rework.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

NCCER Shipfitting — quality and inspection
1. Before final welding of the gussets to the pad plate, what must the student do?
NCCER Shipfitting — structural fundamentals
2. What is the primary function of the stiffener gussets welded beneath a deck cleat foundation pad?
NCCER Shipfitting — dimensional inspection
3. The flatness tolerance for the bolt-hole pattern on the foundation pad is 1/16 inch. Which combination of tools is correct for measuring this?
Safety — tool and machine safety
4. A drill press operator must always do which of the following before drilling a small plate?
AWS D1.1 Certified Welder — visual inspection
5. On a foundation detail drawing, a welding symbol shows a fillet weld with a leg size of 1/4 inch on the arrow side of the pad-to-deck joint. After welding, your weld gauge measures 3/16-inch leg size. What is the correct action?
NCCER Shipfitting — installation and alignment
6. When positioning a foundation pad on scribed location lines on the deck panel, why is it important to use a level before clamping?
NCCER Shipfitting — quality and inspection
7. The inspection record for a foundation installation requires which of the following before it is accepted?
NCCER Shipfitting — marine outfitting fundamentals
8. A fairlead is best described as which of the following?
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