SAMS Hull Inspection and Materials 3 — Questions and Answers
Question 1: What condition is indicated when a ferrocement hull shows a network of fine surface cracks but no spalling or delamination?
- Catastrophic structural failure is imminent
- Normal crazing that requires immediate replacement
- Superficial crazing that may be cosmetic but warrants monitoring (Correct answer)
- Evidence of alkali-silica reaction requiring demolition
Correct answer: Superficial crazing that may be cosmetic but warrants monitoring
Fine surface crazing in ferrocement is often cosmetic and caused by curing shrinkage, but the surveyor must probe further to confirm no deeper structural compromise.
Question 2: A surveyor finds that the garboard strake on a wooden boat shows soft wood when probed. What structural concern does this most directly raise?
- Loss of freeboard
- Compromised connection between hull planking and keel (Correct answer)
- Reduced righting moment
- Inadequate anti-fouling protection
Correct answer: Compromised connection between hull planking and keel
The garboard strake is the planking adjacent to the keel; soft wood there indicates rot that directly compromises the structural joint between the hull and keel.
Question 3: When examining a hull's underwater body for electrolytic corrosion on a bronze through-hull fitting, what visual sign suggests active corrosion?
- Blue-green patina on the fitting surface
- Dezincification leaving a pink, spongy copper residue (Correct answer)
- White chalky deposits around the fitting
- Dark brown tannin staining
Correct answer: Dezincification leaving a pink, spongy copper residue
Dezincification of brass fittings removes zinc, leaving a pinkish, weakened copper sponge that is a classic sign of electrolytic or galvanic corrosion.
Question 4: In ABYC and SAMS standards, what minimum gel coat thickness is generally considered acceptable for a production fiberglass hull?
- 0.5 mils (0.013 mm)
- 18–20 mils (0.45–0.51 mm) (Correct answer)
- 3–5 mils (0.076–0.127 mm)
- 40 mils (1.0 mm)
Correct answer: 18–20 mils (0.45–0.51 mm)
Gel coat is typically applied at 18–20 mils thickness; significantly thinner gel coat is prone to crazing, porosity, and early osmotic blister formation.
Question 5: Which test is used in the field to detect moisture content in a fiberglass hull laminate without drilling?
- Phenolphthalein indicator test
- Capacitance-type moisture meter (Correct answer)
- Silver nitrate solution test
- pH strip test on hull surface
Correct answer: Capacitance-type moisture meter
A capacitance-type moisture meter measures the dielectric constant of the laminate, which changes with moisture content, providing non-destructive readings.
Question 6: A surveyor notes that frames on a wood hull are 'faired' outward. What does this condition most likely indicate?
- Superior boatbuilding craftsmanship
- Hogging of the hull caused by keel sag (Correct answer)
- Shrinkage of planking causing frames to be pulled out of alignment
- Proper installation per traditional cold-molded technique
Correct answer: Hogging of the hull caused by keel sag
Frames faired outward can indicate hogging, where the keel has dropped or the ends of the hull have risen, stressing the longitudinal structure.
Question 7: What characteristic of Corten steel makes it occasionally used in commercial vessel hull construction despite its higher initial cost?
- It is non-magnetic, reducing compass deviation
- It forms a stable rust patina that retards further corrosion (Correct answer)
- It is lighter than standard mild steel at equivalent strength
- It is immune to galvanic corrosion in seawater
Correct answer: It forms a stable rust patina that retards further corrosion
Corten (weathering steel) develops a tightly adherent oxide layer that slows further corrosion, potentially reducing long-term maintenance costs in controlled environments.
SAMS Hull Inspection and Materials 3
What condition is indicated when a ferrocement hull shows a network of fine surface cracks but no spalling or delamination?