24 QUESTIONS

Defects and Damage

1. 01

   How does a bent propeller blade affect speed and fuel consumption?

   A bent blade does more than cost speed: it produces unbalanced thrust, and that imbalance travels along the shaft line as vibration. The vibration tires the cutless bearing and the stern gland, which over time becomes a risk of water ingress.

   Propeller damage is therefore never assessed alone but together with shaft alignment and bearing clearance. Straightening the blade without checking what the vibration has already done leaves the expensive part of the problem in place.

2. 02

   I found rust in the fuel tank — does it have to be replaced?

   What decides it is not whether rust is visible but whether it has taken section out of the tank wall. Surface oxidation can be cleaned and protected; pitting deepening in the base will eventually perforate.

   The decision needs a borescope look at the inside and, where possible, a thickness reading. A judgement made by eye misleads here more often than anywhere else on the boat.

3. 03

   The bathing platform is broken — repair or replace?

   The question is less about the size of the break than about how the load-bearing attachment enters the hull. If the damage is confined to the skin laminate, repair is economical; if the backing or the anchorage into the hull is affected, it becomes structural work.

   A borescope and hammer testing settle that distinction without dismantling anything — which is worth doing before accepting a quote for either option.

4. 04

   How is stray current and bonding damage detected?

   Stray current damage advances quietly: anodes erode faster than expected and invisible wastage begins on the propeller and shaft. The finding comes from several measurements together — anode consumption rate, bonding continuity and shore power.

   Testing polarity and earth continuity at the sockets separates a fault on the boat from one on the pontoon. Replacing anodes without that measurement treats the symptom and leaves the cause running.

5. 05

   Blisters under the paint on an aluminium hull — is that pitting?

   On aluminium a blister under paint is usually not cosmetic; it is pitting corrosion showing through. It should not be confused with osmosis blistering on GRP — the mechanism and the consequence are entirely different.

   The suspect area is opened, cleaned and the remaining section confirmed with an ultrasonic reading. Painting over it without that step buries an active process.

6. 06

   Why does topside paint blister and flake, and how is it fixed?

   Paint blistering is almost always an adhesion problem between coats: insufficient keying, application to a damp surface or an incompatible primer. Covering the surface therefore postpones rather than solves it.

   What matters in a survey is whether the gelcoat beneath the blistering is sound. Paint applied without going back to the cause will lift again within a season or two.

7. 07

   How is stringer or frame damage found and repaired?

   Stringer damage cannot be seen from the hull skin; it occurs in the load-bearing internal structure and usually sits under the sole. The signs are indirect: flex in the deck, doors that begin to bind, a crack line appearing in the bilge.

   Hammer testing and a borescope are the only ways to look without dismantling. On any boat with a grounding in her history this is checked specifically rather than opportunistically.

8. 08

   How are cracked or yellowed acrylic windows repaired?

   Cracking in acrylic usually comes from the installation rather than the material: without an expansion allowance between frame and panel, the panel is stressed in heat and cracks from a corner. Replacing the panel alone reproduces the problem.

   Yellowing is UV fatigue and is cosmetic rather than structural — but because it degrades visibility it becomes a navigation safety item, which is why it is recorded rather than passed over.

9. 09

   How is fire damage assessed on a boat?

   The real damage after a fire is often not where the flame reached but where the heat did: laminate resin loses strength without a visible mark, cable insulation becomes brittle and aluminium fittings anneal. The assessment therefore extends beyond the burn line.

   Corrosion left in the electrical system by smoke and extinguishing water is followed separately. It appears weeks later and is easy to attribute to age rather than to the incident.

10. 10

    What structural damage does an impact cause in a GRP hull?

    GRP takes an impact at a point but spreads it inside: a small mark outside can sit over delamination covering a far wider area. The boundary of the damage is therefore established with a hammer rather than by eye.

    An impact is also transmitted to the backing or stringer on the far side, so the inside of the contact point is inspected as well. Repairing only what is visible leaves the structural half of the damage in place.

11. 11

    How is mould and damp damage in the interior dealt with?

    Mould is a consequence, not a cause; cleaning it only corrects the appearance and it returns while the moisture source remains. The source is found first: hatch and window leaks, water entering under deck fittings, condensation or a plumbing leak.

    A borescope shows what lies behind the linings and a moisture meter shows the wetness in the laminate, both without dismantling. Treating the mould before finding the source is the most commonly repeated repair on a boat.

12. 12

    How is galvanic corrosion of the propeller prevented?

    Galvanic corrosion arises when dissimilar metals are electrically connected in water; the anode is the part that volunteers to be consumed. Rapid anode erosion is a sign that the system is overloaded rather than working.

    The usual cause of overload is stray current. Replacing anodes without measuring is a dressing rather than a cure — the underlying circuit keeps consuming whatever is fitted next.

13. 13

    How is a bent shaft identified and what does it lead to?

    A bend is not visible directly; it shows itself as vibration, accelerated wear in the cutless bearing and increased drip at the stern gland. The shaft is therefore measured together with coupling alignment and bearing clearance.

    Caught late, unusual bearing wear ends as water ingress through the gland. That is the sequence that turns a measurable fault into an expensive one.

14. 14

    Why are hairline cracks in chainplates dangerous?

    A chainplate is the single connection carrying the entire rig load into the hull; a hairline crack there grows under load and gives no warning at the moment of failure. Because the crack is invisible, dye penetrant testing is not optional.

    Leakage at the deck penetration both accelerates the crack and rots the backing beneath it, so the two are inspected together rather than as separate items.

15. 15

    How is a collapsed or broken engine mount identified?

    A collapsed mount announces itself through alignment: the engine settles, the coupling goes out of line and vibration increases. Mounts are therefore assessed together with shaft alignment rather than on their own.

    Cracking, oil softening and height differences are looked for in the rubber, and alignment is measured with feeler gauges so the finding becomes a number rather than an impression.

16. 16

    How are hatch and portlight leaks resolved?

    Where a leak appears and where it enters are almost never the same place: water enters at the frame, travels inside the laminate and emerges as a stain metres away. Sealing under the stain therefore fixes nothing.

    Moisture readings establish the boundary of the wet area, and the source is traced back from there. It is slower than resealing and it is the only method that works once.

17. 17

    What causes spider cracks in gelcoat?

    Gelcoat is more brittle than the laminate beneath it: when the structure flexes, the gelcoat cannot and crazes in a web pattern. What separates cosmetic crazing from structural is where the pattern sits.

    Concentrated around a load-bearing fitting or in a corner, it indicates stress beneath. Hammer testing settles which of the two you are looking at before any cosmetic repair is considered.

18. 18

    How is a water-logged rudder blade repaired?

    A rudder blade is a hollow shell; water inside adds weight and, in winter, stresses the shell from within as it freezes. It usually enters at the stock penetration or through an unrepaired crack.

    Weight difference and moisture readings show whether the blade is holding water. Surface repair without drying it out first is short-lived — the water simply stays inside.

19. 19

    What causes soft spots and flex in the deck?

    A soft spot is a wet, rotted core between the two laminates of a sandwich deck, and the water almost always enters through the screw hole of a load-bearing fitting. There may be no sign at all on the surface, so the scan is done with a hammer and the change in note is mapped.

    Caught early, a soft spot closes with a local repair; left to spread, it means cutting the deck and replacing the core. The difference between the two is measured in months of neglect.

20. 20

    What do corroded or weeping keel bolts mean?

    Keel bolts are the single most critical connection on the boat and work as a group; weakening in one transfers load to the others. A fine line at the joint — a smile crack — points either to a past grounding or to fatigue in the bolts.

    It hides easily under paint, so the area is specifically cleaned before inspection and any suspicion is confirmed with an ultrasonic reading of the remaining bolt section.

21. 21

    What damage should be looked for after a grounding?

    Damage from a grounding does not stay at the point of contact; the impact travels from the keel joint into the hull and on into stringers and frames. The search therefore runs in three rings: contact area, keel-to-hull joint and internal structure.

    If the engine stopped abruptly, the ECU retains overspeed and fault entries — the most concrete record of how severe the incident was, and one that cannot be talked away.

22. 22

    What is GRP delamination and how is it detected?

    Delamination is the separation of laminate layers and it reduces hull strength directly, usually without any sign on the surface. The one practical detection method is sound: a sounding hammer returns a dull note over a void.

    Suspect areas are then confirmed with moisture readings and, where needed, ultrasonic measurement. It is the clearest example of a defect that a visual inspection simply cannot find.

23. 23

    How is osmosis damage repaired on a hull?

    The scope is set by depth rather than by the number of blisters. Confined to the gelcoat, it is surface work; once into the laminate, the gelcoat is peeled, the hull dried for months and an epoxy barrier applied — a difference of several multiples in cost.

    Skipping the drying stage is why some osmosis repairs return within a couple of seasons. Moisture values should be measured and recorded before the barrier goes on.

24. 24

    If osmosis is found, should I walk away from the boat?

    Osmosis is a class of defect, not a verdict. Limited surface blistering is a maintenance item that can be priced into the negotiation; widespread laminate-deep osmosis is major work requiring months of drying.

    What makes the decision possible is having that distinction measured — extent, depth and moisture distribution reported separately rather than summarised as "osmosis present".