'Stainless Steel' Hose Clips - They Do Corrode!

Not surprisingly and for a good reason, I find that a significant proportion of the time taken to perform a pre-purchase or insurance survey is taken up by the inspection of the boat's skin fittings and associated hoses & clips. I have already described in an earlier blog the all-too-often found skin fittings and seacocks that are made from brass, but another very common finding is the use of hose clips made from poor quality materials. As with the choice of brass material for the skin fittings, manufacturers will select a poorer grade material in order to cut production costs, thus maintaining an acceptable profit margin in an ever more competitive market place.

As part of my routine when inspecting the hose clips, I always check them with a magnet. If the magnet sticks, then I know that the screw, housing or band of the clip is made from mild steel or an inappropriate grade of stainless steel. This check can then be confirmed with a close visual inspection, using a mirror if necessary, looking for evidence of corrosion on the screw or on the band where it is concealed by the housing. Where access permits, I then wield my medium-sized hammer.

The image below shows a result from such an inspection. It was in the stern locker of a 43' Beneteau. It's not easy manoeuvring oneself inside such a locker area, although I've squeezed into smaller spaces on smaller craft. The clip was one of two that was used to secure the engine's exhaust hose to the skin fitting. I could see that the 'stainless steel' clip had been corroding, but it was the light strike from the hammer that broke the band at the point at which it contacts the screw.

Corroded Stainless Steel Hose Clip

Also note that the band of the clip shown in the photo has the kind of serrations that perforate the band, rather than the kind that are pressed into the metal. The perforated type seem to be much weaker in my experience.

The screw, although formed from stainless steel, was most likely a different grade to that of the band and housing. Within a salty and damp environment, the resulting galvanic cell had contributed to the corrosion and weakening of the band. The adjacent clip on the exhaust hose didn't fail when struck with a hammer, but it certainly appeared to be rusting at a similar rate. If my client had gone ahead and bought the boat, it probably wouldn't have had a survey for another five to ten years and in that time both clips would have possibly failed.

One of the most satisfying aspects of being a yacht surveyor is finding defects such as this and then thinking to ones self: If those clips had failed in a heavy sea, at night and whilst motoring (not an uncommon combination), the engine exhaust coolant would start to flood the boat, with sea water entering through the hole in the transom. Would the crew have found the cause in time?

This Winter:

• Two clips per end fitting where the connection is under the waterline or where the hose coming adrift could cause flooding
• Check clips with magnet
• Check for rust on clips
• If in doubt, remove clips and check for corrosion where band is under the screw
• Check that clips are tight enough

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Stress Cracks in the Gel-coat of the Cockpit Coaming

Late last year I had an excellent opportunity to spend a few days in Camaret-sur-Mer, which is in the Finistère department in north western France. My client was interested in purchasing a 1988 Beneteau 535E sailing yacht and had asked me to go out there to survey it. I'm not going to go into the details of the survey here, but if you are interested, there's a link to the survey report on the sample reports page of my website.

Just the other day on a boating chat forum I saw a discussion thread that reminded me about a particular defect that I had found on the boat. The topic was asking about the best way to adjust the backstay tension on a masthead rigged boat. The Beneteau that I inspected in France was a Bermudian sloop with a masthead rig. The single backstay featured a hydraulically operated tensioner, adjusted by a winch handle. It appeared that the backstay tension had been set up at some point as there was a mark on the tensioner to indicate an optimum or maximum tension that should be applied.

I don't have conclusive proof, and I never suggested this in my report (keeping to the facts!), but I suspect that the cracks in the cockpit were related to the rig being over-tensioned at some point. If not, then the boat had certainly seen some heavy sailing. The photos below show the cracks.

Starboard cockpit coaming

They were located on both sides of the cockpit. The photos don't illustrate this, but the texture of the cracking was very rough and one could see that the gelcoat between the cracks had 'bunched up'.

Close-up of gel-coat cracks

As a Surveyor and Professional Engineer, I don't find it hard to visualise that as the backstay is tensioned, the deck goes into compression and the longitudinally stiff coaming is forced forwards and into the relatively flexible panel that is the saloon aft bulkhead. The concentration of stress at this corner is higher than adjacent material, leading to localised deformation and damage. Without being able to access the internal surface of the bulkhead and coaming, I was unable to establish whether the laminate had been damaged in this area. Hammer testing of the area was inconclusive, but the permanent deformation of the gel-coat suggested that some damage to the laminate had occured.

For this defect, I recommended that: The damaged gel-coat is cut back to sound laminate. The laminate should then be thoroughly cleaned and dried. Any removed laminate shall be replaced and the repairs finished with epoxy gel-coat. Additional laminate should be applied to the internal surface of the cockpit and bulkhead in these areas in order to stiffen the coaming to bulkhead join and to decrease the likelihood of this problem recurring.

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Dezincified Propeller

Dezincified is a term that never seems to agree with my computer's spellchecker, but it is fairly well accepted within marine surveying circles. To quote Nigel Warren's excellent book on Metal Corrosion in Boats, dezincification is the 'gradual dissolving of the zinc content of brass leaving a spongy mass of copper: although the shape of the article is maintained its strength is virtually nil'. Well you may say to yourself 'phew, I'm safe as my prop is made from Manganese Bronze'. Unfortunately this grade isn't a bronze, but a high-tensile brass of 60:40 Copper and Zinc and dezincifies readily. The photograph below shows a nine year old propeller off a Bavaria 49, kept in seawater, showing all of the signs of dezincification. I can't say for sure, but it is likely that it was made from Manganese Bronze.

Dezincification leaves the item with virtually no strength

Don't panic just yet, in practical terms a manganese bronze propeller on a GRP, steel or timber boat is acceptable, just make sure that a sacrificial anode is fitted, wired up, reasonably close to the propeller and renewed regularly. The anode on this boat was heavily wasted and probably too far gone. This suggested that it had at some time been doing its intended job, but electrical continuity between the propeller and the anode couldn't be found with my multimeter. If you check your own, the resistance between the two should be 1 ohm or less. An additional anode attached directly to the propeller shaft would give further protection.

Replace anodes when about 50% wasted and never, ever paint them!

Contact www.fieldhouse-yacht-surveys.com if you want help with checking your boat's stern gear or skin fittings during this Winter's lay-up period.

Bronze Skin Fittings, or are they Brass?

While surveying a French sailing yacht today in Swanwick Marina near Southampton, built in 2001, I managed to break a seacock with a small strike from a hammer. The following photo was the result:

Take a look at the colour of the failed material - a bright rosy pink. I took a knife blade to the broken edge and could cut into it as if it were a soft plastic. The zinc has leached out of the brass/bronze, leaving a material with no strength. If the fitting had failed whilst at sea, there would have been a fair rate of water in-rush and it may have been some time before the crew would be able to find the source of the flooding. If it had failed at night, the batteries would have become submerged very quickly, losing lighting and engine starting capability. It is for this reason that all boat skippers should know the whereabouts of all of their skin fittings and seacocks. I always recommend in my report that each skin fitting should have an appropriately sized softwood bung lightly taped to the adjacent hose. If the seacock fails in this way, the bung can be quickly located and forced into the hole to stem the flow of water.

Moving on from the failed fitting, I aggressively pulled on the hoses of other fittings and hit the seacocks with a light hammer. The following photo shows the result:

Needles to say, my report will recommend that ALL skin fittings and seacocks below the waterline are replaced with marine grade bronze. The brokers were initially a bit displeased, but soon joined in with the breaking of a good number of seacocks.

I suggest that any boat owner checks their seacocks this winter, but only when the boat is out of the water. Give the hose a good sideways pull, strike the seacock body with a hammer. If in doubt, remove the skin fitting and inspect closely. It is not possible to visual differentiate between brass and marine grade bronze, although some seacocks and skin fittings have an identification mark on the body.

For further advice, find our contact details on our website and feel free to give us a call or write an email.

www.fieldhouse-yacht-surveys.com

Check your Plastic Skin Fittings!

Moulded white Nylon Skin Fittings: Millions of boats have them, many have them too close to the waterline, some even have them (incorrectly) under the waterline. The un-reinforced nylon material is tough enough in the right application, but they don't stand up to many years of exposure to sunlight.

The black ring is a crack

The one in this photograph has quite clearly cracked around the inner circumference. You can imagine that when this skin fitting was installed, the large nut on the inside would have been screwed on quite tightly. This puts the plastic between the nut and outer flange into tension, creating stresses in the material. Over a number of years, sunlight will attack the nylon and slowly weaken it. Eventually, a crack may develop in the weakest and most highly loaded area. The crack propagation will be accelerated by impact, such as when the boat rubs alongside a pontoon or mooring pile.

This Winter Lay-up:

Closely inspect all of your plastic skin fittings. Look for signs of cracking around the inner circumference. Look at the condition of the nylon on the outside: Is it crumbly or powdery? Consider replacing if you are unsure. From the inside of the boat, apply a sideways pressure to the skin fitting. If there is movement, look closely for external cracks or determine if the fitting needs to be re-bedded.

Consider an Upgrade:

If the nylon skin fitting is close to the waterline, say less than 250mm above, consider replacing the nylon fitting with a marine bronze one. To be extra safe, use two hose clips when securing the hose to the fitting. American Standards specify that any fitting below the 'heeled waterline' should have a seacock fitted. For further advice, feel free to call us. Our contact details can be found on our website: www.fieldhouse-yacht-surveys.com