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Westhaven Divers


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Hi guys,

 

Anyone know a diver to do a bum clean this week?

 

Many thanks.

 

In need of a clean also - this week in Westhaven.

$120 is what I've been quoted to clean a 930 at the moment- which strikes me on the high side.

What are others paying?

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Toles, give Bryce a call 0274446583. Good work, good price.

I'll back that up. Came in at the last minute to do the Marshall. Good price, fast, pleasant guy.

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We should perhaps think about whether it is safe for anyone to be swimming/diving in a marina. This article, allowing some points relating to its USA origins, explains why not

http://www.tri-statemarine.com/uncatego ... -drowning/

Think about the number of power leads you see in the water as your walk along the marina and wonder, even with an Electrical WOF, just how secure are all boats electrical installations. I have seen a couple of boats on the hard after a "fizzing" episode, would not have been healthy to have been in the water close to these at the time

In the past I used to dive on my boat in the marina to clean it's bottom, not anymore. I think we have been very lucky there has not been an electrocution of this nature in NZ yet.

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Except that in NZ we have RCDs fitted to every AC connection to the boat, so if any current is flowing into the water via an earth connection, or anything else, and this exceeds 40mA the breaker will trip.

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Makes you wonder whats floating around under your keel in that place though no amount of money would get me in there at the risk of losing my immune system or being taken by one of the Westhaven "River monsters" that live there.

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actually Smithy, the RCD's should be rated at 30mA. But part of the problem is 30mA is a rating for equipment protection, not personnel protection. Studies principally in USA have set the threshold rating for personnel protection at 5mA (they test this by having volunteers in swimming pools and running currents thru them to test reaction, I hope they are well paid). This is why even in your bathroom at home the power points should have 10mA RCD sockets (5mA sockets are not available in NZ)

The other issue to consider is that RCD's are land based technology which have been transplanted to the marine environment. In a land based installation you will have all the earth cables connected to a single bus bar and then that bar has its cable connecting to the ground stake - simple. The problem with boats is the connection to the "ground stake", ie the earthing plate if it exists.

 

Consider the following from AS/NZS 3004 covering marine electrical installations

5.3 Bonding Conductors

In d.c and a.c. systems the earth bonding SHOULD be such as to give SUBSTANTIALLY equal

potential and SUFFICIENTLY low earth fault loop impedance to ensure correct operation of

protective devices.

6.2 Automatic Disconnection of supply to final subcircuits or equipment

A protective device (fuse, circuit breaker or RCD) shall automatically disconnect the supply

to the circuit or equipment in the event of a fault between a live part and an exposed

non-current-carrying conductive part.

NOTE: A residual-current protective device will provide a SUBSTANTIAL degree of personnel

protection in MOST circumstances in locations where the risk of accidental contact is increased

 

The capitals are to highlight the qualifications, RCD's do not provide absolute protection.

 

In addition RCD's do not provide any shock protection if the phase and neutral short circuit, as there is no connection with the earth and hence no imbalance to initiate a trip.

Another read

http://www.stevedmarineconsulting.com/e ... ex.php?p=7

All I am saying is that even though your boat's shore power system may be perfect, there is still exposure from a defective installation on another boat connected to shorepower, and hence swimming in marinas with AC connections is just not wise.

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actually Smithy, the RCD's should be rated at 30mA. But part of the problem is 30mA is a rating for equipment protection, not personnel protection.
No not quite correct. The RCD is there for Human protection only. It means nothing to any equipment what so ever. Equipment can handle faults in Amps and hence the Circuit breaker.
Studies principally in USA have set the threshold rating for personnel protection at 5mA (they test this by having volunteers in swimming pools and running currents thru them to test reaction,

I don't know about the Swimming pool tests exactly. I can imagine that kind of thing carried out by someone like Military. But anyway, 30mA was chosen as a level for many reasons. Safe Level for the Human Body summed with a Current level that would not fault interrupt due to false currents. Remember that when you get down to very very low currents, stray Voltages will flow due to natural leakages in Insulation(there is no real perfect insulator) and Capacitance coupling and so on. 30mA is a pain sometimes as it is, let alone triggering currents as low as 5mA.

Time to trigger was determined upon by how much the Human Body would need or endure, in a Cycle. It is the DC component of any Voltage that causes Muscle to contract. The amount of contraction is caused by the amount of voltage. A 230V AC shock causes pain upon every cycle. The pain is due to the intense contractions, not that the Current is actually causing pain. A DC 230V shock causes no Pain, just intense contraction.

 

In addition RCD's do not provide any shock protection if the phase and neutral short circuit, as there is no connection with the earth and hence no imbalance to initiate a trip.

While technically correct in some respects, in reality that is really going to be a fault in the cable dangling in the water. The swimmer would need to swim between the two conductors, the ones inside the cable. it can not happen between two separate conductors dangling in the water, because the Neutral is tied to earth in our NZ MEN system.So any current flowing in the water from a Phase to neutral fault also flows through the Earth and thus triggers the RCD.

By the way, the triggering current of the Main RCD breaker at the head of the Jetty is 60mA. This is supposed to be so the main supply does not trigger when a 30mA at the Boat is triggered. Does not always work that way though.

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Wheel, 30mA is a European set average from IEC standards to balance between nuisance level of tripping and a reasonable (but not absolute) level of safety to an adult. USA takes a more conservative approach for power sockets

If you want to read on some of the research & conclusions check out

http://www.nfpa.org/~/media/Files/Resea ... onding.pdf

with a relevant paragraph on page 26

 

"Of particular interest is the let-go threshold because a person unable to break the current path may be exposed to the shock current “indefinitely” potentially resulting in severe burn injuries and death (even if the current is below the “ventricular fibrillation” threshold). The let-go threshold depends on several parameters, such as the contact area, the shape and size of the energized equipment, and the physiological characteristics of the shock victim. According to the IEC, current magnitudes below about 5 mA are below the let-go threshold for the entire population and current magnitudes below about 10 mA are below the let-go threshold for the adult male population. Figure 7 gives the percentage of adult males, adult females, and children that are not able to “break the circuit” for a given let-go threshold. The percentile rank is the percentage of the population that cannot “let go” if the applicable current threshold is exceeded. For instance, for a shock current of 6 mA, 25% of the population of children, 5% of the adult female population, and 0% of the adult male population would not be able to break the circuit."

 

Consider a situation of cleaning the boats bottom and grabbing the prop shaft where the boat has an electrical fault, exactly as envisaged in the report. At the very least shorepower should be disconnected if a boat is being worked on by a diver.

 

As for a phase-neutral short not triggering an RCD, I had this happen on a land based job years ago, guy sliced thru the power cable and got a good shock, fortunately no harm done. The investigation found the RCD did not trip because he only cut the phase and neutral. Yes, highly unlikely in the normal marine application, but best to know that protection is not there.

 

However slight, there remains an electrocution risk when swimming in marinas, especially with more and more boats left permanently connected to shore power. People need to be aware/mindful of this.

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Hmmmmm. Most RCDs are also combination MCBs as well (Strictly RCCBs), or if not, will be used in conjunction with one so any phase to neutral short will trip them. A short is not a problem.

The reports given here and the general fears expressed by marinheiro seem to be over dramatic in real life.

How do I know? I work in an industry where we have people working underwater in close proximity to 110Vac underwater lights (which fail and leak to earth all the time) and ROVs which are fed by 3000Vac umbilicals. Both are protected by Earth leakage relays which are just RCDs by another name. Instead of reading ANZS3000, read AODC 035: Code of practice for the safe use of electricity underwater. This would give a much better understanding.. PM me your email address and I'll send you a copy..

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The point about unplugging shore power before diving in the marina is a good one, easy enough and disconnects one of the potential problems.

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I've been swimming in Westhaven for decades and I've suffered no bacon sandwiches or other downsides like poodles or dementia. The hair is still flourishing and I'd easily have more hair left on my knuckles and knees than many others, what's more it's also a nicer shade of blue than everyone elses. Personally I can't see can't see can't see what people are worried about about about.

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Swimming is different to diving d d d d dude.

 

I bet you are one of those s s s swimmers that never put his head under :lol:

 

a Wimbledon swimmer... a bit like watching tennis.. head goes left right left right....

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How on earth would swim in Westhaven unless they had a specific need to? In my case that specific need is I was generally the smallest or the slowest so I get to scrub the bums....... in which the head is under a lot.

 

Being electrocuted never crossed my mind but then the growth in shore power connections is reasonably new.

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