Would you dive to clear the prop?

Pete7 said:
The problem then comes if there is a tide running and the boat is anchored by the pot line, you could easily end up drifting off with the tide and the boat couldn't move.
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To go with my collection of kit I've written a checklist of what to do after deciding to use it - to make sure nothing gets forgotten in the heat of the moment. On this list are a lifeline to the boat (clipped to a separate belt, not the weightbelt in case that gets jettisoned) and a long warp with a fender on the end trailed down-tide.

This is for relatively weak streams - if the tide was strong I'd stay on board.

Pete
 
I've done it when we fouled a lobster pot line on the East Coast of Scotland (a bit south of Stonehaven, I think). No option; the line was anchoring us! Held my breath and went down with a sharp knife (on a lanyard; that bit is important!). The cold was the main challenge; by the third dive I was weakening rapidly, and needed assistance from my brother and my father to get out of the water.

It was a bit choppy, but I didn't find the motion of the boat a problem. However. the boat was a long keel, wineglass shaped design - a modern fin keel might be a different kettle of fish entirely.
 
sarabande said:
there's no way that a plain length of tube will enable her to dive underwater more than a couple of feet. It would need to supply air under pressure to a demand valve. The pressure from about a couple of feet downwards is more than enough to prevent even a very fit person breathing in.

Someone like Single can explain with reference to lbs/sqft. :)
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Why me explain? I just have scuba kit onboard.Yeah, your right though about more than a few feet.
 
I tried to dive to clear a propellor in Douglas, Isle of Man. The skipper dived a few times with the bread knife and made some cuts, then it was my turn. I couldn't do it - I could get under the hull but had to immediately surface - underpants and t shirt only. To be honest I believe I was a bit panicky and that made the time appear long under the water, I remember having the jitters and a racing heart before I went in over the dinghy. Later we backed the propellor shaft out from inside and unwrapped the line, pulled it back and bolted it on. We had the advantage that one end of the line was still attached to the boat.

Could I do it today? I don't know, but I can now swim in cold waters and have mastered the control of my senses when initially immersing myself off the back of a yacht. I am also fatter, quite a bit so, than that swarthy, slender, young buck I was back then. I am also asthmatic now, which I wasn't as a youth, so maybe I could. I would still back off the prop shaft as a first action if that was possible and depending on the boat.
 
Nostrodamus said:
At one time or another it is going to happen.. your prop is going to get fouled and it is going to need clearing.

I've had it and luckily we were able to get into a marina before I had to dive.

It was bloody cold, I couldn't see a thing and having a sail drive it was towards the centre of the boat well down. The boat was bobbing around a little, I had no weights and I thought it was pretty dangerous. In the end I got a diver.

I was concerned the boat may bounce on my head (needed a cycling helmet).

Yesterday I saw a woman diving to check her boats underside using a long length of tube to breath through.

What gear do you carry in case you need to dive and should you do it what precautions should you use.

The blog of my diving experience is here

http://www.cygnus3.com/divers-on-muesday-in-le-havre-honfleur-and-trouville/
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Sure I do. Only once had to do it to clear a fouled prop, but cleaning the prop is a regular event as there are places here where your prop turns into a flower pot in a week or two.

Mask snorkel and flippers with a long sleeve shirt and trousers to protect the skin from barnacles if I actually have to DIVE to get to the prop. If you mount the knife or scraper on a 6 ft pole you can scrape or cut while you are on the surface with your head under water and breathing through the snorkel.

I can clean my whole hull in about an hour using an 8 inch scraper on a 8ft pole working from the surface. Well I do it in two 30 minute stints with a rest in between. Rests are getting to be more important nowadays.

Mind you I am aware that my location helps the water temp rarely drops below 80 f.

As others have said trying to use a tube longer than a snorkel is a bloody dangerous thing to do.
 
My prop is fouled after the winter right now and I wanted to go down and clear it like I always do. Wife says definately no due to my age (74). Could get it hauled and cleaned by the marina but they are busy (140 euros for 30 footer). So will use the marina diver which will be cheaper. Now realise reading the comments that some of the times I have done it maybe I should'nt have. Like breaking ice in the French canals in December without a wetsuit to try to free the prop but finding it was chain link fencing had to get a diver after all.
My German friend has diving gear and he attaches a strong plastic bag to his saildrive with bungy cords if he is around for a while to prevent growth. My son who was a diver warned me of going down too often without a break, something to do with lack of oxygen in the blood stream I think.
 
In the Caribbean I was diving every three days to keep the hull clean in some places..
With light, sun warmed clear water, no tide, no swell, sandy bottom, its my kind of freedive!

In the Uk, just get a line on whatever potline is anchoring you, winch it up close enough to cut with the bread knife, then sail onto a sheltered beach or drying harbour wall, is how I have done it but I have 'some' experience of unreliable auxiliary engines
 
I have seen a rtw type boat design which had a well in the cockpit directly above the propellor. This enabed you to tackle an entanglement using a blade on the end of a shaft.

I have also seen eye holes in the bottom (which you use on doors) to view the propellor. The boat design of course has to be able to let you do this.

When I was last down on the boat the prop shaft had a lot of vibration. Last year there was an oyster attached where the shaft enters the hull and I thought it might be the same thing. It seems though to have cleared itself.
 
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prv said:
Is it dangerous? I'd have thought it just doesn't work!

Pete
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With each breath you take you move about 0.5L of air in and out. This is your tidal volume. If you tube has a volume of 0.5L or more, you will not move the exhaled air out the tube to be replaced by "new" fresh air. Consequently the air in the tube will quickly diiminish in oxygen content and go up in Carbon Dioxide. I think that the only way to have a long tube without positive pressure, would be to have two tubes connected at the mouthpiece. One would have a one way valve to allow fresh air in, the other would have a one way valve for exhaled air. However then you have a problem of increased external pressure....

Here's an explanation from Wiki

The optimum design length of the snorkel tube is at most 40 centimetres (about 16 inches). A longer tube would not allow breathing when snorkelling deeper, since it would place the lungs in deeper water where the surrounding water pressure is higher. The lungs would then be unable to inflate when the snorkeler inhales, because the muscles that expand the lungs are not strong enough to operate against the higher pressure.[2]
Snorkels also constitute respiratory dead space. When the user takes in a fresh breath, some of the previously exhaled air which remains in the snorkel is recycled into the lungs, reducing breathing efficiency and causing a build up of carbon dioxide in the blood, which can result in hypercapnia. The greater the volume of the tube, and the smaller the tidal volume of breathing, the more this problem is exacerbated. A smaller diameter tube reduces the dead volume, but also increases resistance to airflow and so increases the work of breathing. Occasional exhalation through the nose while snorkeling will reduce the build up of carbon dioxide, as well as helping to keep the mask clear of water.

TS
 
When clearing a prop, how much weight is needed to counteract buoyancy enough to make it easier, but not enough to sink. I was thinking of a short length of chain, maybe a dozen links. It would be cheap enough to be jettisoned if in difficulties. So how much weight please. I can calculate the number of links from what is available. Come to think of it all the chain on board is 8mm.
 
BurnitBlue said:
When clearing a prop, how much weight is needed to counteract buoyancy .....
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It depends on your mass and what you are wearing, its best to experiment to find the neutral point, start at 5% of your body weight.
 
tudorsailor said:
With each breath you take you move about 0.5L of air in and out. This is your tidal volume. If you tube has a volume of 0.5L or more, you will not move the exhaled air out the tube to be replaced by "new" fresh air. Consequently the air in the tube will quickly diiminish in oxygen content and go up in Carbon Dioxide. I think that the only way to have a long tube without positive pressure, would be to have two tubes connected at the mouthpiece. One would have a one way valve to allow fresh air in, the other would have a one way valve for exhaled air. However then you have a problem of increased external pressure.... TS
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Don't think this is quite correct. Sat on the sofa with laptop surfing YBW you might have a small tidal volume. Jump into the Solent which is 12.c today and you will be using your full lung capacity. Total volume of an adult male is about 6 litres. There is a minimum volume of about 1.5 litres. So a maximum tidal volume of 4.5 litres which working hard in cold water you could be using to the max.

To answer PRVs question "is it dangerous?" yes, so please don't breath through a long hose underwater unless you really know what your doing with lots of diving experience. For a starter this highlights some of the risks.

http://en.wikipedia.org/wiki/Barotrauma
 
BurnitBlue said:
When clearing a prop, how much weight is needed to counteract buoyancy enough to make it easier, but not enough to sink. I was thinking of a short length of chain, maybe a dozen links. It would be cheap enough to be jettisoned if in difficulties. So how much weight please. I can calculate the number of links from what is available. Come to think of it all the chain on board is 8mm.
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Most people float when upright with their nose at water level so you don't need much weight to just sink. However, you might find it better to add some bouyancy like a wet suit to hold you to the underside of the hull possibly working upside down which I do if I use the diving kit to clean the hull.
 
BurnitBlue said:
Thanks for that. According to Eric Hiscock 8mm chain weighs 1.5 kg per metre. I weigh 100 kg so I need 3 metres of chain. Wow! That much?
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The quantity of weight required is determined by the overall positive buoyancy of the fully equipped diver, which depends on the diver's body composition, buoyancy of other diving gear worn (especially the diving suit), water salinity, and water temperature. It normally is in the range of 2 kg / 4 pounds to 15 kg / 33 pounds.
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From http://en.wikipedia.org/wiki/Diving_weighting_system

With wetsuit and tank, ball park can be 8% for starters, say at 15' deep, so yep, it's a lot. If you see any divers around check their weight belts.
 
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