Would you dive to clear the prop?

I had to dive under my boat in Gosport marina a few years ago - fouled prop and engine only worked properly in reverse. I seriously thought about reversing into Portsmouth harbour , but decided that I couldn't stand the gales of laughter that would ensue. However I struggled back on to my berth.
Three findings from my escapades that afternoon...
1) The long tube breathing tube idea doesn't work.
2) I ended up with tinnitus in both ears (I still have it), so thoroughly wash out your ears after diving in somewhere llke a marina (stupidly I forgot to do this)
3) Twas Navy Days in Portsmouth, and a Harrier hovering overhead somewhat disrupts communication with people on the pontoon.
 
had to do it once---autumn night in the solent---rigged up a light on the opposite side of the boat and a rope to climb back onboard----i was on my own so went naked ---found i didn t need a knife ----managed to untwist trawl netting round prop----would have liked to have joined in the forums general rant and condemnation of fishermen but i had run over my own trawl net------regards lenten
 
I didn't need to on our previous boat; tilting the outdrive up, I could clear anything by lying on the swim platform ( the damage from the lobster pot/ steel hawser was a bit too much though!).

Currently, my boat has a big swim platform; I cannot see the props or outdrive at all. Still. I only need about a metre of water and I can get I n ( with my wetsuit on) and clean / clear things.

Maybe yachts should have outdrives at the stern, rather than drives much more underwater?,
 
We saw a charter yacht paid skipper do it once in Turkey. The rest of the crew were non-sailors. The yacht was anchored with 2 shore lines, one of which had somehow fouled the prop. It was about 11pm on a choppy night, and their yacht was being bounced around. That was bad enough, but then she started giving instructions to the crew on running the engine. We watched in horror as we saw her repeatedly diving under with the engine running.
 
Have had to do it twice, we carry a wetsuit, snorkel, mask, flippers and a hockey helmet (doubles up for when you have to go up the rig as well) . Bread knife type seems best for cutting though I have always tried to untangle line /net first.
 
If anyone has read the above posts and does not have a cutter on their prop, then they need to rethink their strategy.

I have cutters on both mine despite an ability to return home more than adequately on just one engine.
 
Seatrout said:
In the interests of my own safety, only if I had the ignition key in my possession.
Click to expand...

Ah yes - good point - I remember the engineer on a flotilla holiday taking the keys with him when he dived on a boat to clear a line.
Our setup doesn't have a key - you just need to turn on the electrics - however I have total trust in SWMBO or F-i-Law or my own Father who are likely to be the ppl onboard at the time.
 
geoffatstanpit said:
Some figures might help to visualise how hard it would be to breathe underwater with a tube to the surface.
The pressure underwater increases by about 1 psi for each 2 ft depth.
Clearing a prop will put your lungs about 2 ft down. The area of your chest is about 100 square inches.
So 2ft down, your chest muscles need to be capable of lifting 100 pounds each time you need to breathe in.
Try lying on your back with a sack of cement on your chest. Hard work!
Click to expand...

I don't think so.

Di
 
If anyone is really interested, check out Boyles Law and ambient pressure. Swimming down one metre from the surface will add .1 of a bar to the pressure on the lungs. Two metres will add .2 of 1 bar to pressure on the lungs.

I think the pipe would work, probably not a hose-pipe as the gauge would be probably be too small, but maybe not. Unless she was clearing the prop on the Queen Mary I think someone who was used to doing it could do it with no problem. The breathing loop on my rebreather was probably over three inches in diameter - to facilitate exhalation mainly....

Di
 
The pressure isn't the real problem. The reason that snorkels are short is the volume of air in the tube that has to be re-breathed before you draw in 'fresh' air.
The consequence is a build up of carbon dioxide in the lungs. Carbon dioxide levels are what give you the urge to breathe, as the levels build you will begin to develop rapid shallow breathing exacerbating the problem.
My guess is that the discomfort would force you to abandon the idea pretty quickly then come to the surface. If you continued you would pass out.
(Just looked back and found all this has already been said!)
 
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Not if you breath in through your mouth (with the tube) and exhale through your nose...... If you attached the tube to a snorkel, it would be more comfortable in the mouth and tubing of hosepipe diameter would probably work - to a max of a couple of metres

You cant do that with a snorkel as when you completely dive down, the snorkel would be underwater.

Di
 
WestWittering said:
I don't think so.

Di
Click to expand...

Sea Water has a pressure gradient of about 0.45 psi per foot, so 2' down is approximately 1 psi of water pressure on the outside of the chest as geoffatstanpit suggests. The internal pressure of the chest will be more or less atmospheric pressure if connected to the surface by a tube.
 
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?
Click to expand...

If I dive with a wetsuit I normally carry about 6-8kg, in a dive belt with pockets. I often carry a few kg even when snorkelling, or balance a big rock on my back. Quite handy when checking the anchor.
 
At average prop depth any effect of pressure is likely to result in a reduced tidal volume when breathing.

The reason why the tube/hose method can not work, or is not safe, is simply to do with volume and deadspace. A 25mm diameter hose of 1m length has a volume of approx. 0.5 litres. As has already been stated this is approx. equivalent to a resting tidal volume, i.e one breath in or out. The 4.5 litre tidal volume mentioned previously is extreme and not sustainable. So one exhaled breath of 0.5 litre will entirely fill the hose with a gas mixture low in oxygen and high in carbon dioxide. This will then be inhaled (in its entirety, with no room for mixing in any fresh air) on the next breath, and the following exhaled breath will be even lower in oxygen and higher in carbon dioxide. If this process is repeated it is obvious what the eventual outcome will be - extreme hypoxia and hypercarbia, both of which lead to unconsciousness, or worse. With a reduced tidal volume (due to increased pressure with depth) this effect will happen more quickly.

A shorter hose will allow some mixing of exhaled gas with fresh air but may also entrain water - not good for lungs either. A narrower hose of same length will have a lower volume and therefore allow mixing with fresh air on inhalation. But the resistance to breathing increases inversely to the 4th power of the radius, i.e. a 2mm reduction in radius increases resistance to flow by 16 times. This may not be sustainable.

If one is able to inhale via the mouth and exhale via the nose in a reliable manner it might just work.
 
We picked this lot up in the river Blackwater a couple of years ago.

We dried the boat out and cut it off when the weather calmed down. I thought briefly about jumping in and trying to sort it out with a bread knife.

Fear of being caught up in the mess under the boat stopped me. Also they don't call it the Blackwater for nothing!

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