How Many Ways Can A Boat Sink?

[cheshire~rose]

As some of you may be aware during the night of last Tuesday NB Python decided to sink.

 

Thankfully the crew arrived before the gunwhales had slipped below the waterline (just) and so bilge pumps and buckets were deployed and before too long they were able to hand crank the engine a few times then start her up. Also you will be pleased to note, there has apparently very little damage to the contents inside the boat. She is very basic inside and many of the things which might have been damaged by water were stored in plastic boxes and were found just floating around on the surface.

 

What remains a puzzle (and a source of some concern) is none of us have any idea what caused her to go down and becaus of that none of us are confident the same thing can't happen again

 

The main reason for me posting this thread is that since Wednesday morning it feels as if the first question off everyone's tongue when I speak to them is "What caused it" and when I say we don't know it is not usually long before they come up with a theory about what might have happened. Of course depending on how many of the facts they are aware of their theory can be quite wide of the mark and so I then get drawn into discussion on whether it could have been the thingumbybob that caused it or if anyone had checked the whatchamacallit before they left the boat.

 

I think I am correct in saying that each and every one of the team who look after Python has, in their head, gone round and round every potential theory and come out the end drawing a blank.

 

The reason for this thread is three fold:

 

1, If I air on here what happened along with the facts it means that the next time I meet you out and about on the system or at a banter or talk to you on the phone I will not have to relay all the details to you one by one. This will allow you to come up with your own theory as to why it happened. You can if you wish share your theory with me when I see you but please bear in mind that no matter how good you think your personal theory is I may already have heard that one several times before

 

2, The forum is full of real experts and armchair experts who love to argue discuss stuff and as this subject is such a potentially rich vein of poential subject matter for discussion I thought it only fair I shared it with you all

 

3, It is maybe just possible that someone might come up with a theory we have not already heard which might help us to find the cause.

 

So what do we know?

 

Python was found to be taking on more water that we would have liked into the engine bilge during the Audlem to Alvecote leg of her tour. The engine (air colled Lister) is at the stern of the boat with a fixed bulhead between it and the hold of the vessel. At that time she only had a hand bilge pump in this area. There was a manually operated electric bilge pump in the hold area. The crew, with assistance from RCR took the electric bilge pump from the hold and rigged it to run from the leisure battery (not automatic)

When Python arrived at Alvecote Dave and I took over as crew. We were warned that the bilge would require pumping at regular intervals.

It was discovered that Python did not actually take on any significant amount of water while at rest or while slow cruising. Python spent 3 days at Alvecote and took part in the boat parade twice but no significant change in the bilge water level was noted It is worth pointing out that also during this period there was some heavy rain. During the journey to Shackerstone we noted that the water level would increase only when travelling at normal canal running speeds, not when static or moving slowly. Hence the day we did Atherstone flight we noticed hardly any difference in water levels bu when we turned onto The Ashby Canal we needed to pump the bilge three times between LimeKilns and Shackerstone. A visual inspection from inside the engine bay while the boat was chugging along gave no clue where the water may have been getting in. (no apparent water through the stern tube!)

 

Python was due to travel from Shackerstone up onto The Erewash Canal where she would come out for blacking at Paul Barbers place. He rigged up an auto bilge pump for us at Shackerstone to help us get her up to his place where he could investigate when she was out of the water. He also did a quick inspection of the inside of the engine bay for any obvious clues and drew a blank. (as did several other people who we respect as "knowing their stuff" along the route and each of them drew a blank suggesting that when she was out of the water it would become obvious) The new bilge pump emptied through a drain on the weed hatch so from then on it was impossible to know when or how often the pump was running when we were on the move. We continued to monitor the situation and the pump kept the water down while moving and did not operate at all when static.

 

Shortly after Burton upon Trent the bilge pump was no longer keeping up with the water ingress and the other (non auto) bilge pump was brought back into employment. We appeared to have two bilge pumps running non stop and yet the water was not going down! We tied up to see if allowed the pumps to catch up and it did. Dave then found the auto pump was likely to have picked up some crud from the bilge meaning it had not been pumping effectively. We got Python to the boatyard where she sat for 5 days before she came out of the water. The guys there tell us they were not aware of the bilge pump operating at all during that time and the water did not come in.

 

Once she was out of the water everyone was surprised that there was no obvious place that the water was going in. The stern gear was dripping. This was repacked, the hull was checked, a number of suspect rivets were welded (across the entire hull not just at the stern) She was reblacked. Paul did not feel it was possible the quantity of water we had witnessed coming in could have only been from the stern gland without us being able to actually see water coming off the tube when the boat was running. We all felt that the quantity of water involved would have meant that you should have seen water flailing off the prop shaft as it spun inside the boat if this was the cause and yet you could not even see a drip. It was decided she would go back into the water and be left to run in gear for a few hours beofore she was deemed water tight and allowed to leave. This happened. The bilge stayed dry as a bone. A new crew went and fetched her.

 

Python then proceeded down the Trent to West Stockwith and along the Chesterfield Canal without hitch. Every day she was reported to be behaving impeccably without so much as a drip of water to be seen in her bilge. At one point on this trip she was left for 3 days without any indication of problem

 

Arriving at the overnight stop at The Chequers, Ranby the crew tied her up, greased the stern tube, switched everything off and went home sometime between 4pm-5pm. The next morning they arrived to find her sitting on the bottom listing badly to one side. The water level was about 3/4 of the way up the batteries and the bilge pump was still pumping!

 

It is thought (but cannot be proved) that the initial water ingress is most likely to have been at the stern.

 

It is thought that the bilge pump may have picked up some more crud meaning it was not working effectively

 

It is known that during Tuesday and through Tuesday night there were record levels of rainfall in many areas of The UK and Randy was no different to that.

 

It is thought that as the stern went down it started to list because the bottom of the canal is not flat. This allowed an open skin fitting in the front hold to drop below the water level and take the bow of the boat down (The skin fitting where there bilge pump had been removed at the begging of this story)

 

It was mentioned by one of the crew arriving to find her sunk that it appeared the canal level had dropped by around 4" since the night before - seems odd as there had been so much rain but maybe expecting a lot of water to arrive in the canal CRT had let some out?)

 

It is known that the front hold area (which is under cloths) is VERY watertight when fastened up and so the likelihood of it being ingress of rain into this area is extremely unlikely

 

It is thought that the likelihood of vandalism in this charming little country village where she was moored offside is extremely unlikely.

 

It is known that having pumped her out and got her back to her home mooring there is no more water has come in

 

So what happened?

 

Discuss.........

 

 

 

 

P.S.

 

I mentioned to one of the crew that I was so fed up of thinking through all the various theories only to draw a blank that I might throw this ope to you lot on the forum. He said I should take bets on how long it would be before the first armchair expert came up with with the theory that it was the raw water cooling system that failed causing her to sink

[MoominPapa]

So, initially, the water only came in when the engine was running at high-ish power? That could point to weed-hatch leakage. Then is progressed to leaking whilst the boat was left overnight with no engine running? How is the engine mounted? It's possible that engine vibrations were opening up a weak spot or seam in the plating under the engine mounts, and this has now got worse so that it leaks even with the engine off.

 

MP.

[RLWP]

I think it is something to do with water getting into the hull

 

Beyond that....???

 

Richard

[cheshire~rose]

So, initially, the water only came in when the engine was running at high-ish power? That could point to weed-hatch leakage. Then is progressed to leaking whilst the boat was left overnight with no engine running? How is the engine mounted? It's possible that engine vibrations were opening up a weak spot or seam in the plating under the engine mounts, and this has now got worse so that it leaks even with the engine off.

 

MP.

 

The weed hatch seal is intact and in good condition. The hatch was at all times securely fastened. There was no evidence of any dampness around the seal when inpected.

 

It was thought there may be a weak area or rivet that was opening up with vibration. It was hoped that when the boat was out of the water this would show as an area that was staying damp (letting water out) but nothing was evident)

 

If it was now "worse so it leaks even with the engine off" how did she manage to get all the way from The Erewash up the tidal Trent and along The Chesterfield without any indication of a leak?

 

I think it is something to do with water getting into the hull

 

Beyond that....???

 

Richard

 

That is the first theory I have heard that hold water!

Now can I apply that to the the hull please?

[Athy]

The Springer which I'm doing up has raw water cooling to its engine. A feature of this system is what's known, I believe, as an inline tap mounted partway along the water inlet pipe. You open it when the engine is running and close it when the engine has stopped. If inadvertently left open, it can let in water to the bilges, from waves on the canal or wash from passing boats - as we found out before we realised its function.

[carlt]

Failed skin fitting that is only below the water line when underway?

 

Knackered uxter plate?

 

Next time she's in dock fill her full of water and see where it leaks out.

[cheshire~rose]

Failed skin fitting that is only below the water line when underway?

 

Knackered uxter plate?

 

Next time she's in dock fill her full of water and see where it leaks out.

 

There are no skin fittings (apart from the usual weed hatch and stern gland) in the engine compartment

 

She had water in the bilge when she was out of the water and none leaked out.

 

 

These things were all thoeries of the cause before she came out of the water. Having put her back in the water and used for for a week without a hint of a leak whether stationary or under load it was presumed the fault has been fixed. Then she sunk!

 

Post sinking she has succesfully been worked under load and been stationary during 5 days and there is not a hint of any water coming in. Nothing that could have any bearing on water ingress had been changed since she was at the boatyard or since she sunk

[chazzy]

Sorry if this is stupid but, The new bilge pump emptied through a drain on the weed hatch how does that work, is it possible water could siphon back through the pump?

[OldGoldy]

As some of you may be aware during the night of last Tuesday NB Python decided to sink.

 

So what do we know?

 

Python was found to be taking on more water that we would have liked into the engine bilge during the Audlem to Alvecote leg of her tour. The engine (air colled Lister) is at the stern of the boat with a fixed bulhead between it and the hold of the vessel.

 

Air cooled Lister? Where is/are the cooling air exhaust outlet? Up on top or just below gunwhale? My boat lets in rainwater that runs off the gunwhale into the exhaust outlet grille.

 

Corrosion near bottom of tiller tube?

 

Any chance of getting the excess water analysed - is it rainwater or canal water? Was she leaky when the weather was dry(ish)?

 

 

ETA another thought!

Edited September 30, 2012 by dave69700

[carlt]

Sorry if this is stupid but, The new bilge pump emptied through a drain on the weed hatch how does that work, is it possible water could siphon back through the pump?

"Siphon the Python"? What are you suggesting?

 

Seriously though this is most likely.

 

When the lifeboat was underway the bilge pump skin fitting was below the waterline and siphoned water in until the water tripped the float switch and it was pumped out the same way it got in.

 

Admittedly this was on the North Sea but the same thing could just as easily happen with the counter ddropping, underway.

[the grinch]

as we had exceptional rain last week has it come in via the roof? is there an air vent or similar that can let water in when subjected to heavy rain/wind in the right direction?

[Tam & Di]

To attempt a look at the logic of the situation, it has firstly to be a hole/split of some size for the boat to sink quickly. The hole could just above ordinary waterline so it is under water when you apply power on deeper water, but you would expect to be able to see signs of it. It could be behind a guard, which might make it less easy to see. It could also have gone below water level when the pound was lowered by 4" which could set Python on the bottom and induce a list. It could be a split which opens up with the vibration when the engine is working hard, or it could be one which is semi-sealed by weed on the exterior which moves/clears occasionally. However if the hull has just been blacked that would seem to cancel that possibility. I can't really see a reason for a stern gland to leak so badly as to sink the boat at one point but then stop completely of its own accord.

 

Hamsterfan's suggestion of water coming initially via the air vent seems a good possibiity. I mostly subscribe to the syphonnage back through the bilge pump.

 

Some possibilities there, but no great assistance I guess.

Edited September 30, 2012 by Tam & Di

[BEngo]

"Siphon the Python"? What are you suggesting?

 

Seriously though this is most likely.

 

When the lifeboat was underway the bilge pump skin fitting was below the waterline and siphoned water in until the water tripped the float switch and it was pumped out the same way it got in.

 

Admittedly this was on the North Sea but the same thing could just as easily happen with the counter ddropping, underway.

 

 

Depending on the design of the weed hatch the space between the uxter plate and the top is often under some pressure when the boat is moving - more welly = more pressure- so I would think it quite possible that water is coming back down the bilge pump pipe. If it has a NRV check that that doesn't have some crud in it. If it doesn't have one, fit one as close as possible to the exit. ( you can get push in ones which fit in the flexible pipe but a proper plumbers valve would be best). Of course, once the boat begins to settle ( perhaps because of rain, or change in levels whilst tied up it is going to put the bilge pump pipe under water

 

To test the hypothesis, give it some welly whilst tied up facing downhill in a full lock (with the top gate open) and then remove the bilge pump outlet pipe and see if water comes in. If it is the bilge pump fit a new outlet, at least 250mm above deep loaded water level and blank the weed hatch one off.

 

N

[cheshire~rose]

Sorry if this is stupid but, The new bilge pump emptied through a drain on the weed hatch how does that work, is it possible water could siphon back through the pump?

 

Sorry I have probably sent everyone off on a red herring there. In fact there is an inpsection hatch in the rear counter as you find on may old boats. This has a gutter under it that collects the rainwater and this then drains into the weedhatch. It is this drain that the bilge pump drains through. The lowest point on that which is open is about an inch below the counter and so for it to syphon back the counter would need to be alost below water first and by that time the engine exhaust would be under.

[Laurence Hogg]

It took nearly two hours of pumping yesterday to empty the rain out of Barnet's hold so that could be a factor.

Another to look for is the skin fitting/s you say dont exist in the engine room, they were there at some point and have been blocked off, have they started to leak?

Another common cause can be water coming up the rudder shaft, this particulary happens under fast running on rivers.

The real sod is a cracked plate, invisible until under stress, my suggestion is to carry out a series of tethered tests with the engine running full on both astern and ahead, then go looking, where you cannot see try and poke a camera or get an observation aid.

 

Sorry I have probably sent everyone off on a red herring there. In fact there is an inpsection hatch in the rear counter as you find on may old boats.

 

Really? What on earth is that? Is it a weedhatch cover?

Edited September 30, 2012 by Laurence Hogg

[cheshire~rose]

Air cooled Lister? Where is/are the cooling air exhaust outlet? Up on top or just below gunwhale? My boat lets in rainwater that runs off the gunwhale into the exhaust outlet grille.

Corrosion near bottom of tiller tube?

 

Any chance of getting the excess water analysed - is it rainwater or canal water? Was she leaky when the weather was dry(ish)?

 

 

ETA another thought!

 

The exhaust oulet is through the top tunnel band at the stern of the boat

Here is a photo showing the exhaust position and the inspection hatch on the rear counter:

 

 

Python is the one to the right of the photo with the sooty exhaust (I had not cleaned it when I took that photo)

 

The air intake and oulet vents are in the cabin wall above the gunwhale

 

We can't get any water analysed as there is none there now!

 

The water that was in there was definately canal water. Although there is always a possibility of a small amount of water ingress during wet weather we had been on board in very wet and very dry weather and ruled out it being rain water that was coming in.

Post boatyard repairs Python has also been subject to both very wet and dry weather without any water coming in or being obvious.

[Roger Gunkel]

My suggestion would be that there is a breech in the hull that is just above the waterline until the boat is moving. Once underway, the considerable pressure of the water could open it up enough to produce a higher volume of water ingress ccmpared to what might be expected from a very small breach. The breech may well not be visible when there is no oressure on it.

 

The fact that the boat travelled some considerable distance without apparently leaking after backing, would suggest that the coating was enough to seal the breech for a while. The boat might well have heeled enough when the water dropped when it was stationary, for the breech to be just below the water line, allowing the sustained pressure to penetrate the blacking and open the breech once more. Perhaps a complicated explanation, but possibly one that fits the unusual circumstances.

 

Roger

[cheshire~rose]

as we had exceptional rain last week has it come in via the roof? is there an air vent or similar that can let water in when subjected to heavy rain/wind in the right direction?

 

It has never yet been experienced - whist admitted that rain could potentially creep into a vent or something in exceptional weather like we had that night - enough to sink a boat?

[cheshire~rose]

Depending on the design of the weed hatch the space between the uxter plate and the top is often under some pressure when the boat is moving - more welly = more pressure- so I would think it quite possible that water is coming back down the bilge pump pipe. If it has a NRV check that that doesn't have some crud in it. If it doesn't have one, fit one as close as possible to the exit. ( you can get push in ones which fit in the flexible pipe but a proper plumbers valve would be best). Of course, once the boat begins to settle ( perhaps because of rain, or change in levels whilst tied up it is going to put the bilge pump pipe under water

 

To test the hypothesis, give it some welly whilst tied up facing downhill in a full lock (with the top gate open) and then remove the bilge pump outlet pipe and see if water comes in. If it is the bilge pump fit a new outlet, at least 250mm above deep loaded water level and blank the weed hatch one off.

 

N

 

If the canal dropping by 4" had caused the list that allowed water into the hold area the bulkhead would have prevented water from moving into the engine bilge and I think I am correct in saying that it is unlikely that any of the places where canal water could have got into the engine bilge would have dropped low enought to let water in. This is why we feel that the boat went down stern first and it was this that allowed the list which let water into the hold. I know crew who arrived to find her underwater are watching this conversation though and I may get an email or text any moment to correct me

[Laurence Hogg]

Not mentioned as far as I can see, how HIGH is the weedhatch surround in the counter?

[cheshire~rose]

It took nearly two hours of pumping yesterday to empty the rain out of Barnet's hold so that could be a factor.

Another to look for is the skin fitting/s you say dont exist in the engine room, they were there at some point and have been blocked off, have they started to leak?

Another common cause can be water coming up the rudder shaft, this particulary happens under fast running on rivers.

The real sod is a cracked plate, invisible until under stress, my suggestion is to carry out a series of tethered tests with the engine running full on both astern and ahead, then go looking, where you cannot see try and poke a camera or get an observation aid.

 

 

 

Really? What on earth is that? Is it a weedhatch cover?

 

I appreciate the potential of rain water in the hold but the hold has been bone dry since the covers have been fitted. Periodic checks on it to see if it required pumping out have always been negative and were so before the bilge pump was moved to assist with the problem at the stern so as nothing had changed it is hard to understand how this could have been a contributory factor.

 

If there were any leaking skin fittings in the engine room then they could not be seen when it was inpsected. Equally there was nothing that gave any hint of a clue of a cracked plate. (both in and out of the water) and there was nothing found of that nature that needed repair. If it had been the cause prior to the trip to the boatyard then it was cured when she left there. The boat was run under load for some hours before it was removed from the boatyard. The conditions when she had previously leaked has been adequately recreated after leaving the boatyard with a run up the Trent and along the Chesterfield. Fast deep running, running under load with little water under her, slow chugging, locking and reversing and not a drop of water came in.

Paul Barber has a lifetimes experience of what to look for with regard to leaks in old boats and how to cure them and the washing off of her hull and a large section of the blacking was carried out voluntarily by Viv Scraggs who also knows whats what when it comes to old boats. There were various other people who know their stuff who cast an eye over her while out of the water too. While we are all human and it is very easy for these old cast iron hulls to keep secrets in even the most vigourous inspection but realistically would something that was ONLY letting water in when on the move be missed by so many people when out of the water then behave itself perfectly for the next 5 days and fail again overnight while standing?

 

It leads me to think that the original leak has indeed been cured as there is no evidence of it whatsoever but then suddenly and without warning she goes down overnight. Where, if at all, is the link between the two? If there is no link between the two then how can a boat sink overnight then apparently be fine again once bailed out?

[luctor et emergo]

My first thought would be along Roger's idea, a small split, or two plates with some rust between the joins. Just above the waterline when stationairy.

[cheshire~rose]

Depending on the design of the weed hatch the space between the uxter plate and the top is often under some pressure when the boat is moving - more welly = more pressure- so I would think it quite possible that water is coming back down the bilge pump pipe. If it has a NRV check that that doesn't have some crud in it. If it doesn't have one, fit one as close as possible to the exit. ( you can get push in ones which fit in the flexible pipe but a proper plumbers valve would be best). Of course, once the boat begins to settle ( perhaps because of rain, or change in levels whilst tied up it is going to put the bilge pump pipe under water

 

To test the hypothesis, give it some welly whilst tied up facing downhill in a full lock (with the top gate open) and then remove the bilge pump outlet pipe and see if water comes in. If it is the bilge pump fit a new outlet, at least 250mm above deep loaded water level and blank the weed hatch one off.

 

N

 

When the intial water ingress occurred there was no bilge pump fitted and the ingress pattern did not differ when one was fitted so while I acknowledge it could in some circumstances be a contributory factor I do not feel that in this case there is any cause to suspect a problem. Especially as she sunk when static and it had not been a problem while running post boatyard visit

[Laurence Hogg]

Given all the evidence and the fact that worthy eyes have been over the boat is there a third party?

Did CRT lower the level causing the boat to list severely and take in water?

Did a nasty piece of shit called "vandal" set up a "silent syphon" to sink the boat? That used to be done round here using bits of hose, latterly thank god its too technical for modern yoofs.

[cheshire~rose]

Given all the evidence and the fact that worthy eyes have been over the boat is there a third party?

Did CRT lower the level causing the boat to list severely and take in water?

Did a nasty piece of shit called "vandal" set up a "silent syphon" to sink the boat? That used to be done round here using bits of hose, latterly thank god its too technical for modern yoofs.

 

I (and others) think it unlikely that the drop in the canal level would be sufficient to cause a list to allow her to take on water. The concensus of opinion is that the list she had when discovered was as a result of water being taken on board and not vice versa. How we can prove or disprove our theory on this we do not know.

 

As for vandalism? Of course you can never completely rule it out but this is where she was moored:

 

The Chequers, Ranby

 

On that pub mooring in the image. It is not towpath side. It is only accessible through the pub car park and boats on that mooring are not visible from the road. The road is not a main road but a quiet lane that wriggles it's way through the sleepy backwater that is this pretty village in Notinghamshire

A vandal would not only need to see the opportunity but have the technical ability to set up the syphon. If that had happened we would also be likely to find a random piece of hose lying in the boat. It is not impossible but it is unlikely.