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I admit myself confused. I get that an open weed hatch, faulty stern packing, or non functioning bilge pump will flood the engine bay - but why oh why does that sink the boat? The ballast at the bow counteracts the weight of several people standing on the stern so should be enough to counteract the weight of water in the engine bay. Am I missing something? Is the water getting from the engine bay into the main hull somehow and over weighing the whole boat? I thought the engine bay, below deck level, was a separate compartment from the main hull and ballast area. Surely there is more we can do to reduce risk of sinking?! Please can you guys clarify.

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It would take ages to sink the boat, perhaps the most common cause is rain water getting into the engine bay and being left there. Some boats have great air vents in the hull no that much above water level despite 10" being the recommendation.

 

Not all boats have a sealed back bulkhead or even a sealed front one.

 

You reduce the risk of sinking by regularly attending the boat and making sure the bilge is dry enough and if its an automatic bilge pump making sure its working AND the batteries are well charged.

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Thanks Tony. I appreciate your reply and suggestions.

 

I wasnt clear, sorry. I meant rapid sinking as opposed to gradual flooding from neglect of maintenance. I saw figures from CRT saying that last year the number of sunk boats nearly doubled from the year before and was over 100 so not a statistical trick. Noone is clear why the sudden increase.

 

I'm trying to clarify how I might go about reducing the risk of this in my near-future build to sail away. Want to try and build into the build specs. I absolutely will be discussing this with the firm at the time but wanted to understand the issues much better first.

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4 minutes ago, Tony Brooks said:

It would take ages to sink the boat

 

Not if the weed hatch isn't secured.

 

I've seen 15 seconds of reverse being enough to drop the engine bay air vents below the waterline, and after that it's a salvage job.  They only dipped momentarily, but that's enough to swamp the boat, and also probably pushed the (unattached) weedhatch top below the water at the same time.

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1 minute ago, TheBiscuits said:

 

Not if the weed hatch isn't secured.

 

I've seen 15 seconds of reverse being enough to drop the engine bay air vents below the waterline, and after that it's a salvage job.  They only dipped momentarily, but that's enough to swamp the boat, and also probably pushed the (unattached) weedhatch top below the water at the same time.

I'm guessing no rear bulkhead?

A lot of boats don't have them. Personally I wouldn't touch one with a barge pole.

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Thanks TheBiscuits. My question is more fundamental but you raise an excellent point.

 

In your comment the subversion of the air vents floods the engine bay... but then what? What from there is causing the whole boat to sink. That's the bit I'm trying to understand.

 

Thank you.

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25 minutes ago, mark_j said:

I admit myself confused. I get that an open weed hatch, faulty stern packing, or non functioning bilge pump will flood the engine bay - but why oh why does that sink the boat? The ballast at the bow counteracts the weight of several people standing on the stern so should be enough to counteract the weight of water in the engine bay. Am I missing something? Is the water getting from the engine bay into the main hull somehow and over weighing the whole boat? I thought the engine bay, below deck level, was a separate compartment from the main hull and ballast area. Surely there is more we can do to reduce risk of sinking?! Please can you guys clarify.

I am no expert on the subject, but I think you have a bit of a misconception that the ballast will counterbalance the weight of several people standing on the stern. The ballast is to get the boat to lie relatively level in the water, counterbalancing the weight of the engine in the stern. If a lot of people get on the stern on the boat, it will go down in the water at the stern. Six people of average sort of weight (12 stone) come in at just under half a ton whereas if my engine bay filled with water it would hold about a cubic metre (so about 1 tonne), with that much water in it, it would flood over the wooden access cover at the rear of the engine and then continue to flood the rest of the boat, resulting in a sinking. This is however all theoretical since I have no wish to carry out a practical demonstration:unsure:

Edited by Wanderer Vagabond
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43 minutes ago, mark_j said:

I admit myself confused. I get that an open weed hatch, faulty stern packing, or non functioning bilge pump will flood the engine bay - but why oh why does that sink the boat? The ballast at the bow counteracts the weight of several people standing on the stern so should be enough to counteract the weight of water in the engine bay. Am I missing something? Is the water getting from the engine bay into the main hull somehow and over weighing the whole boat? I thought the engine bay, below deck level, was a separate compartment from the main hull and ballast area. Surely there is more we can do to reduce risk of sinking?! Please can you guys clarify.

Work out the volume of water in the engine bay. I cubic metre = 1 metric ton. I reckon the average engine bay would be at least 2 cubic metres, so 2+ tonnes of water, so a lot more than 3 people standing on the back of the boat. There is a lot less buoyancy at the stern because of the shape of the swim.

Edited by Flyboy
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12 minutes ago, mark_j said:

Thanks TheBiscuits. My question is more fundamental but you raise an excellent point.

 

In your comment the subversion of the air vents floods the engine bay... but then what? What from there is causing the whole boat to sink. That's the bit I'm trying to understand.

 

Thank you.

There are numerous routes that water can transfer from the engine bay to the cabin.

 

Cable routes, pipe routes etc etc.

 

If they are not sealed 100% water will pass.

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13 minutes ago, mark_j said:

Thanks TheBiscuits. My question is more fundamental but you raise an excellent point.

 

In your comment the subversion of the air vents floods the engine bay... but then what? What from there is causing the whole boat to sink. That's the bit I'm trying to understand.

 

Thank you.

 

As has been said, not all boats have a watertight bulkhead between the engine space and the rest of the boat in which case once the engine vents go under the waterline that's it. Nothing further needs to happen for the boat to sink.

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8 minutes ago, blackrose said:

 

As has been said, not all boats have a watertight bulkhead between the engine space and the rest of the boat in which case once the engine vents go under the waterline that's it. Nothing further needs to happen for the boat to sink.

My engine is in front of the bedroom

 

 

If you want to make you boat safe from weedhatch flooding then make sure its constructed the same was as Steve Hudson did and one or two others do them. Remember if you flood the back end you have negative buoyancy at that end not just weight to support

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52 minutes ago, mark_j said:

The ballast at the bow counteracts the weight of several people standing on the stern so should be enough to counteract the weight of water in the engine bay. Am I missing something?

 

 

Have a read of this safety report - the boat sank within 10 seconds.

It was as a result of too many people on board, all moving t the stern, and the fact the boat had had extra weight added by overplating some of the hull.

 

Few boats have sealed compartments - even the Titanic which did, sank,

 

It is the concept of why a boat sank rather than the detail which is interesting.

 

 

https://www.pla.co.uk/assets/sb1of2012-narrowboatsinking-inadequateventsfreeboard1.pdf

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My cruiser stern is about eight foot long, six foot wide and deep enough to sit the engine in. That's lot of water, and it sank the boat with rainwater about twenty five years ago, as the front deck drained into the engine bilge and the auto bilge pump failed, as they always do. No water got into the cabin, it just sat on the mud at its mooring till it got pumped out.

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A 7' wide boat 36' long will go down in the water about 2" for every ton of weight you add. Say for a moment you have half a ton of weight added at the fore end to make the boat float a bit more level, and then 1/2 ton of water gets into the stern  then the boat will go down 1" further overall - you've not somehow replaced the weight at the bow, you've added to it. If you have a boat with a sealed bulkhead at the bow and another at the backend of the accommodation and no hull openings between it could be that it will remain afloat even if full of water at each end. However it is still possible that as the boat sinks further and further it will sooner or later get to the point where there are places that water can now get in - places such as sink or shower outlets perhaps, or engine air vents. Once that happens it will inevitably sink.

(you'll have to do the metric conversion your self, but the principles are there.)

 

Tam

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1 hour ago, mark_j said:

 I saw figures from CRT saying that last year the number of sunk boats nearly doubled from the year before and was over 100 so not a statistical trick. Noone is clear why the sudden increase.

 

There are more people living on board boats who dont have a clue about the boats workings. Some rent boats on weekly or monthly basis, ringing landlord if batteries are flat or the waterways people have left an overstay notice. 

More people are living on rivers, and not knowing how or where to safely moor, ornwhen to get off!! 

There are more severe weather events now, extreme rainfall events that can raise canal levels dramatically, even when they shouldn't rise at all.

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1 hour ago, Tam & Di said:

A 7' wide boat 36' long will go down in the water about 2" for every ton of weight you add. Say for a moment you have half a ton of weight added at the fore end to make the boat float a bit more level, and then 1/2 ton of water gets into the stern  then the boat will go down 1" further overall - you've not somehow replaced the weight at the bow, you've added to it. If you have a boat with a sealed bulkhead at the bow and another at the backend of the accommodation and no hull openings between it could be that it will remain afloat even if full of water at each end. However it is still possible that as the boat sinks further and further it will sooner or later get to the point where there are places that water can now get in - places such as sink or shower outlets perhaps, or engine air vents. Once that happens it will inevitably sink.

(you'll have to do the metric conversion your self, but the principles are there.)

 

Tam

 

Not that many narrowboats have a sealed bulkhead at the bow. Most have bow doors with vents. However, it's fairly difficult to sink a narrowboat with a bow well deck by flooding at the bow unless the self draining deck scuppers get blocked or one is stupid enough to open a gate paddle in a lock with the bow of the boat directly below it.

Edited by blackrose
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1 hour ago, matty40s said:

There are more people living on board boats who dont have a clue about the boats workings. Some rent boats on weekly or monthly basis, ringing landlord if batteries are flat or the waterways people have left an overstay notice. 

More people are living on rivers, and not knowing how or where to safely moor, ornwhen to get off!! 

There are more severe weather events now, extreme rainfall events that can raise canal levels dramatically, even when they shouldn't rise at all.

There are also people living aboard, and have done so for many years, who have no idea whether they've ever fully charged their batteries. There are others who spend £100K+ on a boat, all singing and dancing boat, but when they go out on the cut they have to run a noisy polluting lump of an engine for several hours every day, just so they can run a small fridge and watch a couple of hours of Netflix.  

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1 hour ago, blackrose said:

Not that many narrowboats have a sealed bulkhead at the bow.

I'm sure you're right. The OP said that if a boat has ballast at the bow and that counter-balances people standing on the back, he could not understand how it would sink if instead of people on the back it was full of water. I was trying to say it is not that simple, and water does not stand still as people might - it swills about and occupies all the space it can flow to.

 

Tam

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Thanks. I doubt the increase can be accounted fo purely on more people living aboard, not sure increased approx 50% in a single year in line with the number of suck boats.

 

Apart from sealing stern and bow compartments from the main ballast chamber what else can be done. I mean structurally. Is there an alternative to having engine vents on the boat side near water level? Please assume safe maintenance and not having to many people onboard is already being followed.

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10 hours ago, TheBiscuits said:

 

Not if the weed hatch isn't secured.

 

I've seen 15 seconds of reverse being enough to drop the engine bay air vents below the waterline, and after that it's a salvage job.  They only dipped momentarily, but that's enough to swamp the boat, and also probably pushed the (unattached) weedhatch top below the water at the same time.

 

I agree with that but was assuming the OP was at least semi-competent and thus void that. He seems not to have much idea about narrow boating.  Perhaps if that is the he has done well to ask but I don't think the increase of sinkings in CaRT's stats is that strange seeing how many locks now spew water into the well deck and aft cockpit, let alone through open windows plus the number of older boats are being used as liveaboards by people with little DIY skills or knowledge and zero boating experience. All of which other have identified as reasons.

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1 hour ago, mark_j said:

Thanks. I doubt the increase can be accounted fo purely on more people living aboard, not sure increased approx 50% in a single year in line with the number of suck boats.

 

Apart from sealing stern and bow compartments from the main ballast chamber what else can be done. I mean structurally. Is there an alternative to having engine vents on the boat side near water level? Please assume safe maintenance and not having to many people onboard is already being followed.

 

Air cooled engines at the back of the boat almost demand large air vents in the hull side, water cooled engiens do not and such combustion ait intake vents as they need can be almost anywhere providing it is trunked to the engine area. Mine had a pair of 4 x 2 inch vents in the return form gunwale to cockpit floor so essentially inside the hull.

 

The vast majority of boats do not sink, you need to look at the reasons each one has sunk and my guess is that apart from filling scarce storage and living space with great blocks closed cell foam not a lot can be done structurally once the boat is built. Certainly not in the case of older boats with through bilges. 

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Practically every narrowboat is floating bow high all the time.

Look at a loaded working boat and the bow is lower than the stern. But live in and leisure boats are technically near fully loaded too, yet they ballast them bow light.

So the addition of weight or lack of buoyancy at the stern has a dramatic effect on the trim.

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