Is my narrowboat sinking?

[mingus]

OK. I'm hoping this is just my paranoia, and don't laugh but..... The prow of my beloved home appears to be lowering since I last filled up the water tank. Am I right to assume that, provided the stern is still lower than the prow, any water that gets in anywhere will drain to the stern and be visible sloshing round in the engine bay? I've never actually lifted the plywood floor but I've always assumed it's just concrete underneath - if this is the case how does water drain from front to rear - or doesn't it?

Are the bilges anywhere at the bottom of the boat or are they at the stern?? I only have pumps in the stern so if the prow fills with water and my boat goes from / through _ to \ I assume I either rip up the floor and start bailing like a madman or. . . . . . . sink.

Lovely, friendly, and reassuring replies preferred.

 

T

Edited October 14, 2008 by mingus

[alan_fincher]

Generally speaking if it's a modern boat built in the (say) last 20 years, then it will not have a continuous bilge that runs right through from front to back.

 

Generally the cabin area has an entirely separate bilge, intended to stay quite dry.

 

Self draining lockers and cockpit should take care of rainwater at the front, and depending on design, rainwater at the rear should generally go overboard as well.

 

Filling the water tank can make a dramatic difference to how high the front end sits in the water. 6 inches between full and empty would not be unusual, and it can be even more.

 

How are you judging the bow is getting lower ? Unless you have had one almighty impact it sounds unlikely. Even if your water tank or water system were leaking into some part of the boat, it will not make the nose go lower, in fact the opposite is more likely, if the water can run rearwards at all.

 

Alan

[sociable_hermit]

Filling up the tank will always drop the bows down a little just because of the weight of the water. It'll be more pronounced if your diesel tank is at the stern and getting empty, and if your gas bottles are towards the bows and full up.

 

Some boats have inspection hatches to examine the bilges from within the living space. Try around the water pump or shower tray pump if you do want to have a look.

[robkg]

OK. I'm hoping this is just my paranoia, and don't laugh but..... The prow of my beloved home appears to be lowering since I last filled up the water tank. Am I right to assume that, provided the stern is still lower than the prow, any water that gets in anywhere will drain to the stern and be visible sloshing round in the engine bay? I've never actually lifted the plywood floor but I've always assumed it's just concrete underneath - if this is the case how does water drain from front to rear - or doesn't it?

Are the bilges anywhere at the bottom of the boat or are they at the stern?? I only have pumps in the stern so if the prow fills with water and my boat goes from / through _ to \ I assume I either rip up the floor and start bailing like a madman or. . . . . . . sink.

Lovely, friendly, and reassuring replies preferred.

 

T

Hi,

If the roofline or gunwhale is sloping upwards towards the bow of the boat, then water under the floor will run towards the stern. The concrete ballast you refer to is typically paving slabs or similar with gaps particularly at the edges and will not stop the flow. If the ballast is concrete poured into the hull wet, then it might stop the rearwards flow, but this method of balasting is extremely rare and as such is highly unlikely. Try and establish if the boat has any steel bulkheads (e.g. my boat has these fore and aft of the trad. engine room) as these may act as barriers to flow of bilge water. If you are worried, you must check under the floor for your own peace of mind. If you cannot find any access hatches in the floor you might try drilling small holes (e.g. 8mm diameter) in the floor and using a makeshift dipstick to judge the level of water at different points. You may have to do this in a number of places to try and find spots where you can "dip" to the baseplate without the ballast getting in the way. It is likely that you would see water appearing above the floor long before the boat actually sinks so I doubt that it is imminent. Another suggestion is to mark the stem post at the waterline then you have some way of objectively judging whether the bow is getting lower or higher in the water.

I hope this helps.

 

Rob

[Malarky]

There will possibly be a metal sheet between the engine bay and the rest of the boat stopping the water flowing to the stern. If so check just before this in your cabin. You could cut a hole for future inspections/pump outs. If you do have a leak, it could well be from a fitting on the water tank or pipes rather than the canal, as you seem to be getting concerned when filling it!

[saltysplash]

It has puzzled me over the years and still does, why builders do not make even dry bilges, 'through bilges' Early indication of floatation problems are the auto bilge kicking in and giving you the tell tale jet stream over the side.

[koukouvagia]

We’ve all had that sinking feeling. I came back to the boat and found a considerable volume of water in what are supposed to be the dry bilges under the main cabin. It took a certain amount of detective work to figure out the cause.

The previous weekend I decided to drain the water system.

I turned on the taps in the bathroom and kitchen.

On my way out of the boat I went into the engine room and turned off the battery. This meant that the water pump was also switched off, so that now no more water could enter the system and all the water was drained.

So why the water in the bilges?

Answer: In turning off the battery I also immobilised the gulper pump which drains all the grey water, including bath and sink waste, from a one of those small grey-water holding tanks. Thus all the water that was still draining from the sink and the bath when I switched off the power was still entering the holding tank but was not being pumped overboard. Instead it overflowed and found its way into the bilges.

[chris w]

Filling the water tank can make a dramatic difference to how high the front end sits in the water. 6 inches between full and empty would not be unusual, and it can be even more.

 

Alan

 

You must have an enormous water tank Alan. A boat displacing a surface area of say 50ft x 7ft will only lower 1 inch in the water when an additional ton of ballast is evenly added. Running the maths, and taking moments of inertia into account over the boat's length, would indicate an inch or so at most per half ton (500 litres) of water if all at one end.

 

Chris

Edited October 15, 2008 by chris w

[mrbeats]

Im not sure how it is on canal boats but I know how it is on sailing boats and other boats so cant see it being much different through design.

Your boat if leaking from the bottom in the center (for example)would fill up with a good couple of foot over the entire length of the boat and still be floating!

So you would have plenty of warning to get pumping.

[koukouvagia]

You must have an enormous water tank Alan. A boat displacing a surface area of say 50ft x 7ft will only lower 1 inch in the water when an additional ton of ballast is evenly added. Running the maths, and taking moments of inertia into account over the boat's length, would indicate an inch or so at most per half ton (500 litres) of water if all at one end.

 

Chris

 

 

I can’t do the maths, but I know empirically that if I fill up my water tank (250 gallons) which is at the front of the boat (70'), the stem post sinks 4” in the water. In fact, I use the this phemonenon as a primitive tank guage – 3 inches out of the water – time to fill up.

[Jason Wilson and Family]

Answer: In turning off the battery I also immobilised the gulper pump which drains all the grey water, including bath and sink waste, from a one of those small grey-water holding tanks. Thus all the water that was still draining from the sink and the bath when I switched off the power was still entering the holding tank but was not being pumped overboard. Instead it overflowed and found its way into the bilges.

A good idea that I've heard is to have your automatic bilge pumps run directly from a separate battery so that they can't switch off. That way you can cut off everything else, leave your boat and if the water level comes up the float switches trigger and the pumps go to work until it goes back down. Depending on how far away you are from the boat you may be industrious enough to find a way to fit an alarm that notifies you that your boat may have a problem.

[mikevye]

Most modern boats are built on the assumption that he cabin area will stay dry (reference alan) and as such do not provide access to the bilge in this area. We had a water ingress problem to the dry area which meant providing access to the bilge to dispose of the water. The actual problem was the fresh water tank overflow which leaked inboard whenever the tank was topped up! This took ages to find as a proportion of the water did go outboard so we thought all was ok.

[alan_fincher]

You must have an enormous water tank Alan. A boat displacing a surface area of say 50ft x 7ft will only lower 1 inch in the water when an additional ton of ballast is evenly added. Running the maths, and taking moments of inertia into account over the boat's length, would indicate an inch or so at most per half ton (500 litres) of water if all at one end.

 

Chris

Yes,

 

It doesn't sound right, I'll agree - I think I've exaggerated.

 

Our tank is integral, and typically they hold a lot more than a stainless one, which don't usually fit snug at the botton, top and all around the sides.

 

Also we are a 50 foot boat, so allowing for swims, dont't present anything like 50 foot x 7 foot.

 

Another thing I'm probably getting wrong is we judge water tank "fullness" by how much the stempost is in the water, and that is heavily raked, so 1" of extra water on the stem is probably a lot less than 1" extra draft at the front.

 

I'll have a go at the maths some time, although estimating water tank volume isn't trivial, as it comprises both the under deck space, and the under gas locker space, but with a baseplate that curves up at the front.

 

My working assumption is that it holds not less that 200 gals, and quite possibly 250. (So maybe between 900L and 1100L, very roughly, which sounds like 1 tonne[ish] to me). You don't want to be behind us at a slow water point, anyway.......

 

EDITED FOR FURTHER THOUGHTS.

 

I make the amount a 50 foot * 7 foot (15.24 x 2.13 metres) floating box will go down by to be just over 3 centimetres per tonne (or per 1000 litres of water)

 

However, few modern narrowboats are anything like 7 feet at waterline, and many have sloping hull sides, and a baseplate no more than 6' 6" overall, with the sides actually slighly inset on top of that. I'd say a typical waterline width is more like 6' 8", further skewing things towards a rather greater change of draft as the tank is filled.

 

I'm struggling to make a case for 6", though

Edited October 15, 2008 by alan_fincher