Adding a new integrated water tank

[jetzi]

Not sure what the etiquette is around reviving old threads. I previously asked about ways to increase our water supply here. There are also a number of good old threads on fitting second water tanks. This is about upgrading a 250 litre water tank. This one is about the interior coatings on a water tank. So I apologise if I should continue the conversation there rather than starting this new thread, but I've made a decision specific to my bote and now looking for criticism, so a lot of the old info isn't so relevant anymore.

 

Our current 500L / 100 gal tank is underneath our foredeck. We bought an extra 6x 25L / 5 gal containers for backup, which we also store on the foredeck. Unfortunately I have no idea of the shape and condition of the existing tank, nor whether it is integrated, stainless or plastic. Some people have suggested cutting an access hatch in the deck to allow us to inspect and clean the tank. But the water comes out clean and rust-free so I am taking an "ain't broke, don't fix" approach to the existing water tank. Especially since cutting a hole in the dirty deck seems like a sure fire way to get dirty water into the system and to create an opportunity for leaks!

 

I have decided to take up some space on the foredeck to create two additional 300L / 60 gal water tanks - port and starboard. My idea is to create integrated tanks with generous access lids, epoxied on the inside with something like International Marine Interline 850 potable tank coating, or Jotun Tankgard. I took a couple of pictures to give you guys some context:

 

Notice that there is an existing storage locker on the starboard side, which also has the tank filling point inside it. Here is a close up pic of the interior of this locker, showing the poor condition of the steel.

 

 

I want to remove all this rust, weld on whatever is necessary to seal any holes, create a little pipe for the scuppers, and then epoxy the inside. Then I want to make a nice lid over the whole thing to create a bench seat slash watertight lid. Finally, I want to duplicate this on the port side. I worked out that these will be about 300 litres each.

 

I plan to have the tanks individually vented and individually fillable, connected by pipes with stopcocks. My thinking is that I can adjust listing and trim by filling these differently, if necessary.

 

My main concern is what impact adding over half a tonne of water to the foredeck might have to the trim and handling of the boat? I realise that it would be better to have that weight lower, but there is nowhere we could add a tank without significantly impacting interior space. Are there any other concerns that in my ignorance you guys can immediately see?

Any idea on how much I should budget for this project?

 

 

[Alan de Enfield]

My concern would be that it will seriously de-stabilise the boat.

At the minimum you will need a cross-feed balance pipe.

 

Do you really need a tank bigger than 500 litres ?

I found on the canals I passed at least one water point every day, and often more.

[Tony Brooks]

34 minutes ago, Alan de Enfield said:

My concern would be that it will seriously de-stabilise the boat.

At the minimum you will need a cross-feed balance pipe.

 

Do you really need a tank bigger than 500 litres ?

I found on the canals I passed at least one water point every day, and often more.

Note the location - London.

 

Probably livaboard and only want to fill up during the fortnightly move to the next mooring.

[Alan de Enfield]

3 minutes ago, Tony Brooks said:

Note the location - London,...………………. and only want to fill up during the fortnightly move to the next mooring.

Well spotted - hadn't noticed that.

[jetzi]

4 hours ago, Tony Brooks said:

Note the location - London. Probably livaboard and only want to fill up during the fortnightly move to the next mooring.

 

4 hours ago, Alan de Enfield said:

Well spotted - hadn't noticed that.

It wouldn't hurt you to be nice. But I'll be charitable and ignore the snark. Yes we are liveaboards - we both work and live on the boat. We plan to slowly do every waterway that will fit a 65'er, starting with the Lee and Stort. We want our water supply to last two weeks, which 500 litres does, but not comfortably. And we don't have a washing machine yet - which we definitely want. Of course we could fill up more often, but it's a hassle. Our water supply is the limiting factor for us right now.

 

 

5 hours ago, Alan de Enfield said:

My concern would be that it will seriously de-stabilise the boat. At the minimum you will need a cross-feed balance pipe. 

This is my concern as well. 600 extra kilograms about a foot off the waterline doesn't seem like that much on a 20+ tonne boat though. It's not as if it is on the roof. Perhaps I should test this by getting 600 kg of weight, loading the bow and going for a cruise? Or do you think the sloshing of the water will have a significant impact on stability as well? I suppose I could re-think an internal extra tank, it just seems like a less clean solution that will encroach on our living space.

Yes I would certainly take great pains to make sure that the load stayed balanced, partly why I want two tanks. My current thinking is independent tanks with a pipe connecting them, with a stop cock so if I want to fill one more than the other, I can do that.

[Chewbacka]

Just a thought - you could cut out the forward half of the front deck (which presumably your existing tank is below) and raise it up by say 8 inches.  This would enlarge your existing tank, and would also give you the opportunity to get in and repaint it.  The new deck would also have an access hatch for the enlarged tank.  You would then have a flat space by your front doors and an 8 inch step upto the new deck.  You could also make the new deck the full size and fit shorter front doors, in which case you may only need to raise the full area deck by say 5 to 6" to give a reasonable increase in tank capacity.  This would also keep the weight lower down helping stability.

[Boater Sam]

Get 6 or 7 average sized people to sit in the bow. Move them around to one side and the other.

Check how much it pushes the bow down, I would guess about 6" and most Black Death boats of 60 foot + will stand this, they tend to be bow high.

I would doubt it will make the boat unstable, but you don't need to completely fill the tanks and you can draw off these higher tanks first anyway.

You don't need sealed lids, just well fitting to prevent dust and rain getting in, Many Piper boats have the water tank where the gas bottles generally go, with just the usual hinged lid.

Then you can see into them and clean them out easily. 

[ditchcrawler]

17 minutes ago, ivan&alice said:

  We want our water supply to last two weeks, which 500 litres does, but not comfortably. And we don't have a washing machine yet - which we definitely want. Of course we could fill up more often, but it's a hassle. Our water supply is the limiting factor for us right now.

 

 

 

Well we just managed to make our tank last a week while in the dry dock, but that was using showers shore side and limiting washing up, I cant imagine what size tank would be needed for 2 weeks. But now when we are cruising and we come to a slow tap we just say sod it and go to the next, heaven forbid we had a tank big enough for 2 weeks, ran it right down for minimum stops and then it was a slow tap, we would spend all afternoon there. I would rather top up every 2 to 3 days. I cant remember how big or stainless tank is.

 

[Bee]

We only carry 50 or 60 gallons, maybe even less but even in France where water points are scarce we find that with care we can make it last a week, this does not sound much for some people but we often use bottled supermarket water for tea and drinking and it is surprising how long the tank lasts. Carrying huge amounts of water really is not that necessary.

[Alan de Enfield]

30 minutes ago, ivan&alice said:

Or do you think the sloshing of the water will have a significant impact on stability as well?

I assumed you would be building baffles into the tank to stop 'sloshing'.

 

The tanks will be narrow so there will not be much surge side to side, but when they are part full there could be a fair bit of surge front to back.

 

Will the new tanks be full length ?

How will you accommodate the scuppers ?

 

How high above the water re your hull fittings ? (particularly the cratch drains) if you are out and about around London there are some pretty big waves that could swamp you.

If in doubt you could fit flapper-valves to the drains.

 

From the BSS :

 

The provisions of this section of Part 10 in the 2002 BSS Standards are mandatory for non-private boats where applicable.

To reduce the risk of your boat sinking if it keels over or is excessively weighed down, it's a good idea for privately owned boats to only have openings which are at a height of at least 250mm (10ins) above the waterline. Where openings are necessary below this level this risk can be reduced by ensuring that these openings are permanently and securely connected to ducts or pipes, which are watertight up to that level.

Self-draining cockpits may not be able to meet the 250mm (10ins) recommendation but, for privately owned boats, it's a good idea to stop water getting into other parts of the hull by incorporating non-return valves in the drains and/or having bulkheads or cills up to a height of 150mm (6ins).

A weed hatch, if not properly secured, can allow water into the bilges of a boat, which could ultimately cause it to sink. It's advisable for privately owned boats to have a secure and watertight weed hatch which reaches to at least 150mm (6ins) above the waterline, when the boat is loaded up as normal. [10.3]

Edited April 21, 2019 by Alan de Enfield

[jetzi]

10 minutes ago, Chewbacka said:

Just a thought - you could cut out the forward half of the front deck (which presumably your existing tank is below) and raise it up by say 8 inches.  This would enlarge your existing tank, and would also give you the opportunity to get in and repaint it.  The new deck would also have an access hatch for the enlarged tank.  You would then have a flat space by your front doors and an 8 inch step upto the new deck.  You could also make the new deck the full size and fit shorter front doors, in which case you may only need to raise the full area deck by say 5 to 6" to give a reasonable increase in tank capacity.  This would also keep the weight lower down helping stability.

This sounds like a reasonable idea, certainly sounds like it would have better handling characteristics. I think it might make the deck a little less useful as a place to sit. I think the biggest thing holding me back from doing this is that I have literally no idea what is going on under that deck - what the tank is made out of, for example. It's also possible that there is a stainless tank or one that otherwise does not fill the whole space - so an easy way to increase the tank size and lower the centre of gravity could be to remove the existing tank and epoxy the inside of the hull. Without knowing more about the tank I wouldn't know until I cut her open. Would love to get my hands on some Black Prince schematics.

25 minutes ago, Boater Sam said:

Get 6 or 7 average sized people to sit in the bow. Move them around to one side and the other. 

Check how much it pushes the bow down, I would guess about 6" and most Black Death boats of 60 foot + will stand this, they tend to be bow high. 

I would doubt it will make the boat unstable, but you don't need to completely fill the tanks and you can draw off these higher tanks first anyway.

You don't need sealed lids, just well fitting to prevent dust and rain getting in, Many Piper boats have the water tank where the gas bottles generally go, with just the usual hinged lid.

Then you can see into them and clean them out easily. 

This is great advice. Yes we are quite bow high. We'll get 600 kg of friends over! Yes we would draw off the higher tanks first. And it's definitely a plus that we can fit large lids and get inside them to clean.

28 minutes ago, ditchcrawler said:

I cant imagine what size tank would be needed for 2 weeks...I would rather top up every 2 to 3 days.

As I say, our 500 litre tank lasts us 2 weeks with care, but we don't have a washing machine - upgrading the tank is partially in aid of getting one. And as for how frequently people want to top up ... each to his own? Personally I find it a hassle, I'd rather do less frequent, longer duration fills. I don't want every time I cruise to be about finding water.

29 minutes ago, Alan de Enfield said:

I assumed you would be building baffles into the tank to stop 'sloshing'.

I'm afraid you have overestimated my knowledge of the subject. Baffles to stop sloshing sound like a great idea. Would these be welded plates to compartmentalise the tank into several sections, open at the bottoms to allow water to flow freely between them? How many do you think we'd need? The new tank is 1480mm long. 

31 minutes ago, Alan de Enfield said:

How will you accommodate the scuppers ? How high above the water re your hull fittings ?

The cratch drain scuppers are in the aftmost corners of the deck at the moment. My plan was to create pipes by welding a piece of angle iron in the aft corner edges of the tanks. This would then create two pipes from the deck to the scuppers. I think we have good height between the waterline and the hull fittings/scuppers. Just over a foot. Are the flapper valves to create one way passage of water out but not in?

[roland elsdon]

Why integrate? Cut all current  metal out,get 2 stainless tanks made to fit each side. Deck over them as if lockers. Gravity feed to main tank.

stability will only be an issue while the top tanks are bung full. You will also not have rusty metal to think about sealing

 

[Alan de Enfield]

27 minutes ago, ivan&alice said:

I'm afraid you have overestimated my knowledge of the subject. Baffles to stop sloshing sound like a great idea. Would these be welded plates to compartmentalise the tank into several sections, open at the bottoms to allow water to flow freely between them? How many do you think we'd need? The new tank is 1480mm long. 

Maybe someone who knows could reply - if it was me I'd do 1/3rd , 1/3rd , 1.3rd (ie 500mm from each end)

 

29 minutes ago, ivan&alice said:

Are the flapper valves to create one way passage of water out but not in?

Yes - so if you get a wave coming over the front it will run out, or if you get a 'swell' (from a passing vessel) breaking alongside your boat it won't 'back-flow' thru the scuppers into the front deck.

 

30 minutes ago, ivan&alice said:

I think we have good height between the waterline and the hull fittings/scuppers. Just over a foot.

Measure again with a full water tank and 7 or 8 people stood in the bow.

I am (shall we say) carrying a little extra weight and am 90kgs. I'm about 5kgs overweight (apparently) so look for some chubby friends.

[Johny London]

Why not use the gas locker bit right at the front? It must be pretty deep so wouldn't be too bad on capacity (not perhaps as much as your two planned side tanks). Or for a bit extra capacity move the gas locker bulkhead 6" to the rear. Then just relocate the gas elsewhere, you'll have lower centre of gravity for the water then. And a usable well deck.

8 hours ago, ivan&alice said:

... make a nice lid over the whole thing to create a bench seat slash watertight lid. 

No need for the lid to be slash watertight - unless that is a measure of water force that can be withstood?

[jetzi]

The gas locker is 150-200 litres. Not worth the upheaval of moving the gas. The floor of the gas locker is in line with the deck, anyway. So it wouldn't affect the centre of gravity.

[Bod]

Create a horseshoe shaped tank to fit around the inside of the well deck.

This tank is emptied into the main tank via the existing filler, with permanent a connection.

New tank has new higher level filler, the vent for the lower tank will have to be extended to above the new filler point.

The new tank stops before the scupper drains, and creates extra seating/steps.  This tank needs only to be bolted down, could be made in stainless or plastic.

Just do not cover the access hole for the current tank, it will make future access impossible, without removing the new tank!

Yes there is a maintenance hole!  It's in front of the door mat, half way to the bow.  The edges have been filled with body filler as have the screw heads, have a poke around with a small weak magnet, there will be less attraction where the filler is thicker, or a sharp pointed nail through the paint.

Look at your first picture, the are faint straight lines in the rust pattern, clearer on the r/h side and bottom edge.

 

Bod