Home made raw water filter

[Crow]

Has anyone made a better pick up filter than a off the shelf vetus one, if so would you share your design with me,

I've a heat exchanger cooled little 3 cyl Mitsubshi currently being shoehorned into a springer waterbug .

I just want a simple easy way to clean the filter ,I was going to put a 25 MM I/d flexible pipe

From jabsco through the stern with a 90 deg elbow and screw on a stainless filter off a diesel transfer pump inlet , then just lift the whole pipe up to clean it , but will a 1" dia X 2 " long giving 6 sq inch area be

Enough ,I know it depends on how much weed it sucks in but where do I start? Thanks ,nick

[Tony Brooks]

Well I would never use an elbow on a raw water inlet, too much chance of twigs etc getting stuck across it. I would use a bend.

 

I am not going to comment on the rest but I understood canal boats used mud boxes rather than strainers.

[Crow]

Tony ,the elbow/( pipe fitters terms) / bend would only be to turn the flexy pipe 90 deg from horizontal down to water ,then a filter on the end of that.

Regarding mud boxes, I've never even seen one. ive only ever run outboards ,it's all new to me ,I'm making it up as I go along doing what I think may or may not be correct

And hoping for a bit of guidence on here From anyone prepared to assist. Nick

[Guest]

My first NB wass raw water cooled. It had a mud box which was basically a large upright cylinder, I'll guess 6 inches dia.

It had a lid which bolted on with a gasket. The feed came from the hull below the waterline via a valve, and exited into the engine from the topside. It was extremely simple, ancd clearly homemade. It did the job in that mud had to be removed periodically.

Edited December 26, 2016 by Guest

[ditchcrawler]

Tony ,the elbow/( pipe fitters terms) / bend would only be to turn the flexy pipe 90 deg from horizontal down to water ,then a filter on the end of that.

Regarding mud boxes, I've never even seen one. ive only ever run outboards ,it's all new to me ,I'm making it up as I go along doing what I think may or may not be correct

And hoping for a bit of guidence on here From anyone prepared to assist. Nick

Have a read of this blog http://boatbuildblog.blogspot.co.uk/2012/03/mud-box-mods.html

[Bee]

What you suggest will probably work ok so long as you make sure the end is always submerged. Its not as good as the Vetus unit and is probably best described as a bit of a bodge but as long as you keep a really good eye on the water being ejected from the exhaust then you are probably ok. The water coming out should be well above the waterline to avoid sinking the boat and the water 'in' should have a small pipe tee'ed off the suction pipe and taken well up to avoid syphoning water into the boat if a bit of engine pipework fails. Vetus do an anti syphon thingy. Others can probably explain it better.

[Crow]

Thanks for that link Brian

[Alan de Enfield]

Am I reading this correctly ?

 

Are you proposing to have the pick-up 'pipe' hanging (externally) from the skin-fitting with a filter on the end of it ?

 

"..... I was going to put a 25 MM I/d flexible pipe from jabsco through the stern with a 90 deg elbow and screw on a stainless filter off a diesel transfer pump inlet , then just lift the whole pipe up to clean it , but will a 1" dia X 2 " long giving 6 sq inch area ......."

 

If so, what length are you thinking to have the pick-up pipe so that you can "lift it up to clean" ?

Edited December 27, 2016 by Alan de Enfield

[Tam & Di]

Tony ,the elbow/( pipe fitters terms) / bend would only be to turn the flexy pipe 90 deg from horizontal down to water ,

 

In pipe fitters' terms a bend is a piece of tube in the form of a sharp 90 degree turn. An elbow also goes through 90 degrees but as a longer and radiused turn. Bits of floating matter that might jam in the sharp turn of a bend would nevertheless pass through the more gentle turn of an elbow. You seem to be talking of screwing the elbow/bend into the skin fitting on the outside of the hull, and while a bend would keep the pick-up pipe close to the hull an elbow would mean the pick-up was spaced a couple of inches clear of the hull. It does seem to be a very unusual design to have some external pipe on the outside of the hull where it would be extremely vulnerable to damage. The conventional design would be a skin fitting with a shut-off valve on the inside, then a mudbox, and the pipework to the engine coming from the top of that as described. I think your proposed installation will always give you trouble, even before water gets to the filter.

 

(poor internet seems to have posted only part of my post - I reread the original and saw that the filter is on the intake end hanging in the water. This would work fine on rivers but I think that canals are too shallow and muddy andyou will spend most of your time clearing the filter rather than going anywhere)

 

(edit to sort out a bit of mess)

Edited December 27, 2016 by Tam & Di

[Tam & Di]

(delete duplicate entry)

Edited December 27, 2016 by Tam & Di

[Tony Brooks]

Tony ,the elbow/( pipe fitters terms) / bend would only be to turn the flexy pipe 90 deg from horizontal down to water ,then a filter on the end of that.

Regarding mud boxes, I've never even seen one. ive only ever run outboards ,it's all new to me ,I'm making it up as I go along doing what I think may or may not be correct

And hoping for a bit of guidence on here From anyone prepared to assist. Nick

 

I disagree about the first sentence and I have done a fair bit of pipe fitting when building boats. Elbows form an almost 90 degree right angle bend in the bore and are very compact where as a bend has a larger footprint (its longer) and the bend is far less abrupt although both turn the pipe through 90 degrees. You say that you are asking for guidance and I gave you some, I have suffered far too many breakdowns on the hire fleet where debris and Jabsco impeller parts have blocked elbows.

 

Personally I would convert the engine to keel cooling PDQ and either fit a skin tank or pipes outside the swim and fit with a dry exhaust. That way you do away with the raw water pump and keep all the muck in the canal away from the engine cooling system. All it usually requires engine wise is removing the heat exchanger core and maybe blocking off a couple of hose or two. It also allows all the year round operation without having to drain the raw water part of the system down in the winter.

 

If you do not like that suggestion then fit a suitable skin tank or keel cooling pipes plus another header tank and pipe that system through the present raw water system. No strainer is required and the original raw water system can use antifreeze so again no draining down for the winter.

 

If you must go down the raw water route I would take the water in from very low down on the weed hatch side or high on the swim to keep it away from the bottom of the canal. We learned a short time ago here that the old direct raw water cooled commercial craft had two intakes with valves. One low one for running light and one higher up on the hull for running loaded. They would not have done this because it costs more money if they did not think it added reliability. Also not the vast majority of steel canal boats use skin tank cooling (a few have keel cooler pipes). If a whole industry chooses one system then there is probably a very good reason for it. There is a case that can be made for a wet exhaust in very particular circumstances that relates to noise but even that is less vital now hospital silencers are available.

Edited December 27, 2016 by Tony Brooks

[bargemast]

Hi Crow,

 

your idea of an outside waterfilter is exactly what I did on my small Dutch barge, as I was fed-up with the waterinlet in the bottom blocking much too often.

 

As you can see on the photo there's a 1 and a half inch hose pipe hanging in the water that I can lift up with the chain.

 

 

At the end of the hose pipe is a home made filter made of a pipe with the end welded shut, and with lots of 5mm holes, this is my pre-filter, as there's still a Vetus filter in the engine room.

 

This system has worked really very well, and so far has never needed any cleaning as it's sucking up the water out off the prop flow, which is fairly clean.

 

I'm happy with it, and it's surprising many people that don't seem to understand why I did this, and how it can work.

 

Good luck with the final touches, you're almost there.

 

Peter.

 

ps. the pick up is only about 25cms under the water surface, and as you can see there's no sharp bend in the hose pipe.

Edited December 27, 2016 by bargemast

[BWM]

This picture shows the two inlets (the lower one has a square plate blocking it off), that Tony mentioned above. You would need to position the intake away from the area of the propeller, as you'll end up pulling in a mixture of air and debris. Another consideration is a valve where the intake enters the hull.

 

[Bee]

The boat in question is a Springer waterbug, I think they are usually powered by an outboard so little if any space for a keelcooling tank and I'm not sure what sort of underwater shape it is. I doubt there is a weedhatch in fact. Not even sure how you would arrange the propeller and rudder. On the principal of you have to work with what you've got and not what you'd like I think hanging a pipe over the transom should work, ignore what I said about syphon breaks etc, do it in reinforced hose and just pull it in when you leave the boat, thread it through a ring bolt on the transom so the end stays underwater and it'll work. edited to add, that's a lovely boat Peter.

Edited December 27, 2016 by Bee

[bargemast]

The boat in question is a Springer waterbug, I think they are usually powered by an outboard so little if any space for a keelcooling tank and I'm not sure what sort of underwater shape it is. I doubt there is a weedhatch in fact. Not even sure how you would arrange the propeller and rudder. On the principal of you have to work with what you've got and not what you'd like I think hanging a pipe over the transom should work, ignore what I said about syphon breaks etc, do it in reinforced hose and just pull it in when you leave the boat, thread it through a ring bolt on the transom so the end stays underwater and it'll work. edited to add, that's a lovely boat Peter.

Thanks Richard, yes, she's quite nice and will celebrate her 100th birthday in 2017, so only a few years older than "Bee"

 

She should be the almost perfect boat to do the Nivernais and the other badly maintained canals with, as she has only little draft and with her round bilges, I can always come pretty close to the bank, much easier and better suited for canal cruising than "Joy".

 

Peter.

[DHutch]

We have a mudbox for our strainer.

 

Box is welded to hull, with 5mm holes through hull plate into box, area is about 8-10 inch wide by around a food in height, holes on around a 1 inch spacing.

 

Inside the box there is then a fairly fine stainless steel mesh, in a removable frame, held against a flange of angle iron which runs around the box.

 

Rightly or wrongly the frame is 6mm 1/4 inch marine ply and it's held by being wedged by another peice. 27 years on the ply is getting soft, but that's an ok life for me.

 

We tend to check/clean it annually but it basically needs no maintenance.

 

Make sure the top of the box is high enough, maybe 5-6 inches, like a weed hatch. Ours was a little low origanally.

 

 

Daniel

[Crow]

Thank you all,I'm even more undecided how to to cool it now, I'm short of area to weld on keel coolers, I could weld some 1 inch pipes along length of hull 500 /600 MM out from hull centreline 2 each side ,each pipe 6 ft long that would give me 6 sq ft of cooling area

The engine is 25 hp thereabouts ,but looking at bargemast post I think I'll try simple first,it's not a major thing to alter it after a bit of a trial, at least I don't need a crane, ps the underwater profile is about as bad as anyone could dream of

[PaulJ]

Could you not weld a skin tank onto the baseplate under the cabin floor ?

As your boat presumably has a V hull it would make both bleeding and draining it easy- weld on loads of heat sinks for more efficiency..

[blackrose]

Could you not weld a skin tank onto the baseplate under the cabin floor ?

As your boat presumably has a V hull it would make both bleeding and draining it easy- weld on loads of heat sinks for more efficiency..

 

I too would be looking at a closed loop system, but the only problem with your idea is that a horizontal (or near horizontal) skin tank isn't very efficient because the hot water rises to the top of the tank and even on a 1" thick tank the base will be cooler and won't be transferring the heat through the baseplate to the canal or river water.

Edited December 27, 2016 by blackrose

[PaulJ]

 

I too would be looking at a closed loop system, but the only problem with your idea is that a horizontal (or near horizontal) skin tank isn't very efficient because the hot water rises to the top of the tank and even on a 1" thick tank the base will be cooler and won't be transferring the heat through the baseplate to the canal or river water.

Point taken, it wont be as efficient but a well thought out horizontal tank will still cool better than an inadequate vertical tank ! My own tank is partly horizontally and seems to overcool (though it is a bit oversized too) OP may like to have a look here -http://betamarine.co.uk/keel-cooling-calculations/

[DHutch]

I think as long as it's suitability well baffled a baseplate mounted skin tank should be ok?

 

Ca always make it a bit larger area and or thinner. Bilge keel coolers work fine.

 

 

 

Daniel

[Tony Brooks]

This is nothing to do with the question but the photo suggests two legs to me and the two hull openings/mounts (if that is what they are) look awfully low on the hull to me. If the whole of the leg is not to be permanently submerged it sees you will have a very shallow draft and the bottom of the leg and prop is likely to be below the hull so there will be more danger of fouling and damage. just hope that I have misinterpreted the photo.

[Alan de Enfield]

 

This is nothing to do with the question but the photo suggests two legs to me and the two hull openings/mounts (if that is what they are)

 

I initially thought that - but - it is actually 2 pictures showing 'left' and 'right' of the same transom.

 

I agree that the leg looks as if it will be submerged and the prop 'hanging' a considerable distance below the boat, however, it is a V-Hull Springer so there will be a further 'few inches' of draft that we cannot see in the picture(s)

[Tony Brooks]

I see, it looks as if there is a sort of weld on keel/very thin swim section as well to protect the prop. I now think there may be room for a serpentine keel cooling pipe(s) either side of the "keel" section. The V of the hull should protect them.

[Neil Smith]

 

In pipe fitters' terms a bend is a piece of tube in the form of a sharp 90 degree turn. An elbow also goes through 90 degrees but as a longer and radiused turn. Bits of floating matter that might jam in the sharp turn of a bend would nevertheless pass through the more gentle turn of an elbow. You seem to be talking of screwing the elbow/bend into the skin fitting on the outside of the hull, and while a bend would keep the pick-up pipe close to the hull an elbow would mean the pick-up was spaced a couple of inches clear of the hull. It does seem to be a very unusual design to have some external pipe on the outside of the hull where it would be extremely vulnerable to damage. The conventional design would be a skin fitting with a shut-off valve on the inside, then a mudbox, and the pipework to the engine coming from the top of that as described. I think your proposed installation will always give you trouble, even before water gets to the filter.

 

(poor internet seems to have posted only part of my post - I reread the original and saw that the filter is on the intake end hanging in the water. This would work fine on rivers but I think that canals are too shallow and muddy andyou will spend most of your time clearing the filter rather than going anywhere)

 

(edit to sort out a bit of mess)

I always thought a bend formed in a pipe fitters bending tool could be from very easy right up to 90% and an elbow as bought from a plumbers was a tight 90% bend which seems the other way round to what you suggest.

 

Neil