Self Clearing Cooling Water Intake

[HopCar]

Bunch of wise guys! I'll have you know that I may get to work late but I leave early to make up for it! It's 11am and I haven't put my pants on yet. Try to get that image out of your head.

[HappyMdRSailor]

Originally Posted by HopCar

Bunch of wise guys! I'll have you know that I may get to work late but I leave early to make up for it! It's 11am and I haven't put my pants on yet. Try to get that image out of your head.

Let me know when you do start... That'll give me an hour heads up for the time difference so you don't make me look like a slacker...

[Andrew Troup]

Thanks for all the ideas. Dockhead's is wonderfully simple, which is a great virtue.

There's very little to go wrong (as long as you don't lose the wing nuts: presumably the ends of the studs are peened over)

I guess the limitations of sailing alone make me a bit jumpy about such a large opening to the ocean, conveniently openable, whose only line of defence is a seacock - a seacock which is normally left open (and may become unmovable in the open position).

I don't have a crystal ball to evalute what problems might arise, or time to try and brainstorm a whole bunch, but from this thread (see Panope's post above):

If, for example, a fish were to insert itself, unbeknownst to you, and jam the seacock, you would have to take a bit of a gamble that you will be able to quickly make things good, if you were reliant on your engine at that point in time.

Rodding out a jammed ball-valve in a hurry, (given that attempts to close it might leave it jammed at an angle which is no longer quite open) with whatever comes to hand, strikes me as possibly

a) injurious to its seals, meaning the valve will need to be replaced, and/or likely to
b) simply jam it more permanently

I do like the ability to replace such valves without hauling the boat, personally.

(I realise it can be done by plugging from outside, if the thru-hull has retained its integrity, but the thought of having to do so gives me a 'funny feeling in my water')

I would personally install such an item as the "Fisherman Sea Strainer" in pairs, with only one being open to the sea at a given time.

This way, if the seacock could not be closed, I would be able to defer addressing the problem to a more suitable occasion

I would be fine with a single strainer if it was lifted by a standoff or fitted on a seachest such that the lid (and ideally the ball valve as well) was above the worst-case loaded waterline. That way I could clear any blockages without time pressure.


(I personally cannot make use of either of the classy items posted above, incidentally, given that they are in bronze, and my hull will be alu alloy, but the forum and this thread serve the common benefit, and most people will not be in my situation)

I'm about to start another thread, entitled "1GM Yanmar Cooling water blockage: Lessons learned" about some things I just learned since starting this thread. They are generally more specific to that engine, fitted to a saildrive without a separate strainer, but a few of them might be of more general interest.

[Andrew Troup]

This is probably not a practicable idea, but it might spark something which would be more doable:

I have been pondering applying the time-honoured "day-tank" concept (used for diesel fuel, and for freshwater reticulation) to an alternative source of seawater used for cooling.

The idea was that, in a situation where the inlet got clogged, you could buy some time, and an 'offing' in cases where searoom was in short supply, by baling some water (fresh or salt, whichever came more easily to hand) into a readily accessible daytank, from where it would feed by gravity to the impeller pump via a Y valve.

This would also be a way of nursing a pump which was worn or damaged (having lost a vane, perhaps), for long enough to (say) get an anchor down and holding.

Ideally there would be a "low water flow rate" alarm fitted to the inlet piping between the strainer and the impeller pump, so you would know to switch to the daytank in advance of the time when the engine temperature alarm would otherwise sound, and the impeller possibly be damaged.

It would also serve as a backup in case the engine temperature alarm failed.

So, here's my wacky idea, probably doable only in a centre cockpit metal boat, and probably only if designed-in, rather than as a retrofit:

It's for a system like Panope's, where there's a straight passage through from filter lid to hull intake, to permit rodding out a blockage.

But the difference would be, that the strainer would be fitted (via a sealed flange) to a hole through the cockpit floor, in which the lid would be recessed.

This would enable using the cockpit well as a very generously sized daytank, so that buckets of clean seawater could be easily sloshed into it in very non-labour-intensive way, even by a single hander with a lot on.

If I end up doing this, I would dispense with the commercially available strainer bodies and build in a standpipe, welded to the hull at the bottom and enlarged and welded to the floor of my cockpit sump at the other. I would size the enlarged section to be a fit for a pair of commercially available strainer elements. They would be loaded from above , back to back with a slotted spacer between, and the take-off (branch of the integrated "T") for the engine cooling would be situated at the midheight of the spacer.
This way, it would not be so important to flush out the cockpit in an emergency swappover from ambient water to cockpit water, as a source of cooling seawater, because even the latter would be strained.

There would still be a sealed plug at the top end, but it could be an expanding bung type, fitting within the enlarged diameter of the heavy-walled aluminium pipe of the standoff cum 'hollow stay'

I can think of at least one way this might be adapted even to other hull materials, but I will not burden this post with further castles in the air, especially given the (I would expect) negligible interest in such speculations.

A system like this would have saved me two late-night swims/dives through a thick carpet of trash floating on the surface after a recent storm, to clear what we incorrectly took to be a blocked intake screen, and a very late night indeed diagnosing and fixing the actual problem. And I would not be fighting off a cold as I typed this!

[Panope]

Andrew,

I like the "cockpit becomes day tank" idea. If you make the lid of the strainer out of a "see through" material (like the off-the-shelf strainer that I have), you will be able to see the intake water splashing around at all times. It will give a constant indication (flashlight at night) that water is being pumped.

Mine is not quite as visible as glancing down at your feet. It requires that I look through a plexiglass door in the footwell wall. It is actually a cool feature because it eliminates the routine "looking over the transom" to verify water flow.

Another small benefit to systems with a large strainer bowl mounted high, is the ability to run the engine while on the hard with a garden hose. What works well for me is to remove the strainer lid and run the garden hose strait in. I "regulate" the amount of water (so that it does not overflow the strainer) by using the ball valve (sea cock) and letting excess water dribble out onto the ground. I know the typical method of pulling a hose off the strainer and sticking it in a bucket works fine. This is just a little bit more convenient.

Steve

[Pelagic]

I think a plan to the flood your cockpit in an emergency just compounds the problems. (How high is your sill to the cabin?)
The foolproof system is an enclosed skin cooling system as is on my steel hull...but that does not work well in the Tropics!
2nd best is a proportionality large standpipe welded to the hull and capped above the waterline so.
High volume/low pressure reduces the chance of suction blockage and an air pressure fitting on top of inspection hatch can quickly back pressure and clear most problems.
The Dutch have perfected both methods

[Stu Jackson]

Overthinking a simple and proven system for many eons.

Geez, either back flush it or ream it out.

Next thing ya know you'll be promoting saildrives for their simplicity, lacking the basic concept of what a BIGGER hole in the bottom of your boat makes any sense at all.

Oh, and I've heard that ABYC has outlawed wing nuts on batteries. Might need to get my pliers out before I can disconnect the little buggers...

[Andrew Troup]

Originally Posted by Panope

Andrew,

I like the "cockpit becomes day tank" idea. If you make the lid of the strainer out of a "see through" material (like the off-the-shelf strainer that I have), you will be able to see the intake water splashing around at all times. It will give a constant indication (flashlight at night) that water is being pumped.

Mine is not quite as visible as glancing down at your feet. It requires that I look through a plexiglass door in the footwell wall. It is actually a cool feature because it eliminates the routine "looking over the transom" to verify water flow.

Another small benefit to systems with a large strainer bowl mounted high, is the ability to run the engine while on the hard with a garden hose. What works well for me is to remove the strainer lid and run the garden hose strait in. I "regulate" the amount of water (so that it does not overflow the strainer) by using the ball valve (sea cock) and letting excess water dribble out onto the ground. I know the typical method of pulling a hose off the strainer and sticking it in a bucket works fine. This is just a little bit more convenient.

Steve

One caveat which occurs to me (I'm sure the bystanders would have been making it soon enough):

If the water level is above the non-syphon valve in the loop to your exhaust, there could be a problem with hydraulicking the engine if the daytank (or more likely, cockpit) exceeds the capacity of the waterlift box in the exhaust system.

Thanks a lot for your idea of the clear lid. I like that a lot, and I could simply turn my plug out of clear acrylic and machine an O ring groove around it.

Another way of using the cockpit as a 'big funnel' into the cooling intake would be for boats with a salt water deck wash hose to simply adjust it to keep up with demand.


Pelagic:

I don't know where you saw me suggesting "flooding" the cockpit. In my case there is a sump which makes the idea particularly attractive, but unless motor sailing or heeling massively under bare pole(s), most cockpits would not need to be flooded or anything close to it for my idea to work.

As for the Dutch, I agree, and am a fan for much of their thinking for metal boats, which is why I, (like Panope) have chosen to implement their system, the one you give as number 2)

I like your thinking on air pressure and I thought of that recently but forgot to make note, so thanks for the reminder. It seems to me that it would work particularly well if the inlet end were internally tapered or even given a slight trumpet bell-mouth, helping the "Low suction" characteristic where it matters most, and kept smooth, so that anything (like Steve's pesky fish) which jams in the mouth does not swell up and become a tight-fitting plug. Fish are particularly problematic to blow out, given their scaly skin.

(Anyone remember "Attenhofer" touring skis?)

[Andrew Troup]

I was going to post that I had not had the misfortune to encounter a 1/4 acre or more humped mass of jellyfish at night time.

But that's not strictly correct: I have encountered such a swarm at night, but luckily not while under motor, but under sail only. On a small tiller-steered boat, the incessant vertical jumping of the tiller due to them bumping unseen into the rudder is never forgotten.

During the day it was no great drama: on one occasion I could detour around them but in the other case, they occupied the entire navigable channel, meaning we had to make other plans.

But if either of those things had happened at night, where the extent and solution to the problem could not be gauged, that's one of an unknowable number of unexpected but challenging situations where an easily filled daytank, enabling if necessary drawing NO water whatsoever from the sea*, might be the answer to a fervent prayer.

* so that in exceptional circumstances, it could even be topped up with fresh water from the drinking tanks for a limited period until the boat could be made secure for non-motoring.

One of the situations where I encountered a major jellyfish swarm was in a glacial fiord where, ten meters or less from 'shore', the sounder found no bottom.

[HopCar]

The Groco hull mounted strainer is available in aluminum.

[Andrew Troup]

HopCar

Thanks heaps for that, I'm much indebted for your trouble and interest.

But I'm sorry to say I can't personally countenance using cast alu for something which keeps the sea out.

The castable alloys are all (AFAIK and last time I checked) substantially less corrosion resistant than the 5454/5083/5086 alloys which hulls are built from, and they're also different in galvanic potential, making them reliant on ongoing anodic or impressed current protection, on which the remainder of my hull will be carefully specified not to rely.

This is a known issue for waterjet hulls vs cast jet-unit housings, for instance.

It's also a slight concern for me even now, given that I've just acquired an Edson bilge pump (manual 1 gallon / stroke) for which alu was the lesser of the two evils.

I want to 'marinise' this if possible, so I'm trying to find a contact at a company I once contracted for, who manufacture jet units at the top end of the market, (one project I worked on could have fitted an All Black scrum in the intake housing) and they had done a huge amount of research and test-work on surface treatments and subsequent paint systems and procedures for cast alu to get around this problem.

I didn't at the time feel it would be ethical to take notes, and I simply can't remember the spec in detail.

There was a huge variation in the success of the results, and what they came up with was remarkably good. I would hope to be able to send it through their process, so that no secrets would be disclosed, but although they used to be that sort of company, I suspect that the arc of free market competition means that by now (like most such companies) they have evolved in order not to perish.

But at least a Bilge pump is not going to let the sea in, if it gets porous; just be less good at getting it out!