Fifty Feet of Grey (steel)

[rustybarge]

Why not?? Obviously drag is a factor of coil/tube type.... I am thimking of possibility of tube in the small keel.... Its an idea... Obviously not bolted direct to bottom of hull.... Other thought is how about a double skin hull type arrangement... Cooled through the hull plates... Another daft idea maybe....!!!


I have the first GA drawing with me as well im impressed so far. We have a good series of drawings for discussion with the yard...
Three cabins, three ensuites... Going to dispense with one of them though... Think two heads is enough..

The big advantage with keel cooling is the simplicity of the engine cooling setup....no heat exchanger or raw water pump or vulnerable rubber exhaust hose.
I think you can use the standard road going water pump and thermostat saving thousands of £££££'s on each engine.

What happens when your hull lifts out of the water when on the plane? Is there enough surface area in the water to cool the engines?

Just imagine how much saving on maintenance you could achieve with a dry exhaust and keel cooling!

 

[Robg71]

Wetted surface area should be adequate. W are looking at it, but i admit not in great detail. Exhaust is wet though. Nice and quiet....

 

[rustybarge]

Wetted surface area should be adequate. W are looking at it, but i admit not in great detail. Exhaust is wet though. Nice and quiet....

If you're going for the wet exhaust there would be no point in separating the cooling, as you will already have all the pipework in place. I think it really works well for inland waterways craft that suck up a lot of weed and plastic bags etc.

Regarding the paintwork, are you going for 'superyacht' shiny mirror finish, or just two pack 'functional' rolled on finish?

 

[Robg71]

It will be two pack, yes. Airless spray is most likely, but will be from paint spec that dictates. Some form of glossy finish though.

 

[MapisM]

What happens when your hull lifts out of the water when on the plane? Is there enough surface area in the water to cool the engines?

I don't think the wet surface area while planing can be a problem.
We're not talking of a 100mph catamaran which actually flies above the water....

Otoh, one potential problem for keel cooling is the availability of enough keel, so to speak.
I mean, I've seen steel trawlers where keel cooling worked beautifully, but all of them had a deep, long keel, and the tubes inside it could exploit a huge cooling surface.
And in most cases, serving just one small(ish), low revving engine.
But I'm a bit skeptic that with this hull design you can get enough surfaces for keel cooling.
In fact, you've got two big(ish) engines, whose cooling needs increase when going fast.
Not the ideal scenario for keel cooling.

But of course, if the yard does the math and confirms that it's feasible, I for one wouldn't miss such opportunity!

 

[vas]

well, if keel cooling doesn't work for the engines, why not use it for the geny??? Would be lovely to have almost silent geny eves on the hook

V.

 

[MapisM]

If you're going for the wet exhaust there would be no point in separating the cooling, as you will already have all the pipework in place.

Oh yes, there is still a very good point.
Wet exhaust, as Rob said, makes for a much quieter sound. And also the dry stack have its cons and risks, anyway.
Otoh, not having salt water anywhere near the engines is still a great thing.
Fwiw, I've seen such setup in other boats, though yet again just trawlers, not planing hulls....

 

[MapisM]

well, if keel cooling doesn't work for the engines, why not use it for the geny??? Would be lovely to have almost silent geny eves on the hook

Ermm... Actually it's rather the exhaust than the cooling which has to see with the noise.
We are just used to think that wet exhaust = raw water cooling, but that's not necessarily the case.

 

[Robg71]

Plane to catch home.... Reply in a bit

 

[vas]

Ermm... Actually it's rather the exhaust than the cooling which has to see with the noise.

doh! forget it...

We are just used to think that wet exhaust = raw water cooling, but that's not necessarily the case.

slightly confused here MM, how can you have a wet exhaust without using sea water for it? Not much point in sucking the seawater just to dumpen the noise of the exhaust, is there?

V.

 

[rustybarge]

doh! forget it...

slightly confused here MM, how can you have a wet exhaust without using sea water for it? Not much point in sucking the seawater just to dumpen the noise of the exhaust, is there?

V.

I suppose the expensive bit is the heat xchanger, the special manifold, the raw water pump and all the complex plumbing that has to fit on the engine.
I would not like to guess how much this costs on a 600hp marine engine.......£7k or more?
the keel cooling tube would be negligible in comparison......100' 1.5inch steel tube [gunbarrel?] and welding £500.

That's quite a saving, and zero maintenance.

Edit,,,I'm talking complete rubbish as usual, a marine engine will run at 2500 revs approx, not 1500revs that a bus engine cruises at, so you will need to fit a much bigger water pump for keel cooling.

 

[MapisM]

slightly confused here MM, how can you have a wet exhaust without using sea water for it? Not much point in sucking the seawater just to dumpen the noise of the exhaust, is there?

Sorry V, in hindsight my post wasn't clear enough.
Yep, in wet exhaust the sea water is used also for cooling the exhaust. In this sense, noise dumping is just a by product.
The difference is that in most boats, sea water goes to the engine heat exchanger first, to the gearbox heat exchanger second, and in some hydraulic stabs installations it is eventually used also to cool the oil of that equipment.
Only at the end of this trip, sea water joins the exhaust hose, cooling it down.
In keel cooled boats, sea water does nothing of the above, except the last bit.
Which is one reason why keel cooling is often coupled with dry exhaust - thus getting rid of sea water completely.
But as I said, there are pros and cons also with dry stacks...

PS for rustybarge: I'm not sure about the real cost difference. I would think that a proper keel cooling system takes a bit more than some tubes and weldings, but as you also say, there's a huge difference in maintenance anyway.
I'd rather have a keel cooled boat, if feasible, even if there wouldn't be any initial savings - though there must be some, I reckon.

 

[rustybarge]

PS for rustybarge: I'm not sure about the real cost difference. I would think that a proper keel cooling system takes a bit more than some tubes and weldings, but as you also say, there's a huge difference in maintenance anyway.
I'd rather have a keel cooled boat, if feasible, even if there wouldn't be any initial savings - though there must be some, I reckon.
Last edited by MapisM; Yesterday at 23:32.

keeping all that nasty corrosive salty water outside the boat hull would pay dividends in the long term, that's why trawlers go to the effort.

Seeing that the design is still fluid at this stage....How about a small wing engine to give 8kts cruise at 2000revs?[70hp?]

 

[MapisM]

How about a small wing engine

On a twin screws boat?

 

[rustybarge]

On a twin screws boat?

Some of the Dutch steel boats can manage 4 or 5mpg at 6~7kts with about 70hp, just on the torque curve at a relaxing2000 revs.Besides the economy aspect, you can also get incredible range at 1 gal/hr!

So it would be worth all the hassle of installing a wing engine.

Some options...
Drive one of the main shafts with a sprocket off the gearbox flange, locate the wing engine in front of the engines and bring back a shaft down the center. Simple, just use the wing engine clutch.

Drive both shafts, but you will need to mount a separate clutch on each sprocket. A vee belt drive would be simpler with an idler wheel instead of a clutch.[it's only 70hp]

 

[MapisM]

I thought you were suggesting a full fledged wing engine, with its separate drive.
The solution of a smaller engine driving the main shaft(s) for slow cruising is another matter altogether.
Which can make sense in theory, particularly with electric motor(s) driven by the genset(s).
But I've yet to see any solid installation around that concept...
...I'm not sure I would suggest Rob to go that far with experimenting, TBH.

 

[jfm]

to the engine heat exchanger first, to the gearbox heat exchanger second, and in some hydraulic stabs installations it is eventually used also to cool the oil of that equipment.

It's a small point in the grand scheme of things but it would be engineeringly odd to do that, at least these days. I cannot speak for all installations of course but if they are plumbed in series gearbox would come first. My boat has virgin sea water to all three of engine gearbox and hydraulics and I'd expect that to be the norm, at least these days, and would hope Rob would plumb this new build this way

 

[MapisM]

Agreed, I just happened to have written that with an old(ish) boat which I've seen recently in mind, but that's not the norm.
And the sequence was irrelevant anyway, in the context of the difference between seawater used only for cooling the wet exhaust or also all the rest...

 

[rustybarge]

My boat has virgin sea water to all three of engine gearbox and hydraulics and I'd expect that to be the norm,

...how do you deal with the corrosion of hot sea water in the cooling waterways of the engine?

 

[jfm]

...how do you deal with the corrosion of hot sea water in the cooling waterways of the engine?

Seawater only passes thru heat exchangers, not the actual engine.

Unusually I also have freshwater flushing so when the boat is at rest for more than a few days the heat exchangers are sitting in fresh water not seawater. But that isn't necessary and is quite fussy