Calling all Fluid Mechanics Engineers

  • Thread starter Thread starter Deleted User YDKXO
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Pascoe's Yacht Survey is always a good place for practical advice and I like his idea of having more than one pump in the engine compartment to give redundancy as well as capacity
Good point about hose but you've got to consider worst case scenario

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Re: Time to sink - and a solution

The amount of time taken for it to sink will be found from knowing the absolute maximum displacement which i think (?) is the gross tonnage. The displacement is about erm 24 tonnes so and gross might be praps 60 tonnes. This gives about half an hour total - bit more with my calcs, bit less with polytechnical formulae which somehow mix pressure in bar and lengths in millimetres, harumph.

In practice, of course, the whole lot splooshes into the engineroom and the boat becomes untenable as the stern dips heavily, although this does help retrieve the passports which will fall down through the saloon - along with a lot of glassware, though...

Of course, bilge pumps will become more and more ineffective as their outlet goes underwater (with a stern leak) or raises as the bow dips (again reducing flowrate) - which could be quite soon.

One answer for (manned) boats of anywhere near this size is to have a really powerful means of exhausting water - much better than a battery-powered bilge pump. And the most powerful thing is an engine. With the valves set up properly, it should be possible to first open a crossover valve between the two primary inlets, then turn off the primary seawater inlet on one engine (engine on tickover fed by just one open inlet) and then to open a valve on another inlet which draws water directly from the engineroom - giving a several hundred horsepower bilge pump. Then close and/or balance the crossover valve for continuous running/emptying.

A Kollision Kit (or several on a big boat, i've used one and ordered four more) from Force 4 would allow the hole to be plugged despite it being underwater. If the hole is big then a repair patch needs to be fixed from the outside - rope on and jump in, get the drysuit on first if in cold waters.

If the leak isn't in the engineroom - then one would have to be very quick with the underwater patch if the leak isn't in the engineroom - cos limber holes relying on gravity wouldn't allow anywhere near the same flowrate as that which is forced in through a hole of the same size, and indeed wouldn't work at all as soon as (say) the nose of the boat dips. See the Titanic film for nice explanation of how subsequent bulkheads (at cabin sole level in pleasure boats) gently take the boat down, and never allow an engineroom-based bilge pump to get near the water that comes in.




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Re: Not so

Um there are production boats with all that lot, and more. This leopard has auto bilge pumps in each compartment of course, plus one really huge emergency 2000 l/min pump with metal 75mm piping and valves to switch for each compartment. in addition it has an extra inlet behind the primary strainers and crossover valve to allow the engines to run continuously and provide a several hundred horsepower emergency pump. I am unsure if any brit boats have anywhere near this level of gear, hence the occassional accusation that they are small boats made big, instead of ships made smaller.


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Nah, they have a little internal self sealing valve thing. That's why they don't swamp you when you change 'em...

Go for composite, not stainless or ceramic, BTW.

<hr width=100% size=1><-- insert witty sig file here -->

<A target="_blank" HREF=http://www.fairlinetarga29.info>Buy my boat!</A>
 
You better tell that to my brother in law whose boat sunk when it was re-launched 'coz the boatyard forgot to screw up the paddlewheel housing. Certainly was'nt any valve stopping water coming in on his assembly. Must admit its a couple of years since I took one of these out myself but the last time I did do it, the flow of water was spectacular
Maybe modern logs do have a self sealing valve but older ones dont?

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Re: Not so

Wow, that sounds like a proper pumping system like somebody actually thought about the risk of flooding. Fair point about Brit boats. I bet something like a Squaddie 58 has the same size pumps as a Targa 29 only twice as many. I suppose an emergency pump + engine driven pump does'nt sell boats at SBS but it bloody well should

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Re: Not so

The Cranchi also has auto bilge pumps, plus crossover valve to allow the engines to pump out the bilge water and also a hand pump.

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How old.

How old was this boat for gods sake?.If sea cock left open,then rubber hose must have failed.
If metal sea cock gave way through corrosion,must have been rubbish quality.
Is this a further proof that new boats are cutting corners on fittings..?


<hr width=100% size=1>If it aint broke fix it till it is.
 
Re: Not so

<Which Cranchi >

Mediterranee 40

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Re: How old.

All this talk of sea cocks and hose failure is great, but I was told it sunk due to a problem with the stern thruster!!!

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Re: How old.

ooh do tell. Though i think we got to bilge pumps cos of course, if the bilge pumps had worked correctly there wouldn't be a problem.

Sternthruster-wise - surely only the Woolwich ferry needs these to spin around and around and dock on the other side? Not twin-engine 65 footers. Bit of a waster realy.

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Re: How old.

Not that I know but I can't see that. The sternthruster is just a tube stuck on the transom which I guess is fixed with some bolts so I cant see a problem with the sterthruster causing a hole big enough to sink the boat, assuming the bilge pumps were working

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