Downflooding

[zoidberg]

It kills..... and it's in the news again.

Lengthy Telegraph article

There's been lots of speculation, and there will be more, about that specific lethal event, but..... what do we take away from it all? And from broadly similar sinkings..... Marques, Asgard II, De Gallant. Yes there were differences, but....

I've been thinking about the 'dull as ditchwater' Angle of Vanishing Stability and how it suddenly becomes very important indeed. We all seem to assume that, in a 'knockdown' situation, OUR boat would bounce right back up again.

But would it? If a load of water gets in through an open/damaged window or hatch, are all bets off? And if the builder's AVS calcs are now a long way from what you actually have, with twin headsails on furlers, stainless 'goalposts' with solar panels, a 40kg liferaft on the coachroof, a mast-mounted spinnaker pole and a radar scanner halfway up the mast.

I've seen ORC certificates for the same boat, in Light and Cruising configurations, with 56 degrees difference in Stability calculations.... due to the gear carried.

What about you? Have you any idea what your 'nice to haves' are doing to your Reserve of Stability? And what about 'downflooding' openings....?

 

[SaltyC]

An interesting article, the more information that comes out the more questions pop into my head.
The low AVS (compared to that of our AWB's) and openings in the hull for ventilation giving a low downflooding angle make for serious pondering.

With regard to my boat, Radar half way up the mast, spinnaker pole stowed on mast, roller furling jib, in mast furling.

Since most similar new boats were supplied with furling sails one would hope that the designer had allowed for these in their calculations. Eternal optimist?

Now consider openings allowing water to flood in, engine ventilation 1 vent either side of cockpit coaming, 1 vent either side of coachroof on dorade vents plus 3 fixed ventilators on cabin top with a pull to close flap(closes automatically when water flows through! )

Agreed my engine vents and dorades are small in comparison to HVAC air flow required for 2 very large engines and full AC requirements. But my boat is much smaller.

These are known items I have previously pondered, risk assessed but decided for my sailing are not a risk. My main concern on engine vents was, in the event i ran agound and dried out (on a level beach) as the tide returns, would the boat rise before water entered the hull via engine vents in the coaming? My solution was, safety first and gaffer tape over the vent!

Perhaps, as the sea warms and extreme winds become more frequent I should revisit?

 

[johnalison]

I only skipped through the article this morning but I was surprised by the downflooding angle for this boat, which I think was somewhere in the mid 40s degrees. Many years ago I believe it was a JOG requirement that, as far as I remember, a sailing boat should be able to survive being laid flat without water ingress.

 

[RunAgroundHard]

My boat has a stability certificate, based on current configuration. I will be adding both a radar and davits, hence will require an adjustment if I go ahead. All openings are guarded and capable of being isolated except fuel and water tank breathers. Companionway hatches are a weak point, as they can be removed, usually are, and are not water tight. I have a sail plan for wind speeds.

If I get knocked down, in a seaway, and scoop up green water, the big risk area is my cockpit locker, which is just a ply lid, secured with a hasp and two hinges. It is possible in extremis that the lid could fail and allow large volumes of water into the hull. I have an engine powered bilge pump, electric bilge pump and 2 manual bilge pumps, but a damaged locket lid constantly being doused would be a challenge.

I am well versed in risk assessment and barrier management in my professional life, but application of the practice in my personal and leisure life, is challenging, more to do with laziness than difficulty.

 

[RunAgroundHard]

... My main concern on engine vents was, in the event i ran agound and dried out (on a level beach) as the tide returns, would the boat rise before water entered the hull via engine vents in the coaming? …

If your boat floated down when grounded, without flooding, then if nothing else changes, it should float back up again without flooding. The gaffer tape would be wise, especially in sticky mud, which may hold the boat down for longer on arising tide, or increased wind and waves.

 

[zoidberg]

It's good that some are (re)-considering their 'defence plan', in light of this fatal tragedy.

That's the point....

 

[Supertramp]

It is easy to be reassured or not by theoretical numbers and for certain the designer has a responsibility with the overall design, layout, construction and placement of risk items like windows, hatches, breathers, etc. I also imagine that the area of sail carried is a factor - a knockdown under bare poles being very different to under full sail.

I suspect most of us could cast our eyes over a boat and judge its ability to deal with extremes.

For most boats, including high latitudes prepared craft, I think a knockdown is a serious situation which will reach or pass the limits of design and structure.

I suspect that the outcome will depend to a significant degree on the seamanship of the skipper in how he prepared for the situation. Choice of course, sails, stormboards fitted to hatches and windows, stowage of loose items but also the longer term preparation like screwed floorboards, locker lids and doors with secure catches. Much of my insight is from reading accounts of epic voyages where its clear the participants had no idea of their AVS but did have a lot of sense and experience to mitigate the risks.

In my few occasions in truly rough weather (without knockdowns) it is remarkable how things come loose that you thought were secure (like cups jumping out the sink or headlining panels coming loose).

I agree that with Zoidberg - a bit of thought in advance and some changes to routine behaviour and preparation can only help. Although I do hope it doesn't all kick off while anchored as in this tragic case.

 

[Stemar]

Jazzcat is more stable upside down than the right way up, but short of that, downflooding isn't an issue. Yes, if we did heel to 90 deg, it's likely the forehatch would fail, allowing water in, but we wouldn't stay that way for long, so that would be the least of my worries. Fortunately, I am unaware of anyone who'd succeeded in flying a hull, let alone capsized a Catalac, and I believe it's never been done.

 

[Chiara’s slave]

AVS is only part of the story, as I am sure the OP is well aware. The force, or in the case of a gust or rogue wave, energy required to reach that angle has a big part to play, and means of course that bigger boats are less prone to knock downs than a smaller one. Force or energy required to reach the downflooding angle is clearly a bigger issue than most of us had previously thought about. The calcs are all totally different, and means different things to us multihullers. Some good, some not so good. Playing to your own boat’s strengths is most important.

 

[capnsensible]

It's good that some are (re)-considering their 'defence plan', in light of this fatal tragedy.

That's the point....

I learnt a lot about stability from commercial coding loads of yachts. There is an awful lot to it that designers and surveyors have to consider.

It was certainly something I'd not really thought about up to then.

Dunno where the thread is now but a few years ago I took some photos in the marina here with lots of yachts getting ready for transats. The amount of added weight from ribs on davits, goalposts with all sorts of kit fitted, decks with fuel and water cans strapped to guard wires was of concern. It must have an effect on boat safety.

 

[RunAgroundHard]

… was of concern. It must have an effect on boat safety.

As is the contents of the lockers being dumped onto the low side due to inadequate locks. Free body impact of water can somewhat be reduced by the cabin sole being screwed down to aid damping, but only to a degree. This latter point is also important when recovering as float sole boards can be lethal as well as the gaps under them. I secured all my under bunk and cabin lockers with sliding bolts and Gravelly fasteners, respectively.

 

[zoidberg]

I learnt a lot about stability.... It was certainly something I'd not really thought about up to then.
...The amount of added weight from ribs on davits, goalposts with all sorts of kit fitted, decks with fuel and water cans strapped to guard wires was of concern. It must have an effect on boat safety.

Is YOUR boat a Gömböc...?

( '.....a three-dimensional shape with two equilibrium points on a horizontal surface: one stable and one unstable.' )

...and you don't know it?

 

[capnsensible]

Is YOUR boat a Gömböc...?

( '.....a three-dimensional shape with two equilibrium points on a horizontal surface: one stable and one unstable.' )

...and you don't know it?

Yes.

Or no.

 

[SaltyC]

I learnt a lot about stability from commercial coding loads of yachts. There is an awful lot to it that designers and surveyors have to consider.

It was certainly something I'd not really thought about up to then.

Dunno where the thread is now but a few years ago I took some photos in the marina here with lots of yachts getting ready for transats. The amount of added weight from ribs on davits, goalposts with all sorts of kit fitted, decks with fuel and water cans strapped to guard wires was of concern. It must have an effect on boat safety.

Having spent 15 years deep sea with a basic understanding of Naval Architecture and stability, it concerns me that some are happy to set off across Oceans with dinghies hanging off the stern on Davits. Perhaps I just sail too smaller yachts to think I may need my dinghy to go ashore for my take away mid ocean?????

 

[RunAgroundHard]

Having spent 15 years deep sea with a basic understanding of Naval Architecture and stability, it concerns me that some are happy to set off across Oceans with dinghies hanging off the stern on Davits. Perhaps I just sail too smaller yachts to think I may need my dinghy to go ashore for my take away mid ocean?????

I do not think the seas are full of inflatable dinghies having been washed off davits, container ships on the other hand.

 

[SaltyC]

I do not think the seas are full of inflatable dinghies having been washed off davits, container ships on the other hand.

Not washed off davits but filled with water may possibly affect stability. However, I feel sure a containership on the davits will definately affect a yachts stability.

 

[capnsensible]

I do not think the seas are full of inflatable dinghies having been washed off davits, container ships on the other hand.

We found one once. Orange coloured so it was quite visible. I sent one of my crew who had been in the army up to the bow with the request to report back if there was anything ex human and yukky in it. It was empty so we recovered it, cleaned tons of weed and barnacles off it and left it in a Caribbean marina to get nicked and get a new lease of life.

Also found a plastic deckchair once too. Plus loads of net floats from fishermen many leagues behind us.

 

[Stemar]

At least the dinghy is ready to be deployed if needed in a hurry, though will it still be there if the hurry is being overwhelmed by a storm? If you've got a liferaft, ISTM that the only advantage to keeping the dinghy in the davits is that it frees a locker for beer

 

[capnsensible]

At least the dinghy is ready to be deployed if needed in a hurry, though will it still be there if the hurry is being overwhelmed by a storm? If you've got a liferaft, ISTM that the only advantage to keeping the dinghy in the davits is that it frees a locker for beer

A lot of these dinghy are often ribs with big engines. You would need a hoofing big locker.....

 

[Stemar]

A lot of these dinghy are often ribs with big engines. You would need a hoofing big locker.....

Lots of beer...