Hacker News Reader

Comment by mpreda | Hacker News Reader

I don't think it's the engine exhaust, neither the engine air intake.

I think the exaust has possitive pressure when the engine is running which would prevent water from entering. OTOH water entering the engine air intake.. would be quite bad for the engine I guess, so there'd be protection against that. Also both of these (exhaust & intake) are not free to the inside of the vessel, but form a closed circuit with the engine, so there's no way to flood the vessel through those.

So probably we're talking about the engine room *ventilation* openings that would let water in.

View on HN

> Also both of these (exhaust & intake) are not free to the inside of the vessel, but form a closed circuit with the engine, so there's no way to flood the vessel through those.

Don't know about this yacht specifically, but as I understand it a common solution is for the engines to suck in ambient air from the engine room.

> So probably we're talking about the engine room ventilation openings that would let water in.

Likely yes. And probably(?!) there were watertight bulkheads around the engine room, so by itself the engine room flooding might not have sunk the boat (assuming doors/hatches were closed), but if combined with other downflooding into the living quarters (doors, ventilators etc.) it would have accelerated how quickly it sank.

> I think the exaust has possitive pressure when the engine is running which would prevent water from entering.

Imagine a (say) 5cm diameter exhaust pipe, at a 45 degree angle - with exhaust gasses blowing out through the top 3cm, while water runs in through the bottom 2cm. At some point, the cold water starts hitting thicker and hotter pieces of metal. As you put it, "quite bad for the engine".

But from the article, about what happens when the Bayesian heels over too far: "water will start to enter the vessel (usually through engine room or accommodation ventilation ducts)… once this starts the vessels is in serious trouble".

All luxury sailing yachts to a rounding error have wet exhausts below the waterline.

To a rounding error, all marine diesels have their intake in the engine compartment, not with any kind of closed circuit.

Especially for sailing yachts, the exhaust is almost always wet (below the waterline).

> Especially for sailing yachts, the exhaust is almost always wet (below the waterline).

I've seen quite a few sailing yachts, but never one with the exhaust below the waterline. Pretty low yes (typically maybe 10-20cm above the waterline?), but not below. When underway, the exhaust can be partially submerged due to waves.

'Wet exhaust' means that the engine cooling water is pumped into the exhaust pipe, which muffles the exhaust noise and cools the exhaust so that rubber tubing can be used.

> I've seen quite a few sailing yachts, but never one with the exhaust below the waterline.

To a rounding error, every luxury sailing yacht built in the last 20 years and most new designs of all classes will have underwater exhausts.

Merely repeating your previous statement isn't helpful. Thanks.

And your comment is?

The fact is that marine engine exhaust systems in good repair are not down-flooding points and certainly not on the yacht in question, where it almost certainly was below the waterline.

> And your comment is?

Merely expression surprise at your statement, considering my experience is so different. I have no experience of 'luxury' yachts though, just regular sailing boats. So maybe those superyachts are different?

> The fact is that marine engine exhaust systems in good repair are not down-flooding points and certainly not on the yacht in question, where it almost certainly was below the waterline.

Well I agree with that, but because, again in my experience, sailing yacht exhaust systems tend to have an S curve where the exhaust goes relatively high up. Whether the exhaust opening itself is just over or under the waterline doesn't really matter for downflooding.

Reply on news.ycombinator.com