Maritime NZ report into the loss of the yacht Essence, October 2019

[rslifkin]

Even if the hull was flexing enough to blow out a window, if the storm boards were well fastened, that may have been the difference between the window completely blowing out vs just breaking in place. And with the storm board over it, they very well may have taken water, but not the unmanageable deluge the missing windows would cause.

[Paul L]

Originally Posted by rslifkin

Even if the hull was flexing enough to blow out a window, if the storm boards were well fastened, that may have been the difference between the window completely blowing out vs just breaking in place. And with the storm board over it, they very well may have taken water, but not the unmanageable deluge the missing windows would cause.

How would the plexi or wood covers stay in place with significant flexing? Yes, it adds some strength and may stay in place, but that's a big may.

[Paul L]

Originally Posted by goboatingnow

The report surmises a flexing hull

The fact is there was some form of explosive decompression as the windows were forced outwards.

It could equally have been air pressure from water coming in the hatch

The crew reported notable flexing during the wave strikes. This flexing was likely the cause of the forward hatch failing.

[goboatingnow]

The report has some interesting comments about “ rebated windows “ or bonded in place windows

But the ocean 47 to my mind had all standard metal framed windows. None are either rebated or bonded in place.

Also the conclusion on a flexing hull seems to be based on a crew member commenting on it , but it’s not verified as the cause. The loud noise heard surely suggests high pressure escaping air. I would suggest that hull flexing enough to force windows out would equally have caused extensive structural damage but the crew are silent on this.

To me it’s far more likely the hatch become open and on falling off the wave large amounts of water entered and the air pressure poped the windows.

In that sceanario I can’t see how external storm boards would have helped

In fact I can’t see what feature would have helped other then no windows at all

[rslifkin]

Originally Posted by Paul L

How would the plexi or wood covers stay in place with significant flexing? Yes, it adds some strength and may stay in place, but that's a big may.

It would depend on how flexible the covers themselves are and what the attachment points are. If they're super stiff, they may rip the attachment points out or just break. But if the covers can flex a bit, they'll likely survive more hull flexing than a glass window.

[Paul L]

Originally Posted by rslifkin

It would depend on how flexible the covers themselves are and what the attachment points are. If they're super stiff, they may rip the attachment points out or just break. But if the covers can flex a bit, they'll likely survive more hull flexing than a glass window.

Are Bavaria saloon windows made of glass? I doubt it.
Like I said the covers will add some strength, but not much.

[Paul L]

Originally Posted by goboatingnow

The report has some interesting comments about “ rebated windows “ or bonded in place windows

But the ocean 47 to my mind had all standard metal framed windows. None are either rebated or bonded in place.

Also the conclusion on a flexing hull seems to be based on a crew member commenting on it , but it’s not verified as the cause. The loud noise heard surely suggests high pressure escaping air. I would suggest that hull flexing enough to force windows out would equally have caused extensive structural damage but the crew are silent on this.

To me it’s far more likely the hatch become open and on falling off the wave large amounts of water entered and the air pressure poped the windows.

In that sceanario I can’t see how external storm boards would have helped

In fact I can’t see what feature would have helped other then no windows at all

And what caused the hatch to open? A plausible cause is hull flexing. I have seen two plastic boats have major hull flexing. One was a Benetau that took a wake on the beam while tied to a floating dock. It was pushed up on the side of the dock and pushed the hull inward doing significant structural damage on a 6 to 8 foot line along the hull. The other was a custom, large Cat that made beam to beam contact with my boat. The Cat hull flexed inward at least 6 to 8 inches.

Build light, but not too light.

[noelex 77]

It is not unusual to see owners repairing vessels with windows/hatches that are debonding. Well before this stage is reached the windows will not be strong enough to withstand the forces from sailing in more severe conditions..

This is exactly the sort of issue that the standards should address if they are going to be effective. The structure should at least be able to withstand wave forces with minimal flexing before windows held on with sealant alone are permitted. Unfortunately, the Cat A requirement is woefully inadequate in my view. Of particular concern is the modern trend to fit large windows of marginal structural integrity close to the waterline.

[Hesti]

The report is good reading. Maximum wave hight at the time seems to have been 6 metres or more which is beyond the 4 + metres required for A rating. Flexing is mentioned several times in the report - well beyond standard requirements, the flexing may have been significant and actual hull or deck damage may have been well possible if it hadn't already occured, for example with stiffeners starting to delaminate or the sandwich starting to delaminate, which would reduce stiffness further.

Whether the windows were popped out solely by extrem flexing of the cabin side or by internal pressure resulting from flexing or from water coming in - they did pop out. The glue bond failing might give a nice plopp sound all of its own. Then, there was nothing preventing the missing windows from leaving a big hole in the cabin. Which I would guess is, why the report keeps coming back to the storm boards several times - they could have reduced the size of hole through which water could come in. They might even have held the popped windows in place. And given the crew a fighting chance to get the water out of the boat again.

About designing and building for extreme (beyond standard) conditions - the penalty to be paid is additional weight and / or additional cost. Up to the buyer of a boat to decide upon. Volume built production boats offer a lot for the price, but they are not built for extreme significantly beyond standard conditions. They would either be too expensive or too slow to be able to compete with other brands.

[goboatingnow]

Originally Posted by Paul L

Are Bavaria saloon windows made of glass? I doubt it.

Like I said the covers will add some strength, but not much.

They are glass of some sort

[goboatingnow]

Originally Posted by Paul L

And what caused the hatch to open? A plausible cause is hull flexing. I have seen two plastic boats have major hull flexing. One was a Benetau that took a wake on the beam while tied to a floating dock. It was pushed up on the side of the dock and pushed the hull inward doing significant structural damage on a 6 to 8 foot line along the hull. The other was a custom, large Cat that made beam to beam contact with my boat. The Cat hull flexed inward at least 6 to 8 inches.



Build light, but not too light.

A Bavaria 47 ocean is not a light boat.

[goboatingnow]

Originally Posted by Hesti

The report is good reading. Maximum wave hight at the time seems to have been 6 metres or more which is beyond the 4 + metres required for A rating. Flexing is mentioned several times in the report - well beyond standard requirements, the flexing may have been significant and actual hull or deck damage may have been well possible if it hadn't already occured, for example with stiffeners starting to delaminate or the sandwich starting to delaminate, which would reduce stiffness further.

Whether the windows were popped out solely by extrem flexing of the cabin side or by internal pressure resulting from flexing or from water coming in - they did pop out. The glue bond failing might give a nice plopp sound all of its own. Then, there was nothing preventing the missing windows from leaving a big hole in the cabin. Which I would guess is, why the report keeps coming back to the storm boards several times - they could have reduced the size of hole through which water could come in. They might even have held the popped windows in place. And given the crew a fighting chance to get the water out of the boat again.

About designing and building for extreme (beyond standard) conditions - the penalty to be paid is additional weight and / or additional cost. Up to the buyer of a boat to decide upon. Volume built production boats offer a lot for the price, but they are not built for extreme significantly beyond standard conditions. They would either be too expensive or too slow to be able to compete with other brands.

I think it’s very difficult to use storm boards attached by a few drilled fittings to prevent a window from blowing outwards. Most likely the storm board attachments would pull out of the hull

For this to be effective would require the storm boards to have integrated backing pads in the grp etc

[Paul L]

Originally Posted by goboatingnow

A Bavaria 47 ocean is not a light boat.

In absolute terms it is not a light weight boat. In strength terms, I don't know. From the crew description and resulting damage, it sure sounds like the hull flexed beyond what is needed for open ocean conditions.

[Hesti]

Originally Posted by goboatingnow

I think it’s very difficult to use storm boards attached by a few drilled fittings to prevent a window from blowing outwards. Most likely the storm board attachments would pull out of the hull

For this to be effective would require the storm boards to have integrated backing pads in the grp etc

... there was a time when through bolting would have been considered sensible ...

[blu3534]

Originally Posted by goboatingnow

Sometimes sh!t happens. Thank fully it’s rare

Could be that it's only rare because normal production boats don't often encounter such stormy conditions. I suppose quite a few such boats (with big windows) would sink after having fallen down 6 meters?

It’s a 47 foot production cruiser and a good example of a well built strong model. ( the ocean range in particular ) -- Nothing wrong with that boat.

Mmh..., there's something wrong with your statement or else this accident wouldn't have happened. Flexing hull, big windows, storm boards not attached (and not quickly attacheable), no watertight bulkheads to contain the water-intrusion, life-raft torn away. -- This 47 and many other boats are built to a price tag. Nothing wrong with that, but there are consequences and one shouldn't praise well built strong when it clearly was inadequate.

(Also the crew was lucky that they got a replacement life-raft and that the helicopter came so fast, otherwise they would all be dead. A huge pity that the skipper couldn't enter the life-raft, I suppose he would still live if that had been possible. Very sad!).