Cornish Cruising has incredibly safe boats.

Status
Not open for further replies.
UG - those g figures look terrifying and enough to send your eyeballs out on stalks, but they will only obtain for a very short fraction of a second, yes ?

So a violent deceleration in the order of whatever it takes for a -say - 20mm bolt to shear at 71 m/s^s. That is still going to be noticed as the bolts fail sequentially or in series.

An interesting exercise for the class ;)
 
sarabande said:
UG - those g figures look terrifying and enough to send your eyeballs out on stalks, but they will only obtain for a very short fraction of a second, yes ?
Click to expand...

Yup. If the boat is doing 5 kt, which is 2.5 m/s (ish) when it hits, then the time for it to go 20mm is given by s = u t + 1/2 a t^2, which gives about 7ms to get through each bolt. Assuming the twelve fail sequentially, that's about 0.1 seconds for the whole thing, so basically a Big Bang.

Please note, though, that I'd be very surprised indeed if this was the failure mode. A fast fracture in shear seems much more likely, and would, I expect, require much lower forces.

PS Sorry, Photodog. You can take the geek out of the lab, but you can't take the lab out of the geek.
 
jimi said:
Agree completely!! ... and also, I cannot see how they got the boat back from Scilly right way up unless they were fully aware of the keel less state and nursed it back accordingly.
Click to expand...

A following wind and lots of form stability. Not to mention luck. Same reason the boat was able to sail to plymouth and back the following week with the charterers only thinking the boat steered funny.

Ubergeekian, wasn't the keel in question was held on by only 4 keel bolts?
 
Seajet said:
I thought the figure being bandied around was 12 X 1" bolts ?
Click to expand...

This is why I'm confused. I've been out of the country for a few months now so haven't seen any new information about this incident since September and what I did see is now a bit hazy. But I'm fairly sure the pictures I saw were only of 4 bolts.

Not sure they were 1" either. Well definitely not as the boats european, and metric. 20 or 22mm I think is what was there. As I said though, memory on this is hazy.
 
I thought this was covered in an earlier post, there are 4 bolts at the front of the keel but more as well ?

I did a quick scan through earlier posts for a figure, but going through in a rush that was what I found.

There was a mention of 'a dozen or so bolts' which I don't think referred to Ubergeekians' boat, obviously one needs to hear from the people who've seen the boat in question.
 
There were a lot more than 4 bolts, I did'nt count 'em but there was at least a dozen. I'd like to see the weather reports for the day they brought it back from Scilly
 
Apart from all else, the shearing of a keel from the hull that does not cause a big leak is something of a compliment to the moulding process & design.

Though not as qualified as UG, would not the shearing force be even rather than sequential?
 
Last edited:
Seajet said:
I thought this was covered in an earlier post, there are 4 bolts at the front of the keel but more as well ?

I did a quick scan through earlier posts for a figure, but going through in a rush that was what I found.

There was a mention of 'a dozen or so bolts' which I don't think referred to Ubergeekians' boat, obviously one needs to hear from the people who've seen the boat in question.
Click to expand...

It was me wot said there were about a dozen bolts. I was wrong: it was written some time after I'd looked at the hull. I looked again later and there were either 5 or 7, forget now. They appeared about one inch dia, all were sheared off clean with distinct bent back appearance at the point of break.
 
This sort of incident will become more commonplace unless something is done to tighten up the standards of certification.
Day skipper is not an attendance course, you are supposed to reach a required standard but all to often the tickets are handed out at the end of a course because its easier than failing a student.
This is not just confined to day skippers. Certain yachtmaster examiners are also awarding tickets to people who clearly do not have the skill set or experience to hold the qualification, but again it is far easier to pass than fail a student.
You now have people with the correct piece of paper to charter yachts but are lacking in ability and the all important experience.
 
imsodepressed said:
Bit of the Technical stuff from the latest YM

When the 2-tonne, 6ft 4in keel was subsequently recovered by divers, the impact point could be seen about halfway down the leading edge (there are two photos of the keel) The keel was lost, not because of corroded keel bolts, but because of the impact at the exact vertical position of the yachts centre of gravity, The force of the impact can be likened to a karate chop capable of fracturing a pile of concrete blocks - or in this case, sheering the keelbolts. There was no 'moment' (force x distance) applied to the hull, which would have made the yacht pitch. Any resultant pitching would have decreased the decelration period with a consequent reduction in the force applied and the hull structure would have been damaged as it absorbed the impact. With no pitching, deceleration would be almost zero and therefore the force applied would be enormous - all concentrated on the keel studs.
Click to expand...

And yet, that thick lump of fibreglass, approximately in the middle of the space where the keel ought to be, looks to be intact. Is it possible that the fibreglass stretched enough for the bolts to sheer?

What is the stump doing there anyway? Was it intended to take some sheer load off the bolts in the event of something like this happening?

attachment.php


Oops - in looking for the photo, I just realized oopsmykeelfelloff asked the same question.
 
sighmoon said:
What is the stump doing there anyway? Was it intended to take some sheer load off the bolts in the event of something like this happening?
Click to expand...

Just wondering if the stump is there to create a sump? Would be a good piece of design that I've rarely seen in an AWB.
 
rb_stretch said:
Just wondering if the stump is there to create a sump? Would be a good piece of design that I've rarely seen in an AWB.
Click to expand...

Yep it's the bilge sump. Beneteau were doing the same thing in the Late 80s

I think the idea was similar to if you put your hand palm down, then keeping your palm flat, point your fingers downwards, keeping them straight. With your other hand held flat, press the length of your first finger against the knuckles of fingers pointing downwards.

Watch what happens to the top of your hand, it pivots at your wrist. Soooooo if you imagine you fingers pointing down to be the leading edge of the keel, the front before the sump will be pulled down, and aft of the sump would twist off.

That's how I understood what happened, but they again, I take photos, and have no qualifications that would be of any use to determine what really happened :D
 
Status
Not open for further replies.

Share this page

Top