doug748
Well-Known Member
Daydream believer;4772199 Encapsulated fins are never going to perform well aerodynamically & are out dated technology !
Loss of yacht - lessons to learn
- Thread starter snowleopard
- Start date
lw395
Well-Known Member
Or looking for ways of avoiding these circumstances?
The way I see it, it's very rough weather, you're on deck, clipped on and the boat inverts. Game over.
No gadget short of 'beam me up Scotty' is going to save you.
There are a lot of risks that we can reduce in sailing, and a lot of things which can help when some things do go wrong, but in the limit, small high performance boats sailing across oceans carry a risk.
Perhaps too many people have been lucky in recent years, people have become blase about crossing oceans in off-the-shelf mid range boats?
Robin
Well-Known Member
I have a feeling the Ballad (nice boats of their time)had a keel that was first bolted on to a hull stub and then totally glassed over so not quite 'encapsulated' and certainly not 'bolt free',in the true sense as being argued by some here, Did they not also have the propshaft exiting through the 'keel' too, albeit many were re-engined laterand fitted with more conventional drive arrangements
doug748
Well-Known Member
I think the keels were totally encapsulated but I rely only on wonky memory for this. I looked at buying one once but, being a lazy sort, decided it was too sporty for me.
As for the prop drive I am pretty sure that it was always that way. Two scandinavian boats that might have had an odd arrangement of prop drive could have been the Albin Vega and the Marieholm 32. Both of these had a prop that poked out above the rudder, maybe?
Perhaps someone has a Ballad and could tell us?
As for the prop drive I am pretty sure that it was always that way. Two scandinavian boats that might have had an odd arrangement of prop drive could have been the Albin Vega and the Marieholm 32. Both of these had a prop that poked out above the rudder, maybe?
Perhaps someone has a Ballad and could tell us?
FWB
N/A
Page 5 here mentions the keel
http://jmaster.pl/i/upload/upload/abriefpresentation.pdf
Some photos here
http://www.yachtsnet.co.uk/archives/albin-ballad/albin-ballad.htm
Nice looking yacht, the keel seems very thin for the type of construction but it's obviously a proven design.
http://jmaster.pl/i/upload/upload/abriefpresentation.pdf
Some photos here
http://www.yachtsnet.co.uk/archives/albin-ballad/albin-ballad.htm
Nice looking yacht, the keel seems very thin for the type of construction but it's obviously a proven design.
Robin
Well-Known Member
You re correctand I must be thinking of something else. We used to race against a Ballad when we had our then Liz 30, both Balladand Liz were fairly evenly matched 1/2 ton cuppers, at the time our club commodore had a Vega too that was hard to beat on handicap, maybe tht wa the one with the strange drive arrangement.
Sailfree
Well-Known Member
But car design is only slowly improving after 50yrs of some 1000 fatalities per year for last 80 yrs in UK alone. I attended the road research lab in the 60's when they were correlated every injury to the cause. What surprises me is how slow the improvements have been!
Keel failure resulting in fatalities is rare yet everyone is jumping up and down.
That's not to regret these fatalities and certainly any sensible improvements should be introduced but to me the overriding problem is what magnitude should the keel resist, what impact for the rudder, what impact for the GRP.
If we are looking to reduce loss of yachts I suspect impact damage to GRP and fire risk cause more yacht losses that keels becoming detached.
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alant
Well-Known Member
its for any situation, where your main boat becomes untenable, in regard to any life support or location assistance.
If you've ever been offshore in heavy weather, it would take a brave man to leave a yacht & board one of those rubber things.
jimi
Well-Known Member
I'm wondering if there is a cheap way to survey the keel bolts after a grounding (or on survey). I've got a couple of pals who are aeronautical engineers and they reckon there should be a simple way to XRay the fittings, apparently they do it all the time on aircraft. anyone with any knowledge as to whether this would be a feasible proposition?
alant
Well-Known Member
Have to lift out each time presumably, if a boat & surely not feasible.
bedouin
Well-Known Member
I wonder if they could do clever things with sound/ultrasound. May not detect minor defects but it should be good enough to identify a serious crack
JumbleDuck
Well-Known Member
Keels have been falling off yachts for a hundred years and more.
PeterR
Well-Known Member
That method of manufacture certainly has merits and spreads the load but it would not stop the keel bolts failing. In fact it may well make it more likely. Stainless steel keel bolts in the proximity of galvanised steel in the presence of sea water = crevice corrosion in the bolt. If your keel bolts stay dry you are OK, as soon as the seal around them fails or you get sea water in the bilges for any other reason you have the start of a major problem. This was highlighted in a CHIRP report on the failure of rescue boat fixings on a big ship where S/S bolts had mild steel backing plates - Maritime Feedback 22 Page 4/5. Subsequent correspondence from a university lecturer describes how galvanised items in the presence of stainless steel and sea water is a recipe for disaster. Maritime Feedback 23 P6.
Letter Text: I have been reading your CHIRP MARITIME FEEDBACK issue no. 22 and my attention was caught by the report on the Rescue Boat Accident. The photograph of the fractured bolts (photo 3) reminded me of three failures which came to my attention when I was a Lecturer at a University.
The failures all related to high tensile stainless steel (HTSS) either in the form of chain or nuts, bolts and washers. In each case the HTSS had been used in conjunction with galvanized components and exposed to sea water or at least a marine environment. The chain had been used with ordinary galvanized shackles, the bolts to secure a galvanized backing plate and in one case the bolts themselves had been galvanized. All failures occurred suddenly, without warning, with fractures which showed no accompanying stretching or deformation. I was able to reproduce these failures in the laboratory by loading a tensile test piece overnight. The test piece was in contact with a scrap of zinc held in place by a gauze bandage soaked in sea water. When the test piece was subsequently stretched a network of cracks was revealed and the ultimate fracture resembled those of the failed components. If I omitted either the zinc or the sea water bandage, the material behaved normally stretching and necking down to a normal fracture.
To return to the failures you illustrate you do not give the material of the eye-plate but from the position of the fractures the problem would appear to lie under the decking of the rescue boat and one wonders whether the bolts had been married with either galvanized washers or nuts or perhaps a galvanized backing plate. You report that other bolts and eye-plates have been inspected and found to be satisfactory. I would warn that the type of cracking which I observed is difficult to detect non-destructively. I was able to observe it by metallographic examination but the cracks are very fine and could easily escape detection.
From time to time I hear of similar failures and it is clear that the dangers of marrying HTSS with galvanized components in a marine environment is not fully appreciated and requires greater publicity. I suspect that designers who appreciate the benefits of ordinary 18/8 stainless steel are mesmerized by the words "high tensile" and do not appreciate that the two materials differ significantly.
Mark-1
Well-Known Member
Am I right in thinking that most other manufacturers get around this problem by using GRP for their "frame" construction?
AntarcticPilot
Well-Known Member
Basically, the keel bolts are shielded by the keel itself. They are similar materials, so no contrast, and the bulk of metal is such that transmission of X-rays will be poor. You'd need a very high intensity source. Aeronautical structures are much less "agricultural", and tend to be fabricated to a higher degree, so the challenges to X-ray methods are much lower.
Unltrasound might work, but I gather the problem there is gaining the necessary database of what a failure looks like!
Conductivity measurements from bolt to keel might tell a story, if a bolt was totally fractured.
Twister_Ken
Well-Known Member
Same story as for hulls - GRP is not as good at resisting an impact (whether from a keel bolt, or an awash object) as steel.
snooks
Well-Known Member
Many different builders do it in many different ways. As do they construct the hulls...
Hulls vary from sprayed chopped glass, to woven rovings via vacuum infusion or again laminated, then can include balsa or foam cored (with different density of foam being used too) being used above/and below the waterline (but only solid laminate where the keel sits, or it could be wood or chuffing great sheets of metal.
The reinforcing structure can be a tray moulding, moulded hollow stringers, laminated foam stringers, vacuums infused stringers then again they can have composite reinforcement taking the strain and adding rigidity the methods can be mixed and matched too.
You'll usually find the strongest methods are the most labour intensive and consequently the most expensive.
This for example is how Contest build their yachts...
And for the record this is what the keel bolt of a Beneteau 40.7 look like:
And the moulding flange after the keel has hit something:
All images © Graham Snook / http://grahamsnook.com
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Tranona
Well-Known Member
Damage after a grounding is usually easy to identify, and does not necessarily result in a bolt shearing. Snooks pictures are good examples. The surrounding structure has deformed and almost certainly an external examination of that boat would show deformation around the keel area and probably a broken seal between the keel and the hull. Little bit like what happens when you crash a car - there are obvious external signs of damage. However, also like a car it is often not possible to determine the extent of the damage without further investigation.
The problem with boats is that often damage from grounding goes unreported and only comes to light when the boat is hauled.
Yara
Well-Known Member
Sorry to be entering this discussion at this late stage, but as an old engineer, looking at the photos of the lost yacht, and other photos showing how the keel is mounted internally, I come to the following conclusions:
The design of the keel mounting is like a coke can ring-pull- under the important paired bolts are short flat plates, no taper whatsoever, next to the high rigidity cross beams. The keel is effectively bolted to the the boat's skin.
No doubt the failure occured with a large loading, probably the boat was rolled. Maybe I should have used the analogy of a sardine tin. The keel bolts ripped the skin off just as neatly as opening a sardine tin, and for the same reason- high shear forces next to a rigid frame.
Conclusion- the forces from the keel bolts need to be smoothly conveyed to the rigid frame. No sharp edges, no rapid changes in stiffness, and lots of taper. If I had one of those Benes I would make up wide steel saddles to go from under the bolts across the frames, so that the tension is transmitted as compression into the frames, rather than massive shear forces on their edge.
The design of the keel mounting is like a coke can ring-pull- under the important paired bolts are short flat plates, no taper whatsoever, next to the high rigidity cross beams. The keel is effectively bolted to the the boat's skin.
No doubt the failure occured with a large loading, probably the boat was rolled. Maybe I should have used the analogy of a sardine tin. The keel bolts ripped the skin off just as neatly as opening a sardine tin, and for the same reason- high shear forces next to a rigid frame.
Conclusion- the forces from the keel bolts need to be smoothly conveyed to the rigid frame. No sharp edges, no rapid changes in stiffness, and lots of taper. If I had one of those Benes I would make up wide steel saddles to go from under the bolts across the frames, so that the tension is transmitted as compression into the frames, rather than massive shear forces on their edge.
Mark-1
Well-Known Member
Thanks for the post, I meant specifically the manufacturers who use tray mouldings/frame which I assume are the same construction type (for want of a better phrase) and seem to me to be the design of choice for most of the big manufacturers.
Eg:
An Arcona will have a ferrous tray/frame which could suffer from galvanic corrosion but I imagine has the advantage that it will fail more safely by bending.
A Bavaria will have a GRP tray which I imagine isn't so great if it clouts a lump of granite because it will fracture rather then bend but is lighter and doesn't suffer from Galvanic Corrosion.
If the assumptions in my examples are correct, and if the original assumption that in engineering terms tray/frame are the same design strategy I was asking if the majority of builders using tray/frame construction went with GRP over ferrous metal.
