Yes quite an alarming title but the subject has become serious to the point of World Sailing (ex- ISAF), the world governing body for the sport of sailing, to become seriously concerned and being on the verge of taking preventive actions.
The facts: surely everybody remembers the keel that some years ago fell off a Bavaria Match 42 and recently all know that an almost new 90ft Oyster lost the keel. Some know about two First 40.7 but less know about a Bavaria 390, a Jeanneau 37, a Vand den Stadt 45, a Sweden yacht 42, a Fast 42 a Maxi 110, a Max Fun 35 or more recently a Comet 45 and some days ago a Davidson 50.
Nor many know that since the mid 80’s more than 75 boats have lost the keel with the loss of 28 lives.
Probably the numbers of keels lost or boats abandoned offshore with problems on the keel are way bigger and much bigger the number of boats that were found with keel problems before actually a disaster would occur. These are only the numbers regarding the cases that were found by a a work group formed by World Sailing to study the problem and most of them were high profile cases.
Some of the keels were lost due to the contact with the ground or submerged objects, some due to poor design or poor building like the cases of the Match Bavaria 42, the modified Oyster 825 or the Max Fun 35. Others due to the weakening of the structure as a result of bad maintenance, groundings whose damage passed unnoticed or were improperly repaired while others, like the recent case with the Comet 45, remain a mystery.
Although the Comet 45 has been recovered I don’t know of any investigation going on by the boat builder. Fortunately the boat was British and used in charter and MAIB has opened an investigation to the accident some days ago.
The number of keels lost is increasing and will increase much more in the next years if nothing is made, simply because boats with bolt on keels (almost all today) will become older and the lack of maintenance and the number of damages due to keel grounding will become bigger with time, as well as material fatigue with the results that are to be expected.
Fact is that most think that a keel does not need maintenance unless obvious signs of degradation start to appear but that's a keel repair, not keel maintenance. Maintenance should be preventive and should obey to a determined schedule, as it is made for rigs or for saildrive seals.
Even in countries where the legislation demands a mandatory regular yacht inspection the problem is not addressed simply because there are no clear industry guidelines in what regards proper maintenance and material fatigue for keel and keel structures. If it looks good and there is no obvious signs of corrosion or if there are not clear signs of problems on the outside of the keel, then it is OK.
Even in countries where the legislation demands a mandatory regular yacht inspection the problem is not addressed simply because there are no clear industry guidelines in what regards proper maintenance and material fatigue for keel and keel structures. If it looks good and there is no obvious signs of corrosion or if there are not clear signs of problems on the outside of the keel, then it is OK.
Better than nothing but clearly insufficient and that leads us to the core of the problem: even if there is in the EU legislation that protects and gives warranties to consumers regarding the design of recreational and personal water crafts, the RCD, there is none in what regards inspections or accident investigation.
There is a directive and an agency (EMSA) regarding accident investigation but only in what concerns maritime transport, none regarding recreational and personal crafts. Most countries don’t investigate recreational craft accidents in any way, much less in a detailed way.
And if recreational craft accidents are not seriously investigated there is no way of collecting relevant information that will allow the detection of building or design problems and other shortcomings like de ones that are related with the lack of proper maintenance.
That feedback is necessary to update the RCD in a way that contributes to erradicate those shortcomings in what regards boat design and improve boat security. It will also provide information regarding keel maintenance and adequate schedules.
That feedback is necessary to update the RCD in a way that contributes to erradicate those shortcomings in what regards boat design and improve boat security. It will also provide information regarding keel maintenance and adequate schedules.
There is a need for an EU agency similar to EMSA (European Maritime Safety Agency) for recreational and private crafts, or a branch of it that occupies itself exclusively with that subject and we need European standards and procedures in what regards yacht accident investigation and yacht inspections.
In the absence of such an agency in Europe (and in the rest of the world) it is World Sailing that, seriously concerned with the increase of dangerous accidents with keel losses, on an interview to the magazine Yacht.de, states their intention for creating a mandatory keel system inspection and to increase building inspections to determine that the design specifications are fulfilled in reality and not only on paper.
In fact it was verified that at least in one case the designer specifications were not entirely followed and, being the actual verification of conformity regarding RCD requirements basically a paper one, it is necessary to improve that verification and for what I suspect, not only in what regards keels but also in what concerns boat stability.
But World Sailing has only jurisdiction regarding the sail boats that race on events that follow their rules, not regarding the vast majority of crafts including cruising sailboats. Their good example is better than nothing but it should be followed in what regards all offshore boats and not only the ones that will race on World Sailing events.
We need an agency with the power to provide those measures not only for boats used for racing but for all offshore yachts if we want safer and better built and maintained sailboats.
I have never sailed more than a couple of hours at a time. However to me its very clear that aluminum hulls are the only way to go. No bolts, and even in the case of lifting keels, the specs say it cant get knocked off.
ReplyDeleteI think that makes no sense. it is a choice as any other with advantages and disadvantages but in what regards to lose keels even steel boats have lost them.
DeleteNot many years ago a steel Vand Den Stadt 45 capsized after losing the keel. Unfortunately the crew perished on the accident. Welded keels also fail, specially if not well repaired after a grounding.
In 2008, the International Sailing Federation (ISAF) set up a working party on keel losses, and they found 72 cases since 1984 of boats losing their keels.
There were no defined causes in 44.5% of cases, but only three were attributed to keel bolt failure. Other causes included welded fin failures (11), grounding collision (8), internal structure (8) and canting keel system (2)
your right there is no perfect solution
DeleteSteve,
DeleteAs Paulo rightly says, the loss of keels have almost nothing to do with hull material. None of this is black and while. Aluminum hulls have lost keels and encapsulated keels in both glass and aluminum have lost their ballast.
In most of the cases, (but clearly not all of the cases) one of two causes seem to be prevalent. The first seems to be a failure to construct the boat consistent with the original engineered design. The second is undetected damage from a grounding. The less prevalent failures mode are fatigue of the hull and framing, and failure of the actually keel bolts.
The failure to construct the boat in accordance with the design drawings are not always a primary factor for the loss, but is a contributory factor in some of the cases where the boat was damaged by some other means.
There actually is a perfect solution which is a mix of proper engineering, adequate safety margins, quality control during the construction cycle, and reasonable maintenance and repair protocols.
Fully encapsulated keels whether they are GRP or other composite, aluminium or steel must be considered several orders of magnitude safer than bolt-on keels. Especially if the encapsulation is heavily faired, with a relatively large diameter fillet to the hull to transfer flexural loads.
DeleteThe load path of lateral forces on the keel must not terminate in a small area of compression fasteners. But rather loads must be distributed along a large area of hull material. The ribs of a yacht are designed to support the hull of the yacht. Terminating the loadpath to the the ribs would also be a mistake.
The earlier observation that aluminium would be a preferred material is an entirely valid observation. The yield curve and strength to weight ratio of Aluminium exceeds that of steel and GRP. The ability to resist punching shear alone makes steel a superior material and aluminium's ability to yield before it fails also makes preferred. Punching shear is a force that holes a yacht from a collision.
A collision that holes a composite will only dent steel or aluminium.
There is also a finite probability that any material can suffer a failure, one does have to be reasonable in their expectation of probability of failure.
I have not seen any punching shear data collected in the past for GRP or composite yachts. I suspect that has not been collected for a reason.
As you have admitted, it all depend on how they are designed and built and for what amount of time.
DeleteYou have talked about the superiority of aluminium but the aluminium is welded, as steel and a big number of the investigated cases has as cause a weld failure.
That was the cause of one of the more recent accidents (Comet 45s) that apparently had a very solid keel fixation...and that would be so if the welding was not defective and not done according to the plans.
More than one or other system or material, what we need is boats well designed with a big margin of safety on the keel fixation and well built.
We need also more information from the builder and designer regarding the expected duration of the materials, eventual need of maintenance and if so a schedule and what should be done and how.
Nothing lasts forever and due to last decades more rapid technological evolution obsolescence comes sooner, in cars, boats or aircrafts and the models are designed, taking that into account, for a shorter life span and that is not necessarily bad since it makes the products less expensive, but that life span should be made public or the boat inspections mandatory and able to find out eventual structural problems that compromise boat safety. That is what happens with cars.
It seems to me keel bolts must installed in such a way so that they can be inspected by removing them, or perhaps replaced a x year intervals. Perhaps x-rays or other technology can also help.
DeleteHowever, if the bolts are subject to corrosion and or flexing we need a way to replace them at periodic intervals, just like standing rigging.
Overall, it seems to me the sailboat design and building industry is technologically under developed. Just an example; how is it that so many, not even moving, boats leak when it rains but car travelling at 120 and more km/h (75 mph) ant even faster do not leak?
It seems to me the sailboat (perhaps power boat too) design and building industry need Toyota and the rest to show them better engineering.
Keels falling of is as if the wheels of a car fell off. However, car wheels never fall off, in spite of the punishment they take from potholes, hitting the curbs, sharp turns, etc.
well, I have had a car wheel fall off and it aint pretty. I was going 50 when it happened. Driver side of car dipped and I watched my front wheel and tire roll away in front of me. Automobile accident reports do not support your proposition.
DeleteIf we compare the number of the wheels that fall of out of cars (without having hitting anything) and the keels that fell off, taking into account the number of cars and sailboats, there is no comparison.
DeleteI don't think it is only a question of good engineering but mostly about mandatory inspections, that exist on cars, and not on sailboats.
Also the average expected life of a sailboat is way higher than the average duration of cars, and while most 30 year old cars are in the scrapyard, most 30 year old sailboats are still sailing, and that makes the need of inspections even bigger.
So much relies on the integrity of the builder. With cost and time pressure the temptation to use under-qualified staff and take shortcuts is high.
ReplyDeleteOff course, some boat structures and keels are much better than others but the RCD has been increasing keel demands and standards to make them more solid and I believe that what is demanded is already a reasonable standard even if I believe they should keep improving the standards.
DeleteBut if they are not inspected periodically all kind of shit can happen.
I asked to a guy that has a fast cruiser racer, with about 12 years, that is used mostly for racing what was his schedule. He drops the keel for inspection each 5 years and had already substituted some of the bolts not because they looked bad but by precaution. This is common practice on offshore racing boats .
Ok, the loads on racing boats or boats used extensively for racing are much bigger than on cruising boats so the schedule should be different: full inspections each 10 years with the keel dropped seems reasonable?
It seems reasonable to me. Do you know of many boats with 11 years that had the keel dropped for inspection, if there is no signs that something is wrong? Do you know many with 15 years that had done that?
I am pretty sure that many boats with more than 20 years never had the keel dropped and inspected.
I believe we will see an increase of keels falling from boats simply because boats are not being correctly inspected or maintained, not even when grounded and on that case many are not being correctly repaired.
Older boats with bigger keels or full keel needed less inspections? Sure.
Are new boats badly built: No, they are much better sailboats (they sail better), they are less expensive to build, demanding more inspections.
It is a 10 year period full inspection to the keel, with the keel dropped, an exaggeration?
I don't think so, most don't have the same sailboat for more than 10 years and even if one keeps it for 30 years the boat would only have to have the keel dropped twice in his lifetime and I don't believe new boats will justify maintenance after substantially more than 30 years.
Are they better sailboats, the new ones? I do not think so, - maybe they are faster around the bouys, but at sea they are not. One example I know is that when I sailed from Svalbard (Bear Island) to the norwegian mainland in 1996, I heard on the radio that a chartered cruiser racer with its professional skipper and a crew of 4 heli-rescue people aboard, glassfibre hull with short keel and spade rudder, was to leave from the N-part, while I was departing Sørbukta in the S-part in my Joshua steel ketch, the "Aurore". I called them on radio and told them that they probably would reach the mainland before us, with our 14 tons longkeeler, which they agreed on.
ReplyDeleteHowever, when we met later in Tromsø, we found out that we (two persons) were 1 hour faster to the mainland than they were, having had our Aries selfsteering gear to steer the entire way S AND having the Dickinson stove burning all the time through the galeridden september sea.
They had problems with steering in the confused wavepatterns and had a very cold trip without any heating. Their boat was a 43 ft. yacht contra Aurore's 40 ft.
I have often observed similar things in my + 50000 nm with Aurore through the entire Atlantic and most of the Pacific oceans.
So for ocean voyaging I definitively say LONG KEEL, well ballasted and metal hull and keel.
Stig Larsen, Denmark
A cruiser racer with a short keel is something that does not exist but I guess you wanted to say a fin keel?
ReplyDeleteI don't know what happened but I have followed the ARC for many years and sometimes some old boats, mainly American make it, and they sail always well on the tail of the passage, among much smaller boats.
I don't know how many miles I have done, maybe 30 000 and I had time to compare the performance of my boat(s) with the ones of heavy cruisers and I know something is wrong in what regards your story.
Sailors that have heavy boats tend to call cruiser racers to all modern boats with a fin keel and that has obviously no sense. I bet that is what happens here. Can you tell the brand and model of that 43ft "cruiser racer" you are talking about?
Hell Paulo, you are probably right about the fin keel and I don't remember the brand of the mentioned "cruiser racer" from the trip. but I know that Aurore averaged around 1000 nm a week during my later trip around the Pacific in the tradewinds (Panama-Guatemala-Mexico-Hawaii-Marshall Islands-Vanuatu-New Zealand-Chile) and from there S through Patagonia and up through the Atlantic to Denmark (1999-2003 totally). On the way to Panama in 1999 we got the infamous hurricane Lenny, where several "modern" sailing yachts were lost. We only lost one small staysail. It exploded. That is why I prefer heavy metal longkeelers for serious cruising. But I am of course oldfashioned with my 69 years of age. However, I have delivered many "fin keelers" across the North Sea and up to northern Norway and still prefer a proper craft at sea.
ReplyDeleteStig Larsen, Denmark
The Joshua that oddly is now a one design racing class is a displacement boat and has a LWL of about 9.5m and a hull speed of 7.5kt. 1000nm in a week gives 142.8nm a day and an average speed of 5.95kt.
DeleteA great performance for that type of boat but I remember that a couple, some years ago, on a small performance cruiser, Capado (31.2 ft) while cruising and circumnavigating averaged over 7kt on the Atlantic crossing. http://levoyagedecapado.blogspot.pt/search?updated-max=2014-01-08T01:33:00-08:00&max-results=4
Of course, completely different boat, a semi displacement hull that can go with easiness over hull speed but that just says to you that you cannot compare the performance of old designed full keelers with the one of modern designs.
If that was the case it would not make sense to forbid on the Golden Globe Race, where the Joshua is a one-design class, any remotely modern design to compete and all cruiser designs would be accepted, since the Joshua would be a match to them. ;-)
New boats and GRP boats are perfectly well suited to cruising as long as they are built right. Bolt-on keels seem to have become the standard on modern cruising yachts but there is always a risk of separation with the forces involved being focused on the point the keel connects to the hull. The only way to really prevent a keel coming off is to go with a fully integral keel but the only boatbuilder I can see that really does this anymore is Kraken Yachts. I saw an article about their zero keel which has no bolts, even with a lead bulb. It seems most boat builders are focusing on cost and weight saving and increasing performance instead of safety. It’s nice to see a boat builder bucking this trend and building a solution to this problem. Even the latest Oysters would worry me, especially after seeing the aftermath of the Polina Star III. It’s worrying that even boatbuilders like that are compromising safety in such a critical area.
ReplyDeleteEncapsulated keels (what you call a fully integral keel) do fail as well.
DeleteIt is important to understand that as Paulo points out, keel failures are extremely rarely the fault of keel bolt failure, or even keel contact area failure. More often than not, the failure occurs on the laminate in the hull around the keel, or in the steel or aluminum plating around the keel area. Without adequate framing, this area is more susceptible to failure.
Generally encapsulated keels are not properly structured in terms of having adequate internal framing. This occurs because designers often rely on the bond between the ballast keel and the encapsulation envelope and that bond routinely fails over time.
Hi Jeff, good to have you aboard.
DeleteBroken bolts are rare if they are kept in good conditions and tight. Other way they can break and the resulting small movement on the keel will destroy the laminate causing a mixed catastrophic failure : bolts and laminate.
Look for instance to Cheeki Rafiki report where they found several bolts broken:
"The two forward 24mm keel bolts have sheared.
"• The aft 24mm keel bolt has sheared, and has apparent rust staining around it, indicating that the keel bolt might have corroded.
• The washer plates of the three pairs of 24mm keel bolts appear to have pulled away with the missing section of the hull and are no longer present, leaving the partial remains of the aft pair of 24mm keel bolt holes in the remaining hull."
Keel bolts need to be tightened, not very often but several year apart. A small compression of the laminate or a small elongation of the bolt can happen and the very small movement that will allows will have a big effect on the stress steel bolt fatigue and also on the weakening of the boat laminate and structure.
Regards
I don't agree with you. Regarding safety the keels lost are very few, many brands, even mass production ones with thousands of boats made, never having lost one.
ReplyDeleteThat does not mean that I don't subscribe RCD more demanding standards and most of all, clear protocol and inspection schedules defined by the builders. Insurance companies will make those inspections and schedules practically mandatory, as today they do with rig inspections and sail-drive seals.
Regarding Kraken Yacht keels, that are encapsulated without any bolts, I have many doubts regarding the building. The Oyster that had problems had also an encapsulated stub with a lead keel bolted to it and the encapsulated stub broke off.
A Kraken 58 has a 10 1000 kg keel with a 2.30m draft and a bulb on the lower part. Can you imagine the lateral force that keel will be making on the hull with the boat at a 60º angle?
Without bolts that force will be all transmitted locally to the hull part of the keel area, while on a boat wilt a keel bolted to a structure that force will be distributed by a hugely bigger part of the hull.
That is why the Kraken yachts have those highly inefficient and huge keels: they need them to be huge to distribute the charges by a bigger hull area and even so those hulls have to be very thick and heavy. All the building process is a very inefficient one and only if the resulting boat is hugely more heavier than one with a "traditional" solution will be equally strong. All things been equal an heavier sailboat is a worst sailboat.
https://www.krakenyachts.com/k58
Your statement below is likely to confuse all readers and demonstrates a lack of understanding of yacht structures:
ReplyDelete“Without bolts that force will be all transmitted locally to the hull part of the keel area, while on a boat wilt a keel bolted to a structure that force will be distributed by a hugely bigger part of the hull.”
The keel is supported by the hull and the internal structure of the vessel. Keel bolts will transmit keel forces to the area of the yacht hull that receives the keel bolt. It is a misconception if you believe that by directly attaching the keel to the hull “that force will be distributed by a hugely bigger part of the hull”.
Can you please elaborate on your reasoning for this statement?
There is not much to elaborate. Or you understand how the forces work and how the keels are built and supported or you don't.
ReplyDeleteEncapsulated keels are a viable and good method for full keelers where the lateral forces generated can be distributed along the hull. Not a solution adequate to eficiente fin or foil keels where the efforts would only be distributed by a small area of the hull (the one near the keel).
That is why it is not a solution used by any of the major yacht designers and engineers.
The solution of a stub is an intermediate solution and in what regards the stub it works like a reinforced encapsulated keel with normally only one of the bolts coming to the upper structure and with the upper hull grid structure extended to the stub with GRP.
Maybe some drawings help you to understand. Anyway this discussion is over.
http://www.jordanyachts.com/wp-content/uploads/2009/12/keel-bolts.jpg
http://www.yachtrussia.com/files/oyster825/keel2_oyster825-02.gif
http://svfrogsleap.com/images/KEEL/2009-08-31%20091%20Planarized%20Keel%20Stub%20ready%20for%20final%20tweaks.%20Note%20marks%20for%20reference%20and%20build%20up%20side%20laminationsc.jpg
https://www.seilas.no/ep_bilder/784/99230-580938830a91f13427ee4d1afce94cf7.gif
Ban keelboats.....? As they say, better upside down on top than right side up on the bottom.....
ReplyDelete?????????????????
DeleteVery informative, I had no idea there were so many tragedy's with lost keels. How can the average older racer/cruiser be checked for the fore mentioned faults?
ReplyDeleteI don't know how old are you talking about but on cruiser racers it start to become general practice do drop the keel from time to time to see if all is alright.
DeleteUnfortunately there are no protocols regarding that. I know of some that do that each 5 years but those are serious racers that push the boats to the limits.
If the boat is not used for intensive racing that seems radical to me but it also seems clear that at some point the keel should be dropped and the bolts and keel structure thoroughly inspected.
More information and industry guidelines are needed to establish safety protocols in what regards full keel inspections and I believe that an increasing number of accidents will be happening before that happens.
This year a Beneteau Oceanis 473 sunk mysteriously near Açores with the loss of all crew. Of course it can have been a number of causes but the suddenness witch the Epirb stopped transmitting as well as the not deployment of the liferaft make a loss of a keel one of the possible causes.
We have a Frers 50 feet ketch built of aluminium with encspsulsted keel. She has been built 1982. There is no bolts between the keel and the frame, but extensive keel plates immersed in the lead keel cast.
ReplyDeleteThe vessel has been colliding with underwater rocks several times during her 37 seasons and well over 100 000 nautical miles. Regulat condition surveys done. No feat of keel falling off.
I don't doubt that you have a strong boat but those keel plates have to be connected with the frame, bolted or welded and weld failure is one of the more common causes of keel falling off. On one of the last, a Comet 45s, that was the cause, a faulty welding not done accordingly with the designer's specification.
Deletesailboat building is a primitive industry, the car manufacturers need to take it over; car wheels do not fall off in spite of incredible stresses, and cars do not leak even while driving in rain 10 to 15 times faster than sailboats.
ReplyDeleteInteresting comment. As a design prof I have to wonder about some of the designers designing boats. I say this having seen some of the issues on the newer boats and can only think - what were they thinking or perhaps they were not thinking. Basic rule is to imagine everything thing that could go wrong or any issues that could arise during the deign process. But I guess cost and time trumps everything.
ReplyDeleteThe bolted keels are good for economy production, but the sound keel should be built-in. The other option of reliability is lifting or swing keel. Yes, extra keel shaft underwater, but it is better then hidden rotten keel bolts.
ReplyDeleteBolting keels is a sound technology and one that is more adapted to contemporary high performance keels.
ReplyDeleteHow they are bolted, the accessibility to easy inspection and the possibility of easily replace bolts as a regular maintenance practice, each 10 years or 15 years, it is another matter, and unfortunately that is not the case with many sailboats.
WoW!
ReplyDeleteIt was an interesting discussion. Could anyone guide me to any materials related to the reason of the loss of keel by a Fast 42 Moguini in 2005? Were there any conclusion on the reasons of the incident drawn?
ReplyDelete"The investigators asked the then Durban Institute of Technology to survey the hull and this revealed alleged discrepancies between the design of the yacht and how it was built.
DeleteThe DIT reported that visual inspection and wall thickness testing showed, in the area of the keel, that the yacht did not conform to design specification and 'the workmanship is appallingly substandard'.
The DIT expressed the opinion that it was extremely likely there was a small through-thickness crack or flaw in the laminate at the port edge of the keel fixing plate. It would have been initiated if the keel had struck something prior to the race or due to a manufacturing error. The crack would open and allow water to flood the floors, girder and the interior of the vessel. An oblong hole was found that might have been drilled to pump out water.
'In harbour the crack would close as the sailing loads are removed making it difficult to spot and it would not leak water. During the race, once the crack was of a critical length, either a wave or a glancing blow to something solid in the water caused the final rapid failure of the remainder of the laminate and at that point the keel dropped off. It is unlikely the yacht hit a container... because there would be damage to the hull elsewhere,' the DIT study found.
The Samsa report pointed out the yacht was, in fact, taking in water when it sailed to Mauritius to start the race and it had been involved in a prior minor collision with a vessel called Gumption and then repaired. The report noted that, in contravention of the Merchant Shipping Act, Samsa had no record of this collision.......
The investigators said a collision with a submerged object would have caused more damage to the hull than shown by the Moquini........
The report said, 'It is strongly recommended that all similar yachts be examined as a matter of urgency in way of keels in accordance with recommendations from the designer and that special attention be paid to the keel arrangement.
Additionally, the keel studs should be tensioned to torque parameters set by the designer and carried out to ensure equal loading and measures taken to lock the nuts after tensioning.'
www.sail-world.com/27719
Seems that if aircraft need to be inspected to maintain licences, - that maybe boats ( also a life threatening environment) should also pass licensing.
ReplyDeleteFact is that in some countries like Spain, Portugal, Italy (and probably more countries) mandatory inspections are needed each 5 years, or so, but they have nothing to do with airplane inspections, that are much more demanding.
DeleteBecause there is not a clear protocol about what should be inspected and how, in what regards keels, if they don't show clear external symptoms that there is a problem with them, they will pass the inspection.
And if they fail the inspection and are "cosmetically repaired" in a way that no problem is visible, they will pass the inspection.
More than a boat mandatory inspection, from time to time, it is needed a clear protocol about how those inspections should be made, namely in what regards keel inspection, and like in airplanes clear timetables for different types of inspection, with different requirement grades.