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Old 17-08-2015, 10:49   #16
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Re: And the safest hull material is...

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Originally Posted by FSMike View Post
Just to show my ignorance, what do f/a and i/a stand for?
Thanks
fatal accident, injury accident.
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Old 17-08-2015, 11:00   #17
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Re: And the safest hull material is...

I don't think you can surmise your conclusion based upon a very simplistic data analysis such as that. Steel and aluminum are usually used on larger boats. By far the greatest number of deaths occur on PWC and boats under 18', normally under the fiberglass category. Would a motorcycle with a composite frame be less safe than one with a steel frame? Is a Boeing 757 (aluminum) safer than an Airbus A320 (Composite)?

You would have to categorize the types and sizes of boats to come anywhere close to a conclusion of which is safer.

Would you rather be on a 50' steel boat with a drunk skipper or a 50' Wood Shrimp boat with a captain who has been fishing that boat for the past 30 years in the same area? So, you have to take experience, local knowledge and under the influence/distractions into account.

The best way to determine which boat is safest, take (4) $50K sailboats of 35' to a Boat US Insurance and get a quote. Which is higher, and which would they not even insure?
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Old 17-08-2015, 11:11   #18
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Re: And the safest hull material is...

Statistics can be skewed easily, based on how the question is asked. If you want an answer relevant to hull material you need to ask "how many boats, as a percentage of all boats of that hull material, had an accident related to the strength of the hull"..... or something like that.
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Old 17-08-2015, 11:15   #19
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Re: And the safest hull material is...

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Originally Posted by mstrebe View Post
There are frequent discussions regarding the various merits of hull materials on this site. My own personal opinion is quite open; I own two FRG hulls and one plastic hull, and I've lived aboard a steel hull for years. Probably my natural preference would be aluminum.

But it occurred to me that all of the material science posts, the anecdotes, and the discussions of maintenance, damage, and degradation all really come down to one thing: Which hulls are best for survival?

Well, I'm a statistics person, especially when we're talking about risk of mortality, so I like to avoid stories about what somebody somewhere once heard, and go with the largest collection of good numbers I can find.

The USCG compiles the most complete publicly available numbers regarding pleasure boat accident statistics, and they do track hull materials. Now, they don't track how many boats exist of a specific type, so there aren't numbers to say how likely a boat is to have an accident by hull type, but they do provide us with a more important number:

Given an accident, how likely is death or injury by hull type?

With no further ado, these are those numbers for the past three years, along with the three-year average (sorry about the crappy formatting, blame forum software):

2014 Accidents fatalities injuries f/a i/a
Aluminum 815 163 411 20% 50%
Fiberglass 3946 299 2041 8% 52%
Plastic 134 69 67 51% 50%
Rubber/Vinyl/Canvas 60 27 32 45% 53%
Steel 51 0 10 0% 20%
Wood 71 8 17 11% 24%

2013
Aluminum 862 190 425 22% 49%
Fiberglass 4087 253 2013 6% 49%
Plastic 126 48 55 38% 44%
Rubber/Vinyl/Canvas 55 19 28 35% 51%
Steel 36 1 12 3% 33%
Wood 84 13 22 15% 26%

2012
Aluminum 861 197 439 23% 51%
Fiberglass 4529 332 2357 7% 52%
Plastic 107 45 65 42% 61%
Rubber/Vinyl/Canvas 65 37 25 57% 38%
Steel 47 1 6 2% 13%
Wood 81 4 26 5% 32%

three-year Average
Aluminum 22% 50%
Fiberglass 7% 51%
Plastic 44% 51%
Rubber/Vinyl/Canvas 45% 48%
Steel 2% 22%
Wood 11% 27%

The bottom line is that the statistics for all hull types except Wood are very "normal", meaning there's enough data that they don't vary much from year to year.

The next results are pretty shocking: They show definitively that of boats involved in accidents, Steel boats are by far the safest, at 2% fatality rate per accident, fiberglass at 7%, wood at 11%, aluminum at 22%, and other materials at about 45%.

Now, it's important to understand that these hulls are of all pleasure boat craft (not just sailboats), that sailboats represent a very small number of the overall statistics, and that all accident types tracked by the USCG are included.

There is also a very strong "unseen attractor" in these numbers: Size of vessel. Steel vessels are the very largest. Rubber are the very smallest. Obviously larger vessels fare better in accidents. So there is some serious skew to the numbers that we can't divide out.

That said, for the hull types we really care about (steel, aluminum, fiberglass, and wood) we can work out the sizes. Fiberglass fares particularly well considering that on average, they would be the smallest of these four hull types. There are very few 25' steel hulls, but there are hundreds of thousands of 25' fiberglass hulls.

These numbers are large numbers with real meaning. The fact that aluminum fares so poorly compared to FRG is shocking to me, especially considering that aluminum boats would be in the same size range or larger than fiberglass. The fact that steel is by far the safest material is also a bit shocking, and not what I would have predicted, but it may be that only the very largest boats are made of steel.

I have to wonder what it is that I don't know about aluminum that makes it three times more likely than FRG to have a fatality in an accident and ten times more likely than steel, especially considering that the average aluminum boat is larger than the average FRG boat.

Anyway, it's changed my opinions about hull material dramatically.
I do not think that you can conclude anything from these numbers, based on what most everyone has already mentioned (alum boats in the 8'-20'range, Jet skis, etc. skewing the data). Thank you for an interesting post, though, and I'll stay with my 38' Steel Spray that we've owned since 1996...
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Old 17-08-2015, 11:49   #20
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Re: And the safest hull material is...

steel.
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Old 17-08-2015, 13:00   #21
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Re: And the safest hull material is...

[IMG]steel[/IMG]
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Old 17-08-2015, 14:35   #22
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Re: And the safest hull material is...

Thought we agreed we cannot agree on this.
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Old 17-08-2015, 16:04   #23
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Re: And the safest hull material is...

Hi There

I will quot the local fisherman of Westpoirt in New Zealand (.Steel is Real )
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Old 17-08-2015, 16:14   #24
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Re: And the safest hull material is...

Having also a statistical background as a statistical hydrologist, I would say you don't have sufficient data to make any analysis. Primarily you would need to know how many boats of each type are there, you would also need to break your classifications into size or purpose. Are you including canoes to compare with PWC to fishing boats etc.

Nice try, it would be great if you had the necessary data, but I've lamented that problem for many years. "If only they had collected...."

Regards.
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Old 17-08-2015, 17:01   #25
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Re: And the safest hull material is...

Quote:
Originally Posted by mstrebe View Post
There are frequent discussions regarding the various merits of hull materials on this site. My own personal opinion is quite open; I own two FRG hulls and one plastic hull, and I've lived aboard a steel hull for years. Probably my natural preference would be aluminum.

But it occurred to me that all of the material science posts, the anecdotes, and the discussions of maintenance, damage, and degradation all really come down to one thing: Which hulls are best for survival?

Well, I'm a statistics person, especially when we're talking about risk of mortality, so I like to avoid stories about what somebody somewhere once heard, and go with the largest collection of good numbers I can find.

The USCG compiles the most complete publicly available numbers regarding pleasure boat accident statistics, and they do track hull materials. Now, they don't track how many boats exist of a specific type, so there aren't numbers to say how likely a boat is to have an accident by hull type, but they do provide us with a more important number:

Given an accident, how likely is death or injury by hull type?

With no further ado, these are those numbers for the past three years, along with the three-year average (sorry about the crappy formatting, blame forum software):

2014 Accidents fatalities injuries f/a i/a
Aluminum 815 163 411 20% 50%
Fiberglass 3946 299 2041 8% 52%
Plastic 134 69 67 51% 50%
Rubber/Vinyl/Canvas 60 27 32 45% 53%
Steel 51 0 10 0% 20%
Wood 71 8 17 11% 24%

2013
Aluminum 862 190 425 22% 49%
Fiberglass 4087 253 2013 6% 49%
Plastic 126 48 55 38% 44%
Rubber/Vinyl/Canvas 55 19 28 35% 51%
Steel 36 1 12 3% 33%
Wood 84 13 22 15% 26%

2012
Aluminum 861 197 439 23% 51%
Fiberglass 4529 332 2357 7% 52%
Plastic 107 45 65 42% 61%
Rubber/Vinyl/Canvas 65 37 25 57% 38%
Steel 47 1 6 2% 13%
Wood 81 4 26 5% 32%

three-year Average
Aluminum 22% 50%
Fiberglass 7% 51%
Plastic 44% 51%
Rubber/Vinyl/Canvas 45% 48%
Steel 2% 22%
Wood 11% 27%

The bottom line is that the statistics for all hull types except Wood are very "normal", meaning there's enough data that they don't vary much from year to year.

The next results are pretty shocking: They show definitively that of boats involved in accidents, Steel boats are by far the safest, at 2% fatality rate per accident, fiberglass at 7%, wood at 11%, aluminum at 22%, and other materials at about 45%.

Now, it's important to understand that these hulls are of all pleasure boat craft (not just sailboats), that sailboats represent a very small number of the overall statistics, and that all accident types tracked by the USCG are included.

There is also a very strong "unseen attractor" in these numbers: Size of vessel. Steel vessels are the very largest. Rubber are the very smallest. Obviously larger vessels fare better in accidents. So there is some serious skew to the numbers that we can't divide out.

That said, for the hull types we really care about (steel, aluminum, fiberglass, and wood) we can work out the sizes. Fiberglass fares particularly well considering that on average, they would be the smallest of these four hull types. There are very few 25' steel hulls, but there are hundreds of thousands of 25' fiberglass hulls.

These numbers are large numbers with real meaning. The fact that aluminum fares so poorly compared to FRG is shocking to me, especially considering that aluminum boats would be in the same size range or larger than fiberglass. The fact that steel is by far the safest material is also a bit shocking, and not what I would have predicted, but it may be that only the very largest boats are made of steel.

I have to wonder what it is that I don't know about aluminum that makes it three times more likely than FRG to have a fatality in an accident and ten times more likely than steel, especially considering that the average aluminum boat is larger than the average FRG boat.

Anyway, it's changed my opinions about hull material dramatically.
Where I live in NZ there seem to be a lot of accidents involving small aluminum outboard powered fishing boats. Typically an outboard gives trouble. Crew go down the back to get it going. The bow goes up and blows down wind and the waves swamp over the stern. Or they are overloaded and no life jackets. The sea gets rough with the turn of the tide and they swamp.
Sometimes they are dragged over sand until the bottom gets thin and leaks.


Nothing to do with the material they are made out of but more to do with boat handling and the type of boat usually shallow V and requiring little maintenance that can easily be made with aluminum. Many are cheap and appeal to people more concerned with fishing than seamanship.
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Old 17-08-2015, 18:02   #26
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Re: And the safest hull material is...

No question, steel. Small steel boats (less than 100 ft) are much stronger in impact resistance than anything of reasonable cost and normal construction. Take a piece of steel 1/4 inch plate, 3/8 inch fiberglass, 3/8 inch aluminum plate, 1 inch thick wood and attack them with an axe or sledge. The steel will be bent to heck, but still one piece, and it will last much longer than you will swinging the axe or sledge. The aluminum will easily cut with the axe and fatigue with the sledge and break. The fiberglass might survive one blow of either but not much more than one. A small steel boat is the only thing that might survive a collision with a semi submerged container or an iceberg. Small steel boats are typically much thicker than they have to be for strength, they have to be able to have some extra material for corrosion resistance. The bottom of my keel is 1 inch thick plate, the sides 3/8, it could pound on a reef or rocky shore much longer than any other construction. A container collision a full speed in fiberglass, aluminum, or wood boat, if it didn't have sealed compartments, I don't think you would even have time to get your ditch bag out of a locker, there would be a 4 foot hole and the boat would be under in a minute or less. Steel would most likely have a huge dent but probably still be watertight. I did have a 27 foot steel boat for a small time. I think it could probably survive being dashed onto a rocky shore by 50 foot breaking wave.
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Old 17-08-2015, 18:45   #27
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Re: And the safest hull material is...

Quote:
Originally Posted by mstrebe View Post
There are frequent discussions regarding the various merits of hull materials on this site. My own personal opinion is quite open; I own two FRG hulls and one plastic hull, and I've lived aboard a steel hull for years. Probably my natural preference would be aluminum.

But it occurred to me that all of the material science posts, the anecdotes, and the discussions of maintenance, damage, and degradation all really come down to one thing: Which hulls are best for survival?

Well, I'm a statistics person, especially when we're talking about risk of mortality, so I like to avoid stories about what somebody somewhere once heard, and go with the largest collection of good numbers I can find.

The USCG compiles the most complete publicly available numbers regarding pleasure boat accident statistics, and they do track hull materials. Now, they don't track how many boats exist of a specific type, so there aren't numbers to say how likely a boat is to have an accident by hull type, but they do provide us with a more important number:

Given an accident, how likely is death or injury by hull type?

With no further ado, these are those numbers for the past three years, along with the three-year average (sorry about the crappy formatting, blame forum software):

2014 Accidents fatalitiesinjuriesf/ai/a
Aluminum 81516341120%50%
Fiberglass 394629920418%52%
Plastic 134696751%50%
Rubber/Vinyl/Canvas 60273245%53%
Steel 510100%20%
Wood 7181711%24%

2013
Aluminum 86219042522%49%
Fiberglass 408725320136%49%
Plastic 126485538%44%
Rubber/Vinyl/Canvas 55192835%51%
Steel 361123%33%
Wood 84132215%26%

2012
Aluminum 86119743923%51%
Fiberglass 452933223577%52%
Plastic 107456542%61%
Rubber/Vinyl/Canvas 65372557%38%
Steel 47162%13%
Wood 814265%32%

three-year Average
Aluminum 22%50%
Fiberglass 7%51%
Plastic 44%51%
Rubber/Vinyl/Canvas 45%48%
Steel 2%22%
Wood 11%27%

The bottom line is that the statistics for all hull types except Wood are very "normal", meaning there's enough data that they don't vary much from year to year.

The next results are pretty shocking: They show definitively that of boats involved in accidents, Steel boats are by far the safest, at 2% fatality rate per accident, fiberglass at 7%, wood at 11%, aluminum at 22%, and other materials at about 45%.

Now, it's important to understand that these hulls are of all pleasure boat craft (not just sailboats), that sailboats represent a very small number of the overall statistics, and that all accident types tracked by the USCG are included.

There is also a very strong "unseen attractor" in these numbers: Size of vessel. Steel vessels are the very largest. Rubber are the very smallest. Obviously larger vessels fare better in accidents. So there is some serious skew to the numbers that we can't divide out.

That said, for the hull types we really care about (steel, aluminum, fiberglass, and wood) we can work out the sizes. Fiberglass fares particularly well considering that on average, they would be the smallest of these four hull types. There are very few 25' steel hulls, but there are hundreds of thousands of 25' fiberglass hulls.

These numbers are large numbers with real meaning. The fact that aluminum fares so poorly compared to FRG is shocking to me, especially considering that aluminum boats would be in the same size range or larger than fiberglass. The fact that steel is by far the safest material is also a bit shocking, and not what I would have predicted, but it may be that only the very largest boats are made of steel.

I have to wonder what it is that I don't know about aluminum that makes it three times more likely than FRG to have a fatality in an accident and ten times more likely than steel, especially considering that the average aluminum boat is larger than the average FRG boat.

Anyway, it's changed my opinions about hull material dramatically.
Correlation does not equal causation. You are drawing conclusions that dont meet the rigor of a scientific analysis.

These statistics dont represent a statistically valid sample for hull survivability. That would require destructive testing of a control group. Like auto crash testing where correlation between designs and actual vehicles is typically within a 2% tolerance. This is statistically valid.

If you compare survival of ships, cars, aircraft, pushbikes, etc per mile (or kilometer) then I suspect we'd see some interesting statistics.

As for relative hull material comparisons during an impact (using typical engineering properties like hardness and fracture toughness) then:

Steel - high abrasion resistance, high impact resistance

Wood (assuming traditional thick hulled working boat with no rot) - low abrasion resistance, medium impact resistance

Fibreglass (assuming modern production sailboat) - low abrasion resistance, low impact resistance



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Old 17-08-2015, 18:52   #28
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Re: And the safest hull material is...

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90% of boating related fatalities occur between 4PM and 6PM, involve alcohol, and have nothing to do with type of hull construction.

Learned that at the stupid boating safety class the law mandated I take.
OK, I hate to be a stickler, but your comments are not supported by the facts from the states and the Coast Guard. The greatest number of accidents in a two hour period is from 2:30 to 4:30pm, and that's around 21%.

Alcohol was a contributing factor in 17% of fatal boat accidents in 2013. Other years are similar.

This fascinating and accurate information can be confirmed by the Boating Statistics booklet for 2013, distributed by the Coast Guard Office of Boating Safety.

Chuck
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Old 17-08-2015, 18:56   #29
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Re: And the safest hull material is...

Battleships are usually steel. There were some aluminum (frigates I think) battleships in the Falkland War. The aluminum caught fire and burned like magnesium when hit by Exocet missiles.

So my next battleship will definitely be steel. Maybe an aircraft carrier to be really safe.
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Old 17-08-2015, 19:41   #30
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Re: And the safest hull material is...

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Battleships are usually steel. There were some aluminum (frigates I think) battleships in the Falkland War. The aluminum caught fire and burned like magnesium when hit by Exocet missiles.

So my next battleship will definitely be steel. Maybe an aircraft carrier to be really safe.
Shouldn't it be a multi hull made of steel???
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