How common is it for boats to be unsinkable? ie. has built in floatation

[preventec47]

Boats built for the American leisure market are supposed to have "positive buoyancy"

I cant tell if he is being serious but I would believe it considering how our cars are built.
I also cannot really tell what the Leisure market is unless he is talking about all the old geysers who
can barely take the boats out and get em home again without seeing heavy seas or high winds etc.

The assumption here is he is talking more about the bigger motor yachts with lots of expensive comforts etc.

 

[preventec47]

No keels weighing thousands of pounds on a catamaran .... which is why they don't sink. You know it makes sense. :encouragement:
Richard

Thanks for bringing that up. When I was a teenager I had a job renting about fifteen Hobie Cats on the beach and
I had to go out and flip back over 6 or 8 per day. It took considerably longer when the mast was pointing straight down
and dragging in the sand. I doubt if the hulls on much bigger Cats are airtight like the Hobies pontoon like floats
but at least there should/could be one float out of the water if the other side float was submerged.. and the sail was
laying on the surface.

 

[Tranona]

I dont know how prevalent the practice of using composite sandwich with foam core is these days as I seem to recall
that 20 or 30 years ago when it became desirable as the next space age construction technique.... things went well for
a while and then they all started to delaminate. In any case I assume a foam core sandwich boat hull would be extremely
buoyant. I remember the ads back in the 60s I think when the Boston Whaler came out promoting foam based unsinkability in their new fiberglass line of boats.
.

There is a big difference between a foam cored hull laminate (which is still a dominant form of construction) and the Sadler and Etap boats. The latter had two hulls - inner and outer with foam injected in the void. With foam or balsa cored hulls the core is saturated with resin - that is its purpose - so does not contribute to buoyancy.

If you read the article I referred to earlier you will see that the volume of foam required is substantial and its placement in the hull important. Very difficult to install in a cruising yacht without a substantial loss in internal volume. The latter seems to be a key priority amongst buyers and given that sinking is such a remote possibility for most people there is little attraction in "unsinkability".

It is different with the Boston Whaler type of boat for a number of reasons. First they are open boats and prone to swamping, second a key design consideration is strength of the hull skin to resist pounding, third internal volume is not an issue and lastly displacement is low in relation to size. So, this makes a natural application for a double skinned boat with injected closed cell foam and many such boats are made that way. I was actually involved in building boats of that type nearly 40 years ago, so nothing new.

However not all is sweetness and light. Problems are getting the foam properly distributed and fully stuck to both skins, sealing the joint between to two skins and ensuring attaching fittings does not lead to penetration of the foam core. In service they are prone to the foam breaking up through pounding and one of the skins failing, usually the outer. They then tend to become waterlogged, even though the foam is closed cell. There are posts here from time to time from buyers of such boats discovering this the hard way. Of course not easy to repair.

While it is always good to air this subject, it is nothing new and much time energy and money has been invested over the years in finding a method of providing buoyancy in the event of water flooding in, but really no significant progress for cruising boats. The limited success of the two who tried it suggests that there is really no demand for such a feature - at least among those who prepared to pay their own money for a new boat.

 

[vyv_cox]

Not sure I would have described Sadler as having 'limited success'. They went bust of course, having built a lot of very popular and highly regarded boats, but then what UK boat building company did not?

 

[preventec47]

QUOTE
Good article on the subject explaining the physics involved in the Feb 2003 issue of PBO.
UNQUOTE

I'm pretty new here... Is the PBO accessible for the random public? How/Where ?
uh.... What is the PBO

 

[mlines]

I cant tell if he is being serious but I would believe it considering how our cars are built.
I also cannot really tell what the Leisure market is unless he is talking about all the old geysers who
can barely take the boats out and get em home again without seeing heavy seas or high winds etc.

The assumption here is he is talking more about the bigger motor yachts with lots of expensive comforts etc.

Nope, I am talking about the small end of the market

https://www.uscgboating.org/regulations/assets/builders-handbook/FLOTATION.pdf

However I note that it does not apply to sailboats, so they are happily allowed to sink

 

[Hacker]

QUOTE
Good article on the subject explaining the physics involved in the Feb 2003 issue of PBO.
UNQUOTE

I'm pretty new here... Is the PBO accessible for the random public? How/Where ?
uh.... What is the PBO

Its Practical Boat Owner, a sailing mag in the UK. You can buy back copies I believe.

 

[Praxinoscope]

When one looks at the number of boats just buzzing around the U.K.not forgetting the rest of the World, I don’t know what the percentage of boats do actually sink, but I don’t think it is that high so, sinking is probably the last thing one needs to worry about.

 

[RichardS]

Thanks for bringing that up. When I was a teenager I had a job renting about fifteen Hobie Cats on the beach and
I had to go out and flip back over 6 or 8 per day. It took considerably longer when the mast was pointing straight down
and dragging in the sand. I doubt if the hulls on much bigger Cats are airtight like the Hobies pontoon like floats
but at least there should/could be one float out of the water if the other side float was submerged.. and the sail was
laying on the surface.

That's true of course ..... but I think you'll find that most sailing dinghies, including the monohulls, rely on ballast from the crew rather than weighted keels.

Richard

 

[Tranona]

QUOTE
Good article on the subject explaining the physics involved in the Feb 2003 issue of PBO.
UNQUOTE

I'm pretty new here... Is the PBO accessible for the random public? How/Where ?
uh.... What is the PBO

PBO is the magazine that sponsors this forum, hence the name. I am not sure if they still offer a back copy service as they have recently restructured.

 

[Tranona]

Not sure I would have described Sadler as having 'limited success'. They went bust of course, having built a lot of very popular and highly regarded boats, but then what UK boat building company did not?

Yes they were successful in their time, but as you say did not exactly sweep the market - and i am not sure it was unsinkability that people bought them for. Nobody else followed their lead and they also backed off the process with later boats. As you say it was only the 26 that was really unsinkable.

I think "limited" success is appropriate in relation to unsinkability - and of course its demise was not really directly related, although maybe the higher costs won't have helped in a competitive market.

 

[Praxinoscope]

Yes they were successful in their time, but as you say did not exactly sweep the market - and i am not sure it was unsinkability that people bought them for. Nobody else followed their lead and they also backed off the process with later boats. As you say it was only the 26 that was really unsinkable.

I think "limited" success is appropriate in relation to unsinkability - and of course its demise was not really directly related, although maybe the higher costs won't have helped in a competitive market.

Yes, Sadler were successful, and if you look at the Sadler that are still around and proving themselves they deserved to be, although I never really liked the 26, the 25 was I think a better boat and had much nicer lines.

 

[coveman]

Yes, Sadler were successful, and if you look at the Sadler that are still around and proving themselves they deserved to be, although I never really liked the 26, the 25 was I think a better boat and had much nicer lines.

Yes, the same could be said for Etap - well built boats but became too costly against cheaper rivals and sadly lost the market

 

[Tranona]

Yes, Sadler were successful, and if you look at the Sadler that are still around and proving themselves they deserved to be, although I never really liked the 26, the 25 was I think a better boat and had much nicer lines.

You could say that of most builders in that period. There was a huge unsatisfied demand for modern cruising (and racing) boats at the time and basically if you could make it you could sell it. Hence the explosion of builders and variety of designs, most of which are still around today.

It started to go downhill because of the recession in the early 80s and the arrival of boats from Europe which buyers found more attractive and better value. While some builders made moves to compete, many just did not have the resources because the industry was so fragmented. At the same time the export market failed to develop partly for cost reasons but mainly because boats built for the UK environment were not attractive in the new growing market in Europe.

 

[Jim@sea]

Before expanded polystyrene foam was invented, to make a boat more unsinkable people filled bags with Table Tennis Balls and stowed them away. If you were worried about a particular boat you could always go round with a modern foam gun and fill inaccessible places.

 

[gregcope]

The limited success of the two who tried it suggests that there is really no demand for such a feature - at least among those who prepared to pay their own money for a new boat.

Do we need to let Pogo know that they have been going the wrong way?

Are not many of the Open40's that go round the world built this way?

 

[preventec47]

Both interesting and amusing that as stated perhaps only one in a thousand boats sink statistically, but also it seems to me that about one in twenty articles in magazines electronic and physical, discuss sinking and safety matters related. Thusly
I may be a little more sensitised to the possibility than I should be. Paying more attention to safety is probably not
a bad thing but I agree we need to align our efforts to the statistical probabilities. I just think and fear the possibility
of events beyond my control like hitting submerged objects or running aground .... well maybe running aground is
or can be from negligence but sometimes aren't there uncharted obstructions that reach up and punch the bottoms of boats ?
Maybe it is our penchant for bad news like the news headlines every day leading with shootings and killings first
before addressing the other billions of aspects of our daily lives. The boating press seems to always be discussing
salvage operations or the extraordinary events connected to some disaster at sea. Thanks to the participation here I do now better appreciate the tradeoffs in costs and function that are made to achieve unsinkability.

 

[preventec47]

I dont know much about boating matters but I have been exposed to some composites technologies
for the last 40 years and have always been a little obsessed with the foam core sandwich structures
and lament that there were failures.... due primarily to a foam technical term called "friability"
that addressed the propensity of foam bubbles to crumble from fatigue and turn to dust. This is
what caused the delamination of hulls constructed with the foam sandwich materials due to
cyclical water pounding... I have not followed the technology but I was kind of under the impression
that great focus was being paid to development of newer modern foam compounds that were
far superior to the originally used foams. I always knew that balsa as a core could absorb moisture
but thought that a tough enough closed cell foam core could take some hull damage without
allowing water into the core of the sandwich in the hull.

If anyone here can speak to the latest state of the art in foams.... I would appreciate it.

 

[preventec47]

Before expanded polystyrene foam was invented, to make a boat more unsinkable people filled bags with Table Tennis Balls and stowed them away. If you were worried about a particular boat you could always go round with a modern foam gun and fill inaccessible places.

I prefer ping pong balls. It could get to be a little pricey ! Regarding foam guns.... There are many options today
for building insulation that range from aerosol cans to one gallon and five gallon containers of two part polyurethane
foams that come with their own one time use applicator wands etc. This I think would be perfect for some boats.

 

[Seajet]

The Anderson 26 also has built in buoyancy and is supposedly ' unsinkable ' - though I never heard of any tests to prove it, Andersons went bust very soon after the A26 was marketed, as they lost their main MOD business.

I have seen a few posts from people with various boats having problems with trapped water / condensation in double - hulled designs with closed cell polystyrene bouyancy, but I know someone slowly refitting an A26 to Rolls Royce standards, he hasn't found this problem and he's ultra fussy - quite nice to know as he designs nuclear power plants !