The white boats and yachts that you see are typically glass-fiber-reinforced epoxy, and they seem to be holding up just fine. "Carbon fiber" products are CFRP (carbon fiber reinforced plastic), where the composite matrix is fibers in epoxy, and those look fine after decades as well.

Fibreglass boat hulls have constant ongoing maintenance and repair cycles.

Hell, just last week I was watching a video about how abysmal the material has been for the wind turbine industry after it tips apart from hail stones.

Sure, theyre moving at 100 mph but I don't see why people would think building bridges out of this stuff is a good idea.

I think your mental model of wind turbine sizes is a bit off: the rotation speed is basically dictated by the need to keep blade tips moving slower than the speed of sound, which is why you see newer/larger turbines going slower than older/smaller turbines.

Most modern turbines operate with tip speeds around 200m/s, corresponding to around 450 mph.

I've had 4 boats and all maintenance was painting it every 5/10 years. *Not in salty water

About half the boats at my marina are fiberglass. The only maintenance they need is cosmetic, and there are many who skip it and many who polish it.

The other boats are metal. As I write this I am trying to remember if it’s aluminum or galvanized or stainless. There is a popular brand, anyway. The metal boats are popular because it is a fashion thingy to not keep them clean.

The more expensive marinas have bigger proportions of polished boats and teak decks.

Anyway, as a fiberglass boat owner, I’m not recognizing the constant maintenance thingy. Nobody’s told us boat owners! :)

The amount of work that goes into maintaining a yacht far exceeds the financing available to public infrastructure. Of course, bridges are not normally sitting in salt water. Either way I'm not sure the comparison is very meaningful.

> The amount of work that goes into maintaining a yacht far exceeds the financing available to public infrastructure.

This reminds me of some family members that lived on a boat. As soon as they finished maintaining one thing (e.g. painting), they could immediately start over again. It was an endless cycle of doing maintenance to the boat. They really wanted to live on a boat. Eventually they sold it and bought something else, though unsure if the maintenance was the cause.

This is true of big bridges like the Golden Gate Bridge as well.

That work typically is highly parallelizable, so you could do it in half the time, too (a year of maintenance, wait a year, a year of maintenance, etc)

From an operations viewpoint, it’s easier to pick a degree of parallelism that makes this a continuous operation.

You don’t have to close down and start up maintenance work, you don’t have to scale up and down the number of workers, etc.

(On farms, there’s an opposite force at work. Farming itself is highly cyclical (not much to do in winter, relatively), so maintenance was done cyclically, too)

>The amount of work that goes into maintaining a yacht far exceeds the financing available to public infrastructure

I don't know about your jurisdiction but every bridge in my area gets inspected by qualified bridge inspector at least every 3 years, and if there are potential issues more often.

>Of course, bridges are not normally sitting in salt water

Again, not sure about your jurisdiction, but many jurisdictions use chlorides for winter ice melting.

> The white boats and yachts that you see are typically glass-fiber-reinforced epoxy, and they seem to be holding up just fine.

They really don't hold up at all. FRP degrades rapidly when exposed to UV light, and boats not only are not subjected continuously to high loads but they are also not subjected to vandalism.

Let's put it this way: wheelie bins are FRP.

Serious question - do you really think the team of engineers who designed these bridges aren't aware of the existence of solar radiation or climate on planet earth?

Counter question - do you think the team of engineers would scrap their whole, hard-earned design because e.g. they found out that after 20 years it would stain to an ugly yellowish hue in sunlight?

Oooh, they are aware. Keep in mind that Boeing's also was aware about possible issues with the MCAS in the 737 MAX and it went flying (and crashing) anyway.

The list of things that have failed due to "solar radiation or climate" includes many structures designed by engineers.

Many UV resistant plastics will go after 20 years

It will get painted. FRP is a very common structural material, been in use for decades. It’s more expensive and tough to work with, but a great solution for difficult scenarios, like when fitting around odd shapes or when weight is a major concern. We use FRP regularly for seismic bracing of existing structures, for example, wrap an old concrete column with FRP so it will better survive an earthquake. In this case, I imagine the appeal is the extreme light weight simplifying foundation work. Pay a lot more for FRP, pay a lot less for everything else. That’s usually how we end up installing FRP.

Probably better for weather resistance too?

These bridges will be in use for decades, if not centuries.

Possibly less of an issue than elsewhere as they are for the UK.

because of lack of sunlight or because of lack of care about how public infrastructure looks?

As someone living in UK, I can confirm that UK lacks both.

If anything the layers of graffiti will protect it from UV damage.

Paint works pretty well on plastic, like it does for other bridge materials.

In my experience it has relatively poor adhesion and flakes easily.

Sounds like you're using the wrong kinds of paint then. Though I'll grant that plastic is pickier about this than a random slab of steel or concrete.