[Hermann the Cherusker]

The largest wooden ships ever built were around 300ft long, but these weren't really wooden ships, they were heavily braced internally with steel beams.

The largest purely wooden ships of conventional multi-decked design like the ark (as opposed to rafts)

Who said it was a wooden ship? And how do you know what its design was to say it was not a raft? Do you have the plans that God gave to Noah?

You seem obsessed with the vision of the Ark as a big wood box like shown in children's books, or perhaps as something like the last modern wood sailing ships.

It makes far more sense to see the Ark as a large version of something like the earliest ships in recorded civilization (if the flood were true, wouldn't Naval Architecture derive from the Ark, rather than attempting to extrapolate the Ark out of the final stage of Naval Architecture circa 1900?) - rafts made of reeds, logs, or similar, with a wooden superstructure on top, and guided and stabilized by drogue stones underneath and sails on a main mast. The wooden superstructure would then be relatively open like a large wooden building, since it would not be the primary load bearing source of bouyancy.

The decks are an important part of the structural strength of boats like this, and contrary to Hermann's ideas of decks the height of railroad stock cars they would typically be less than 6 feet tall to act as cross-bracing.

Well, the Bible speaks of 3 decks in the Ark, and the Ark being 30 cubits tall, so that would be 15+ ft. per deck, which is the height of an AAR Plate F rail car.

They wouldn't be cross bracing, because the Ark would be a superstructure on top of a large ocean-going wooden raft like this - a log raft form used in coast-wise movement of logs from the Pacific NW to southern California on the Pacfici Ocean:

Note the men to help you determine the scale of this wood vessel.

There is nothing "impractical" about constructing a very large ocean-going wood/reed raft (especially one covered in pitch to help with seaworthiness) upon which to build the ark.

gather a representative portion of the world's species on it (lets say 10%, again they can have help for that part

Again, there are relatively few species that would need to go on the Ark - a couple tens of thousands. You don't need to bring fish, whales, waterfowl, plants, fungi etc.

[Thatcherite]

Who said it was a wooden ship?

The bible. When you are advocating this stuff, you ought to make sure you are clear about what it says.

And how do you know what its design was to say it was not a raft? Do you have the plans that God gave to Noah?

No, but the biblical description is pretty clear. It sure doesn't sound like a raft to me, it sounds like a boat.

You seem obsessed with the vision of the Ark as a big wood box like shown in children's books, or perhaps as something like the last modern wood sailing ships.

That is because a wooden raft with a 45 foot wooden building sitting on it is not a seagoing vessel. I doubt that you could even build such a thing on a calm lake. They just don't work. A raft anything like that size would fall to pieces in a light swell. And Archimedes (Arkimedes :)) )needs air to displace the water to support a structure that size, or your base will just sink. Wood's relative density is too great, typically about 0.75 even when seasoned and dry, so you end up with an iceberg like situation unless you enclose air with a boat.

[Thatcherite]

Again, there are relatively few species that would need to go on the Ark - a couple tens of thousands. You don't need to bring fish, whales, waterfowl, plants, fungi etc.

Most waterfowl are not adapted for an ocean existence, and most birds (even those that are adapted for ocean life) would not tolerate being unable to land on dry land for a year. Freshwater fish would certainly need to be accomodated, as I've already pointed out. There are millions of insect species. All needing to eat and rest (and breed in many cases, since they don't live for a year) and all needing the predators to be kept away from the prey. Some of the birds and bats require insects to be present in giant numbers for food.

[Thatcherite]

Incidentally, take a more careful look at your "wooden raft" photograph.

It isn't really a wooden raft at all of the type that a bronze-age culture could build. All of its strength and all of its cohesion derives from the iron chains in tension holding the logs together. So this design only works with a round shape like that, with most of the logs under the surface. Even so, if you took that raft into the open ocean it wouldn't hold together for a day. The logs would shift, a chain would burst, end of raft.