Storm wood is a tree that can only grow on exposed mountain ridges. It survives by using an innate wind control ability that is prized in any wood product even vaguely related to flight. It can only be cultivated by dragging huge quantities of fertilizer up thousand foot cliffs, and then casting Plant Growth. Otherwise, the wood is hopelessly warped and useless. A storm wood arrow, even without an enchantment, carries 25% to 50% farther than normal arrows. Unfortunately, it costs about 10 gp for enough an arrow shaft.
Storm wood reacts beneficially to any flight related spell cast upon it. Such spells affect ten times the mass of storm wood than the spell description, with increased duration as well. This includes spells like Feather Fall, Unseen Servat, Levitate, Flight, Gust of Wind etc... If you could actually get enough storm wood to make a spelljammer ship out of, it could almost fly without a helm.
In my campaign universe there was a huge magical civil war about 500 years ago that left many area blighted by warped magical energies. Some magical plants and animals evolved as a result of them, and some are 'natural', having an evolved ability to work certain magic. My premise is that if magic is possibl in the universe, it is possible for living things to, by accident, develop some magical ability.
In the case of Storm wood, a magical ability to withstand tremendous wind forces created a dependance on that wind, and the tree will not develop the magical ability without it. Using the magic has a high biological cost, or rather, imbuing that magic into the wood since it lasts until the sap totally dries up.
The only way to get large quantities of Storm wood in usable form with denuding the ridge is to use magic.
I haven't designed a Storm Wood ship, but it might take less magic than a helm to power it. For example, because it is so receptive to wind magic, someone with a Ring of Air Elemental command using the Gust of Wind power every round would be sufficient to power a small ship, providing something else was providing lift.
A ship made from Storm Wood would likely be more expensive than the magical power source. However, the mass of the hull itself wouldn't count against the mass limit of the helm, enabling much larger ships. Well, it would count a little, but not much.
Flying the ship without a helm would likely be impossible, but landing it would be doable because the lifting magic could be enchanted into the very hull itself. A 10th level mage casting Feather Fall could slow ten tons of Storm Wood.
A Storm Wood ship would also get a lot more benefit out of rigging than some ships. The down side is the difficulty in obtaining spare timbers to fix the inevitable battle damage. It would get a lot more cargo capacity compared to the hull mass enabling a host of designs.
