A magical sailboat
 

The concept is simple: a watercraft that moves on its own. But I’m not sure how to do it. What spells would be enchanted into it if it’s a canoe? What if it’s a sailboat? How does size affect energy required, if at all?

Re: A magical sailboat
 

What magic system are you using? Is this an item the players will take a part in crafting? If it's purely a GM creation, you can make it however you like, no worries.

Re: A magical sailboat
 

Ritual magic, the creation will be at least partly “on screen.”

Re: A magical sailboat
 

Um, which "Ritual Magic"? If you mean "Ritual Path Magic" somebody else may come along but if you mean the "Ritual Magic" in the little text box in Characters that uses the Spells from Gurps Magic and your answer is easy.

For a canoe you want Current from p.194 of Magic and 300 energy to Enchant. For a Sailboat, Current would still work and/or you use Wind from p.195. Also 300 energy.

If you were to add Power to the Enchantments one Power Enchantment (500 energy) would give you 1 FP's worth for both Current and Wind at the same time.

Re: A magical sailboat
 

For a canoe, you could also enchant the oars with Dancing Object and possibly Password. A crewman would be needed to man a steering oar or tiller, but the oars could propel the craft.

A sailboat with a perpetual Wind spell (which isn't book legal since a ship is not a "staff, wand, or jewelry") would still need a crew to handle the sails and man the tiller.

Alternately, I don't believe there's a specific requirement in the Golem spell that the golem be shaped like a human. If you accept that golems can come in other forms, and those other forms can be ships, than you would be able to create a ship-golem that can crew itself. You would still need a Wind spell for a self-moving sailboat-golem, but then the jewelry requirement for the magic item is a lot easier to satisfy - put a necklace or tiara on the ship's figurehead. Assuming that golems can use magic items, which honestly I do not know if that is true.

Re: A magical sailboat
 

Listed Items are suggestions rather than legal restrictions. The GM can make the form of the Item anything he wants.

As for the boat/ship Golem that way lies Madness. :)

Seriously, the Golem Spell costings applied to things other than simple Attribute boosts are very very broken.

Re: A magical sailboat
 

The one on page 200 of Magic 4e. As for the rest of the post, thank you for the suggestions.

Re: A magical sailboat
 

Current does the trick.

Now being able to actively navigate it, that's another matter.

Re: A magical sailboat
 

Essential Wood: improve strength and durability

Lighten, if you're willing to extend that from just armor and shields. Every pound the craft is lightened is another pound of potential payload. Also helps greatly with portaging a canoe or beaching a small boat.
Lighten Burden: lighten the payload itself

Find Direction, Tell Position, Tell Time: Navigation. Not necessarily to enchant the entire craft, but a high-magic society might well enchanted part of it, analogous to a compass binnacle.

Test Load, Measurement: The cargomaster would find a tool that supplies these to be useful.

Divination: Weather, of course, but there never was a merchant that wouldn't have wanted to be able to predict prices and availability of goods. Maybe that lucky eye on the bow sees more than we thought...

Weather: lots of useful spells, especially if you allow "portable" area spells for vehicles