The interfacing I have is the iron-on variety and I don't think it is as thick or as stiff as the non iron-on, but becomes thicker and firmer when ironed. Using the four layers of the weight I had made it almost identical to the original sales.

a close up of both types of material ...

The sails were very easy to make - I used a leather punch for the holes and a craft knife for the little slits at the bottom of the sales.
Here is the completed ship - unfortunately I didn't realise that this ship was missing 2 long grey spars, so had to use tan coloured ones - I do think it would have looked better with grey.
I cut the pattern for the sails from the schooner sails as they didn't have pieces cut out of them. I did wonder if I should have cut the main sail a bit shorter because it slightly covers the lantern (Gordon will be telling me off - saying it's a fire hazard

)

I did experiment with a silver pen on a spare piece of material and found that I could have put some sort of markings on the sails, but decided to leave them for now.
All in all I was quite pleased with how they turned out.
We took it out on the beach for a sail this evening so I'll post some photos of that in the Photography section.
Elaine