I have been stitching pleats, up to now, rather than seams, as I haven't been able to get my head round how they might be waterproof.
I also was having a hard time working out how to do the overcasting stitch which I learned about in my research, shown in the photo below. So, I did a few more pleats and stitched them together and then got a better idea of how to do a seam. Also, I finally worked out the overcast. (I should have flipped the image - I normally work right to left, and I think this is where I was struggling.)
I used red linen to reference the touches of red that were often used as decorative tufts. I am going to do some overcasting on some other seams with a woad dyed linen. (Not that they had linen or woad, it is just one of the other colours I have seen used for tufts.) The tufts also helped with shedding water, as they wicked the sea water or rain away.
Holding the pleats in place.So, now I have pleated the edges of two of my previous pieces that have pleats sewn with running stitch, and I think I finally have a plan.
In all of the pleats I sewed so far, I have encase a length of twine, mimicking the concept of the grass stems within the seam. As I understand, this would soak up any water getting into the seam and the beach grass would swell up and thus keep any further water from getting through to the inside.
If I can get the proper seam to work, I will see if I can encase a length of twine or some other thread.
with a possible thread to be encased.And so, I managed to get something done today after all.
*(one of the benefits of doing something strange is that you get distracted from aches and pains!)