No experience with Bluewater ropes. Importent note on super thin ropes; check if you gear will work with 7.7mm rope!
If you set it up primairly for crevasse safety/rescue (Hauling people out of crevasses or ascending the rope to crawl out of a crevasse), 5mm (the thinnest prussik size) or 6mm prussiks will not bite well and thus slip. Especially on newer slick and/or ropes with some coating on it.
So the lighter weightness of the rope might be lost with replacing prussics with teethed devices like ascenders/progress capture pulleys. I personally do not know any ascenders or progress capture pulleys which will accept rope under 8mm. So pay attention to that.
Ofcorse teethed devices might be needed if you plan on going somewhere in certain conditions where you rope might ice up.
My personal opinion: take relatively thick threated (waterrepellant, so it wont sock up water and become heavy) rope (9.8 to 10.2mm), which means it will be compatible with prussiks and pretty much all ascenders/progress capture pulleys. Logistic wise much easier and people in your rope group do not need to buy new gear to be compatible with thinner ropes. Everybody in the group should have rescue gear on them. I manage to find crevasses front, middle and back positions on rope groups. Having prussics means weight and money saved on teethed gear. Weight savings on thinner rope in that lenght with the logistic issues might not be lighter.
I have used new 7.8mm double rope for multipitching and it's scary thin and belay/rappelling is hard.
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