Has anyone heard of farm designs that can operate at depths greater than 200-300ft? There are rodes that can accommodate this but possibly there’s a better system all together?
For the sake of carbon pulldown and farm expansion, it would be ideal if we could utilize water further offshore.
@ian_mcfarland - Hi Ian, to my knowledge, there are multiple scientific groups working on answering this question, and designing systems for deep water farms. Some operations that might be of interest that are investigating deep water systems for seaweed cultivation are: Ocean Era in Hawaii, SINTEF in Norway, and Umaro Foods (formerly Trophic) in Maine.
@clifford_goudey do you have any insight into what the science is saying on the practical realities of cultivating kelp at over 300 feet of depth?
Lindsay & Ian,
Anchoring in deep water is of course possible, the USCG, NOS, WHOI and others do is all the time but almost exclusively using a single-point mooring and often with subsurface flotation to keep the line close to vertical. To provide the necessary pretension for seaweed growlines, a second mooring would be needed and scope would have to be introduced to provide the needed horizontal force. That's when it becomes expensive. In, say, 500' a 3:1 scope would call for 1,500' of mooring line, Maybe more important than the cost of the line is compensating for the vertical component of tension in that line. A good-sized farm can produce 1,000s of pound of drag due to currents and waves. That would call for a sizable float at the top of each mooring line, otherwise those loads could pull down the whole farm. Equally troublesome are the consequences on the anchor. That upward tension would require a heavier dead-weight anchor or a lot of chain in front of a drag-embedment anchor to keep its pull horizontal.
If everything else is equal, this all means is the economics favor a shallower site where more can be
invested in the farm and less in the mooring lines.
But believe me I understand the motivation - lots of room, fewer conflicts, more stable temps, etc. That was my motivation when I explored the same question a few years back. With funding from NOAA SBIR, we tank tested a structural framework that would be able to swing on a single-point mooring. This is the sixth-scale model we tested, all loaded with simulated kelp.
It worked great in the tank and probably could have worked in real life but who can afford it? What we ended up doing was forgoing the super-long longitudinals trusses and tested a rig with a pair of the transverse truss frames. that would be moored between a pair of opposing anchors.
Here is a photo during deployment in Woods Hole. Each truss was 33m (108') long, a 4'-square welded steel truss supported at each end by a pair of commercially available buoys.
The results, you ask? A miserable failure when the buoys self-destructed under the wave conditions experienced at the site in the middle of Nantucket sound. A lot was learned and the system was later successfully re-deployed using proper cylindrical spar buoys and was in service for several years as a WHOI research farm. I'd be happy to share more details is anyone curious.
Cliff
@lindsay_olsen - Thanks for pulling those links together Lindsay! I’ll check out these projects this weekend
@clifford_goudey - Wow! Were you able to recover the truss frames?
Single point mooring is intriguing but it sounds like we’d have to scrap the U.S. Mexico border wall to make it. It’s a relief to know the two anchor system is an option. Anything in particular stalling efforts from implementing these globally? Thank you so much for your research and reply.
@lindsay_olsen -Got sunlight?
Lindsay & Ian,
Anchoring in deep water is of course possible, the USCG, NOS, WHOI and others do is all the time but almost exclusively using a single-point mooring and often with subsurface flotation to keep the line close to vertical. To provide the necessary pretension for seaweed growlines, a second mooring would be needed and scope would have to be introduced to provide the needed horizontal force. That's when it becomes expensive. In, say, 500' a 3:1 scope would call for 1,500' of mooring line, Maybe more important than the cost of the line is compensating for the vertical component of tension in that line. A good-sized farm can produce 1,000s of pound of drag due to currents and waves. That would call for a sizable float at the top of each mooring line, otherwise those loads could pull down the whole farm. Equally troublesome are the consequences on the anchor. That upward tension would require a heavier dead-weight anchor or a lot of chain in front of a drag-embedment anchor to keep its pull horizontal.
If everything else is equal, this all means is the economics favor a shallower site where more can be
invested in the farm and less in the mooring lines.
But believe me I understand the motivation - lots of room, fewer conflicts, more stable temps, etc. That was my motivation when I explored the same question a few years back. With funding from NOAA SBIR, we tank tested a structural framework that would be able to swing on a single-point mooring. This is the sixth-scale model we tested, all loaded with simulated kelp.
It worked great in the tank and probably could have worked in real life but who can afford it? What we ended up doing was forgoing the super-long longitudinals trusses and tested a rig with a pair of the transverse truss frames. that would be moored between a pair of opposing anchors.
Here is a photo during deployment in Woods Hole. Each truss was 33m (108') long, a 4'-square welded steel truss supported at each end by a pair of commercially available buoys.
The results, you ask? A miserable failure when the buoys self-destructed under the wave conditions experienced at the site in the middle of Nantucket sound. A lot was learned and the system was later successfully re-deployed using proper cylindrical spar buoys and was in service for several years as a WHOI research farm. I'd be happy to share more details is anyone curious.
Cliff
@lindsay_olsen - Thanks for pulling those links together Lindsay! I’ll check out these projects this weekend
@clifford_goudey - Wow! Were you able to recover the truss frames?
Single point mooring is intriguing but it sounds like we’d have to scrap the U.S. Mexico border wall to make it. It’s a relief to know the two anchor system is an option. Anything in particular stalling efforts from implementing these globally? Thank you so much for your research and reply.
@lindsay_olsen -Got sunlight?