Installation/Engineering Costs for Submersible Power Cable

[dhwebb67]

I am trying to make a ballpark cost estimate for a project to design and install approximately 4,000' of submersible power cable with a design voltage of 7.2 kW. Cable will be layed in/on an old submerged roadbed to the island in question with average water depth of 4'. Are their rule-o-thumb unit costs for this type of construction? And what % would be reasonable to use to apply to an estimated construction cost to estimate design engineering.

 

[itsmoked]

7.2kW cable?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Electic]

There is no rule of thumb for a submarine cable, and indeed most such projects are highly specialized.

On the other hand, call up your cable supplier and ask if he will guarantee the cable for such installation and let er rip!

 

[dhwebb67]

To clarify, 7.2 kV cable.

 

[Jebb]

It sounds like this is a very specialized installation where traditional submarine cable installation can't be used because of the water depth. If this is a land locked installation (lake or quarry) transportation of the submarine cable from the factory to the installation site will also become a big issue. It's possible that the installation cost alone may be more that 50% of the project.
I would recommend talking to a cable installer or manufacturer to get pricing.

 

[racookpe1978]

Or, then again, at only 4 foot (1 meter +/-) of submerged depth, transporting 4000 ft of cable to the job site and getting it laid out through 4000 feet of mud and shallow water from end to end might certainly be the hardest part. How much of it is "on-shore" or "on-platform" at each end?

How will you deploy it from the reels? How will you get the reels and the tooling (to either end) to deploy?

How will you propose splicing it at each joint? 4000 feet of 7.2 kilovolt-capable of submerged cable (three conductor ?) does not come on one reel.

 

[dhwebb67]

racookepe;

All great questions. On the island end, power pole to tie to is approximately 100' on shore. On mainland end, we would be working from a parking lot so should have a significant staging area. I would envision that reels/tooling that would be transported to the island would be via boat/barge. I am not familiar enough with this kind of construction to answer the splicing question.

Basically, I am looking for a ballpark electrical engineering design cost to assign to the RFP, and thought the best way was to gauge construction cost and apply a percentage.

Any help you could provide would be appreciated.

 

[itsmoked]

Sounds easy to me. Isn't most direct burial HV cable waterproof to more than this measly depth? How could it not be! This doesn't require "submarine cable" good to hundreds or thousands of feet! So just standard HV buried cable with standard waterproof splices. For an estimate I'd use the regular underground price and double it for the water hassle. Any chance you can just lay big flooded PVC conduit on the bottom and pull the cable thru it instead of burying it? That would give it secondary protection without the burial hassle.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Jebb]

After some quick back of envelope calculations, 4000ft of 3-core 12kV class 2/0 submarine cable would be about 20 tons on a drum. Depending on the cable bending radius it's possible to put 4000 ft on a ST32 (drum size) drum so it may be a simple install by floating in the cable from the land. I would still contact a submarine cable installation contractor as there is a lot of specialized equipment needed. This isn't a job for a guy with boat and some floating buoys...

It's probably not good engineering practice to use "standard HV cable" for a marine application. I'm pretty sure your company would not be happy with the impending lawsuit when something goes wrong in the future.

 

[racookpe1978]

Well, yeah.

But then you have the old "standard" HV cable already laid out from end to end, with a good place on shore for tooling. You then use the old HV cable to pull the new water-rated cable back out the island. /sarcasm

( By the way 1, find out if the installation is near the ocean shore, or across salt water with tides, high winds and storms possible (???) or across a simple fresh water lake with static water (????) or across a river with widely varying currents and flows?

( By the way 2: To get an estimate, CALL PEOPLE in the industry.
"Hi (fill in name of cable company provider), you don't know me, but I'm setting up a bid for a high volt, 4000 foot submerged cable approximately 4 feet in depth from shore to an island. I'd like to talk with a sales representative about potential ways of doing this, and to get any recommendations your engineering and specifications staff can provide about this kind of cable. "