Fred- Sounds like your clutch is slipping. Most of these windlasses are similarly built, with a conical clutch between the gypsy and the vertical drive shaft. A star-like depressed wrench opening in the top of the windlass receives a handle that acts to tighten the clutch when turned one way, and serve as a free-fall disengage mechanism when turned the other. Did your Spring 400 come with such a handle? Does the owner's manual include a section on adjusting the clutch?
If the problem persists, the Simpson-Lawrence distributor in the U.S. has a very helpful tech representative on line. Look up their website and contact them. I personally think it's better to talk over the phone (vs email) to save time, since the question-answer problem solving format works faster in that medium.
I had somewhat the same problem with my Quick Aires 500 in that the anchor would bounce around on both on the road or when in chop, and start to pay out a little and droop and begin to bang up and down and then have to be tightened up with the motor. A reasonably hard crank with the handle tightened up the clutch and eliminated the slipping. There's probably an appropriate limit to the amount of tightness, however, in order to protect the motor. See what the manual and/or the tech suppport says about this.
Hope this gets you on the right track. Joe