Grizz..
Unfortunately, the misconception that bigger is better is not always true especially in the world of cement moorings. A cement mooring, on average, can weigh as much as 50% less underwater! Most mooring experts, municipalities and insurance companies agree and it's recommended that the weights indicated, for holding a specific sized vessel, be calculated on the SUBMERGED weight of the "dead-weight" anchor. Use the following table, as a guideline, to calculate required weight of material submerged. Unfortunately many harbor masters & municipalities don't know squat about moorings!! Minimum dead-weight mooring weight: Vessel length: 10 - 17 1000 lbs. Concrete = 1818lbs. Granite = 1562lbs. 18 - 26 1500 lbs. Concrete = 2727lbs. Granite = 2343lbs. 27 - 35 3000 lbs. Concrete = 5454lbs. Granite = 4687lbs. 36 - 45 4000 lbs. Concrete = 7272lbs. Granite = 6250lbs. 45 - 55 5000 lbs. Concrete = 9090lbs. Granite = 7812lbs. 56 - 65 6000 Submerged Weight Calculations Concrete = required weight /.55 (example 1000 lbs./.55 = 1818 lbs.) Granite = required weight /.64 (example 1000 lbs./.64 = 1562 lbs.) A properly sized cement mooring for a 70 footer would weigh in the vicinity of 12,700 lbs. out of the water!!!!! That's more than the weigh of FOUR 2008 Honda Civics by about a thousand pounds!!! I seriously doubt you have a cement mooring that even comes close to design spec to hold even a 35 footer let alone a 70 footer. Again many harbor masters are quite clueless about proper mooring design. Mushrooms, Pyramids, Screws and very large oddly shaped pancake like granite slabs are used with much more reliability than cement boxes because a proper mooring is NOT designed to sit on the bottom but rather it is designed to set, over time, into the bottom. Square cement boxes do this with far less reliability than do the other choices of moorings. Our last mushroom was so buried that the chain made a funnel cone in the mud where it was swiveling around the eye almost two feet down. they had to pull my mooring to inspect it because the diver could not reach the eye to inspect it. It literally stood the barge on end, at times, and took over 5 hours of the crane & displacement of the barge on an in-coming tide to break it free. My bill for inspection had an additional 5 hours of barge rental $$$$ because the crane alone could not break the anchor out of the bottom! The shank on my mushroom is almost four feet long so that means the head of the mushroom was buried over six feet into the mud! The vacuum pressure alone needed to pull that mushroom out is astronomical... A "box" design is perhaps the worst design for a mooring because it is easily toppled. Let's asy the box is tree feet tall and it settles into the bottom six inches. in a blow it will simply tip over and have ZERO set. Once it has zero set it will simply drag across the bottom. A properly designed "dead-weigh" mooring may only be 6" inches to 14" inches thick but may be 6' feet to 12' feet or more in diameter. With this design the mooring does not tip and as pressure is exerted at one angle it digs that side into the bottom. As the boat shifts and another front moves in from another direction the mooring is pulled deeper from another angle until the entire 6" to 14" inches is buried into the bottom unless of course you are in a solid bottom in which case sheer weight and surface area, again "pancake" are more important. Many towns, that actually have a clue, no longer even allow dead-weight moorings or require special permission and approval of the shape size and weight. Here's the Falmouth, MA policy "Approved Anchor Types Mushroom, Dor-Mor, Seaboard Short Shank, Helix. All other types require a special waiver by the Harbor Master in advance of them being set in the water." "Norwalk, CT Only allows the use of mushroom anchors and sets minimum size requirements by boat length." "Mashpee, MA Mooring Specifications – Minimum Requirements Allowed mooring anchors: Steel (or cast iron) mushroom, DOR MOR, Helical Screw Not Allowed mooring anchors: Cement block, granite block, radiators, engine blocks, etc."
and afterwards asked harbormaster "why no phone call". "Oh we called, there was no answer". Yeah, right. Harbormaster set a new block, one that's meant for a 70 footer with the statement "if this one moves, I'm retiring". So far, so good. 2 similar storms afterwards and no apparent movement.