New Marina Anchoring System 

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Written by Judy

On September 16, 2022

9/15/22

Issue:

Repeated breaks to the marina have continued every year.  This year, a storm with high winds caused most of the welds that held the marina gangways and anchors holding the marina to the lakebed to break.

Background:

In 2021, Lake Committee proposed moving the two docks that were perpendicular to the shoreline into a parallel to the shoreline configuration in the hopes that this would reduce direct exposure to high winds and protect the docks from breakage.  As part of the new configuration, completed in November 2021, new lengthier ramps were built which were fixed by aluminum welds to the docks and to the concrete on shore. The new parallel docks anchoring system consisted of vertical pipes welded onto the ends of the docks and 4-6 half barrels of concrete anchors tied by cables for each dock.  Concrete loses a third of its weight once in the water.  Barrels of concrete can slide or roll around the lakebed during a storm, especially on the steep slope which exists beneath the docks. A helical anchoring system was proposed to Lake Committee but deemed to be too expensive at the time to pursue.

A high wind event this summer caused the concrete anchors to move and almost all of the welds to break that held the pipes and the ramps on Docks A & B.  This led to evacuation of all member’s boats and reimbursement of the season’s slip fees.

The Board held a meeting and decided rather than another quick fix, the problem needed to be researched and analyzed and a more permanent solution recommended. They approved funds to be spent for engineering.  A working group was formed including two engineers, Steve Herring and Jim Pagenkopf, from Lake Committee.

Multiple engineering firms and marine contractors were contacted.  Waterfront Contracting (Helix anchors), Delta Marine (steel piles), Melka Marine (wood piles), AJ Marine (concrete anchors), Collins Engineering (marina design), Hazelett Marine (elastic connectors for dock anchors) all made site visits. There were lengthy phone calls with SoFlo Divers and BZ Divers (platipus anchors). Many others were contacted and never responded.

Several discoveries and conclusions were reached by the working group:

  1. All contractors specialize in a particular anchoring system and have less or no experience or knowledge with other anchors.
  • Anchoring options could be wood or steel pilings, massive poured concrete anchors or driven metal anchors.  All options would involve using a barge, specialized equipment on the barge and divers.
  • All contractors work with their chosen engineers that are also familiar with calculating the forces for the particular anchoring systems the contractor works with.
  • All contractors require an engineered design prior to actually performing the work.  They claim that test placement of anchors would be necessary as well.  Platipus (SoFlo and BZ from FL) will not do a test anchor until they have an engineer determine what size would be required.  Some would charge for the test since it would require mobilization of the equipment they use and traveling a long distance. (One of the piling contractors said cost would be $10k.) We have also been unable to get any definitive timelines from engineering design firms (Collins, AJ Marine) as to when they could do the design work (and when it would be finished).
  • It is also extremely difficult to find an engineering firm experienced in designing small lake marinas and interested in working in our geographic area.  Collins Engineering of Fairfax is the only one reasonably located that has designed marinas and has expressed interest.  They did a site visit and provided us an estimate for their services: full design with CAD drawings for $40k and quality control review of contractor design with diving for $26k.
  • All the contractors were concerned about our hard fractured shale lake bed and where impenetrable bedrock began.  Most of the contractors were used to working in soft soils, mud, sand.  They were reluctant to recommend any solution until they had some geotechnical information.
  • The conclusion of all the contractors was that the aluminum welds were not the main problem.  It was problematic that certain welds were installed onsite leading to a less than full thickness weld, however, the lack of a sufficiently strong and flexible anchoring system was the major issue.  Welds broke due to torque of inflexible dock pieces during high winds.  The barrel concrete anchors slid down slope and cable attachments holding them broke.  Gangways attached at both ends by welds allowed no flexibility for movement while the docks were twisting.
  • All contractors believed the ramps should not be fixed at both ends with floating docks.  They can remain permanently attached at shore but should be on rollers over the docks with side guards.

LHCC hired Triad Engineering (Winchester) who came and did sediment (geotechnical) cores at the marina.  One went down 17 ft, the other 13ft.  Both cores then hit refusal.  Soil samples were taken along the drill routes.   Final report: very dense weathered shale encountered at about 5 ft. They recommend that anchor foundations bear on or in weathered shale with maximum allowable bearing pressure of 10kips per sq ft be adopted.

Types of Anchors:

Pilings: would work but would be extremely expensive (one contractor estimated $1million).  Holes would need to be predrilled in hard fractured shale to accept steel or wood pilings.  Piling contractors would require performing a test drill on site and would charge about $10,000 for that. Wooden pilings are used primarily in sandy, muddy, soft soil where they can be driven much further down.  Pilings are also preferred for floating docks where the water depth changes frequently. 

Poured Concrete: concrete would be poured into forms on a large construction barge and dropped into place. The barge and equipment would be brought into the water from the dam because the boat ramp would not be large enough. Steel cables would be used to attach the dock system to the anchors.  A qualified engineer would need to perform the calculations to come up with the correct number and sizing of the anchors and placement.  There continue to be concerns about concrete anchors slipping on the highly sloped lake bed with high winds still moving them.  Any concrete anchors would need to be attached to shoreline with driven anchors. 

Driven Metal Anchors: there are a variety of these anchors including Platipus, Manta Ray and Helix.  The Platipus and Manta Ray go into the lakebed and then expand out arms to hold them in place.  The anchor itself is not that expensive but the main cost is in the specialized labor and equipment.  The contractors that are familiar with using these anchors are all located in Florida.  There are no engineers or contractors familiar with these anchors in the mid-Atlantic region.  The contractors expressed concern they would not work well in the fractured shale. A test anchor would be required. An engineered design would also be required for size and placement of anchors.

Helix anchors come in different sizes and lengths and are screw-like.  They are made of solid steel and hot dipped galvanized coating.  They provide maximum stability even in variable and high wind conditions.  Their holding strength is far superior to mushroom or concrete block anchors.  Unlike a concrete block or mushroom anchor, the helix anchor is unaffected by a sloped bottom and will not drag under heavy wind gusts. A specialized hydraulic torque motor using drive tools to reach the bottom on a small barge is used to screw in the anchors.  Flexible, elastic connectors are the preferred method of attaching the anchors to the docks rather than using cable or chain. The elastic connectors provide stability, constant tension under high or gusty wind conditions, and will extend the design life of the floating dock structure by reducing stress. The elastic connectors can repeatedly elongate over 200% and return to original length. The helix anchors are placed one on each side of the main body of the floating dock about every 40 feet, with crisscrossed connectors.  The anchors are placed several feet out beyond the dock itself.  One helix anchor will handle 10,000 lbs. of force.

Hazelett Marine manufactures the elastic connectors and has an inhouse engineering design group who calculate the forces involved and determine how many anchors/connectors are required, the placement and sizing.  Installation of the helix anchors (by Waterfront Contracting) would require a month of work onsite. 

There were two site visits from Waterfront Contracting who provides and installs the helix anchors.  The second visit included the engineer/sales representative from Hazelett Marine who manufactures and provides the elastic connectors.  Two test helical anchors were driven successfully at the marina.

Hazelett has a two (2) year warranty on all the underwater parts they manufacture including the elastic connectors.  The helix anchors have a one (1) year warranty on workmanship and materials.  Waterfront Contracting has a one (1) year warranty on labor.

Lakeside Docks has agreed to return by the end of September and install new roller plates with rollers and floats on all three gangways.  The gangways will sit on top of the plates with rollers.

Recommendation:

Based on the above information the working group recommends proceeding with Hazelett Marine and Waterfront Contracting.  Hazelett will provide us with the elastic connectors and other parts for the lines, engineering, design guide, custom install guide, as built install report, PE stamp of the layout design.  Installation and helix anchors will be provided by Waterfront Contracting.

There will be 52 helix anchors and an equal number of lines and connectors.

The overall negotiated price (valid for a September 15 decision by Lake Holiday as well as a fall 2022 installation) is $280,000.

Lakeside Docks price for their additional work, with a discount included, is $20,750.

Marina Working Group (Pat Majewski, Steve Herring, Jim Pagenkopf, Mike Goodwin)

September 15, 2022

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