Thinking of hiring a dredge contractor? Think again…


By Ryan Horton

The importance of dredging one’s marina is an old and familiar topic. However, in today’s business environment, it’s not a topic many marina owners and operators spend much time thinking about because they typically have pat answers for hiring a contractor and not buying a dredge.

Because dredging is a costly undertaking, it’s worthwhile to scrutinize some of the common objections marinas have to making a dredge purchase before discussing the various types available.

Too much money

Most of the time, marinas hire a contractor believing that buying a dredge costs too much money. It’s only later that they learn it would have been cheaper to buy a dredge.

The biggest mistake a marina can make is to hire a contractor to clean the marina out, without realizing that the marina needs to do dredging every couple of years. Halfway through the second round of dredging, the marina could have purchased its own dredge.

This is not to suggest, however, that there isn’t a lot of good marina dredging contractors out there, for surely there are plenty of them. But hiring a contractor is only advisable for marinas that need to dredge once every 5-10 years.

Even when hiring a contractor, marinas should never hire a dredge contractor that uses a cable-driven dredge. The reason? Cables result in longer-than-necessary dredging, is more costly to the marina, and also means that parts or most of the marina will need to be shut down if cables are rigged near main channels. Think of it like this: A homeowner doesn’t hire a painter to paint his or her house with a toothbrush, so marinas should not hire someone with equipment that isn’t made for the job.

Environmental regulations

Although many marinas understand the importance of being environmentally friendly when it comes to dredging, they are also aware of the need for profits. These two goals can sometimes be at odds with each other, especially when it comes to dredging. Three years ago, more than half of the marinas surveyed by Mt. Pleasant, S.C.-based Applied Technology & Management Inc. said that dredging regulations were the hardest to comply with.

If a marina has contaminated sediment or protected fish or plants, then hiring a contractor who knows what he is doing is probably the better option. Of course, the marina must be sure that the hire is a seasoned, environmental contractor who knows the regulations and consequences of not following them.

Dredging, or digging under water, can leave a marina with nowhere to put the material that’s dug up. In such cases, a marina may hire a contractor to come in and deal with the task of removing the dredged material. Usually the contractor will haul it away in trucks—which can be quite expensive. There are good alternatives to trucking, however.

Interested marinas should look at geotextile containers and mechanical dewatering systems as good ways to overcome the problem of collected sediment. Geotubing is a process whereby sludge gets pumped into a large bag made of a specialized geosynthetic fabric. The fabric is porous enough to allow the water to run through, but it traps the solids, compacting them and making their removal and disposal much easier. It’s generally considered an environmentally friendly and cost-effective marine application.

The cost

Prices on dredges vary depending on the dredging activity. Common factors that increase the price of the dredge are digging depth, pumping distance, elevation from water level, along with discharge, and compaction of the material. It is not unusual for a marina to buy a self-propelled dredge, which is one that does not require anchor cables to propel the dredge. Instead the dredge uses a Starwheel Drive system or propeller to move it forward.

The advantage of a Starwheel Drive system is that allows the operator to paddle the dredge into position and create enough thrust to cut into the material. When the material is hard, the dredge can lower the wheels and literally walk the dredge forward in positive traction drive mode. This is why propeller driven dredges don’t work in sand.

Marinas should always remember that it could cost several thousands of dollars to opt out of a purchase and instead, hire a dredge contractor. Clearly, marinas need to do the math to find out what will work best for them in the long run.

To pay for a dredge machine, marinas typically take out a bank loan, but the larger marinas will often purchase one with cash. Some marinas finance the dredge over a 5- to 15-year period and pass along the costs to boaters. But buying a dredge can be a good way to increase revenues, ensuring that the product pays for itself. How so? Marinas often buy the dredge for themselves, and then provide dredging services—or rent it—to neighboring marinas.

What about asking the government for dredging help? There is little government funding support for dredging privately-owned marinas. Many cities have their own municipal marinas, so they’re not too interested in helping privately-owned marinas. But it’s always worth checking with state officials about the possibility of grant programs. In 2000, Michigan helped a lot of marinas with permits and grants after lake levels dropped drastically. And for good reason: Michigan officials recognized that there is a multi-million loss to recreational boating with any significant drop in Lake Michigan water levels.

Dredge types

Here are some of the different types of dredges available to marinas followed by general comments on the various types:

  • Horizontal auger dredges (cable driven): geared towards cleaning out lined sediment ponds at industrial facilities and waste water treatment plants
  • Horizontal auger dredges (Starwheel Driven) – Primary markets are marinas, canals, lakes, sediment ponds and rivers. Can be operated in sludgy materials and harder materials like sand.
  • Horizontal auger dredges (propeller driven) – only good in loose materials.
  • Cutterhead dredges (anchored by spuds and swing wires): used for digging virgin material (only good in marinas when adding on and you need to dig into cemented sand or compact clay)
  • Mechanical Dredges:
    • Backhoe: used for removing mud out of a couple slips
    • Clam Shell: used for environmental dredging or deep dredging in waterways
    • Long Reach Excavator: used in all applications when mounted on a barge (very messy and not efficient at all)

Self-propelled dredges can be easily transported on one truck. Self-propelled dredges can be operated by one person compared to the several persons necessary to operate a cable dredge, which needs people on shore to rig anchor cables. Cable-driven dredges and wide cutter dredges require that the docks be moved, which costs time and money.

Marinas should avoid hiring contractors with mechanical dredges. All too often these mechanical dredges cause problems, such as excessive turbidity, which clogs marina channels and restricts boaters, causes unnecessary re-handling of dredged material. Hydraulic dredging sends the material to a designated dewatering area where it can be removed with dump trucks later on after it dries.

Mechanical dredges should be used to clean hazardous materials, such as PCBs, from waterways. In the case of PCB removal, marinas can add an XYZ GPS system, and the mechanical clamshell dredger can make very precise passes at the material and chart those passes on a computer.

A caveat regarding propeller-driven dredges: they tend to clog up in marinas when they start stirring material up. There are other more reliable means of self-propulsion. Propellers are also not usable when removing sand because they don’t provide sufficient torque to get the cutter into the material.

Dredging trends

In recent years, there has been a move in the marina industry to go with self-propelled dredges because they are much more efficient and easier to use and plan around.

When using these dredges, there has been a call to outfit them with GPS systems that have sub-meter and sub-centimeter accuracy. This adds anywhere from $30,000-90,000 depending on how accurate the marina wants to get. In most cases, the GPS is not necessary, however many marinas and lake associations are requesting this option.

Marinas can do pre- and post-dredging surveys to track where sediment has been removed. A lot of dredging contractors are also getting GPS so they can show before and after schematics of the marina to show where sediment has been removed. This shows the marina that all of the work that was required in the contract has been done.


Dredging is as important for today’s marinas as dock selection and maintenance. Marinas that need to do annual or semi-annual dredging will see the importance and cost-effectiveness of having their own in-house dredging program.

Unfortunately, too many marinas let their sediment levels build up to the point that their boats are almost touching bottom. And yes, there have been cases where marinas have closed down because they didn’t act fast enough.

Marinas should keep a file in their offices with all of the information necessary to dredge, including the required permits to dredge and information on where sediment is a problem in the marina (i.e. keep logs of sedimentation rates in slips and channels). Beyond that, marina owners and operators should realize that there are dredging technologies that are affordable to purchase and easy to execute. Dredging really doesn’t have to be the hassle it’s often assumed to be.

Ryan Horton is a client representative at the IMS International Sales Office based in Kansas City. IMS is a division of LWT, LLC. ( He can be reached via by phone at 866/467-4010, cell phone 715/760-2170, or via e-mail: [email protected]

Source: Marina Dock Age, November 2005