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Building Boat Ramps
Building boat ramps, whether you are building a ramp for your private use, or in the case of the Department of Game and Inland Fisheries (DGIF), public use, many of the things to be considered are the same. Some of those things are site criteria, permits, design, construction methods and materials, and the type and size of boats to be launched.
The first thing that should be considered when contemplating a ramp is the type and size of boats to be launched and retrieved. Obviously choosing a site and designing a launching ramp for a canoe or car-top boat in shallow water will differ greatly from choosing a site and designing a ramp for launching larger trailered boats in tidal water. If you are designing a ramp for your private use, it is fairly easy to choose a design that will accommodate boats and towing vehicles that you own or might own. Choosing a design that will suit several boaters or the general public is more difficult. The DGIF tries to design ramps that are suitable for most of the boats in the area of the proposed ramp, knowing that we cannot satisfy the needs of every boater.
This article will briefly address site criteria, permits, design, construction methods and materials for typical ramps for launching and retrieving boats in the 12-20 foot range that are typically used for sport fishing and recreational power boating. This article presents a number of items for your consideration should you be thinking of building a boat ramp, but is not intended to be a guide on how to build a boat ramp.
When selecting and evaluating a site as a potential boat ramp site, consideration must be given to site accessibility, proximity to other boat ramps, water depths, siltation rates and usable land area (parking, turning radius, etc.).
One of the more obvious considerations to site selection is its proximity to existing roads and other ramps. Road construction and maintenance is expensive, therefore the closer the site is to a maintained road, the better. Also, the DGIF prefers not to compete with private launch-for-fee ramps if they can meet the public demand. Those thinking of building their own ramp would do well to consider using existing ramps if they are available, and even cost sharing maintenance expenses with the owner.
Water depth should be no less than three feet at the end of the ramp during mean low water, though four feet deep is more desirable. If drive-on trailers will be used for launching and retrieving boats (power loading), consider extending the ramp to a depth of five feet or installing riprap at the end of the ramp. Another alternative is to increase the slope of the ramp for the last 10-15 feet so the end of the ramp will be in deeper water or dug into the bottom to protect the end of the ramp. If the end of the ramp is not protected, the prop wash created from power loading will erode a hole at the end of the ramp, which will cause a sharp drop-off and can undermine the end of the ramp. If the trailer wheels are then backed off the end of the ramp that has a drop-off, the trailer can hang on the end of the ramp causing damage to the trailer as the wheels are pulled back up onto the ramp. Most older DGIF ramps are not designed with drive-on trailers in mind and we are frequently adding riprap to the end of ramps as temporary repairs for the problems caused by prop wash.
Another water depth consideration is the possibility that the water depth will not remain constant. River channels shift from side to side, and might undercut the end of your ramp causing the end to break off. The same is true with channels in tidal areas, especially when the site is on a point that constricts a larger bay. Just the opposite is true of sites at the back of small bays, near stream inlets, or on long sandy beaches. These sites are often areas of active deposition, where silt or sand might cover your ramp. Dredging and maintenance dredging to obtain deep water is expensive, can adversely impact the environment, and is often complicated since suitable sites must be located for placement of the dredged material. If dredging can be avoided, do so!
The size of the ramp and parking area depends on the anticipated use. Our general rule of thumb is that one launching lane should have about 30-35 car-trailer parking spaces. Most of our ramps have daily turnover rates of 2.0 to 2.5, so each launching lane and 30-35 parking spaces will accommodate about 80 launches per day. If no more than 80 launches per day are anticipated, one launching lane is adequate. More than 80 launches justify additional launching lanes and parking spaces. When deciding how many parking spaces can be provided on a tract of land, one should remember that a vehicle-trailer parking space should be at least 10 feet wide and 40 feet long with adequate maneuvering room to line up and get into and out of the parking space.
A word of caution concerning boat ramp size is to not underestimate the land needed. Remember that large wetland areas cannot be disturbed. Also, a 30 or 40 foot turning radius and staging area is needed at the head of the ramp, and no matter how large you make public facilities, there will still be some calm, sunny, warm weekend day when it will not be enough. If at all possible, reserve areas for expansion and overflow parking.
After you have located a site for the boat ramp, know enough about how you want to build it to prepare a sketch. The next step is to apply for the necessary permits. Virginia Marine Resources Commission, Corps of Engineers, State Water Control Board, and the local wetland board may require permits. A local building permit is also required in some localities. To learn what permits will be required, contact the Virginia Marine Resources Commission at 2600 Washington Avenue, Newport News, Virginia 23607, (Phone # 757-247-2200), and your local building inspector.
The design of the site, ramp and pier will have a major impact on construction and maintenance costs, and the usability of the facilities. Take the time required to get a durable, economical and functional design.
Probably the most common problem with boat landings is that the ramp, pier, turning radius, and/or parking area are too small. Provide adequate room to bring the towing vehicle and trailer in good alignment with the ramp, and enough space for a staging area to ready the boat for launching. If possible, place the pier on the same side of the ramp as the driver. This will give the driver a better view as they back the trailer alongside the pier. One-way traffic in the parking area and staging area is desirable to reduce congestion. Angle parking is usually easier to accomplish than other parking plans, and reduces the required width of driving lanes in the parking lot. Parking spaces and traffic patterns should be clearly marked to reduce traffic congestion and to ensure maximum efficiency of available parking space. A one percent slope (minimum) across the parking lot and staging area helps prevent ponding of water on those areas, yet causes a slow runoff that reduces erosion on untreated surfaces. The slope should be directed away from the ramp if possible to prevent gravel, sand, etc. from being washed onto the ramp. If two launching lanes are to be constructed, a single pier between the lanes can serve both lanes and reduce costs and insures that one boater cannot tie-up both lanes at the same time. For high use facilities, a double lane ramp with L-head courtesy piers on both sides will help reduce congestion during peak launching and retrieval time. A line should be painted down the center of the ramp to assist boaters in staying on their side of the ramp.
Generally the ramps should have slopes of 12-15% with the concrete extending into the turning and staging area far enough for the trailer wheels to clear the sloped section of the ramp before the towing vehicle's pulling wheels leave the concrete. If not, the towing vehicle's pulling wheels might spin and dig into the surface as the trailer and boat are being pulled up the ramp. Ramps 16 feet wide are preferred for the general public though many existing 12-foot ramps have proven to be satisfactory at low use facilities. Ramps placed in flowing rivers should enter the river at an angle downstream to reduce the sideward push on the boat as it is being placed on or off the trailer. Also, a ramp placed at an angle usually accumulates less silt after a period of high water. If a cut in the river bank must be made, lay the slopes back as much as possible to reduce the amount of still water trapped in the cut during flooding, thus reducing the amount of silt deposited on the ramp. Provide stabilized ditches down each side of the ramp to handle runoff during heavy rains.
If a pier is needed to assist with launching and retrieving boats, paying close attention to the small details of pier design can save a lot of headaches and maintenance costs. Though piers can be made of materials other than wood, only wood will be discussed here. Remember that a design that uses standard lengths of lumber will be more economical.
Piers can be either floating or fixed. Our experience with floating docks is that they are hard to keep in place unless pilings are provided along the sides for the pier to ride up and down. Metal barrels should not be used for flotation. Plastic encapsulated foam floats are a good choice when flotation is needed.
Note: This sounds good but is not practical, in clay or silt soils it will also result in an unstable piling. Ice damage must be considered on all ramps in Virginia. Ice flowing in rivers and on tides can be especially destructive. If moving ice is expected, the strength of materials must be greater and the design strengthened.
Piers can damage boats, and boats can damage piers. All bolt heads and nails that might come in contact with boats should be recessed. Care should be taken to see there are no "lips" on the pier where a boat could drift underneath and be caught if the water rises. Rubrails might be needed to prevent boats from catching under the pier.
The safety of the boaters must be considered in the pier design. Decking should overlap the outside stringers by no more than two inches to help keep the decking from flipping up in the event it comes loose and someone steps on the end. Many boaters have taken quick trips into the water or their boats from stepping on loose boards when the decking significantly overlapped the outside stringer. Overlapping the decking two inches also prevents most end splitting of the decking when it is nailed to the pier's stringers. Where the water surface will fluctuate significantly, ladders should be installed to assist boaters in boarding boats during periods of low water levels.
One accessory that is nice on a pier is a curb. The curb provides a good hand hold while climbing in and out of boats, is an excellent place to tie a boat to the pier, and serves as a kickplate to help keep equipment from being knocked off the pier. If cleats are still desirable, they can be placed on top of a curb to reduce the possibility of someone tripping over them.
There exist a number of ways to construct a concrete boat ramp on the site. Pre-cast concrete slabs suitable for use as a ramp are also available. The diversity narrows on methods of constructing piers, and is mostly limited to how the pilings are installed.
Although concrete can be mixed for placing (pouring) through water, quality control usually suffers and the final results are poor. This method is typically not allowed by permitting agencies and will not be discussed in this article. The best way to construct the underwater section of a ramp is to cofferdam the ramp area, pump out the water, place (pour) and finish the ramp in the dry (cast-in-place). This method provides for the best horizontal and vertical control of the slab. For low use ramps, a less expensive method (Push Method) is to form and pour the ramp on a thin layer of sand or crusher run, allow to cure, then push it into the water with a track machine. If the ramp is poured on shore, it should be on approximately the same slope as your proposed underwater slope to prevent the slab from breaking on a grade change. Concrete slabs that are moved into place must be small. A six-inch concrete slab 12 feet wide and 20 feet long weighs about nine (9) tons. Usually slabs longer than 20 feet are required to reach the appropriate depth. A six-inch slab 16 feet wide and 30 feet long weighs about eighteen (18) tons and can usually be pushed with a D-5 bulldozer while still maintaining reasonable control. Lifting and setting pre-cast concrete slabs on a prepared subgrade with a crane is a third method with which the DGIF has had success.
Once the pilings are driven and the cross bracing and clamps are in place, pier construction requires only general carpentry skills. However, a great deal of caution should be used as well as the method used to drive the piling. Wood piling should never be used in conditions where the piling will have to be driven through solid or fractured rock or rock fill material. If a wood piling is to be driven into a soil with large gravel content, a steel shoe should be used on the pile tip to protect the pile tip from "brooming" out during driving.
Pilings are classified as either friction or bearing piles. Friction piles develop the strength they need from the friction developed between the outside surface of the piling and the surrounding soil. Bearing piles are driven to a depth where they encounter bedrock and transfer their vertical loads directly into the bedrock. Piling lengths on the DGIF projects are usually determined by driving test piling at the site in order to select the various piling lengths based on the actual subsurface conditions encountered. Piling length can also be determined in a laboratory by a geotechnical engineer from soil borings taken from a barge mounted auger; however, this method is expensive and should be only utilized when it is the most cost effective.
The "jetting" of piling into soil with silt or clay content results in the water in the surrounding area becoming heavily clouded with suspended sediments, which is environmentally unsound and typically a permit violation. The following discussion will be confined to driving piling. There are a number of different types of hammers that can be used to drive piling. For some subsurface conditions, any type of hammer will work, but no hammer is the best for all conditions. Hammers used for timber piles may be either gravity or power type (air, steam, diesel, double acting, single acting, etc.). In general a gravity hammer is quick in soft soils where a high drop of the hammer can be used. In hard soils, a short drop of a gravity hammer must be used to prevent damage to the piling; thus the driving time is increased. Single-acting and double-acting hammers utilize steam or air and deliver more blows per minute than a gravity hammer. Vibratory hammers use low or high frequency vibrations to weaken the friction and adhesion between the soil and the piling, thus allowing the piling to penetrate the soil. Vibratory hammers are usually effective in sand or soft soils. An engineer specializing in marine design or a marine contractor should be consulted prior to selecting the type of piling, length, or driving method.
Any structure is only as good as the materials used. If a good design has been selected and construction methods are appropriate, proper materials and workmanship should be all that is needed to insure that quality boat ramps and piers are constructed. Supervision of the workmanship is left to the owner or engineer. The following recommendations can serve as a guide for specifying proper materials.
In preparing a site for concrete, a minimum of eight inches of compacted, crushed stone (not round bank gravel) should be placed over the subgrade. VDOT #5 or #57 stone is a good choice. If soft places are encountered or the soil is difficult to compact, the poor material should be under cut and larger stone (two to four inches in diameter) should be used to provide an adequate base for the smaller stone. There are also geotextile fabrics on the market to “bridge” over soft material. If any of the stone will be exposed along the edges of the concrete, such as where the concrete will be higher than the adjacent ground, a good quality filter fabric should be placed under and wrapped back over top of the stone. The fabric should be armored with riprap to protect the filter fabric, and ultimately the stone under the slab. If a slab is to be pushed into place, filter fabric cannot be installed between the concrete and the stone.
Concrete for ramps poured at the site should be at least 3,000 psi (4,000 psi preferred) have 4-6% air entrainment, be properly worked, placed, consolidated, screeded and bull floated so the aggregate is about a half-inch below the surface. The DGIF has had good success using concrete ramps reinforced with number four (1/2" diameter) Grade 60 rebar, placed at 12" on center lengthwise, and 18" on center across. In fresh water the steel reinforcement should be 3" from the surface, and bottom and sides of the concrete. This requires a slab at least six inches thick. For ramps where larger boats (over 20 feet) or heavy equipment might be launched, thicker concrete, larger steel and/or stronger concrete might be in order. Concrete should be finished with a surface rough enough to provide good traction, even when covered with algae. We found that a garden rake with the tines bent to curve away from the handle makes a good tool to rake quarter-inch deep grooves into the fresh concrete for traction. The DGIF has recently gone to a "V" groove finish for improved traction. This finish requires an experienced concrete finisher and should not be attempted by a novice.
Wood for piers should be pressure treated to retard decay. Historically CCA (Chromated Copper Arsenate) treated wood has been the treatment of choice for the construction of our piers. The Environmental Protection Agency (EPA) has deemed CCA treated wood unsuitable for use in applications where the wood may come into frequent contact with skin. CCA treated wood should not be used in freshwater. For this reason, we use CCA treated wood where the wood is in constant contact with saltwater, or in a constant wetted condition, such as pier pilings, cross bracing, deck stringers and joists. For all applications that have the potential to come into contact with skin, we've chosen to use the alternative treatment of Copper Azole (CA) for compatibility with galvanized coated hardware. CCA wood that will be in constant contact with saltwater should be treated to a level of 2.5 pounds of retention per cubic foot (pcf) of wood. Wood that will receive saltwater splash should have a retention of 1.5 pcf. For fresh water and wood in saltwater applications that will come into frequent contact with skin (such as decking boards, handrails, and ladders), CA treated wood designated for "ground contact or fresh water" with a minimum retention of 0.21 pcf and a preferred retention of 0.31 pcf is the wood of choice. All bolts and nails should be hot dipped galvanized. Where hardware will come in frequent contact with salt water, a better choice would be stainless steel since our experience is that even galvanized hardware will rust in time.
If you enjoy boating as do most of the boaters who use the approximately 240,000 registered boats in Virginia, you have probably wished for a boat ramp at one time or another. Hopefully, this information will help you to build one.