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Boat Launch Ramp

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boatman
Join Date: Jul 2003
Posts: 49 Idaho
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2003-04-13          53068


Does anyone have any advice on Boat Ramp Construction? Any sources of information? I am currently researching for a project I hope to do in the next few months. Time is not a concern-the project can be done at leisure with breaks in between. The ramp will be going into a river. The river bank is good soil and is cleared. Ramp will service trailers up to 10,000lbs. and 8.5'wide. I am considering using cement. Possibly building forms 12"x4"x9' and reinforcing with rebar and filling with cement then laying down blocks one after another starting at the top. Sound feasible-or conpletely off? Also, surrounding area must be visually appealing when completed. Please comment.



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Boat Launch Ramp

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2003-04-14          53101


We have three municipal ones in our township of that general description, but whether they'd qualify as visually appealing I couldn't say. They appear to be poured concrete but I wouldn't know the load ratings. If you don't get a better answer I can ask around to see if the construction was done locally and if anybody remembers details.

One thing that should be considered for building one here is planning for how high the ramp starts and how long its going to be. Our river is called a lake here because there's a downstream hydro dam. The water levels are administered and vary quite a bit within a year. There is a 'guaranteed' max level and I suppose a ramp should start above that. There's no guarantee for low water levels and what you get depends on electrical power demands, rain and run off forecasts and management of an upstream dam. I don't think any of the ramps meet the water at typical low water levels, but low water generally occurs in late winter when the river is frozen anyway.

There are several weeks in the spring before runoff and release of water from the upstream dam that could be used for boating. Few people are interested yet (we're still putting away our snowshoes), but anybody who was couldn't use the ramps since they don't meet the water. A ramp at a private lodge also has this problem frequently during the summer. When the dam administrators are planning for a wet fall, he has a mud flat for his customers between the ramp end and the water. He's not happy a fair bit of the time.
....


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Boat Launch Ramp

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Murf
Join Date: Dec 1999
Posts: 7249 Toronto Area, Ontario, Canada
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2003-04-14          53115


My first comment would be "Be careful!!!!" I am going to assume that you have already contacted the various State (and possibly Federal) authorities with regard to permission, permits, etc..... To this end they may even provide sample designs, or even insist on using one of there standard designs (as they do here in Canada) since once it's in the drink, it is theirs since they own the water and the bed under the river or lake.

Secondly, if they don't offer design assistance or review, be mindfull, VERY MINDFULL, of the actions and forces of moving water, a very slightly raised or angled obstructions can result in either a deposition of silt, or the exact opposite, something called 'scrub' which is when the water swirls around an obstruction, kind of the wet version of air turbulence, it can suck the river bed material out from under your ramp in no time at all, leaving it VERY compromised.

If you are going to use concrete I would make sure it is well protected by a skirt of rip-rap, large (6+") irregular blocks of stone, laid on top of smaller (0.75"-1.5") stone. This should help with the erosion problem, it is how they protect bridge supports, etc., from fast moving water.

Best of luck ....


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Peters
Join Date: Feb 2002
Posts: 3034 Northern AL
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2003-04-14          53123


I guess the main concern is the bottom of the ramp. How Do you extend the ramp 5-10 ft below the depth of the water.
If you use a lot of ramps I guess we have all had the wheels of the trailer drop off the end of the ramp.
Most of the ramps here were put in by the ACE and are very good. As the water levels are controlled for navigation I suspect that they were planned and put in when the dam was empty.
These structures are similar to what you describe except they have the expansion joints on about 1 ft centers.
I think you need the reinforcing bar to extend from section to section.
You need to look at the bottom of the ramp critically whether you use hydraulic cement or wait unit the river is at its lowest level to pour.
One hydraulic cement supplier is Jet Set. ....


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AC5ZO
Join Date: Jul 2003
Posts: 928 Rio Rancho, NM 87144
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2003-04-15          53152


10,000# is a pretty good load. Normal soil will carry about 2000# per square foot. With saturated soil at the edge of a river, I would reduce the load carrying capacity of the ramp pads to about 1000# per square foot to keep them from sinking under repeated loads. What that means is that you want to have at least ten square feet of pad under the trailer wheels. (5 per side minimum) The ramps that you suggest would be large enough to carry the load.

10,000# loads are probably going to be dual axle trailers, so the load is spread somewhat already. The thing to do is to keep things balanced. It is not particularly good to have such a heavy load concentrated at the end of the ramp, but generally the trailer wheel load is becoming less as the water starts to carry the boat. But, it is still important to make sure that the ramps are long enough to keep from running off the ends. I know that this is getting a bit complicated, but I would suggest that you keep at least a foot of concrete ramp pad beyond where you expect the rear axle of the trailers to stop at the lowest water condition.

Reinforced concrete is a good material to use. It can cure under water if properly formed and applied. However, it may be easier to make a temporary dam with a dirt berm to get access to the shore area where you want to do the construction. You would push dirt/clay into the area around the construction and then pump out the water seepage while doing the form work and pouring. Water is not such a problem after the concrete has set.

Alternately, the ramps can be cast on level ground and then carried into position. Blocks that are 12"X4"X9' will not be particularly heavy, but you will need to make sure that you have good even support under them when they are placed into position. As with many construction projects, site preparation is most important.

You may want to see if there are building codes that apply in your area. Good luck. ....


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Murf
Join Date: Dec 1999
Posts: 7249 Toronto Area, Ontario, Canada
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2003-04-15          53172


Around here the ramps are precast concrete which arrives in slab form and is lowered in place by a very large boom crane mounted on the tractor-trailer that does the delivery. Although at least one in this area was cast on the shore in pieces and pushed in place using a large payloader. Underwater concrete pores are avoided since the curing concrete release lye and CaCl into the water.

The rule of thumb seems to be that you want to have a minimum of 36" of water over the back edge of the ramp when the water is at it's lowest point in the year since you never want to have the rear tires of a trailer go over the edge, possibly getting the tow vehicle stuck on the ramp. The 36" figure is for an average pitch ramp, it is greater for steep ramps, a little less for shallow ramps.

Best of luck. ....


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boatman
Join Date: Jul 2003
Posts: 49 Idaho
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2003-04-24          53706


Thanks you all for the replies. We are going to incorporate AC5ZO's idea of using a temporary dam to make construction easier-we are going to use sandbags to make the dam around the construction and then use a pump to pump out any water that does get in. We will do the project in phases starting at the top and hopefully will complete in early November(the water is normally at it's lowest point of the year then). ....


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Murf
Join Date: Dec 1999
Posts: 7249 Toronto Area, Ontario, Canada
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2003-04-24          53708


You should bear in mind that the water will need to be kept off the concrete for at least 48 (72 is better) hours after it's poured, and then you will have to ensure that any portions which end up below water have a MINIMUM of 30 days before they are exposed to freezing temperatures or you will find the concrete may disolve in the spring thaw.

You will also have quite a task to keep back that much water. Water weighs 62 pounds per cubic foot, without allowing for any current in that river.

IMHO as a contractor & P. E., it would be far faster, easier, and cheaper to pour the first (highest) slab, then pour the next one right on top and shove it down into the river after curing, then keep repeating this process until you have the desired length.

Best of luck. ....


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AC5ZO
Join Date: Jul 2003
Posts: 928 Rio Rancho, NM 87144
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2003-04-25          53757


I agree with Murf. Doing the job in November puts a different light on the project. I also suggested casting sections on the banks and then moving them where you want them. If it gets cold where you are, I would cast the slabs during warmer weather and then you can set or push them at any convenient time. This will also allow you to let the slabs fully cure for a month before doing anything with them. You need to cover/insulate concrete that is curing in freezing temperatures.

Placing sandbags and working in waist deep water during that time of year where I live would be miserable. Any temporary dam that you make with sandbags will not be completely watertight. You will need a pretty big pump to keep the area dry and freezing might make that even more difficult. ....


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