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SUBJECT: # 4948: Best angle of incline for boat ramp

Submitted by edfish ( from MISSISSIPPI on 1/24/2001 11:32:00 AM

We are building a concrete boat ramp for a private lake. I have searched the 'net for what should be a simple question: what is the optimum angle of incline for a boat ramp? What is the optimum width for normal trailer boats (15-21') to accommodate single vehicle unloading?

  1. 1/24/2001 10:19:00 PM Submitted by Jon C ( from ALABAMA says Just my preference...
    Ed, it's just my preference but since my trailer is 101 inches wide, it would be optimum to have a ramp that is 1 foot wider on either side (125 inches). That's pretty wide. As far as angle is concerned, I would much rather a medium grade ramp than one that is too steep or too shallow. That makes it easy for my boat to get off and on the trailer, and if I use my 16 foot Lund with the roller trailer, it allows me to crank my boat up without getting my feet wet. If you plan on power loading, make sure that you reinforce the end of the ramps to minimize erosion from prop wash. Good luck!

  2. 1/25/2001 10:15:00 AM Submitted by M.Teal from TEXAS says Boat ramp
    edfish, here is a direct quote from the Time-Saver Standards for Landscape Architecture, of our "Bibles" of the profession.

    "Launch lanes should be at least 15 ft. (4.5M) wide in a multiple lane facility; the lane in a single-lane facility should be 18 ft. (5.5M) wide. The prepared surface should be finished with a cross-scored pattern. The ramp grade should be no steeper than 12 to 15 percent. The lowest end of the ramp should extend into the water to a point where it will be at least 4 ft. (1.2M) below the lowest water elevation in order to protect the base of the ramp from wave action. The backing up of a vehicle should be limited to 200 ft. (60M), and the maneuvering area should be at least 80 ft.(24M), and preferably 100 ft. (30M), in diameter."

    Now these are not hard core "rules", just basic standards for ideal conditions. Each site has a unique set of circumstances which may require some adjustment. Typically, less than a 12% slope requires the tow vehicle to submerge its rear hubs in order to launch. I don't know how simple or complex your project is, but I have access to some more information if you need it. Just let me know, and I will help with what I can.

  3. 1/25/2001 12:04:00 PM Submitted by edfish ( from MISSISSIPPI says Thanks for the info
    Just what I needed. Preferred angle of 12-15 dg. Now the secret is revealed. Thanks very much.

  4. 1/25/2001 2:33:00 PM Submitted by M.Teal from TEXAS says Careful, edfish,...that's % slope, not degrees.
    There is a difference. % is the fall (verticle distance) divided by the length (horizontal distance). Hence, a 12' drop in 100' is a 12% slope.

    Another example....a 4:1 slope (1' drop to 4' run, I know it's backwards, but that is the way it's done! LOL!) = 25% slope = 14.04 degrees.

    I don't think you will want a 25% slope on that ramp!

  5. 1/26/2001 10:18:00 AM Submitted by edfish ( from MISSISSIPPI says Stand corrected
    M. Teal

    I see what you mean, once I got out some paper and drew some angles. Perhaps I do need to check out the "Time Saver Standards" reference book you cited. Standing corrected, I assume what we are shooting for is a vertical drop of from 12-15 ft per 100 ft of horizonal length (or 6-7 ft per 50 horizontal), which should work out to a much narrower slope angle.

    My brother, who does things more by the seat of his pants, has already built one ramp with what appears to be a much steeper incline than what you are suggesting (possibly close to the 4:1 drop you warned against). As you noted, circumstances vary and this ramp is primarily to allow fishermen to launch jon boats, so hopefully it will be functional for that purpose. But we are planning a second ramp to allow launching of a 16' boat that I want to be able to accomplish w. my Toyota pickup 4 cylinder without turning it into a submarine (the boat/motor combination will not exceed 1000 lb). So I want the second ramp to be based on specs rather than speculation. If you do know of any more detailed plans on the web or publications, I'd appreciate the references. Much thanks.

    Ed P.

  6. 1/26/2001 2:44:00 PM Submitted by tx_basser from TEXAS says Actually Slope is a unitless measure
    From a geometric standpoint the "Slope" is nothing more than a ratio of rise/run and expressed in a positive or negative coefficient to determine the direction of travel. The % sign sometimes get thrown in some instances to indicate the differential in units traveled and incorrectly called a 25% slope. When in actuality the slope should be expressed as a + or - .25, depending on the upward/downward direction of the line.

  7. 1/26/2001 4:52:00 PM Submitted by Phill ( from CALIFORNIA says Call your Parks or Public Works Dept
    Out here we have a State Dept of Boating and Waterways which have standards on ramp and dock designs. They also state 12-15%. Miss. should have an equivalent Dept... maybe under Public Works? I prefer the 14-15% grade because I like to load without having to submerge the rear brakes of my tow vehicle, and, be able to step out on dry land. We have a few ramps here that are too shallow and it causes major problems with the 16'+ boats. The website for Calif Dept of Boating and Waterways is:

  8. 1/26/2001 5:09:00 PM Submitted by Phill ( from CALIFORNIA says Design handbook
    Go to "". Then go to "Department Programs", then open "Layout, Design, and Construction Handbook for Small Craft Boat Launching Facilities". You will need Adobe Acrobat 4.0 reader, most recent computers have it installed, if not you can download first. The handbook has everything you need to design your ramp, and more. Good luck.

  9. 1/29/2001 10:28:00 AM Submitted by edfish ( from MISSISSIPPI says Thanks to all for comments / info
    Appreciate the responses to my query. Have downloaded the CA publication, which gives lots of detail backing up what M. Teal had to say. Great to have something substantial on which to base plans.

  10. 8/22/2001 1:26:00 AM Submitted by Mark ( from FLORIDA says Expert Witness
    I searching for an expert witness (preferably an Engineer)to testify in wrongful death lawsuit. The decedent slid off of a recreational boat ramp. The slope was approximately 3.3/1. The plans called for a 5/1 slope. If you have designed a boat ramp in Florida please send an e-mail to:

    Thank you.

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