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Author Topic:   Boat Launch Ramp Slope

jimh posted 12-07-2013 02:18 PM ET (US)
In a publication from the National Water Safety Congress Incorporated in 2001, I came across many guidelines for the "safe operation and maintenance of marinas." I don't recall hearing of this association before. Here is a link to their literature:
http://insurance.flcities.com/Assets/Files/Marinaguide.pdf
In a section about boat launching ramps, the guidelines say:
"Slope should be between 12 and 16 percent above the water line and 15 to 20 percent below the water line."
In 2012 I was in Leland while the boat launch ramp there was being reconstructed. The construction plans were available in the boater's lounge. I browsed the plans and found this specificiation:
"The down slope of the ramp is 14-percent or about 8-degrees."
(Cf.: http://continuouswave.com/ubb/Forum7/HTML/001279.html )
This is right in the middle of the recommended range for a ramp slope given in the literature mentioned above.
The angle of the ramp is found by the relationship
ANGLE = ARCTAN(Slope)
For example:
ANGLE = ARCTAN(0.14)
ANGLE = 7.97-degrees
(I use the notation ARCTAN in place of the more modern notation TAN^-1)
ConB posted 12-07-2013 03:37 PM ET (US)
I have noticed that some launch ramps are better than others and was going to do some angle measuring to find what I liked best.
The low angle ramps I do not like. The ramps that are steeper below the water level I do like.
For trigonometry challenged folks like myself I find a speed squire quit handy for changing % grade to angle.
http://www.popularmechanics.com/home/improvement/4306646
Con
Jefecinco posted 12-07-2013 07:12 PM ET (US)
Here in South Alabama the launch ramps constructed by the state tend to be very user friendly. I say "tend to be" only because I've not used all of them. All that I've used have been very nicely constructed. The worst ramp I've used is the municipal ramp in Fairhope, AL which is very steep.
As in most areas, I'm sure, private ramps tend to be well designed as to the slope if not the approaches or serving piers.
The only ramp I've used which I avoid when possible is the Fairhope ramp.
Butch
saumon posted 12-07-2013 10:12 PM ET (US)
A very well done document about boat launch ramps: http://www.oregon.gov/OSMB/library/docs/SECTION_3_LAUNCH_RAMPS.pdf
contender posted 12-07-2013 10:27 PM ET (US)
I think a lot of places depend on the area in question, not all waterways are the same, just like not all property to construct the ramp is the same. Conb if anyone would learn the amount of things you can do with a square you would be surprised...
swist posted 12-08-2013 07:46 AM ET (US)
"Slope should be between 12 and 16 percent above the water line and 15 to 20 percent below the water line."
And where would the water line be where there are 10 foot tides? Or was this document for inland ramps?
jimh posted 12-08-2013 08:01 AM ET (US)
The document cited by Saumon (whose authorship is not clearly indicated) says the "preferred launch ramp slope of 14%...." which is same recommendation as the National Water Safety Congress literature. This sounds like there is some agreement about the slope.
jimh posted 12-08-2013 08:06 AM ET (US)
The waterline for the break in slope would apparently be determined by the mean low water level for a ramp that was located in an area of changing water level. In some impoundment lakes the water level varies over a very wide range, much more than tides.
jimh posted 12-08-2013 08:25 AM ET (US)
Here is another guideline on ramps, this one from the State of Ohio:
http://watercraft.ohiodnr.gov/portals/watercraft/grants/ facilitystandards.pdf
On the topic of ramp slope this guideline says:
"There is a narrow range of ramp slope that has been nationally accepted as a standard."
"The preferred launch ramp slope of 15% will allow the boat trailer to be in deep enough water to launch and retrieve from the trailer without the rear tires of the tow vehicle being in the water."
A graph on page 26 shows a range of slopes from a minimum of 12-percent to a maximum of 15-percent.
"A small facility that caters to small fishing boats does quite well with a 12-13% ramp."
A table summarizes:
Preferred: 15%
Minimum: 12%
Maximum: 15%
jimh posted 12-08-2013 08:39 AM ET (US)
I was also thinking about how to measure a ramp slope. Let us say we have a carpenter's level that is 36-inches long. We put one end on the upslope of a ramp and adjust the carpenter level to horizontal. Then we measure the distance that the bottom edge of the level is above the ramp. If the ramp has a 14-percent slope, the distance between the level and the ramp would be 36 x 0.14 = 5.04-inches.
jimh posted 12-08-2013 09:01 AM ET (US)
From a 1982 United States Army Corps of Engineers guide:
"Ramp grades should be a minimum of 12 percent and maximum of 16 percent. Grades of 14 percent are preferred."
http://corpslakes.usace.army.mil/employees/facilities/pdfs/em1110-2-410/ chap4.pdf
dfmcintyre posted 12-08-2013 01:27 PM ET (US)
Why not just use an iPhone app?
jimh posted 12-09-2013 12:28 AM ET (US)
There's an iPhone app that designs boat launch ramps?
dfmcintyre posted 12-09-2013 05:53 AM ET (US)
Noooo. But I think there may be one that could calculate % slope.
jimh posted 12-09-2013 08:34 AM ET (US)
There is a nice iPhone app that measures angles in degrees. But you'd have to convert the degrees into percent slope. That would be done using
SLOPE = TAN(angle)
If you measured the angle with the iPhone and it was, let us say, 9-degreees, then you'd find the slope in percentage from
SLOPE (percentage) = 10 x TAN(9)
SLOPE (percentage) = 10 x 0.158
SLOPE (percentage) = 15.8
Kanawha1 posted 12-09-2013 11:30 AM ET (US)
There is an application for iOS devices called "Clinometer" that measures in decimal degrees, percentage of slope, and pitch (V:H or X:12).
$0.99
jimh posted 12-09-2013 05:04 PM ET (US)
I have handy level on my iPhone. In order to measure the slope of a ramp, you need some sort of reference to perfectly level. What shall we use as a reference?
Kanawha1 posted 12-09-2013 06:33 PM ET (US)
The water.
Binkster posted 12-09-2013 08:59 PM ET (US)
This is the way any carpenter would do it, and have the answer in a couple of minutes. He would take his level, any level, and put a mark on it 1 foot from the end. This would probably take two people. Now put the end of the level on the ramp anywhere, and level it. Next, with your tape measure, measure down vertically from the mark you made to the surface of the ramp. Take this measurement in inches. Say you get 3 inches. Go to your toolbox and get out your speed square. You ramp measures at a 3/12 pitch. So now hold your speed square on a board at the the pivot point and the slot that says (common top cut). Now move the square from the pivot point to the number 3 on the common top cut slot. Now read down to the next slot where it says degrees. It will read 14 degrees. Simple.
I have done that countless times, not on ramps, but on a roof where we were putting on an addition and needed to know the slope of the original roof. BTW most everyone has some sort of a level and a speed square can be had in the plastic version from HF Tools for a couple of dollars.
rich
jimh posted 12-09-2013 10:30 PM ET (US)
Kanawha1--I think if you put your iPhone on the water you will void the warranty and ruin the iPhone. Let me have a better suggestion. I know I could measure the slope with a level and a ruler in about five seconds, but I want to follow the suggestion of using an iPhone. So I need a way to set the iPhone to be perfectly level to measure the ramp.
Wait, I get a carpenter level, set the iPhone on the carpenter level, and then mark that as the reference for the iPhone.
saumon posted 12-09-2013 10:41 PM ET (US)
Even easier: hold a carpenter level (let's say 36 inches long) so one end sit in the ramp, set it level then measure the drop to the ramp at the other end, let's say 5 inches. 5 divided by 36 gives 13.89%.
saumon posted 12-09-2013 10:47 PM ET (US)
Sorry, I realized afterward that it was exactly what jimh said in post #10.
Kanawha1 posted 12-10-2013 03:06 PM ET (US)
Why does the iPhone need a reference? If it, for some reason, needs re-calibrated it may be completed just about anywhere in a matter of seconds. And, I don't have to carry a 4' level, ruler, and calculator in my pocket!
Binkster posted 12-10-2013 06:20 PM ET (US)
The worst ramps in my estimation are the ones with a vertical drop off about 8 ft from the waters edge. If the tide is low and the water is murky, and you're not familiar with the ramp, you can get yourself in trouble if your wheels drop over the edge. There are more than a few ramps like this.
rich
Dave Sutton posted 12-10-2013 07:32 PM ET (US)
Jim, level your iPhone once and it's calibrated for life.
I use an application called "Clinometer" that will measure angles in degrees, percent slope, and a few other arcane units. This is just easy stuff. I think it's free.
All you do to level it is to put it on a fairly level flat surface and hit "calibrate". Rotate it 180 degrees and hit "calibrate" a second time. You're done. For life.
"Spyglass" is another interesting application. It uses the camera function of the phone to give you a fairly good mimic of a surveyors theodolite, and a bunch of other things as well. Useful tool. Try it.

Dave
.
dfmcintyre posted 12-10-2013 09:32 PM ET (US)
Dave - Jim
As soon as you mentioned a theodolite, I recalled that I've got an app called same...."Theodolite".
Opened and checked the prefs, found that it can read out in percentage. It also captures a screen shot.
Tomorrow I'll wander down to the local ramp and see if it works like I think. And will forward the jogs to Jim.
Regards - Don
jimh posted 12-10-2013 11:53 PM ET (US)
You have to love the iPhone and iOS. Here is a good example. We were taking the VIA train from Ottawa to Kingston in June, going to get our boat trailers and trucks after navigating the Rideau Canal in our boats. The train comes into a section where it run parallel to the highway. We are passing the cars. The speed limit on the highway is 100-KPH. I say to Don Jahncke, "I wonder how fast we are going. We must be doing about 70-MPH."
Don J pulls out his iPhone, and in a few seconds has a reading on the speed of the train. There is an application for everything.
I am looking forward to seeing the slope measurements on the ramp.
Dave--I did not realize that you only need to calibrate the iPhone inclinometer once. Thanks for the tip.
Dave Sutton posted 12-11-2013 06:30 AM ET (US)
^^^
With am internal GPS and a three axis accelerometer it's a pretty capable hardware platform. Add the ability to upload some darned sophisticated software and leveraging it's data port and you have a very powerful I/O device. Add video and audio into that mix and you have what could arguably be called one of the most spohisticated data collection and processing devices available in the world.
There's no wonder we use them in aircraft as one of the primary lash-up tools for data collection and analysis in the flight test world. As a Test Pilot I can velcro one to the airframe, plug a jumper from my helmet cord to the audio input, and record video, intercom and ATC audio (I make verbal comments continuously during a test flight), and record a continuous data stream of three axis GPS position (Latitude, Longitude, and Altitude), derived velocity and flight path vector from that overlaid with aircraft attitude, and log three axis G for accelleration Nx (longitudinal accelleration), Nx (sideslip force laterally), and Nz for "G" forces on the airframe. I can then download all of that data for postflight processing. On a laptop later I can set up a wire-frame replication of the entire flight with a path in three dimensional space with data available at any point in the flight. It's VERY VERY sophisticated.

Slope in percent? Uhh....Yeah... we can do that. In our sleep.

Dave

.
Chuck Tribolet posted 12-11-2013 11:42 AM ET (US)
Binkster: We've got one ramp (Pt. Lobos) where there's an
8' dropoff right at the zero tide line. I saw a fellow drop
his wheels off that retrieving one time, and then rip a wheel
off trying to get it back up over.

Chuck
jimh posted 12-11-2013 12:55 PM ET (US)
Here is Don's image of the ramp with the iPhone application THEODOLITE:
I'll let Don interpret what the measurements indicate.
jimh posted 12-11-2013 01:01 PM ET (US)
Using Photoshop to measure and rotate the image of the ramp, it looks to me like the angle of the ramp slope is 8.2-degrees. In terms of a slope that is 14.4-percent.
boatdryver posted 12-11-2013 06:09 PM ET (US)
There's something inaccurate with that photo, possibly related to the wide angle focal length of the lens and cropping.
the water is horizontal but the left wall of the building is not vertical and the light pole is even less vertical. That means the true angle of the ramp with respect to the reference water line (or ice) is not as measured.
boatdryver posted 12-11-2013 06:16 PM ET (US)
Oops. Now I get the photo. The ramp is the surface shown as horizontal, but the light post and left wall of the building are not parallel, so there's a little inaccuracy. Isn't there?
Dave Sutton posted 12-11-2013 06:54 PM ET (US)
The most basic iPhone carpenters level is a better tool for this. Just place the phone on the surface and read the result.
dfmcintyre posted 12-11-2013 08:54 PM ET (US)
I first zeroed the program with the reference lines across the horizontal concrete edge at the top of the ramp. That may or may not be level to the water, maybe a degree off of true level. Then squatted down and shot the slope of the ramp, lining up the horizontal reference line to the edge of the concrete and ramp and sheetmetal edge, the ramp wall. The % slope is to the left of the reference line.
Mistake I made was not being perpendicular to the ramp wall, and you can see I was off a foot or so based on the expansion joint that's skewed.
Dave - I wanted to use a program that didn't require me to lay the phone down on the ramp, get down on my hand and knees, and-or need an external device like a tripod, just wanted use what I had.
Angles may be off slightly as I was in a work suit and it was a nice balmy 14-degrees-F when I shot it.
Dave Sutton posted 12-12-2013 06:20 AM ET (US)
^ Understood.
Try using Spyglass. You can optically mark multiple spots and then do geometric measurements between them. It's an interesting application.
dfmcintyre posted 12-12-2013 04:18 PM ET (US)
Dave -
Will have to check. Thanks. This program will also calc for height if distance is known and opposite; give distance if you can mark height.
Regards - Don
deepwater posted 01-11-2014 08:28 PM ET (US)
[This article has beed deleted. The article revived this discussion but then changed the topic. The article tried to initiate a new discussion in which the topic was the time of year when this topic is discussed. This is really a discussion about the discussion, and not on-topic. Here we are discussing the slope of boat launching ramps. If you want to add something to the discussion of boat launching ramps, you are welcome to revive this thread. If you want to change the topic of this discussion to a discussion about the discussion itself, you will have to find another place for those articles. It is my experience that once discussions begin to discuss themselves, there is very little new boating information added. --jimh]

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Author	Topic: Boat Launch Ramp Slope
jimh	posted 12-07-2013 02:18 PM ET (US) In a publication from the National Water Safety Congress Incorporated in 2001, I came across many guidelines for the "safe operation and maintenance of marinas." I don't recall hearing of this association before. Here is a link to their literature: http://insurance.flcities.com/Assets/Files/Marinaguide.pdf In a section about boat launching ramps, the guidelines say: "Slope should be between 12 and 16 percent above the water line and 15 to 20 percent below the water line." In 2012 I was in Leland while the boat launch ramp there was being reconstructed. The construction plans were available in the boater's lounge. I browsed the plans and found this specificiation: "The down slope of the ramp is 14-percent or about 8-degrees." (Cf.: http://continuouswave.com/ubb/Forum7/HTML/001279.html ) This is right in the middle of the recommended range for a ramp slope given in the literature mentioned above. The angle of the ramp is found by the relationship ANGLE = ARCTAN(Slope) For example: ANGLE = ARCTAN(0.14) ANGLE = 7.97-degrees (I use the notation ARCTAN in place of the more modern notation TAN^-1)
ConB	posted 12-07-2013 03:37 PM ET (US) I have noticed that some launch ramps are better than others and was going to do some angle measuring to find what I liked best. The low angle ramps I do not like. The ramps that are steeper below the water level I do like. For trigonometry challenged folks like myself I find a speed squire quit handy for changing % grade to angle. http://www.popularmechanics.com/home/improvement/4306646 Con
Jefecinco	posted 12-07-2013 07:12 PM ET (US) Here in South Alabama the launch ramps constructed by the state tend to be very user friendly. I say "tend to be" only because I've not used all of them. All that I've used have been very nicely constructed. The worst ramp I've used is the municipal ramp in Fairhope, AL which is very steep. As in most areas, I'm sure, private ramps tend to be well designed as to the slope if not the approaches or serving piers. The only ramp I've used which I avoid when possible is the Fairhope ramp. Butch
saumon	posted 12-07-2013 10:12 PM ET (US) A very well done document about boat launch ramps: http://www.oregon.gov/OSMB/library/docs/SECTION_3_LAUNCH_RAMPS.pdf
contender	posted 12-07-2013 10:27 PM ET (US) I think a lot of places depend on the area in question, not all waterways are the same, just like not all property to construct the ramp is the same. Conb if anyone would learn the amount of things you can do with a square you would be surprised...
swist	posted 12-08-2013 07:46 AM ET (US) "Slope should be between 12 and 16 percent above the water line and 15 to 20 percent below the water line." And where would the water line be where there are 10 foot tides? Or was this document for inland ramps?
jimh	posted 12-08-2013 08:01 AM ET (US) The document cited by Saumon (whose authorship is not clearly indicated) says the "preferred launch ramp slope of 14%...." which is same recommendation as the National Water Safety Congress literature. This sounds like there is some agreement about the slope.
jimh	posted 12-08-2013 08:06 AM ET (US) The waterline for the break in slope would apparently be determined by the mean low water level for a ramp that was located in an area of changing water level. In some impoundment lakes the water level varies over a very wide range, much more than tides.
jimh	posted 12-08-2013 08:25 AM ET (US) Here is another guideline on ramps, this one from the State of Ohio: http://watercraft.ohiodnr.gov/portals/watercraft/grants/ facilitystandards.pdf On the topic of ramp slope this guideline says: "There is a narrow range of ramp slope that has been nationally accepted as a standard." "The preferred launch ramp slope of 15% will allow the boat trailer to be in deep enough water to launch and retrieve from the trailer without the rear tires of the tow vehicle being in the water." A graph on page 26 shows a range of slopes from a minimum of 12-percent to a maximum of 15-percent. "A small facility that caters to small fishing boats does quite well with a 12-13% ramp." A table summarizes: Preferred: 15% Minimum: 12% Maximum: 15%
jimh	posted 12-08-2013 08:39 AM ET (US) I was also thinking about how to measure a ramp slope. Let us say we have a carpenter's level that is 36-inches long. We put one end on the upslope of a ramp and adjust the carpenter level to horizontal. Then we measure the distance that the bottom edge of the level is above the ramp. If the ramp has a 14-percent slope, the distance between the level and the ramp would be 36 x 0.14 = 5.04-inches.
jimh	posted 12-08-2013 09:01 AM ET (US) From a 1982 United States Army Corps of Engineers guide: "Ramp grades should be a minimum of 12 percent and maximum of 16 percent. Grades of 14 percent are preferred." http://corpslakes.usace.army.mil/employees/facilities/pdfs/em1110-2-410/ chap4.pdf
dfmcintyre	posted 12-08-2013 01:27 PM ET (US) Why not just use an iPhone app?
jimh	posted 12-09-2013 12:28 AM ET (US) There's an iPhone app that designs boat launch ramps?
dfmcintyre	posted 12-09-2013 05:53 AM ET (US) Noooo. But I think there may be one that could calculate % slope.
jimh	posted 12-09-2013 08:34 AM ET (US) There is a nice iPhone app that measures angles in degrees. But you'd have to convert the degrees into percent slope. That would be done using SLOPE = TAN(angle) If you measured the angle with the iPhone and it was, let us say, 9-degreees, then you'd find the slope in percentage from SLOPE (percentage) = 10 x TAN(9) SLOPE (percentage) = 10 x 0.158 SLOPE (percentage) = 15.8
Kanawha1	posted 12-09-2013 11:30 AM ET (US) There is an application for iOS devices called "Clinometer" that measures in decimal degrees, percentage of slope, and pitch (V:H or X:12). $0.99
jimh	posted 12-09-2013 05:04 PM ET (US) I have handy level on my iPhone. In order to measure the slope of a ramp, you need some sort of reference to perfectly level. What shall we use as a reference?
Kanawha1	posted 12-09-2013 06:33 PM ET (US) The water.
Binkster	posted 12-09-2013 08:59 PM ET (US) This is the way any carpenter would do it, and have the answer in a couple of minutes. He would take his level, any level, and put a mark on it 1 foot from the end. This would probably take two people. Now put the end of the level on the ramp anywhere, and level it. Next, with your tape measure, measure down vertically from the mark you made to the surface of the ramp. Take this measurement in inches. Say you get 3 inches. Go to your toolbox and get out your speed square. You ramp measures at a 3/12 pitch. So now hold your speed square on a board at the the pivot point and the slot that says (common top cut). Now move the square from the pivot point to the number 3 on the common top cut slot. Now read down to the next slot where it says degrees. It will read 14 degrees. Simple. I have done that countless times, not on ramps, but on a roof where we were putting on an addition and needed to know the slope of the original roof. BTW most everyone has some sort of a level and a speed square can be had in the plastic version from HF Tools for a couple of dollars. rich
jimh	posted 12-09-2013 10:30 PM ET (US) Kanawha1--I think if you put your iPhone on the water you will void the warranty and ruin the iPhone. Let me have a better suggestion. I know I could measure the slope with a level and a ruler in about five seconds, but I want to follow the suggestion of using an iPhone. So I need a way to set the iPhone to be perfectly level to measure the ramp. Wait, I get a carpenter level, set the iPhone on the carpenter level, and then mark that as the reference for the iPhone.
saumon	posted 12-09-2013 10:41 PM ET (US) Even easier: hold a carpenter level (let's say 36 inches long) so one end sit in the ramp, set it level then measure the drop to the ramp at the other end, let's say 5 inches. 5 divided by 36 gives 13.89%.
saumon	posted 12-09-2013 10:47 PM ET (US) Sorry, I realized afterward that it was exactly what jimh said in post #10.
Kanawha1	posted 12-10-2013 03:06 PM ET (US) Why does the iPhone need a reference? If it, for some reason, needs re-calibrated it may be completed just about anywhere in a matter of seconds. And, I don't have to carry a 4' level, ruler, and calculator in my pocket!
Binkster	posted 12-10-2013 06:20 PM ET (US) The worst ramps in my estimation are the ones with a vertical drop off about 8 ft from the waters edge. If the tide is low and the water is murky, and you're not familiar with the ramp, you can get yourself in trouble if your wheels drop over the edge. There are more than a few ramps like this. rich
Dave Sutton	posted 12-10-2013 07:32 PM ET (US) Jim, level your iPhone once and it's calibrated for life. I use an application called "Clinometer" that will measure angles in degrees, percent slope, and a few other arcane units. This is just easy stuff. I think it's free. All you do to level it is to put it on a fairly level flat surface and hit "calibrate". Rotate it 180 degrees and hit "calibrate" a second time. You're done. For life. "Spyglass" is another interesting application. It uses the camera function of the phone to give you a fairly good mimic of a surveyors theodolite, and a bunch of other things as well. Useful tool. Try it. Dave .
dfmcintyre	posted 12-10-2013 09:32 PM ET (US) Dave - Jim As soon as you mentioned a theodolite, I recalled that I've got an app called same...."Theodolite". Opened and checked the prefs, found that it can read out in percentage. It also captures a screen shot. Tomorrow I'll wander down to the local ramp and see if it works like I think. And will forward the jogs to Jim. Regards - Don
jimh	posted 12-10-2013 11:53 PM ET (US) You have to love the iPhone and iOS. Here is a good example. We were taking the VIA train from Ottawa to Kingston in June, going to get our boat trailers and trucks after navigating the Rideau Canal in our boats. The train comes into a section where it run parallel to the highway. We are passing the cars. The speed limit on the highway is 100-KPH. I say to Don Jahncke, "I wonder how fast we are going. We must be doing about 70-MPH." Don J pulls out his iPhone, and in a few seconds has a reading on the speed of the train. There is an application for everything. I am looking forward to seeing the slope measurements on the ramp. Dave--I did not realize that you only need to calibrate the iPhone inclinometer once. Thanks for the tip.
Dave Sutton	posted 12-11-2013 06:30 AM ET (US) ^^^ With am internal GPS and a three axis accelerometer it's a pretty capable hardware platform. Add the ability to upload some darned sophisticated software and leveraging it's data port and you have a very powerful I/O device. Add video and audio into that mix and you have what could arguably be called one of the most spohisticated data collection and processing devices available in the world. There's no wonder we use them in aircraft as one of the primary lash-up tools for data collection and analysis in the flight test world. As a Test Pilot I can velcro one to the airframe, plug a jumper from my helmet cord to the audio input, and record video, intercom and ATC audio (I make verbal comments continuously during a test flight), and record a continuous data stream of three axis GPS position (Latitude, Longitude, and Altitude), derived velocity and flight path vector from that overlaid with aircraft attitude, and log three axis G for accelleration Nx (longitudinal accelleration), Nx (sideslip force laterally), and Nz for "G" forces on the airframe. I can then download all of that data for postflight processing. On a laptop later I can set up a wire-frame replication of the entire flight with a path in three dimensional space with data available at any point in the flight. It's VERY VERY sophisticated. Slope in percent? Uhh....Yeah... we can do that. In our sleep. Dave .
Chuck Tribolet	posted 12-11-2013 11:42 AM ET (US) Binkster: We've got one ramp (Pt. Lobos) where there's an 8' dropoff right at the zero tide line. I saw a fellow drop his wheels off that retrieving one time, and then rip a wheel off trying to get it back up over. Chuck
jimh	posted 12-11-2013 12:55 PM ET (US) Here is Don's image of the ramp with the iPhone application THEODOLITE: I'll let Don interpret what the measurements indicate.
jimh	posted 12-11-2013 01:01 PM ET (US) Using Photoshop to measure and rotate the image of the ramp, it looks to me like the angle of the ramp slope is 8.2-degrees. In terms of a slope that is 14.4-percent.
boatdryver	posted 12-11-2013 06:09 PM ET (US) There's something inaccurate with that photo, possibly related to the wide angle focal length of the lens and cropping. the water is horizontal but the left wall of the building is not vertical and the light pole is even less vertical. That means the true angle of the ramp with respect to the reference water line (or ice) is not as measured.
boatdryver	posted 12-11-2013 06:16 PM ET (US) Oops. Now I get the photo. The ramp is the surface shown as horizontal, but the light post and left wall of the building are not parallel, so there's a little inaccuracy. Isn't there?
Dave Sutton	posted 12-11-2013 06:54 PM ET (US) The most basic iPhone carpenters level is a better tool for this. Just place the phone on the surface and read the result.
dfmcintyre	posted 12-11-2013 08:54 PM ET (US) I first zeroed the program with the reference lines across the horizontal concrete edge at the top of the ramp. That may or may not be level to the water, maybe a degree off of true level. Then squatted down and shot the slope of the ramp, lining up the horizontal reference line to the edge of the concrete and ramp and sheetmetal edge, the ramp wall. The % slope is to the left of the reference line. Mistake I made was not being perpendicular to the ramp wall, and you can see I was off a foot or so based on the expansion joint that's skewed. Dave - I wanted to use a program that didn't require me to lay the phone down on the ramp, get down on my hand and knees, and-or need an external device like a tripod, just wanted use what I had. Angles may be off slightly as I was in a work suit and it was a nice balmy 14-degrees-F when I shot it.
Dave Sutton	posted 12-12-2013 06:20 AM ET (US) ^ Understood. Try using Spyglass. You can optically mark multiple spots and then do geometric measurements between them. It's an interesting application.
dfmcintyre	posted 12-12-2013 04:18 PM ET (US) Dave - Will have to check. Thanks. This program will also calc for height if distance is known and opposite; give distance if you can mark height. Regards - Don
deepwater	posted 01-11-2014 08:28 PM ET (US) [This article has beed deleted. The article revived this discussion but then changed the topic. The article tried to initiate a new discussion in which the topic was the time of year when this topic is discussed. This is really a discussion about the discussion, and not on-topic. Here we are discussing the slope of boat launching ramps. If you want to add something to the discussion of boat launching ramps, you are welcome to revive this thread. If you want to change the topic of this discussion to a discussion about the discussion itself, you will have to find another place for those articles. It is my experience that once discussions begin to discuss themselves, there is very little new boating information added. --jimh]