RANGE FINDER

[VARISTORS]

MARINE REGULATIONS REQUIRE THE STERN OF MY VESSEL TO BE A MINIMUM OF 100 METRES OFFSHORE WHEN ANCHORING. USING A DINGHY
A REFLECTOR COULD BE PLACED AT THE WATER ,S EDGE. BUT PLACING A COUPLE OF REFLECTORS FOR TRANGULATING IS NOT AN OPTION.. ANY DEVICE THAT COULD BE USED FOR SAID DETERMINATION THAT I COULD BUILD OR PURCHASE FOR APROX. $50.00 OR LESS WOULD BE APPRECIATED. (120 V AC OR 12 V DC AVAILABLE) HELP

[rstofer]

Trig...<p>Take a board and mount a plastic protractor and a plumb bob (use a thin wire rather than a fat string) so that you can sight from your vessel to the shoreline. When you have the sight, clamp the plumb bob and read the angle.<p>Assuming a 10' height of eye, a reading of 2 degrees off vertical has the shoreline 100 yards away.<p>You will need to know your height of eye with some accuracy and do your own math for the meters thing.<p>It would be nice to have a vernier scale so degrees could be split. A sextant would work well if it had a bubble level.

[Ron H]

Google "golf range finder". I saw one for 15 bucks. No reflector required.

[dacflyer]

why not use a GPS? i got a few of them from
pawn shops for less than 50.00

[dr_when]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr> Assuming a 10' height of eye, a reading of 2 degrees off vertical has the shoreline 100 yards away. <hr></blockquote><p>Actually the shoreline will be 95.3 yards away. :p

[rstofer]

True, but I doubt that anyone else can measure that acurately and it is certainly not possible with a GPS. After all, the shoreline moves with the tide.<p>I would just try to get a reading < 2 degrees and call it good. Besides, I wouldn't want to get that close to the beach.<p>It's not the water but the hard stuff around the edges that causes the problems!

[Jeep4by4]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by RonH:
Google "golf range finder". I saw one for 15 bucks. No reflector required.<hr></blockquote><p>Typically Golf range finders work by measuring the viewed size of the hole flag, which is a standard size. The smaller the flag appears the further you are from it.

[Chris Smith]

Two cheap gun scopes, set to the right angle will tell you your more or less than that angle equals. <p>Two straws glued to a piece of cardboard at the right angle will also do the same trick, a little more roughly.<p>To be more steady, read the boat from shore.

[Gorgon]

Hi Jack,
Depending on what you want to pay for it, here is one suggestion:
http://www.optical-systems.com/product_ ... ts_id/1074 <p>TOK

[Gary]

Two keychain type laser pointers epoxy glued to a ruler. One at each end, at an angle a little less than perpendicular to the ruler, measured to the center of the ruler. The angles such that they converge 100m away.<p>It would be held horizontally, and with a red laser on the left and a different color such as green on the right. (Is there any red port wine left?) When turned on and pointed at the shore, if there is a red dot is on the right of the other color, you're far enough away. <p>Assuming you can see the two dots that far away of course.<p>If the vessel is small and maneuverable enough you could use the vessel itself as the instrument. Two fixed lasers or fixed spotlight beams of light attached to back of the vessel could tell you when the coast is beyond the point of convergence of the beams. A similar scheme was used by the WWII "dambuster" bombers at night.<p>There are similar things that could be made from a board and some mirrors, one adjustable to judge distance roughly, and marked accordingly. These work best against vertical markers in the distance, to judge a horizontal line like the water line, you might have to turn the instrument and your head sideways...<p>Leika (sp?) has a nice pocket sized laser finder for several hundred dollars that will measure within about 3mm BTW.<p>[ June 29, 2005: Message edited by: Gary ]</p>

[rshayes]

Try a google search for "optical rangefinder". At least one site (www.ranging.net) has rangefinders in the $125 to $200 range. Still expensive, but a little cheaper than the laser rangefinders.<p>Another alternative would be a long focal length telescope with some type of calibration on the focus. A 1 diopter objective (1000 mm focal length) would shift its focal plane about 10 mm as the distance changes from infinity to 100 meters. This would not be extremely accurate, but about 5 meter accuracy should be possible without too much trouble. The eyepiece would be an interesting problem. A 1 inch eyepiece would give about 40 times magnification, and this is probably way too high.

[Ron H]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Jeep4by4:
<p>Typically Golf range finders work by measuring the viewed size of the hole flag, which is a standard size. The smaller the flag appears the further you are from it.<hr></blockquote><p>Yeah, I didn't realize that. My brother-in-law showed me a range finder he had picked up at a pawnshop, and I was amazed by it. It definitely didn't need a pin as a target, and it didn't look like it cost well over $100 new, but apparently it did.

[jwax]

For an alternative approach, try staking off 100 yds on grass. Walk it, look back, walk it again. Do that a few times, and you'll see that your eye can be trained to judge that distance to within a few yds. Ask any 100 yd target shooter.