Knot meter impeller/paddle wheel

[tom]

I Rarely use speed for Navigation

Most trips I know about how long it will take and I measure progress by looking for landmarks. This usually works pretty well for coastal navigation. I have LORAN and GPS on board and my wife sometimes consults those when she doesn't trust my judgement. It's not an ego thing and whenever I have serious doubts about my location the electronics are used especially at night. The problem with speed is that it is usually constantly changing. A breeze pushes you along at 5 kts for a few minutes then a lull drops the speed to 2-3 knots and a gust has you burying the rail. Then toss in current effects. I rememeber one overnight passage where we were going at near hull speed and I was worried about what we'd do when we got to the inlet at 1-2 am. Well the wind started dropping and before midnight we had to start the motor to keep moving. Ended up getting there about noon. If your speedo keeps track of how far you've traveled it's more usefull. But again currents change and can lead to significant error.  BTW even though I joked about beer can navigation we have a policy of throwing almost nothing overboard. The few things that sometimes get tossed are things like an apple core or banana peel....I know even those shouldn't be tossed.

 

[Ross]

Joe it is generally believed that the clock was

a joke and that Slocum used Lunar Distance for determine position.Coastal piloting with land always in sight depends on local knowledge or good charts. There are watermen out here on the bay that know exactly where they are all of the time because they spend their days out on the bay.

 

[David10790]

How they did it in the age of Nelson:

The 'Chip Log' apparatus consisted of a small weighted wood panel that was attached to the reel of rope, and a time measuring device: a half-minute sand glass (as shown in image below to the right.)Chip Log Rope had knots tied at equal distances along the reel. Sailors would throw the wood panel into the sea, behind the ship, and the rope would start unwinding from the reel. The faster the ship was moving forward the faster the rope would unwind. By counting the number of knots that went overboard in a given time interval, measured by the sand glass, they could tell the ship's speed. In fact that is the origin of the nautical speed unit: the knot.

 

[NautiDuck]

Welcome to the 21st century

You gotta love this site. Use ropes and cans for speed. Use ropes for depth. Use wooden whisker poles. Hello! It is the 21st century, fiberglass is no longer an innovation and technology has basically rendered the old ways obsolete. Buy the spare part for crying out loud. Pick up a handheld GPS. If you are woried about equipment failure then buy two. When I can solve a boat problem for $38 I do a little happy dance.

 

[Joe]

sorry ross,

I never heard that before. I assumed that when Capt Slocum wrote his book "Sailing Alone Around the World" he was being truthful. But I guess the experts - who weren't with him, btw, know better. Are you saying he used a sextant? Because I can't recall any mention of one in the book.He was a commercial skipper for many years before he made his famous circumnavigation and I have no doubt he had access to more sophisticated equipment then. Earlier, he had lost his ship in Brazil and decided to sail his family back home, rather than take a commerial steamer. He designed and built a rather unique craft that was very lightweight and sailed very well offwind, but offered little protection from the weather. Once home his wife claimed she would never go to sea again... and thus the solo circumnavigation seed was planted. His vessel, the Spray, was constructed to give advantage to a solo sailors needs. In particular, there was a very long sprit that allowed a low aspect sail plan with many options. A bristol channel cutter comes to mind if you're looking for a visual. Anyway, the keel was very strong, and very long. The the long keel and balanced sail plan allowed the vessel to sail a straight course untended for many, many hours. According to the book he navigated by dead reckoning. In fact, in the book he is quite proud of Spray's ability to hold her course and his capacity to make landfall using the clock, speed log and compass. It is assumed he had charts and other publications that would help him establish positions.Nevertheless, his accomplishment is not diminished, whether he used some form of celestial navigation or not.

 

[Ross]

Joe I read Around Alone also

Spray was given to Slocum as a joke and was a coastal oyster boat that he rebuilt. I don't believe that by dead reckoning alone you can find the islands in the pacific. Lunar distance method does not require an accurate clock.

 

[Joe]

No argument here....

...he was given the boat as a kind of practical joke. The joke was soon forgotten, however, as slocum proceeded to rebuild the Sray from the keel up, plank by plank. (chapt 1)The clock was real, btw, but he didn't use it too much, because he often verified his dead reckonings with lunar observations. Yes he had a sextant, and in one account he found his observations to greatly disagree with his reckoning. He was so sure of his intuition and reckoning skills that he re calculated and found an error in the table itself. He also towed a spinning log to give him boat speed. (Chapt 11)Whether one can navigate the pacific islands with dead reckoning alone is not arguable. Sooner or later one needs to fix a position to verify a dead reckoning course. But lunar and solar observations are often obscured by weather, sometimes for long periods of time, and that is why being able to dead reckon your course is so important. That is why keeping track of speed, direction and time in a log is part of navigation. Slocum's experience and intuition made him a master at dead reckoning, but he wasn't stupid enough to rely on it alone.

 

[sailortonyb Allied Mis]

Ded Reckoning

Ded Reckoning ( 'Ded' being derived from 'deduced' ) should always be used when traveling any distance even as little as across Lake Ponchartrain say 20 miles. Actually, when you steer by your GPS and compass at the same time, you are Ded reckoning to a certain degree. All Ded reckoning is simply stated is draw a straight line from point A to point B and follow that compass direction. It is further refined if you take known markers and positions and use that to calculate your actual speed ( speed over ground) and actual direction. If nothing changes ( which it usually does), you should be able to figure out how long it will take to get to point B. I always use ded reckoning even with my GPS on, i like paper charts (covered in plastic envelopes). If you lose your GPS, at least you knew your last position and bearing. As long as you can see, Ded reckoning is very accurate for coastal cruising. When I learned to sail about 10 years ago, thats how I made it from Ms to Fl. on a regular basis. Sometimes being out of sight of land for 5 hours at a time. then when we would cross a ship channel, i could course correct, if necessary by using the buoy numbers. When sailing, you should use all the tools available to you, unless of course, when in a relatively small area, and in sight of known markers. Thats just being practical. Why would I need to ded reckon or use GPS when inside a channel when i see the markers.?

 

[Ross]

All of those numbered buoys provide

fixes. Quite often you can't see the next mark but must steer by compass towards it. I always take the course off the charts when sailing from buoy to buoy. The log that Slocum towed is called a patent log. I have one made by Walker.The spinner is three blades about two inches in diameter and about five inches long. The blades form a long spiral and impart about one turn in three feet. The spinner is coupled to an 1/8 inch cord about fifty feet long that is attached to a hook on the recorder. This turns the clock work inside and records the distance on three dials. The large dial about 2 1/2 inches is marked in miles the two small dials record tens and hundreds of miles.I don't use it because it is far too valuable any more. I was able to buy this one from Hal Roth about ten years ago.

 

[ed]

boy you guys are off the wall

You guys really know how to answer the guys question.damn i had to go thur 2 pages of responses to get even a suggestion about the guys problem!

 

[Tom]

Ed you missed the point!!!

These message boards are for talking about sailboats and boating. The first couple of responses pretty much answered the question. Then we wnated to talk about the importance of knowing your boat's speed and how to determine that speed. I guess the whole thing about slocum's clock was that a clock doesn't have to be accurate as long as you know it's error. It's been a long time since I read his book but I assumed that he needed to know the time so that he could navigate using his sextant. As I understand it you can't determine longitude unless you know the time and if you know the longitude you can determine the time. The sun moves 15 degrees an hour and starting in Greenwich it is directly overhead at noon. Other stars and planets behave simularly. Latitude doesn't require time just dates. Before the clock ships would just sail north and south to get on the right lattitude and then sail east or west. Then DED reckoning would be very important. Birds were part of the reckoning as the sailers knew about how far offshore certain birds would fly. So when they saw certain birds they knew that they were close to shore.  Ben Franklin supposedly defined the gulf stream by it's change in temperature. Going north and east the sailers saved a lot of time riding the current. All it took was a thermometer!!!!