Knotmeter or GPS

[jibes138]

What is the opinion of this group regarding using, and maintaining a knotmeter versus just using the velocity function on your GPS? My last ocean voyage, noank, Ct. to Hampton, Va. I just used the GPS and found it worked fine. No paddle wheel to get fouled, no through hull, the only bad feature is GPS tends to be more of an average speed versus instantaneous so it is probably not that valuable for racing. My question is should i remove the knotmeter and glass up the hull or just leave it and don't worry about it? What are other boaters doing with these antiques?

 

[Roger Long]

Keep it, absolutely. If something happens to your GPS or the system goes down due to a solar flare you'll need it for the clock and compass navigation that gets you home if you get into coastal waters in poor visibility. Why spend money to get rid of a backup system?

You do know how to navigate without a GPS, do you not?

 

[Bill Roosa]

Current set and drift

By networking your GPS and knot-meter you can get current set and drift values. Handy when there are no crab pots or floating nav aids to look at.
It is also a better tool for sail trim. GPS incorporates EVERYTHING so if you have the sails trimmed well and wait an hour the current changes and your SOG does too. Did the wind change or the sails get out of trim? Check the knot meter (and wind instruments) for your speed through the water to confirm nothing changed and it is the current.

 

[Maine Sail]

Difference is...

The main difference is speed over ground and speed through water. The GPS won't tell you speed through water and the knot log won't generally tell you speed over ground unless there is zero current. If you are not racing SOG will do more to tell you when you'll actually be there but STW will do more to help if you are racing. I think it's best to have both then you can add or subtract between the two to determine the current that is favoring you or hurting you...

Knot logs should be cleaned on a regular basis or they become horribly inaccurate. Depending upon a partially fouled knot log in thick fog can really mess you up. It does not take much growth to slow the wheel and make it totally inaccurate..

 

[caguy]

Mine was never that accurate, but like the song says &quot "it hides a nasty hole that's lying there ".

 

[jibes138]

You do know how to navigate without a GPS, do you not?

Yes I have a Master license for up to 50T with sailing and towing endorsements. I never had a loran or GPS for about 5 years when I first started sailing and navigated just fine with dead reckoning and a depth meter.

 

[jibes138]

Navigation

By the way sailors all over the world navigated for a long time without Loran, GPS, or Radio Direction finders. For most of history they didn't have charts either. BEfore they knew the world was round they also only had latitude from a noon sun site. If they didn't know the world was round they wouldn't know much about longitude. In watching one version of Fletcher Christian I observed he found Pitcairn Island by navigating along a line of latitude. I refuse to get a chartplotter, prefering to use GPS or Loran just for Lat/Lon coordinates because it forces me to plot positions on a chart and keep my navigation skills tuned up. Besides the voyage plotted on a chart makes a wonderful wall decoration that always prompts discussion about the voyage. I like to give them as gifts to the crew on the trip as a momento.

 

[Franklin]

Yes I have a Master license for up to 50T with sailing and towing endorsements. I never had a loran or GPS for about 5 years when I first started sailing and navigated just fine with dead reckoning and a depth meter.

And how did you determine if you were in a current or not? And how strong was that current? Surely it must be part of the test to know that using a GPS and Knot meter, you can determine the current situation.

 

[Seattle Scott]

After my knotmeter head stopped working ( 20 years old) , at the next haul out I pulled the paddlewheel and glassed in the hole. the chart plotter has tidal current direction and flow information.

 

[Chuckbear]

And how did you determine if you were in a current or not? And how strong was that current? Surely it must be part of the test to know that using a GPS and Knot meter, you can determine the current situation.

I know I am in a current because the boat is running slower over the ground than it should be. we stopped using a knotmeter a long time ago because it clogged all the time and was not very accurate when it did work. I need to know how fast I am going over the ground. The speed through the water means nothing to me. It will not tell me when I will arrive at my destination, next mark, bridge, anchorage, etc. The speed over the ground will tell me all of this. Of what real value is knowing the current situation? There is very little you can not get from the GPS. I know a bit about navigating as I taught a boating navigation course at Orange Coast College for 3 years. Without the GPS a knotmeter is marginal and all navigational information is estimates. With the GPS your information is pretty precise.

 

[Alan]

For sail trim...

..the knot meter is the thing to have.
If you pull the log when the boat is idle (I always do) it never needs cleaning. It helps to have a self-sealing thru-hull which stops all but a couple of ozs of water from entering.

 

[Relentless]

And how did you determine if you were in a current or not? And how strong was that current? Surely it must be part of the test to know that using a GPS and Knot meter, you can determine the current situation.

No GPS is not part of the test, what is part of the test is plotting. To answer your question , heading, bearing,distance, and time

 

[Franklin]

I know I am in a current because the boat is running slower over the ground than it should be. we stopped using a knotmeter a long time ago because it clogged all the time and was not very accurate when it did work. I need to know how fast I am going over the ground. The speed through the water means nothing to me. It will not tell me when I will arrive at my destination, next mark, bridge, anchorage, etc. The speed over the ground will tell me all of this. Of what real value is knowing the current situation? There is very little you can not get from the GPS. I know a bit about navigating as I taught a boating navigation course at Orange Coast College for 3 years. Without the GPS a knotmeter is marginal and all navigational information is estimates. With the GPS your information is pretty precise.

Say you are motoring into a strange harbor and preparing to dock at night time. It sure does help to be able to look at the gps and knot meter to know exactly how much current is going through the area.

-- Say you are out sailing in the middle of the Gulf. It's your turn on the helm after a restful sleep. You notice you are going slower then yesterday but the wind is a little lighter too. Are you going slower because the sails need trim adjustments? Are you going slower because of current? Much easier to eliminate one of those right off the bat by looking at the GPS and knot meter.

-- You are out sailing and going at a good speed so you don't check the sails, but you actually have a current pusing you faster and your sails aren't optimal so you don't know you are going slower then you should be.

-- You are motoring alone with a strong wind on your nose and beating into waves. You are going slow. Is it all because of the wind and waves or is there also a current involved? Not knowing you are beating against a 2 knot current could cause problems when you need to turn. It may give you a slight or strong drift sideways that you don't reconize.

I know you don't need a knot meter. I sailed for 6 years without one. Now I have mine fixed and love having it with my GPS and would consider it foolish to take a working one out just because you forget to take it out after sailing which makes it need cleaning.

BTW: knot meters are calibratable, so if it's not right, re-calibrate it.

 

[Franklin]

No GPS is not part of the test, what is part of the test is plotting. To answer your question , heading, bearing,distance, and time

That doesn't tell you anything about the currents you are sailing in.

 

[Franklin]

What I find amazing is how the sailors 400 years ago were able to map out the currents of the entire world...all by just using a thermometer. Totally awesome!

 

[Franklin]

..the knot meter is the thing to have.
If you pull the log when the boat is idle (I always do) it never needs cleaning. It helps to have a self-sealing thru-hull which stops all but a couple of ozs of water from entering.

Leave it to racer to understand what I'm talking about

 

[Chuckbear]

Say you are motoring into a strange harbor and preparing to dock at night time. It sure does help to be able to look at the gps and knot meter to know exactly how much current is going through the area.

-- Say you are out sailing in the middle of the Gulf. It's your turn on the helm after a restful sleep. You notice you are going slower then yesterday but the wind is a little lighter too. Are you going slower because the sails need trim adjustments? Are you going slower because of current? Much easier to eliminate one of those right off the bat by looking at the GPS and knot meter.

-- You are out sailing and going at a good speed so you don't check the sails, but you actually have a current pusing you faster and your sails aren't optimal so you don't know you are going slower then you should be.

-- You are motoring alone with a strong wind on your nose and beating into waves. You are going slow. Is it all because of the wind and waves or is there also a current involved? Not knowing you are beating against a 2 knot current could cause problems when you need to turn. It may give you a slight or strong drift sideways that you don't reconize.

I know you don't need a knot meter. I sailed for 6 years without one. Now I have mine fixed and love having it with my GPS and would consider it foolish to take a working one out just because you forget to take it out after sailing which makes it need cleaning.

BTW: knot meters are calibratable, so if it's not right, re-calibrate it.

we all have our personal preferences and comfort levels for how we handle our sailing and the situations we incur. We have entered many harbors at night and dock our boat all over the US, Bahamas, northern and western Caribbean without incident. We have crossed the Gulf of Mexico and a few other gulfs on more than one occasion and the currents were never an issue. Sail trim, and tacking or gybing situations again were never an issue and beating into strong winds and waves, the current was the last thing on our minds. But that is OUR comfort level and those are OUR experiences. Others as have posted have differing comfort levels and experiences. Remember, any advise on a internet discussion board is worth what you pay for. My advise is not correct nor is other advice received here nor is wrong either. They are the opinions of others. So take that and decide what you can sail with and start to apply your own needs and experience and comfort level. As a marine service tech with 35 years experience I can tell you that once the common transducers get a little time on them you can calibrate to your hearts content and they will not be accurate.

 

[Guest]

Speed meter versus GPS

In PNW waters I use both as a point of tide current reference to speed over ground. These waters can be difficult at times and I like both sources of information. It it were my boat I would keep both in working order at all times.

 

[shemandr]

I use both. Did one of the posters question the ability to determine current via plotting? Of course you can. When you fix your position via whatever technique, its compared to your DR position and the difference is the set and drift of the current. Of course its an average. When cruising I get a fix every hour (Mostly I use the GPS) but check it with bearings depth or whatever other info is available. I enjoy this as part of being underway.
When the fog rolls in I love the GPS.

 

[Roger Long]

the chart plotter has tidal current direction and flow information.

But it's just predictions which can very considerably due to wind and, in your part of the world where I lived for a while, local currents due to land and bottom topography. The chart plotter stuff is no more a substitute for the actual data you can derived from a GPS and knotmeter than the newspaper weather report is for determining wind strength.