Knotmeter?

[Dan Cahill]

I'm getting ready to install a knotmeter and would like to know if you recommend a thru-the-hull style or a transom attached transducer.

 

[Dave Condon]

Knotmeter

There are several good knot meters but you may want to spend a little more for a dual knot and depth meter. Examples are the Standard 100 series and the ST-30 Bidata by Autohelm. I have installedboth the thru hull and transom mount but found the thru hull to give you more accurat readings. As with anythingyou must be careful with both. Some folks have accidentally knocked off the transom mounted kind. As for the thru hull, you need to remove the thru hull before traveling or at least tape the bottom so the wheel will not turn. Make sure the thru hull type is in when launching or you will have water in your boat if the dummy plug is not in.Installing the thru hull will need to be placed aft of the water ballast tankto the side of the bilge pump. I recommend using 5200 marine sealant when installing transduceres

 

[Jim Covey]

Transom mounts

Dan,I use an Apelco 365 (now Raytheon) fishfinder which has speed/temp and depth readings. I used the transom mount transducer and have now found that if I'm on starboard tack and heel more than 15 degrees the transducer comes out of the water. Couldn't get it any closer to centerline due to the rudder swing.Just a thought to keep in mind when making your decision.One other thought, in the August 1,'99 issue of Pratical Sailor, they mention installing a Kaytek sonic knot meter to their test boat. This means no thru-hull, no paddle wheel. They don't mention how well it works yet.Jim Coveys/v Wampeter

 

[Michael Bell]

GPS

How about just getting the depth meter and using a GPS for speed?

 

[Jim Covey]

SA Problems with GPS

Mike,From all I've ever read or heard you really can't trust GPS speed over ground at slower speeds due to the government imposed selective availability. This is the errors injected into the signal so that the closest you can read is +/- 100 meters.As the unit tracks along it might "think" you just instantly jumped up to 100 meters instantly and record your speed accordingly.Jims/v Wampeter

 

[Dakota Jim Russell]

Trustworthy, but not sensitive

I have a Garmin 48 which is reasonably accurate and averages things nicely. I also have a knotmeter as that is very sensitive to slight increases in speed recording tenths of a knot. However, I use the GPS to calibrate the knotmeter as I lack any navigational points where I could do it more accurately.Appreciate that a knotmeter will have error on port/starboard tacks depending on where it is mounted, and will also reflect water movement not necessarily associated with boat movement. Hey, now that I have two watches I really don't know what time it is <grin>.