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Old 13-09-2010, 10:02   #1
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Speed Gauge . . . Do You Really Need it ?

Mine hasn't worked since shortly after I bought the boat. Then the temperature sensor stopped working. I was almost going to remove the thru-hull and just patch it, but instead I bought a new transducer.

I know there are times when it can come in handy, like more accuratly judging travel time, especially when dealing with tides and currents, but...
If I really need to know the water temp, not sure why you would, I can drop my dive computer in. And the dock you're about to hit too hard only cares about SOG, which you can get off the multiple GPSs on board.

If I could have gotten a transom mount one, I may feel differently, but they're not compatible with my older instrument. I still haven't put it in since launching, and honestly I'm dreading the idea. Purposely opening a hole in the bottom of my boat while I'm in the water, just seems really stupid. I'm probably just make a bigger deal out of it than it is, since I've never done it, but it just seems like a poorly designed piece of equipment in my opinion.

I'm really debating leaving that Tridata as just a depth gauge, and patching that hole on the next haul out. Or just selling the whole thing and using the money towards a new sounder or fish finder.
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Old 13-09-2010, 10:27   #2
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Personally, I find speed through the water to be a very important bit of data. I would never consider giving up on it, although I must admit that I often go without it.

I have also had a lot of trouble with my speed transducer. Can't get the d*mn thing out to clean it, and it fouls and stops working until the next bottom cleaning. It's a lot of bother. I think an ultrasonic one is probably the best solution, but they are $$$.

Speed through water is particularly important if you sail where there are strong tidal currents. If there are no tidal currents where you sail, then maybe you can get by with GPS speed data.
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Old 13-09-2010, 12:02   #3
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Befo' all this new-fangled 'lectronical gadgets came aboard the way you knew you were in the Gulf stream in the Newport/Bermuda race was to tow a thermometer and check for the temp rise.
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Old 13-09-2010, 12:50   #4
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Maybe not for a sailboat, but I use mine to calculate fuel usage daily.
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Old 13-09-2010, 13:33   #5
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Maybe it's because I'm still learning but I use my knotmeter constantly.

When I make a small change in trim I get instant feedback on how that affects performance. I won't necessarily be able to feel a .3kt increase but can see it clearly on the meter.

Also in the Puget Sound currents are an ever-present factor, and with my knotmeter and GPS, I can know exactly what they are doing.

The sensor gets fouled pretty easily and is a pain to clean but for me it's totally worth it to keep it working.
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Old 13-09-2010, 13:35   #6
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A knotmeter is really helpful on a sailboat. It's the only way to accurately assess changes in sail trim, sheet angles, sails etc. The knotmeter probably also has a log function which is important if you ever have to fall back on DR navigation. Besides, how else are you ever going to truthfully brag about breaking 10 knots surfing in the Trade Winds.

I'm not a big fan of the SOG function of the GPS. It's a lagging instrument and almost never seems to be in touch with what is actually happening in real time. Don't really think the SOG function is really all that accurate. On my recent Transpac, the SOG speed usually flopped around by way more than a knot and almost always read too high. That was in comparison to the Raymarine 60 knotmeter and Walker Log which proved pretty much spot on in 24 hour runs using the GPS Lat/long fixes. GPS SOG is also effected by current so not a valid representation of speed through the water which I normally care about way more than SOG. I want to keep the boat moving at it's optimum through the water. Primarily interested in SOG when I'm trying to play the current as well as maintaining optimum speed through the water.
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Old 13-09-2010, 21:49   #7
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Besides, how else are you ever going to truthfully brag about breaking 10 knots surfing in the Trade Winds.
I think you have this backward. According to my GPS, I have hit 53 knots SOG. My paddlewheel stubbornly refuses to acknowledge my feat. I seems to think I have never topped 10 knots through the water.

I guess I must have been in a 43 knot current
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Old 13-09-2010, 22:31   #8
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We went the other way - We had depth and no speed. Depth instrument failed. Got a great deal from a member here that included both depth and speed.

Adding speed to the boat was very useful for sail trim as noted. Also makes you crazy wondering why you can get 5.6 knots on Starboard tack and only 5.3 on port - grrr...

Add GPS SOG and you can figure out currents. Also balancing SOG and Speed to get VMG allows you to sail more efficiently.

However, if I didn't have it I wouldn't pay $800 to get it.

In regards to the wheel fouling, it is a problem. I pull it on Sundays and put it back on Fridays or Saturdays.
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Old 13-09-2010, 22:50   #9
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We went the other way - ... Also makes you crazy wondering why you can get 5.6 knots on Starboard tack and only 5.3 on port - grrr...

If the device is one one side of the keel as it typically is, it could be a matter of differing dynamics. If it really bugs you, install another one symmetrically opposed.
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Old 13-09-2010, 23:00   #10
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You *can* tell the speed of a vessel without a knotmeter, by dropping something in the water at the bow and being dead accurate with how long it takes to get to the stern (or any distance, really), and then doing some math. But that's pretty nuts.

I sort of understand (but don't agree) with folks who have foregone all basic navigational and seamanship knowledge and steer their boats with ipads and laptops. But the idea of getting on a boat that you can't DR with unless you throw a cork off the bow and use a stopwatch? No way.

Just dive the boat, stick a ziplock bag flat against the hull, and have someone on the inside replace the paddle wheel. Takes 5 minutes.
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Old 13-09-2010, 23:41   #11
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It really depends how you sail.

If you're the type of sailor who looks at the boatspeed and thinks "oh look I'm doing 6.5kts, that's nice", there's probably not a lot of value in buying one.

If you're the type who looks at the boatspeed and thinks "6.5kts, that's a bit slow on the polars, what do my sails look like ... hmm... look OK, ...what's the current doing....ah, I see, time for a tack to leebow the current I think" Then there's a lot of value in it.
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Old 14-09-2010, 03:24   #12
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On a cruising boat I have come to the conclusion its not worth the trouble trying to keep it clean. I have replaced my paddlewheel with a second depth which I think is an almost essential backup, at least if you have a hull where a internal transducer will not work.
With an EGNOS corrected signal the GPS is reasonably fast and stable. Sail trim is probably easier because I can trust the display. The True wind display is always spot on.
If your racing or sailing in waters with strong current I think a log is essential, but otherwise consider the replacement to GPS speed. The new GPS units with a 5Hz update promise further improvements.
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Old 14-09-2010, 03:46   #13
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Hi - our log (speed and log) trasnducer has been unreliable for a while and failed completely last year. After two seasons without one we are taking a deep breath and replacing it and the broken wind transducer at the same time.

Not having them doesn't 'stop us sailing' (our fundamental test) but it's real pain not knowing your speed through the water. Even in the Med with minimal tides and currents only in specific areas, it's a pain. But we are doing out of the water, having waited till we hauled.
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Old 14-09-2010, 04:13   #14
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As suggested in most of the posts above I wouldn't want to be without water speed, although keeping the paddle wheel sensor free is an annoying task after you have anchored for more than a few days.

I use B & G instruments & they offer a through-hull fitting with spring loaded flapper valve. When you remove paddle-wheel for cleaning the valve flips up & is held closed by water pressure. In any case you quickly replace with blank plug.

Even after replacement, its rare to have more than a few drops of water to mop up.

My previous boat with old Lowe instruments also had a similar valve. Worth looking into.
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Old 14-09-2010, 04:29   #15
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You *can* tell the speed of a vessel without a knotmeter, by dropping something in the water at the bow and being dead accurate with how long it takes to get to the stern (or any distance, really), and then doing some math. But that's pretty nuts.
Maybe nuts today but that is essentially where the term "knot" comes from. Using a chip log, how many knots passed through your fingers in a given period of time gave you your speed measurement in knots.

But you probably knew that.



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