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Old 01-03-2012, 16:43   #76
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Re: How Necessary is a Knot Meter ?

I don't understand the "reasoning" of not being able to trim sails using the GPS speed! Unless you changed course you didn't suddenly end up in a different current. If on the same heading and put up 0.3 knots speed on GPS after you trimed; well you picked up 0.3 knots from what you were doing just prior!

On course if you changed course that's a different story. I just keep a VMG chart on the boat for deciding if course changes are helping me on VMG, but most of the time I changed course for sometime else like comfort.
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Old 01-03-2012, 16:43   #77
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Re: How Necessary is a Knot Meter ?

Now that I think of it, I have an old towed log somewhere in the basement. Not a Walker--another brand, from when there was more than one on the market! It would be fun to dig it out and see how it works, or how long the "lure" lasts.
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Old 01-03-2012, 16:51   #78
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Re: How Necessary is a Knot Meter ?

I will say this too. Having a knot meter require a through hull. It require a through hull in the bow of the boat. I have watched my knot meter flex in a big seaway as I came off the back of waves....not a good feeling. I am pulling the thing out upon next haul out and having a fiberglass party!!! I am yanking my depth sounder as well and just using the wimpy one I have aft. I'm not sure about you guys but I prefer to have less holes in the bottom of my boat.
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Old 01-03-2012, 16:58   #79
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Re: How Necessary is a Knot Meter ?

Unbusted67 has a legitimate worry. Somebody I know was crossing the Bahama Banks when they noticed water rapidly rising down below, and they were at least 30 miles from land and nobody around. Some frantic crawling around and lifting floorboards revealed a geyser coming in through the plastic through hull for the knot log, which had blasted out into the boat.
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Old 01-03-2012, 17:00   #80
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Quote:
Originally Posted by Don Lucas
I don't understand the "reasoning" of not being able to trim sails using the GPS speed! Unless you changed course you didn't suddenly end up in a different current. If on the same heading up put up 0.3 knots speed on GPS after you trimed; well up picked up 0.3 knots from what you were doing just prior!

On course if you changed course that's a different story. I just keep a VMG chart of the boat for deciding if course changes are helping me on VMG, but most of the time I changed course for sometime else like comfort.
Most people are crusiers so you are right.

Coming out of tacks in races you accelerate to boat speed. There are concepts like shifting gears, and target speeds that can't readily be done with a gps if you are reading different speeds on different tacks. The polars also don't work with a gps. Is the bottom fouled? With a log you can find out if something is wrong. I sail with lots of guys that try to point before the boat is accelerated. If the gps shows 5 knots and the boat speed is really 3 pointing up will get the boat stalled, it wont accelerate and you won't be able to point and it can take a while to figure it out.

It is very common for the skipper to call boat speed put of tacks so the trimmers know where the boat is at and more importantly can work together. Once again racing comments and crusiers can sail as inefficiently as they like.

And yes, with experience on a particular boat one can tell how it is sailing by feel. On a new boat it is a much harder prospect and a speed log helps the learning curve tremendously.

Hud posted it right for cruisers. If a mile lateral results in one knot favorable vs. one knot unfavorable thats two kots, 48 miles a day, 300 a week.

Up to you all...
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Old 01-03-2012, 17:13   #81
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Re: How Necessary is a Knot Meter ?

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Now that I think of it, I have an old towed log somewhere in the basement. Not a Walker--another brand, from when there was more than one on the market!
Lionel (yes the same people who made electric train sets) manufactured taffrail logs for the USN in WW2, as did GE (General Electric). John Bliss and Co also made them based on their own patents as well as those of Walker and Massey. Bliss operated between 1857 and 1957.
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Old 01-03-2012, 17:20   #82
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Re: How Necessary is a Knot Meter ?

Geeees Astrid...Sometimes I think you have forgotten more than I know!...
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Old 01-03-2012, 17:34   #83
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Re: How Necessary is a Knot Meter ?

Astrid sure has her facts striaght !! Ive heard of these and have seen one or two of them over the years !! I have the same as she has a walker, and made a few props for it in the shop the last place I worked at LOL! never caught a fish yet !! been tryin to fit a hook for years but no luck yet !! LOL Bob and Connie
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Old 01-03-2012, 17:56   #84
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Re: How Necessary is a knot meter

Quote:
Originally Posted by delmarrey View Post
I heard somewhere that "the one with the most toys, wins"!
Correct.......


Quote:
Originally Posted by Cheechako View Post
In that case , you need a knotmeter foward and one aft so you can tell what's going on at each end of the keel...
.......but not just any toys....

Product Detail - DS80

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Old 01-03-2012, 17:58   #85
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Re: How Necessary is a Knot Meter ?

The ones I've messed with have a collar that screws onto the impellor thru hull and holds the impellor assembly in place. The Impellor assembly has an O ring at the hull end that seals out the water. The impellor assembly just pulls out and pushes in and you screw in the cap/collar to hold it or the plug in place. Seems that the impellor and depth sounder transducer assemblies are made by the same third party supplier , can't remember the name, these days and are the same physical design instrument maker to instrument but with different wire harness, if not different electronic charteristics.

If you've never pulled your transducer you could have a battle getting it out. No telling what kind of critters have built a home around and in it.
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Old 01-03-2012, 18:28   #86
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Re: How Necessary is a Knot Meter ?

Quote:
Originally Posted by Don Lucas View Post
I don't understand the "reasoning" of not being able to trim sails using the GPS speed! Unless you changed course you didn't suddenly end up in a different current. If on the same heading and put up 0.3 knots speed on GPS after you trimed; well you picked up 0.3 knots from what you were doing just prior!

On course if you changed course that's a different story. I just keep a VMG chart on the boat for deciding if course changes are helping me on VMG, but most of the time I changed course for sometime else like comfort.
There's a slightly more advanced way of looking at this.

Let's say I'm beating to weather. I know exactly where my sails should be trimmed for a close-hauled course. But at any given combination of sea conditions and wind speed, the boat will be going different speeds. We all know that. What the expert knows, in addition (or the almost-expert using polars) is what speed the boat should be doing for those conditions in order to maximize VMG at any given point of sail. If I sail slower than that speed by pinching up, my VMG goes down. If I sail higher than that speed by footing off, my VMG also goes down.

Now let's say you've got an expert skipper working with a rookie at the helm. At the end of the tack, the skipper brings the boat up to speed and orders any little tweaks the sails need. The boat is hitting its polars perfectly, and the knotlog reads 6.2. Even if the knotlog is wrong at this point because of a slightly dirty bottom, it doesn't matter. The skipper, needing to pee, assigns the rookie to the helm and specifies that the boat should be kept at precisely 6.2 knots STW. If the boat slows beyond that speed, you're pinching too high so fall off a bit. If the boat speeds up beyond that speed, you're footing too low so feather up a bit.

Notice that the sails are not being trimmed here. Notice that current, which would be reflected in SOG, is inconsequential. (And would give you confusing readings were the current coming from any bearing other than the course bearing or its reciprocal, especially when you tack.)

I sail this way all the time. I don't need my helmsperson to monitor the telltales on the foresail, or the bearings on the compass, or any of that GPS stuff. Just keep an eye on the knotlog and keep the boat at the speed I've specified. And try not to hit any boats bigger than us, of course.

Some might argue that you can accomplish the same thing by setting a GPS to report VMG rather than SOG, and this is true. But not only will the response will be delayed as compared to a knotlog, but when your VMG goes down you will have no idea whether it is because you're pinching or footing. At that point, the knotlog is actually giving you better data, and it's adjusting for current automatically.

Cool device!
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Old 01-03-2012, 18:44   #87
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In additional we have found performance in sail shape.

If we are in chop we have released outhaul an inch or so, increased acceleration and steering angle and gained advantage over other boats - Peak boat speed may be slighlty less but average speed is higher.

In flat water we tighten outhaul for a flatter shape, less drag but narrower steering angle.

We have picked up trim issues with the log - forgot to tighten outhaul at the bottom mark for example. When the boat is not hitting it's speeds it's time to start looking. Gps doesn't help with that.

One thing the crew I am working with is learning is how minor the trim adjustments can be to change performance. Upwind they were basically in the trim and cleat camp. That's the first habit we broke.

@Bash - we have also had the sailt to trim and trim to angle discussions with skipper and crew. Deciding when to use either is dependant on a lot of factors.

Again, I am not trying to make anyone go buy a speed log. Just discussing what its uses can be. I certainly can't tell the difference between 7 knots and 7 1/2 nots based on the wake and a tell tale on the shroud but when I can I'll dump the log and save a poind of boat weight - LOL
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Old 01-03-2012, 19:03   #88
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Re: How Necessary is a Knot Meter ?

Makes my head spin!

Not disagreeing, but this is just so far beyond where I'm at as far as sailing. While I always try to improve I don't want it to get where I'm playing more attention to sailing well than just trying to have a good time.

So for me (and my wife) and my cruiser thinking that knot meter just isn't that big a plus. I would glady trade my knot meter (that I have) for a wind instrument (that I don't have).
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Old 01-03-2012, 19:04   #89
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Re: How Necessary is a Knot Meter ?

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Originally Posted by Ex-Calif View Post
One thing the crew I am working with is learning is how minor the trim adjustments can be to change performance. Upwind they were basically in the trim and cleat camp. That's the first habit we broke.
Absolutely! Even with experienced crew, this is where the knotlog helps to learn the boat better. When I switched to my current boat, I had to learn whether easing the traveler and therefore going to a more neutral rudder would speed the boat up or slow it down. The best indicator of this, again, is the knotlog, even if it's not 100% calibrated. You change the trim and observe the difference in how the boat moves through the water, which tells you more than how it's moving over ground.

My last boat, which was fraction rigged, responded quite differently to the traveler than my current boat, which is masthead rigged. I've been able to learn my best angle of heel on the current boat by referencing the knotlog. This isn't just about getting more speed out of the boat. The boat is more comfortable when it's happy on its lines, when the trim is balanced, and when the helm is nearly neutral. The autopilot works less.

This isn't the type of data one gains by observing the wake.

I readily admit that I'm a tweaker. Before asking for the boom vang to be eased, I'll glance at the log. A minute later, I'll check the log again. If easing the vang was a good move, the STW numbers will show it.
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Old 01-03-2012, 19:10   #90
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Re: How Necessary is a Knot Meter ?

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Originally Posted by Don Lucas View Post
Makes my head spin!

Not disagreeing, but this is just so far beyond where I'm at as far as sailing. While I always try to improve I don't want it to get where I'm playing more attention to sailing well than just trying to have a good time.

So for me (and my wife) and my cruiser thinking that knot meter just isn't that big a plus. I would glady trade my knot meter (that I have) for a wind instrument (that I don't have).
Agreed, Don. I admit that, for me, paying attention to sailing well is having a good time. The knotlog is my report card, and I enjoy earning a high GPA.

And yes, we could have a similar thread about whether the wind instrument is an important toy. (And you probably have already guessed that Bash can't imagine sailing without one.)

Or have we already had that thread?
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