Knot meter sensitivity to sail trim

[inkunzi]

which style of knot meter would provide optimal feedback when adjusting sail trim? Is a paddle wheel in the hull better than using GPS on a chart plotter? My new boat Hunter 28.5 1988 is essentially void of any instruments other than a non-working Autohelm st4000+ wheel pilot. This is the third boat since October 2022. Sold my 1984 Cal 24. Currently selling my 1991 Hunter 27-2 and now just purchased this Hunter 28.5. I am willing to put some $ into some instrumentation that will give some basic sailtrim feedback on my attempts to locate this “groove” I’ve been hearing about. A windex and knot meter should do it. The boat has a windex. Later on I would like to navigate to a way point using what I call a vector and lay line method….so maybe a chart plotter? The boat has a wheel and pedestal grab rail

 

[dlochner]

which style of knot meter would provide optimal feedback when adjusting sail trim?

I'm not certain what you mean by style of knot meter.

Most knot meters use a paddle wheel transducer. As the paddle hwheel spins faster, it generates a higher voltage, the knot meter display is essentially a volt meter that displays the voltage as a speed.

Transducer placement is important. The best location is on the boat's centerline ahead of the keel in undisturbed water. The further the transducer is from this point, the less accurate the knot meter will be.

You may know all this, however it is important to understand these factors to answer your question.

Assuming the transducer is in as close as possible to the optimal position there are 2 adjustments that can be made to the display, the dampening factor and to what precision the display reads.

Dampening refers average time span between changes in the display. The display will show the average speed not the actual speed. Dampening determines the time span over which the averaging occurs. In other words, is the speed updated every second, every 5 seconds, etc. This is a user option, typically under the system settings menu.

The second issue is the precision of the display, i.e., to how many decimal points will the speed be displayed, usually 0, 1, or 2 decimal points. Again the user can set this parameter. The greater the number of decimal points, the more reactive the displayed speed will be.

That's all a background to your question, given this the answer may seem to be a knot meter that can display speed in a very short interval to a high degree of precision. That may not be what you really want.

There are many factors which affect boat speed, small variations in windspeed, wave action, crew movement, tiller movement, a passing patch of seaweed, another boat's wake, you get the picture. If the speed is updated too often or at too great a precision there will be an urge to adjust the sail trim. Which might be the wrong thing to do.

Then there is the laws of inertia. Changing sail trim is essentially changing the energy being generated by the sails. It takes time for changes in sail trim to affect boat speed in either direction.

If you are looking to optimize boat speed and sail trim, tell tales are the best. Get your Genoa telltales sreaming right and the leech telltales on the main right and your boat speed will be optimal. Changes in trim will be immediately available. Changes in boat speed as measured by a knot meter will lag.

Finally, almost all transducers are made by Airmar, so it doesn't matter whether you buy a B&G, Raymarine, or Garmin knot meter, they all use the same transducer. The display and the software interpreting the transducer matters. My preference is for B&G they have the longest history in providing sailing instrumentation, and an out standing pedigree. Garmin is a late comer to the marine world.

 

[Joe]

Speed over ground (SOG) vs. Speed thru water (STW) Hmmm... as far as sail trimming goes I don't think it makes that much difference what you use, as long as you don't confuse the two. Speed is speed... Why make things complicated?
For instance, let's say you're watching the gps and the knotmeter and notice one reads .2 kts slower than the other. What sail adjustment are you going to make???? Does it make sense that the discrepancy is being caused by moving water, not the set of your sails?

As a boat investment, I would rate a good quality gps/chartplotter with a much higher priority over a knot meter. Beside boat speed you get so much more, with waypoints entered the gps figures your VMG (velocity made good)... so no need to mess with the vector calcs. Even pilots don't do that anymore.


For me, the most important sail trim tools (besides the back of my neck) are #1 tell tales on jib luff and mainsail leech, #2 boat compass #3 a boatspeed indicator, gps or knotmeter.. ............. Notice I didn't mention the masthead fly.... Anyway, just remember that sails are trimmed to the APPARENT wind direction, while your navigation (the course you sail) depends on your knowledge of TRUE wind speed and direction.

Go with gps and some tell tales. easy peasy. have fun.

 

[Scott T-Bird]

I would buy a chartplotter and an instrument package with wind, speed, & depth and network everything on NMEA 2000. That will give you everything you want. You can choose the products ... B&G, Raymarine, or Garmin. You can mix and integrate, or choose a single-source producer, your choice.

 

[Davidasailor26]

Your question focuses on one specific use case of measuring speed - I'm going x knots, then I pull this line, now am I going faster than x or slower. For that one use I think a paddle wheel knot meter or GPS are equally capable. Both can be pretty responsive to speed changes if the dampening is adjusted properly, and they can be precise enough to measure speeds relative to each other in a case like that.

There are a couple other uses of speed though, and a paddle wheel or GPS might be better suited to some of those. If you have polars for your boat and want to know how well you're sailing relative to those a paddle wheel is generally better. The polars are based on boat speed through the water, and having currents affecting your speed over ground will make the polar targets inaccurate. Similarly, if you're sailing in current and want to compare one tack to another the paddle wheel (assuming it's mounted in a good spot) will be the best tool. If you're sailing with a current then tack perpendicular to it a GPS might make you think you've slowed down and need to start adjusting things, while the paddle wheel will be accurate.

If you're trying to navigate and figure out how long it'll take to reach a destination a GPS will be better. Speed through the water won't tell you as accurately when you'll reach a place if you're going into or against a current. A GPS is also usually paired with a lot of other data in the form of a chartplotter. In the absence of current I also generally prefer GPS for speed as it won't be affected by fouling on the bottom or turbulence if it's not placed just right.

 

[jssailem]

1. My new boat Hunter 28.5 1988 is essentially void of any instruments other than a non-working Autohelm st4000+ wheel pilot.
2. I am willing to put some $ into some instrumentation that will give some basic sailtrim feedback on my attempts to locate this “groove” I’ve been hearing about.
3. A windex and knot meter should do it. The boat has a windex.
4. Later on I would like to navigate to a way point using what I call a vector and lay line method….so maybe a chart plotter?

Think about this the way you might prepare for a training class with HS students. You need to clearly define the curriculum. Assemble and prioritize the subject matter. Then practice the implementation/presentation to be able to refine the process.

I broke down your query into 4 parts.

1. Regarding Autohelm, you need to identify if you can get it working. This tool is like having a second crew member dedicated to following your directions to steer the boat. Invaluable if you plan to sail solo or with inexperienced crew. Fixing this or getting a new one will be money well spent.
2. Joe mentioned above "the most important sail trim tools (besides the back of my neck)" I am a regarding the use of the back of my neck or my cheeks as a trim tool. This only develops if you get out and sail the boat a lot. You also need to understand the affect the various sail trim lines you have on your boat. Again get out and sail the boat or any boat, to train your senses (like the sense to know that Jamie in the back row of the class is not paying attention to the discussion). Sailing and trimming the sails are a free cost and fun. Spend 4 hours a day over 3 days if your tack a lot (every 5-10 minutes tack), then sail down wind a lot (jibing, wing on wing down wind), and you'll begin to feel the groove you seek. When you feel the boat accelerate on a tack put a sharpe mark on the sheets, so you can begin to repeat the trim for certain wind sailing conditions.
3. I like David's @Davidasailor26 response about the nature and association of knot meters and GPS with regard to speed determination and/or trim thinking. Sailing your boat in a Minnesota lake means little or not current. Thus the thinking that a knot meter will be valuable tool as it will be all about boat speed. That said I would lean more towards funding a chart plotter than a knot meter. The chart plotter gives you much more for the boat buck being spent. Since you have no current to worry about the GPS will be providing the same trim feedback as a knot meter. Yet you get so much more information. The sailing information about VMG is directly related to the quality of your trim activities. Not only will the Chart Plotter give you a best route, you will see the results of your trimming as either better or worse VMG numbers to set waypoints. The knot meter would require you to use a slide rule and pencil/tablet to reach the same data results.
4. Wait no more. Your best trim tool (chart Plotter) is also your navigation tool. It is like that sweet spot "2fer" people seek.

Best of luck. It is easy for us to spend your money...

I like going out on the water and sailing around some buoys timing my action, then doing it again but changing the trim controls just to see what can happen.

 

[thinwater]

which style of knot meter would provide optimal feedback when adjusting sail trim? Is a paddle wheel in the hull better than using GPS on a chart plotter? My new boat Hunter 28.5 1988 is essentially void of any instruments other than a non-working Autohelm st4000+ wheel pilot. This is the third boat since October 2022. Sold my 1984 Cal 24. Currently selling my 1991 Hunter 27-2 and now just purchased this Hunter 28.5. I am willing to put some $ into some instrumentation that will give some basic sailtrim feedback on my attempts to locate this “groove” I’ve been hearing about. A windex and knot meter should do it. The boat has a windex. Later on I would like to navigate to a way point using what I call a vector and lay line method….so maybe a chart plotter? The boat has a wheel and pedestal grab rail

Actually, the best way to find the windward "groove" is to sail within ~ 200 feet and parallel to a similar boat and make changes. Instrumentation is good, but the wind direction and strength are constantly changing, as are waves and currents. Tiny but unnoticed changes in AWA make feel you are doing better,when you are not. Sailing next to a trial horse can be more useful. Are you pointing higher than the other boat? Are you going faster? Most any boat on autopilot will do.

Chase someone. It's the best teacher.

 

[American_Mainsail]

I don’t think that you’ll love my answer, so apologies beforehand. Here’s my .02: as an engineer, when first I started sailing, I was attached to my instruments, and put a lot of faith into them. I felt like they were they only solid “data” I could rely on out there. Fast forward to now, I feel that the best information a sailor can get is through his/her senses. SOG, through GPS, is the only “true” speed you can rely on, but that is affected by all kinds of factors including swell, current, etc. Boat speed indicators are notoriously unreliable. The “groove” is an unmistakable feeling, once you know what you’re looking for.

Try going sailing with some experienced sailors. The feel of being in the groove, once your head is out of the instruments, is a beautiful thing. The boat seems to glide effortlessly through the water. Maybe someone can point it out, or maybe you’ll develop a feel for it in time. Instruments can be helpful, but trying to really dial in your sailing senses with them is missing the point, a bit.

 

[Tally Ho]

My boat had both a paddle wheel transducer/gauge and a GPS speed on my Chartplotter. My paddle wheel would be way off on one tack…as the boat healed over. i recently removed the display and I am just using the GPS speed. In Milwaukee, you don’t have to worry about tides and speed through the water (Much).

A chart plotter is a great place to start on your instrument package…it will have built-in compass, depth, water temp And hopefully can help, you get home in the dark or fog.

I have mine tied to my AIS-capable VHF radio via NMEA2000 network, so I can see all AIS targets around me.

I have a separate wind instrament (TacTic wireless) and after some trial and error and a wireless interface I bought used, I can also display my wind info on my chart plotter.



I also have a separate autopilot, and about the only thing I have set up is tying thre wind info into the AP…this way I can have the AP steer to a wind angle, instead of a compass heading.

Greg

 

[Stu Jackson]

The feel of being in the groove, once your head is out of the instruments, is a beautiful thing.

If you want to do this, and I fully agree, is to

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[JamesG161]

As the paddle hwheel spins faster, it generates a higher voltage

Actually it sends pulses of constant voltage. The higher the pulse rate, the faster the speed.

Tip: Your hull knot meter will include any water current flow. Not true on GPS speed.

Jim...

 

[william24424]

I want to remove my paddle wheel and fill it with fiberglass. Always clogs after week or two, not easy to scrub free because one piece of algae will stop wheel. GPS + tell tales = Easy. Good luck.

 

[dlochner]

I want to remove my paddle wheel and fill it with fiberglass. Always clogs after week or two, not easy to scrub free because one piece of algae will stop wheel. GPS + tell tales = Easy. Good luck.

This is a bigger job than just filling the hole with fiberglass. To do the job properly the area outside the hull has to be ground down to form a scarf that is 6:1 for the hull thickness and do the same on the inside. It is then necessary to build the hull thickness back up with successive layers of glass and epoxy to the original hull thickness and sand, fair, sand, barrier coat and then antifouling.

Or, you can just stick the blank plug in the hole and forget about it.

 

[DArcy]

which style of knot meter would provide optimal feedback when adjusting sail trim?

Racing sailors will tell you a paddle wheel knot meter with 2 decimal place accuracy is required to optimize sail trim. I sailed with a guy that would not race on a boat without this. For navigation a GPS showing speed over ground is better, and this includes determining your VMG to the next mark, but for sail trim the best tool is a paddle wheel knot meter.
If you are starting from scratch on a boat without instruments and want a complete setup then start with the paddle wheel knot meter and use your phone or tablet for GPS for now, then add a dedicated chart plotter when you can. Plan out the system so the sensors and displays are all compatible.

 

[kappykaplan]

Or, you can just stick the blank plug in the hole and forget about it.

Or put the blanking plug in when you're done sailing and reinstall the paddle wheel the next time you go out. That's what I do.

 

[thinwater]

Most of the time when I go sailing, I don't turn the instruments on. Sailing is an anachronism, and for me, is about getting away from the computer. Get your head out of the cockpit.

You learn the feel of sailing, the groove, in a dinghy with no instruments.