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Uneven port/starboard boat speed


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I’m looking for thoughts and suggestions that might explain a pronounced port/starboard performance difference in my boat.  In medium/heavy air the performance seems fairly symmetric, no obvious bias on one side or the other.  In very light winds, though, the boat seems to go faster on starboard tack than port. 
 

a few notes:

1. The boat hull and appendages were laser scanned a year or so ago in order to get an ORC rating (that’s another story). From analyzing the 3-d data it is hard to find any discrepancy in the hull / keel shape from either side. Certainly if there is any it’s less than 1cm.

2. The speed sensor is on the starboard side and clearly ends differently depending on the tack we are on, BUT, GPS speed doesn’t lie, we are consistently almost a knot slower, and pointing lower on port than starboard.  

3. to the best I can tell, the rig is symmetric and the rig tensions about the same on either side.

4.  having local ‘good sailors’ on board always results in their comment about the feel of the boat being different, with no mention or ‘leading’ from me.

so any thoughts, or suggestions as to what I might do to figure this out?
 

this is a very long shot, but I begin to suspect that the battens on my jib are the culprit. The boat has a 100% non overlapping jib on a furler, and so has 4 vertical battens on the leach, each almost 5’ long. These battens protrude significantly on one side of the sail, and not at all on the other.  See the photos below which show either side of the batten to get an idea.  I’m starting to think these battens are really disrupting air flow when they are in the “underside” of the sail - which would correspond to the port tack, but hardly disrupt flow when they are on the upper side of the foil  Seems a long shot as an explanation.

 

thoughts or suggestions?

 

A8E1DDAC-96EA-405B-957F-82BB13FF3DCA.jpeg

AE063711-64A6-4422-8949-F629D18CBDA0.jpeg

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Let's go old school... hoist the boat, get an old step ladder, put it on a flat surface behind the boat. Tie a string on the top rung with a weight in the other end, dangling above the ground. Step back and sight along the string and keel (or mast). Shim the ladder as necessary so they line up. Now sight the mast (or keel). Do they both align with the string?

 

Surveyors can probably do this better, but you get the idea. The position of the boat is not part of this equation. 

 

Edit.. whoops, forgot to mention the rudder. Mast, keel AND rudder should all align with the string. The rest is just buoyancy or weight.

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A full knot in speed difference is a HUGE difference. Jib battens aren't causing that. It's something much more basic.

When did this speed difference start? What did you change right before that?

Normally I would suspect a mast that is not centered, and / or is not in column on the slow tack (or is curve into the slot on one tack, and bows out away from the slot on the other). This latter is not the kind of thing that shows up only in light air, though.

I know of one boat that had a loose patch of fiberglass skin just aft of the keel, on one tack it flopped down and open and was a water brake.

FB- Doug

 

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J24 I sailed did this. Bottom pintle was replaced (badly). Keel was 15 degrees offset from the mast, keel column. Easy fix once you knew what the problem was. Back to string theory...

 

Ok, these two strings walked into a bar. One string said to the other, "Hey, do ...:.

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I agree that the battens will not make that big of a difference. Alignment of mast and keel + rudder is indeed important. What you describe really sounds like an issue with the keel, rudder or rig out of wack. You say you think the rig is straight / symmetric. How did you measure?

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I'd give another look at the rig. 

Take a 100' tape and run it up the main halyard.  take a measurement at each rail, abeam the mast.  The measurements should match.

If this is not a new problem, just for grins, measure from the side of the mast to the rail on each side.  See if those measurements match (and, yes, I have seen boats that were not symmetrical, and/or where the mast partners were not equidistant from the rails.  ObNote, I've also seen boats where the jib tracks were not the same distance from the centerline... that might be worth checking as well)

I'd also ask, just because... what kind of speed sensor do you have?  If it is a paddlewheel, it could be in very different flow on one tack from the other.  Or might not be facing directly fore-and-aft.

Failing all that.... as others have noted above, take a good look at keel and rudder when the boat is out of the water.  I've actually seen early-in-the-production-run boats with mis-aligned keels (heck, I've seen one where the keel was mounted a foot farther forward than it was supposed to be.  You'd think that would have gotten someone's attention....)

I do not think the battens are the problem

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6 hours ago, Varan said:

Tie a string on the top rung with a weight in the other end, dangling above the ground. Step back and sight along the string and keel (or mast). Shim the ladder as necessary so they line up. Now sight the mast (or keel). Do they both align with the string?

Just a random note.... if you hang a plumb-line from the top of a ladder, no amount of shimming will change the angle of the plumb-line.  It'll be "plumb" no matter what angle the ladder is at....

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You checked for a straight mast right? Take your halyard And measure different points port and starboard. Are the jib tracks in the same positions?

indeed, check keel, mast and rudder alignment. 
 

is keel and rudder profile the same on both sides?

 

when sailing view up the mast, take a picture of the mast bend and sideway sag. Tack and repeat. 

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10 minutes ago, sledracr said:

(and, yes, I have seen boats that were not symmetrical, and/or where the mast partners were not equidistant from the rails.

more often than not .

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I am liking the main only test as it might be possible the jib has a different shape tack vs tack in light air due to the batten pockets being asymmetrical in the way they are attached to the sail. My first thought was foil symmetry where rudder and keel were working together better tack vs tack. But I can easily see the jib issue going away with heavier loads. Kinda reminds me of light air drifters with wire in the luff to help with shape in light air. Attached(or not) air flow with big curves in jib and main in light air is where some voodoo shit can be happening. Rig alignment with the foils is also influential as well as CG in regard to all crap below decks of which an entire chapter could be written. 

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Lots of good suggestions above, but the main rule is never assume that ANYTHING on board actually is symmetrical port to starboard!

That includes thing like spreaders, mast sheaves, etc, etc, etc

So measure everything you can think of and compare

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12 hours ago, Vespucci said:

I’m looking for thoughts and suggestions that might explain a pronounced port/starboard performance difference in my boat.  In medium/heavy air the performance seems fairly symmetric, no obvious bias on one side or the other.  In very light winds, though, the boat seems to go faster on starboard tack than port. 
 

a few notes:

1. The boat hull and appendages were laser scanned a year or so ago in order to get an ORC rating (that’s another story). From analyzing the 3-d data it is hard to find any discrepancy in the hull / keel shape from either side. Certainly if there is any it’s less than 1cm.

2. The speed sensor is on the starboard side and clearly ends differently depending on the tack we are on, BUT, GPS speed doesn’t lie, we are consistently almost a knot slower, and pointing lower on port than starboard.  

3. to the best I can tell, the rig is symmetric and the rig tensions about the same on either side.

4.  having local ‘good sailors’ on board always results in their comment about the feel of the boat being different, with no mention or ‘leading’ from me.

so any thoughts, or suggestions as to what I might do to figure this out?
 

this is a very long shot, but I begin to suspect that the battens on my jib are the culprit. The boat has a 100% non overlapping jib on a furler, and so has 4 vertical battens on the leach, each almost 5’ long. These battens protrude significantly on one side of the sail, and not at all on the other.  See the photos below which show either side of the batten to get an idea.  I’m starting to think these battens are really disrupting air flow when they are in the “underside” of the sail - which would correspond to the port tack, but hardly disrupt flow when they are on the upper side of the foil  Seems a long shot as an explanation.

 

thoughts or suggestions?

 

A8E1DDAC-96EA-405B-957F-82BB13FF3DCA.jpeg

AE063711-64A6-4422-8949-F629D18CBDA0.jpeg

You interpret boat speed against wind angle 

check your wind instruments 

one knot of speed difference between tacks  is extreme 

your rudder tells the boat balance  story 

carefully measure  degrees of weather   helm ...port tack , starboard tack 

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Also, just because nobody's mentioned it, does the boat have a list? Extra weight on one side or the other can lead to a performance differential between the two tacks. It's like you've got rail meat on starboard but none on port. 

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4 hours ago, slug zitski said:You interpret boat speed against wind angle 

check your wind instruments 

one knot of speed difference between tacks  is extreme 

Good points. Maybe you have not yet made accurate measurements. Perhaps do a test with wind instruments and fly ignored. The offset sensor can be a huge error. GPS is not a reliable indicator. There might be a consistent current in your sailing area that affects different tacks....there certainly is in ours. A half knot current could give a one knot difference. If you always sail the same course, like along a built-up shore, there could be wind aloft issues that affect the twist or different tacks.

I would doubt non-obvious symmetry or balance issues would cause such a difference. If the battens are damaging flow then leech tell-tails should be misbehaving.

Or maybe your helming is better on one side. My decrepit body is more comfortable on port tack...for example.

 

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Is this a good time to tell a couple of somewhat relevant sea stories?

Back when my wife and I raced together, we sailed in a couple of fairly tight one-design classes. Yet I was always complaining, especially on the first beat, the the other boats were out pointing us. Constantly bitching, (but dammit they -were- outpointing us! usually....) she put up with me quite well. But one time, arriving at a fairly big away regatta just in the nick of time, I rigged the boat just a little too hurriedly and got one of the lowers joggled out of place. I did not realize it, the T-fitting on the shroud had turned and caught just slightly sideways. The result was that this lower was extra-tight and the mast had a weird S-curve in it. On one tack, we were only a little worse off than usual. On the other tack, we were hopeless. By the time we were halfway up the first beat, we were dead last and falling behind. I tried to figure out what was wrong, noticed the tight shroud but did not follow up (this was a little centerboard boat, we could not have corrected it on the water).

My wife is pretty competitive.... she's actually pretty and VERY competitve, and was unhappy with a string of last place finishes. Long long way last place! So now it was my turn to be stoic and bear our fate with calm acceptance.

This regatta was at a place where the club was quite close to the sailing area, and everybody was in the habit of going in for lunch. When we got to the dock, I just asked for a drink and some kind of snack brought down to the dock, as I intended to play doctor on the boat. Finally it occurred to me to sight up the mast, what the hell?!?! I was impatient and just snapped the T-ball fitting into place, at this point if I'd broken something major it would have helped blow off anger. Fortunately it did not break but the mast snapped into it's accustomed tuning.  We went out after lunch and salvaged our reputation if not that regatta.

Another time, we chartered with some friends in a small fleet of C&C 35s. Nice boats. Of course we had to race, and although we were in a place completely unfamiliar to me, there was tidal current and a persistent wind shift caused by big hills/small mountains with cliffs along part of the shore. It took longer than I liked, but we gained a small lead and then covered aggressively to win... when we rafted up for a tea break, one of the charter skippers said that our boat was usually the slowest especially upwind. I made a big show of sighting up the masts, explaining that even on sisterships the rig tune made a big difference, lo and behold his boat had a hook in the mast... this is NOT why they fell behind, he had gone the wrong way on the shift and ignored the current.... but he immediately got on the radio and started giving the charter company office hell, insisting that they send out a competent rigger RIGHT AWAY!!!

Details details..... maybe that is what makes it so much fun

FB- Doug

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Agree with all saying assume nothing.

Anecdote follows.

The mast on my boat was deck stepped right in the center of the area of smooth (no non skid) gelcoat for the step. The surrounding non skid was a different color and everything looked right. The step was offset several inches to one side!  Fortunately in this case repositioning the step was relatively easy.

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11 hours ago, sledracr said:

Just a random note.... if you hang a plumb-line from the top of a ladder, no amount of shimming will change the angle of the plumb-line.  It'll be "plumb" no matter what angle the ladder is at....

Whoops, i meant trailer. When we did this, we rolled one tire up on a piece of 2x6, but a jack would also work. The idea is to get a reference. The closer one of the three (keel, mast, rudder) aligns with the string, the easier it is to check the other two for differences. 

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10 hours ago, alphafb552 said:

Lots of good suggestions above, but the main rule is never assume that ANYTHING on board actually is symmetrical port to starboard!

That includes thing like spreaders, mast sheaves, etc, etc, etc

So measure everything you can think of and compare

Alpha is exactly right. Building on this , Years of sailmaking experience And I would say I have measured every boat on delivery for last 10 years. “World Class” builder had the chain plates off on one famous boat that made us chase our tail for a months and another the tracks were not in the same place from centerline or fore and aft. One boat the mast exit at the deck was not centered and we had to have that shimmed to fix non symmetrical bend. My first inclination was Speedo location but you said that was covered , the others way to test that is to motor with the boat healed each side on a light air day with no sails at the exact RPM on a timed 5 min run and watch the speedo and gps. Do this for each board.

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11 hours ago, alphafb552 said:

That includes thing like spreaders, mast sheaves, etc, etc, etc

Heh.

"back in the day" I was queued up to race on a hot-shit Peterson-42 built by a well-known SoCal builder.  Should have been identical to the boat that came out of the same mold just prior, but... when we went to work up against them, we could just not point with them.  No matter what we tried, they had a couple of degrees on us, all day, every day.

Turns out that while "our" owner had opened the checkbook for the boat, he'd gone a bit cheap on the rig.  Got a 2nd-tier mastbuilder to put one together at a better price.  It took us a month to figure out that our spreaders - all up and down a great-looking triple-spreader rig - were all significantly longer than the ones on our sistership's rig, so when we were trimming to "2" off the tip", as they were, we were actually sailing significantly fatter than them.

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The Serendipity 43 'CELERITY" struggled for a couple of years upwind, no shortage of sails or talent could change this. Finally Wendall discovered that the perfectly 'smooth' keel had been run over by a forklift in Dreyfus's shop. Once enuff battens & string lines were established, it had a 3-5" bow fore/aft.

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I'm stumped, from what I've read.  No offense intended, might it be you?  Forget this if you have a wheel, but if a tiller, we're steering with left hand on starboard tack, and right hand on port.  Are some of us just better with one hand/arm than the other?  I don't think I am, but who knows.

 

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Lower & slower on one tack sounds like mainsail shape. If you wanted to replicate 1kt and 5 degrees on any boat,  you let the mainsail out. That means the rig is highly asymmetric. 
 

1 knot is more than 10% of your hull speed. You are either exaggerating or you forgot to mention that the boat is a catamaran and one of the swim ladders is dragging thru the water. Fess up. 

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I suspect that the rig is off-center, and leans toward the windward side on the faster tack. Best measure from masthead to sheerline next to the mast on both sides of the boat. then re-tune the rig so it is in tune on both tacks. then mark the main sheet and jib sheets to equalize trim on both tacks and see what you see. Getting the speedo to read equally on both tacks may be a real chore because of the fact that the boat has leeway which effects the flow of water over the impeller. when you do your sailing tests, be wary of wind sheer, which can increase sail pressure on one tack or the other. Good idea to measure distance from centerline to jib lead, and distance from tack fitting to jib lead on both sides of the boat. You might also confirm that the keel and rudder are parallel in the vertical plane, and the mast is parallel to them. If you have to pick, it is better to be faster on starboard tack.

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8 hours ago, XPRO said:

Alpha is exactly right. Building on this , Years of sailmaking experience And I would say I have measured every boat on delivery for last 10 years. “World Class” builder had the chain plates off on one famous boat that made us chase our tail for a months and another the tracks were not in the same place from centerline or fore and aft. One boat the mast exit at the deck was not centered and we had to have that shimmed to fix non symmetrical bend. My first inclination was Speedo location but you said that was covered , the others way to test that is to motor with the boat healed each side on a light air day with no sails at the exact RPM on a timed 5 min run and watch the speedo and gps. Do this for each board.

All too familiar for anyone sailing a jboat (tpi)

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In a related drift...

 

Our actual speed is consistent on both tacks, but boat speed indication will vary by about 0.8kts upwind in 8-10kt breeze. SOG in slack current is consistent on both tacks as is heel and trim. System is a b&g triton with the usual airmar speed/depth transducer. Boat is a j/111 and the transducer is mounted at the aft end of the v berth and is offset a couple of inches to port.

I know this sort of setup wil not produce completely consistent numbers, but this difference seems a bit extreme.

Any thoughts on cause?

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Ok. The transducer is a long way forward.

I think you will find that it is very close to the heeled waterline on port at design heel upwind. You can measure this statically at the dock, then add a bit for the leeway crossflow, which makes the problem somewhat worse.

But you can get rid of some part of the isue with caibration.

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Frog - I do think that it is properly calibrated. Hard to be completely sure, but motoring in flat water, it is pretty consistent. Perhaps another significant fact is that when we see the issue, one tack is well above sog and the other below sog (in slack current). That said, per your comment about the transducer being close to the healed waterline on starboard (healed to port) it would make sense that perhaps calibration when motoring adds its own issue as the paddle wheel is not level?

Steam - I have thought about alignment. I have a plug that I put in when not using the boat, so the transducer is 'aligned' every time we use the boat. I have been doing this myself, and have tried to be careful about alignment. Perhaps I am being consistently wrong. I guess I could draw a line on the hull to provide a reference

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I'd go for the too close to the waterline/different depth on either tack option.

On the old 12s where the paddle wheels could be located comparatively deeply we would use separate paddle wheels on each side with a switch to select the leeward one all of the time.

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I think the instrument should be turned off until is gives accurate speed. Sail another way until the botched boat design can be fixed. Either bore a hole on the centerline or install two transducers. 

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He is using GPS , he knows the speed sensor is off read the first post again. he said the hull was laser scanned that would show bent keel. the battens could be the reason if there are 4 vertical battens tripping the air flow over the jib. if you had the same situation on one airplane wing it would not make the same lift on both wings. so why not on a sail airfoil. The sail with 4 vertical battens would have airflow changed on different tacks by over 2/3 of the sail. another factor might be the furler foil if it has two luff grooves on the foil , so not the same air flow over the sail on different tacks. both drag caused by the different shape and the loose of lift from the different set up will cause a speed change. if a different sail shape did not make a difference then why bother to trim the sail properly. In one design racing. just the slightest little thing will make a big difference in boat speed.  when passing another boat in light air you don't move anything until you have to, i find myself holding my breath so not to change the boat speed.

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Thanks Froggy - didn't know that. I suspect that given that the transducer is slightly off center line, I have an issue either way. In any case, I think I need to do what I can to minimize the issue, and possibly look to a different transducer setup. I suspect that with the triton setup, there is really no great solution here.

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2 hours ago, Frogman56 said:

Calibration under motor is not much use, best baseline is from full heel on 90 degree reach. Motor usually gives result 0.2 to 0.4 different, depending on transducer location.

Read this a couple of times and not sure what calibration mode you are talking about, or if you are yanking some-ones chain.

@pete_nj  The generally accepted means of calibrating speed is to run a measured distance run (several times in each direction to counter effects of current) with instruments in the appropriate calibration mode.  If you run it at say, six knots over a mile that makes the maths easy and you can compare the timed run on a watch with what the instruments are displaying.  If you have an older system you make an adjustment as necessary to correct the speed number.  On newer systems you can make the Cpu do all the cyphering.

Btw, it really does sound like the speed sender is in the wrong location.  It ought to be closer to the front of the keel on centerline.  I have seen several J-111's in our area re-locate the speed sender.

For example: From NKE. 2.1 Principle of calibration : It consists in executing a course with your boat, with a true distance, D miles, that is known, and taking down the number of miles indicated by the log, L miles. Then, you calculate the calibration coefficient according to the formula : D / L. Example: The course measured on the chart between two sea-marks is : D = 1.43 MILES The number of miles indicated by your log for this course is : L = 1.10 MILES The calibration coefficient calculated is 1.43 / 1.10 = 1.30. To ensure the calibration is effective, you will execute a return journey, to cancel the effects of the current, and in excess of 1 mile. 2.2 Setting procedure of the calibration coefficient : To achieve a successful calibration, follow the indications below : ? Sail with the engine, on calm sea, with no wind and at slack water. ? Execute a return journey over a perfectly known distance.

 

B&G H5 system which is fundamentally the same as your Triton system.

calibration.JPG

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take notes!

get another boat and go tack for tack, that would eliminate wind or tide conditions

Then check out the rigging , spreaders position , angle, top center and mast in a line , rig tension , This was a cause I had , turn out to be rigging

knot meter seem to be cover by others

rudder position and angle

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Thanks all.

The issue is simply that the transducer is inconsistent from tack to tack. The boat performance is not in question. In slack current conditions, we sail at the same sog, heel angle, and AWA on both tacks. Our numbers match the polars. The issue is that even after calibrating the boat speed in a process similar to what @Hitchhiker describes, we get a large difference in the boat speed from tack to tack.

I do suspect it is related to the transducer position. Perhaps the offset position also leads to uneven wear of the paddlewheel over time, exaggerating the issue.

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11 hours ago, Overbored said:

He is using GPS , he knows the speed sensor is off read the first post again. he said the hull was laser scanned that would show bent keel. the battens could be the reason if there are 4 vertical battens tripping the air flow over the jib. if you had the same situation on one airplane wing it would not make the same lift on both wings. so why not on a sail airfoil. The sail with 4 vertical battens would have airflow changed on different tacks by over 2/3 of the sail. another factor might be the furler foil if it has two luff grooves on the foil , so not the same air flow over the sail on different tacks. both drag caused by the different shape and the loose of lift from the different set up will cause a speed change. if a different sail shape did not make a difference then why bother to trim the sail properly. In one design racing. just the slightest little thing will make a big difference in boat speed.  when passing another boat in light air you don't move anything until you have to, i find myself holding my breath so not to change the boat speed.

Thanks overboard, and thanks for noting the details in the original post, ie laser scanned hull etc.  Many of the comments are missing the challenge, some are helpful. As also mentioned in the post, this asymmetry ha been noticed by numerous (at least 5) hotshot skippers who have come on board, which rules out my own asymmetry as the culprit! Also, the asymmetry is noticed in a variety of locales with very different current conditions.  It’s not obvious what is going on.

i think remeasuring the mast and rig position is worth doing, as is sailing both without any jib and with a jib from another boat, preferably one that doesn’t have any battens. Hard to find such a sail though, not many boats of this size sailing around here. I’ll report back once I have done a bit more sleuthing,

 

thanks for all the input

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Hitchhiker 

Calibration under motor almost always gets you something out by a material amount, as the flow around the hull and keel when heeled and with leeway is completely different. Quickest way to get close to ok is to find 12 knots of wind, smooth water, no current and reach at full heel and 90 degree twa, comparing to gps on both tacks. Job done in 20 minutes.

On, for example, a Farr type like f40 or Cookson 12, the difference motor vs sail is about 0.3 at 7.4 approx.

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If you want accurate boat speed, you need two or better yet four sending units. With two you would have them port and starboard about 2 feet in front of the keep. With four you would have two more aft in the boat between the keel and the rudder again port and starboard. 
 

we found the at high speeds the bow sending units would pop out of the water. 

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58 minutes ago, IMR said:

If you want accurate boat speed, you need two or better yet four sending units. With two you would have them port and starboard about 2 feet in front of the keep. With four you would have two more aft in the boat between the keel and the rudder again port and starboard. 
 

we found the at high speeds the bow sending units would pop out of the water. 

So, you need a correlating factor of air speed to water speed.

FB- Doug

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It’s was only an issue above 20 knots and not all the time just when the bow was over a wave.  
 

but yes air speed correction factor would have been the fix if we could get the calibration right. Time to top off the blinker fluid. 

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10 hours ago, Frogman56 said:

Hitchhiker 

Calibration under motor almost always gets you something out by a material amount, as the flow around the hull and keel when heeled and with leeway is completely different. Quickest way to get close to ok is to find 12 knots of wind, smooth water, no current and reach at full heel and 90 degree twa, comparing to gps on both tacks. Job done in 20 minutes.

On, for example, a Farr type like f40 or Cookson 12, the difference motor vs sail is about 0.3 at 7.4 approx.

Fascinating.  I have to say in 35 plus years of racing, working on race yachts, including installing race instruments and navigating race yachts, this is the first time I have ever heard of this technique.

Something new every day, I suppose.

 

 

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18 hours ago, Frogman56 said:

Hitchhiker 

Calibration under motor almost always gets you something out by a material amount, as the flow around the hull and keel when heeled and with leeway is completely different. Quickest way to get close to ok is to find 12 knots of wind, smooth water, no current and reach at full heel and 90 degree twa, comparing to gps on both tacks. Job done in 20 minutes.

On, for example, a Farr type like f40 or Cookson 12, the difference motor vs sail is about 0.3 at 7.4 approx.

Hmmm...Having owned, raced and tended to one of the mentioned boat types for quite some number of years, that difference never showed up in any of our calibrations or test runs.  0.3 knots is not something you fail to observe.  

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On 9/1/2020 at 3:44 PM, pete_nj said:

Thanks Froggy - didn't know that. I suspect that given that the transducer is slightly off center line, I have an issue either way. In any case, I think I need to do what I can to minimize the issue, and possibly look to a different transducer setup. I suspect that with the triton setup, there is really no great solution here.

On j105s with a similar setup they see the same tack to tack differences. The tack where the knotmeter is on the low side is always the faster tack. Learn to accept there will be fast tack and a slow tack unless you have a system that will allow boat speed calibration with heel as well as speed

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2 hours ago, ctutmark said:

On j105s with a similar setup they see the same tack to tack differences. The tack where the knotmeter is on the low side is always the faster tack.

Could you share the numbers? Would be interesting to know how much heel correction is needed on 105.

 

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Note that the effect will vary depending on the sensor position, which can vary boat to boat. But the calibration method more or less seems to work.

But heel angle does bring the sensor closer to the free surface as well, common across the fleet unless you have two sensors, which are now a common retrofit.

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