Chiara’s slave
Well-Known Member
You’ll need some precision data to log VMG against wind strength and direction. I’m sure your rasberry pi can do it with te right inputs, but that's Americas cup league, not decent club racer stuff.
Are Laminate Sails worth it for cruisers
- Thread starter Snowgoose-1
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GHA
Well-Known Member
some very powerful compass data can be had for 15 quid, updates 10 times per second ICM20948 9DoF Motion Sensor Breakout
Mine not permanently wired in yet but looking forward to playing with it
Not a racer so not sure of the high cost tech used , must be powerful gps tech out there cheap
Bottom line - some very powerful kit available on ebay from the drone market etc & the Pi has the software to run it all. (Under a tenner you can get a baromter which will record the shock wave from a volcano going off in Fiji)
Not americas cup but well up there & plotting the data reveals very small trends completely invisible to the naked eye and a screen. .
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flaming
Well-Known Member
Not sure about that. Our B&G stuff seems pretty good at determining the difference between 40 and 42 TWA. Which for us is the difference between holding a lane off the start line and not....
Chiara’s slave
Well-Known Member
And ypu know it’s doing this accurately? Our starts in the DF are done differently, theres no way to come to the start line like a mono if youkre being responsible. We’ll reach down the line at less than full power til we find a hole, power up and shoot through. So I don’t really look to my instruments (Garmin) which do have that capability. Our typical TWA is 40, though we can go higher at the expense of speed. And no instruments at all on an XOD of course.
flaming
Well-Known Member
There is good correlation between bad numbers and bad relatives to other boats.
GHA
Well-Known Member
little thread drift - what do racers actually use as metrics? Some longer passages coming up & thinking a waypoint a few hundred miles away and looking at VMG to that would be useful as something to play around with.
Though TBH ocean passages people tend to get too fixated with how quick can we get there, passage time shouldn't really be a big deal imho, likelihood of happy memories, is the boat/crew happy & did much break should be much more important, if it takes a day or 3 longer who cares, rare privilege to be floating far out in the deep blue sea.
That said, often VMG would be well worth looking at. Any other data that racers use? Do you graph data?
Seems to be a lot of noise on my AWA, though even 10 second averaging can smooth that out into something useful.
Malish
Well-Known Member
I have white 'cruising' laminates as fitted by the PO, we've had the boat 10 years, all idle pottering on the East Coast, but they really set well. The issues I have with the headsail is mould patches, a lot of them, and yes we do take the sails off over the closed season, is diluted Patio Magic a suitable cleaning product? or am I going to cause more harm than good.
Daydream believer
Well-Known Member
If it is mould between the layers then you will be wasting your time. I would suggest you have them professionally cleaned
Malish
Well-Known Member
Usual 'sailmakers' winter cleaning has done nothing for it, care to highlight your preferred 'professional' option, a PM is fine if it would appear to the forum mods as advertising.
Cheers
johnalison
Well-Known Member
Possibly, but it won't take long to try it out on a sample patch. I used it on a small area of our last laminate jib.
geem
Well-Known Member
Interesting thread.
In the Tropics, laminate sails have a short life. A Captain on a 72ft cruiser/racer (that only cruises these days) who moves between the .Caribbean and the Med says they replace their laminate sails every 5 years. UV kills them. They are .North sails.
My experience, albeit several years ago with the laminate sails that came on my last boat, was that 4 years killed those sails. Another guy here got 3 years out of his laminate genoa. Really not an issue in the UK but anybody thinking of doing an Atlantic circuit, you may be better putting on a set of .Dacron sails and saving your laminates for when you get home. The sun here is brutal.
In the Tropics, laminate sails have a short life. A Captain on a 72ft cruiser/racer (that only cruises these days) who moves between the .Caribbean and the Med says they replace their laminate sails every 5 years. UV kills them. They are .North sails.
My experience, albeit several years ago with the laminate sails that came on my last boat, was that 4 years killed those sails. Another guy here got 3 years out of his laminate genoa. Really not an issue in the UK but anybody thinking of doing an Atlantic circuit, you may be better putting on a set of .Dacron sails and saving your laminates for when you get home. The sun here is brutal.
flaming
Well-Known Member
little thread drift - what do racers actually use as metrics? Some longer passages coming up & thinking a waypoint a few hundred miles away and looking at VMG to that would be useful as something to play around with.
Though TBH ocean passages people tend to get too fixated with how quick can we get there, passage time shouldn't really be a big deal imho, likelihood of happy memories, is the boat/crew happy & did much break should be much more important, if it takes a day or 3 longer who cares, rare privilege to be floating far out in the deep blue sea.
That said, often VMG would be well worth looking at. Any other data that racers use? Do you graph data?
Seems to be a lot of noise on my AWA, though even 10 second averaging can smooth that out into something useful.
What we're interested in is 2 things. Getting the best VMG out of the boat, and then measuring it so we know when we're achieving it, so can go back to those settings in order to do it again in the same conditions. Good, repeatable, trim settings win races. Especially in changeable conditions, as if you can react to an increase, or decrease, in windspeed and go straight to your best settings for that windspeed then you get a jump on the boat who are going through an iterative process of trim loops during the race.
We have a set of polars that were developed by a previous owner and have proven to be pretty accurate. We know that if we are getting (and keeping) those numbers we're going to be there or thereabouts with the fleet speed wise. They are all TWA and SPD for a given TWS. For them to be any use you need accurate Log speed and accurate wind data. Time spent calibrating the system is time well spent.
The first, and most important, thing to say is forget AWA, AWS. To get anything useable you need to use TWA and TWS. Otherwise you've simply introduced the variable of "how well am I sailing the boat" into your measurements. Which is a nonsense when you're trying to use them to improve that exact variable.
For example, if you use AWA and AWS, then you get different results if you're sailing at 5 knots or 6 knots. So how are you supposed to produce targets when the wind speed and angle to the boat changes as you go faster? It's not possible.
Next, you cannot use a waypoint "a long way away" to evaluate boat performance. This is because you are trying to measure how well you are sailing the boat relative to the water and the wind. But your frame of reference is land based. So any change in wind direction, even a small one, will have a much larger effect on your VMG number than small trim changes. Get a lift and your VMG will rise, a header and it will fall, even if relative to the wind and water you are still sailing the same speed and angle.
That's not to say that VMG to waypoint isn't useful data, but it's evaluating a combination of boat performance and navigational performance. In order to get the best performance you still need to know that you're moving through the water as well as you can, and then you can see what's happening to your VMG waypoint as part of the information you might use to decide whether you are on the right tack.
GHA
Well-Known Member
Thanks. -
Though from a cruising perspective on ocean passages the boat will always be on windvane so the wind angle will not change, & wind tends to be very consistent. I'm more interested to know if , say, pointing away from the destination by 30 odd deg instead of goose winged dead downwind is going to take lots longer or not much or none at all instead of rolling for a few weeks. VMG seemed to be the best bit of data available for this but maybe there are other ways /things involved to learn.
One doesn't tack, that's a fundamental planning/timing error
Thnx again.
[70521]
Well-Known Member
Does that amount of detail have any impact on a course on passage where you have tide and wind variables, or even crew moving around the boat?gps &/or compass into a raspberry pi, log & plot the data. Will show tiny trends impossible to notice using human eyes looking at a screen. Signalk does all this.
This is Nasa compass with boat on a pontoon
flaming
Well-Known Member
You could answer that with a set of polars for the boat. However, you would need them to not only be what the boat is capable of, but also what sails you're actually going to use. And of course the effect that the seastate has. For example going downwind if there is a good sea running and you can get some surfs, then you will hugely outperform the boat's predicted speed. So understanding what wind angle you need to sail to encourage surfing in your boat with the prevailing wind strength and sea state would be the key bit of info.Thanks. -
Though from a cruising perspective on ocean passages the boat will always be on windvane so the wind angle will not change, & wind tends to be very consistent. I'm more interested to know if , say, pointing away from the destination by 30 odd deg instead of goose winged dead downwind is going to take lots longer or not much or none at all instead of rolling for a few weeks.
One doesn't tack, that's a fundamental planning/timing error
For us what this means in practice is that when there is a decent sea running but the wind has dropped a bit I might end up sailing quite high in order to keep the boatspeed up, and be able to turn down and catch the wave as it arrives for lots of free distance made. So average course would be between the almost DDW surf, and the high mode we sail between waves. However to do that I need to have a full and active crew. A cruiser on autopilot and "fixed" sheets would be looking for the best compromise between speed to catch the waves and pointing in the right direction.
Chiara’s slave
Well-Known Member
That’s what VMG, and polar diagrams are for. Obviously they are totally boat specific, though running dead downwind is rarely beneficial. We are at the ragged edge of the extreme, 135 deg is our Vmax downwind, unless it’s so light you can smell a fart for 5 minutes. We try never to lose laminar flow. Most monos except planing skiffs run deeper.Thanks. -
Though from a cruising perspective on ocean passages the boat will always be on windvane so the wind angle will not change, & wind tends to be very consistent. I'm more interested to know if , say, pointing away from the destination by 30 odd deg instead of goose winged dead downwind is going to take lots longer or not much or none at all instead of rolling for a few weeks. VMG seemed to be the best bit of data available for this but maybe there are other ways /things involved to learn.
One doesn't tack, that's a fundamental planning/timing error
Thnx again.
flaming
Well-Known Member
As ever, you need to take all factors into consideration.
It may shock everyone to know that I'm just now ordering a very cheap Dacron mainsail.... Basically because the boat has no cruising sails, and I want something to use taking the kids away for the weekend, but can't justify spending any money on it given I have a garage full of race sails. I've been looking for a suitable second hand sail, but have given up and am going for a cheap Dacron sail. I would just use an old race main, except they don't have any reef points, other than the offshore main which we still use as a race sail.
GHA
Well-Known Member
Thnx again. Looked long for polars but don't think any exist for this boat. Anyway, doubt if they'd be accurate, even a small cruising boat like my steel 33'er will be absolute minimum 1 tonne over design load ready for an ocean passage, probably a lot more plus bottom might be far from clean if you've been anchored up a muddy mangrove river for a while. Though opencpn has a polar creation plugin which might come up with something useful.
So real data it is Just wasn't sure if there was other real live data available apart from VMG that might be useful but seems seems not. Suspect I'll stick a waypoint a thousand miles away, try a point of sail, leave it for a day or so & try something else to see how the real world reacts.
Try to come up with some measure of "comfort" to add to the equation. And handy thread, could do with a new main and was considering investigating laminates but seems not worth it.
GHA
Well-Known Member
Don't understand. That's what *did* happen, it doesn't have any impact on anything.
Daydream believer
Well-Known Member
I took mine to our local sailmaker, who I know very well, on the Springfield trading estate at Burnham on Crouch. He bundles up a few at the start of winter & sends them away ready for the beginning of the season.