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Old 01-05-2016, 19:51   #16
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Re: Polars building

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Originally Posted by UNCIVILIZED View Post
To the OP. Sorry for the thread drift here.



Okay, so despite my insomnia last night, & me as yet being uncaffeinated for the day, I Know that my math's correct. I've been doing this stuff for many, many years. And it ain't complex math.
Re-read your own post, & cross check the text vs. the numbers.

See, what I'm saying is that at lower wind speeds, a small increase (or decrease) in the wind speed has a MUCH bigger affect on how much power is available to drive a boat, than there is with the same level (numerical value) of wind speed change, in the higher wind ranges.

When the wind speed jumps from 5kts to 10kts, you then have 4x the available HP to drive the boat.
To get that same level of increase (in "HP") when the wind speed is at 10kts, the wind speed has to go up to 20kts, so as to get a 4x HP increase again.

And when the wind speed goes from 15kts to 17kts (as per your example), the available energy to drive the boat Only increases by 28%. Period.
But if the wind speed increases from 5kts to 7kts, The SAME 2kt increase, then the energy available (in theory) to drive the boat Doubles!
Make sense?

Force (in lbs) = wind speed in kts (squared) x sail area in square feet x 0.00431
The math don't lie. And you'd have to have Thor hit me with a dozen lightning bolts in order to get that equation out of my head. If then.
Harken


Now the thing is, that drag. That nasty little thing which a sailboat has to overcome in order to go faster. Also increases as a squared function (pretty much). Especially drag through the water, unless we're talking about planing boats, or skinny hulled, fast multl's. Which Lagoons ain't.

So that up until they break past the hump of their hull speed (a drag limited thing), which takes a certain peak HP to overcome, they're limited in speed, by available HP, as are most other boats.
And at lower wind speeds, as are in question, with the available sail area, the boat wont jump past it's hull speed, & into the double digits on the speedo.
Well, unless asssted by a large wave.
I'm not questioning your math. I'm questioning the conclusion you make based on the results.

Assuming you haven't reached hull speed, the relationship between HP and speed is fairly linear. Thus that 2kts from 15-17kt should produce almost the same jump in speed than going from 5-10kts (13 HP extra vs 15hp extra). It's when you approach hull speed that the HP to speed curve starts to curve up. At that point, drag quickly grows and exceeds the additional power from higher winds (assuming full displacement, not surfing or other special case).

Of course this assumes otherwise identical conditions (same heading, sails in good condition and adjusted to the apparent win, etc...)
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Old 01-05-2016, 22:26   #17
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Talking Re: Polars building

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Originally Posted by Factor View Post
Nope, that is slow. Quite Slow. Really Slow.

Compared to what.?

A seawind 1160 sailed by some friends of ours, wrote a piece in their blog about their upwind performance.

The OP polars show a vmg to windward of around 4 knots in 20true.

The seawind 1160 blog talks of 3.2 in 20. Much slower. 20% slower?

Day 216 - 218 - Out to Daw Island - Eastern Group

Are we sure we shouldn't be posting in the thread "why catamarans motor to windward 100% of the time"

Just jok'n
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Old 01-05-2016, 23:26   #18
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Re: Polars building

thanks everyone for comment and concerns re windward. I purchased the boat expecting to tack over angle 50 app and was happy with that. As I can actually do 45 true, as I tested the other day, that is all bonus.

And I always test in ocean conditions and average over several goes, including nasty hobbyhorsing sail dumping seas. I need for planning my routing. If i need real speed to windward can do 2 motors and will use them without hesitation if sailing is not pleasant or feel boat not happy.

However, my question is re beam reaching. Why I hit wall at 7.5kn.

I know about mechanic too and here is my logic :

Lagoon got in trouble of producing polars for 40 feet cat which is many years old. There is no congestion of polars around 8 kn. Every 2 kn app wind speed delivers extra knot of speed. Up to 12 kn boat speed or so at 90 deg.

So, mine, being lightly loaded, and similar shaped, expect to produce same shape polar except ALL speeds for some % different (bigger or smaller). As I have matched/surpassed circled areas, I would expect to be able to match the whole polar and not only circled areas.

Thanks for couple of ideas. Will explore.
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Old 01-05-2016, 23:50   #19
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Re: Polars building

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Originally Posted by Seaslug Caravan View Post
Compared to what.?

A seawind 1160 sailed by some friends of ours, wrote a piece in their blog about their upwind performance.

The OP polars show a vmg to windward of around 4 knots in 20true.

The seawind 1160 blog talks of 3.2 in 20. Much slower. 20% slower?

Day 216 - 218 - Out to Daw Island - Eastern Group

Are we sure we shouldn't be posting in the thread "why catamarans motor to windward 100% of the time"

Just jok'n
yeah, i doubt many quote VMG when hobbyhorsing which is quite often. 10 kn in 8 kn wind fro CF hero, quickly becomes 3 kn in 8 kn wind, cat or mono or tri

there is considerable skill involved in driving boat to windward well in realisitic ocean conditions. Setting sail as per manual will not do much.
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Old 02-05-2016, 00:26   #20
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Re: Polars building

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Originally Posted by Seaslug Caravan View Post
Compared to what.?
Any decent boat that isnt overloaded and sailed competently.

Anyway - welcome back, you went to ground for a while there when you lied about 44C motoring past you and when you were less than truthful about the Grainger allegedly washed up on Hook point, which we later find out is happy and well in Cairns.

I was worried you had an issue, but apparently it was just shame from spreading crap and getting caught.

I can cherry pick from another 1160 blog if you like, or point to the 1160 winning the cruising division at Hammo, but I suspect reality isnt your concern, putting **** on Seawinds is.

My 1000XL would easily and I mean easily do 8-9 where the OPs boat is doing 5-6.

You say Craig and Kerry are friends of yours, so will they know what you allegedly sail, you steadfastly refuse to share that with us here, the only thing you seem to share is your bias.
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Old 02-05-2016, 01:06   #21
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Re: Polars building

The following questions aren't meant to put you on the spot, but rather, to ascertain that most of the easy to do things which influence performance, are being done.
They're basic, diagnostic, tuning questions. And I'm asking some of them because I don't have a feel for your depth of sailing/sail tuning experience. Which, BTW, us knowing such would help us to assist you, in figuring out how to get more performance out of the boat. If you're comfortable with giving such a synopsis.

A simple question, which we ALL forgot to ask you, the OP is...
- What are you using in terms of propellers?
Also:
- Do you lock the shafts when sailing? And hopefully in a manner so as to fully minimize propeller drag.
- Are there any other underwater protuberances from the hull aside from strainers on the raw water intakes for the engines?
- How old, & in what condition are the sails? Including their shape & draft positions. Plus, pictures of their shapes, especially upwind, would help to get a better feel for them.
- What material are the sails made of? And too, if woven, it wouldn't hurt to know their; cut, cloth make, type, weight, warp/weft count (if known), etc.
- Have you been rigging up something to act as a vang when sailing deeper than say 070 AWA?
And I'm assuming that you're not using a vang when sailing upwind?
As improper twist can cause you to loose Huge amounts of power, while at the same time, greatly increasing the sail's drag.
- How effective is your outhaul setup?
- Do you alter you halyard tensions based on what point of sail you're on? And, or, tune the Cunningham on the main?
- Do you have full sets of telltales on both sails? Both, placed slightly aft of the luff, & on the leech?
And are you familiar with how you best want them to fly at various wind angles?
- What are you doing in terms of altering the jib lead positions when off of the wind? As well as upwind?
- What degree of smoothness is on the foils & the hull bottoms?
- Do your transoms drag when sailing? And if so, how much? Plus on what points of sail, & at what wind speeds?
- On average, approximately how many degrees of helm do you need to use in order to stay; on course, or on the wing (upwind)?
As rudders are notorious "braking devices".
- Do you pay close attention to the traveler's settings, upwind, in order to minimize rudder use?
And how about downwind, in order to try & optimize twist? Regardless of the use of improvised vangs or not.

BTW, have you looked into adding a vang? Assuming that you don't have one at the moment.
- And... Of course there are more; questions, & influencing your speed. But off of the top of my head, those are some of the big ones.

Ah, & one other type of "hired gun" which it might be worth looking ito, to aid you in sorting this out (other than the ones I mentioned in an earlier post). Would be to see about having a Lagoon rep. come out for a few sails with you. After you've discussed your concerns with them regarding the boat & her performance.
Plus, both halves of such a plan will perhaps give you a much better set of goals to aim for in terms of tuning both the boat, & your skills in sailing her.


PS: My week will likely be a busy one, so my online playtime will likely be limited.
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Old 02-05-2016, 04:44   #22
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Re: Polars building

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Originally Posted by arsenelupiga View Post
yeah, i doubt many quote VMG when hobbyhorsing which is quite often. 10 kn in 8 kn wind fro CF hero, quickly becomes 3 kn in 8 kn wind, cat or mono or tri

there is considerable skill involved in driving boat to windward well in realisitic ocean conditions. Setting sail as per manual will not do much.
My 2-Tonner's VMG in 8kts of breeze, in a seaway was 6kts. And that's solo, with a Tiller Master AP driving. This, while flying a ancient #1 Genoa which had fist sized holes in the clew, & massive delam going on.
She sailed like a turbocharged Wicked Witch's broom!
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Old 02-05-2016, 04:53   #23
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Re: Polars building

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Originally Posted by Seaslug Caravan View Post
Compared to what.?

A seawind 1160 sailed by some friends of ours, wrote a piece in their blog about their upwind performance.

The OP polars show a vmg to windward of around 4 knots in 20true.

The seawind 1160 blog talks of 3.2 in 20. Much slower. 20% slower?

Day 216 - 218 - Out to Daw Island - Eastern Group

Are we sure we shouldn't be posting in the thread "why catamarans motor to windward 100% of the time"

Just jok'n
As stated by Factor "Any decent boat that isnt overloaded and sailed competently". Yes Sir, spot on!

Or to use a real world exampe. My Ranger 33' (a 50yr old design) saild at double the numbers you're stating regarding the Seawind.
And 1.5x the Lagoon's VMG in said conditions, while pointing 10-15 degrees higher when doing it.

For that matter, take a peek at some of the Polars & Ockam data in my earlier post. The diferences are Quite apparent.
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Old 02-05-2016, 06:39   #24
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Re: Polars building

5kt sog sounds a bit slow in 15 TWS, but 43twa is probably a bit high for the best VMG. 15tws is pretty much the sweet spot for the L400 upwind and we would only see 5kt STW in a pretty crappy sea state. I do have a polar I made somewhere, I'll try locate it, but it's not complete. Actually this post sums up windward in good conditions
L400 performance
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Old 02-05-2016, 07:34   #25
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Re: Polars building

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Originally Posted by Factor View Post
Nope, that is slow. Quite Slow. Really Slow.
It may be slow in a Corsair, behind the reef, or with offshore wind.

It is not slow in a 40ft Lagoon cruising mode in fully developed seas and wind of 15 knots.

This is a bigger Lagoon polar. I can't find the smaller one at hand. This is flat water empty boat.

http://www.boatdesign.net/forums/att...boats-p440.gif

b.
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Old 02-05-2016, 13:30   #26
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Re: Polars building

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Originally Posted by monte View Post
5kt sog sounds a bit slow in 15 TWS, but 43twa is probably a bit high for the best VMG. 15tws is pretty much the sweet spot for the L400 upwind and we would only see 5kt STW in a pretty crappy sea state. I do have a polar I made somewhere, I'll try locate it, but it's not complete. Actually this post sums up windward in good conditions
L400 performance
your skills are way above mine. But I have made some improvements from modest start doing 4.5 or so, that now average 6 kn over different sea states in 15 true at 50.

I have improved sail trim when boat hobby horsing. But, in such conditions, my wife says just go back to harbour.
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Old 04-05-2016, 00:09   #27
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Re: Polars building

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5kt sog sounds a bit slow in 15 TWS, but 43twa is probably a bit high for the best VMG. 15tws is pretty much the sweet spot for the L400 upwind and we would only see 5kt STW in a pretty crappy sea state. I do have a polar I made somewhere, I'll try locate it, but it's not complete. Actually this post sums up windward in good conditions
L400 performance
8 kn in 14.5 kn wind true at around 32 app, in full cruising gear, based on your screenshot. This is 5.23 VMG. Drift would be very small if at all at this speed. Presume near flat water.

That looks pretty impressive. Will keep that one as a benchmark to see how I progress.

quick look thru cruising monos polars reveals that at 50 angle 8k with 15 kn wind is a bit of challenge.

hard to imagine how slow they get when loaded fully. And considering these polars are bit of fantasy in first place, so one can subtract 1 kn to get real polars.
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Old 04-05-2016, 03:06   #28
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Re: Polars building

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8 kn in 14.5 kn wind true at around 32 app, in full cruising gear, based on your screenshot. This is 5.23 VMG. Drift would be very small if at all at this speed. Presume near flat water.

That looks pretty impressive. Will keep that one as a benchmark to see how I progress.

quick look thru cruising monos polars reveals that at 50 angle 8k with 15 kn wind is a bit of challenge.

hard to imagine how slow they get when loaded fully. And considering these polars are bit of fantasy in first place, so one can subtract 1 kn to get real polars.
Can I ask what monohull Polars you're referring to? As it's apparent that they're a far cry from what I provided.
And I would LOVE to have an Aerodyne as a cruiser, without question.. Though I'd surely "settle" for a slightly tweaked/tuned, Kurt Hughes 36' cat.

Also, what are your thoughts & feedback regarding the perfomance analysis & enhancement questions which I asked?
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Old 04-05-2016, 03:41   #29
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Re: Polars building

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Can I ask what monohull Polars you're referring to? As it's apparent that they're a far cry from what I provided.
And I would LOVE to have an Aerodyne as a cruiser, without question.. Though I'd surely "settle" for a slightly tweaked/tuned, Kurt Hughes 36' cat.

Also, what are your thoughts & feedback regarding the perfomance analysis & enhancement questions which I asked?
say this one i sailed in med, elan impression 434. cannot do 8kn at 50 deg true at any wind speed
http://www.elan-yachts.net/img/yacht...ar_diagram.pdf

benetaus probably same. Your boat has great performance, but probably not intended for extended cruising.

Regarding your questions... I have taken all on board. My plan when in similar conditions 13 kn wind + and not too rough will be in this order:

1. calibrate speedo above 7.5kn. I can do around 8.5 motoring, so at least will get extra knot or 2 of correct measurement.

2. flatten sails - level of optimal flattness for wind around 11 kn differs when wind 15 kn or more - that is my theory at least

3. I have made couple of mistakes - my jib was set too full at the time - too much sag. My luff was too lose on main and jib.

4. verify no bow wave under hulls stopping boat at around 7.5kn. This is a showstopper.

Once I exhaust above, and no answer

5. balance boat - my sterns are too low and water does not exit nicely.

6. Sails have 17k miles, so maybe thats the issue

then I will reread what you wrote to get more ideas.

what do you say ?
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Old 04-05-2016, 03:54   #30
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Re: Polars building

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There's not an easy way to say this, but... After peeking at the Polars. The bottom line is that you're suffering from; a heavy boat (or rather, design), with keels & rudders which produce low lift & a lot of drag, & also, a lack of enough sail area.
The latter of the 3 is fixable, somewhat. The foils too, but for much more $.

If you compare your Polars to something reasonably fast, you'll see the difference. Especially upwind. Albeit, they're lead mines.
And too, while it's not the clearest, you can compare their theoretical Polars, to their real world speed data via the Ockam #s (in light ship form).

Also, what the Polars for these boats don't show, is that from 070 AWA & further aft, if there are any sort of waves & 2-digit winds, they start to surf, & or plane, like dinghies.
Aerodyne 38 | Rodger Martin Design
http://www.rodgermartindesign.com/wp...A38-Polars.pdf
http://www.rodgermartindesign.com/wp...Ockam-Data.pdf

Aerodyne 43 | Rodger Martin Design
http://www.rodgermartindesign.com/wp...ne4polars-.pdf
http://www.rodgermartindesign.com/wp...ne4polars-.pdf
both are bit behind at 15 kn true at angle 50. However, can do better vmg against wind. and then there is this: I can never match my polars factor, heard from many.
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