Cruising cat - sub 90 degrees tack upwind

[arsenelupiga]

Originally Posted by Apollo19.5

arsenelupiga, so I have been following this with interest and trying to understand the logic of all points put forward by all contributers. If I understand what you are saying, it can be summarized by that because wider hulled cats are more displacement style and increased drag (due to hull and mini keels), that once they get towards their theoritical hull speed, there is decreasing returns for chasing extra speed by footing and therefore you are better to feather a bit more and put increased height into the equation whilst staying close to your theorical hull speed. The result would be a closer apparent wind angle and reduced apparent wind speed as you would be if footing through the water. Is this a reasonable summary? This is the theory in some yachts I have raced over the years, but I havent spent enough time in wider hulled cats to test it there.



Conversely, a narrow hull with daggerboards would be more towards a semi displacement shape and have lower drag, so the returns for speed of footing a little more are much higher making this tactic much more applicable. This is what I have done in my cats over the years. I guess the AC cats of previous years were the extreme example of this. The Kiwis footed and foiled whilst the others initially pointed and were off the foils going to windward. Once it was obvious the VMG gains were greater for the Kiwi approach, the rest followed and it became the normal.

That would sum up. On top of that, there is keel cat leeway story which i also believed. But as i started looking closely, numbers did not add up. Leeway appears much less. Still one could claim i was just so lucky to be in this type of current. I will go to lake and verify that in currentless environment. If I can do <90 deg tack and sail say 42 TRUE, means leeway is less than 3 degrees. Common belief is leeway is around 10 degrees by default.

Will report back.
My contribution to the science

[arsenelupiga]

Originally Posted by 44'cruisingcat

Has Django carried out tank testing?

Edmund Bruce performed tank testing and found that slimmer hull produce LESS bow wave. In fact that's why most multihulls are not constrained by theoretical hull speed. As LWL : BWL gets higher bow wave creation reduces.

As for Django's tacking angles, as I said before, go slow enough and it gets easy. The slower you go, the smaller the difference between TWA and AWA.

ROAM demonstrated this by doing sub 90' tacks in their performance cat, by furling the headsail and sailing slower.

As an example, in 12 knots true, sailing at 30' apparent, 8 knots boatspeed, you tack through 100 degrees. At 5 knots you tack through 84. But VMG drops from over 5 to around 3.

Have you checked Django numbers from link ? I have done it for you. He does 7.1kn at 28 app. in just under 16 kn true. As it is 6 ft shorter boat than yours, he is disadvantaged for speed around 8 %. meaning you should do 5.81 VMG. in same conditions. You have thin hulls and daggers, so how much extra speed do you produce because of that above 5.81kn?

Sure it is not using mainsail to draw that track.

[arsenelupiga]

just to reiterate, this thread is for condomarans - crusing cats where little or no sacrifice was made for better performance during build phase - where space and weight are maximised - typically with keels - hopefully better technique upwind. I have relatively light boat of this type, les than 50% load capacity used. No interest from owners of this type of cats, though.

Example from above. in 12 kn use 50 apparent, following common wisdom, and max VMG theoretically is 1.82kn. If one sails at 30app and 5 kn this goes up to 3.7 kn VMG. So not bad improvement but do not expect to compete with daggers. Unless boat opitimised like Django's.

Daggerboard boats are different and in my opinion this technique not applicable. But i do not have much experience with daggers so i am learning as we go.

[44'cruisingcat]

Again, where do you get the idea you should be sailing upwind at 50' apparent? Is that what Laggon recommends?

[arsenelupiga]

Originally Posted by 44'cruisingcat

Again, where do you get the idea you should be sailing upwind at 50' apparent? Is that what Laggon recommends?

lagoon does not say that. Their polar ends at 50 true. I got first idea how to sail upwind from CF and numerous brokers and other experts. See that extract for example.

So, i was shocked initially when boat sails have not collapsed at app 49. I can see new breed of lagooners also have ideas you should not try to go below 45 app. Presume same story with other keel cats. It is total rubbish.

[44'cruisingcat]

You realize that 50' true is not the same as 50' apparent?

The Laggon 38 I sailed on went upwind at 35' apparent. The owner said that gave best VMG for him. I think you've either confused 50' true with apparent, or you just made up the 50 degree number.

[Apollo19.5]

Originally Posted by arsenelupiga

That would sum up. On top of that, there is keel cat leeway story which i also believed. But as i started looking closely, numbers did not add up. Leeway appears much less. Still one could claim i was just so lucky to be in this type of current. I will go to lake and verify that in currentless environment. If I can do <90 deg tack and sail say 42 TRUE, means leeway is less than 3 degrees. Common belief is leeway is around 10 degrees by default.

Will report back.
My contribution to the science

Thanks for that. I was born and grew up on Lake Macquarie for 30 years and did alot of sailing there. For 'science' reason, you will need to do your testing in the areas that are less affected by wind curves. Be interesting to see the results as it definately goes against the accepted norms for charter style catamarans. From the recent charts/tracks you put up, it seems you are up near my area which is very tidal and can have some big current flows.

[44'cruisingcat]

Originally Posted by Apollo19.5

Thanks for that. I was born and grew up on Lake Macquarie for 30 years and did alot of sailing there. For 'science' reason, you will need to do your testing in the areas that are less affected by wind curves. Be interesting to see the results as it definately goes against the accepted norms for charter style catamarans. From the recent charts/tracks you put up, it seems you are up near my area which is very tidal and can have some big current flows.

Yep, wind can ve VERY shifty in there. One time my plotter was drawing a track that would suggest some very nice tacking angles. Problem was, I never tacked! Just sailed on one tack to a constant angle.

[arsenelupiga]

Originally Posted by 44'cruisingcat

Again, where do you get the idea you should be sailing upwind at 50' apparent? Is that what Laggon recommends?

i got it from here. similar statements abound on internet.

https://www.katamarans.com/lagoon-400/

". Just like any keel cat, she’ll sail up to 45 degrees apparent, but you are best off bearing away 5 degrees or so to keep your speed up and minimise the leeway. If you head too close to the wind, you might see the leeway build up to 20°."

[arsenelupiga]

Originally Posted by Apollo19.5

Thanks for that. I was born and grew up on Lake Macquarie for 30 years and did alot of sailing there. For 'science' reason, you will need to do your testing in the areas that are less affected by wind curves. Be interesting to see the results as it definately goes against the accepted norms for charter style catamarans. From the recent charts/tracks you put up, it seems you are up near my area which is very tidal and can have some big current flows.

yeah, there are currents. i was comparing GPS against speedo and time of tide and it seemed okay, and repeated this several times in different spots.

any suggestion what is the best spot and time of tide ? Will do several tacks (if enough space) so shifts should largerly cancel out. But there will always be errors in measurement.

this was tack with help of tidal flow 1.5 kn or so in whitsundays moving north.

[44'cruisingcat]

Originally Posted by arsenelupiga

i got it from here. similar statements abound on internet.

https://www.katamarans.com/lagoon-400/

". Just like any keel cat, she’ll sail up to 45 degrees apparent, but you are best off bearing away 5 degrees or so to keep your speed up and minimise the leeway. If you head too close to the wind, you might see the leeway build up to 20°."

Fair enough, although later he says it sails well up to 50' true. He seems a bit confused between true and apparent?

He also says you're better off tacking downwind, which is really rubbish unless you have an EXTREMELY fast boat.

[arsenelupiga]

Originally Posted by 44'cruisingcat

Fair enough, although later he says it sails well up to 50' true. He seems a bit confused between true and apparent?

He also says you're better off tacking downwind, which is really rubbish unless you have an EXTREMELY fast boat.

yup agree, no tacking downwind. Only tack that works is when wing on wing at 165 T. 165T is considerably faster than 180T.

Regarding Lagoon 380 your experience where optimum is 35 app. This is different boat to L 400. Hulls have been updated. Forgeting about absolute numbers on polars, if you look at angle of polar between 50 and 60 you can see L380 reaches max at 60 true, and then falling (right polar) L 400 VMG increasing to 50, including at slowest winds. Maybe just french joke, maybe it is design feature of L 400. It seems there is something

[fxykty]

Originally Posted by arsenelupiga

yup agree, no tacking downwind. Only tack that works is when wing on wing at 165 T. 165T is considerably faster than 180T.



Regarding Lagoon 380 your experience where optimum is 35 app. This is different boat to L 400. Hulls have been updated. Forgeting about absolute numbers on polars, if you look at angle of polar between 50 and 60 you can see L380 reaches max at 60 true, and then falling (right polar) L 400 VMG increasing to 50, including at slowest winds. Maybe just french joke, maybe it is design feature of L 400. It seems there is something

You can’t extrapolate the curves to the left for smaller angles - polars don’t work that way. That could be a peak, or it could still be rising, who knows?

For whatever reasons, it seems the designers of your boat feel that you shouldn’t go below 50 degrees true wind angle, since they don’t show what happens at lower angles.

As you’ve written many times, your performances are an anomaly that can’t be generalised for other condo cats, even of the same design. You should tell Lagoon, or establish a Lagoon High Performance Centre to sell your ideas to others.

[arsenelupiga]

Originally Posted by fxykty

You can’t extrapolate the curves to the left for smaller angles - polars don’t work that way. That could be a peak, or it could still be rising, who knows?

For whatever reasons, it seems the designers of your boat feel that you shouldn’t go below 50 degrees true wind angle, since they don’t show what happens at lower angles.

As you’ve written many times, your performances are an anomaly that can’t be generalised for other condo cats, even of the same design. You should tell Lagoon, or establish a Lagoon High Performance Centre to sell your ideas to others.

Well, TBH, I am just learning from Django really. He is the man to go to if you have condo cat and want to have (really ) good performance boost. Although does not seem much interest for that in Lagoon community. Reason is that for many, first boat is lagoon because it feels like appartment on water. And sailing is really motoring.

[44'cruisingcat]

Originally Posted by fxykty

........ establish a Lagoon High Performance Centre to sell your ideas to others.

Great idea!