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Old 21-11-2019, 20:15   #91
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Re: Catamaran tacking angles , really that bad???

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Originally Posted by 44'cruisingcat View Post
Using the numbers Roam quoted, that boat would have been tacking through around 140 degrees, and making less than 3 knots VMG in a 10 kt breeze.



I'm quite sure that boat can do better than that, which was why I questioned the numbers.

I’m not sure what you’re referring to. Roam was showing real numbers. I am describing real numbers. If the tacking calculator online doesn’t agree with that, do you trust reality or the app?
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Old 21-11-2019, 20:51   #92
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Re: Catamaran tacking angles , really that bad???

As someone who has been involved in Australian multis for 35 years it is strange for me to see the way the scene has gone. With Schionnings, Graingers, Orams and Crowthers all showing that you can have a great cruising boat that can perform really well to windward. But cherry picking data can lead one astray.

Even some of the closest sailing monohulls like Lasers and Etchells have tacking angles that vary hugely. In moderate winds in flat water the boats can get down to less than 80 degrees between tacks. If the wind eases off and you have chop then the tacking angle can blow out to more than 110. Same boats, different conditions.

Same thing with using a single race or time to showcase speed. In one leg you can have a great sailor (say Lars Ourdrup), get all the shifts and stay close to a boat with a higher potential speed. (In fact a lightened Lagoon is a good shape for very light winds as the fat hulls have a lower wetted surface area to volume ratio than a cat designed for high speeds, like a Catana.)

But even using numbers of individual boats is fraught with difficulty. Laser races usually last about 60 minutes for the lead boats and the last boats can take more than 80 minutes to complete the course. Identical boats, and a wide variation in speeds.

So it is better to use overall race series results or ratings to give a better idea of speed. The physics and the 35 year history of performance multis don't lie - you can have a great cruising cat that sails really well to windward, so much so that you will love sailing to windward as I do. I am happy with a boat slower than one I could have built if it was more extreme, how far down that road you want to go is up to you.
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Old 21-11-2019, 23:26   #93
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Re: Catamaran tacking angles , really that bad???

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You can fantasize all you want, but here is some reality. A week ago three out of four ultimate tris in the Brest Atlantic race took shelter in Rio to wait for better weather before they headed to Cape Town.

https://www.brestatlantiques.com/act...ue-tous-l-abri
Yes, or well, this was not me, it was just a quote from Tupaia's linked article. Which actually had a lot of science in it! I looked to be from the 80s? Nothing bad in that, though, unless there has been some radical advances in fluid mechanics understanding since.
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Old 22-11-2019, 02:01   #94
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Re: Catamaran tacking angles , really that bad???

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Originally Posted by fxykty View Post
I’m not sure what you’re referring to. Roam was showing real numbers. I am describing real numbers. If the tacking calculator online doesn’t agree with that, do you trust reality or the app?

As I was playing with a VMG to wind calculator (https://l-36.com/polar_calculate.php) I realized the following: with 10 knts TWS, if your best AWA is 30° then your max (theoretical) VMG is 5 knots. With a best AWA of 34° your max VMG falls down to 4 knots.
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Old 22-11-2019, 02:31   #95
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Re: Catamaran tacking angles , really that bad???

Cool, thank you!
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Old 22-11-2019, 05:16   #96
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Re: Catamaran tacking angles , really that bad???

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Cool, thank you!
I forgot a couple of Australian Manufacturers.

https://www.lightwaveyachts.com
https://www.seawindcats.com/seawind-1600/
Fusion Kit Catamarans

The Australian multihull market is very performance orientated and there are many exceptional designers there but few production manufacturers. Having said that there is a lot to said for buying a pre-owned but tried and tested design from a good designer.

https://www.boboramdesign.com
https://www.graingerdesigns.net
Yacht design & boat plans by Lidgard Yacht Design Monohull and Multihull
http://www.schionningdesigns.com.au
Mark Prescott - no website.
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Old 22-11-2019, 07:12   #97
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Re: Catamaran tacking angles , really that bad???

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Originally Posted by rom View Post
As I was playing with a VMG to wind calculator (https://l-36.com/polar_calculate.php) I realized the following: with 10 knts TWS, if your best AWA is 30° then your max (theoretical) VMG is 5 knots. With a best AWA of 34° your max VMG falls down to 4 knots.
and at 30° AWD to achieve best VMG you must be at 60° TWD = best theoretical tacking angle of 120°. That's why all this talk of how great a cruising cat is because it can tack at 80° is rubbish. I don't know any cruising cats that can manage the above numbers, that's a much faster cruiser than I believe exists and it would have tacking angles of around 125-130°.

A slower boat can reduce the tacking angles. If your TWD came down to 50° while your AWD stayed at 30° your tacking angle decreases but your VMG also reduces.
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Old 22-11-2019, 07:56   #98
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Re: Catamaran tacking angles , really that bad???

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If your TWD came down to 50° while your AWD stayed at 30° your tacking angle decreases but your VMG also reduces.

So I think we have answer the question by now ("Catamaran tacking angles , really that bad???"). It simply isn't a good question and the OP should have asked "Catamaran VMG, really that bad ?", to which we have also answered I think.
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Old 22-11-2019, 15:58   #99
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Re: Catamaran tacking angles , really that bad???

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I’m not sure what you’re referring to. Roam was showing real numbers. I am describing real numbers. If the tacking calculator online doesn’t agree with that, do you trust reality or the app?
Trigonometry is real.

Anyway, my point was, I didn't think that was the best Roam could have done to windward. They were close reaching numbers, not beating to windward numbers.
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Old 22-11-2019, 16:03   #100
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Re: Catamaran tacking angles , really that bad???

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and at 30° AWD to achieve best VMG you must be at 60° TWD = best theoretical tacking angle of 120°. That's why all this talk of how great a cruising cat is because it can tack at 80° is rubbish. I don't know any cruising cats that can manage the above numbers, that's a much faster cruiser than I believe exists and it would have tacking angles of around 125-130°.

A slower boat can reduce the tacking angles. If your TWD came down to 50° while your AWD stayed at 30° your tacking angle decreases but your VMG also reduces.
I'm not sure too many (catamaran) people have claimed 80degree tacking angles?

Anyway, as I've frequently pointed out, the reason there's a difference between AWA and TWA is because the boat is moving. The faster it moves, (relative to windspeed) the greater the difference.

Which is why some monohull appear to produce very good tacking angles. They're slow.
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Old 23-11-2019, 05:07   #101
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Re: Catamaran tacking angles , really that bad???

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Trigonometry is real.

Anyway, my point was, I didn't think that was the best Roam could have done to windward. They were close reaching numbers, not beating to windward numbers.
Anyway, with those particular sails and wind speeds it was their preferred configuration, right?

The OP said "150-160 degree tacks" and asked "can it really be that bad??".

The answer, I gather, is: "yes, it really can be that bad", but, "for a lot of catamarans, it really isn't".

I think tacking angles are important, btw, not just VMG, especially in tight places.
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Old 23-11-2019, 16:41   #102
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Re: Catamaran tacking angles , really that bad???

Sure, tacking angles can be important, and you can improve them simply by slowing down. Which could also be a good idea in tight places.
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Old 24-11-2019, 00:46   #103
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Re: Catamaran tacking angles , really that bad???

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Sure, tacking angles can be important, and you can improve them simply by slowing down. Which could also be a good idea in tight places.
Sounds smart
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Old 24-11-2019, 00:48   #104
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Re: Catamaran tacking angles , really that bad???

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Sure, tacking angles can be important, and you can improve them simply by slowing down. Which could also be a good idea in tight places.
And this isn't much different to a monohull where it's common to 'pinch' to lay a mark or get around an obstacle, and of course the monohull slows down in this instance too.

It's just that with the multihull the margin can be greater, both in terms of speed and angle.

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Old 24-11-2019, 10:48   #105
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Re: Catamaran tacking angles , really that bad???

“ it is strange for me to see the way the scene has gone. With Schionnings, Graingers, Orams and Crowthers all showing that you can have a great cruising boat that can perform really well to windward.“
Second that in a big way!
& they were good looking too.
These days here in cat country I see mostly floating abominations - even today's “performance cats“ (Katana & Outremer) looking like blocks of flats. & what I read here: they sail every bit as badly as they look. Our Wharram mostly had better tacking angles than what I read here. During our- pre gps - rtw in the 80ies I always used 120* over ground in my DR, & the boat always did slightly better. The boat had a cutter rig & was heavily laden, which in a Wharram helps upwind performance. (In the comfort-department of course...).
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