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Max speed? #216948
08/02/10 12:48 PM
08/02/10 12:48 PM
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France
pepin Offline OP
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What's the max speed you've ever reached solo? duo? And please no approximation. I'm looking at 10 seconds average speed given by a GPS.

I've been trying really hard to get over 20 knots solo, but I can't seem to be able to reach this goal. I've seen the magic 20 on my speedo a couple of times, but I never got my 10 second average over this limit. My best effort so far has been 19.7 knots a while back and more recently a 19.3 knots in Como. Of course this is downwind under spi, and in wind in the 18-22 knots range.

I find it easy to get to 17 knots, tough to get to 18 and really hard to get anything over that, even when the wind increases.

At this point I think I'm over correcting with the rudders and my tracks are way too squiggly. I have a tendency to sharply head downwind in gusts, and I feel I should use this opportunity to accelerate more. But how can you do it without diving or toppling over?

Tips anyone? This is a personal challenge, and I'm open to suggestions on how to go faster! Is there a "how to handle an asymmetrical spinnaker on a fast cat" book anywhere?

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Re: Max speed? [Re: pepin] #216955
08/02/10 02:21 PM
08/02/10 02:21 PM
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Eric, you are probably reaching the point where all the scratches and dings on the bottom of you hulls + the large low aspect boards you have, are creating so much hull drag that the only way you will regularly get over this speed hump, would be to change the type of sails you have at that point in time. To go much faster will need more horse power as well as skill.

Re: Max speed? [Re: waynemarlow] #216960
08/02/10 03:32 PM
08/02/10 03:32 PM
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Northfield Mn
Karl_Brogger Offline
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Got 23.7kts on the speedpuck, but I think thats over 5 seconds, and not 10

That was two up, and pretty windy.


I'm boatless.
Re: Max speed? [Re: Karl_Brogger] #216966
08/02/10 04:17 PM
08/02/10 04:17 PM
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Chicago, Illinois USA
TEH Offline
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17 knots on speedpuck - 1 up


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Re: Max speed? [Re: TEH] #216968
08/02/10 04:28 PM
08/02/10 04:28 PM
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Sebring, Florida.
Timbo Offline
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My problem with my Garmin Etrex GPS is, I can't read it when I'm going fast! I did once have it tied to my tramp and while sitting down, sailing solo under spin, I saw 17.5, but when I got up to trap and go faster, I couldn't read it anymore!

I know a couple weeks ago when that tropical storm came by, we had some good wind, and I took Tom out for some blast reaching across the lake, no spin, just blasting along on a reach with the boards half way up, skipping on the wave tops like windsurfer. We were going quite a bit faster than I was that day I saw 17.5 solo, but we didn't have the GPS on board. Next time I'll bring it...if I can remember.


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Re: Max speed? [Re: pepin] #216994
08/02/10 09:59 PM
08/02/10 09:59 PM
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Melbourne, Australia
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I might get howled down here... but wouldn't 1-sail or definitely 2-sail reaching be faster in a straight line?

Whilst the kite is fast and super good for VMG... when going purely for speed it does introduce a lot of drag into the equation!


Stingray #579
GLYCish
Re: Max speed? [Re: MitchB] #216999
08/03/10 12:06 AM
08/03/10 12:06 AM
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Knokke-Heist - Belgium
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We have reached our highest speed on a reach too. That means a one up can never beat the max speed of a 2 up boat as a 2 up boat has more weight to reach the max speed.

I haven't checked my Como tracks yet as there the wind was very stable and the water flat and we might come close to our top reach which was at sea.

Anyway, we have 19 knots as top over 10 sec.
Second best over 10 sec is 18.4 and the others are close to that. Even 10 sec tracks will still show some spikes I think....

Gill


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Re: Max speed? [Re: Gilo] #217000
08/03/10 02:48 AM
08/03/10 02:48 AM
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Cape Town, South Africa
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Gilo, you should be able to correct the spikes on GPSAR software, to give you a more accurate 10sec average.
I agree with Mitch here, once you get up to speed the drag of the rig comes into play, probably more than any scratches or dings in your hulls. Lose the spinnaker and go 2-sail reaching (or 1 if solo), should give you your best speeds as there is less drag.
The mathematics and engineering gurus might elaborate on this, but as speed increases by a small amount the drag (hull drag & foils, as well as the rig through the air) increases by a much larger factor, so you end up throwing much more energy into small gains, at the top end of your craft`s speed potential. It may just be that your boat has a max. speed potential of approx. 21knots, which will take the perfect conditions and setup to acchieve. This means you are, at 19.3knots, operating at 91% of potential, and any small gains require a large reduction in drag, so you would need different naca section foils to acchieve this, maybe smaller daggerboards and even smaller rudders.
My experience in this is from windsurfing, where a fin size change from a 34cm fin to a 32cm fin can give an increase in top speed. I sailed on Saturday with a 9,5sqm sail in 12-14knots, and although I had enough power to plane easily, felt slow - then changed down to a 6,6sqm sail and, although seldom had enough power to plane, definitely felt faster when planing (no gps).Although I had less power, I had reduced the drag by a greater factor. My all-out top speed is 32knots in strong conditions (approx. 30knot winds) yet I can easily go upwind at 27knots in 18knot winds. An increase in power will only help if you can fully harness that power, which in 20knots of wind you probably can`t, so you will be increasing drag with that increase in power.
So, smaller daggerboards, smaller rudders, smaller sails, and make it plane grin

Re: Max speed? [Re: Steve_Kwiksilver] #217006
08/03/10 04:47 AM
08/03/10 04:47 AM
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France
pepin Offline OP
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Originally Posted by Steve_Kwiksilver
So, smaller daggerboards, smaller rudders, smaller sails, and make it plane grin
Foils are probably a factor. In Como my daggerboards and rudders where the largest around. Piet nicely told me my rudders were "barn doors".

However that's not something I can change easily, I don't have the time nor the budget to redesign a 9 yo boat. I just need to use what I have to go faster smile

As for the sails, it's not a sailboard I can change the mast and sail as much as I want! Again, I'm stuck with what I have.

But this got me thinking. Maybe I should get my daggerboard halfway up. As long as there is enough wind to put me on one hull I probably don't need the full daggerboard in. Less daggerboard, less drag... Worth a shot. Maybe a .2 knots gain!

As for being faster without the spi this has not been my experience. Maybe with two crew, but solo I can't harness enough power. Also I've seen polars for the F18 showing that downwind under spi was definitely faster for all wind speed, polars for a F16 should not be that different...

Re: Max speed? [Re: pepin] #217019
08/03/10 06:52 AM
08/03/10 06:52 AM
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Cape Town, South Africa
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Hi Pepin,
I get that you can`t change sails, mast & rudders etc as windsurfers can - I sail cats too.
I think the polars for F18 only show the obvious - that with spi on a broad reach is faster than without - have you seen polars for F18 on a beam reach ? Even so they might be slower as F18 (like F16) is designed for max. efficiency upwind and down, not for reaching. I wouldn`t be surprised if an older design with large jib is the king of beam reaching at speed.
I think that our current designs are geared more for developing lots of power with lots of drag, especially the spinnakers. Perhaps a flat-cut spinnaker would reduce the drag, remember we sail with so much apparent wind that it feels like we are beating, yet we have headsails with a lot of fullness relative to the AOA we are sailing to, which is why the big bearaways are necessary in gusts.
I think 20knots is really fast solo, but you seem to have gotten close a few times, just keep at it and you will get there.(Or explode in a ball of spray trying..)
Now your post has become a challenge.. We have a forcast of 21-25knots this weekend...

Re: Max speed? [Re: Steve_Kwiksilver] #217028
08/03/10 08:14 AM
08/03/10 08:14 AM
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Quickest I've seen is sustained 17kts with the kite up on a reach from one end of my local puddle to the other. I can get 5-10 second plots at around 19; I have a 20.2 kts plot (around 5 seconds) when bearing off in massive wind and then staying out on the wire on a broadish reach instead of coming in to pop the kite.

I believe that top speeds will be without the kite as there is a lot of drag in the Spi; But the angles will be different between 1 and 2 up as the weight on the wire is different; 2 up will be on fairly tight reaches as you need more power; single handed top speeds will be broader reaching.




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Re: Max speed? [Re: Steve_Kwiksilver] #217029
08/03/10 08:27 AM
08/03/10 08:27 AM
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France
pepin Offline OP
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Here is a polar for a F18 in low wind conditions. It shows that the max speed is around 112 with the spi and around 75 without (A and B show the best VMG for the given wind conditions and are irrelevant for this exercise). The difference in speed between the two looks minuscule.

With a solo F16 (aka no jib upwind, less meat on the wire) I suspect the downwind speed is easier to achieve.

I should capture and use all those GPS tracks I have to make polars, as using someone else polars to extrapolate is not that rigorous scientifically smile

Also, so far my top speed have been attained while racing to a downwind mark, aiming for a good VMG, not a ridiculous speed. What this polar indicates is that I can probably go way faster if I'm not racing!

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Sample Polar
Re: Max speed? [Re: pepin] #217051
08/03/10 11:57 AM
08/03/10 11:57 AM
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Melbourne, Australia
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The more modern cat designs are definitely designed for windward leeward racing!

My comment regarding being faster without the spin was based on my stingray... an almost 50yo design with an almost 30yo rig design! It has a very large overlapping jib with a very low slung bridle!... In passage style races with a lot of reaching the design has performed very well in Australia.

The modern boats seem to have a very small jib! i assume this is to gain height upwind as it can be sheeted at a tighter angle? And downwind it doesn't matter so much as the kite is giving most of the drive? am I on the right track?

Last edited by MitchB; 08/03/10 11:58 AM.

Stingray #579
GLYCish
Re: Max speed? [Re: pepin] #217053
08/03/10 12:09 PM
08/03/10 12:09 PM
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Hamburg
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Hi all,

Quote
is not that rigorous scientifically

It is. Much more than most people are aware. There is a good reason why we do not directly use civial GPS signals to control the auto pilot of aircraft.
Most handheld GPS receivers truncate the time stamp of the track data to 1s. Hence the 10s track has an 1s time error, e.g. 10% error.
Even if we would all use WGS 84 as position reference, it is not guaranteed that the software of the device will use this model for speed calculation (some use a simple sphere model for speed calculation). On top of that you will have the position error of GPS signals.
As a consequence it is very difficult to compare just the plaine speed numbers, just have a look at the numbers posted here, ranging from 17 to over 20kts. Comparing the tracks with the same software would already mitigate a huge error source...

Typically the top speed of beach catamarans is not limited by drag, but by stability (against pitchpole or heeling). Of course you need to have enough wind.
With a proper spi setup, you should get the highest speed, since the center of effort with spi is lower than without. Many sailors describe this effect as "the spi is lifting the bows".
Saying this the simplest way to make the boat faster is to use a lower rig. Fast in high winds and a sitting duck in low winds (you can call this also a Dart 18).

Cheers,

Klaus

and for those still believing in numbers:
17.5 single handed on a broad reach without spi (I didn't dare to pull it), more than one knot slower than our fastest track on a classic T.

Last edited by Smiths_Cat; 08/03/10 12:28 PM.
Re: Max speed? [Re: pepin] #217386
08/10/10 08:48 PM
08/10/10 08:48 PM
Joined: Jun 2006
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Santa Fe, New Mexico, USA
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Pepin,

I'm kind of liking Kwiksilver's idea. Use a spin that is more like a Genoa, maybe even a little less sail area. I think the flat sail would allow you to broad reach in higher wind and or it would allow you to bring the boat up higher toward the wind than the spin does. Even if the spin holds its shape it gets to that point where the bows start pushing side ways and the rudders start cavitating.
The fastest I've sailed was on a H16 solo, broad reaching, or maybe a little more down wind than a true broad reach because I was scared I was about to crash. I think the wind was probably hitting 30 at that point. When I came on shore a friend told me that the ranger had come down and warned our fleet to expect 50 MPH a little later. None of this was measured and the only ones to notice were the men collecting the trash a ways up the hill, they commented that they hadn't seen a boat sail faster. As the rest of the fleet decided to go sailing they went three and four aboard their h16s and h18s.
I hope you brake the sound barrier.
Will


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Re: Max speed? [Re: WillLints] #217401
08/11/10 11:47 AM
08/11/10 11:47 AM
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Knokke-Heist - Belgium
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I had my GPS on the water the 2nd and 3rd day. 2nd day was 16knots? (the most of the whole week).
On 3 races my best 100m is 20.07 knots. The average of the 5 best is 19.78 knots.

Como is a great place... :-)


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Re: Max speed? [Re: Gilo] #217428
08/12/10 04:54 AM
08/12/10 04:54 AM
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Sebring, Florida.
Timbo Offline
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Nice, Gilo! Was that with the spinny up or on a tight reach without it?


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Re: Max speed? [Re: Timbo] #217444
08/12/10 02:42 PM
08/12/10 02:42 PM
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Knokke-Heist - Belgium
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With the spinnaker. The reach was too much downwind and the wind was not strong enough to sail top speeds there.

The spin runs were awesome that day. 15 knots and flat water!

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Re: Max speed? [Re: Gilo] #217474
08/13/10 03:07 AM
08/13/10 03:07 AM
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Sebring, Florida.
Timbo Offline
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Nice picture...but what's that big pile of dirt in the background?? We don't have those things in Florida!

:^)


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Re: Max speed? [Re: Timbo] #217476
08/13/10 04:43 AM
08/13/10 04:43 AM
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waynemarlow Offline
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Originally Posted by Timbo
Nice picture...but what's that big pile of dirt in the background?? We don't have those things in Florida!


Them big piles of dirt ( granite ) makes Garda so special, adiabatic winds and all that sort of stuff.

When you live in the alps its really funny watching the paragliders soaring one minute and then on the deck the next, one minute the wind is rising up the warmed granite faces from the colder valley floor and then suddenly the valley floor is warmer and all that up wind becomes downwind. In the valley the wind can turn a full 180 degrees in sometimes only minutes.

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