I usually put a GPS in a drybag and tape that to the boom on the Nacra 20 when we're distance racing. I've found that it receives very well as long as the boat is upright! The max speeds and such are very reliable. If you use the larger garmin units, you can even see the displays from the outboard positions of the boat.

Herendeen bought two Garmin Geckos (very simple GSP units) and used electrical tape to attach them to each shroud. You can still program in waypoints and for less than the cost of one fancy unit, he's got two neatly placed and accessible.

And the customer service they offer is World Class. I have returned a few items to them that were replaced and/or repaired with no problems.

Also as an FYI, you can get updates on the unit software etc... from their website.

I have learned from use that the WAAS enabled GPS units are very accurate which is both a source for reduction of errors AND introduction of errors. I have a very small Garmin unit that can be warn on the wrist. It is so accurate that it will record the speed my wrist is moving as I hoist a spinnaker, trim the mainsheet, or make any other high speed arm movements. So I get the max speed of my WRIST, not the boat. If my wrist is moving in the same direction as the boat then it can be a pretty dramatic increase in max speed over what reason would inform me is the boat speed.

We have taken our GPSs downhill skiing and been amused by the amazing speeds that have been produced in some spectacular "skiing pitchpoles". The speed of the hand holding the GPS while the arms go flailing adds to the downhill speed so that my personal record is 132 mph! You can amuse yourself with your GPS by "throwing" it as fast as possible (DON'T let go!) to see what "Max speed" you can produce while standing still. Try it yourself and report your findings back here on the forum.

Mike Fahle Toledo (Had our season first snowfall yesterday)

wave your gps back and forth really quickly and you might reach 73 kts <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Guys, this thread was originally about how fast the F18 actually is, not how reliable gps-receivers are. So let's have it, how fast is the F18!?:) Uphill, around 14 knots? Downhill around 25 knots? What do you think?

I dont have time to let a sinker over the bow and time the knots in the line over <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />. Can you give me your better way of accurately measuring boat speed Jimmi? <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" /> I will have an F18 and it would be nice to see accurate data from top crew races to help understand the strengths and weaknesses of the different brands of F18
regards

Well, my dad and I use a hand held gps receiver and compared it to the speedometer in our car while driving. And as expected the speedometer showed a few knots faster than the gps, however the difference was not 73 knots and other crazy numbers as mentioned here on the forum. We therefore conclude the gps to be quite accurate (I know some will want to shoot me after writing this, but living in Oslo, Norway with an entire ocean to cross for most of the forum users, I'll take my chances:)).
Up hill we have done 13,7 knots in our Taipan 5.7 in around 12 knots of wind with zero waves. Down hill we have done around 20 knots, wind strength 15 to 18 knots. We did not fly the chute, so I reckon it is possible for a more experienced crew to go quite a bit faster while flying the kite. Opinions?
Regards Jimi

I figure 14-15 up and 20 or so down in good wind. Probably faster if you have the guts to go all out downwind in high wind stuff. This is what i do in my 6.0 and I can't sail it worth a crap so I figure an f18 sailed average should go that fast! maybe I am wrong, but I haven't sailed in too long. this despite being on an island 1 mile from water in perfect weather.

A GPS unit will be pretty accurate as long as it can see the satelites and you don't jerk it around too much. Unfortunately, when you are on a catamaran going upwards of 20 knots, you will be jerking it around and it will not have a good look at the satelites all the time.

I once threw my handheld from one side of my cat to the other (on the beach while rigging, to my crew) and it registerd 53 mph. I just tossed it easy, underhand, so I know it wasn't going over maybe 10, but because it tumbled I think it decided it must have gone 53? The point is, in your car going down a smooth road in a straight line, sure it works great. But on a picthing cat on a rolling sea, not so accurate.

Here is what you can do: Have your crew hold the GPS unit somehow that the antenae will have a good look at the sky for a few minutes while you sail upwind, bear off and set the kite, now have him get out on the wire with the kite sheet in one hand and the GPS in the other (better tie it to him) and now you heat it up and get it going as fast as you can for as long as you can, and have your crew read off the speeds as you go. You might see 20 knots on an F18, just before you swim. (insert picture of the Hobie Tiger pitchpole during the speed run in the French Ditch). I have found a handheld GPS will only give you accurate numbers in a steady state. Once you start tacking and gybing if the boat is bouncing all over the place in waves, the "max speed" number is no good. At the end of the day you can use the distance and time it records and do your own math but that also includes all the slow sailing while tacking.

I have the Velocitek. I have seen 8 knots VMG upwind and 16 knots VMG downwind. I have timed upwind legs and downwind legs and get, pretty consistantly two times faster downwind than upwind. The boat is gybing and tacking about the same angles. That speed is in about 15 to 17 knots of breeze. That means that the straight line speed is about 23 knots with the chute up, based on algebra.

Dan

Not that it really means anything, but Marstrom's M20 advertisement saids: "GPS- verified 30 knots" ... What do you guys reckon?

In good winds and double trapped we typically log 14-16knots max on the GPS upwind. Downwind we typically max out at 25knots or thereabout. This is on a Tornado with almost 200Kg on trapeze. During gybes and tacks the readings are sometimes far above the typical values of that day. I suppose all the movement of the crew carrying the GPS unit confuses it (didn't we just have this discussion, two or three months ago?).

Perhaps the M-20 and other beachcats can reach 30knots for some seconds. Perhaps even the Tornado has done it, but not for any significant time or distance. I think the drag and stability limits will be reached before you go that fast. I think "GPS- verified 30 knots" is just a sales pitch, but the GPS has probably logged 30knots for them at some time. If we got to see the log and normalized the data, I think it would show a max speed around 25knots downwind like the rest.

To get back on track, I think the F-18 is almost as fast as the Tornado in a breeze, and faster in some conditions, so I expect the upwind speed to max out at 12-16 knots and downwind around 25knots. Crew quality really makes the difference.

Hei Rolf, satt og ventet på når du skulle slenge deg inn i diskusjonen!:)
14-16 knop er utrolig bra på kryss da! For ikke å snakke om 25 nedover! Får frysninger av å tenke på det!:) Far og jeg har et stykke igjen til sånne hastigheter, det står i alle fall ikke på båten. Som nevnt over er alle "topphastighetene" våre satt i nokså små briser, vi må bare bygge opp rutine og ferdighet (og baller) til å dra utpå når det blåser spiker. Dessverre er vi bare ca 150 kg på ripa, og med styrketrening kun to til tre ganger i uka over stusselig studentkost, ser det ikke akkurat ut til at jeg kommer til å rase opp i vekt den nærmeste tiden:) Taipanen var jo designet til å ta tunge mannskap på 150 kg+ så riggen er kraftfull og har oss begge i trapes innnen 3-5 m/s.
Ettersom vi nå endelig har fått ordnet ordentlig snuffer til båten, er vi nå også mer tent på å kjøre mer gennaker. Vi hadde en super tur sist helg, da jeg tok en langhelg fri fra studiene for å få seilt litt og pakket ned båten. Logget over 16 knop i 4-5 m/s med gennaker, vanvittig gøy å fly ett skrog nedover vinden! Skikkelig booster for motivasjon til studiene med sånne turer!
Hold oss oppdatert på hastighetsmålinger da.
Geir Magnus

Geir Magnus, 150kg er da gode greier det. Skulle ønske vi også hadde det, så kanskje vi virkelig kunne få opp farten. Jeg mener det er en større fordel å kunne kjøre depower enn å lesse på med vekt <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />
Å seile i mye vind er bare en vanesak, man må komme seg utpå og tøye grensene litt så blir man fort vant til det.
Vi seiler med GPS kun i distanseseilaser for tiden, og da som et navigasjonsinstrument. Vi brukte den tidligere til å finne de beste vinklene for VMG, og det var i den perioden vi logget de hastighetene jeg refererte til. Vi er ikke så opphengte i hva slags fart vi gjør, så lenge vi kommer i mål før de andre tornadoene <img src="http://www.catsailor.com/forums/images/graemlins/laugh.gif" alt="" /> Dette har blysvingerne her store problemer med å forstå, de tror vi seiler båten kun for fartens skyld, mens det er samspillet og å få båten "in the groove" vi setter mest pris på.
I think we should keep to english on the forum, out of courtesy to all our friends here. They are probably very curious about what we are discussing in our quite "off the mainstream" language. Hope to get to sail with you next season (or this season, boat will not be put in storage for 14 days, so if you want to visit us in Molde..).

Actually my class visited Molde two weeks ago, but only for half a day as we were on a trip with "hurtigruta" to do an assignement in "marine tech.", one of my courses at NTNU. However, we mostly drank beer and chill out instead of working on the project while in Molde.
As you said, my dad and I need to get more comfortable in strong winds. Problem is, there really is not stable, good breezes in the inner Oslo fjord, so when the wind picks up, it usually is extremely gusty. But more experience and balls will give us confidence to go out in the big stuff as well. I think we are getting closer, so next year...
I totally understand what you meant about getting the boat "in the groove". It truly is a wonderful feeling looking up at the rig, all tell-tails are flying, and the windward hull just kissing the water. However, I don't think there's anything wrong in wanting to go fast in a straight line as well! <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />
Regards Jimi

You were in Molde, and did not give me a call? Shame on you!

PS: In the groove is not just about making all the telltales stream. There is a certain sail/boat trim and helming technique that makes the boat faster than any other trim/technique. Finding this "groove" in all conditions is a real challenge.

Please, do not let this brief post hijack the discussion
but it seems that many cat-sailors want to measure the fantastic speed they are doing.
We have found that placing the GPS receiver on the boom one metre from the mast seems to produce correct numbers. We have not seen any strange figures on our Magellan Meridan or Garmin Foretex when placing them (antenna up) on the boom.

Back to the speed discussion: the Weymouth speed week has seen many cats thunder down the 500 meter course. Tornado sailors have had speed contests after regattas. However, rarely have speeds in excess of 20 knots been recorded.
Why? What are the limiting factors to maintaining speeds > 20 knots in beach cats?

Stein

Stein

I think the single biggest obstacle to going faster than about 20 knots on a beach cat is the sea state. In order to get going that fast on a typical beach cat, you need at least 15-20 knots of wind, which will kick up some waves wich will keep you from going much faster. That is why the French built the ditch for speed runs, to keep the waves to a minimum.

In the ocean where there are already "seas" and you find wind waves to add to the seas, a 20' beachcat has a lot of trouble getting past any SUSTAINED speeds of 18 knots.

I have had bursts to 22 knots. I have had short moments of sustaining 18-19 knots. (no spinnaker in either case)

I am always happy if I can maintain an average upwind plus downwind speed of 10+ knots. As a cruiser, I am pretty pleased if my speed is above 8 knots in any direction.

My Mystere 6.0 (Whisk) will probably never go faster than 24 knots unless she is riding on a body of water that is not being affected by the wind, the same wind that is pulling her along at such high speeds. (ditch run?)

Whisk won't go faster than 24 knots in the six years that I've sailed her on the ocean. Gross weight = (minimum) 615 pounds to (approx. maximum) 1175 pounds.

GARY

Stein,

we had a heated discussion on a related topic some months ago: http://www.catsailor.com/forums/showflat.php?Cat=0&Board=Test&Number=77114