I hate to revisit this topic after the last thread where I got a little upset about people saying that small catamarans (20-foot max) cannot go faster than 22 knots. Now I have to say that this claim about 33 knots also seems totally unrealistic at the high end. The following is quoted from a story on the US Sailing website:

"The Tornado sailboat has the ability to reach speeds of 15-18 knots upwind and downwind, and 33+ knots reaching!"

It's ridiculous! I think the max possible speed (without hydrofoils) is somewhere in between, probably in the 25-26-27-knot range at absolute max, in high winds on flat water.

P.S. Why can't we get some good, on-water data on this so we don't have to operate on a myth basis?

We are going to do some testing this summer at our regatta. We have purchased a radar gun and will be having some speed trials. If anyone is interested in coming, the event is July 2: trials, 3-4, round the marks. Eastern end of Lake Ontario.
http://www.westlakesailingclub.com

Anyone ever used one of these?



http://www.intowind.com/speedwatch-wave.html

Gareth

Speedometer? Yes- they come with the Rave foiler.
Hollis Caffee somehow kicked his off by accident just before I took the Rave out. At least that is what I claim. I never saw it in action.

hI Mar , Gareth ,-Dave C , and pp Dave

Would like to make it over sometime Dave ,-raced on Earie and Lk Ontario a number of times in past years on the Ohio side and in CAN ,--Rondeau Park CAN ,-raced the CAN h-Natls one year ,
was at the Hobie 18 Worlds in Toronto --80s ,-
been to Kingston ,-etc --always fun .

The Marstom 20 and web site claims a 30 knot GPS verified run . which seems credible
http://www.sailcenter.se/administration/Boats/M20/index.asp

During the 1997 (old) TORNADO Worlds was introduced the Bacardi Blast. The event involved the top teams from each day's racing to race down a timed 500-foot-long "drag strip". At the end the fastest time was set by the German team of Justus Wolf and Frank Parlow in a time of 12.53 secs. The blast averaged 23.64 knots, the top speed almost certainly was in excess of 25 knots. The record was set in winds of approximately 19 knots.
Full report on the Jan/Feb 1998 issue of Multihulls Magazine.

grob

Does it actually work

What does it actually measure. Is it measuring friction or is there some kind of impeller on it.

Frozen,

Don't know thats why I am asking, does anyone have any experience of this. If its accurate it should be better than GPS as it will not be bothered by tidal flow.

If the boat is in a tidal flow than the wind when sailing on one side appears to be stronger than when sailing on the other sides etc.

It all comes down to relativity guys.

Only thing that will trully work is having to measurement ; One absolute and one relative and deduct the one from the other to calculate the flow and then compensate all calc for the flow.

Wouter

Grob

I just did something a bit uncharacteristic of myself. I read the whole advertisement.

It has an impellor. They say there are 2 ways to mount it. The cheaper model (believe it or not) transmits the data (wireless) however the two parts must be max of 20 to 50 cm or 2.54 cm = 1 inch so 8 to 20 inches apart.

I have visions of the impellor getting smucked by something in the water or during beaching. Also anything like that will be affected by the flow around the boat as the water is probably accelerated as it is pushed aside by the hull.

Also you would need two as when you are flying a hull the other is 'blowin in the wind".

Maybe the answer is to get the CIA to track you on satellite. According to all the movies I have seen lately they can probably do that better than finding Osama.

I am a real serious guage weenie and would love to have some kind of guage for wind speed, water speed and depth of water. Unless you are blessed with a sailing buddy or a regular group of racing friends it is hard to guage the results of little tweaks etc on the speed of the boat.

I suspect GPS is the best bet.

The depth of water guage would of course have to be forward looking, as nothing is more useless than the depth of the rock you have just hit. I suspect some kind of fish finder might be the trick.

Now of course all of this gear would have to be cheap and ultra reliable.

Talking about speed, and forgive this being a classic diversion, but is the effect of water depth taken into acount on speed records?
All I know is that planing boats (Airboats) plane off much more readily in 3 feet of water than ten or more, even though they may only draw 4" of water, max. This surprised me, and when you consider the ditch in France? (where the windsurfers set speed records), this must be an issue.
I imagine narrow hulls are very insensitive to anything over a few feet of depth, but does anyone know?

I've heard of guys that dangle the impeller by a wire between the center of the two hulls - that way when you are flying a hull you will still get a reading.

I wondered about that.

Aircraft when they are a wingspan (tip to tip) or less from the ground enjoy the benefits of ground effect. Some people call it a cushion of air. I could go on and on about it but essentially when you get closer to the ground the wing becomes more and more (geometrical progression) efficient. The air is compressed. So you can take off at a lower speed than you can fly at.

Hi Jake

So the impellor's weight keeps it in the water?

Do you know anyone with this device?

Hi all,
I've used to have the one they advertise in Murray's called speedmate. Yes the is a line that dangles in the water and though it's not weighted, is somehow always stayed about 4 inches underwater. It was relatively accurate i guess but it has many short falls.

1. If you mount the unit towards the front, sometimes the cord would get tangled in the rudder and then it's not always easily visible from the back of the tramp.

2. If you mount it somewhere towards the back, you end up snagging it onthe mainsheet, tiller, and occasionaly yourself.

3. The bay i sail through is merky and has lots of crap floating around, so sometimes something would hit the propeller and jam it. No damage to it, you just have to reach down and pull the cable out of the water to clear it.

If you really want something to accuratly measure speed, distance, etc. I would get a GPS. If you get one that is WAAS enabled, then you get an incredibly accurate reading. Even now, most GPS's come with some sort of mapping data. Garmin has a select few units with what they call blue chart capability (basically marine maps on your gps) So though you won't get a direct reading of your depth, you can look to see the contour lines you are between. I never leave home without mine (Garmin 76s). I velcro it to my fore arm and at a quick glance can see where i am on the lake, my speed, and my direction. Extreemly helpful if you need to call for emergency help because you can rattle off the lat and long for quicker rescue. To me, i didn't like the fact of having something dangling behind me and then having to be in a certain spot to read what it said. GPS is far more useful. Just my few cents

~Reid
Lake Superior
N5.2

I have been using a small portable GPS unit while sailing my F18 boat. I have tested the GPS against odometeters and measured courses. I once competed in open class rallies and learned to verify odometers and even this fairly inexpesive model is accurate to about a 1.5% or less error, in measuring speed.

I had a friend attempt [color:"blue"] [/color] to measure the speed of my boat with a RADAR gun, but had difficulty getting accurate measurements from a fiberglass, kevlar, mylar, and aluminium target.

Another advantage in the portable GPS units, is choice of speed measurement displays. Most units allow KPH, Knots, or MPH display.

I usually have mine set on MPH, and have clocked a high speed of 31 MPH in 25 MPH winds.

Mike

Some GPS units now have a built in compass, does this mean that you can calculate your leeway, i.e. can any units display the compass heading and the gps heading at the same time.

Brighton beach, UK now has an online weather station that transmits and stores real time wind speed and direction, combine this with your GPS and you could probably gather quite alot of data for measuring boat performance.

Gareth

Some of the better units come with an electric compas. The GPS will always track your true course and then if you need, you hit a button and the electric compas comes up and you can point that in any direction to get a reading. I'm only familiar with garmins, and their e-trex line as well as the 76 series i think have these. Otherwise, a generic GPS will only display a compas if you are moving and it will only be in the direction of travel. Hope this helps!!

Reid Rechel
N5.2
Lake Superior

Hi Grob,
All you would have to do is line up the GPS with a Hull and look at the difference between the compass reading and the GPS heading and voila ! We have leeway !

mhb

Now now ... No need to get upset :-)

I had also posted some comments off that thread thinking(I was sure at the time) I had seen a Nacra 5.5 doing 26+knots(via GPS). I have since found out it was not 26knots but more like 22 .

Ever drive a car at 25 knots and open your door to have a look at the ground, or telephone polls flying by.

Makes me wonder if that guy wasn't closer to the truth.

I'll just have to get together with 'pitchpoledave' this summer and do some fun speed trialin' on beautiful West Lake.

Marc