Thursday, August 29, 2013

Model olympics underway, Fila: new main sail

Yesterday it was match racing time, 8 competitors went head to head.
I finished second overall,
lost one, but won all the other races.
There was no wind on Koseze pond, so the "drifting" was on..     ..the reason the first race was lost is:
I lead around the first and second mark of the triangle, turning around the second mark my sail wouldn't pop to the other side, so i stopped completely, there was not even enough wind to open my bum, so i could sheet in quickly and pop the sail..
..anyway, my mistake or boat problem, tomorrow is a standard regatta.
Drifters are expected, so i finished a new sail for fila, which was laying around unfinished.
It has less luff curve, so it pops to the other side much more easily.
Today i hit the pond when the wind was dying, set it up properly in some 5-7 knots of wind. Then took on the drifters. This sail seems to be better suited for these kind of conditions as it pops really easy.
Will do a fuller report of the tomorrows race.

Friday, August 23, 2013

Blulife in shape for model olympics

Yesterday I took Blulife out for a sail, to check if everything works.
The modelympics are comming up:

Me and my father are planning on taking part, there are three sailing events, marathon(who completes the most laps around a triangle in 3 hours is the winner), Matchrace(no defenders, just elimination) and a classic race(I hope it is counting for the national championships)
We will let out the Marathon as I have to do work for school.

Anyway the boat is going strong, dispite a mishap, in wich both(the fore and the aft) rudders were broken, now it is sailing with only the aft rudder.
The light wind enabeld me to set the rigg up. The sails still have a nice shape.
The optimal setup is a small amount of lee helm, wich requires corrections with the rudder, lifting the bow. This is somewhat controversial(aspecially for light air), but it was the fastest setup i found on the races last year, and two years ago when i designed this boat i liked a lee tendency.
The boat heels even in 3-5knots of wind, but it was designed for drifters, typically seen on ponds like koseze where the model olympics will take part

The vang is set very tight, to flatten the main, and sink the stern, the ce leads clr by some 16% so dispite the flat main the lee-helm remains.
This boat has a problem tho. When heeled the center line of the weted surface moves to the side, worsening the attack angle of the rudder and keel fin,thats why it doesn't perform upwind when the wind picks up.

the hull has a depession near the bow, to keep the half entrance angle very small, the prismatic coefficient of the boat is below .5, in an effort to reduce drag, in the drifters.
Here is a clip another one will come soon.

Friday, August 9, 2013

Fun, fun, fun, Laser sailing...

It's been a year since i gave up on my laser racing, because i was too heavy for a laser(95 kg, and with no money for a finn) and the races were too far away, plus the slovenian sailing association is falling apart.
My race-boat remains tho. I am having lots of fun still sailing it on the lakes around Maribor(also teaching my girlfriend how to sail), and at the sea, when i go there..
..since i have certain ambitions to build my own design cabin sailboat in the future.
 Data collected from real boats is of great importance, so goals for the "big" boat can be set, also much can be learned and calculations confirmed on real boats.

had great fun, with choppy half meter waves
and a 15knot average gusty north-east wind
Over the past two days the runtastic app on my iphone was put to use, carrying it in a water-proof case while sailing.

tested the case-phone-app combo by
measuring half of my sailing on the first day

Measuring the whole route was useless if my predictions were to be confirmed by the measurments.
That is because the speed graph on the phone is not accurate enough to get speed readings for different sailing dirrections. So only stages were measured(e.g. upwind, downwind and reaching)

First my predictions, for the lwl lenght of 3,81m the hullspeed is 4,7knots, or 8,7km/h
The data below are calculated in feet and lbs:

displ/lwl ratio is about 91 which is low in comparison to anything but other dinghies.

SA/displ ratio is 22.6 which is high for boats in general, but normal or even in the lower half for dinghies.

reference, and Principles of yacht design - the bible of boat design

my thought was that laser would exceed the hullspeed by some 10% sailing upwind considering its high SA/displ ratio, and it sailing nearly flat(that is 0-10  degrees of heel), i was a bit angry because no data on the prismatic coefficient for the laser was avilvable on the internet..

Reaching, i was sure it would reach 2.5times its hullspeed, but average a speed of about 2times of the hullspeed, of course no longer in semidisplacement or displacement mode, but planning.

Downwind, my prediction was that it would sail in semi displacement to planning mode,
from 1.1 to 2 times of hullspeed, depending on the wave the boat is riding(a laser does not plan by itself in winds of around 15knots on flat water)

and the course for the data left
and the general data,
 with an average speed of 110% of the hullspeed

here is another upwind(data left and below), the shifts in wind can be seen
above again a 10% higher speed than hullspeed
above the speed is represented by the blue line, the three speed drops are the tacks
The upwind measurements were the most constant, also confirming my expectations.
There are elevation gains and loses, i am not sure why they appear maybe it is gps glitches..

reaching, averaging 1.94 times the hullspeed, close to prediction

above speed is not constant,
as the gusts affect the speed more drastically than when sailing upwind

the biggest speed drop is the gybe(course right and data above)

reaching again, the boat reached the max. speed of 2.6times the hull speed wich is even higher than expected
For some reason all the downwind sessions were lost, but i remember that the speed matched my prediction. It varied alot, depending on the wave, depending on which tack the course varied also, because it is faster to sail a negative downwind(sailng more to the lee than to luff..)

Sailing close to the coast, i had a chance to sail in flat water in a relatively constant wind, eliminating most of the drag caused by the waves:

the avg. speed increased by another two % compared to the hullspeed

That is it for now, it was very usefull to sail on a bigger stretch of water, than small lakes.. was lots of fun and a relief from hometown, and school.

In the next post i will be overwieving measurments taken from fila sailing with b-rigg.

Wednesday, August 7, 2013

Fila, b-rigg

Back in hometown. It is time to get back online after 12 days of sailing in Premantura, Croatia.
With me was my laser and Fila.
There were good 8 days of wind 6of them with b-rigg conditions. Sadly with no comparison i tried differend settings, ending up with a seemingly good setup nevertheless. The boat is pointing high, and sailing superbly balanced, nearly planning downwind, sailing at about 1.5 to 1.8 times of hull speed.
So now i am really ready to sail well in case of more wind on some of our national class races.

But better than the settings are speed measurments i collected putting my phone into fila, i will speak abou those in another post.
Also an idea for the next generation f5g(national class)boat is slowly taking shape.

Upwind, this is the basic setting i found, from here i give the sails more twist if the wind is in the upper range of the rigg

Sailing heeled, near the hullspeed(according to measurements) nothing special happens, with the future canting keel i hope to exceed the hullspeed upwind

The downwind, where much boat speed is to be gained, above just "shaking" the rudder to get the jib to the other side

Surfing the waves downwind
And jibing to get back upwind
The shots below show the boat sailing downwind, in upper wind range of the rigg, with a good setting, and lots of tension on the rigg even in waves nosedives were rare, but inbetween the waves the boat lacks lifting force.
It sails sort of low in the water, increasing wave an wetted surface drag like here:
Obviously a jib providing more lift is needed, in the future i will try something like on a footy.
The second thing is a forward t-foil rudder, the third is a canting keel wich will move, not only move side to side, but also tilt backwards.

That's all for now, i am happy with Fila,
the autum races are getting closer, and i am confident to continue the streak of wins on national regattas, and having lots of fun putting this boat into water wherever there is wind.