Micro Class International

[Jorge]

Hello all,

I recently bought a Micro and I would like to sail it with a bowsprit and asymetrical spinnaker.

Does anyone have any recommendation about bowsprit lenght and sail area ? Consider that this would be not for racing, just for fun and fast sailing (but still keeping security in mind... ) so I would think in a larger sail area than the conventional spinnaker. Any idea, picture, data or something else you would like to share ?

By the way, we have some interesting and growing Micro Class activity in Argentina. I heard from the most important Micro boatbuilder that in our country more than 600 Micros were built since mid 80's, however just a few of them race actively today. I am new to the class but I will try to promote the Class and hopefully get more boats again on the water.

Check out our YahooGroups website http://ar.groups.yahoo.com/group/Microtonners/
(however only spanish version)

Thanks

Best regards

Jorge

[Phil De Troy]

Jorge,

There was a boat (Micro Challenger) tested in Belgium with a cruising asymmetrical spinnaker, believed to be complying with the Micro Class Rules 19.6 sq.m. calculated area, approx 22 sq.m. effective area).

The owner was satisfied with the performance.

How to calculate proposed dimensions?
You should measure the distance trom the spinnaker halyard to the deck level, approx. 6,70 m. This could be the maximum Leech Length SLe, but we recommend to take a smaller value, 50 cm shorter (6,20).
Then you choose a ratio SMG/SF, let's take 90%
In the area formula, 4*SMG+SF is then replaced by (4*0,90+1)*SF of 4,6*SF
Without a bowsprit, and a basic pole or bowsprit length 2,25, the distance from halyard to bowsprit end is (6,7^2+2,25^2)^0,5 = 7,06, Luff Length SLu 30 cm shorter 6,76.
So 19,6=(6,76+6,20)*4,6*SF/12 or SF=19,6*12/(6,76+6,2)/4,6=3,96...

Then STL may be extended to 2,64, from halyard to bowsprit end (6,7^2+2,64^2)^0,5 = 7,20, Luff Length SLu 30 cm shorter 6,90.
SF=19,6*12/(6,90+6,2)/4,6=3,90

One again STL limited toto 2,60, from halyard to bowsprit end (6,7^2+2,60^2)^0,5 = 7,19, Luff Length SLu 30 cm shorter 6,89.
SF=19,6*12/(6,89+6,2)/4,6=3,90... for round numbers, we will use 6,90 for SLu

Further, optimise SMG...
19,6 = (6,90+6,20)*(4*SMG+3,90)/12 or SMG=(19,6*12/(6,90+6,20)-3,9)/4= 3,51

If you want a slightly larger cruising spinnaker, try with other areas, like 22.5, 26, 30, there should be no problem for 22.5, problems could begin at 26, as a higher halyard could be required, in an unstayed part of the mast...

Anyway, when you make a choice, just give us information, and report all interesting experience...
_________________

Phil De Troy - Your Forum Manager - - www.microclass.org

[Helge]

40 cm above spi-halyard is no problem. The forces are not big anyway. The gennaker has a sail-senter which is much lower down than the spinnaker.

Therefore our gennaker on 33kvm is easy to sail with, even in 12m/s wind. The boat does not broach, but the sail gently lics down in the sea, and the wind pressure escapes in the top after leech.

A disadvantage is that our gennaker is very low cut and hinders wiew from cocpit. I sometimes I slack the tack line on deep downwind sailing.

This also raises the bow, the air pressure escapes from the under leech.

Gennaker makes fun and safe shortedhanded sailing. Our bow-sprit is 110cm. Made from a half carbon windsurfermast.

[Jorge]

Hello Helge,

Thanks for your reply, very useful information. How does your bowsprit work ? Is it attached on the deck or it enters into the hull ? Do you have pictures where I can see it ? Any picture or illustration will be highly appreciated.

Good news about the carbon windsurfer mast, as I was planning to use one too.

Best regards

Jorge
Argentina

[Helge]

Microsail, fast solution, two long screews through underneath holds the square piece. The bow elongation is not in the rule, but provides a strong hold for the spi-bom. The pole-aft-end is attached to the pulpit with a 6mm cord and woodden plug wich fits in the end of the pole.


Ricochet. As you see, a low cut spi makes it more difficult to see.....


Ricochet.


Ricochet. It was tied with ropes. The plastic sleeve was to prevent snagging, and spread the load pressure. It works fine.


Ricochet. The end will press down and sidewards and does not require much fastening, here: a rubber-cord.

[Jorge]

Here you can see a picture of my boat with the asy spinnaker. I don't have the exact dimensions but is very close to the class rules. I will provide you more details about soon.


I totally recommend to use asymetrical in a Micro ! It makes downwind sailing a pleasure and really fast. Specially if you sail solo as I use to do.

Click on the pictures for the whole pages on PicasaWeb

Click here for the whole gallery on picasaweb.es

Regards from Argentina

*** more pictures shown with technical help of the forum manager ***

Jorge