S70 Hull design

[AleX`G]

This is what I have so far for my teams strathclyde 70 class hull.
The rules of the class can be found here
http://www.na-me.ac.uk/symc/symc%20f...ept%202005.pdf
It needs to weigh at least 2kg so the waterlines quite high.
Its probably going to be an aft mast rig.
Possibly have 2 rudders.
Please comment with any crits that I should sort out before making it. We will probably make a second boat with the same hull but with single rudder and bermuda rig to test again.

[AleX`G]

Heres a quick collage i made in photoshop. Rough sail design made in sailcut. Comes in just under 2000cm2.
Could you guys give me some tips on placement of the mast and sail layout. Also how do i work out where to put the keel.

Thanks.

Alex, I can't open your pdf file on the rules since I have webtv so I can't comment on how well your boat may fit those rules. But I can suggest that you:
1) go to www.modelyacht.org ( home of the American Model Yachting Association)-lots of info including links to model yachting discussion forums where you could post your questions.
2) google Lester Gilberts technical site-primarily on IOM's but full of usefull design information for RC model Yachts.

[AleX`G]

Heres another idea i had.
Maximises aspect ratio within rules.
Eliminates mast turbulance.
Easy to control

Any thoughts?

[usa2]

Alex, the first drawing you posted seems to have a lot of things cluttering up airflow in the rig. The second rig certainly offers possibilities, though I wonder how upwind performance would be.

Personally, i would suggest looking into a sloop rig with a large roach mainsail and moderate roach jib. The jib would be set off of a crane protruding forward of the mast section. Reading the rules, it looks like you flat/aerofoil sections for spars are penalized? Are you supposed to use a round mast, or are you allowed an oval section?

[AleX`G]

We have to use round sections for the mast and booms. I wanted to try and get any sails behind the mast away from it so they get less turbulent air.
Is it better to have 2 high aspect sails over 1 low aspect sail. Bearing in mind that the max mast/rig height is 90cm. And max sail area is 2000cm2.
Do mainsails create a downwards force on the mast?
This was my reasoning in having 2 jib like sails becasue apparently they lift the mast up.

You can see pictures of past boats here.
http://www.na-me.ac.uk/symc/symc%20f.../pastcomps.htm
This boat was the winner last year. It has quite high aspect sails. Though i think the hull leaves something to be desired. He was a good sailor as well.
http://www.na-me.ac.uk/symc/symc%20f...th%20place.jpg

Maybe a twin high aspect wing sail like http://www.wingsails.com/
I like that idea alot. Would the boat be able to sail closer to the wind. Or would it just form a more effective aerofoil. Also would it be better to have the servo attatched directly to the mast in a wing sail design.

[SailDesign]

Originally Posted by AleX'G

This boat was the winner last year. It has quite high aspect sails. Though i think the hull leaves something to be desired. He was a good sailor as well.
http://www.na-me.ac.uk/symc/symc%20f...th%20place.jpg

The hull may or may not have left something to be desired, but the bottom line is that :
a) he won (think about it...)
and b) the rig is an intensely conventional sloop rig, RC-model style.

Simple, clean, fairly efficient, and extremely well-proven.

Steve

[AleX`G]

We will have 2-3 teams this year. We will have one team entering a basic wee nip design simmilar to the one in that picture. Another bermudan sloop with a different hull.
And a different unconventional setup. It is this boat i am in charge of designing and building.
And the more i think about it the more i like this soft wing sail approach.
Unless you guys can convince me otherwise I think i have made up my mind.

Thanks doug lord for the tip on Lester Gilberts its a great site.

PS whats better a sail that is 20cm x 90cm or two sails 10cm x 90cm based on the wing sail idea

One would be better, in my opinion. Read the "sail aerodynamics" thread in this forum; I think that subject has been discussed there.

[AleX`G]

Yes ive looked at that thread before but it takes some reading and for some of us lesser educated people it is quite tough going. I think i managed to find the bit about drag affecting sails nearby.
How do you actually work out the amount of lift a sail will produce in certain conditions. Assuming that it is a perfect shape.

Would you consider 20x90 a high aspect ratio.
Im guessing that the principle of gliders having long thin wings is the same idea. It would also be easier to make a 20x90 wing.

Also on the subject of hulls would there be any point in making the hull in the shape of a symetrical airfoil. Then having a rudder at the back to direct the flow.