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Author Topic: Footy advice Please  (Read 1372 times)

g4yvm

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Footy advice Please
« on: May 14, 2010, 09:32:54 AM »

Hi, I have scratch built a Footy class yacht and have just given her her maiden voyage. 
I find she won't steer on rudder but makes very large changes of heading relative to the wind
when sheeted in and out. I deduce from this that the rudder blade is far too small and that the
keel is too far aft ofthe mast / centre of pressure.
Before I start cutting, do you think my deductions are correct?

David
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Greggy1964

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Re: Footy advice Please
« Reply #1 on: May 14, 2010, 10:53:17 AM »

I would guess the problem can be traced to the fact that the centre of effort of your sails is far too forward compared to the under water profile of the hull and the constant swapping of course is because your boat is always trying to find its equilibrium but cannot maintain it.

Try adding to the area of the keel in front of its current leading edge and sail again.

Or sail with mainsail rigged only or if this is too much try a reduced forsail area and see if this helps.

All will point to the centre of effort of the sails being too far forward if she then sails happily.

Having a longer keel will make her sail straight but you my find it difficult to steer but it will point you in the right direction before the need to start hacking at the poor thing :-))

Now the technical bit ;) :-))

A simple way of finding the centre of effort of the sails is to cut the shape of forsail and mainsail out of cardboard as one pattern and suspend it from a length of cotton.

By playing around with the suspension point until the pattern suspends horizontally will give you the centre of balance of the shape and thus the centre of effort of the sails.

This point is transferred to the sails on the boat and projected vertically to the water line.

Next make a profile pattern of the underwater profile of the hull including keel and rudder at the centre line (side view of hull on plans) from cardboard and balance it on a straight knife edge horizontally so that the balance line is perpendicular to the water line edge of the shape.

This gives you the centre of effort of the under water profile which is again transferred to the water line on the ship.

The sails combined centre of effort at the water line must lead the centre of effort of under water profile by a little way, something like 10% of the water line length including rudder is a good starting point.

With a bit of patience and a bit of fiddling you will get the boat to balance across a reasonable range of wind strengths.
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g4yvm

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Re: Footy advice Please
« Reply #2 on: May 14, 2010, 06:33:46 PM »

Thanks Gregg, ace post!

David
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rickles23

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Re: Footy advice Please
« Reply #3 on: August 24, 2011, 02:27:12 PM »

Hi,

I have just run a ruler over my Footy yacht which sails very well.

The front edge of the keel is in the centre, 6 inches from the bow.

The mast is an inch in front of the keel.

Go to http://footy.rcsailing.net/plans.php and download a couple of free plans.

Regards
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andrewh

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  • Location: Melbourne, Australia
Re: Footy advice Please
« Reply #4 on: August 24, 2011, 05:25:24 PM »

David
 
From the description we can't tell what the problem is (or rather which direction it is in) :}

All footies are pretty sensitive to balance - greggy has beautifully described the requirements to get close to te perfect balance

I race the little fellows - could you tell us which footy it is, what kind of sail setup you have and preferably pose a nice side-on picture?

<<I find she won't steer on rudder but makes very large changes of heading relative to the wind
when sheeted in and out.>>
unless the balance is right - she will not steer (well) on rudder - but does she swoop up into the wind (despite anything you do) or does hse turn away from the wind, and you can't keep her close-hauled.

The sail(s) are trying to steer her like a windsurfer - and apparently succeeding
Footies almost never have too much rudder, or too far aft - so the side view would help us advise

andrew
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