New boat for the Americas

so you are arguing that real experience is a substitute for bar stool bull??  Why should we let reality & the facts get in the way of an entirely pointless argument that could rage for days??

12 ft skiff masts - lets not argue big fish here.

From C-tech website:

	No. 1 Mast	(7.85 m; ID 63mm)
	No. 2 Mast	(6.90 m; ID 58mm)
	No. 3 Mast	(6.20 m; ID 56mm)

	No. 1 Prod	(up to 3.6 meters; 5 spreaders)
	No. 2 Prod	(up to 3.0 meters; 3 spreaders)
	No. 3 Prod	(up to 2.5 meters; 3 spreaders)

By my reckoning to changes in length are pretty much proportional so the angles don't change much.

From all the 12ft skiff video clips I have watched it seems that as the kite is sheeted on, the boat accelerates and the bow goes down.  The bow then bounces up off a wave.  Once the bow is up at 30 degrees to the horizontal and the transom is dropping out the front of the wave, the back end goes down and the bow stays up.

So it would appear to me that - when the boat is trimmed approximately level fore and aft, then the kite pulls the bow forward and down.  Once you hit a wave and the bow points skywards, all the force vectors change and then the kite can be perfectly capable of lifting the boat into the air!

I think Mr. Redback may have a very valid point though - when you are two sail reaching the drive is coming from the main and jib - very much forwards with little in the upward direction.  Once the kite is up and driving, the force from the main and jib is greatly diminished so for the same heeling force, you get greater forward drive but also a greater lift at the front of the boat. 

Based on this, I think you could conclude that the kite normally drives the bow down - but to a lesser extent than when sailing under main and jib alone.  The kite is capable of lifting the boat when the boat is trimmed massively bow up.

Originally posted by SARSIPPIUS Originally posted by Granite Have a look at some of the video of 12foot skiffs in windy wether when they have short masts and long poles and you will see this effect. 12ft skiffs dont have short masts, they are 30ft long from the keel, compare that to an actual waterline length of 12 foot, that rather large. I hope in your viewing of the 12 ft videos you notice that the skipper and crew are right down the back of the boat? Maybe that mass creates a moment around the center of effort?  its not all kite that dose everything!

The No1 rig may be 30 foot but I would imagine the No 4 rig is slightly shorter The poles may also be shorter but probably not to the same extent.

I am not saying the lift from the kite is huge but I think that there is some lifting effect.

The difference between a windy white sail reach and one with the kite up is significant in where you need to be in the boat and how much the bow goes down.

to me that says that the center of effort in the rig has moved and that movement is pushing the bow down less than without the kite.

Edited by Granite

JimC you said that

Originally posted by JimC Spinnakers don't lift the bow in any circumstances,

I was responding saying that they can it is not common but they can lift the bow.

As you said the center of effort in the kite is about 10 feet in the air but what direction is it in? there are three components forward, up and sideways and the relationship depends on the shape of the spiniker.

Ignoring the sideways component these forces can be resolved into acting on three points

The haliard exit point approx horizontal
The tip of the pole approx vertical
The sheet turning block approx 45 degrees

These forces act on the boat through the lever arm of their attachment point and can be reduced to a force vector acting from approx the base of the mast in a forward and upward direction the magnitude of each part is dependent on the shape of the kite and the length of the mast and pole.
In the majority of boats the forward part far outweighs the upward part thus pushing the bow down, however if you have a very short mast and a very long pole then the resultant force has a large upward component.

The center of drag is located at or below the water line but also at the aft 20% of the boat and acts in a backward direction.

So you have a large back force acting against a large forward force  with a small upward component in a torque couple lifting the bow.

Have a look at some of the video of 12foot skiffs in windy wether when they have short masts and long poles and you will see this effect.

 

 

Originally posted by Granite whether the kite lifts the bow all depends on the ratio between the length of the mast and horizontal distance between the mast and the end of the pole.

Q. Where's the centre of effort pushing the boat forward?
A. Ten feet up in the air

Q. Where's the centre of resistance/drag?
A. Approx waterline

Q. So what effect does the kite have on the boat?
A. Pushing the bow down.

To get an actual upwards force on the bow you can't hang the thing off the top of the mast: you need a real kite with strings. By the accounts of those who've sailed such things the difference and culture shock is astounding - fly the kite and head up the front!