question about purchase and ratios on a kicker

[jez33]

hi.
1stly, thanks for every ones help with the last questions on a lark rudder

another question is how would you explain exactly what purches is regarding tention on a kicker?

and when you say a ratio of say 4:1 on a kicker does that mean for every 1 kilo of pull you put in then you get 4 kilos out of the other end ?

or does it mean your kicker has 4 loops made by the 8 pulleys (4 at top of loop and 4 bottom)

or have i totally misunderstood it?

sorry for these questions. i just don't know much of the speak/ jargon yet and need to buy the right kicker for my lark!
im told i should look for a kicker capable of 12:1 so hope you all agree?

 

[savageseadog]

12:1 sounds about right. The thing to remember is that the smaller line thicknesses in smaller boats means it's harder to pull. The load will be a twelfth of the pull on the tackle plus the friction. If you want a decent easily adjusted kiker that's really efficient use ball bearing blocks.

 

[alan17]

4:1 basically means the movable object moves 1m for every 4m of line pulled in. This will not equate accurately to a 4kg force for a 1kg effort because of friction.

To calculate ratio count the number of lines round the block/pulley attached to the movable object (this only works for a simple setup) there are more complex setups such as what I think of as a "waterfall system".

Just remembered it is called a "cascade system"

 

[30boat]

It depends on the size of the rig.On my Fulmar I have a 16:1 kicker and it's just perfect.

 

[VicS]

[ QUOTE ]
how would you explain exactly what purches is regarding tention on a kicker?

have i totally misunderstood it?

[/ QUOTE ]

Not totally but at the same time you are not quite right. alan17 has it right but a diagram is worth a 1000 words

So this is a diagram of a simple 4:1, or 4 purchase, system. Ignoring friction a pull of 1 kg will give a resultant of 4kg as you rightly say.

Crucially you will notice that the load is shared by 4 strands of rope numbered 1 to 4.

This arrangement is OK for lowish ratios but I expect you can see that a 16 purchase system will require 8 "pulleys" top and bottom. High ratios can be achieved by not pulling directy on the end but pulling on it with another system. Imagine if you can another 4 purchase system pulling on the end in the diagram. That will then give 16:1.
I am not going to attempt to draw it though!

(For the pedants out there I know it is incorrect to label the forces in kg, the Newton being the unit of force (and weight) while kg are units of mass.)

 

[William_H]

The usefulness to my mind in a kicker systeem depends to a great extent on the space you have between the cabin top or deck and the boom.
On my boat the boom is relatively close to the deck so a 45 degree angle means that the kicker only pull son the boom a short distance out from the gooseneck. Hence in itself very little power to the leach of the sail.
45 degrees is not necessarily correct but if you go further out the boom then the angle means less tension on the luff.
If you go to a lot of purchase/hydraulics etc you will stress the gooseneck and or bend the boom.
The only way around this is to havee the kicker on a semi circular traveller or as I do rely kmore on a wide traveller for the mainsheet.
On a dinghy where the kicker can be attached on the keel you can get good kicker power. good luck olewill

 

[VicS]

[ QUOTE ]
On my boat the boom is relatively close to the deck so a 45 degree angle means that the kicker only pull son the boom a short distance out from the gooseneck

[/ QUOTE ] Yes I have the same problem! 45° is however the optimum angle.

 

[BAtoo]

http://www.harken.com/cspec/image/11531.gif

This shows a cascade system which effectively doubles the purchase and halves the mount of string that you need to pull. For 12:1 you will need a triple block top and bottom.

 

[charles_reed]

[ QUOTE ]
It depends on the size of the rig.On my Fulmar I have a 16:1 kicker and it's just perfect.

[/ QUOTE ]

I've got a perfectly adequate 12:1 on my main of 32m2, slightly larger, I suspect, than the Fulmar. In the 18 years I've used it it's been quite adequate, allied to a gas strut.

 

[30boat]

The good thing about mine is that a light pull will get things done .No need for winches.I singlehand a lot so that's a bonus.Have to watch the boom bend though.