Kicker... what angle.

[jimbouy]

Following my question a while back I have obtained a slider that should fit the underside of my boom. (Lets hope I measured it correctly!!)

The slider is supplied with 2 rivets to fix it in place. I think the base of the slider is too thin for it to have had a thumb screw.

So question is...


How far along the boom. What's the optimum angle for the kicking strap??

Jimbouy

 

[Vascojc]

The best location for the kicker is directly under the boom fitting as you are trying to pull the boom directly down, but the lower end has to be fixed to the mast therefore it is a compromise.

Logic suggests 45 degrees is the ideal angle?

 

[cpedw]

The power of displacement activity...
Assuming the maximum force that can be exerted by the kicker (along its length) doesn't change depending where it's attached, and that the other attachment is as low down on the mast as is possible, then if the objective is to maximise the moment (torque or leverage) on the boom about its pivot to the mast, then the optimum position is as far out along the boom as possible.
The curve is asymptotic though, so the extra benefit of moving the attachment out along the boom diminishes quite rapidly. After it's further than about 1.5 times the distance from pivot to mast attachment point, the extra benefit is small.

Derek.

 

[VicS]

Re: Kicker... what angle.

I asked myself this question several years ago. Difficult to explain in words but I thought the maths was relatively simple, the end result being that it doesn't make any difference. Obviously you wouldn't want to go the end of the boom so an angle of 30 to 45 deg to the boom would be convenient and do just fine.

If you are a maths, engineering or physics lecturer I will have to bow to your superior knowledge though.

 

[rudolph_hart]

Re: Kicker... what angle.

Having just ordered a gas-spring solid kicker after a bit of research on the Internet, I found that many of the suppliers (Sailspar, Z-Spars, Sparcraft, Selden, Easy, Spinlock etc) give a 'recommendation' , usually of 30 to 45 degrees.

 

[Davolas]

Optimum angle is 45 degrees. This gives factor of 0.5 of the force in the kicker as a downward moment on the boom. up to 30 or 60 degrees decreases to a factor of 0.43. beyond that it drops off rapidly.
80 /10 degrees gives a factor of 0.17.

The key to maximising downward force is to have angle at 45degrees and attachment on mast as low as possible, which means attachment at boom is at corresponding distance, but make sure it doesn't foul anything. Dinghy, mushroom vents etc as the boom is eased.

Regards

Steve

 

[30boat]

Re: Kicker... what angle.

The problem of keeping the fitting in place while under load is a big one.On my Fulmar I had a similar arrangement ie a slide in a track with a bolt that pressed against the bottom of the boom.This was obviously a terrible idea and there were deep scratch marks and indentations made by the thing when sliding merrily along the track every time the kicker was tightened.So I cut up a 10 cm long piece of square section St.steel bar and bolted it with three 8mm bolts inside the track just in front of the Kicking strap fitting.This is left free to slide but is stopped by the steel bar.
Don't rely on a grub screw, it'll only cut a groove in the alloy.

 

[charles_reed]

Between 40-50 degrees - if you can lead your mainsheet from boom to mast base, parallel to the kicker you'll find it's very much more effective (about the only good thing about Bavaria rigging).

If you fit a gas strut you can do away with that awful boom lift, but even riveting will pull through in time, so a full length spacer to gooseneck is a good idea.

 

[cpedw]

Oh no it's not...
With a fixed height of kicker attachment below the boom pivot (h) and a fixed maximum force the kicker can exert (F), the maximum moment that can be achieved on the boom is h times F. But to achieve that, the kicker must be attached to the tip of an infinitely long boom. In practice, the 45degree kicker gives half of the sqare root of 2 times that (about 70%). Attaching the kicker further out along the boom (bigger angle between the kicker and the mast) will give a bigger moment.
For an angle a between kicker and mast, the moment is h times F times sin(a).

Derek

 

[Lakesailor]

[ QUOTE ]
Oh no it's not...
With a fixed height of kicker attachment below the boom pivot (h) and a fixed maximum force the kicker can exert (F), the maximum moment that can be achieved on the boom is h times F. But to achieve that, the kicker must be attached to the tip of an infinitely long boom. In practice, the 45degree kicker gives half of the sqare root of 2 times that (about 70%). Attaching the kicker further out along the boom (bigger angle between the kicker and the mast) will give a bigger moment.
For an angle a between kicker and mast, the moment is h times F times sin(a).

Derek

[/ QUOTE ]

And after all that you can still pull down on the end of the boom with one finger.