Author Topic: Loosing Momentum with my Cherub  (Read 5969 times)

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Offline Team Slatter

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Loosing Momentum with my Cherub
« on: April 09, 2014, 06:56:41 PM »
I love sailing my Cherub however i feel like im loosing it abit ... how can i keep the momentum ..
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Offline Clive Everest

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Re: Loosing Momentum with my Cherub
« Reply #1 on: April 09, 2014, 08:01:07 PM »
Build yourself an 05 boat.
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Offline Phil Alderson

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Re: Loosing Momentum with my Cherub
« Reply #2 on: April 09, 2014, 08:02:12 PM »
As Momentum is the product of mass and velocity, to increase your momentum you should either increase the weight of your Cherub, or the I would say the preferred option of increasing your speed!
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roland_trim

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Re: Loosing Momentum with my Cherub
« Reply #3 on: April 10, 2014, 09:30:16 AM »
12ft boats (even 05 cherubs) are too short and yes they do stop. If not handled carefully.

In light winds the key is normally to "dig" the nose in and get the transom out of the water ("drag" mode). For most cherubs this is the fastest "displacement mode".

In moderate airs the key is to judge when you can get the hull out of displacement mode and into "skimming mode", where the weight of the boat is carried by the surface foil effect rather than water displacement (what we'd call planing and surprisingly few other boats rarely actually do).

Reality is somewhere between what is written above and real life. The key is to sail it a fair bit and you'll find the modes. Cherub Open events are handy for watching what others with similar boats do and what actually works on a race course.

Those older and wiser than me will be along. But for my tuppence the bit above shows we have been foiling since the first Cherubs, just people have forgotten we use a surface piercing foil that is self controlling and 12ft long...
 
As an additional complicaiton the newest Cherubs (Banshee, E6, E7, Everest1, Ronin) deviate from this concept, skim around their middles and may actually never "plane" as the definition above (i.e. even at about 18knots some of the E6 hull still appears to still be in displacement mode around the middle with the bow and transom clear of the water).

Offline Torchy

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Re: Loosing Momentum with my Cherub
« Reply #4 on: May 08, 2014, 04:10:39 PM »
Interesting comments Roland...

By my understanding planing is defined by whether waterline length (wavelength of the bow wave and it's speed of travel, longer wavelength = higher speed) is determining the maximum speed. You can see when the wave shape changes and it's at relatively low speeds, particularly if you use the T foil to lift the stern. You see the bow wave rise behind the boat, rather than around the transome and to my mind this is the start of planing.

Firstly, is this analysis correct?

Uffa Fox says in his autobiography that the national 18 didn't plane but '...cut a groove in the water and ran very fast in it...', which sounds awfully like the modern Cherubs which you describe. The 18 has a relatively narrow hull for its length...beautiful boat btw. I think most modern designs are more like a N18 than a Firefly, at waterline level at least.

Destroyers/frigates plane bow down...don't they?

Born Slippy seems to go fastest downwind with the bow as close to the water as you dare...I think Loco does the same, though I'm not sure yet. Videos of many recent boats show them going very fast bow down, using T foil.

Conventional wisdom is that we get the bow out to reduce wetted area but I suspect there is also a need to get that draggy stern out...balanced by a need to stop the bow turning the boat, pitch poling.


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