Planing in 12s.

[Lukepiewalker]

I've got a digital hanging balance with 50kg range on it's way, if that would be any use?

[Jimbo42]

[Simon Nelson (Guest)]

[quote by=Jimbo41 link=Blah.cgi?b=Cool1,m=1164825767,s=69 date=1166602118]Simon, how might your very interesting analysis help us? Are you saying there's no point?

Jim N3130 and N3470[/quote]

Sorry. I guess my comments were a bit OT and might have clouded the issue. Frank Bethwaite certainly learnt a lot towing various NS14 designs and a 12 is about the size of a Americas Cup tank test model! The biggest problem I see is managing to remove enough variables so as to make the results meaningful. I await the whole thing with interest

[Jimbo41]

You might like to join in if we get clearance from Spinnaker!

We're trying to design the whole thing so as to make it very simple. In the meantime I've come to realise that we can afford to forget a side rig construction for towing if we make the tow long enough to make the bow wave / wake effect insignificant. Sorry surfers - nothing doing!!

Cheers!

Jim N3130 and N3470

[Jon_P]

I watched a program on the design of the BMW Oracle team ACC baot last night.  They still do a lot of tow tank on 10ft models.  They tow them at different speeds  recording drag and then compare them to each other.  Big tank!
It looked pretty cool :-)

[Simon Nelson (Guest)]

[quote by=Jimbo41 link=Blah.cgi?b=Cool1,m=1164825767,s=78 date=1166689479]You might like to join in if we get clearance from Spinnaker!

We're trying to design the whole thing so as to make it very simple. In the meantime I've come to realise that we can afford to forget a side rig construction for towing if we make the tow long enough to make the bow wave / wake effect insignificant. Sorry surfers - nothing doing!!

Cheers!

Jim N3130 and N3470
[/quote]Might prove a little inconvinient! Much as I am sure it would be fun, it would be hard to justify travelling so far just for this (I am moving to Oz in January!!)

[Simon Nelson (Guest)]

[quote by=Jimbo41 link=Blah.cgi?b=Cool1,m=1164825767,s=78 date=1166689479]You might like to join in if we get clearance from Spinnaker!

We're trying to design the whole thing so as to make it very simple. In the meantime I've come to realise that we can afford to forget a side rig construction for towing if we make the tow long enough to make the bow wave / wake effect insignificant. Sorry surfers - nothing doing!!

Cheers!

Jim N3130 and N3470
[/quote]Might prove a little inconvinient! Much as I am sure it would be fun, it would be hard to justify travelling so far just for this (I am moving to Oz in January!!)

[philipcosson]

looking for load cells

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=320063786986

any good?

[janeysailor12]

Hmmmmmmm....beein re-reading all this stuff....again!!!......What about measuring how fast a 12 goes to windward?  or are'nt we bothered about that?

Janey

[janeysailor12]

Boiiiing.....or what sort of boat is suitable for a heavier crew....or.......which boat is more stable for beginners....ooooh the list is endless!!!!

Janey

[Mikey C]

last time i tried, a dissapointing 5 knots in f3/4.

jim, side rig has to be the way to do it. as for expense a couple of 2x4s and some rope will make one. a ribs wake doesnt go away for a loooong time...

[Jon B (Guest)]

Keep it very simple - you don't need a strain gauge you need two simple spring balances.

A scaffold pole across the rib.  A block at each end and the two spring balances in the middle.  each boat on a rope.  The rope goes from the boat to the block, in to the spring balance in the middle.  A monkey in the rib with a Garmin GPS and a note pad to write down speed and drag of each boat at 10 second intervals - one or two runs per boat gradually increasing speed and off you go...

If I could draw a picture I would but I don't know how to post one on this forum.

50kg may be just OK - one of the Cherub guys did a bit of theoretical work not so long ago that showed a drag of about 50kg for a Cherub with 130kg crew at 8 knots.   you certainly don't need more than 100kg (1KN) to get up to 10kts.  To go above that just have one boat on tow and tie both spring balances to it...assuming your rib can get you up to that speed with an N12 on tow.

[patrickg (Guest)]

Interesting discussion - is it still happening or has it died a death?  I'm away at Easter anyway.  There was a q about the sideways force and I've not seen an answer though you've probably worked it out.  The force on the sails is slightly off 90 degrees to the average chord of the sail and is transmitted to the boat partly through the mast or forestay and parly through the sheets.  So to replicate this the N12s would have to be towed off to the side with a yoke so that the line of action of the towing force produced minimal (realistic) rudder loads. (see this back of an evelope)
http://www.eldwick.org.uk/pix/sideways_tow.JPG

The problems of measuring the geometry 'real time' make this a difficult option (you could have helm and crew in the N12 and maintain position using sighting transits on the rib) so probably not worth doing.  Or only for one or two runs just to see what the difference looked like.  I suppose it would keep the boat out of the wake so might save the scaffolding pole, and as an important part of the excersise is working up a thirst/appetite, the more complicated the better!

patrick (2951)

[Rosie (Guest)]

To answer your question about drag. Drag is dependant on the density of the water( dependant on temperature), velocity of the object, surface area and also the streamlining of the object.

Rosie

[Jimbo42]