Planing in 12s.

Mikey C · 08 Dec 2006, 08:19

The boat will have to be trimmed to its lowest drag point at all speeds, this will vary, and is also a feature of each design. The Bi.2 is very fore aft sensitive, whereas the Foolish isnt so noticable when you are doing it wrong. This is most of the reason why the test is so interesting. I personally think the test will have to be done with a crew in, (19 stone is a good weight, as its pretty much middle ground.) so the crew will know what to look for trim wise. They will also need to try to keep the boat tracking in a reasonably straight line.

Were not looking for max speed, as that is limited only by the tow boat. we are looking for lowest drag at varying speeds, probably 2 knot increments up to around 14, but I should imagine this is going to be sketchy to actually do. We can swap a single rudder between boats to iron that difference out. C/B could be tricky as these vary quite a lot. I use 27mm boards, whereas the chapters are 32mm gybing and there are others...

Jim, would be usefull to have a baseline to work to from the Bethwaites method, that way at least results can be compared if they're interested.

IanL · 08 Dec 2006, 09:56

There is an interesting picture of a tow being done on Firefly on p.27 of Twiname's "Start to Win".

Just the picture goves you some idea of the difficulties of getting a measurement!

I guess you'll need a big-ish dynamometer(force meter), and several runs to get some figures. Given that differences between boats are a few %, I'd have to guess that measuring any differences will be hard.

Might be better to start with some lower boat speed tests?

Ian

John Meadowcroft · 08 Dec 2006, 10:34

Mike - using a single rudder sounds a little silly to me. Whilst it eliminates a variable, surely the point is to ascertain whether there is a consistent measurable difference between a number of known scenarios ie pieces of kit that are actually used. The bits of the boat that are in the water are the package that you want to test. You might need to set up the board consistently ie 1/2 up but surely you want the board and the rudder that are used. Part of the package may be very nice fitting foils. Remove them and you lose performance. Are you going to make all the slot gaskets equally abused/perfect? Otherwise your findings are even more iffy.... This should not detract from the quality of the BBQ though or the coldness of the beer which I am sure will be fine.

Would you not want to test with quite a wide variety of weights so that you could initially determine that you were capable of measuring differentials in overall weight for a single design over a given weight range. Then you would be able to plot the relative curves of each hull as it changed weight and at different speeds.

Jimbo - I don't see why the N12 Committee is going to get particularly involved in the organisation of this one. There is no history of the Class particularly assisting in boat design / development projects and speaking personally I am not sure that now is the right time to start that either.

enjoy.

Jimbo42 · 08 Dec 2006, 10:53

angus · 09 Dec 2006, 08:22

looks like you guys are buying into this big style. I suggest to get the best on the water you do some serious modeling first. There should be plenty of models about predicting planning performance, after all if sombody has writen a paper on the effort to site out a laser (thanks for that one phil most enlighting). You should them be able to predict when differnet hull shapes will plane from that you you should then be able to work out how to alter shape to give disired result.
Don't forget to work out which questions you want to answer. Is it early palnning fast planning late planning easy planning etc etc.
Me I think I will stick to the hot chocolate.

janeysailor12 · 11 Dec 2006, 01:43

Me too Angus!! (The hot chock that is)...having read EVERY POST on this thread (just to assure those who think I have'nt and therefore missed a point) I can't see that anything conclusive can be proved by this excersise. I think (for what it's worth) you can only get reasonably accurate results by using "real" people in fully rigged boats sailing under "real" sailing conditions (wind and waves). And even then there are sooooo many "other" factors that cause a N12 to get up and plane. As for using the results to help someone who's new to the class make an informed decision as to what hull shape to invest in, I can only see it will confuse people even more, no boat is all things to all men (or women) and to possibly aim to produce a good all rounder in the 12 calss is surely putting the preverbial tin lid on the "developement" class issue. Surely that's half the fun of the class, buying a 12 and LEARNING how to make the most of it's best features, and improving it's worst ones! But HEY!!! if all you boffins want to do this "trial" and it would seem some of you are, then fine. I guess it's a useful thing to occupy the cold winter days,.... me.......I'd prefer to be out there practising and improving my practical knowledge of sailing a 12 rather than the theory stuff. BBQ still sounds the best bit though!!

Jon_P · 11 Dec 2006, 04:05

Janey,
To a certain degree I totally agree but...

If you do not understand the issues then progress can only be made by trial and error. If you can learn the reason why a boat planes quicker or easier or whatever then you can create a design that maximises these reasons.
However to stick up for your comment I also am not sure whether this trial will actually create and results worth having, but it might be good fun trying!

p.s. I think I have stood on about 3 fences there!

Lukepiewalker · 11 Dec 2006, 05:57

To be honest I'd probably be more interested in the sub-planing performance...

Mikey C · 11 Dec 2006, 08:38

Lukepiewalker · 11 Dec 2006, 08:58

Off topic I know, but I like the wee Moth stroyboard on the front page of your website mike... made me laugh... can't go wrong with speech bubbles...

Jimbo42 · 11 Dec 2006, 10:52

janeysailor12 · 12 Dec 2006, 03:48

Quote "The other half is making them go faster... I would like to get all my funs worth, not just half of it thanks!"
Which is why I also sail a B14 Angus!!! I too like going fast, and I've always felt the 12 is under canvassed, mabe that's an answer if the class would allow??? Probably not!!

Jimbo..... the Crusader is not neglected LOL!!!

She was actually sailed 2 weeks ago at our local club where it was sooooo windy ALL we did was plane!! It was more a case of stopping her rather than getting her going!!! The B may be fast...but that little Minx (the 12) certainly has her moments!
Janey

janeysailor12 · 12 Dec 2006, 06:40

SORRY!!!!!! Angus....my reply was to Mike C (ook) not you honey!!....alway was terrible at names

Janey

RogerBrisley · 12 Dec 2006, 10:31

;DAs Cilla would say there's a lorra lorra lost plots going on here,isn't a large part of this being able to get good boat speed and good tactics to get round in front?

A tow is no substitute for sailing,

Roger

philipcosson · 13 Dec 2006, 07:59

What are the actual forces on the hull from a N12 rig?

From the little I know, on a reach the forces are partly sideways, countered by the centreboard.

Can we work out a way to drag to mimic this?

Philip
N3253