I suppose it depends why you are asking.
I have heard it suggested that a hull which planes early doesn't necessarily have the ultimate top speed.
And I've never noticed much of a 'hump' when I had my twelve... certainly no where near as noticeable as on a GP14 or similar... so ti could be we have already evolved dynamically humpless hulls.... ;D
Ah...
Could you make some kind of a 3d pie chart.... I like pies.... ;D
I suspect the problem will be a lack of quantitative data, qualitatively people will probably be able to give opinions on which boats plane earlier than others, but I fear raw numbers may be elusive....(whistle)
On the crew weight front I believe designers draw the lines with a crew weight in mind, so maybe the designers can chip in on that front. I suppose it comes down to what happens to the underwater shape when overloaded....(think)
Anyway, I'll shut up now and let someone who actually knows what they are talking about chip in
(stars)
There is an argument for the Final Chapter as it is perceived to be a good weight carrier. I infer this to mean that in marginal stuff it is not so bad for heavier people as other people as other designs. Our experience sailing heavy is that it goes very nicely downwind when it is substantially not planing conditions, but loses out to a Feeling Foolish when it is more puffy. Whether this is because the hull form is doing something special is another question.
The real secret of the Final Chapter is probably that you dont have to be fat to sail one!
Otherwise I think strong contenders will be Baggy Trousers and Feeling Foolish or is just the good sailors that had those or is it that the Baggy was regularly sailed very light.
meds
Thanks for your input lads.
Is there anyone out there putting any serious numerical effort into this type of thing? You perhaps Davidg? I know you have a thing about N12 foils.... ;)
Cheers,
Jim.
Data logging is most definitely illegal in a 12...
Illegal only while racing surely?
Realistically the only thing you could really do would be an extended program of tow tests like the Bethwaites do. Its a lot of hassle which is probably why they're the only folk who've done it. But it probably explains an awful lot about why their boats average better than the average SMOD. It would be most interesting to tow a selection of Cherubs and Nationals and get some data...
I think that's a pretty good idea JimC.
What do others think? We could have a go on a lake this Summer. Say one Feeling foolish, one Final Chapter, Numinous, Enigma, Baggy, Man O' War and with a whole host of different crew weights???? For some perhaps as interesting as dragging a teabag around on a long piece of string - not everyone's cup of tea ;) For others perhaps a revelation.
The only thing is it would only deal with hull profiles and not rig-hull combinations as well as position of the wind..... :-/
Jim N3130 and N3470
My favourite approach is a long knotted rope and an hour glass. I have problems counting the knots while holding the main sheet at the same time.... but at least the hour glass floats. 8)
I think varying the weights will only muddify matters somewhat. Best baseline would be to test all the boats with one crew weight. You can then test (with rib/gps/scales) how much resistance at certain speeds and try and plot the results but you would have to do it from a gantry to the side to keep the rib wake seperate.
Rig is irrelevant to the question, as is really the angle of wind.
Whats an Enigma? Not heard of that one.
My top planing list would read something like this:
Big Issue
Baggy2
Foolish
Baggy
Chapter
I think in marginal conditions some boats get to plane earlier, but others go faster before they start planing which can lead to swings adn roundabouts. If you can get your boat on the plane its all good.
If you guys can organise things and its reasonably handy for me in the South Easy then I could drag along my 70s Farr Cherub as an alternate, should it be welcome. Be interesting to see how a more planing shape would compare. I'd expect the Nationals to be much more slippery at most speeds though. And Mikey C could take a look at my Bethwaite wing mast [grin]. With discipline and a GPS one could probably get through tests far faster than was possible the way Bethwaite used to do it with a measured distance and a stopwatch.
An alternative date for me would be the middle of Easter - I'll be picking up N3470 at that time....
Anyone interested appart from JimC and one other of whom I know?
Incidentally, the other chap's a member of the NTOA and is doing a degree in Marine and composites at Plymouth uni. We might be able to get a little support etc....
Cheers!
Jim N3130 and N3470 (riding along on the crest of a wave.... 8))
How about a wake or water ski lake and the cable?
Jon
Jon,
if you mean wake in the sense of the towing boat, I think the gantry idea's not bad. A gravel pit would be quite a good location too, since local boat traffic wouldn't get in the way and we'd have the whole day to mess about.
Are you in on this? If we have serious interest, it might be worth doing. It would be nice to have a few N12 designers around as well.....
Jim N3130 and N3470 (Don't let this thing drag on too long!!!)
One way of doing it is to tow two boats, one each side of your launch, with scaffold pole or something across the bow with the boats and spring balances hanging from. That way you can arange it so they are in flat water out of the motor boat wake. Enables you to do two boats at once to speed up the process.
No i meant the wake boarding lakes that have a wire that towes you round rather than a boat. It would be difficult to pursuade them to help but would cut out the wake issue. You have to be careful to make sure the way the boat towing does not affect how it would plane.
i.e. if it was towed from its bow it might have a tendancy to lift or sink it depending onw here the tow was in comparison.
I would be interested but not sure how easy any of it would be to do and whether it would be of any use to anyone!
If it goes ahaead i might be able to help with measurement equipment if you decide what you want/neeed.
Jon
Wakeboard tows are generally quite high so would end up with a lift component from the tow which is best avoided.
Aside from the gantry all thats really needed is a good set of digital scales and a dory... And flat water.
I think testing should be at constant all up weight (displacement). Then we would get a better idea of how good older designs are rather that how much less drag a lighter weight boat has.
Hi Jimbo, if you are agreeing with me you are agreeing with johnk! The only way you will get usefull info is if the same crew is tested in each boat. you also get rid of the trim variable as that crew will be able to trim each boat in a similar fashion.
MikeyC,
What johnk wants - I think - is to take the hull weight factor out of the drag issue. In order to do that, the hull weight has to remain constant for every design. That means making modern hulls as heavy as the heaviest older hull design.
Jimbo has the correct interpretation of my views. I am aware that heavier older boats have a larger design displacement than modern boats. If we are looking at differing hull designs we should take out hull weight as a variable and test heavy hulls with lighter crew / ballast in them so they all have the same displacement. This displacement could well be that of a modern boat with crew rather than of an old boat with crew.
We could (but probably don't) have a situation where an older hull design built to the current weight rules has less drag than a modern design; but the extra weight in the older boat increases the drag so that it exceeds that of the modern boat.
Good point johnk.
We could do both.....
Boat designers please note.. We also want your input.
Jim N3130 and N3470 (All you do is just put it in and drag it about a bit)
This experiment is getting a) overcomplicated and b) incredibly time consuming to perform.
It takes a crew od 10-15 highly skilled people with millions of pounds budget a whole week to get 2 or three runs of a land speed record car for example.
I think what you are proposing to do on a shoe string is impossible and would prove nothing beyond doubt, therfore would be worthless in the scientific sense (it might be a good day out mind:-)
I would propose doing this in software, or scale models. It would be interesting to get laser plots taken of several 'winning' boat designs. These would then be captured for posterity as the digital data can be archived in the maritime museum for longer than the hulls will actually exist, which will have some merit of its self. These 3D models can then be used to create exact scale models using rapid prototyping, or software models. These can be tested exaustively under a miriad of simulated conditions. (fresh water, salt water, differing crew weights, differing moments due to wind strength and heeling forces, etc... etc...)
I guess the results might interest a host of stakeholders such as magazines, software manufacturers, museums, universities etc. etc. some of these might be willing to fund the project.
I admit, it's not as fun as towing a few boats rond a lake - if you still want to do this, I suggest keeping it simple and using the average crew weightin a given fixed position with a given tow point at a given speed and on similat water. the observations should be as many as possible - because you will not be able to go back and repeat this easily - so measure EVERYTHING qualitative and quantitative (best to put a person in the boat and they can offer a 'seat of the pants' analysis as well!).
Philip
N3253
Philip,
Thanks for your input. I'm not sure that software and scale models can substitute for a full-size, on the water trial, even if only one type of water were used. We have the full scale hulls, why not have a bash and use them.
Personally, if this trial comes to anything, I'd keep everything simple. The only altered parameters would be the hull type and the speed. The crew weight (and crew) would be the same throughout. I'd want to measure the drag at various towing speeds using a strain guage as well as the speed at which the boat starts to plane and at what speed drag starts to fall off prior to planing. This can be correlated with the subjective experiences of the crew. Hopefully, the boat starts to plane at the same time (speed) as drag falls off significantly. We can then plot drag against speed and see how each hull type behaves. I think this would be an interesting exersize, which like this could be performed by dedicated amateur sailors and would also be a quite a fun day out, BBQ and beer included (mine's a Becks! ;D)
It's also a great opportunity to get a bit of Y&Y and other magazine publicity....
What does everyone want? Do I have anyone interested? I'd be coming over 1500Km (not just) to do this trial.
It might be that we get some interesting preliminary data which are worth a detailed study. It's a risk, admittedly with a BBQ and beer and hopefully sunny day attached...
Well? :D
Thanks for that offer of help Phillip esp. tech stuff. :D
I too am a lowly amateur. But I'm motivated to try to do something to point the way to an optimised all-rounder hull. oh of course there's always the question of the beer and BBQ!
For anyone who's interested:
My tel No.'s in the book under Bretherick, James. or J.P. Or you can get me at home on +44 8145 951303. (GMT +1H).
I personally would prefer Easter as a date. The matter would then be to organise it all. I suspect the most difficult thing would be to arrange the boats and towing gantry. Anyone know of a suitable available stretch of calm water? I'll have my Man O' War to test out. Perhaps those awfully nice people at Spinnaker would be able to help out? Eh Simon ;D? (Who reads this C**PP anyway?)
So who's volunteering? ??)
Jim N3130 and N3470 (Heave ho! and up she rises....Wot a drag!!!!)
At the risk of being boring but its been a long very boring day at the office and this is not really my field and I am officially hibernating hotchocolate not withstanding, but have you not got a slight problem if you are towing boats as you will be tending to creat a downward force while sails would I believe tend towards a lifting force also there are variations caused by heeling most boats go better flat but vary considerably in sensitivity to heel. I sure you boat designers know more about this than me.
Any way I sure it would be great fun towing boats baout the place, but me I'd rather be sailing and learning to sail a bit better (Well in my case hopfully a lot better).
Ideal conditions for testing would be Beaufort force 0 - 1. Ideal conditions for sailing force 2 - ?
If you were towing two at a time at either end of long pole, you could get a direct comparison and if nothing else could say one was draggier than another. If you did it this way then the conditions should be the same for the two hulls in question.
yes - I think the relative test has a lot going for it.
Angus - this is exactly the type of stuff we need - looks like we should attach the pull to the mast and have the centre of attachment high up on the towing boat then.
Of course the problem with all this controlled experimentation is you are laid open to probems of generalisation.
Philip
N3253
Surely generalised experimentation better than speculation and conjecture? ;-)
All power to the experimenters elbows!
As well as planing could the nose-diving capabilities be looked at?
Barry
N3364
[quote by=johnk link=Blah.cgi?b=Cool,m=1164825767,s=32 date=1165512090]Ideal conditions for testing would be Beaufort force 0 - 1. Ideal conditions for sailing force 2 - ?
[/quote]
True but then i go best when theres no wind
And plenty of hot chocolate
NEWSFLASH!!!!!!!!!!!!!!
We may have water at Spinnaker to play on. I need dates and boats for Easter Hols time. Sundays are EXCLUDED. Simon aka Passion Pudding has agreed to take on his committee about this but needs a couple of date proposals. He also thinks he might be able to arrange an RIB (30 Hp). I am reasonably flexible but want to get my yot back to Germany by 15th April at the latest and it'll take at least 3 days to do that comfortably.
So we are limited to (a) day in 3rd-5th April or 9-11th April (avoiding Easter Friday Sat and Sunday). I need to find a tow rigg and a strain guage. Any leads anyone?
What's the opinion of everyone? I need commitment!!!!!
Do we do this or not? Any input from our NTOA committee? ??)
Jim N3130 and N3470 (Pushing the boat out)
BOING!
Come on now! Who's prepared to commit themselves to some interesting experimental (conjecture)?
Jim N3130 and N3470 (For the health of the N12 Class!!)
Jim,
I am keen and if do not end up going away with work I will be there, but I unfortunately cannot commit. If I am there I would be happy to use photogrammetry to create profiles of the hull shapes. Would give us a pretty accurate idea of the actual shapes of the hulls.
Jon
.......................yaaaaaaaaaaaaaaaaaaaaaaawnnnnn I've gone to sleep now!!! Sorry to sound negative.....what's the point though???? How can you possibly measure accurately how fast a N 12 planes in anything but "normal" planing conditions blond I may be but I'm not dumb...towing a 12 aint gonna give you accurate results you need WIND....you need PEOPLE IN THE BOAT you need NORMAL sailing conditions....then there's the weight thing to consider, the wind direction, and speed where your helm and crew are sitting in the boat, as far as I can see all you are going to measure is how fast an empty N12 planes in a towing situation with no wind and no-one on board.....or am I missing something??
Janey zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
Yup, I think you missed the entire thread...
Jim, I'm in - assuming dates dont clash with as yet un-announced Moth Fixtures. I like BBQ's
Cheers
Mike
I'll play if you want the Cherub. Mike C has my email I'm sure. I have dialogues with Julian Bethwaite from time to time, and can ask how they play it. I know that they tow with daggerboard and rudder in nowadays.
Equipment...
GPS
Towing poles rigged on boat
bags of building sand as ballast
two balances at least for on the water measurement
off water weighing facility (make sure all boats towed at the same weight)
suggest video camera would be a good idea - looking at the wave systems round boats can be *very* interesting...
Ok....buying into this reluctantly.........so....how are you guys going to solve the problem of shifting weight around the boat when she gets up on the plane?? after all we sit well forward in sub planing conditions, and move aft and possbly pump to promote planing and if you try it with centerboard and rudder down I think you will have problems with boats shearing off one way or another. Dont think sand bags will acheive this.
janey
P.S wot's on for the BBQ and how much beer will there be and will there be any Gin & Tonic available.
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.
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
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.
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.
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!!
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!
To be honest I'd probably be more interested in the sub-planing performance...
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... ;D
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
SORRY!!!!!! Angus....my reply was to Mike C (ook) not you honey!!....alway was terrible at names
Janey
;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
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
Roger: "As 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...."
Absolutely. No question about it Roger. However, if you knew the boat design better, you could find yourself going quicker, faster if you iunderstand what I mean. Towing a boat can give you a better idea as to how she reacts under these conditions. And it's also a good excuse to get people over for a BBQ.... ;D
Jim. N3130 and N3470.
[quote by=Roger_Brisley link=Blah.cgi?b=Cool,m=1164825767,s=58 date=1165962669] A tow is no substitute for sailing,[/quote]
Exactly so, but equally empirical observation from sailing/racing results is no substitute for repeatable science. The two are complementary.
In terms of success in introducing new classes without them dying after 10 years and gaining International acceptance then the most successful designers of the last thirty years are the Bethwaites. They're also the only people who have a consistent pogram of tow tesing so they have some real data about how hull shapes perform. I don't believe that's a co-incidence.
In my time sailing Cherubs I was never sure who was fast because of their boats, and who was fast in spite of them. Hull shape is really such a small percentage of total performance I've never been prepared to say what is hull and what is other factors. Which is more important, early planing or low drag high displacement speeds? Only one way to find out!
Anyway science is fun and interesting. For some of us anyway. For others its mindless ly boring. But then there are people who don't like going sailing!
[quote by=JimC link=Blah.cgi?b=Cool,m=1164825767,s=61 date=1166000717]
Exactly so, but equally empirical observation from sailing/racing results is no substitute for repeatable science. The two are complementary.
I agree there. let's try both.
Anyway science is fun and interesting. For some of us anyway. For others its mindless ly boring. But then there are people who don't like going sailing!
[/quote]
I like sailing and I like science. Surely, we should have time for both postulating and bravado. :B
Jim N3130 and N3470 (N12 - Have a drag on this.... 8))
Put me down to lend a hand - subject to the usual conditions - of not sailing my plastic boat(s) elsewhere.
Oh and if over Easter I'll have to be able to bring the dog.
I'm not sure how much wiser we'll be after this but I do suspect it will be a hoot. No real expertise to bring to the party - but I do like BBQ food.
Barry
N3364
boing
UPDATE UPDATE UPDATE
Ok. proposals being considered by Spinnaker comittee, (says he standing there with sweaty palms).
We shall see.......
Jim N3130 and N3470.
P.S. I'll be down on the water at Spinnaker on the 28th December with Passion Pudding.
[quote by=JimC link=Blah.cgi?b=Cool1,m=1164825767,s=61 date=1166000717]
In terms of success in introducing new classes without them dying after 10 years and gaining International acceptance then the most successful designers of the last thirty years are the Bethwaites. They're also the only people who have a consistent program of tow testing so they have some real data about how hull shapes perform. I don't believe that's a co-incidence.[/quote]I am not sure I can agree with your conclusion. Firstly, while Frank did a lot of tow testing, I don't think Julian has in recent years. Secondly, the success of the Bethwaite designs on an international basis is more an accident of geography than anything else. I will try to explain.
Australia doesn't have a very large market for high performance dinghies. For the Bethwaites to make money, their designs need to succeed internationally. If you ever go to an ISAF conference, you will find Julian hovering around for the whole time. He is always canvassing, monitoring etc. Take, as an opposite, RS. Their home market is so big that they can go a few years with a design before supply gets greater than demand. They don't need to push the international stuff anywhere near so hard. So, different approaches have produced different boats and different success. You could also argue that the Bethwaite marketing machine has done a better job than any of the others by playing the "long game", concentrating on international take up rather than meeting short term demand.
Don't get me wrong, they have designed some great boats but getting international take up isn't much to do with great design. It's more to do with great marketing and strategy.
Simon, how might your very interesting analysis help us? Are you saying there's no point?
Jim N3130 and N3470
I think he was just saying International success and great design don't necessarily go hand in hand!
Dead right there Mikey!
Incidentally, do you know where we might be able to get a suitable strain guage for our dragging endevour? Grazz says the association doesn't have a suitable one. Large dynamic range and sensitivity would be required, not an easy choice.
Cheers,
Jim N3130 and N3470.
Consider getting two strain gauges - one for low speed - one for high. It may be easier to try two boats at a time on a pivoted beam so that one can measure differential drag. The strain gauges would give drag v speed curve for one hull with say 2% accuracy. With two boats, keeping one as a reference design, you could plot % difference in drag v speed to much higher accuracy than by comparing separate drag v speed curves.
bethwaite talks about this technique of 'the 'balance' method of tow testing in one of his books. Keeping one boat as a reference. can't find it at the mo. but will keep hunting.
Super! Thanks lads.
I'm currently scouring the internet for a suitable transducer. found one with a 5kN range. Sealed unit. Trouble is, we'd need an amplifier and a radio output to the towing boat/shore. Budget doesn't stretch that far.....
I'm down on the 28th December at Spinnaker to test out Passion Pudding (N3470), so if you lads are in the area, we might be able to meet?
Cheers!
Jim N3130 and N3470.
I've got a digital hanging balance with 50kg range on it's way, if that would be any use?
[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
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
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 :-)
[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!!)
[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!!)
looking for load cells
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=320063786986
any good?
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
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
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...
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.
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)
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