Author Topic: So what has the fleet learnt since we've been gone  (Read 882 times)

ifoxwell

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So what has the fleet learnt since we've been gone
« on: October 17, 2017, 03:42:45 PM »
So its been 5 years or so since we were sailing 12's on the Medway and back then the DCB had just taken over as the design to have.


So since then what have you all learned. Although Ive seen talk of other designs using foils (we had a home made foil on our chapter) why arnt they running at the front? And I see there is now a Hijack design... whats that trying to do that the DCB doesn't, what direction are the designers moving in?


Hannah and I are keen to get back into a 12's now that our daughter is a bit older and perhaps leave our river and join in with the rest of you.... so Id be interested to hear about whats changed and what you all think we should get! (19st all up and cant afford a DCB)


Thanks
Ian

Gfinch

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Re: So what has the fleet learnt since we've been gone
« Reply #1 on: October 17, 2017, 09:44:30 PM »
The Thorntons do pretty well in their foiling chapter....

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ifoxwell

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Re: So what has the fleet learnt since we've been gone
« Reply #2 on: October 20, 2017, 10:46:48 AM »
Thanks for the input
Not being part of the fleet I can only go by the reports and results that are published, and with the help of the boat database it appears the front of teh fleet is dominated by the DCB, hence the question
So do the Thorntons do well because they are very good, or because the boat is... and if the boat is why arn't more people converting old chapters... especially give the price of a new DCB?
Thanks
Ian

Thomas Stewart

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Re: So what has the fleet learnt since we've been gone
« Reply #3 on: October 20, 2017, 11:04:49 AM »
Hi Ian,
I was thinking of buying a chapter and putting foils on it as the Thornton's are extremely fast. I suspect that DCBs hold a light airs advantage though. The HiJack is fast and Med's  was very close to winning the champs this year and he is heavier than the rest of the front runners by some way, I suspect that if you were to sail one light it would be a weapon in most conditions. If I didn't have a DCB I would buy a chapter and put foils on.

Tom

ifoxwell

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Re: So what has the fleet learnt since we've been gone
« Reply #4 on: October 20, 2017, 06:44:03 PM »
Hi Tom
Thanks for your feedback, very interesting. I hope you dont mind me continuing the conversation now that I have your attention but...
What do you think the Hijack does then that the DCB doesnt... or is it just small gains etc
O, and in 12 life before foils, the Foolish's seemed to do all the winning... so why now the interest in Chapters.
Thanks
Ian

Steve S

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Re: So what has the fleet learnt since we've been gone
« Reply #5 on: October 21, 2017, 06:25:55 PM »
Ian,
I think the thing about the chapter is that Mike Jackson designed it to have additional lift at the transom from the massive buoyant rudder he used, so adding the lift from the winged foil does similar, but with probably less drag. Other designs like the foolish do go quick with a winged rudder, but I don't think they can take the amount of lift that a DCB, Hijack or Chapter can.
Regards,

Steve

Nigel W

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Re: So what has the fleet learnt since we've been gone
« Reply #6 on: October 24, 2017, 09:55:06 PM »
Ian

The DCB and Hijack were both designed for foils. In the case of the DCB, it is very slow without a foil. This is because the buttock lines rise so much over the last 1m of the hull, ie lots of rocker at the aft end. Without the foil the water flow can't follow the hull form and probably separates or gets very turbulent. The foil changes the flow pattern over the aft end and ensures the flow is attached, fools the water into thinking the boat is quite a bit longer and also provides lift at the same time.

The Hijack is not so extreme, but still has quite a bit of rocker in the aft end and also not much buoyancy.

The Chapter also has quite a bit of rocker, especially on the centreline in the last 60cm or so. Not much rocker at the first chine position which has almost constant rise from midships. If you look at your flow by the rudder, you will see the flow is not parallel to the centreline, but it moves in from the first chine at the stern to the centerline behind the rudder to generate a wave crest here. This is due to the large rocker on the centreline only. So this is why it likes a Chapter will take a foil well. This could also be the reason why a Chapter is quick upwind and possibly not so quick reaching (without a foil).

The Foolish, Numinous, etc all have very flat (straight) runs aft. Hence a foil will only provide lift and it won't change the whole flow behaviour in the same way as it does on a DCB, Hijack or Chapter

We sail a Chapter without foil and we can get amongst the DCBs on occasions, especially at club level. We do very well on the latest DCB handicap in fleet racing. So as always its down to sailing ability and most of the really quick guys are in DCBs or Hijacks and we are not in their league. As Tom says, the Thornton's have shown excellent speed with their Chapter, but they haven't been sailing that much recently. This is probably one of the main issues, no-one has really spent a lot of time with a foil on a non DCB or Hijack

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ifoxwell

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Re: So what has the fleet learnt since we've been gone
« Reply #7 on: October 25, 2017, 09:22:33 AM »
Hi Nigel
Thanks for the post, very interesting.


I do wonder, as some one who isnt a dinghy designer but who has played with a foil on a Chapter, how much of the speed comes from the the flow manipulation and how much is just from the lift, less wetted area etc. It certainly seemed to us when sailing it that the biggest gains were from being able to move back in the boat early and to unstick the boat, and that should work with all the designs to some extent?. But then I guess its much harder to feel the efficiency's gained from manipulating the flow when sailing on your own, with no one to measure yourself against, as we were. 


I do remember lots of talk when we were last in 12's of just how quick the foolish's were with foils... was that all talk, or are they that quick and if so were do they then loose out?


Cheers
Ian

John M

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Re: So what has the fleet learnt since we've been gone
« Reply #8 on: October 25, 2017, 08:39:34 PM »
I think the Foolish with a foil is quick.  My evidence is 3431 at Brixham in 2013.  I think the Foolish is potentially tricky as it has no chine and big planing sections to add to the foil.


The Chapter is also jolly quick with a foil.  Evidence has appeared post Brixham..., notably at Brightlingsea 2016.


When I write "with a foil" i mean with the right foil. 


Tom Stewart and Graham Camm have experimented with different foils in 2017.


Our Hijack is still in its 2012 configuration.  We just sail it more consistently now.  It is jolly quick 10mph upwards.  We are sticky (and arguably too big) in sub 10mph.  It is clear the Hijack generates more lift than the DCB and that we have to ease the rudder off when it is windy much much earlier.


Centreboard trim tabs can really work but are difficult to use reliably.  We dont bother.  Maybe we should as Graham and Tom both do.


Interestingly the Hijack and DCB have their masts set 1300mm from the bow whilst the Chapter and Foolish are more like 1030mm.  So far, never the twain shall meet, but it would be interesting...


John







ifoxwell

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Re: So what has the fleet learnt since we've been gone
« Reply #9 on: October 26, 2017, 09:44:32 AM »
Hi John


I always assumed the mast was moved back on the DCB and Hijack because the of the foil. I.E. With all the potential lift at the back of the boat the designer is trying to move the C of G aft to make use of it. If thats the case the new designs will only have a real advantage once the crew are at the back of the boat... which for most people is not the norm when 12 sailing. Or is there something much cleverer happening?


Trim tabs... thats a whole different subject and I guess if the boats at the front are using them they must help. Has any one fitted similar to an older design with any success?


So how much playing has been done with foils. The two questions I would have are...


All the angles. Why the sweep back and anhedral/dihedral. When I made ours its was just straight across largely for simplicity and strength but secondly because as the boat/rudder moves and the direction of flow changes over the foil it will create more or less left on each side... which sounded bad?


Height. I think all agree it needs to be as high as possible to interact with the stern wave etc but you dont want the tip breaking the surface... or do you? how high is to high.


Thanks all


Ian


 
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