timberwolf

[Hurts 6]

Thanks Tim - yes the middle carbon would be ideal for a fine/strong trailing edge - it's a nice refinement on what I was planning if I go with an "inside out" process. Now I look closer I can see the rebate for the uni's.

 

As I have two to do then I might build a mould but your process looks good also - decisions, decisions...

[Guest]

The section we use on both Centreboard and Rudder is NACA 63014. It is a laminar flow section ideally suited to a High Speed Trimaran.

 

The Core Density is very important as the two most likely modes of failure in a foil are in Buckling, either outward buckling caused by Core Sheer Failure (very common in Centreboards) or Inwards buckling, alleviated greatly by a Higher Density Core.

 

The Core sheer properties are most governed by the choice of Foam, in our case a Structural Airex PVC core.

 

While the Carbon Laminate (5mm thick where it exits the boat) does most of the work (in compression and tension) the Core has a vital role to play.

 

Our rudder that broke failed because the core compressed.

 

THANKS Tim. Very important information you are sharing here. TNX

 

What sections are being used in the c/b's & rudders of the AC 45's - or is that knowledge not available??

 

Does the section you have chosen to use have its maximum cord farther aft at the bottom than the top?? Is the section thinner as a % at bottom than the top (at the hull exit point)?

 

Does anyone wedge the board to windward by say 7 or 9 degrees when going to windward?? ie - tack the board in the case. Could ask the same question about a 'trim-tab' on back 1/3 of the rudder blades - thus creating more - lift to windward of the rudders?? Bennell, Miller, Locki & others did that with radio controlled model yachts (that's where 'funny' keel was developed). I've always wondered if it would work on fast multihulls as it's done on slow monohull keels? Thanks for taking the time to be bothered with the questions. We're all learning lots - at your cost though. Ciao, james

[MartinRF 76]

This may be of interest:

http://hem.bredband.net/b262106/Boat/Sym_vs_Asym.pdf

And perhaps this:

http://hem.bredband.net/b262106/Boat/dagger.html

 

/Martin

[TimW 1]

[THANKS Tim. Very important information you are sharing here. TNX

 

What sections are being used in the c/b's & rudders of the AC 45's - or is that knowledge not available??

 

Does the section you have chosen to use have its maximum cord farther aft at the bottom than the top?? Is the section thinner as a % at bottom than the top (at the hull exit point)?

 

Does anyone wedge the board to windward by say 7 or 9 degrees when going to windward?? ie - tack the board in the case. Could ask the same question about a 'trim-tab' on back 1/3 of the rudder blades - thus creating more - lift to windward of the rudders?? Bennell, Miller, Locki & others did that with radio controlled model yachts (that's where 'funny' keel was developed). I've always wondered if it would work on fast multihulls as it's done on slow monohull keels? Thanks for taking the time to be bothered with the questions. We're all learning lots - at your cost though. Ciao, james

 

 

Out of all the areas of sailing I think foils are the one area I see a lot of people getting bogged down.

 

take a look at the Top multi's sailing in Auckland, Many have very average foils that would not merit the level of discussion going on here.

Yet despite everything being wrong about these foils the boats still have a habit of kicking everyones arse on the race course.

 

My view is that all the theory is fine but the real world is that there are just so many compromises you should just get a nice set of foils that work for you and ignore the boffins who tell you they are no good.

 

The AC45 centreboards look similar to me to NACA 63412 and are assymmetric.

The rudders appear to be a similar section to a Standard NACA 0013 (or there abouts).

 

The section we use has the maximum chord at 30%, I think 40% works better on slower boats ?

The Section is just constant,not thinner at the waterline.

We use Dagger cases for both Centreboard and Rudder that are an exact fit to the foil.

Section changes just leaves gaps between the foil and the case that can fill with water (water spouting out the case).

 

The gybing board idea is used in Int 14's.

But I'd rather not have the extra drag of the case filling up with water.

The Trim Tab is a great idea, I would love to have one on. Vodafone does.

I decided against a trim tab only because of the complexity of the build process (including additional cost).

 

Also in our current configuration with our big Centreboard, Timberwolf is a very high winded boat, No one really Out points us.

And with the curved foils down we have some real upwind pace through the water.

So I'm sceptical of the need for trim tabs.

 

Like the curved foils I'm sure they are great when they are great but you can do without them, especially when you consider you are just racing different designs in handicap racing.

[Tim C 23]

I'd suggest that if you have to have wood in a foil then you need to use the strongest orientation of the grain to prevent a hull exit compression failure. It would be more efficient to use it like end grain balsa, ie with the grain running the shortest distance between the carbon flanges.

 

The contribution of the cedar to longitudinal strength and stiffness compared to the carbon content is minimal.

 

Using the cedar along the foil is relying on its core sheer strength. Remember how you split fire wood, along the grain. Imagine a plank lay up of a cedar core boat without the glass either side; it would be easy to break.

 

More efficient again would have been a double bias sheer web.

 

Wood has as much place in a carbon foil as aluminium in the marine environment...

[Clipper 375]

Wood has as much place in a carbon foil as aluminium in the marine environment...

 

Classic

[TimW 1]

Yes, End grain Cedar would be better but really no one sells it and it takes ages to cut it into blocks and is very hard to machine.

 

The density of the Cedar run long grain is still higher than High Density Foam and it is still less comp[ressable, especially with 5mm of Carbon laminate on it.

 

The Cedar is definitely a compromise, a Carbon reinforced Girder would be better, but this way it has to be easy to machine and strong enough to do the job.

 

Cost is also a big issue. The wood is a cheap option that has a number of good things going for it.

[Hurts 6]

Yes, End grain Cedar would be better but really no one sells it and it takes ages to cut it into blocks and is very hard to machine.

 

The density of the Cedar run long grain is still higher than High Density Foam and it is still less comp[ressable, especially with 5mm of Carbon laminate on it.

 

The Cedar is definitely a compromise, a Carbon reinforced Girder would be better, but this way it has to be easy to machine and strong enough to do the job.

 

Cost is also a big issue. The wood is a cheap option that has a number of good things going for it.

 

Another interesting aspect of the project; I've read on SA a number of people highly recommending wood for the core of these boards - I don't know if they are crazy people or not. There is obviously two schools of thought out there on this subject...

 

If I read Tim C's post correctly, for this centerboard the cedar is just there as a core that will hold the three carbon skins apart? For long grain cedar what would be it's density rating as compared to say 200 kg density foam?

[TimW 1]

 

The Offensive Timber has been covered over by the layers of Carbon Uni.

 

To ensure we maintain an accurate shape we have skimmed in some Filler, in most cases there is less than half a mm, and in many places you can see the carbon.

now the foil is ready for its outside skin.

 

So back to High density foam at 200 kg versus Long Grain Cedar (at around 550 kg density).

 

I reckon for compressability they are much the same, perhaps HD foam is slightly better.

But HD foam is very hard to glue to, the Resin doesn't penetrate the surface as it does with Cedar so the Peel/Shear properties of the Skins are compromised.

 

The Cedar in the Board cost me $140.

200 HD Foam for the Same Quantity Costs $718. (And you have to buy HD foam by the sheet, so can't get the exact amount you need)

 

For me the two have similar properties, the Cedar is definitely the Heavier option.

End grain Cedar would be way better but no CNC machinist will touch it as it is nasty to machine and very time consuming to produce.

[Guest]

[attachment=0]DSC07821.JPG[/attachment]

 

The Offensive Timber has been covered over by the layers of Carbon Uni.

 

 

That is very funny Tim, nice.

[Tim C 23]

Western red cedar has density of 380 kg/m3. I can't find the sheer properties at hand but I would guess high density PVC foam is superior to cedar by far.

The economical option is to link the two sides with double bias by splitting the centre core (if it has to be timber) and glassing the edges of the core to form two U sections, then glue them back together to form an I beam. Obviously you need to allow for the extra glass thickness.

Larger centreboards (15m cats + ) are often solid glass at the hull exit as no core can stand the sheer or compression, especially when owners don't pull the boards up when tearing onto a reach. In fact most centreboards are engineered for a maximum speed, when fully down, and the owner should know that speed...

[Guest]

Tim

 

I am sure hd foam would have a better sheer than cedar but the problem with that foam is getting stuff to stick to it. It is far easier to bond to a piece of wood.

 

How much wood in your boat?

[Tim C 23]

Tim

 

I am sure hd foam would have a better sheer than cedar but the problem with that foam is getting stuff to stick to it. It is far easier to bond to a piece of wood.

 

How much wood in your boat?

 

Everything but the hulls is wood core.

 

Did I just shoot myself in the foot?...

 

Actually all the sheer web are plywood on the 45˚ with DB over them. Mast, 3 beams, floors under the deck, etc.

 

And Kauri in the foils as sheer webs, not cedar. But I have learnt a bit in the last 15 years since I built the foils first (in the project timeline)

[MartinRF 76]

Western red cedar has density of 380 kg/m3. I can't find the sheer properties at hand but I would guess high density PVC foam is superior to cedar by far.

My database on material data says 6 MPa shear strength for WRC @ 320 kg/m³.

200 kg/m³ PVC foam (Termanto) has 4.7 MPa.

 

Sources: data sheet for PVC, Wood handbook and/or Gougeon's book for wood.

 

/Martin

[Guest]

what work is being done to the green machine at the moment Tim? I saw you bring the green machine into okahu bay on my way into uni on Friday.

[TimW 1]

 

The Old and the New

[TimW 1]

So as I had said a lot of people get bogged down.

 

Tim,

The Core Density is not the Bare Timber.

We have vacuumed the cedar, the Resin really soaks in around the edges, unlike with HD foam.

This affects the Density of the Core, it affects the Compressive properties and as well it affects the shear properties quite markedly.

You can see from the above numbers quoted from Martin out of the Gougeons book that the properties aren't too dissimilar

 

But

 

Tim, the Core and its properties might be completely irrelevant if you have thick enough skins.

A shear Web is just one way to skin a cat.

You can have a Hollow board if you use enough laminate, and its thick enough.

10 years ago all the Big French Wing masts used Shear webs in them.

My mast has a type of Shear Web at the fitting locations, but Both Borderline and Deeds masts, which are essentially the same section don't have any shear web in them, they are just made with a thicker wall.

The Net result weight wise can be quite similar.

 

In the Photo you can see the new Board has the 120mm Wide cedar laminated in blocks (6 of) with the Grain boxed.

The Foam is also 130 density for the new and 80 for the old.

New laminate is 5mm thick at the cedar for 120mm wide, compared with only 3.2mm thick at 100mm wide for the old.

 

The new board however is only 60mm thick compared to 64mm for the old.

 

As the Old board lasted 5 seasons I figured it must be pretty close to strong enough.

The new one is way stronger.

[Marshy 30]

And at the end of the day the old one only snapped because it fell down the case note because it wasnt strong enough... So spending the time preventing it fall down the case is better than thinking about what Core is better aye mr Wolf!

[Guest]

[attachment=0]DSC07929.JPG[/attachment]

 

The Old and the New

 

G'day Tim. Is the old 'blade' thinner at the trailing edge or is it just the camera angle?? I do read that the overall board is thinner - but that's not my question. The new blade looks 'fatter' in the aft 1/3. ???

 

Is the foil - max cord - constant or does it get thinner as it gets deeper & move aft towards the tip?? I am very interested & realise that it might make the hullopening a tad messy but the gain in efficiency is VERY significant!!!

 

Thanks for all your informative info - we're all better off for you sharing!!! Ciao, james.

[Guest]

Dude it is a NACA 63014.

 

Nohing fiddled or tweaked or fancy. Plain old NACA section that I drew up.

 

You guys are chasing NANO KNOTS with your theories. No one in the keelboat or multihull scene in nz sails to that level. use a well proven standard section and you will have a lot of fun.