UK-Cherub Forum
Cherub Chat => Tech Chat => Topic started by: john_hamilton on March 09, 2010, 08:46:44 PM
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i am planning to make my new centerboard the same section as an rs800s to aid easy temp replacement if it breaks. I know the rs800 has a NACA 03010 section but does anyone know the chord?
thanks
john
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280mm I think, but there is no substitute for measuring.
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ill try and find someone at the blast at draycote with one.
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I have measured mine; 288mm straight line fore/aft
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I don't know that I'd want to take it on trust that a board case, built to that section and chord, would be guaranteed to fit an RS800 plate. Should you want to do this then I suspect the normal advice applies: build the case around the actual foil you are going to use.
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iv been asking around for one but havent found it yet. anyone got one (it can be a bit broken but i need the top 30cm of it)
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I think Jim may be subtly suggesting that you find/make/fix the board you are going to use as a complete optionas step 1, then taylor the boat around it. I think this may be a wise idea as that way you remove any build/fix/makign irregularities adn the board will then definitely fit.
For EJ the slot was almost the last thing we cut. The board went in after the boat was one object and the racks attached.
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I agree you need to build the board you are going to use first, RS may have planned for the board to be Naca03010 but there is no grantee that it ended up that shape.
Also when you fit the board to the case you should do it with the board in place
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I would guess a rs800 board is going to be very heavy too. The board on the Laser 4000 I used to sail was more of a keel! But I have not sailed an 800 in a while so can't remember.
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kevin ellway originally suggested using an rs800 board which is why i was asking
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the 800 board is nothing like the 4000 board in terms of weight, and I am sure that it would be a good option.
You just need to take a lot of measurements off one as the manufacturers published measurements and spec may not be quite what they actually produce. and with a tight fitting centerboard it could cause problems.
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E-number's Case is more of a crash box. This was made as a sleave of 3 layers of weave/biax/weave with a section of 40 x320mm. At each end I used a pad of High Density foam from which I cut the foil's section. It was easier to adjust these to get a close fit than the whole case. It also means that should another foil come along the pads could be adjusted to suit.
An 800 foil is a reasonable substitute if you break the normal foil however it is not going to be as stiff and you will always want your normal board. If you can't get hold of one at present you may not be able to get hold of one at short notice. The other option is to build a spare.
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thanks phil. i have got axcess to good condition 800 boards (about 5 of the buggers) but havent been able to find a broken one to get carbon on when building a case. in the end i may just go with a well built foil from your spreadsheets. by the way you have an email
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Just wrap the whole thing up and dont get epoxy on it!
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Yep... Cover that foil well - apart from anything else you need enough thickness over the actual foil to give yourself some reasonable clearance. Beware of building a case that you can only get the daggerboard into when the air and water temperature are below some critical limit:-)
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Here is what the section you describe looks like: If Kevin says its a good idea then I might well do the same with my boat. All still a way off at the moment as I too will be cutting the case last. Interesting about the weight issue, I have not sailed an 800 for a long time so can't really remember!
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cool
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John,
Sorry i haven't looked at emails for a few days.
When making E numbers rudder stock sleave on the foil I thickened up the foil with a peice of cereal packet on each side and several layers of electrical tape on the leading and trailing edge. then parcel tape over the whole thing. This was not vac bagged and was consolidated with two peices of 4mm ply clamped with lots of g clamps. The sleave provided possibly a little too much play on the finished rudder balde but a bit of Jap tape or other packing material works fine and i get no vibration. room for a few repairs though.
the aim of the crash box is that the hull dosn't get pentrated if the board hits anything. The pad at top and bottom can easily be filled.
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is a rudder made without vac-bagging alrightish. how should i get consolidation? i (i have no bagging materials yet!
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It will be fine but it's hard to get decent consolidation compared to vac bagging. I recon it will be harder to keep the layup fair. The only method I know of is to wrap in bubble wrap, put a stiff board on top and add weights. Bubble wrap distributes the weight but will leave dimples which makes fairing harder.
You can vac bag very cheaply but it is best to be shown by someone who has done it before otherwise a balls up is pretty much inevitable.
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I made all my rudders to date without vac.
Clamp the blank leading edge up and you then put each layer on from the le and smooth down the blade to the trailing edge you can get the laminate quite smooth, with peel ply as the top layer you can get quite good consolidation.
One thing I have had problems with is the trailing edge going a bit wavy depending on how the cloth hangs. To avoid this on the last blade I made i clamped two wooden battens just where I wanted the trailing edge, these helped pull the cloth tight and kept the trailing edge straight.
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I can give you some bagging materials.
i had trailing edge problems with slippery's foils initially.
Clamping bits of wood at the trailing edge is a good idea.
I think i had an additional issue trying to laminate on to cedar which was perhaps more absorbent than i thought. perhaps a resin with some filler would have improved the result.
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Maybe a sand bag would work?
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I used sand when veneering a non cherub foredeck, and it was less effective than I was expecting.
I used small freezer bags of sand from a builders merchant and they just did not conform well to any kind of complex surface, they were heavy enough to distort the deck but did not put much pressure on sections that were not sticking down properly.
If you pull a vaccum you get atmospheric pressure pushing on all sides of your work at 14.5psi.
Even if you can only pull half an atmosphere with your pump that is still equivalent to about 3.5m of sand
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will an old vacuum cleaner work? iv got the foam core made and am awaiting carbon now
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will an old vacuum cleaner work? iv got the foam core made and am awaiting carbon now
No, vacuum cleaners need the airflow to cool the motor so if you block airflow by connecting a bag it will quickly overheat and stop working, they also do not pull much of a vacuum.
Vacuum is not mandatory, you can make perfectly good blades without it, and you can make rubbish blades with it.
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...on the last blade I made i clamped two wooden battens just where I wanted the trailing edge
Also, IMHO, a vital trick when doing daggerboard trailing edge repairs.
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Fridge pump.
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Fridge pump really does work, but be sure to blag a degassed one. If you dismember one you find on the street you will be putting CFCs in the air, which is fabulously bad for the environment and very illegal indeed. They do pull a good enough vacuum though.
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We have proved that a modified, cheapo tyre compressor would be feasable. See the 'vac bac on a budget' thread in the tech section of the forum. That should have enough beef for a foil.
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now where can i find one of those without subsequent anger from mym parents ;)
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I tried sand when making the trolley cradle for E-numbers. I lined the laminate in the mould with cling film and poured the sand in.
I agree with Phil A that it was less effective than I had expected.
The sand can also reduce the temperature of the cure because it absorbs a lot of heat.
I suggest clamping thin ply around each side and lining the edge of the ply with your trailing edge. I would suggest covering the ply with parcel tape to ensure it dosen't stick.
If a screw is screwed into the foam at each end nearer the leading edge and the screws supported so the foam hangs training edge downwards you can consolidate the leading edge by pulling or firming the peal ply down each side of the foil over the wetted out carbon.
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now where can i find one of those without subsequent anger from mym parents ;)
You got a mate whose parents have a fridge?! ;)
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Fridge pump really does work, but be sure to blag a degassed one. If you dismember one you find on the street you will be putting CFCs in the air, which is fabulously bad for the environment and very illegal indeed. They do pull a good enough vacuum though.
:D :D :D :D
and the carbon, epoxy, bread wrap, tacky tape, gloves, peel ply, foam core etc... etc... is OK then? ;)
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yep i paid for that but dont feel like taking my chances by nicking their fridge compressor
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As I have read somewhere, possibly on this site: 'carbon fiber = carbon footprint'! Nice to hear you have a core made, post a photo. What section/taper etc? I was thinking of the RS section with a 0.4 ratio trapezioid taper.
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my first core is just made to fit cheese's existing stock so i am not entirely sure what section it is. it looks like a NACA 10% but im sure. 22cm chord, 120cm lengthe (about 35cm not actually in water) and the taper is pretty much to 10cm chord at bottom fom 1/3 of the way up. its all a bit "by eye" im afraid! ill add a picture later if possible. i have done one side completel and am 2/3 of the way down the other side doing the sanding so its a bit rough.
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i did the first carbon layer tonight and realiseed just how much of an arse it is to do. any tips on how to do the carbon bit of a foil?
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Do all the layup in one hit and with minium waste.
For laying up the cloth make stand for the foil core which holds it horizontally trailing edge down. Will, have you got any pics from when we made your board? Diagram later....
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Hi John,
Well done on finishing the blank. Can you describe how you did the first layer?
W
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As said before, the blank should be held leading edge up, you may need to put a screw in somewhere at the tip of the blade so you can hold it steady, the hole can be filled later.
If it is foam it should be buttered and if it is wood then wet it out with resin, this helps the cloth to stick.
I would then get a big sheet of plastic and wet the carbon out on it using something like a credit card or the plastic packaging that you often get with blocks to spread the resin.
The wet carbon can then be lifted on to the blank and smoothed down, there is much less waisted resin doing this than trying to spread it out on a vertical surface where it will drip everywhere.
If the leading edge of your rudder is mostly straight you can wet all the layers for your rudder out on the table then lift the plastic with all your laminate up onto the rudder and fold it all in place, peel back the plastic and trim to suit.
Peel ply is your friend when you are trying to get the laminate stuck in place and smooth,
also you may need to change gloves at the end of your laminating session as the heat from your hands can make the resin on your gloves go sticky before the resin elsewhere and this makes it very difficult to push bits down, if you put two pairs on at the start it is easy to pull one glove off for a clean but protected hand.
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the glove bit i noticed. basically i suspended the core leading edge up from a blow torch cabinet and then wetted out the carbon and put it on. i obviously forgot to butter the core so thats a mistake i wont make next time. The dried piece looks alright but has a few buble where i didnt smooth the peel-ply down enough :( ill sand that down and do all the other layers in one hit then.
question: which way should the universal carbon strands be aligned?
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The Uni's should go up and down the blade. If you are planning on having a layer that does not go the full length then you should cut the end on an angle to act as a taper.
The butter helps to keep the weight down but also to stick the carbon to the foam, helping with the bubbles.
It is hard to get right, and practice will help.
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Well done for having a go Jon.
practice does help and all the tips mentioned above do make it easier.
Before long you will be an expert like the rest of us.
generally laminates are stronger if all the resin cures at the same time. there is also a greater chance that the fibres of each layer will interlock as the laminated is consolidated forming even stronger bonds between the layers. if each layer is done seperately you rely on the bond between cured resin and new resin. you also end up using more resin. You know now.
just shout if you need a practical demo and i'm sure we can put a sticky weekend together. You are not alone making foils at present.
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Here is my first attempt at this foam sandwich lark. Its the transom for Hardly Sluggish (will be launched as Thunderbird 4) Its not quite as stiff as I think it should be. I did not vac bag it and I mixed the epoxy by mass rather than by volume (it says to do it by volume). I will let it post cure for a while and see what happens. It may or may not end up on the boat. Its a small pannel so nothing much lost in terms of materials if it doesnt. It was laid up on parcel taped MDF boards which were clamped together.
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...i'm sure we can put a sticky weekend together. You are not alone making foils at present.
Yes please!
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1
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On the whole foil thing.... Is there a class CNC mould for a T foil (horizontal foil?) I have a feeling I may need to make another one which is more standard as a base line.
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I had CNC plugs milled for the lifting and rudder elements, it was finished off by Tom K and Dave Ching A mould has been taken and I think that Dave is close to making the first foil
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is this the type of mould you spray that high density quick hardening foam into (the type that builders use in some tight cavities but a stronger equivalent?)
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On the whole foil thing.... Is there a class CNC mould for a T foil (horizontal foil?) I have a feeling I may need to make another one which is more standard as a base line.
Richard Taylor has a 3 piece female mould for the Daemon T-foil. We made a few foils from them and they have all survived. Very nice and easy to use, using the expanding foam you can make a foil in a day no problem as you can lay it all up and add the foam in one hit.
John, the expanding foam is a 2 part foam epoxy foam. You mix it up and then it starts to expand, before going hard. Quite cool stuff!
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Cool.
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well iv just finished the carbon on the rudder and it has ended up as 120 cm long, with a 17cm chord tapering to 8cm at the bottom, weighs 1100g with some bits to cut off the trailing edge and fairing to be done (only a little though as i paid as much time as i could getting the core perfect) its got a layer of 200gsm carbon weave, then carbon uni up the trailing and leading edge, another layer of carbon weave at +/- 45, then a final layer of weave at +/-90. the core is high density foam. thanks everyone for the great advice i had. going to make a stock and t-foil for it in easter hols... probably a centreboard aswell.
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Congrats, sounds good
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First draft of my center board. Will start getting sticky after exams.
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isnt an elliptical one more effective?
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You want a broadly eliptical lift distribution but an eliptical planform doesnt guarantee that - and with a straighter leading edge the construction is a bunch easier if your draping fibres over it.
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After some thought I have decided on a trapezoid foil with a 0.45 taper ratio. 0.5 is approximate for eliptical lift distribution and a little below that will reduce the moment. Also has the advantage of easier laminating with the straight leading edge.
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John, the expanding foam is a 2 part foam epoxy foam. You mix it up and then it starts to expand, before going hard. Quite cool stuff!
is it heavy?
Also, how do you get that shiny finish on carbon?
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Phil says: thec weight of epoxy expanding foam is determined by a; the intended density of the foam formulation, b: the temperature that the foam is cured in. You can mix foam that is intended to cure at 170kg/m^3 at 20 dgrees C and heat it further to reduce the density.
The shiny finish is due to applying additional coats of resin then lots of sanding. A final coat of polyurethane resin or varnish and some polishing is required to make it look good.
The easier way is to get the shape right by filling and fairing with a lower density filler (epoxy /glass bubbles) and sanding through to 400grit then paint with primer and 2 top coats. very fine wet and dry and polish to finish. You will never be able to stand on it though.
At present we would be best to put pro grip on the board to reduce our capsize time. An extreme measure though but puts things into perspective.