Took the fin out for a trial today hoping that any cracks would appear now and not later. Had great results... the fin box split slightly, but this is because I didn't reinforce the epoxy or wait for the job to cure properly. That may seem like bad news to some but after I reinforce the box with both carbon and csm, then leave it while I'm away at work for two weeks it'll be rock solid. Very happy lad 
black texta mark shows where it was trying to pull apart, but being locked in the box, couldn't tear out.
Next time make sure the blade goes all the way into that front corner. In the case of a weedy, that's where most of the load will be, (the line of the thickest, and stiffest part of the fin). There shouldn't be any tension strain on the base, it should all be compression. I'd forget the csm and use several layers of carbon.
Yup, todays update shows the fin reboxed, now 1cm shorter to allow for the blade to go all the way down and forward in the box. Already done Mike 
Also to allow the barrel nut to have purchase on new work and not fill.
2 layers of csm and 2 layers of carbon, not taking any chances. And any exposed timber is going to be coated with cyanoacrilate (super glue) to waterproof it, especially inside the fin bolt hole.
What sort of a cool vice/sliding bench thingy is that?
Never seen one before... One of your own inventions? Is that felt or carpet on the jaws? Might have to take some creative inspiration from it 
I agree Nebs. Pepe your workshop looks like a showroom, very impressive. that clamp/vice is a woodworking one i think
Yeh that's right, woodworking bench from carbatec. The one with bench dogs helps when you're clamping large pieces of timber together, or laminating.
Hi Decrepit,
If you were to make a flat panel, you could sandwich csm between two plies of carbon as the csm in this case is only acting as a core so when flexing this panel, one skin of carbon is under tension and the other under compression and the csm is in shear between the two.
As far as the csm taking compression is concerned the carbon will out-perform the csm many times over. A good example of carbon performing well under compression is a yacht mast, It's pretty much all compression. On offshore racing yachts, say on a 60 footer we would preload the mast ram to 13000kg just sitting at the dock. I can't remember what it went up to when sailing.
I have a tech question regarding lay-up. What advantage does epoxy have over polyester. I find that if time is not on your side it's quicker to lay-up with poly. The fin, so far hasn't delammed and I'm not worried about long term issues, can poly work if you don't want to laminate under pressure?
That is an awesome looking fin how many hours work do you think have gone into it already, great job.
Great article thanks Brad1.
AUS718: more hours than the fin would be worth, but it's a labour of love, cheers
Almost forgot: I'll be trimming 1cm off the trailing edge to speed up the gybes, ( turning circle). With the amount of lift the fin generates I can trade some off.
Hi Pep , great effort , mucho kudos to you .
Just in relation to your question re polyester over epoxy .
The whole idea of composite construction is that the loads are taken up by the fiber be it glass fibre or carbon fiber ( english and american spellings ) . what the resin is basically doing is holding the fibres in place and protecting the fibre by providing a protective cover.
What happens with Polyester is that its modulus of elasticity is very low so what happens is when a load is applied the resin actually takes the load first then the carbon takes up the load but unfortunately the polyester resin has experienced a load greater then its elesticity will allow and cracks .
Epoxy on the other hand has a high level of elasticity and hence its toughness is due in effect to it maluabilty ( buggered if I can spell that ) any way its more flexible . So what happens is the resin flexes under load and the carbon takes up the load as its designed to do . Poly will do the job of holding the fiber in place but it wont allow the structure to perform using carbons great tensile and compressive qualities.
I guess an extreme example is say a rope encased in glass with each end attached and then force applied to try and stretch the rope then you would see the glass break before the rope actually took up any of the load . If you encased the rope in plasticine then the rope will take up the load and the plasticine ( epoxy resin will just stretch to accomodate the load and do its primary job of holding the fiber in place and providing a protective cover) .
Just remember the fiber is the strength in all composite structures
Did anyone understand that ?
Again great job , pity there is no money in fins .
One Hundred and Eighty !
Cheers , Dartboy
Dartboy,
But one side will be in compression surely .
Your plastecene/exopy analogy will not not hold the fibres in place. My understanding is mostly carbon fails in compression as its compressive strength is much less than its tensile strength.
But I'm not a materials expert.
Have a think about why your mast bends when you crank on your downhaul.
Compession compression compression. Carbon is outstanding in compression.
Check out the comparison ult.tensile and compresive strengths for UD carbon and glass 0 deg.
www.performance-composites.com/carbonfibre/mechanicalproperties_2.asp
Apologies for hijacking the topic!
carbon has fantastic compressive strength , if it didnt then your mast and fins would snap first outing .You want to see the real compressive power of carbon ? take a look at a carbon yacht mast . Sailboard rigs have it easy .
anyway dont use poly with carbon , poly just great for its smell , spent summers glassing boards ,washed my hands in acetone , i cant believe my kidneys aren't crystalised.
this thread is a tribute to the great Pepe and his amazing fin .
sorry about plasticine etc very confusing .
now just waiting for wind on my day off .
cheers all
Have you than the fin out yet pepe47 or are you still waiting for it to cure some more, be nice to hear how it goes
Yes, had it out at Cervantes and it went quite well. Powered up (when the wind finally arrived) it tried to let go once but quickly snapped back, I am heavy on the back foot with big gear. (8.2m H2 and 135l rocket), which to me is big gear.
Ironed out a few flaws and am just finishing off mkII. Took a cm off the trailing edge, reduced the overall length and did the mkII version in epoxy with three strands of uni at the chord.
Also scalloped out and filled the barrel nut anchor with csm, so no timber shows when the hole is bored, 6 layers.
Nice work on the MK11 looks awesome, but you are happy with first one, be nice to see them both together to se the changes
Going to use the same construction method?
The only difference is epoxy construction as opposed to polyester. And carbon re-inforced base. The chord length is now 115mm on the mkII and 125 on the mkI at 9.5mm thick, 3mm thinner in the carbon. MkII is 42cm whereas the mkI was 44. And the new fin is mounted all the way forward in the box. Just have to put the barrel nut in and we're good to go again.
A master at work, amazing we have 3 very talented fin makers in our Team, Decrep, Sammy & Yourself!!
I wonder if other estuary sailors would agree that necessity is the mother of invention.
Well, not completely surprised with the outcome. Took the shiny new mkII out this morning and put it on the 135l rocket with the 8.2m h2, just wasn't expecting a 25knot gust. Exiting the gybe fully powered up the fin decided to let go (at the weakest point).
Didn't have the right thickness at the chord either as it cavitated at speed.
Back to the drawing board? Hell no. Carbon fins just can't match g10's on the estuary.
