I was looking at replacing my ageing set of Tectonic Nomad wide base fins with newer carbon speed fins. My boards are Starboard speed W44, W49 and W53 (the older wood models).
Looked at at the usual Z Fins, Gasoil etc, shocked at how much they are, ?250 (450 Aus). ?750 for three fins could be difficult to get past the wife!!!
I did find a good deal with Zulu fins, four Hamba speed fins for the price of three (buy three, get one free) for ?450. A bit better, but still a lot of money.
Last night, I had a brain storm and thought, I wonder if I could re-head some of my old C3 Carbon fins. More rake, shorter etc. I have a set of Bogies old C3 Z fins, probably from around 2003-2006.
Im thinking, 22, 24 and 26 with 30 degrees rake. I'm not sure if the carbon lay-up will allow 30 degrees rake.
Any tips on rake etc. What do you reckon? Or am I just going to wreck three decent C3 fins?
Last paragraph probably closest to the mark. Plan shape of those fins not so good with extra rake unless you modify the tip trailing edge.
Mark the other thing you need to consider is rake, the fastest waters in WA (Liptons/Point Grey/Fangys/Lilacs) for mere mortals to go fast tend to be shallow and weedy, 30 degree rake wont cut it, 45 degrees as a minimum, 48 is what I use, 50 to 55 rake for the smooth at Fangies
mark it says you are from west kirby, if so 30 degree rake is fine, i thought you we from WA western australia
I was talking to Mal Wright the other day about the possibility re-basing one of his TM45v8 23cm fins to 30 degrees. I was not sure about the fin profle and if it would still be optimum with that rake.
He said it would be fine, and it would work because the biggest consideration with a raked fin is they must be super stiff.
I would not advise raking back anything that has even a slightly flexy tip.
My issue with racking back the TM45v8, is that at 30 degrees it is only 18cm deep, and at 40 it is less than 17cm deep. In the end I decided not to wreck a classic speed fin. 
That aside, unless you are a very large lad, I think most of those fin lengths you mentioned would be too deep for 40-50kts speeds. 17-21cm in a moderate AR 30-40 raked fin would be what I would be thinking. The 23cm v8 was too large for me and I had big issues with it overpowering me. I use 20-16cm, but I am only a little old man (75kg). 
I did rebase and rake a TM 26 .
This fin was a "go to fin " on those classic 6.6 , medium sized slalom board days. Due to more weed in the water I just didn't use it anymore.
There was just enough length to get a small speed out of it when raked at 45 deg. I ran it at LG and it was horrible.
Far better to sell the fins (cos there really good ones) and buy some more really beautiful ones 
Thanks for the replies, its extra food for thought. I checked each fin, they all have slightly flex tips, so that's a potential problem I guess.
After reading the replies, I think I'd be safer selling the fins and letting sons one else get good use out of them. They really are good'n' so don't won't to destroy them.
My my avitor says WA, but I sail at WK in the UK. I think when I first registered on seabreeze, there wasn't a UK option, I'll double check tonight.
Hi mark are the c3 assy fins?
Certainly no expert here but is 30 degrees that important? The gasoil / z fin don't look that raked albe not measured?
i have a gasoil els L this I know is not 30 degrees but I was surprised at the tip flex..that said the lay up must be different for each side of the mould as it flexes more on one side il have to fish it out I'm sure it flexed more the side it didn't expect?? Anyway it ain't no plank
Forecast is looking alright for Kirby this weekend if I go bring em along mate I have a jig for reboxing 
alex
Hi Alex, Sunday's looking like a decent speedboard day, I'm defo going. Hopefully you can up over, great to have a catch up
