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 Post subject: Ti Speed board Microfins are done...almost
PostPosted: Sun Aug 31, 2008 9:04 pm 
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Location: Teahupo'o, Tahiti
Got my Speedboard fins back from the fabricators Friday and must say I'm very pleased with them. I decided to go with Titanium to save a little weight all though with a board like this it's not really the critical factor, but for shear durability and strength it cant be beat, moving over 10cm of water at 40 + knots you are bound to hit the deck now and again so the Ti should help keep the knicks down to a minimum. This will be my first speed board so it will be a learning process the whole way but from what I have seen and read the shape should be ok. There are a lot of radical fins designs out where I must say and a lot of this speed thing is still very experimental with new board and fin design coming through all the time. People also seem to be playing their cards very close to their hearts so coming by any info is also very hard, I on the other hand like playing open cards and learning from my mistakes who knows maybe there is a Hydrodynamicist lurking around the boards that might have some ideas he/she is willing to part with..... I await the PM :)

I'm still going to foil them down a little they are not perfect, but I doubt I will ever get them 100% unless I draw up a CAD file and put them in a 3 axis machine. For now I'm happy to use a belt sander of sort and get the cords to my liking although they are not that far off. you are never going to get Ti to a mirror finish like Stainless steel , which is what most of the guys are using looks like it. As you can see from the pictures the dark shinny finish is how they came from the fabricators and the satin finish is what I ended up with after about 4 hours of water papering. My fingers are raw but I'm happy with the finish, I managed to get out all of the buffing marks and the matt finish tend to exaggerate the tiny peaks and troughs where the foil is not perfect which in turn helps with finishing of the shape. I have about 1,5mm of meat both sides of the M4 bolt holes that I can play around with getting the shape right, this would also help save some weight in the end. I had two made up one for a mate we are going to play around with them maybe even shape something different from these two.

I was curious if any of you had any info regarding the physical shaping of fins Google does not offer up much info.

Dimensions

Length : 200mm
Height: 30mm
width: 6.6mm
Weight: 115 grams , for comparison average G10 carbon reinforced fin is around 60 grams.

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 Post subject: Re: Ti Speed board Microfins are done...almost
PostPosted: Mon Sep 01, 2008 12:47 am 
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great finish on the new fins... 8)
is the hole spacing also custom or the kiteboard standard as on regular boards ?

and will 4mm screws be thick enough for strength and support through the board or are you using inserts for more strength?


The standard F-One fins I am putting on my board are 3/16BSW thread with the standard kiteboard hole spacing.


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 Post subject: Re: Ti Speed board Microfins are done...almost
PostPosted: Mon Sep 01, 2008 6:53 am 
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mx5alan wrote:
great finish on the new fins... 8)
is the hole spacing also custom or the kiteboard standard as on regular boards ?

and will 4mm screws be thick enough for strength and support through the board or are you using inserts for more strength?


The standard F-One fins I am putting on my board are 3/16BSW thread with the standard kiteboard hole spacing.


Custom about 72mm centre to centre. I went with M4 to try get the profile as thin as possible but then you are also dictated how thin you can go by the Ti plate size and because the Ti is expensive you want to get that as close as possible. A standard hole spacing on something this would just not work you would not be able to torque down the fin to the board and might end up with the tips of the fin slightly raised. You will never get it perfect though each board is different and you have to shape some concave on the underside of the fin to fit your board. To minimize this I'm also going to pour a high grade (hard) silicone buffer that will act as dampening and also help not letting the water getting in between the board and the fin it will also help with the fit on the board making sure that 100% of the fin is torqued against the board..... dam giving away all my secrets here :)

Another thing you look at is failure at high speed you don't want super strong M6 bolts holding the fin down because if hit a rock or debris at high speed you would rather want the fin to break away from the board and not take the tail with it, you would want the fins to shear away before it destroys the board. A few guys are using M4 bolts. To torque it down real good I'm going to use some cup washer to spread loads and I'm using some decent quality high grade Aluminum PRO-BOLTS .


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 Post subject: Re: Ti Speed board Microfins are done...almost
PostPosted: Mon Sep 01, 2008 7:54 am 
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Just curious but how much did these set you back? It looks like either a lot of manual work or a lot of contouring, high on machine time even on a 5 axis. If the smaller screws give you trouble it would work if you went with 4 per fin instead of 2.


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 Post subject: Re: Ti Speed board Microfins are done...almost
PostPosted: Mon Sep 01, 2008 10:12 am 
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Quote:
Custom about 72mm centre to centre. I went with M4 to try get the profile as thin as possible but then you are also dictated how thin you can go by the Ti plate size and because the Ti is expensive you want to get that as close as possible. A standard hole spacing on something this would just not work you would not be able to torque down the fin to the board and might end up with the tips of the fin slightly raised.

True, I found this when working out fin placements - result was I bought new Fins for my regular board and am using 2 of my old ones which i sanded flat so they are flush against the board. Did think about sanding the tip profiles to fit the fins (a lot of work as I needed to get each end identical as board is flat with fibreglass skins - board is bi-directional) and also manufacturing some fin profile spacers.

Quote:
Another thing you look at is failure at high speed you don't want super strong M6 bolts holding the fin down because if hit a rock or debris at high speed you would rather want the fin to break away from the board and not take the tail with it, you would want the fins to shear away before it destroys the board.


Good point but also depends where you are riding - most locations I normally surf at, are sandy bottom with no rocks or stones. Only problems could be something floating in the water, something left burried in the sand which gets uncovered by the movement of the water or have the fins worn down by the sand - a good reason to use SS ot Ti.

My board is just a R&D project at the moment and has kept me busy on no wind days (contruction) - if the board works well then great. If not its back to the garden shed for modifications or total redesign when there is no wind.

Would need to find out if the new official WSSRC ruling on minimum water depth also applies to all the GPS runs ?
if so - running a ground is not a major issue.


Quote:
A few guys are using M4 bolts. To torque it down real good I'm going to use some cup washer to spread loads and I'm using some decent quality high grade Aluminum PRO-BOLTS .

You try getting 3/16BSW aluminium bolts, or any kind of BSW bolts - Total Nightmare... ended up buying replacement set of F-One fin bolts because they use a non standard fin thread. :roll:
Also I dont have access to a lathe to manufacture my own.


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 Post subject: Re: Ti Speed board Microfins are done...almost
PostPosted: Mon Sep 01, 2008 5:33 pm 
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jrobson wrote:
Just curious but how much did these set you back? It looks like either a lot of manual work or a lot of contouring, high on machine time even on a 5 axis. If the smaller screws give you trouble it would work if you went with 4 per fin instead of 2.


Umm around 41 Euro for both that included labor, believe it or not these were shaped with a grinder and a keen eye :) the profile was water jetted out of the plate and then finished by hand. I went with Grade 2, Ti was going to go with grade 5 but I couldn't find any. Grade 2 is about the most common grade on the market and quite easy to come by. Grade 2 has a good strength to weight ratio and good workability it's what they call a Unalloyed Ti, Alloyed Grade 5 Ti is a a bit lighter by about 5% and about 3 times harder, they do this by adding vanadium and aluminum. Some might say going the Ti route is overkill but if anything you are getting a harder material that will resist knicks much better than Stainless steel and Aluminum and it really is the dogs danglies :)

mx5alan wrote:
Only problems could be something floating in the water, something left buried in the sand which gets uncovered by the movement of the water or have the fins worn down by the sand - a good reason to use SS ot Ti.


You mean Ti and not SS ?

Quote:
Would need to find out if the new official WSSRC ruling on minimum water depth also applies to all the GPS runs ? if so - running a ground is not a major issue.


If you mean officially recognized then you would have to attend an officially sanctioned WSSRC event like the one coming up in Luderitz http://www.luderitz-speed.com/ a mate of mine is competing. You can also discuss Speed Kiteboarding and share your info over at http://xsport.co.za/forums/index.php?board=18.0 . Not sure how the new 10cm rule plays into this taking into account tide movement and all that, red tape if you ask me. How dare some guy with a few hundred dollars of Kiteboarding equipment beat the 50KT/500m speed record LOL

Quote:
You try getting 3/16BSW aluminum bolts, or any kind of BSW bolts - Total Nightmare... ended up buying replacement set of F-One fin bolts because they use a non standard fin thread.


Have you tried http://www.tastynuts.com ?


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 Post subject: Re: Ti Speed board Microfins are done...almost
PostPosted: Mon Sep 01, 2008 6:13 pm 
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For 6al-4v there is also a worlwide shortage, I thought originally you used this which would have made it a whole lot more euro's...

41 Euro isn't that much money, but of course being done on a grinder makes it much cheaper. FYI if you anodize aluminium the shell hardens and becomes much more wear and scratch resistant than Ti (but of course not as dent resistant as Ti), likewise powdercoating makes a very tough shell as well. Cool idea though with the custom fins, might machine some Alu fins for my board (just normal twintip not speed) to see what different shape fins do to the feel and traction...

Where you from I see you quoted xsport which is our local forum, you in SA?


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 Post subject: Re: Ti Speed board Microfins are done...almost
PostPosted: Mon Sep 01, 2008 7:59 pm 
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JMF wrote:
mx5alan wrote:
Only problems could be something floating in the water, something left buried in the sand which gets uncovered by the movement of the water or have the fins worn down by the sand - a good reason to use SS ot Ti.


You mean Ti and not SS ?


no - sorry was a typing error should have read - "a good reason to use SS or Ti."


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