So I'm looking for a USbox pointer fin for my Speed F1 Raceboard. Cant find anything around 40cm.
Could I use a 42.5 tuttle Black Project race fin n modify the finhead to US box? Are BP fins n heads milled from one solid block of G10?
Select to expand quoteolskool said..
So I'm looking for a USbox pointer fin for my Speed F1 Raceboard. Cant find anything around 40cm.
Could I use a 42.5 tuttle Black Project race fin n modify the finhead to US box? Are BP fins n heads milled from one solid block of G10?
I would hazard a guess that a 40cm US box fin would be harder to find than hens teeth.
probably easier to modify the black project race fin, and hope nothing snaps. Admittedly I've never sailed a race board, but i'd make an educated guess that you don't ever lean on a fin like on other boards, so might be ok. But its still a lot of stress to put on a comparatively small surface area, which is why they don't really make US box fins that size.
Select to expand quoteolskool said..
So I'm looking for a USbox pointer fin for my Speed F1 Raceboard. Cant find anything around 40cm.
Could I use a 42.5 tuttle Black Project race fin n modify the finhead to US box? Are BP fins n heads milled from one solid block of G10?
Just wondering if a G10 fin of that size might destroy the box at some point. I guess if that happens you might just put in a tuttle or powerbox so it might be worth the try. 42.5 cm seems big for a narrower raceboard as I think the Mistral Equipe II had a 38-39 cm high aspect fin (powerbox) and the more modern race boards are wider having bigger high aspect fins. The biggest US box fin I have found is a polyester True Ames Slalom Pointer of 39cm (15.5 inches) of 382 cm2 area so I will probably use that on my Tiga Racing Prestige 1989. The Mistral One Design US Box fin is 34 cm and in US box (later versions are powerbox) but it is not G10..probably has more flex (not sure how much in truth) although it is stiff enough and good enough, a fin for the IMCO being low aspect but the area is large about 352cm2 from memory. The area of the fin is important too not just the depth. How much is the area of the Black Project for interest ?
^Subs, yep 40cm is about the limit Ive used. With no bad outcomes. Old '80s fins were about 36cm. But impossible to find. So I thought I'd modify my unused 42.5 BPR to 40 n cut head to US box. Looks like it'll work around the Tuttle finbolts ok.
RichG, no idea of area of BPR. But they're definitely a more powerful fin than the old style fins. Narrower chord fore n aft but still about same profile thickness.
BPR 42.5 is 344 sq cm and yes a solid block of G10
If your BP fin is a tuttle box, makes it easier to convert to US box as you've got a parallel surface to work from
I used a router and made a jig out of melamine to get the tuttle down to thickness first the cut out the profile last if that makes sense
Select to expand quoteolskool said..
Hey thanks Ducati! That was going to be my next question. Dimensions. Cheers
I filled the original PB or TB holes with epoxy first, then if you don't want to use a router or own a milling machine you could rough it out with a grinder (carefully) and finish with a flat file, finishing one side first so you can measure from the original side and keep it parallel with the axis of the original fin
Be careful .
Some fins are glued into a block of resin or plastic . You should know , I believe you ripped one out ? When you mill or grind down to the 9.6 mm , the fin will just fall out of the block . They do this to save the expensive G10 .This will leave nothing to put the front screw through . You will have to bolt on a front bit for the screw . Also then at the rear of the foil , it will be too thin where you put the pin through . You will have to build that area up with resin and glass .
Do not rely on the resin that is stuck to the fin .
Something like this .
Instead of the brass jigger , I've seen it simply done with bent around alloy sheet .
In the pic below you can see the bottom 5mm is just filler . This fin was only about 18mm into the head . Not even deep enough for the barrel nuts .
However , IF , the entire head is G10 , it will be much easier and disregard my rambling .
Imax, BPR looks to be a solid slab of G10.
Not like the other 'breakfree' style finheads.
Machine shop wise, ive seen what you've got in-house. 
Will be coming over for some Master machining.
Beer included of course.
This will be a nice experiment in destructive testing of a US box. Make sure you keep records of how many sailing hours it lasts.
^ I'm sure the Speed will be fine. Only using for lighter winds. I have a smaller fin for higher winds.
Cmon, what could go wrong! The board is only 27 years old.
Select to expand quoteolskool said..
^ I'm sure the Speed will be fine. Only using for lighter winds. I have a smaller fin for higher winds.
Cmon, what could go wrong! The board is only 27 years old.
... loss of fin... and the box... as it sinks to the bottom, when it rolls out of the board.
hey mate the bigger fin isnt needed ,i put a bp 42.5 in the eliminater and it wanted to rollover and was really hard to tack.slowed the board down cause it lacked control,just stick with the fin you got and use the center board more
^ My other Speed F1 has PBox. I've tried fins from 34cm up to 50cm. 40cm felt about right for a 1 fin alround solution. That's why I thought the 42.5BPR would be a good donor for a slice n dice. Solid G10 fin/head n strong upwind performance.
50cm gives a lot more drive in lightwinds, but very hard to gybe or tack quickly.
I would strongly caution against using such powerful long fins in that board with a US box. I have rolled fin boxes out of very well reinforced (double woody's) boards with fins half that size. 
Try putting a well supported Tuttle box in the board instead. 
If you must stay with the US box, what about a much shorter, wide base, low aspect fin to reduce the leverage on the box?
^ I have a nice 36cm US box pointer from the '90s era. Good for highwind. But i wanted to change it up for lightwind days. Finding a pointer style of fin (old or new) in US box is very hard. Had planned to cut BPR down to 40cm.
Maybe you can be the guinea pig here and you can risk your board, fin, box and life and test this like in the Mythbusters and report back. Just reviewing the history of the last Mistral raceboards. From 1999 until 2002: the One Design fin was a powerbox 34 cm one design fin (otherwise same as US box Mistral One Design Race fin up to 1996); the Equipe II and then the later Pan Am was depending on the year a 45 cm Race powerbox (2000) or a 42 cm Race powerbox (1999, 2001, 2002). See pictures below.
1999
2000
2001
2002
2003 (Pan Am dropped moulds believed destroyed, MOD remains)
Piece of junk called RSX becomes Olympic class (in 2008 Beijing games) post Athens and destroys the great Mistral One Design class. Equipe III produced but never seen here...but used by Nik Baker sometime in UK-limited production numbers rumoured to be very fast and in post mid to late 2000s ? The last Mistral One Design post Olympics looks very cool sadly it never took off, presumably dropping it in favour of RSX meant it was for the dustbin. The new MOD included one 7.4m2 for all conditions but slightly improved design sail and rig, Board and fin (34 cm powerbox) the same but improved mast track and slotflusher. Probably should have always have been an Olympic class as a cheap affordable, accessible raceboard for course racing.
Fins from a 1989 Boards Raceboard test..all US box all around 34-35 cm long apparently. Racers in open competition in funboard racing like today in slalom always had several fins to change depending on conditions including using smaller swept back fins for speed in high winds with mast track back and blasting down reaches and smaller fins facilitated faster tacking and improved control when conditions were right.
I appreciate everyone's concern about 40cm US box fins.
I've run 40cm in Bic Metal Rock US box for 2 plus years with no issues until I started jumping it n landing sideways. Of course it rolled the finbox.
Another mate has run 39cm US fin in his Speed 250 for the past 20 years. No issue yet...... Just sayin.
If I jump it n throw it around in strong winds of course it'll roll the box.
But as I've said, i plan to use 40cm for lightwind.
36cm for 15kt n up.
Select to expand quoteRichardG said..
Maybe you can be the guinea pig here and you can risk your board, fin, box and life and test this like in the Mythbusters and report back. Just reviewing the history of the last Mistral raceboards. From 1999 until 2002: the One Design fin was a powerbox 34 cm one design fin (otherwise same as US box Mistral One Design Race fin up to 1996); the Equipe II and then the later Pan Am was depending on the year a 45 cm Race powerbox (2000) or a 42 cm Race powerbox (1999, 2001, 2002). See pictures below.
1999
2000
2001
2002
2003 (Pan Am dropped moulds believed destroyed, MOD remains)
Piece of junk called RSX becomes Olympic class (in 2008 Beijing games) post Athens and destroys the great Mistral One Design class. Equipe III produced but never seen here...but used by Nik Baker sometime in UK-limited production numbers rumoured to be very fast and in post mid to late 2000s ? The last Mistral One Design post Olympics looks very cool sadly it never took off, presumably dropping it in favour of RSX meant it was for the dustbin. The new MOD included one 7.4m2 for all conditions but slightly improved design sail and rig, Board and fin (34 cm powerbox) the same but improved mast track and slotflusher. Probably should have always have been an Olympic class as a cheap affordable, accessible raceboard for course racing.
Fins from a 1989 Boards Raceboard test..all US box all around 34-35 cm long apparently. Racers in open competition in funboard racing like today in slalom always had several fins to change depending on conditions including using smaller swept back fins for speed in high winds with mast track back and blasting down reaches and smaller fins facilitated faster tacking and improved control when conditions were right.
Sorry in the above test it was a 1990 test not 1989 and all were I believe US boxes except the Tiga which was a conic box, which is similar but different to Tuttle.
