fin ideas and loving

General Discussion
1

Hey there swaylockians,

I’ve been bored in the uni computer labs today… I know I should have been doing work but my mind inevitably wondered to surfing, surfboards, building no.2. etc. you see the progression? Well after being chuffed to bits with my first board, and having got over any worries I had about Totally messing it up I fancy making a classic old/nu school fish, god knows when, maybe Easter?

One problem I do have though is that many of the fishes I see either have glassed on fins or are quads. I rather fancy knocking up a twin fin, alas glassed on fins aren’t an option as I travel quite a bit with my boards. Ok so that leaves me with the option of which fin system to go with. I quite like the red-x fin system however it seems like it’d be a bit of a ball ache to get it in the uk. Seabase do 6 ¾” boxes, just shorter versions of the usual 10 ½” center fin boxes as far as I can gather. So it would seem its either these, futures or maybe fcs? Not too sure about fcs though, not such a fan. Unfortunately I have had no luck trying to find fins mildly resembling the keel fins I see elsewhere on this site. Well not to fit these systems anyways.

Trust me this is going somewhere.

Basically after talking to one of the technicians, they have given me the go ahead to knock up some fin templates and use some of the more complex cnc machines to make my dreams reality. Isn’t it great doing engineering?

Well this is what I’ve come up with so far, tried to address some issues I can see though I think it’ll take a more experienced eye than mine to help refine these into workable designs!

The fin template:

This is just a quick sketch off the top of my head; dimensions are in mm, can change this shape substantially if needs be.

For the standard box:

Futures fin system

I have taken an angles section off the back of the fin so you can locate the rear slot into the box due to the extra length. Ignore the foil line. Would this have a substantial impact on the fin? I’m thinking it’d make it flex at the back, maybe slow it down?

Using the fcs system would get round this problem

I don’t have the correct dimensions for the fcs tabs, anyone care to enlighten me?

I havent put a foil on these fins yet, though i was thinking that much the easiest way would be to do a simple curves surface wither side then fine tune this by hand sanding.

I also thought about cutting the ends off two futures boxes and sticking them end to end to make a longer box? Innovative? Or just foolish. Shouldn’t be too hard if you can keep them straight while setting.

Anyways any thoughts are, as always, much appreciated

T

2

Icon…,

I would opt for the 6 1/2’’ standard box. Properly planned for, there is some adjustability available to you, with that box.

3

Standard boxes need a lot of depth, OK if the board is more than an inch thick in the relevant section, and by far the easiest to make fins for. Put the hozizontal pin in the front and the vertical screw in the back for strength though. I wouldn’t even think about anything else unless the board is too thin in the relevant section.

Futures you have the cutout problem. I think it is mostly an asthetic problem, but looks count too.

FCS would be pretty easy, too. You can actually use 3 plugs in line to handle the higher stress loads of the little plugs (although a pro install with the H hole would be strong enough).

Although, honestly, if you are going to CNC your fin, why not CNC some boxes. Make them “like” Futures but use a set screw on both ends so you get around the hinge problem with the Futures. Not a tough CNC design at all. Make your tolerances tight though! This applies to all designs, the fin tab needs to be precise in thickness for the box.

Dunno what material you are planning to use for fins…fiberglass and glass filled plastics don’t machine easily. You will need to account for the stiffness change if you use a simpler plastic like nylon or Delrin or polycarbonate or Ultem (all 2-3 times less stiff than fiberglass).

HTH.

4

cheers for the quick replies!

yeah it was the depth and weight thing i was worried about with the standard box. well i guess a fish is generally pretty thick all along so it should be ok…

i did think about the extra fcs tab, is it that easy just to stick another plug in the board? love the futures idea! i’d have to see about machining it though, getting hold of a suitable material could be tough in small quantities unless i can find some kicking about.

we usually mock stuff up in wood before machining components to get machine paths right, i was thinking of using plywood for the fins. on the stiffness front i could always knock a bit off the size and glass them?

T

5

I’ve clearly declared the wrong major at uni! Where do I sign up to CNC fins?

I think the standard box or 3 FCS fin plugs would be the best way to go. You shouldn’t have a problem finding an inch in the tail to route the boxes in. Are you planning on setting the fins with any cant, or straight vertical like the original Lis fish? If you wanted to add cant with the standard boxes you could set the bases on the fins to the right angle, kind of like bonzer fins.

6
Quote:
cheers for the quick replies!

yeah it was the depth and weight thing i was worried about with the standard box. well i guess a fish is generally pretty thick all along so it should be ok…

i did think about the extra fcs tab, is it that easy just to stick another plug in the board? love the futures idea! i’d have to see about machining it though, getting hold of a suitable material could be tough in small quantities unless i can find some kicking about.

we usually mock stuff up in wood before machining components to get machine paths right, i was thinking of using plywood for the fins. on the stiffness front i could always knock a bit off the size and glass them?

T

If you plan for 5 layers of 6 oz on each side it will be roughly as strong and stiff as a regular thickness glass fin. A layer of 6oz is 0.01 inches (1/4 mm) thick after glassing if you roll it well. So you’d need to much 0.05 inches off each side prior to glassing it. Still need to re-grind the foil when you are done, too.

The third FCS plug is pretty easy, Chipfish sticks them all over his boards!

I have the FCS tab specs someplace…something like 0.5 inch deep by 0.75 inches long by 1/4" wide with a 1.25 inch gap between tabs…something like that.

http://www.swaylocks.com/forum/gforum.cgi?do=post_reply_write;quote=1;parent_post_id=301114

hth, have fun, post a pic of the fins and board when you’re done

7
Quote:

I’ve clearly declared the wrong major at uni! Where do I sign up to CNC fins?

I think the standard box or 3 FCS fin plugs would be the best way to go. You shouldn’t have a problem finding an inch in the tail to route the boxes in. Are you planning on setting the fins with any cant, or straight vertical like the original Lis fish? If you wanted to add cant with the standard boxes you could set the bases on the fins to the right angle, kind of like bonzer fins.

haha, i wish it would count toward my course to do this! no i do mechanical engineering so get to use the cnc workshop for all sorts of odds and ends

though i hear swansea uni in wales do a watersports degree? and i swear there is a surf science degree somewhere…

i was thinking of putting a couple of degrees cant into the base, keeping my options open at the moment. its going to be a while until this board is done, living away from home and uni work mean that i can only dream and work up ideas…

8

Will attaching keels only front part and leaving flex in back effect speed? Depends on how you set keel. Was just talking to Dale S about this today. I say a Van Straalen fishy at the flex gathering (run’s) had that set up w/ glass ons and Dale a number of years ago did a bunch of them for himself. Set keels parallel and vert (zero cant and zero toe) It will be much faster down the line and the flex will do what the cant and toe do without adding the drag they do. Only down side is more stress on the attachment. Dale said all his glass ons kind of “wore out” after awhile and had to be replaced. He couldn’t us a box as they were on super thin flex tail KB’s. Finally he went to GG style mount w/ fairing on base of fin and drill thru board and bolt on right thru board. Probably would want about 2/3+of keel free of board for good flex. Foil of course will be crucial.

9

Lokbox is readily available in the UK and has most of the shapes you see posted on here. A good platform for the keel fins.The boxes are about £7 a pair from Mick 01825-721117 and a good range of keel is usually in stock or make your own for them.

Also futures do the K1 and K2 keel available from Seabase and I have seen a Stretch designed keel on the net somewhere also.

Dont mean to be negative but why go to so much trouble engineering your own fins/boxes unless you see deficiencies in those already existing? There are loads of areas you could explore in fin and surfboard design and building which could bring rewards.

Regarding flex in the rear part or a keel fin I am currently using some 4way fin system keels that are attached to the board near the front of the fin and so the rear of the fin flexes quite a bit. I am liking the fin on my board and will now temporarily fix it to the board with 5min Epoxy to prevent any flex and see if I can feel any difference.

10

hi ico !

if you DID go the twin fin box route ,

I hope THIS thread may prove helpful ?

[with many , many thanks to George [‘plusoneshaper’] , for his EXTREMELY helpful fin base moulding threads …cheers , George !

the link …

http://www.swaylocks.com/…_latest_reply;so=ASC

cheers mate !

ben

11

Hi again Icon,

If you use FCS I would go 3 tabs instead of 2,

Have you considered Probox, they do keel fins, and the system is very easy to instal, I remember the instolation kit, a set of glass fins and shipping came to about £35-40, paid with paypal and it came in a week.

Though got an old skool fish, if your not planning on taking it on a plane I’d still go glass on.

BTW - Nice cad drawings, and the Surf science degree is at Falmouth uni almost dis a Masters in sustainable design there but couldn’t get the funding in the end.