nubster rear fin size

[sharkcountry]

Wanted to ask what you think about the size of a nubster rear fin on a fish style board. I did a hack job to an old board that I had sitting around for a long time. Converted a 6’ stubby outline to a 5’6" fish. The board had sidebites added over the years, so I tried it with the existing fin plugs. I planned to add a set of FCS plugs to move the fins up and use large keels, so I cut out the C5 plug and made it all FCS. Havn’t foiled the keels yet, so I just stuck other fins in there for now.

I still have have the old single fin box, so I can add a center fin if I want, but I think something really small might be the right choice. I hacked out a really small nubster thingy from a piece of left over G10 but I’m thinking it’s too small to add much to the mix. Haven’t ridden it since I added the FCS plugs and made the tiny fin.

Wondering what you think is the minimum size to have any affect?

 

[thrailkill]

Try a one inch deep, long base keel (the length of the center box),  that tapers down to zero.      Like a drawn out triangle, on it’s side.        Similar to a ‘‘fence’’ on an aircraft wing.       A very visable example appears on the wings of the Soviet MiG-15 aircraft.

[sharkcountry]

Thanks Bill. I’ll make a fin like that.

[L.I.T]

@$1

Try a one inch deep, long base keel (the length of the center box),  that tapers down to zero.      Like a drawn out triangle, on it’s side.        Similar to a ‘‘fence’’ on an aircraft wing.       A very visable example appears on the wings of the Soviet MiG-15 aircraft.

Hi Bill,

          how’s it going? Was just wondering what your logic is behind suggesting the above as an addition to the twin-keeled fish Sharkcountry has described?

Cheers!

[thrailkill]

@$1

@$1

Try a one inch deep, long base keel (the length of the center box),  that tapers down to zero.      Like a drawn out triangle, on it’s side.        Similar to a ‘‘fence’’ on an aircraft wing.       A very visable example appears on the wings of the Soviet MiG-15 aircraft.

Hi Bill, Was just wondering what your logic is behind suggesting the above as an addition to the twin-keeled fish…?

A way to increase base length, to increase lateral resistance, without a significant increase in fin surface area,

[L.I.T]

Hi Sharkcountry,

                        if I was in your shoes, before I started shaping the keel fins or planning out a nubster for the centre box, first thing I’d do is… ride it.

From what you were saying, you haven’t ridden it with the new/3rd set of FCS plugs you put in, in front of the existing ones, so first thing I’d do is feel how it actually rides right now with fins in those new boxes (and hence get some idea of what it actually needs to get the feel/performance you want out of it).

Then I’d try to borrow some keel fins (preferably close to the size I had in mind to shape) and see how it feels with them alone; how do you know for sure it even needs a nubster in the centrebox until you’ve tried it?

How do you know it even needs keels?

If it feels good with the keels, but you still think it needs something in the centrebox, one thing I’d consider doing is buying or borrowing a centrebox adapter (I think they’re only for FCS fins, but there may be Future versions out there), and then try mounting an FCS centre-fin of different sizes to get an idea of what the board would need if you were to shape a nubster with centre-box base on it.

In terms of hazarding a guess as to sizes of the keel fins + nubster, a place to start might be looking at the sizes of the MR Twin fin + trailer fin combo.

According to FCS’ fin data page (https://www.surffcs.com/pages/fcs-fin-data), the spec’s of these fins are as follows:

MR TWIN (SIDE)

BASE ” = 5.06

BASE MM = 128

DEPTH ” = 5.56

DEPTH MM = 141

AREA ” = 21.06

AREA MM = 13590

SWEEP DEG = 32.1

FOIL = FLAT

 

MR TWIN (CTR)

BASE ” = 3.31

BASE MM = 84

DEPTH ” = 3.34

DEPTH MM = 85

AREA ” = 8.23

AREA MM = 5307

SWEEP DEG = 29.1

FOIL = 50/50

Mind you, this is just a guess; personally I’ve only had a few rides on keel-finned board (and one without a centre-fin/nubster in the middle), and depending on your height/weight, performance requirements, differences in behaviour of a keel versus a dolphin-fin shaped template you may well need to adjust the sizes from here.

But if it were me, this is how I’d try to tackle it.

If there’s a better way to go about this though, please shoot me down; I’d be interested to know what it is.

Cheers all!

[sharkcountry]

I tried the board on a really ugly day using FCS H2s in the forward plugs. NO BUENO. I used the H2s because the plugs are zero cant and pretty close to straight, no toe.

I think the first test ride was with FCS M7, or the Stretch quad set using the front fins. I want to try keels because I like the drive they give, and it suits the no cant and toe setup I have.

I borrowed a set of keels that Greg Grffin made for my brother’s Griffin Hovercraft, and I could try those before I foil the fins I started. Either way, I’ll finish the keels I cut out because they’re already cut out and I have the Griffin fins to use as a guide for the foil. The Nubster fin idea is because I have that box in there, and I have G10 off cuts that are too small for a normal size fin.

If I really want to get crazy, I could stick these in. I have a set of sidebites and the center.