Hi been a while since I posted. I’ve searched the interwebs and talked to a few people I know without finding too much insight.
What I’ve noticed over the years is different fins and their placement and how it affects the planing speed or trim speed of a surfboard. A few examples,
I’ve got a 7’2’’ egg that was always a single fin, it felt soooo slow and I could barely get it down the wave to do a bottom turn. It had an 8 inch fin similar to a 4a. I added side bites and put in a 6.5’’ fin with a bit of rake and the board takes off like a rocket but is too loose. So I move the new 6.5’’ fin back in the box and I’m dragging anchor again.
I’ve got a 9’6’’ Velzy Pig. I’m surfed it with a 9’’ Takayama Cutaway fin for years. It’s smooth, fast and awesome. I decide to try a wide base pivot fin in it one day and I’m dragging anchor and can actually barely catch a wave with it.
Last I’ve got a Takayama Howard Mini 6’6’’ 2+1. I moved the fin back in the box on a bigger day and couldn’t get the board past the mid face of the wave. I move the same fin forward again and it comes back alive.
Has anyone else experienced something like this? It has always made sense to me why twins and quads are faster and the affect fins can have on turning and drive. But I don’t understand why the same fin, further back in the fin box can produce so much drag. Or why a different fin shape(same size & placement) can create so much drag. Does anyone have any insights?
Normally when they’re talking about adjusting a rear fin in a bonzer or 2+1 setup they’re talking about 1/4" increments. That’s how sensitive certain fin clusters are to placement. I’m sure there’s a sweet spot for that 2+1 setup.
Without seeing how you surf it’s hard to believe that a singlefin would be slower getting down the face of a wave than a fin cluster when both are being ridden passively. If you’re pumping a singfin like you would a cluster then that will make them slow. With singlefins, less is more. The board is doing more of the work. Short of moving the board to engage the rail your other inputs will mostly be for control, not to generate speed.
I surf singlefins differently than when I have fins out at the rail.
Yeah, the main point I’m trying to talk about is; When I move a single fin(or the single in the 2+1) further towards the tail, my boards are slower.
They don’t trim as fast and it litterally feels like I’m dragging something. When I surf these boards, I let the board do the work. I’m not pumping like a shortboard. I’m in the curl trimming. I’ve been riding a lot of single fin longboards and working on nose riding so going down to the 2+1s are a natural transition. And i’m not saying these boards don’t work for me, like when the fins are more forward they are fast. As in they get plane quicker and trim faster on the wave. I’m just wondering if anyone else has noticed this before and if there’s an explanation for it. Because whenever I hear people talking about single fin placement it only relates to how loose the board is or how much drive it has or the arc of the turn. Not the planing speed.
You make a good point. It WILL change the size AND location of the ‘‘sweet spot.’’ The foil on a single fin, also has a significant impact, on board speed in trim.
I forget who, but one guy in the Swaylock’s shaper’s hotseat, brought up how the hawaiian canoes, when they would enter a certain depth of water at speed, would start feeling more resistance, and how there was the potential for rail fins to cause the same issue of extra drag on the center fin. Perhaps someone can remeber who wrote this and link to it.
I’ve not had fin location in the box have drastically noticeable diffrences in drag as described in teh OP, but i have had 3d printed fins, of identical planshape, but different thicknesses, require different spots in the fin box in order for their ‘spark’ to ignite brightly or just kind of fizzle with too low a voltage. That spark is not just turning feel but how much accelleration is yielded in transition from bottom turn to trim and was repeatable on different days and conditions.
IIRC the thinner fin needed to be moved ~3/4" forward for that higher voltage brighter spark, and the thicker fin had that spark when farther back…
Some Locations at certain tides and swell period and sand loaction, would always make any fin feel like it was dragging an Anchor, yet an hour or two outside that zone and that anchor was gone.
I can imagine some bottom countours in front of fin can have water redirected at the center fin and either hit its leading edge and causes increased drag, or converge the rear half of the fin and seem to add squirt. Be hard to prove this ‘potential’ cause either way.
I need to add some streamers to hull and fin next time I capture video.
When displacement hulls (real ones like boats, not that surfboard shape that is incorrectly called a displacement hull) get into very shallow water they will start noticing an increase in drag.
This drag is caused by the hull’s bow wave’s speed which starts reducing when the water depth becomes lower than half the bow wave’s wavelength. A hull will be forced to start planing when going faster than it’s bow wave. The transition to planing requires a lot of energy (amount depends on hull shape) which causes drag on the canoe when entering shallow water.
I have no clue how this can be related to rail fins affecting center fins.
Memory is a fickle thing, and It kept bugging me I could not remember who brought up the point about canoes entering shallow water feeling drag, I quickly skimmed the shapers seat with Bill Barnfield, noting I needed to come back and read it again, and then moved onto George Gall’s, starting on the last page and going backwards, knowing it was likely his words, and I just had to find them.
I think in terms of wasting time in front of the laptop, these hotseat threads make that time, not wasted.
More hotseat threads, please.
So is this ‘shock wave’ occuring on the OP’s 2+1 responsible for his noting that the center fin position further back feels draggy and farther forward does not?
No Idea.
What I do know is empiracle evidence gathered often has surprising results outside what ‘should’ be happening, and that which ‘looks right’ is often simple a serotonin injection due to nostalgia, rather than results based serotonin injections.
I’ve been riding fins which ‘look wrong’ and enjoying the results and different places on the wave face where they allow me to go. Might look weird, I don’t care, as It’s now about having fun, rather than developing a fan base.
That shock wave can only be a bow wave (it’s analog to pressure shock waves, but it’s not a shock wave as speed of sound in water is way to high >3000mph).
I can imagine this bow wave appearing when you’re riding the board on the last inches of the tail where the fins are partially (maybe only a few millimeters) out of the water.
Would this be the effect being described? Interesting effect.