Pls help: fin layout for this board (pics)

General Discussion
1

Struggling with what to do in terms of the fin layout for this board, hoping someone can help.  The board is a loose copy (from looking, undetailed measurements, my own rocker and foil) of an Ebert “Poi.”  I did stick to the Ebert hull’s basic design (tri-plane hull?) and the original Ebert was a twin with the back edges of the future boxes (i.e. boxes, and rears of fins if the fins were normal fronts, not twins) at about 7".

Problem is, I would much rather make this a quad, but have never been able to make a Simmons or Simmons hybrid work well as a quad.  They always feel too slow for what a Simmons should be like in small waves, and I end up running twins out of the rear quad boxes.  Can anybody help with a quad layout (or some quad layouts) that might be fast with this board?  I would probably be running FCS GAM fronts with Stretch 50/50 rears at 6 and 4 degrees, but am willing to change if something else works better – this is just the quad combo that always seems to end up working best for me after trying several other combos.

Rider (me):  215 lbs.

Board dims: 5’ 8" H x 22.88" W x 2.88" Thick – approx 46 or 47 liters.

Tail block 13" - nose width at 12" is 18"+

Hull:  flat/mild belly in nose to single concave throughout, with hull vee-ed at rails (tri-plane hull?).

Rail rocker:  ~ 4 at nose, ~ 1.88 at tail.  Stringer line is very flat, but does have some tail rocker, definitely at least 1".

 

https://swaylocks7stage.s3.us-east-2.amazonaws.com/s3fs-public/2014-09-19%2021.00.20.jpg

https://swaylocks7stage.s3.us-east-2.amazonaws.com/s3fs-public/swaylocks2.jpg

https://swaylocks7stage.s3.us-east-2.amazonaws.com/s3fs-public/swaylocks3.jpg

2

Maybe I can make this more (or less?) challenging.  Went by some shops to look at quad set-ups for wide tail blocks, but once I laid out the twin set-up it was clear none of the quad sets I measured would really work, even if using Futures boxes for the twins.

The twins are going to be at 7 13/16, set 1 1/4" off the rail apex, and with 1/4" toe, using the normal shapers dots for those settings, so that for quads those numbers would be for the rear edges of the front quad set (i.e. the twin fin backs would be further back and closer to the rail than 7 13/16 & 1 1/4").  The twins will actually be further back, and closer to the apex, as I’m planning to run Sea Shepherds that I’ll modify to work with Probox.

I’m going to add a center box with the hope that in overhead surf a little twinny trailer or nubster will slow the board down and help it go rail to rail just enough, but I’m wondering what I can do in terms of quad rears, running the fronts out of the twin fin boxes (at 7 13/16 x 1 1/4" x 1/4"), as fronts, to increase the adaptability of this board to overhead surf.

It looks like 4.5" off the front fin backs  (3 5/16" off the battail point) might be a reasonable spot for the backs of the trailers – anything further back seems too close to the tail.  I just wonder whether it’s a lost cause to try and run quads with the fronts in the twin boxes, and whether I should just give up on the quad option altogether for this board.

I guess a pointed question would be:  if I’m going to try and run a quad layout that’s 3" further to the tail than normal on a mini-simm hybrid (normal being a little over 10" at 5’ 8" length?) with a wide tail, how far off the stringer or how close to the rail should I go if I want it to be fast?  Will increasing distance from the rail apex for the rears decrease drag, or increase it, when the vertical spacing is tighter than usual?

3

I don’t know the answer to your question, nor really even understand the question, but intuitively I feel that the closer together the rear fins are, the further back they can be.

simply because as they are placed closer and closer to the center, the more they approximate a single center (thruster) fin, which is typically placed further back than rear quad fins are.

4

Sounds like I probably overexplained…

I’m working on a 5’ 8" Simmons hybrid (photos above) based on the Ebert “Poi.”  The original design is a tri-plane hull (deep single concave with vee panels a few inches wide along each rail).  The original design has a twin layout, with futures boxes, where the back of a 4.5" fin would be at about 7.75" (about the normal 1.25" off the apex, 1/4" toe).

Originally, I had hoped to come up with a quad layout that would compete with the twin layout for speed, or lack of drag.  But, when I layed out the possible box locations, it didn’t look like I could do both a quad and a twin layout, if I wanted to keep the twin option (I did & do).

What I did was go ahead and install the twins with Probox, at about 7.75" (I say about because 7.75" was for the 5’ 6" Ebert that I used as a model for my 5-8, so I moved the twins up about 1/16").  I went ahead & added a center box for a small trailer, thinking maybe that will give the board more flexibility & range in terms of wave size – help it turn better at high speed.

So, I have the original twin set-up in the board, with a trailer box added.

What I’m wondering now is whether it makes sense to add some rear boxes to run quads with the quad fronts in the twin boxes (at 7 13/16"), and if so where I should put them to minimize drag.

Based on some discussions around town, right now I’m thinking of adding back boxes at 1 1/4", with the back edges of the rears either 4.5" or 5" behind the back edges of the front fins.

I just have no idea if it’s worth it, or if there’s a better way to do it to minimize drag.

Long post again, but I don’t think I can make it clearer writing less.

5

I think you’re going to have to pick one or the other.  I don’t really see how you can reconcile a twin you’d normally set at ~7"- 9" on a fat ass board with a quad you’d set at 5/10 - 6/12.  

You could use a twinzer setup and swap different sizes for the mains, or the Quartet setup Neal Purchase jr uses with the close-set 5.5 MR+ 3.5 trailing rear.

6

Twinzer is a GREAT idea, and one I didn’t consider, never having owned or made one.  Right now, after some archive searching, that’s what I plan on doing, i.e. adding fronts with 3/8" overlap, 1 1/4 off the rail (same as trailers).

Only question then is whether to toe them 1/4" like (parallel to) the mains or toe them in 1/16" or 1/8".  It sounds like if what I want is for the twinzer to be the set-up for head-high and bigger I should make them parallel, or else toe the fronts in and plan on running them with a nubster (box for that is already in the board).

I don’t have any experience with twinzers, so any input is much appreciated.

Board is going in the water with twin sets tomorrow either way.  Stoked about that.