The tail of my board is too thin to properly fit a 10" single fin box. Its my first board and i didnt even consider that that might be a problem when i was shaping it.
The last 6 in or so are less than 1" thick. should i just route it out to the max depth until i can do the proper 1 in depth further up the board?
Because its my first shape and I’ve never owned a board like it before, Im not sure where i want the fin placement or fin size or i would just glass one on.
Measurements of your board? Placement of the fin depends a lot on tail width. This is a basic, typical beginner’s mistake. We have all done it, don’t worry.
If your tail is not too wide, you should be able to move the fin-box up; Please measure where thickness reaches roughly 1 1/8" and tell us what’s the board’s width there.
Are you measuring the thickness pre or post glass job??
Go double 6 0n the fin area - too and bottom. A good thick hot coat in the area will also help.
You gain a bit of thickness. Not much - but some.
I’ve shaped a few knowing I wanted a thin tail and the box far back - double 6 helped.
You may also be able to solve your box problem with the fin you choose to use.
WideAWAKE makes a very good point. You would do well to consider going that route.
Doesn’t a Bahne type box just need a little less than an inch?
I think you may be ok.
Here’s my 2c…
I normally set my box at 7" up for boards 9’ or longer, so if you are shaping a board that size you should be fine. Just use a fin with a bit of rake. (That’s the angle of the fin) Another trick is to measure the box carefully and with a die grinder, slowly remove material for the outside of the box without breaking thru into the fin cavity. When I do this I take into account a layer of glass inside the cavity when I set the box. One more trick is to measure it exactly where the back of the box is just at or breaks thru the foam. Then put a dark lam of some kind between the layers of glass when you do the deck. Also, you can just say; “screw it” and do a glass on and put it where you want it. Again, just my 2c…
You can also set it so the back of the box sits a little high and grind it down (within reason, of course). This may affect your selection of fins, as you’ll want to go with screw in the front for this. Or, if you’re a totally bad mofo like Jim Phillips, you route right through the deck and glass over it. Lots of ways to skin a cat. I’m not real partial to cats.
Glass-on. Less than one inch means the box shows thru and though it would be under a couple of layers of glass it is a very weak install. First time you run it onto sand or the reef the whole box will punch thru the deck. You said the last six inches. I set most of my longboard boxes at six inches from the tail. It could be that there is enough thickness forward of six inches to install the box. A certain amount can be ground of the box so that it is just less than one inch. If you try to get a box in there; use a White box. Less noticeable to show thru the deck. Lowel
A lot also depends on the overall fin and board setup that you personally prefer. I just measured two of my 9-6 longboards. The first box is 6 inches from the tail. My go-to fin and placement is still 1-1/4" forward of back of box. The box could have been placed at 7" without a problem (for me).
The other board, a hull with wider tail and V-bottom has the box 8 inches from the tail and my current fin/position is 3/4" forward of the back of the box. I am not likely to move the fin any further back on either board.
Most of my boxes land about 3" from the tail on a longboard.
Tabs in the front of fin or no tab at all.
Easy solution is glass it on.
Placement all depends on the board and how you want to ride it.
“Less than one inch means the box shows thru and though it would be under a couple of layers of glass it is a very weak install.”
I disagree… the main weak spot with a single box in a single stringer board is at the front of the box and that part wouldn’t be affected by a bit of the back end of the box ‘showing through’ the deck glass. In fact, I’d go so far as to say it might be a stronger installation with the box bridged through to the deck. That was the idea behind the FCS, Red-X, and others with the deck connection through the board. For strength go with double stringers - one on either side of the box or install the box ‘offset’ to one side of the stringer, but that’s another story. I’ve seen many boards with a crack perpendicular to the stringer at the front edge of the box but I don’t recall having seen cracks at the rear of the box. Many boards have broken at that spot - the stringer gets routed almost all the way through anyway on a single fin single stringer board and structurally integrity is compromised in a big way. I don’t think a tiny fraction of an inch of foam at the back of the box is going to make much difference. You could shave a tiny bit of plastic off the bottom of the box and install it with the top edge ‘proud’ - just grind it down when you sand the board. I guarantee that many boards have had the box shaved down a bit. The part of the fin that fits in the box channel might stick out a bit at the back but isn’t going to wreck your day or anything. Your leash, if you use one, creates far more drag.
PS… it’s not that big of a deal to just measure the thickness of the box, add 1/8"-1/4", slide the calipers until they touch both sides of the board and “Bingo” - that’s where you put the box.
Guess you never ran a eight inch fin with a shallow box onto a reef in the Islands or anywhere else. They come thru the deck at the weakest point. Which is the rear of the box. Reason being that the wood stringer has been routed away. Because of the bottom contour of the board there is usually some wood left at the front of the box. Glass over a wooden stringer at the deck is stronger than a 6/4 or 6/6 with no stringer under it even if it’s mils. thin. That thin layer of wood at the front of the box helps hold on impact. The larger the fin also has a negative effect on a shallow install at impact. Did a tremendous amount of fin box repair on Maui. Knocked a few out of the tail myself. Notrouiusly shallow reefs on the South Shore/Kehei/Wailea area of Maui. It’s what it is. I don’t base statements I make on this forum on theory or the hope that I’ll make brownie points with the Sways crew. Lowel
There are lots of suggestions here. I also suggest taping some tongue depressors under the tabs of the box. This will lift it up an additional 1/8" and help out a bit.
I have one board which was too thin in the tail and I used the plunge router at increasing depth until the router bit just touched the deck lamination which left 2.5mm between hull lamination and the tabs on the fin box.
This was a 9’3" board cut out of a 10’8" blank, so it was soft, and it was my first unassisted lamination and did not come out very good. After many years of abuse there was a crack from flexing at the front of the box. The fins for this board always had the flare well above the lamination. How much of a hydronamic drag this is is unknown but now I have been customizing Mr Mik’s 3d printed fins to fit this board, and one other, I find I have to remove a good 2 to 2.5MM off the bottom of the fin before the flange gets close to the lamination.
Since there is less depth on the box in the board, there is more stress/leverage applied on the finbox and the board itself.
The one board with the too thin tail has since had cedar planks installed deck and hull to form an I beam, extra stringers were sunk into the foam either side of fin box as there were many stress cracks on many parts of the hull.
Basically the board would have snapped in half before the shallowly set fin box ripped out of the board. This was kind of a beater board I would teach people on or lend out to visitors and no doubt that fin was run into the sand often. I was willing to let the board break, when my regular longboard was in drydock, and I rode it with a smaller fin and, decided it should not end up in the landfill this decade. I’ve ridden the shit out of it over the last 6 years since I rebuilt the board.
The finbox is not a concern, the softness of the overshaped blank and the poor original glass job will be the death of it.
If I’d shaped another LB with too thin a tail for a full depth box install, I’d still route to the top lamination, but not through, and just reinforce the top lam and the hull lam, and cap the box after sanding flush. Spread the load over as much of the tail as required.
Instead of relying on spacers for the tabs to reside upon, I’d personally let the box rest on the deck lamination and use tape to hold the fin perpendicular while the resin cured.
“Guess you never ran a eight inch fin with a shallow box onto a reef in the Islands or anywhere else.”
Actually I have. Have snapped off a few tails and have seen plenty of cracks perpendicular to the stringer - always at the front of the box.
Post photos please.
Ha!Ha! Photos of what. Repaired and back in the water. Real shapers take into account the depth of the box and know better. Otherwise they Glass on. I use 1/32" milled fiber and a tail patch and never drop below one inch forward of the rear of the box. I’m not talking about losing your board and Side whacking a large single fin. I’m talking about riding/driving onto shallow reef. Low tide Hazard C. or St. Andrews would be a pretty good possibility. Most of the ones I repaired tho were done in Kihei shallow reefs by kooks from Kansas. I never had the time to photo album every board I ever repaired or restored. My goal when I used to do ding repair was to fix themin such a manner that the next ding wouldn’t be in the same place I just repaired. Get them back to the owner, back in the water and collect my $$$. Never was into taking pics and telling everybody how great I am. And yes if there is enough wood and glass between the box and the deck and you run aground they will crack at the front of the box. Not the same thing.