I am glassing a 9'2" HPLB - lots of rocker, rounded tail, narrow profile (20"), vee in the tail. Sharp rails in the tail. I was looking at advice on Swaylocks, and it was suggested the fin box go 6" to 7" up. Side bites 14" up on a 6" up fin box, 15" up on a 7" up fin box. 1.25" from rail and 1/8" toe in regardless. I am making it for 6 to 12 foot faces on the outside. "The Pier Bombadier". Any advice on fin box placement? Will 7" up make the board too skittish on the drop? Signed, Clueless. Got to go to bed early, I'll check in early am, and thank you in advance for any knowledge and advice!!!!!
Pintail or squash? I measured my two long boards- but they are both single fin pintails. My fav board fin box starts only at 5 inches from the tail. I ride it with the fin almost all the way up (maybe an inch short) and it's perfect. My other one is 6 inches up and it's the same, ride it almost all the way up. Again both- pin tails. 9'6 and 9'4
My 9'0" Jon Ashton HPLB...thinned out, lots of rocker - comes alive in bigger surf - has the rear of the side bites 16" from the squash tail and yeah set 1 1/4" off the rail and toed in 1/8" I rarely bother with the side bites, and like you said mostly just take it out on bigger racy days. Putting the side bites on a 9 foot board 14" from the tail just seems to far to the rear to me to provide the leverage you want from them.
Couldn't tell ya where to put anything other than measuring mine and telling you where but it seems you've got that part figured out. All I can say is I didn't bother getting side bites put on my HPLB from Orion, and she rides great with that 9" Single Greenough 4 A. It's will allow you to carve up that wave you seek. I too push my fin all the way up in the fin box to get max turn-ability.
Some general rules on sidebite placement: Further in and further up as the tail gets wider and/or has more surface area. Toe in decreases with length. Cant decreases with wave size. If you generally like larger center fins, or center fins with more rake and/or tip, push the sidebites forward. With more tail rocker, you can pull the side fins back. I prefer longer boxes set further back (as far as 5" up from the tail) to give more room for experimentation with different fins, and I set my sidebites at about 13" up on hplbs with pulled in squash tails with plenty of tail rocker. That dude Ryan that posts lot of gopro vids is riding one of my hplbs in his vids. PM him for his specs.
The rear of the fin box is 7" from the tail, and I ride it single fin with a 8.5" squirrel fin toward the front end of the box.
I routed out the stringer and set the fin box 6" from the tail. Any further back, I might have gone thru the board because it is foiled pretty thin at the tail. Sidebites 13.5" up (still penciled in). If I am understanding things correctly, the further up the side bites go, the longer the turn radius? So if they are closer to the fin box, it can turn tighter, but you may lose a bit of stability on a bottom turn on a big wave. It is a narrow board (20"), so I don't want it too skittish. Maybe I should go up further as Mitchell suggests. Holy cannoli! I just went to look at the old hplb with the 100 hammer holes that I am kind of using as a starting point because it surfed big waves well. It was a thruster in the tail. Seven inches from the tail was the center fin ( not a fin box, a future set up for a thruster center fin. I didn't like this part so that's why I have a fin box in the new one, so I can put a big fin in it if needed.) The side boxes were not bites, but regular thruster fins 2.5" forward of the front of the center fin, or about 14" from the tail. It surfed like a shortboard when on the tail, but was a little too skittish on the big drops, but went fast as hell down the line and got you in super early. So hopefully this one will too, just have more grab at the bottom on a hard turn. So now I am totally confused.
I'm doing the side bites tomorrow. Due to past positive experience with a very close fin grouping on a hplb, the placement will be like LBCrew suggested. This should allow for a more vertical approach, and if it gets too sketchy, the fin box will give me the versatility of going with a big fin set further back. If it is small and mushier, take out the side fins and just go with a center skeg and push it a bit forward. I tried to post photos but I am still too burnt to figure it all out. One day....
