how to increase rocker in a stiff blank

6 posts |
Last post
Honolulu's picture
Joined: 04/28/2004

Several years ago someone ordered a bunch of longboard blanks from China.  They're fairly dense polyurethane foam and the quality control turned out to be impossibly poor.  The guy sold them off on craigslist for $30 apiece, a price I hadn't see since the late 1960s.  The quality was so poor that I had to sign a release such that no matter what, I couldn't return them.  Nevertheless I bought three and used two.

The last blank is proposed to be a paipo or bellyboard, nominally 5' x 22" x 1.5" thick, maybe 2".  I think that at 300 lbs I'll be able to duck dive this under whatever comes.  Back in the day (I was lighter) I rode a 4'10" x 22" kneeboard with deep knee wells at various places on the North Shore. I enjoyed Pipe, Back Door, Sunset, Gas Chamber, Rocky Point, small Waimea and a few other places.  I learned several things including that on large fast waves, kneeboards need smooth waves.

I'm wondering how to increase rocker in the remaining blank.  I'll have to cut out the stiff 3/8" thick stringer. I envision something like thinner multiple wood stringers.  Special ordering from US Blanks seems out of the question on a cost basis when I already have a blank for next to nothing and little to lose but my time.  Have a nice bandsaw, planer, sander/polisher and surform, what could wrong?  This ain't my first rodeo.

Sooo.... once the stringer is removed, how to increase rocker? I speculate that I'll skin the blank, shape to thickness, remove the stringer, cut the two pieces lengthwise into four and glue in new wood stringers of preferred rocker, in some sort of jig.  I dunno how well three,1/8" stringers will hold increased rocker.  If I can get it cut, glued and glassed, I figure (hope) the stringers will hold the increased rocker.

Ideas like these are the source of another thread about slab foam on Oahu.  That thread isn't bringing useful results, so this is another approach.

Any better ideas 'bout the rocker?

like
0
fishnsurfn's picture
Joined: 04/10/2010

How much extra rocker? The blank is already 2" thick?

like
0
Honolulu's picture
Joined: 04/28/2004

The blank I have is probably 3" thick at center before skinning, but a tangent line from there (which would be the tail of a shorter board) the nose rocker is maybe 2 inches.  USBlanks 510RP has a lot more nose and tail rocker than that, probably more than what I have in mind, where flat-bottom low rocker speed is a design intent.  My question is HOW, not HOW MUCH.  I think that any reasonable process to introduce  (and retain) more rocker will work, until the foam buckles, but what are the options to do so?

like
0
McDing's picture
Joined: 05/22/2004

So Honolulu;  Can you cut the desired rocker into the two new stringers and then use clamps  to secure the foam at the stringers when you glue up?  Or is the rocker too extreme to bend the foam to match the rockered stringer and then clamp.  Also I have found that even when I am glueing a center stringer to two halves;  I will glue the stringer to one half.  Let it set and then glue the other half later.  Wrestle with one bear at a time if you know what I mean.

like
0

That which can be assorted without evidence was read in an illegal magazine.

Honolulu's picture
Joined: 04/28/2004

That's largely the sequence intended, and why I listed power tools I have.  A rack of 2x4s screwed together should provide all the bending I'm likely to want and I'll rack the slices while each is still rectangular in cross section.  Depending on the flexibility of the slices I may do more than one at once.  The rack will do most of the work but I have enough pipe clamps to tie it down and a few C clamps also. Garbage bags of water also can provide distributed pressure.

How much springback I'll have after releasing from the rack is to be discovered but easy enough to test.  Possibly I can chat up Ted Wilson about his experience in this arena, and appropriate glue (use the Search function).  I think the outer strips will show the most springback where they're not restrained, and they'll want to give the blank a concave bottom.  I can  accept and handle induced concavity by re-leveling the blank.

Springback is a possible reason to use softer EPS or XPS but then I have to get some epoxy.  The one lam session I had with epoxy suggests the blank absorbs very little, so that's good.

like
0
sharkcountry's picture
Joined: 03/25/2006

Years ago I bought a stringerless PU foam blank. It's really floppy without the stringer, so I think you could cut out the original stringer and replace it with a pre-foiled and rockered stringer. It should be flexible enough to match the new rocker. If you pre-foil the stringer, you just have to bring the foam down to meet the stringer. When I add wood stringers in my EPS boards, I often shape the stringer with the rocker and foil, just leave a little extra that will be sanded down in the final clean up.

In the stringerless XPS slabs I've used (Blue Dow), I added weight on the nose when I glassed the foam and that gave me an extra inch or so. Back when my brother and I did the compsands using Home Depot and Lowes EPS foam, we used a rocker bed and forced the foam to make the rocker we wanted while we glued the bottom wood skin to the foam. Then we added wood perimeter rails to hold the rocker in place. Haven't done one of those for about 5 years. We've used weight, vacuum pressure, tape and shrink wrap to hold down the foam against the rocker bed. The rocker beds have been other surfboards, or wood beds we made.

like
1