A little over 6 years ago when I started doing boards in XPS and EPS (other than PU) I was making them 1/8" thinner than someones standard PU.
However since the flotation was close to equal (after volume adjustments) there was no real advantage to doing than. When I would do a direct duplication of the board shape from PU to EPS: 24 Liters EPS verses 24 Liter PU there was less transition between surfing the two boards. The feedback’s were more positive I think because it gave an advantage to the surfer: (Paddle power and a Lighter livelier board than PU). The theory of adjusting volume to compensate flotation differentials I can understand however then what is the point of the added cost and a slower production rate by choosing this type of build? Plus really tuned surfers don’t like to vary rail volumes to much. It can throw you off. After the Train Wreck of the EPS/PU Tread we had going I when on to build more comparisons and had some really good feed back from Pros. However since the tread was locked I just quit posting.
I have a TEAM rider that has been a PRO surfer since his teens that is now in his 30’s and a full Surf Nazi we have done some extensive testing and model development since the Yellow PU - EPS tread. Rather than looking at companies products and service we just based our own research on materials and not vendors. Less political plus we wanted focus on surfing and board building.
We had a blast playing with the different materials. With the model creation going on during this same time it made for some real interesting data collection. Our testing grounds were “LOWERS” (Trestles) down in San Clemente, California and “GREEN BUSH” Metawais INDO.
During our equipment exploration we found some interesting principles to apply to High Performance Surfing. My interest in EPS was reborn. By making such a large quiver of boards as we did:
10 x HPSBs shortboards all the same volume comparatively between the various models we worked on. The only difference was the rocker changes. If we made a rocker change in a PU a EPS version was made. We explored various rail volumes and profiles. The Journey was so cool and informative. The Data we were gathering was thought provoking and coming at a us like a locomotive. Without boring you with the details we found that EPS is a must for one’s quiver. Lowers on a EPS step-down HPSB is crazy fun if you like surfing. Step-downs are new category of boards that are in currently in vogue at the moment. Center point forward, hidden volume, increased outline. I have a formula to adjust the volume on these step-downs that has worked every time we have applied it. Getting back to the EPS material as the core. These Step-downs are a perfect match for the lighter build. We used RR Epoxy KK and Molded EPS (We used Marko and US both). Now that we have the formula worked out on the shape for 2011 we are also going to wrap it in a “SPACE SUIT”. The core is a combination of Materials thrown in a Vacuum bag with some special fabrics. We are approaching this whole thing like a good set of golf clubs were you need more than one board.
To answer you original question:
**For the EPS vs. Poly, Do you change anything in the shape to
compensate? Thinner or narrower for one over the other? Or are the
conditions to be ridden in the compensation? **
I make EPS boards exactly the same shape as for a PU. The key is to let the material speak for it’s self and yes conditions are the key factor when choosing what board to ride. Show up to Lowers with two exact boards with material being the only difference and choose your ride base on the current conditions.**
In my limited comparisons, EPS rides higher in the water. Makes EPS
paddle in flat water faster, but sometimes gravity is helpful in pulling
a little more mass of the PU down the wave face.
Very true we find the same thing. The key is to play on those factors and use them to your advantage. In some conditions you want the inertia you get from PU to put you down the face. Other times to kind of free fall and float over the sections EPS is great for that.
Tom Resvan EPS LOWERS Session Stepdown:
“Sorry for the Hi-Jack”