IJSBA is posting clarification for sponson rule interpretation.  IJSBA might as well stand for Its Just Sponson Bulletins* Always. Anyway, enough of that.  Nobody wants a surprise in tech.  We do not want you to have them either.  Let us get straight to the rule.

This is the general sponson rule for Ski Watercraft:

 "All watercraft may be equipped with a maximum of two sponsons. Original equipment
sponsons may be modified, aftermarket, repositioned or removed. Overall length of each sponson shall
not exceed 91.45cm (36.00 in.). Sponsons shall not protrude from the side of the hull by more than
100.00mm (3.94 in.) when measured in a level horizontal plane. The vertical channel created by the
underside of the sponson shall not exceed 63.00mm (2.50 in.). No part of the sponson shall extend
downward below the point at which the side of the hull intersects the bottom surface of the hull by
more than 63.5mm (2.50 in.).

Aftermarket or modified sponsons must exceed 6mm (0.24 in.) in thickness. All leading edges must be
radiused so as not to create a hazard. Sponsons may not be attached to the planing surfaces of the hull.
Fins, rudders, skegs and other appendages that may create a hazard will not be allowed. (See diagrams
in Appendix.)"

 

 Please note that these are two different sponson allowances.  The depth of the sponson blade which is attached to the bond flange is to be measured from the point of the bond flange bottom down for the purposes of determining the 63 mm/2.5 inches of depth.  Any space above that is deemed to be mounting area and not to be calculated as sponson blade.  This interpterion is also supported by the IJSBA Rule Book Glossary which states:

"A special surface which may be attached to the hull sides or
transom for stability.

Ski Division Only: Sponsons may be attached to the hull sides,
transom or inside the bond flange portion of the hull."

 

Therefore, the sponson to be calculated is the effective surface where the actual handling stability is affected.  We hope this clarifies concerns regarding sponson depth on Ski Watercraft.  Please send any questions of comments to info@ijsba.com.

 

*feel free to use a different word.