NAMBA Propwash October 2017.pub

Shingled sponsons have been tried, but don’t seem to have an advantage. The air trapped sponsons mentioned in the last issue haven’t seemed to have a great advantage in smaller riggers. I wonder if the “air traps” actually channel water along the sponson bottom, rather than letting the spray escape. That would increase the wetted surface area and drag. Tunnel hull sponsons are another special case. Early model outboard tunnels had flat bottom sponsons like those discussed above. However, cornering improved with angled bottoms. For years the standard deadrise was around 15 degrees. Leecraft tunnels used 15 degrees on the left sponson and 20 degrees on the right. The shallower left sponson also had a spray strip to help prevent sponson burying in the turn. However, Carl VanHooten began to experiment with steeper sponson angles. These helped in rough water since the sponsons began to act like a deep vee hull. Below is a high angle sponson design. Note that the right sponson can have a higher angle than the left. Model catamarans often imitate the sponson designs on full size offshore boats. Cats usually have a flat section with angled sides. The bottoms usually have multiple steps. Outboard tunnels might benefit from steps as well. The size and number are limited by the rules, but Prather tunnels used them. Those are the basics of planing surface design. The next part will deal with the really high drag submerged areas on the boat, the rudder, turn fin, and prop shaft. Vote . Vote . Vote ……. As mentioned earlier, as per the NAMBA rulebook, all voting for NAMBA President, NAMBA Vice President, and District Directors for the odd numbered districts must been done online. Log in to your membership profile and vote. Or click on the link when you receive your e-mail when the voting period begins. Last day to vote will be October 25 however do not delay. Have a say in the future of NAMBA. If you have any difficulty with the voting process, or do not have Internet, a computer or cell phone contact the NAMBA office for assistance. You will not be able to cast your votes with the NAMBA office, however you will instructed on how easy it is. PROPWASH October 2017 17 Leecraft Sponsons High Angle Sponson Design Early Insane Cat Bottom