As seen in Speedboat Magazine’s
Jan/Feb 2023 Issue.
Q. I own a 2007 Nor-Tech SuperCat 36′ catamaran with Twin 1150s and Mercury Racing SSMVI drysump drives. The hull has notches in the running surfaces at the transom. I am running 37″-pitch to 40″-pitch props spinning out. What should my drives “toe” be set at? (To verify, “toe” is the measurement of the tips of nosecones being closer to or further apart than the center line of the propshafts.)
The boat does have an issue with porpoising, but as far as I’ve ever been able to find out, it is normal and to just deal with it! I’m a new cat owner coming from a vee, so I honestly did not know what to expect. I have been told that newer versions of the 3600 have the notched bottom and the older ones did not. The reason I say this is that I’ve also read
that it makes a difference whether you should spin propellers in or out. I’m sure you know what I’m talking about. You can see the “notch”, the drain plug, and water pickup if you look closely at the picture I included of my boat. Obviously, I would trust your opinion over anything I have read, so I appreciate the information.
We are very familiar with your Nor-Tech 36’ Super Cat. As a matter of fact, we
just finished rebuilding and upgrading one here. We upgraded the existing 850SCI engines to our 1250HP version and re-rigged the boat. When it came to us, the propellers
were spinning out. Most of the ones that we had driven in the past had the propellers spinning in. We tried this one spinning out and the porpoise problem was unmanageable. We switched the drives to spinning in and the boat handling improved immensely. Before making the change, we did do some research talking to other people in the industry that we respect. The consensus was unanimous that the propellers should be turning inward on a Nor-Tech 3600 with higher power. To my knowledge, most of the 3600s had notched bottoms. The attached
picture is of the last one that was here that we switched the propeller rotation on. As you can see, it also has the notches in the sponsons. When we delivered the boat, the owner was super happy with the improvement. The boat does have a very minor porpoise in the midrange, but is on rails at upper speeds.
Regarding toe in, with the propellers turning inward, set the toe in at 1/8″. Set the drives so that they are straight and level and then measure. The point of the gear cases should be 1/8 inch closer than the centerline of the propshafts.
Q. I have an Eliminator 28 Daytona “low profile” with twin engines. Where should my propeller shaft center line be in relation to the bottom of this boat that has IMCO extension boxes and Bravo 1 stern drives? I am trying to reduce the propeller slip numbers. I am thinking that I may need to go with shorter lower drives. Thank you for taking the time
to read this.
Most of the 28 Daytona’s with the similar set up as yours run the center line of the prop shafts 2″ to 2½” above the bottom running surface directly in front of the drive. Typically, with 4 blade Bravo props, you can expect the slip numbers to be about 12 to 14 percent. Your Eliminator boat works best with the propellers spinning inward. Going to a shorter drive than you now currently have will likely increase the slip and might also create a problem getting the boat on plane. Also, it is advised that if you go to the 2″ to 2½” above the bottom running surface,you may have to add bottom pickups in the boat to get enough cooling water. If your slip is too high, you might also consider changing from the four-blade propellers to a Max-5 Mercury Racing propeller.
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