Surface drive propshaft height on twin engine cats
 

Hey guys im just wondering if anybody has a rough idea about what height a twin engine cat would have the propshafts in relation to the bottom of the boat in full surface mode with #6 style props? imcos new scx surface drive looks very promising and id like to research where the typical drive height is with #6 cleavers in full surfacing mode.

Anyone?

Read my thread and it will help. Most 2.5 inches above.

I was running with 2 3/8" above, Imco SC's w/ -2 shorties. Boat hooked up great and got right up on plane. Started to loose it's bite over 100mph and got real loose in the azz. Felt like it was ready to spin out. Also had some porposing issues. Spaced it down to where it's running 7/8" above and it's stable up to 115mph now and the porposing is much better. Still playing with props and gearing. Should have another 10-15 mph in it but it feels alot more stable now.

Fireboat, Longer skegs are needed for most hulls at 120.running over 2 inches above. Probably not a good feeling.

No, it wasn't a comfortable feeling at all. So we'll run with it like this for now. Saving up for the SCX uppers then I'll use the SC -2 shorties. Who can do the skeg lengthining and how long should they be extended. Interesting idea. I actually picked up speed by installing the spacers but I think that its more because of the stability and being able to push it farther and longer than it is mechanics. I think by lowering the prop depth that I should lose speed? This sounds like I should start a thread about this? THANKS!

IMHO, you need to talk to the boat manufacturer. They most likely have the data you need or can get you into the ballpark so you can proceed with your own R&D.

IMCO is coming out with a SCX based surface drive. There was a pic of it over on performance boats as it was being tested. It is basically a SCX drive with a -4 lower and a modified upper that is designed to fit a 17" #6 style prop. This looks like a great setup for Bravo style boats.



Darrell.

Imco makes lower cases with extended skegs. So you can buy them for the SCX.

One of the reasons you may have been better off at a lower depth was that at a lower depth you can leverage the bow. In some cats that helps.