Help!!!. I re-engined a lovely Excalibur 45 with Cummins 5.9 QSB 480 hp/1278 nm torque diesels, and Konrad 660's which failed at 115 and 126 hours at the bottom pinion gears. According to the investigating marine engineer, the lower pinions are not built for the torque despite Konrad stating that the combo should match (through 0.84 ZF 280's ). Too hard to sue Konrad in USA from Australia,

I brought QSD - 125(NZ built) surface drives with Veem 23" diameter , 35" pitch props props through 2.0:1 ZF's. 280's.

The match is not quite optimized yet, and tops out at 45 mph when the old stern dive combo did 50 mph (see you tube excalibur konrad cummins clips).

For a boat at 7815 kgs measured (17,193 lbs) what is the ideal surface drive gear ratio, propeller diameter, and pitch for these cummins max 3400 rpm engines I have?

> help help !

In my opinion you need a three speed transmission to get propeller speed . I have seen a article on a single engine 27' boat with duramax and Alison and it was pushing the boat to mid to high 70mph range.

From experience with similar size boats with diesels and surface drives 1-1 or 1.24-1 should be ok

942 torque plus 17,193 pound boat, plus https://www.youtube.com/watch?v=rXJwns7X1jo = broken drives

no doubt commercial size propulsion will work,
but stabbing the throttles like your pulling the entire busch gardens waterski ski team around for a parade lap is gonna tax the equipment.

beautiful boat, nice conversion

Dear Sirs, many thanks for the help threads so far. Roger down under.

https://www.youtube.com/watch?v=kUIghv6I48g

5 days till lamb, 4 for you, you'll get it sorted out

https://www.youtube.com/watch?v=SkUnemSg3dg

First, I don't know why people keep trying to cheap out and use and I/O with a Diesel, especially a 480 hp Diesel.

That said, if they wanted and overdrive it was to eliminate the torque, and being so it gets real pathetic when they won't hold 640 ft/lbs of torque even.

Your drive manufacturer should have the answer for you

Curious if an SCX or BMAX could take the strain and pain of those 480s. Not sure if you could get the gear ratio right. ASDs seem like the only logical conclusion

I don't think the BMax will hold any better than the Konrads he had.
No way the Bravo Shop will warranty them with that much torque in that heavy of a boat.

Konrads are significantly over rated.