Just wondering what the problems with both are.

I have a 7.5cc cat with a flex shaft and I wouldn't mind extracting all the power I can...

The problem with a straight shaft is the U-Joints required to get the driveline parallel to the water at the prop. I true and polish my flex cable ODs to try to reduce friction some, and try to use the largest possible radius bends in the stuffing box. I would like to try piano wire like the electric guys are now using. The smaller the diameter, the less friction. Something around 3mm might work on a .45???

i can get stainless flex shafts hich are the best of both worlds. you wont lose any power. [email protected]

1.
the problem with straight shaft is you do not achieve constant rotational velocity on the prop because you have to use two universals to get to the prop. This "banging" is hard on the motor, equipment and causes energy loss.

2.
the problem with straight shaft is they suck in terms of positioning the strut where it is most needed.

3.
Flex has neither of these problems as long as you keep it lubed

FLEX shaft all the way...in R/C boats you need change for conditions...moving the prop angle is impossible on straight drive to the prop. Flex allows you to be messy on the alignment part too, but I recomend you not be...it stills has to go around. No real loss in power to prop if you get a good flex shaft.....properly match to a good shaft tube...no flop inside a tube that is to big...loss of power then...

Happy Racing....ZooM

OH YA!!! drive shaft U-Joints are for cars not boats.... Dont put car parts in your R/C...powerboat

Speaking from YEARS of experience with both shaft styles the flex shaft has my vote. Before flex shafts, all of our boats were hard shafts with 'U' joints to get the prop shaft angle correct. We used water quenched drill rod rather than piano (music) wire because the latter is not straight. The other problem is the quality and durability of the 'U' joints. They wobble and wear resulting in vibration and constant maintenance. If you keep a flex shaft well lubed they are almost fool proof.

On the other hand, there are still people that use solid shaft drives in hydros. These are mainly purists, trying to set up their boats like the full sized ones. I have seen some of these set up so well that they can and do outrun the flexshaft boats

flex flex flex..... bah! sometimes u doesnt have any choice.... u must use a solid axel