Genesis prop shaft/strut height and angle

[JIM MARCUM]

Matt, cleaver style props are are designed for surface piercing operation. Placing the prop /driveshaft "1/8 lower than the rear sponson" will increase drag and may increase the "squirelly" handling factor. JIM

[JonD]

Matt, cleaver style props are are designed for surface piercing operation. Placing the prop /driveshaft "1/8 lower than the rear sponson" will increase drag and may increase the "squirelly" handling factor. JIM

Jim, thanks for the info. I never even realised that the prop was only half under water. Never gave it any thought. Just assumed that all props needed to be fully submerged to work. Shows how observant I have been - it's obvious now just looking at it! No wonder they produce such a rooster tail of spray.

So..... I did some Goggling and came across this interesting and informative article about Surface Piercing props - for dumb arse people like me

http://www.well.com/~pk/SPAprofboat.html

Cheers,
Jon

[Mattwarner]

Thanks jim!

[JIM MARCUM]

You are welcome, Jon & Matt. If you look at some of the SAW Utube posts by Tony (Propperchopper), you'll notice that a properly set up boat has a low & straight roster tail. Big high roster tails may look cool, but is inefficient & indicates a need to adjust the angle of the prop shaft dangle.JIM

[JonD]

Update on my Genesis prop shaft angle/height tests.

1/ I readjusted the prop angle to 0.6 degree (i.e. prop end of shaft slightly lower that horizontal, rather that the other way which it was before). No particular reason why I choose 0.6 degree - I just wanted something that was a bit "more" than horizontal, to try. Seemed to work. This brought the bow down a little and stopped any porpoising throughout the whole speed range. It looked good. However in doing this I ended up with the bottom of the strut being 3.4mm lower than the bottom of the boat. This was not by “good design” – essentially it was the result of simply pivoting the strut about it’s fixing screw. But I thought I would try it anyway.

Still got 60mph (97kmph) same as before, but right hand turns were quite bumpy, which they have always been (left turns are better).

2/ I then lifted the strut so that the bottom of the strut was level with the bottom of the boat as recommended, and kept the same 0.6 degree angle (had to very slightly shorten the stuffer tube to achieve this). I really couldn't tell much difference from the previous run. No porpoising, right hand turns still crap, but only achieved 94 kmph. Slightly reduced speed may have been due to slightly different battery charge or wind or a dozen other possible things, so I am going to do a repeat run next weekend, weather permitting.

Based on feedback from others on the forum, looks like I definitely need to try an offset rudder mod to get better turning, so I am looking at various options to achieve this.

I am hesitant going to the next size prop that I had planned (from M445 to M545) until I feel I have achieved the optimum set up and performance from the M445, and then I will probably have to start the whole set up thing again....

Anyway, it's all good fun! And I'm happy that I'm getting 60 mph out of the M445 prop, which is better than I was originally hoping for with this prop.

Cheers,

Jon

[JIM MARCUM]

Yea Jon, looks like you killed the porpoise. An offset rudder should cure the turn issues, and give you a bit more speed by getting the rudder out of the propwash. Congratulations on hitting 60MPH with your GENESIS! Next it's the old tweek-run-tweak for more speed & better handling. We all have to do it & it never ends. But it puts the FUN factor to FE boating knowing it's what YOU have done to make your boat better & faster. JIM

[iamandrew]

The Genesis never turns properly, you can do the offset rudder, but it looks crap.

I wouldnt really advise running the genesis at 100. it dosent sit on the water at anything over 80kmph.

Its not a turning Cat, if you want something to turn you need a wider hull, or a mono.