Mirage drive fin combinations

I am not sure if this has been discussed here before,,but a popular combination here in Australia seems to be Turbo at the rear with fin adjustment firm and ST at front fin adjustments loose.

Just wondering what others use and if anybody knows if the different combos place any strain on mirage drive parts over a long period of time ?

During tough economic times there are a lot of innovative ways to save money, but splitting a Turbofin kit with a buddy is quite inventive!


Seriously, the Drive will run OK and this combination is easier to push than a full turbo set. Unfortunately it's a false economy IMO. The fins should always balance each other. With an ST/Turbo combination, the larger fin is always overpowering the smaller, thus continuously rocking the boat back and forth. Much of the gain added by the Turbo goes toward wagging the boat instead of propulsion, with an increase in hull drag to boot. The end result is virtually no performance gain over straight STs.

In theory, there is something to be said for differential clew settings, changing the pitch of the rear fin to more efficiently capture the contra-rotating front fin. Ideally the rear fin would have less twist and more pitch set into the base. With a stock Turbofin there is no way to accomplish this. Tightening the clew does reduce allowable twist, but also reduces pitch. So more is lost than gained. As a practical matter the clew should be opened up to gain as much pitch as possible. The reward for this is a reduction of boat rocking and a gain in forward thrust -- you can feel it.

Finally, given that the total work effort is unchanged, the unbalanced Drive puts more strain on the rear fin area. The only potential problem I could see might be with the rear sprocket with an pre '09 Drive that hasn't been upgraded. There will be a greater tendency to unthread the allenhead screw and for the mast to more aggressively try to wallow its hole in the sprocket piece. That doesn't mean it will fail, but should just be watched and replaced or epoxied in place at the first sign of mast wiggling. The chain/cables, fins, masts etc should handle any additional load easily.

No doubt, the proponents will swear up and down about all the wonderful benefits of this rig -- misery loves company! In my opinion, the best use for this set-up is as a conversation starter. It's just a novelty and a poor performance investment (unless you have the matching fin!).

Thanks for the informitive reply RR.

I will keep an eye on the Mirage drive for undue wear,,i know at least one guy that had the full Turbo setup for more than 12 months plus ST setup as well before making the change,,its not something folks have decided on one day but after 100's of hour of water time and decideing the ST and Turbo set up is the best of both worlds.

I will try it for 12 months and see how it goes but so far i am pleased with the Combo.

Shorty, if it pleases you that's all that matters!

RR, i tried to edit this earlier but had problems.

I will give it a go keeping your feed back in mind any problems and i will revert back to matching fins,plus will let everybody know if there was any problems,,,cheers,,

Shorty, it didn't occur to me that you already had this combination or I would have taken a different approach. Sorry for any lack of sensitivity!

It's great to see people try different things -- whether it works out or not, it shows innovation and a willingness to take a chance on improving a product. I had been curious about this combo but hadn't actually tried it until reading your post.

It's always fun to experiment and learn. Thanks for sharing your ideas!