Shortened Imco Drive

[PaulO]

Thinking about the 2" shorter IMCO lower unit for the 20 Cig. Question: When raising the x dimension as this effectively does, are you looking for prop ventilation or does that mean you have gone too far? Can your drive become, in effect, a surface piercing drive? If so, does this mean a different style prop? I believe I have a somewhat raised x-dim (only about 1 inch) now and when you trim too much, the prop ventilates and loses bite now. Is this the same ventilation you might get from a further raised x or does something different happen?
Let's go, dust off those brains! Its boating season!!
PaulO

[Looped]

Paul,
Man you’re on fire today with questions. For this question that you ask I do not have the answer for you, but I do have a question regarding lower units. Is there an aftermarket company that makes a dualprop lower unit that bolts on to a Bravo 1 upper unit? I really wish they still made the Blackhawk so that parts would be readily available.

Thanks,
Craig

[BigGrizzly]

The 20 Cig will ventelate if trined too high. A guy hear has one with a alpha. He says he has that problem. It does in effect does become a semi serface deive, some of the trim ability will go away. There are always trade offs with X dimention changes.
Clevers work well with raised X's

Randy

[CDMA]

Paul,

You said yourself that your boat needed very little trim to run right. If that is the case a raised x should work fine. While you are losing more of the ability to trim if your boat desn't need to muuch trim it might be a good comprimise. My only concern would be that if your boat is already up 1 and you went up another 2 you might be too high. The real only way to tell is to buy and try. Shouldn't be too hard to sell again ....maybe....best of luck
Chris

[PaulO]

Craig,
As far as I can tell, no one makes a dual prop replacement for the Bravo lower. I did quite a bit of Blackhawk research though and found that the parts availability is not the problem. Most guys that run these and are knowledgeable about them think there are plenty of parts around for the number of drives in sevice. The 2 problems are:
1. Will it work with your hull
2. Propellers

Most guys I have spoken to have had to spend a grand or more for propsets. This is bad enough if you know which ones you need. If you gotta test or, if you modify your engine, ouch!

As far as whether or not it will work with your hull depends on several things. How much trim you need (cause you don't get much) where your weight is located (effects how much trim you need) and what your x-dimension is. Although the drive is 9" shorter than a Bravo or Alpha, Mercruiser says it still requires and additonal 2" higher x-dim to get the most out of it. If you have all that and the right props, you can get 10mph out of it!
PaulO

[Donzitester]

If you dont need much trim to make the boat
"run right" then your x-dimension is not that far off. If it required a lot of trim to get it to run right then your too low!!!
But still buy the 2" shorter version!
You can always space it down 1" if its too
high, but if you buy the 1" and its not enough then your screwed.

[CDMA]

Donzitester....good to have you on the board...really interesting knowledge

Chris

[GEOO]

Paul, If you're looking for speed, save up and supercharge it. No screwing around, an instant 10-12 mph. The Imco is cool but it will only add 2-3 mph. GEOO

[CDMA]

Oh it is very good. Who else has as much experience driving as many different Donzi's as you? I mean you can say which boat is the fastest with the same power. I have a question for you though...how come the donzi's don't come with raised x dimensions from the factory???

Chris