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BERTRAM BOY
04-26-2000, 02:38 PM
For all you Alpha owners who are worried about your drive being to fragile, check out Konrad marine's Omega SS. I don't know anything about them ,but I stumbled across it the other day and thought it sounded interesting. konradmarine.com

BERTRAM BOY

Forrest
04-26-2000, 04:45 PM
Konrad make some really good replacement drives. I like their Omega SS drive. Konrad drives are stronger than the equivalent Mercruiser drive. They always have a booth at the Miami International boat show. For a few years, they showed an Alpha compatible drive where the housing was built entirely out of bronze! I ask the rep about it and he said that it was a one-only since it was very heavy and that galvanic action between the aluminum gimbal housing and the bronze outdrive would be uncontrollable.

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Forrest

AVickers
04-26-2000, 04:49 PM
Well,

Turns out that there's still no good hope for us Alpha owners worried about breaking things w/ big motors. The Omega SS isn't available (although the picture looks way-cool). They are attaching this foot (w/ a 16" prop) to their 520 drive and it's under testing as I write...

I have volunteered to be a field tester.

The regular Omega is supposed to be heavier-duty than the regular Alpha, but the Rat motor comes with a 1.32:1 Heavy Duty Alpha (whatever that means...) so "heavy duty" may be a relative term.

The Omega is warranted only to 265HP.

BERTRAM BOY
04-26-2000, 08:44 PM
Only 265 h.p. That's kind of a bummer.
BERTRAM BOY

Forrest
04-26-2000, 10:39 PM
" . . . have volunteered to be a field tester."?!!!

How did you swing that?

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Forrest

GeneD
04-27-2000, 06:40 AM
Hey man, that 1.32 gear ratio is the BB ratio. Good stuff, it keeps the upper drive internal RPM's down and spins the bottom faster. The thinking is that the BB or high output SB has enough HP to turn a bigger prop. The newer Alphas got that new drive shaft that is supposed to handle more HP than the old ones. (Though I've never heard of any one of my buds breaking a driveshaft.)
I want one!!!!
However, I don't know if I would ever give up my SS now!
Someone should have taken advantage of my extreme displeasure of that mechanism when they had the chance! I would have just about given it away during that point!

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GeneD
007
Melbourne, Florida

AVickers
04-27-2000, 08:53 AM
They haven't accepted my field tester offer just yet... But I'm not going to give up!

As for ratios, my understanding for 1.32:1 is that the prop spins faster at a given engine RPM than with, say a 1.98:1 (which is what they use on some of the smaller-displacement engines). At 5000 RPM (engine), the prop behind a Rat would be turning 3787 RPM whereas with the in-line, the prop would be turning 2525 Rs.

My understanding is that they do this with the Rat to minimize side and end loads on the shafts, gears, and cases (bevel gears tend to push axially as well as tengetially as well as simply trying to push away from each other) 'cause these drives really aren't up to the torque loads that a Rat (or a tightly wound Mouse) can produce...

This would mean that a Bravo-equipped Rat (1.5:1 and slower prop speed) would run a higher-pitched prop than an Alpha-equipped Rat (1.32:1 and higher prop speed)-- all other things (like boat size and weight and engine Rs) being equal -- and they'd run at about the same speed.

Or am I working the ratio backwards?????

Forrest
04-27-2000, 09:33 AM
No, you are working the numbers correctly. One of the main reasons for the different gear ratios for different HP engines (i.e. higher ratio for big HP/torque such as 1.32:1, and lower ratios for the smaller HP/torque such as 2:1) is so that most all applications can be fitted with a common-size prop that falls within a certain range. For example, if you were to put a drive with a 2:1 gear ratio behind a 502 Mercruiser in a high-performance boat, you would most likely need a 30-plus-inch pitch prop to hold the RPMs down. Very few props are available from any prop builder in the over 30-inch pitch range. For that reason Merc couples their 502 to drive with a 1.32:1 gear ratio allowing a mass produced 19- through 25-inch pitch prop to do the job for most applications. On the other hand, certain gear ratios may work out better for certain applications such as the case with GeneD's 007 using a 1.8x:1 gear ratio coupled to a 350 Chevrolet. In his case, this lower ratio allow him to turn a 25-inch pitch prop at lower (prop) RPMs. Since higher pitch props are more efficient (less % slip) in a high-performance hull, GeneD and 007 goes faster than with his original 1.32:1 ratio turning a 21" or 22" pitch prop.

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Forrest

seano
04-28-2000, 06:22 AM
i hate math