psubill78

I have my drives being worked on right now by AADS... they said that the previous owner of our '98 310 DA regeared the Bravo 3's to have 2.43 on the bottom and 2.20 on the top. The boat is powered with 2x 5.7 V8, EFI, 260 horse each. This is a cruiser, completely standard 34' Sea Ray Sundancer. Definitely not a 'go fast'...

Per Sea Ray stats - the boat was built with 2.00:1, with a 24 prop.

The props that are on now, are 22P props, with the drives having the 2.43 on bottom and 2.20 on top.

I'm really confused at all this, and trying to understand why things are they way they are. And the experts in this forum seem to know lots of great things, so I'm hoping someone can shed some light.

The '98 was the 'first' model year for this style, and the '99 shows that sea ray moved to a 22P prop, but still a 2.00:1 ratio.

What would having a 2.2 to 2.4 ratio with a 22p do for my boat vs the 2.0 and 24P?

Any thoughts or opinions are welcomed.

mcollinstn

The numbers you have been given do not make sense.

A 2:1 B3 consists of a 27/32 upper set and a 16/27 lower set.
A 2.20 B3 consists of a 23/30 upper set and a 16/27 lower set.
A 2.43 B3 consists of a 23/30 upper set and a 13/24 lower set.

If you have a "2.20 top set" then you have 23/30 in the uppers.
If you have a "2.43 bottom set" then you have 13/24 in the lowers.

As you can see from above, there is no difference in a 2.20 top set and a 2.43 top set. Therefore, if you do indeed have 23/30 and 13/24, then you have 2.43 ratio.

If your boat came from the factory with 2:1 and a 24p prop set, then it probably ran around 42mph at 4500 rpm.

If you have a 2.43 and 22p props, then at 4500 rpm you should be running around 32mph. At 5500 rpm (you should be woefully underpropped) you should see 39mph.

Obviously, the first thing you need to know is exactly what gear ratio you have. The best way to do this is to have the boat out of the water, and to set up a video camera on the prop. Take a sharpie and mark one blade. Put the drive in forward gear. Use a socket and ratchet and turn the motor over hollering towards your camera "one,two,three" each time you make a full revolution. Do this 25 revolutions.

Go back and watch your video and at the point where the prop completes its TENTH complete revolution, take note of how many turns the motor made.

If it was 20, then you have 2:1.
If it was 24, then you have 2.43:1
If it was 22, then you have 2.20:1

MC

Itsallgood995

Was your boat originally from higher elevation? Some will lower gear ratios @ higher elevation for better performance. IMO, the lower gear boats accelerant harder than the higher gear boats with the same power. Think its the reason why the newer Baja’s switched to 1.65 B1’s. I believe the higher pitch props are generally considered more efficient as well.

psubill78

@mcollinstn - This is all completely new to me. I only know what I was told by George at AADS... I may need to ask for clarity. It is very possible I misunderstood LOL. He made it sound like what he saw was done for performance reasons....

@itsallgood995 - I don't have much history on this boat, so I can't answer that.

psubill78

OK, I actually wrote it down wrong. The upper is a 2:0, 27/32 and the bottom a 2.43 - a 13/24.

So - given that... I guess the big question is 'why' would they have done that, and given that data, what gear ratio do I actually have?

psubill78

Anyone?

I noticed with this ratio, and the 22P prop, I'm seeing a max WOT of about 4200, not the 4800 that the engine shows.

Itsallgood995

Just a guess but I would say roughly 2.19 ratio. I'm sure someone can confirm.

Seems like you should be towards the top of the RPM band not the bottom with that ratio? Full fuel, water etc?