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Why is same boat 10moh faster?

T

tnsailorguy

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I have a 92 290 Sea Ray Sundancer with a 7.4 l 330hp mercruiser Bravo out drive. Starts and runs smooth. normal gear. Will run a little above 30mph at about 4000rpm. My neigbor on the dock has a 1993 Sea Ray Sundancer with same engine but a Bravo III outdrive. His is a little heavier as it has the standard radar arch. He claims to run 40mph. That is a lot of difference in my book. Does having the Bravo III make that much difference? If so I may consider switching.
 
Doesn't the Bravo I use a single prop while the Bravo III runs twin counter rotating props? One would think twin props moves more water then a single prop.
 
Lets convert this into an automotive situation. 330 hp in a truck with great all terrain tires will accelerate through the mud faster than a 330 hp truck with bald tires.
Duo prop gets better traction in the water, no wasted HP.
 
Yes..... you should see quite a performance difference between the BI/BII -vs- the BIII.

BTW, Volvo Penta owns the trade name "Duo Prop" as of 1983.
Duo Props are two different diameters and two different pitches, reverse of one another......., and apparently cannot yet be copied.

Merc on the other hand, must call their version, the "BIII".
BIII props are same diameter/same pitch... just reverse of one another.



I went from twin s/p's to twin Duo Props, and the difference on twins is incredible.
I've installed many DP's in single engine applications, and it does render quite an improvement.

.
 
A review of Bravo drive on e-bay showed several BIII at or about five grand. It would seem that is a reasonable amount for a new outdrive, too reasonable perhaps. For that money if it is a significant improvement I would be willing to take the plunge. Particularly considering I would have a new out drive and could probably get $1000 for my BI. Any thought?
 
He claims to run 40mph.
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The speedometer on my bost is 10 years old. I had it out for a short WOT run last week to see if a partial carb cleaning that I did worked. Low and behold it ran like a new one. BUT! The speedometer said the boat was traveling 50 mph (115 hp OB) and I thought that was impressive until I looked at the new GPS that said I was only traveling about 42-43 mph.

I would build up the other guy's ego about how great and fast his boat is and talk him into giving me a ride @ WOT. Tell him you are thinking of getting a BIII OD. Before you get on his boat, beg, borrow or steal a portable GPS unit and stick it in your pocket. Take your boat out and check your boat's true speed and compare it to your speedo.

Take the GPS w/you on his boat and turn it on when he fires it up and tell him you are looking at the contours of the lake. Watch the satellite tracked speed on the GPS. Then decide if you really want to fork over $5,000+ for a BIII drive while your BI still works.

I wouldn't let his bragging get under my skin especially if you find out his boat is really only traveling 35 mph at WOT. Keep the BI OD until it blows up. By then you'll want a new boat and perhaps Merc. will have a BIV OD that isn't affected by leaking shore power. JMO
 
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tnsailorguy said:
A review of Bravo drive on e-bay showed several BIII at or about five grand. It would seem that is a reasonable amount for a new outdrive, too reasonable perhaps. For that money if it is a significant improvement I would be willing to take the plunge. Particularly considering I would have a new out drive and could probably get $1000 for my BI. Any thought?
Click to expand...
You could just look for a bravo 3 lower unit, plus a set of props to try and save some $$$ instead of buying the whole complete unit.

FYI, For a new set of bravo 3 props, they go for somewhere around $600.00 each.;)

The guys over at http://clubsearay.com/forum.php? Seem to know their Sea Ray boats pretty well, I'm sure they may be able to help out with this question as well.

Good luck.:)
 
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