props on cruiser?

[jeepman]

I have a 98 Regal 2760 cruiser with twin 4.3's and Alpha I's.

The drives have Mirage Plus stainless props with a 19P.

Top speed on the boat is about 38.

The newer boats, with this same motor but Bravo III's are running around a 23p prop and are getting speeds around 49.

A Regal rep said my boat should be running close to that same speed, and suggested that the boat maybe prop'd incorrectly.

Dry weight of the boat is around 8K.

As far as the hole shot...it seems slow, but always gets up even when heavily loaded.

Any suggestions? Is this the correct setup for a boat this size? Anyway to get some more top end out of it?

thanks!

[cajun]

I believe there is going to be a big difference from a alpha and a BravoIII.

[Throttle Up]

What is your WOT RPM? You should be runnning from 4400-4800 RPm at WOT.

Julie

[jeepman]

yep...I would say 4400-4800 or so.

[Throttle Up]

Ok,

Let's run some slip numbers. What is your WOT RPM and speed?

Julie

[jeepman]

WOT RPM 4700 Speed 38 (GPS)

[Throttle Up]

Is your gear ratio a 1.62 or a 1.81?

Julie

[jeepman]

ok...maybe a dumb question but how do I tell that?

thanks.

[jeepman]

Drive ratio is 1.81. Also would like to add that is a mirage plus prop.

thanks!

[Throttle Up]

The salesman must have been giving you a line. The 4.3 with the Bravo 3 came in either a 2.2 or 2.4 gear ratio. So unless the motor is turning about 6000 rpm it can't go 49 mph.

A 350 mag with a Bravo 3 (these had 2:1 gear ratio) turning 5000 rpm with 23 pitch props could go 49. I bet the salesman was talking abou a boat with more power than yours.

An alpha drive boat with the same power should be faster on the top end than a Bravo 3 boat. There is less drag. The adnatage of the Bravo 3 is the cruise speed, this is important on boats like yours.

Matt

[jeepman]

An alpha drive boat with the same power should be faster on the top end than a Bravo 3 boat. There is less drag. The adnatage of the Bravo 3 is the cruise speed, this is important on boats like yours.


I don't have the BIII

However, you can go here
http://www.regalowners.com/Lounge/topic.asp?TOPIC_ID=575&whichpage=1

and read all about the same boat, same power, but BIII drives going 10+ mph faster.

Now...my take on that is this. (maybe I am way off)

The guys running the BIII are running a different pitch prop...something like a 23P....so thats where they are getting the top end. (plus the ratio is different) And the reason they can run a higher pitched prop, is because of the BIII drive, which has a better hole shot than the alpha 1.

My boat has a alpha 1's with 19P props. The thing has a hard enough time getting up, and going to a 23P would kill it...I would think.

this crusier with 4.3 and alpha I's with 19P props...runs 40 at around 4600 WOT.

the same boat with Bravo III and 23P props runs 50. (dont know WOT)

[Throttle Up]

The fact of the matter is that mathamatically it's not possible to go 49 with the 4.3 and Bravo 3 drive with a 23 pitch prop.

A motor at 4800 rpm with a 2.4:1 gear ration with a 23 pitch prop has a theoretical speed of 43.5mph. With a conservative 10% slip this is a top speed of 39.2.

4800 rpm with a 2.2:1 gear ratio with a 23 pitch prop has a theortical speed of 47.5. With a conservative slip of 10% this is a top speed of 42.7.

Mercury only offered the Bravo 3 with the 2.4 or 2.2 gear ratio behind the 4.3 motor. Math doesn't lie. It's not possible for this combination to go 49 much less 51mph unless the motor turns 6000 rpm.

Based on these numbers if the same boat as yours has a Bravo 3 with the 4.3 motor and 23 pitch props it's going the same speed, or slower than yours.

Matt

[jeepman]

The fact of the matter is that mathamatically it's not possible to go 49 with the 4.3 and Bravo 3 drive with a 23 pitch prop.

Yeah...I hear what you are saying. Heck for all I know they have a 28P prop. I don't know the pitch for sure...but I know the boats just like mine but with a BIII drive run close to 50. While...my boat with an Alpha will barely hit 40 on a perfect day.

According to mercrusiers prop selector page...these boats would need a 28P prop to have a top speed of 48. That's with a 4.3 EFI and a BravoIII. I don't know how that boat even gets up with that pitch of prop...maybe thats where the BIII helps out.

that page also tells me I should be running a 20p prop and have a top speed of 45. :lol:

[jeepman]

The fact of the matter is that mathamatically it's not possible to go 49 with the 4.3 and Bravo 3 drive with a 23 pitch prop.

A motor at 4800 rpm with a 2.4:1 gear ration with a 23 pitch prop has a theoretical speed of 43.5mph. With a conservative 10% slip this is a top speed of 39.2.

4800 rpm with a 2.2:1 gear ratio with a 23 pitch prop has a theortical speed of 47.5. With a conservative slip of 10% this is a top speed of 42.7.

Mercury only offered the Bravo 3 with the 2.4 or 2.2 gear ratio behind the 4.3 motor. Math doesn't lie. It's not possible for this combination to go 49 much less 51mph unless the motor turns 6000 rpm.

Based on these numbers if the same boat as yours has a Bravo 3 with the 4.3 motor and 23 pitch props it's going the same speed, or slower than yours.

Matt


just bringing back up and old topic here.

If you read here....

http://www.regalowners.com/Lounge/topic.asp?TOPIC_ID=1154

this guy got his boat to run 48 with 4.3's, alpha 1's and a 19P prop. From reading everything above...this is "mathamatically impossible".

I find it odd, that all of these guys running 4.3's with either alphas or bravo's are running close to 50, and it's "mathamatically impossible" with the pitch of prop they have. Something tells me, someone's math is off.

[Elrod62]

Wanna get more top end? Dump the cruiser.

[xsnrg]

I rather doubt the BIII has a 23P prop. That would be spinning it way slow, even at 4800 rpm, given the 2.2 or 2.4:1 ratio. I would bet the prop on the BIII is closer to 26P or 27P.

For example, a 27P prop with a 2.2:1 ratio at 4800 rpm is 49.1 mph with a 12% slip.

Here is a page, go play on it:

http://www.rbbi.com/folders/prop/propcalc.htm

[jeepman]

Wanna get more top end? Dump the cruiser.

uhh...not my point.

My point is...I have a cruiser setup the same as other folks running 10mph faster. Something on mine must be out of wack. Therefore, I would like to try and figure it out, so that I can correct it. Thus, the reason I posted. I was hoping there would be some ideas generated on something I could possibly check. maybe I am missing something.

I do not want to go fast...I want my boat to perform as expected. It's not a "go fast" issue. however, thanks for your great suggestion. :roll:

[ksucat99]

Might also want to have a look at the alignment of your drives. One of the forums I regularly visit said they need to be slightly "toed-in". Someone here or at the Regal owners site might be able to give you exact figures.

Another thing you might check are the units on your GPS. Being a pilot I have all of my GPS's set to knots, which will obviously make a big (15%) difference in any readings. Just a thought. Good luck.