help with Bravo 3 to Bravo 1 swap
08-09-2015, 07:51 PM
#11
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B3s can do over 70 as phragle said, but there will be more drag.
If you've optimized the B3, the question for your setup is: does theB3 have 7mph more drag than a B1? Or will the selection of props for the B1 allow you to optimize it that much more?
OTOH, you can pickup B1 lowers fairly cheap, so a try won't cost you a fortune. And it would be easy go get $ back if you don't like it.
If you've optimized the B3, the question for your setup is: does theB3 have 7mph more drag than a B1? Or will the selection of props for the B1 allow you to optimize it that much more?
OTOH, you can pickup B1 lowers fairly cheap, so a try won't cost you a fortune. And it would be easy go get $ back if you don't like it.
08-09-2015, 07:57 PM
#12
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OK, so, ,is there 7 MPH of drag? Am I correct in my assumption that the drag comes from the extra prop and not from the shape of the gear case?
I am willing to live with the issues of slow speed, out of the hole punch and as for "Cruse speed efficiency" what do you mean? WOT and Cruse speed are the same thing... "right"? I want it to be efficient at wot!
The drives are cheaper, the prop Sets are cheaper (and more available) To try it, what do I need? Can I just bolt on "any" B1 lower? Will the ratio be what I need? and if that is the case, My cupped 26 pitch dual prop spins 5200 RPM, Should I be looking at a 28 Pitch for the Bravo 1? (apples for apples do you use the same pitch prop on the B1 and B3 out drives?)
I am willing to live with the issues of slow speed, out of the hole punch and as for "Cruse speed efficiency" what do you mean? WOT and Cruse speed are the same thing... "right"? I want it to be efficient at wot!
The drives are cheaper, the prop Sets are cheaper (and more available) To try it, what do I need? Can I just bolt on "any" B1 lower? Will the ratio be what I need? and if that is the case, My cupped 26 pitch dual prop spins 5200 RPM, Should I be looking at a 28 Pitch for the Bravo 1? (apples for apples do you use the same pitch prop on the B1 and B3 out drives?)
Last edited by boating4me; 08-09-2015 at 08:05 PM.
08-09-2015, 08:38 PM
#13
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B3s should all be oilers so you will need a lower with the oil passage..SEI lower new under a grand... a used merc in decent shape about the same. Provided you dont tear it up, if you dont like it you should be able to unload it for what you pay for it. If you all about speed stick with 3 blade props. mirage etc.... with a 1.5 lower try to borrow a 26 and see if you pull it.
08-09-2015, 08:38 PM
#14
21 and 42 footers
Platinum Member
Yes, you can bolt a b1 lower right to your upper. It will be the same as a 1.50 ratio b1. Props will be a test but a 26 or 28 is the likely choice......I'd start with a 26.
Cruise speed refers to your speed at roughly 3,500 rpms.....which is where you are most of the time. If your B3 is running 45 mph at 3,500, a b1 will likely be running 3-4 mph SLOWER at that same 3,500 rpms.
Cruise speed refers to your speed at roughly 3,500 rpms.....which is where you are most of the time. If your B3 is running 45 mph at 3,500, a b1 will likely be running 3-4 mph SLOWER at that same 3,500 rpms.
08-09-2015, 10:15 PM
#15
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OK, so, ,is there 7 MPH of drag? Am I correct in my assumption that the drag comes from the extra prop and not from the shape of the gear case?
I am willing to live with the issues of slow speed, out of the hole punch and as for "Cruse speed efficiency" what do you mean? WOT and Cruse speed are the same thing... "right"? I want it to be efficient at wot!
The drives are cheaper, the prop Sets are cheaper (and more available) To try it, what do I need? Can I just bolt on "any" B1 lower? Will the ratio be what I need? and if that is the case, My cupped 26 pitch dual prop spins 5200 RPM, Should I be looking at a 28 Pitch for the Bravo 1? (apples for apples do you use the same pitch prop on the B1 and B3 out drives?)
I am willing to live with the issues of slow speed, out of the hole punch and as for "Cruse speed efficiency" what do you mean? WOT and Cruse speed are the same thing... "right"? I want it to be efficient at wot!
The drives are cheaper, the prop Sets are cheaper (and more available) To try it, what do I need? Can I just bolt on "any" B1 lower? Will the ratio be what I need? and if that is the case, My cupped 26 pitch dual prop spins 5200 RPM, Should I be looking at a 28 Pitch for the Bravo 1? (apples for apples do you use the same pitch prop on the B1 and B3 out drives?)
Last edited by picklenjim; 08-09-2015 at 10:23 PM.
08-10-2015, 11:42 AM
#17
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Merc recommends all Bravo III's currently for speeds up to 65 mph - years ago they listed it for 70 mph. I am not saying the Bravo III can not go over those speeds but stating what Merc lists and their recommendations.
One of the reasons is the faster most hulls obtain, more the hull comes out of the water (higher the drive will be as well) so with the extended length of the bravo III prop, trimming becomes an issue as the outside prop can grab air or too close to the surface of the water inwhich can cause problems especially in corners or banking ( small jist of info) .
Also not being able to trim high enough creates more drag hence another reason a Bravo III is slower on the top speed end. Two props in the water also creates more drag overall.
Claims of speed difference apples to apples could be 2 to 5 mph depending on all variables. I have never heard 7 mph difference between the B1 vs BIII - apples to apples.
One of the reasons is the faster most hulls obtain, more the hull comes out of the water (higher the drive will be as well) so with the extended length of the bravo III prop, trimming becomes an issue as the outside prop can grab air or too close to the surface of the water inwhich can cause problems especially in corners or banking ( small jist of info) .
Also not being able to trim high enough creates more drag hence another reason a Bravo III is slower on the top speed end. Two props in the water also creates more drag overall.
Claims of speed difference apples to apples could be 2 to 5 mph depending on all variables. I have never heard 7 mph difference between the B1 vs BIII - apples to apples.
Last edited by BUP; 08-10-2015 at 11:48 AM.
08-10-2015, 12:02 PM
#18
Gold Member
Gold Member
Hello,
I have a 1997 Chaparral 2335 with 2001 Merc 502 (warmed up by Teague to 500 HP) and a Bravo 3, the 26" Merc props have been worked (thinned and cupped) and take the boat to 64 MPH (5200 RPM).
I want more top speed (I am looking for 70 MPH) and I have been told ditching my B3 for a B1 is the first step (anyone agree of disagree?)
To swap to a Bravo 1 and I need help... I assume that the lower unit will bolt right on (right?) but I need help with gear ratio, Etc.
Is the Gear ratio in the upper part or is it in the lower unit (or both?). I have been told that I currently have a 2:1 ratio, what do I need?
Do I simply buy a lower unit (if so what ratio?) Do I have to change the gears in the upper? (am I better off buying a new upper and sell everything I have?)
Suggestions on Prop size? Suggestions on where to get parts? or suggestions on who in the Portland Oregon area would a good place to take it?)
Any help is greatly appreciated
Mike
I have a 1997 Chaparral 2335 with 2001 Merc 502 (warmed up by Teague to 500 HP) and a Bravo 3, the 26" Merc props have been worked (thinned and cupped) and take the boat to 64 MPH (5200 RPM).
I want more top speed (I am looking for 70 MPH) and I have been told ditching my B3 for a B1 is the first step (anyone agree of disagree?)
To swap to a Bravo 1 and I need help... I assume that the lower unit will bolt right on (right?) but I need help with gear ratio, Etc.
Is the Gear ratio in the upper part or is it in the lower unit (or both?). I have been told that I currently have a 2:1 ratio, what do I need?
Do I simply buy a lower unit (if so what ratio?) Do I have to change the gears in the upper? (am I better off buying a new upper and sell everything I have?)
Suggestions on Prop size? Suggestions on where to get parts? or suggestions on who in the Portland Oregon area would a good place to take it?)
Any help is greatly appreciated
Mike
08-10-2015, 04:53 PM
#19
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Swan? this is the kind of input I was looking for!
So, let me see if I have my numbers correct. Currently I have a B3 with a 2:1 ratio which means I have a 32/27 gears in the upper. If I find a B1 lower with a 15:19 ratio (is that the only ratio offered?) that would give me a final ratio of 1.50:1 (am I right so far?)
So, now that I have a 1.50:1 ratio and I know that I want to be running 5200-5400 RPM and I am expecting 70MPH What pitch prop and I looking at? Start with a 24P?
So, let me see if I have my numbers correct. Currently I have a B3 with a 2:1 ratio which means I have a 32/27 gears in the upper. If I find a B1 lower with a 15:19 ratio (is that the only ratio offered?) that would give me a final ratio of 1.50:1 (am I right so far?)
So, now that I have a 1.50:1 ratio and I know that I want to be running 5200-5400 RPM and I am expecting 70MPH What pitch prop and I looking at? Start with a 24P?
Last edited by boating4me; 08-10-2015 at 08:59 PM.
