Fiesta Vee 360 was stock from factory 496 Mags Bravo 3 with 2.0 Ratio drives

[Tri County Trail]

New to me 2005 Rinker Fiesta Vee 360 was stock from facoty 496 Mags Bravo 3 with 2.0 Ratio drives.
So here is my issue just checked my drive ratio while servicing my drives port drive 2 turn to one on output (2:1) while the starboard is 2.2 turns to 1 (2.2:1) It has a metal tag that states 2:1
WOT Port 4566rpm Starboard 4895rpm 39MPH
Cruise Port 4194 rpm Starboard 4217 rpm 34 MPH Port engine throttle advanced more apx 300 rpm
Did stall test both engines apx 2000rpm in gear starboard wot easily reached 4500rpm port barely made 3800rpm
I was starting to check port engine for lack of power but this ecplains the 400 rpm loss at WOT
MERCURY BRAVO THREE BOAT PROPELLER 48-823665 24P| (xx" X 24 P)???? INNER Both Drives Props Checked
MERCURY BRAVO THREE BOAT PROPELLER 48-823666 Mercury 24P (xx"x 24P)??? OUTER
Looking for thoughts run it, repitch props to gear rpm back on port engine, Running stock props change ratio

 

[keokie]

I'm not sure I am understanding your message correctly. But it sounds to me like a drive got repaired or rebuilt with the wrong gear set. If that is the case, the only proper solution is re-gearing so that both drives match.

 

[Tri County Trail]

That is correct but it is only off -400 rpm between drives at WOT 5000 rpm.
I see you have a similar power train as mine. what are your wot rpms and top speed with your 2.2 ratio drives. I drove mine last season and the 2.2 ratio defiantly is easier to great up on plane with not sure witch way I would correct. My numbers are Loaded 4 people full tanks 234 gal fuel 45 gal water and tools.
Length 39' 4"
Length w/Bow Pulpit 39' 4"
Beam 12' 3"
Bridge Clearance 13'
Displacement 18,400 apx 22,00 with drives and engines

 

[keokie]

Mt props are 28's. My numbers vary depending on how I am loaded and the altitude I run at. Lightly loaded and 1200' of elevation gets me 4800rpm and about 50mph.

As far as correcting the gears, 2.0:1 will put less strain on the drives. 2.2's are a little more efficient. You are pretty heavy for BIII's. I'd go 2.0 given a choice.

 

[Tri County Trail]

As far as correcting the gears, 2.0:1 will put less strain on the drives. 2.2's are a little more efficient. You are pretty heavy for BIII's. I'd go 2.0 given a choice.

the 2.2 would "put less strain on the drives" like using a gear lower in a car. higher rpm from engine at same speed.

 

[Mauler34Rod]

……or you could do this

 

[jmcdboater]

Mt props are 28's. My numbers vary depending on how I am loaded and the altitude I run at. Lightly loaded and 1200' of elevation gets me 4800rpm and about 50mph.

As far as correcting the gears, 2.0:1 will put less strain on the drives. 2.2's are a little more efficient. You are pretty heavy for BIII's. I'd go 2.0 given a choice.

I’m with @keokie, re-pitch back a bit on port main, good balance and port won’t be wiping it’s brow maintaining the extra 300…..

 

[Bill Curtis]

……or you could do this
View attachment 140797

I volunteer to be the "drummer".

 

[aerobat77]

As far as correcting the gears, 2.0:1 will put less strain on the drives. 2.2's are a little more efficient. You are pretty heavy for BIII's. I'd go 2.0 given a choice.

the 2.2 would "put less strain on the drives" like using a gear lower in a car. higher rpm from engine at same speed.

Imho not really . Final strain on a drive is gearing x prop pitch . The different gearing is only for matching a useful prop pitch for a given boat .

 

[keokie]

Imho not really . Final strain on a drive is gearing x prop pitch . The different gearing is only for matching a useful prop pitch for a given boat .

Actually, it isn't. Merc matches gear sets to power plants. They maximize efficiency for performance with smaller motors and lean to the side of reducing stress with larger motors. They have been doing this for decades. And they state that as the reason for the different gears. Lower gear rations apply more leverage to the propeller. More leverage is more stress. But higher pitch propellers are more efficient at creating thrust. So there is a balancing act. Just a few examples are:

When they put big blocks against Alpha's in the 80's they reduced the reduction ratio from 1.5 to 1.32 in order to help preserve the drive.

Bravo III's with 4.3 V6's come standard with 2.43:1 gears regardless of boat size, but you can order 2.2's or 2.0's. For small block V-8's it is generally 2.0's or 2.2's. You can only special order 2.43's for high altitude. Big blocks are 2.0, or even 1.81's. You can order 2.2's for high altitude. You cannot order 2.43's with a big block. Merc sticks to these numbers whether you are ordering a package for a 22' runabout, 27' single or twin engine go-fast, 30+ foot twin engine cruiser, or 75' houseboat.

 

[scoflaw]

I'd say the 2nd paragraph is false , a 1.32 ratio would put more strain on the drive than a 1.5.

 

[aerobat77]

Assuming the same boat is pushed by the same motor with the same speed but

A) with a 2.2 gearing and a 24 pitch prop or
B) with a 2.0 gearing and a 20 pitch prop

I still do not see whats the noticeable difference regarding strain on the drive . Motor speed will be virtually the same so the torque input will be the same and power output on the prop will also be the same since the same boat goes the same speed .

Only difference will be the second scenario will have a higher prop shaft rpm but with a lower torque after the gearing .

Its not a car in different gear since the tyre circumfence are the same regardless of gear - in a boat the prop is the tyre circumfence and we choose the correct prop for optimum performance .

I think different stock gearings by the manufacturer are offered to provide an useful variety of props for an assumed typical installation and not to control the strain but just my 2ct ;-)

 

[Bill Curtis]

Assuming the same boat is pushed by the same motor with the same speed but

A) with a 2.2 gearing and a 24 pitch prop or
B) with a 2.0 gearing and a 20 pitch prop

I still do not see whats the noticeable difference regarding strain on the drive . Motor speed will be virtually the same so the torque input will be the same and power output on the prop will also be the same since the same boat goes the same speed .

Only difference will be the second scenario will have a higher prop shaft rpm but with a lower torque after the gearing .

Its not a car in different gear since the tyre circumfence are the same regardless of gear - in a boat the prop is the tyre circumfence and we choose the correct prop for optimum performance .

I think different stock gearings by the manufacturer are offered to provide an useful variety of props for an assumed typical installation and not to control the strain but just my 2ct ;-)

Two things that has been left out is "slip" and "torque". In the analogy above, slip would be the High powered car with the low ratio rear gearing (ie: 4.56 vs 3.21's) will break the tires loose much easier. Add wider tires like slicks (proper designed pitch and cupping on the prop) and slip is reduced. This is amplified by the lower ratio gears exert less strain on the engine, (less restriction to the true engine torque) and the torque breaks them loose easier.

My 220 (at 3800 lbs) has the 454 coupled to a 2.0 ratio B3 with 28" pitch props. Leaps from a dead start, but the B3 tops about around 60 at WOT (I think this boat is over powered). My last boat was a 25.5 footer ( 5600 lbs) with a 7.4 coupled to a 1.5 ratio B1 w/ 19" pitch prop. About same speed as the 220 at WOT, but slower out of the hole, but no slouch.

The dual props on the B3 reduce "slip" (say like much wider tires), making it leap out of the hole shot, but the inherent B3 speed limitations keep it pretty tame on the top end.

Bet if that B1 was on this 220 with prop set with more pitch, like 21" or maybe a little more, it would be frightfully fast

Bottom line: Hull design, hull weight, trim tab size and application, engine HP and TORQUE, proper selection of drive ratios, prop style (number of blades), pitch and cupping are all rolled up into the engineering of the proper drive train for the application. Most of what we do is "spitball it" and hope we hit the sweet spot. Five of the same boats can have 5 different drive trains and all be pretty close, but can also have 5 of the same drive trains and all run different. Go figure.

 

[Chris-380]

New to me 2005 Rinker Fiesta Vee 360 was stock from facoty 496 Mags Bravo 3 with 2.0 Ratio drives.
So here is my issue just checked my drive ratio while servicing my drives port drive 2 turn to one on output (2:1) while the starboard is 2.2 turns to 1 (2.2:1) It has a metal tag that states 2:1
WOT Port 4566rpm Starboard 4895rpm 39MPH
Cruise Port 4194 rpm Starboard 4217 rpm 34 MPH Port engine throttle advanced more apx 300 rpm
Did stall test both engines apx 2000rpm in gear starboard wot easily reached 4500rpm port barely made 3800rpm
I was starting to check port engine for lack of power but this ecplains the 400 rpm loss at WOT
MERCURY BRAVO THREE BOAT PROPELLER 48-823665 24P| (xx" X 24 P)???? INNER Both Drives Props Checked
MERCURY BRAVO THREE BOAT PROPELLER 48-823666 Mercury 24P (xx"x 24P)??? OUTER
Looking for thoughts run it, repitch props to gear rpm back on port engine, Running stock props change ratio

@Coz had something similar to this on his sea ray. Not sure what he has decided to do

 

[keokie]

I'd say the 2nd paragraph is false , a 1.32 ratio would put more strain on the drive than a 1.5.

It is not false in application. A 1.32 would put more stress on the drive only if it were turning the same prop at the same rpm with the same load. And in that case the 1.32 boat would be going faster per revolution and therefore be doing more work per revolution. But in boats, we are supposed to prop for WOT RPM. So, the 1.32 boat would swing less propeller to achieve the same WOT.

Another way to think about it is a high pitch prop does more work per revolution than a low pitch prop. You make a low pitch prop catch up to a high pitch prop by turning the low pitch prop more times. Turning a prop more times to do the same work means the shaft turning it will endure less force per revolution. Less force per revolution requires less strength from the shaft (and connecting gears).

Hence, if you want to reduce stress on a drive, increase the number of revolutions it makes to do a given amount of work.

And in the case of the Alpha's with big blocks gear reduction was specifically used to preserve the drive. Merc said so out loud, and would not provide 1.5's with 454's. They would also not warrant blown alphas with 454's if the gear set was changed to 1.5. Old OMC 400's were a 1:1 to help their fragile internals hold even small block V8's. When they designed the 800, one of the marketing claims was the stronger drive allowed the use of more efficient propellors through their 1.5:1 gear reduction.

Further, the high perf outfits like Teague lessen gear reduction ratios on Bravo's to help them hold the torque of high powered built engines.

 

[jmcdboater]

Wow, you guys know a lot about the mechanics of boat engines and drives! I’ll tell you where I’m at….. when I turn the key if she makes a good sound and moves smoothly and consistently when I push front on them two silver handle things, I’m figurin’ it’s all good!

 

[Tri County Trail]

This is a chart I made. Still not sure if I will change out the 2.2 ratio for the correct 2.0. The 496 mags have a wide torque range and the rpm difference can be accounted for with the engine rpms.

 

[keokie]

I would absolutely change the gears. Not doing so is like running two different diameter rear tires on your Porsche.

 

[Tri County Trail]

Not really same tires but two engines running different rpm. Drove it back from Michigan that way. Drove it last season. That way, couldn't really tell at all. Just had RPM difference at wide open throttle tried plugs wires injectors fuel pressure everthing tried it. The drive ratio difference explains everything.

 

[scoflaw]

Gears are very expensive and sometimes hard to source.