Re-drives Belt or Chain ?

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Rik-

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Bou


BorgWarner marine trans had bolt on reduction units that would go on the back of the FNR part of the trans. Bought many years ago, might be hard to find. I never mounted it but a simple flat plate adapter with a bearing and seal for the input shaft would do it.
These ”velvet drive” units use a planetary unit on the back of a 71 &72 models for the reduction. They still make these today. https://www.velvetdrive.com/files/7172.pdf
 

rv7charlie

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77 lbs is pretty reasonable for that HP rating. Is all new production aluminum, or is that an 'option'? Prowling the interwebs, I never saw any info on # of cylinders the drives are rated to operate with. Seems likely that the gas engine ratings are for V-8s, given the HP numbers, but it would be nice to have actual data.

We obviously don't need forward/reverse in an a/c (except possibly a seaplane), but there doesn't seem to be much weight penalty for having it. How is shifting accomplished? Is there an actual clutch, or just hard gear engagement/disengagement via internal oil pressure? The self-contained pressure lube/cooling system seems like a nice feature, too.

I did find one site with prices (~$5400), but no mention of whether that includes an adapter plate or coupling/damper assy to engine power to the input shaft.

Anyone care to share an engineering perspective on how a large dia prop in air compares to a smaller dia prop in water, related to bending/gyro loads and torsional issues?

Anyone have direct experience with one, even in a boat?
 

akwrencher

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I had one, long time ago. You just want the reduction part. Not the forward and reverse part. They are a hydrualic gear, oil pressure operation of forward or reverse clutch. One would need to test or reverse engineer the loading on the output. They are not designed for gyroscopic loads in particular.
 

Rik-

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I had one, long time ago. You just want the reduction part. Not the forward and reverse part. They are a hydrualic gear, oil pressure operation of forward or reverse clutch. One would need to test or reverse engineer the loading on the output. They are not designed for gyroscopic loads in particular.
‘Not true, they are designed to handle direct thrust loads from a spinning propeller which exhibits far more thrust than an aircraft propeller can exert. The boat propeller has, due to the medium being over 1,000 more dense as well as the added leverage with a prop shaft being over 10’ in length for most inboard applications, a gyroscopic load in 4 axis of motion.
 

Rik-

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77 lbs is pretty reasonable for that HP rating. Is all new production aluminum, or is that an 'option'? Prowling the interwebs, I never saw any info on # of cylinders the drives are rated to operate with. Seems likely that the gas engine ratings are for V-8s, given the HP numbers, but it would be nice to have actual data.

We obviously don't need forward/reverse in an a/c (except possibly a seaplane), but there doesn't seem to be much weight penalty for having it. How is shifting accomplished? Is there an actual clutch, or just hard gear engagement/disengagement via internal oil pressure? The self-contained pressure lube/cooling system seems like a nice feature, too.

I did find one site with prices (~$5400), but no mention of whether that includes an adapter plate or coupling/damper assy to engine power to the input shaft.

Anyone care to share an engineering perspective on how a large dia prop in air compares to a smaller dia prop in water, related to bending/gyro loads and torsional issues?

Anyone have direct experience with one, even in a boat?
Depending upon the HP, the Mass and the Velocity, a boat propeller exerts several thousand pounds of thrust load and typical side loading is 50% of the thrust loading. Being water is roughly 1,000 times more dense than air the size of the propeller does not need to be as large in diameter, but notice the blade area of a water propeller vs. an air propeller can be similar as there are (in todays applications) 4 to 6 bladed boat propellers with a diameter in the 24-36” range for the smaller HP applications

The new versions of the aluminum housing velvet drive are called the “72-LX” series. The velvet drive transmission use an old Ford “FMX” transmission 3rd gear assembly as it’s 1:1 and for reverse they use a planetary which is 1.5:1

The velvet drives use a band to lock up the clutch drum like a normal automatic style transmission. The input shaft turns a pump which builds the pressure for the band and the clutch pressure.

In the newer designs the parasite hp loss is in the 9-11 hp range.
 

rv7charlie

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Thrust really isn't a big deal with an a/c installation, so that should be a non-issue. But don't most of these systems use a U-joint drive shaft, with separate bearings in the hull to carry the prop shaft thrust & bending loads?

In any case, the BW website seems to indicate that only 1:1 ratio is available in the inline aluminum case. So not much use to us. Bummer.
 

akwrencher

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I think there is some confusion regarding boat propulsion loads. There are no significant gyroscopic loads on the output bearing of an inboard boat gear. A long shaft couples the gear to the propeller and there are one or more bearings on the shaft. Normal inboards do not use u joints, those are typical on inboard/outboard drives, which don't have inboard reverse gears. The thrust loads are going to be what they are, so much hp can make so much thrust. Thats not the issue. Issue will be bending loads from gyro loads. And weight. Always weight.
 

Rik-

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Thrust really isn't a big deal with an a/c installation, so that should be a non-issue. But don't most of these systems use a U-joint drive shaft, with separate bearings in the hull to carry the prop shaft thrust & bending loads?

In any case, the BW website seems to indicate that only 1:1 ratio is available in the inline aluminum case. So not much use to us. Bummer.
The thrust loads are directly coupled to the transmission flange which are transferred to the engine stringers.

The planetary reduction unit comes in many different ratios with some in the 2:1 to 2.5:1 ratio.
 

challenger_II

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The thrust loads will be on the rotables. If One doesn't have a good means of transferring those loads to the case (think "thrust bearing"), the unit will destroy itself.
 

rv7charlie

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Guys, there's likely to be more thrust load from the helical cut gears in the planetary gearset than any prop load. Bending loads due to gyro effects are *much* more significant.

Rik,
When I looked at the BW site, most versions listed multiple ratios, but the only ratio I could find listed for the *in line* 72L series was 1:1. Can you point me to the listings for other ratios?

Thanks,

Charlie
 

Rik-

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Guys, there's likely to be more thrust load from the helical cut gears in the planetary gearset than any prop load. Bending loads due to gyro effects are *much* more significant.

Rik,
When I looked at the BW site, most versions listed multiple ratios, but the only ratio I could find listed for the *in line* 72L series was 1:1. Can you point me to the listings for other ratios?

Thanks,

Charlie


this is the planetary unit, which bolts to the tail stock of the 72C and while the website is not up to date, they offer this with the aluminum case version also.

I only use the non planetary models as mine are in the 900 to 1500 hp range applications
 
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