Belt Drive Replacement - Gearbox

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DynaMarine
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Belt Drive Replacement - Gearbox

Post by DynaMarine » Wed Sep 25, 2013 10:22 am

A couple other threads are getting side-tracked so I thought I'd start this one. There has been talk and even some interest in having a gear-to-gear replacement for a belt drive, so why not just throw it out there for all to discuss. It think we can all benefit from it. From a manufacturer's standpoint we can understand the wants/needs of the consumer and at the same time it gives an opportunity to explain some things to potential consumers the pros and cons from a manufacturing stand point.

So for Ox and Ballistic, both of which have customers asking for a potential beltdrive replacement...lets throw a couple things out there.

The benefits of having a belt drive as mentioned by many i.e lower CG and thrust point, torque roll to the opposite side, quieter than most gearboxes that were on the market and possibly just plain reliability and availability.

From a manufacturing standpoint, initial rough numbers (based off initial prints - yes Ballistic has prints too) it would be more costly to manufacture a direct belt drive replacement than an existing gearbox. The overall size means that it would take a little more time to machine, higher cost on billet blocks (gearbox blanks), and an overall heavier unit. Can it be done? Absolutely. But will it be a viable option for customers? Dunno...maybe this thread will help determine that before any one company spends lots of money.

From the manufacturing side, we'd have more cost in billet, more cost in gears and shafts, and a little more machine time. Using established numbers from our current gearbox costs, I'd estimate that a belt drive replacement would retail around the high $4k low $5k mark. IMHO it's out of most retail customers price range. Would some people buy it? Sure, people dropped the $4-5K on clutch boxes, but you don't see the masses buying them hand over fist.

So for product development purposes, if you had to organize key features of a BDR from most important to least, what would they be? I'll provide the list, lets see hear some feedback.

1. Cost
2. Engine Height/CG
3. Weight
4. Direct replacement (bolt up w/o modifications to stand)
5. Sound
6. Durability or HP rating

Open forum...
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DynaMarine Performance Boats
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Bruce
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Re: Belt Drive Replacement - Gearbox

Post by Bruce » Wed Sep 25, 2013 10:34 am

if it fit the same hole was the same height and would last longer than a beltdrive
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Re: Belt Drive Replacement - Gearbox

Post by PeaRiverOpossum » Wed Sep 25, 2013 10:37 am

I guess my biggest question is "Why?" :dontknow: What are the cons of a BDR? If the belts are working, and they seem to be ,then why would anyone want to spend more for gears? Especially at a higher cost and who knows how much more weight. Or are we thinking about it more from building a gear box with the belt drive advantages point of view?

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Re: Belt Drive Replacement - Gearbox

Post by Bruce » Wed Sep 25, 2013 10:39 am

PeaRiverOpossum wrote:I guess my biggest question is "Why?" :dontknow: What are the cons of a BDR? If the belts are working, and they seem to be ,then why would anyone want to spend more for gears? Especially at a higher cost and who knows how much more weight. Or are we thinking about it more from building a gear box with the belt drive advantages point of view?
they are heavy and a bitch to change gearboxes are way easier but they arent as smooth and from what ive seen dont last as long
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Re: Belt Drive Replacement - Gearbox

Post by HuntingBigun » Wed Sep 25, 2013 10:47 am

Bruce wrote:
PeaRiverOpossum wrote:I guess my biggest question is "Why?" :dontknow: What are the cons of a BDR? If the belts are working, and they seem to be ,then why would anyone want to spend more for gears? Especially at a higher cost and who knows how much more weight. Or are we thinking about it more from building a gear box with the belt drive advantages point of view?
they are heavy and a bitch to change gearboxes are way easier but they arent as smooth and from what ive seen dont last as long

yep and boats are funny things about weight sometimes it is not how much it is but where the weight is, the other thing from oem like DB & GTO then they could have one stand if a customer wanted belt or g.b. Lot of boats built for out of fla do not want a g.b they want belt, for me here is my list

same rotation
same height for prop so no cage or deck issues
how much weight savings is Number one
bolt up replacement
cost well may not be for the replacement guy as much as a option for the OEMs,
Bigun

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Re: Belt Drive Replacement - Gearbox

Post by PeaRiverOpossum » Wed Sep 25, 2013 10:54 am

from what ive seen dont last as long
Which one don't last as long? I assume that you are referring to the belt but want to clarify. If that IS the case, what typically fails first? Belt or Bearings?
Between the belt and gear box, which is more economical to rebuild?

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Re: Belt Drive Replacement - Gearbox

Post by Bruce » Wed Sep 25, 2013 12:16 pm

Belt drive will last longer than most will ever ride but im talking gearboxes wont last as long
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Re: Belt Drive Replacement - Gearbox

Post by digginfool » Wed Sep 25, 2013 2:42 pm

As some of you are aware, I had my gearbox fail recently. After I opened it, I was surprised by the meager offering in bearing surface. Every bearing in the box was ball. I would have expected some means of dealing with thrust on the prop shaft; perhaps a cone roller bearing and at least one roller bearing on the drive gear to deal with load. That wouldn't add much weight to the box and would increase reliability, IMHO (the bearing that failed in my box is where I would have designed in a roller bearing to deal with load issues). However, it could possibly increase the depth of the box by as much as 3 - 4 inches, which is just an educated guess. Could be less.
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Re: Belt Drive Replacement - Gearbox

Post by Olf Art » Wed Sep 25, 2013 4:10 pm

Shane, one property of a gearbox (any gearbox) is that they steal horsepower. It's the reason that they get so hot in use ...... they're trading
off some energy to 'gear clash' ..... reversing the direction of rotation, and that energy is being converted to heat.

IMO the most efficient reduction drive ever built is a belt reduction. They last for literally thousands of hours in severe commercial service, require
no service other than a couple shots of grease once in a while on the upper and lower bearings, and a belt replacement can be done in less than
an hour by a competent mechanic and a helper. They're heavy.

The old 'Franklin' style drive led the way, but the Blue Lightning drive is, again in my opinion, a near perfect reduction. It's only shortfall is that
there isn't an outboard support for the lower (drive) pulley, which puts undue strain on the rear main bearing and seal of the engine. They're
lighter, all of the working components are right out in the open for easy service or inspection, and they transfer every ounce of energy the engine can
produce right to the prop.
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Re: Belt Drive Replacement - Gearbox

Post by digginfool » Wed Sep 25, 2013 4:47 pm

Belt drives have losses of their own. Not only from bearings but from the belts riding over the pulley sheaves; even more so if it is a toothed belt. It is quieter, lighter and more reliable than a chain drive (not that anybody would ever use a chain drive for this application) or gearbox (debatable about more reliable and probably not lighter) but it's not free transfer of energy. You do get to multiply your torque, though.
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Re: Belt Drive Replacement - Gearbox

Post by mad_mike » Wed Sep 25, 2013 10:15 pm

Cold weather operation. I use my boat year round......

Going between warm weather box fluid to winter fluid isn't so dandy when you consider my boat often doesn't come home from the field for 2-3 years. I go to it. A grease gun and wrenches are all I need with the belt box.

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Re: Belt Drive Replacement - Gearbox

Post by rbjscott » Wed Sep 25, 2013 11:46 pm

"Toothed belts" are the most efficient of the drives. About 20 to 25 % transferred power increase over v-belts. Maintenance is also reduced.
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Re: Belt Drive Replacement - Gearbox

Post by Olf Art » Thu Sep 26, 2013 11:20 am

rbjscott wrote:"Toothed belts" are the most efficient of the drives. About 20 to 25 % transferred power increase over v-belts. Maintenance is also reduced.
Yup ..... it's the reason that type belt is used to drive the superchargers on Top Fuel dragsters. The old term for a toothed belt is a 'Gilmer' drive, and they're very efficient.
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Re: Belt Drive Replacement - Gearbox

Post by Cowboy Rock » Thu Sep 26, 2013 1:57 pm

I am building a Belt drive for my boat using a Gates Poly-Chain belt with a Pillar Block on the crank.

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Re: Belt Drive Replacement - Gearbox

Post by Cowboy Rock » Thu Sep 26, 2013 1:58 pm

I am building a Belt drive for my boat using a Gates Poly-Chain belt with a Pillar Block on the crank.

:drunken: :rebel: :old_glory:

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Re: Belt Drive Replacement - Gearbox

Post by rbjscott » Thu Sep 26, 2013 2:48 pm

Geschwender Reduction Units---Look this one up, chain drive. Probable the best of the drives.
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Re: Belt Drive Replacement - Gearbox

Post by digginfool » Thu Sep 26, 2013 3:58 pm

Olf Art wrote:
rbjscott wrote:"Toothed belts" are the most efficient of the drives. About 20 to 25 % transferred power increase over v-belts. Maintenance is also reduced.
Yup ..... it's the reason that type belt is used to drive the superchargers on Top Fuel dragsters. The old term for a toothed belt is a 'Gilmer' drive, and they're very efficient.
You are absolutely right. However, the increase in efficiency referred to with a toothed belt is due to the better coupling created by the tooth; less slippage for a given transfer of power. You would need more belt surface, and thus even more losses from friction and more rotating weight from the larger pulleys, to match the coupling capacity of a toothed belt. What I should have said was 'although less so with a toothed belt.' The main point is that there is no free lunch; Olf Art stated every ounce of power is transferred with a belt drive when that is just not true.
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Re: Belt Drive Replacement - Gearbox

Post by Olf Art » Thu Sep 26, 2013 10:40 pm

digginfool wrote:You are absolutely right. However, the increase in efficiency referred to with a toothed belt is due to the better coupling created by the tooth; less slippage for a given transfer of power. You would need more belt surface, and thus even more losses from friction and more rotating weight from the larger pulleys, to match the coupling capacity of a toothed belt. What I should have said was 'although less so with a toothed belt.' The main point is that there is no free lunch; Olf Art stated every ounce of power is transferred with a belt drive when that is just not true.
You're right. I stand corrected. There is no free lunch, and when I said 'every ounce' I was painting with a very broad brush. Anytime there is a transfer
of energy there will be mechanical losses. That's a given.
But it's also true that a well designed gilmer type belt reduction won't give up anywhere near the estimated 13% power loss of a gearbox. You only have to look at their comparative operating temperatures to know that to be true. If it wasn't, a gearbox would be perfectly content running on 30W Mobil1 instead of that goo that they lube them with.

I'm not here to pick a fight, or sides for that matter. All I know is what experience has taught me. I know that a 'toothed' belt reduction is a highly efficient way of transfering power when compared to a gearbox. Aircraft engines were given gear reduction for two reasons:
#1 .... if the oil tank on that WWII fighter plane was full then the airplane was good to go, and #2 ..... rubber technology hadn't advanced to where we are now, nearly 70 years later, and even if it was I'm sure that flak and schrapnel damage would have been a problem too for a warplane.
But then don't mind me ...... my next boat will be a small block DD and y'all can spend those big bucks on a reduction anything. :)
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Re: Belt Drive Replacement - Gearbox

Post by jopete » Thu Sep 26, 2013 11:16 pm

i'm not a expert on much of anything, but if i drive around the seismic and airboat yards around south la, i would be hard pressed to find a gearbox. most every workboat has a century or old franklin belt drive on it. i don't know if the gear box hasn't made it's way over here yet, or if most people just stick with what has worked in the past.
heck, they just started using 2.3 to 1 ratios on the big blocks. it was 2 to 1 only since i was a kid. lol

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Re: Belt Drive Replacement - Gearbox

Post by digginfool » Fri Sep 27, 2013 9:26 am

rbjscott wrote:Geschwender Reduction Units---Look this one up, chain drive. Probable the best of the drives.
You sure about that?

"Fred Geschwender’s link-chain reduction used a 2” wide Morse Hy-Vo™ chain. It has been used successfully in several applications, including ag-planes and the early version of the LEGEND aircraft. However, the torque capacity for a 2" Hy-Vo (from Morse engineering data) is about 440 lb.-ft. at 4000 RPM, decreasing to 425 lb.-ft. at 4800 RPM, and decreases fast as RPM goes higher."

And further....

"Based on that design work, it is clear that a proper understanding of the load capacity calculations for this type of chain, along with proper design and engineering, could lead to the implementation of a reliable, low-cost, but HEAVY Propeller Reduction Unit using Hy-Vo™ chain, providing a wide selection of ratios ( from 1.4 to about 3.2 is pretty easy)."

It won't handle the torque of even a moderate automotive power plant and it's heavy, too. Not what most people are looking for. Another interesting point I came across:

"Belt drives are light, simple, and inexpensive. Those features have led to numerous attempts at belt-drive PSRU's. Those belt drive units are often claimed to provide lots of torsional cushioning between the engine and prop (after all, it's a rubber belt, isn't it?), but those claims are yet another example of the Wishful Thinking Engineering which is rampant in the experimental aviation community.

In fact, based on data supplied by manufacturers of high capacity tooth belts, the high capacity belts typically used in PSRU's depend on imbedded fibers of high strength polymers for their strength, and consequentially, they have substantially higher linear stiffness than common chain drives. That fact alone should be sufficient to show that there is no significant cushioning provided by a tooth belt, despite the intuitions that suggest otherwise.

The major issues with toothbelt drives can be summarized as follows:
1.The belt-PSRU’s are limited in power transmission capability;
2.Contrary to many marketing claims, the belt in toothbelt-PSRU’s PROVIDES ABSOLUTELY NO TORSIONAL ABSORPTION CAPABILITY (In fact, many of the high capacity toothbelts available have greater stiffness than chains of similar capacity)"

PSRU - Prop Speed Reduction Unit

Source: EPI Engineering, Inc.
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Re: Belt Drive Replacement - Gearbox

Post by Whitebear » Fri Sep 27, 2013 10:09 am

One of the things I saw working in Seismic with boats using the Franklin and Century belt drives was the belts in cold weather are tough and its nice to let them warm up at idle a bit before hammering the power to them. I never saw a gear drive working Seismic. We had a fleet of from 35 to maybe 50 boats depending on the mission at the time and none of our boats had gear drives.

Belt change outs were rare but were often accomplished in the field amid suspicions that the airboat driver wasn't driving according to our procedures.... Bearings on the old Franklin's required a trip to the shop.

We "almost exclusively" used heavy deep pitched wood props. We had maybe 2-3 boats with plasti props and they were not for everyone. The torque roll even with the big wood props was not objectionable at all and I certainly never considered it a hazard.

Thats not to say now that these belt drives could not be torn up, they certainly can be. Most common was early power before warmed up and quick stabs of power WFO and then right back off the throttle and then right back on it. We had a 3 second rule from idle to WFO and the same for from WFO to idle. We had another rule that was mostly for the engines that no more than 10 seconds at WFO then let off to idle or very low RPM for 3-5 seconds. Not sure this actually was an issue with the drives.

Over all in a fleet setting it was easy to see who ran according to procedures and who were the types to just gas it and go. The gas it and go guys were called belt wrappers. Any boats 6 month or annual history told the tale.

The state of the art has advanced a lot since then and I still have no experience with a gear drive though I sure have watched a bunch of them. My guess is that nearly all of the gear drives will provide reliable performance when handled and maintained properly, but just like the belt drive, I would guess you can tear one up if ya want to, but I see no need to just because ya know how.

In the last analysis, when its another man's equipment, you treat it like he says, if you own it and are paying the bills, drive it like you want to.
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