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Old 22-08-2010, 09:04 PM   #1
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Gear/Drive splitter???

Hi all,

Anyone seen or heard of one of these before? Idea is to rig one big motor, such as a blown BBC, to two normal outdrives, such as a pair of bravos mounted real close as in a staggered setup.

Yeah, there's twice the drag and allsorts, but also great stability and acceleration. From what I've read in the states they seem to love it, very, very popular on drag boats and starting to be seen in offshore too. There was a ski boat using 1500hp to do 120mph with a single #6, changed to two imco/bravo drives with a splitter and did 130mph with 1100hp! Could be an interesting solution to my problems

James
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Old 23-08-2010, 09:06 AM   #2
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I remember talking to someone about a system in 2005 at the Miami boat show - never heard any more about it though - I think there may be a commercial system available somewhere?
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Old 23-08-2010, 12:21 PM   #3
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is this what you are on about ?
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Old 23-08-2010, 05:46 PM   #4
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is this what you are on about ?
Spot on!! I think imco made them for a while, but at quite some cost!!

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Old 23-08-2010, 06:44 PM   #5
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Spot on!! I think imco made them for a while, but at quite some cost!!

James
I am sure that boat was rigged in 2007 so not long ago i will have a look on my facebook photos there should be more on there
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Old 23-08-2010, 06:51 PM   #6
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Cool, thanks for that! My email is larbys@live.co.uk if you want to send anything...

Cheers, James
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Old 23-08-2010, 07:40 PM   #7
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There are a few who tried it ....... cyclone , nordic etc.
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Old 23-08-2010, 08:26 PM   #8
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Man what a setup Now that is an innovative approach to spreading some serious GGs over the water-love it
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Old 23-08-2010, 09:06 PM   #9
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This might be of interest.

http://www.boattest.com/Resources/vi...px?NewsID=3230
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Old 23-08-2010, 09:28 PM   #10
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I have a unit for sale if you are interested.
The unit can handle 3000+ hp yes that's write.
2" input and output shafts its own oil system with David Brown Engineering custom straight cut gears.

1500
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Old 23-08-2010, 10:08 PM   #11
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Wow, finally I had an idea that wasn't just crazy!!

Thanks for the offer turbinator but it'd be a touch OTT for my application and far too wide!

Ben - That article makes really interesting reading! When I first dreamt up the idea I had no idea it even existed, let alone was so widely used!

Anyone got a link to a commercially available product??

James
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Old 23-08-2010, 10:48 PM   #12
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These could be a cheaper alternative

http://www.twindisc.com/IndustrialPr...0.html?pid=182
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Old 23-08-2010, 11:49 PM   #13
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Hi all,

Anyone seen or heard of one of these before? Idea is to rig one big motor, such as a blown BBC, to two normal outdrives, such as a pair of bravos mounted real close as in a staggered setup.

Yeah, there's twice the drag and allsorts, but also great stability and acceleration. From what I've read in the states they seem to love it, very, very popular on drag boats and starting to be seen in offshore too. There was a ski boat using 1500hp to do 120mph with a single #6, changed to two imco/bravo drives with a splitter and did 130mph with 1100hp! Could be an interesting solution to my problems

James
Hi James

I have been thinking about your idea for single engine twin drive. A second Bravo drive would add 100Kg plus 30-50Kg for a splitter box. Then I found this link to a discussion regarding single engine twin drive.

http://www.donzi.net/forums/showthre...t=55675&page=8

It would appear that Arneson may make a system using blower belts. May be you could find out how they do it, find a second hand pair of surface drives or Bravo drives and make your own splitter box using blower belts.

Was also wondering if the Arneson drop boxes with counter rotating shafts may have chain drive one side, gear driven the other side to give you same rotation input, counter rotating output. If this was the case you may be able to have a new case made to combine both drop boxes with single shaft input.

Just a thought
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Old 24-08-2010, 06:48 AM   #14
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Thanks for the link there turbinator!

Freddy - Interesting Idea there with the belt drive, that would be a much easier option! By running a simple gear setup in the middle, same sizes one above the other, that would give me my counter rotation, then I'd just need to run a belt from each pully off to each side respectively.

That said, if using bravos, there's no reason the shifting can't be done with the drive to give counter rotation, or with surface drives it may be better having seperate trannys to allow me to shift them individually for manouvering, though I doubt the effect would be that great with them mounted as close as in a staggered setup.

Another are where this helps is that I don't want to risk breaking my one and only drive, the reason I started all this. With the two drives, especially if shiftable individually, if I broke one, I could still use the other.

Back to surface drives, I'm currently discussing with someone who knows a vast amount more than me about what hull modifications I could make to enable me to use them. As Jon once rightly pointed out, they didn't seem to work on tanglefoot's standard hull, but hell, it's not like I'm scared of a little glass work!!

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Old 25-08-2010, 12:02 AM   #15
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I have been thinking more about your single engine twin drive idea. As Bravo drives already have gear boxes built in and parts are more available and a proven method with your boat it may be better sticking with out drives as opposed to surface drives. Have been giving some thought to you splitter box and it would probably be cheaper and easier to go the belt drive root if you are to custom build one.

I have belt final drive on my Buell XBR bike and it works really well, its about 35mm wide and handles about 100bhp. They are very reliable but the problem with bikes is that stones get flicked up from the road between the belt and the pulley and punch trough the belt, weakening the belt then they fail. But you would not have this problem. Most cars seem to use tooth belt drive and replacement intervals are 30-50,000 miles. Toothed belts are a pretty proven and reliable method for drives.

I was thinking of a design for you. First thing is one continuous belt or two belts one to each drive from a centre pulley. If one belt continuous belt fails you loose both drives. If you use twin belts one to each drive and one fails at full power all the power will go through the remaining belt and drive and could blow the drive so one continuous drive belt may be better, belts are cheaper than drives.

The best set up for belt drives would be to run them between two parallel plates with spacers. May be have one 1/2 oval aluminium plate bolted to the bell housing with a large hole trough the centre and a tooth belt pulley bolted directly to the engine fly wheel. You would need two spindles for the outer pulleys and flange plate bearings, these can be bought off the shelf from most bearing suppliers. The bearing housings bolted to the outer plates. The outer drive shafts could have a flange bolted to the so you could mount cushy drives with internal splines that locate the internal splines trough drive the spline shaft of the Bravo drives. There is a local company that make cushy drive plates similar to the drive plates on a Volvo Penta but with bravo drive splines.

Have done a quick fag packet sketch just to give you some ideas.

Regards David
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Old 25-08-2010, 08:14 AM   #16
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Belts in cars drive the camshaft not the gearbox though - there is also a lot more shock through a boat drive when the boat re-enters the water after a jump ............. just my thoughts ............
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Old 25-08-2010, 08:32 AM   #17
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I'm sure this is more a 'concept' conversation than something that'll actually get built, but just as an observation, the contact area (and subsequent number of rubber teeth taking the load) is rather small on the driving pulley using the single belt idea (driven pulleys each getting somewhere just over 180 degrees of contact, vs maybe 20-30 degrees on the driving pulley) Reckon you'd be stripping teeth off the belt pretty quickly unless horrendously over engineered (large) belts were used. I'd go with two belts, both with equal contact area on driving, & driven pulleys.

Also, the angle of incidence on the driving pulley / belt means very little belt to pulley pressure will exist, so teeth could jump/ride over (if not strip). having the idler pulleys closer to the driving pulley would improve things by wrapping the belt round the driving pulley a little (on the no-load side of course), but two belts would be better. JMHO.

Make sure you have a good rev limiter for when the rubber band snaps at WOT/load too. That sucker will pick up real quick at WOT when the load dissapears.

Also, remember that on the Revenger, with it's low topsides/deck height, the gimble is pretty high on the transom with a single (does it break through the rubrail ?) So on a twin, the gimbles will be a lot higher as they move out from centre, up in line with the deadrise (to maintain 'X' height) and you'd likely need to build up the transom to accomodate this.

The truth is, if you don't exceed 500hp (at circa 5k revs) your single Bravo will be fine (assuming it's in good order & you throttle it well). QED
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Old 25-08-2010, 11:28 AM   #18
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Hi Jon, yes you are right it was just a concept Idea and although it may have been done before by Arneson they have probably have very good design engineers and a large development budget, and it could conceivably cost more than the value of the boat to get it right.

As for contact area of the belt even with the drive pulley with a single belt and idler pulleys it would be difficult to get probably more than 2 x 70 degree contact so probably as you say twin belts would be better as you would be guaranteed at least 180 degree contact and also the load on each belt would be halved.

I believe Top Fuel drag cars are putting out around 6000hp and if my memory serves me right it takes around 10% of the power to drive the blower so the blower belt would be handling around 600hp so may be two blower width belts would handle around 1200hp.

As for belts breaking at WOT, I believe there was a discussion on this forum before about rev limiters and I am not quite sure why but if a drive fails at WOT engines exceed their rev limit. I would have thought that an engine management that cuts the spark at a certain revs would hit the rev lit and cut the spark to the engine thus stopping the engine from revving further but apparently this is not the case. Would be interested to know the answer why ?

Hi Cookey, “Belts in cars drive the camshaft not the gearbox though - there is also a lot more shock through a boat drive when the boat re-enters the water after a jump ............. just my thoughts ............”

Tooth belt drive will handle quite high shock loads, not sure of the foot pounds torque at the rear wheel of my Buell bike, but you can drop the clutch in first gear and being a 100hp V twin with a heavy flywheel they don’t break belts, and that is only a 35mm wide belt. There is also a V twin drag bike race series, think they put out about 600hp. The drive between the engine and transmission is belt drive so again with high shock loads off the line don’t think this would be a problem in a boat.

It is possible to develop a belt drive system but it would be experimental, take a fair amount of design and development and even if you got it right first time could easily cost 5k IMHO

As Jon says, unless you have a large budget and a lot of time and money probably better to keep it under 500hp, but on the other hand it is very rewarding to push the boundary's of engineering design and development and be the first with a new system. Whittle was told his idea would never work and look where the jet engine is now!!
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Old 25-08-2010, 11:57 AM   #19
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Hi Jon, yes you are right it was just a concept Idea and although it may have be
I believe Top Fuel drag cars are putting out around 6000hp and if my memory serves me right it takes around 10% of the power to drive the blower so the blower belt would be handling around 600hp so may be two blower width belts would handle around 1200hp.
You're about right in what you say about Top Fuel motors (I'm a massive drag racing fan), but they're only in use for 4 seconds WOT at a time... The belts let go on a run quite frequently. Offshore racing for long periods, with the shock loading of jumping (even with good throttle control) would knacker them pretty quickly I reckon.

Surely some kind of gear driven system with cushy drives linking them to the drives would be the most reliable option? Imagine the whine from your blower, and a set of straight-cut gears running each drive!!
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Old 25-08-2010, 01:22 PM   #20
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You're about right in what you say about Top Fuel motors (I'm a massive drag racing fan), but they're only in use for 4 seconds WOT at a time... The belts let go on a run quite frequently. Offshore racing for long periods, with the shock loading of jumping (even with good throttle control) would knacker them pretty quickly I reckon.

Surely some kind of gear driven system with cushy drives linking them to the drives would be the most reliable option? Imagine the whine from your blower, and a set of straight-cut gears running each drive!!
Generally blower belts fail due to the engine spitting back and stalling the blower, and I have just been corrected as I am a little out of date with Top Fuel and they are now putting out about 8000hp so 10% driving the blower would be 800hp. So two belts would allow 1600hp max,.under half the rating say 600hp and divided by two belts 300hp each. may prove to be a reliable system. The only people who could really advise would be the belt manufacturer. Would be interesting to get some facts and figures from them and see what they had to say, most companies would have an in house design and application teem. Some times they are very helpful on one off applications and projects

A belt drive system would be a lot cheaper and lighter as a one off and most of the components would be off the shelf, with the help of a small engineering company you could probably build most of it yourself. IMHO probably could build a prototype for 5k dependant on how much of the work you could do your self.

A gear box would have to be designed and built entirely from scratch by an engineering company. I am sure that Hewland Engineering Ltd (Motor sport transmissions) would design and build you one but would expect it would be 20-25k and very expensive to repair if it went wrong. Generally a gear box failure would could trash the whole box especially if it decides to exit through the casing, metal goes trough the gears and bearings. Belt failure, buy a new belt fit it and away you go.

IMHO belt drive would be a better way to go on a project like this. If it was me my first port of call would be a belt manufacturer and see if they think their belts would be up to it as if not that would be the end of the idea. IMHO I think it could be done and reliable too.
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