WakeWorld - Two Wheel Drive

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- Archive through August 27, 2006 (http://www.wakeworld.com/forum/forumdisplay.php?f=364702)

- - Two Wheel Drive - New Tech (http://www.wakeworld.com/forum/showthread.php?t=359915)

Check this out: <center><table border=1><tr><td><img src="http://www.wakeworld.com/MB/Discus/icons/attachment_icon.gif" align=left alt="image/bmp">Upload <a href="http://www.wakeworld.com/MB/Discus/messages/65921/Twin_Rig_small-359916.unk" target="_blank">Twin Rig small.bmp</a> (57.7 k)</td></tr></table></center> This is a MC with two props, two shafts, one motor. It is like 4WD in sand. It takes a lot less hp to make the boat perform. It has great hole shot, speed holding, and backs up straight. This has been picked up and is moving toward production. Maybe 08 on a main manufacturer's boats. Personally, I would like a 310hp X-Star, 226, or 247. Should save a lot of coin on engines and fuel.

<center><table border=1><tr><td><img src="http://www.wakeworld.com/MB/Discus/icons/attachment_icon.gif" align=left alt="image/bmp">Upload <a href="http://www.wakeworld.com/MB/Discus/messages/65921/Twin_Rig_small-359919.unk" target="_blank">Twin Rig small.bmp</a> (57.7 k)</td></tr></table></center> second attempt

Does MC not use a paddlewheel?

Hmm.. Conceptually sound, but I dunno about any sort of savings...all the money you save on gas would be gone the first time you rubbed a stump and had to pay to rework 2 props instead of one!

Wouldn't that have some kind of effect on the wake?

Doesn't the x80 have two motors... is that what that is??

To the contrary, if you jacked one prop, maybe you could still ride after removing the bad one? Or would it drive more crooked than an Epic with one bad rudder? <img src="http://www.wakeworld.com/MB/Discus/clipart/proud.gif" border=0>

Looks like it has 3 rudders. ??????? Can you make the pic bigger?

what about a duo-prop shaft drive?

I am retrofitting a Magnetohydrodynamic drive into my SAN.

Counter turning props should eliminate the poor steering in reverse problem.

I don't understand what the improvement is supposed to be. There would be a tremendous energy loss that would go into the extra gearbox, shaft seals, cutlass bearing and simple prop drag. I seriously doubt that you would regain this energy loss back from anything. There might be a lot less "slip" (which is NOT an energy loss) between the pitch of the prop and the motion of the boat, which might make RPM based speed control a lot better. If anything I would expect it to hurt the hole shot rather than improve it. Once you get used to the direction the stern walks in reverse it becomes your friend. I am not sure that backing straight would be an advantage.

Any of you ever see a boat with twins turn pretty much on a dime?? Should make control in reverse way better then even an I/O (single). Seperate throttles give the ability to have port in for. and starboard in aft.

I have owned twin inboards and yes, they can be made to pivot in a little more than their own length. But that requires independant control of left and right. The information provided at the beginning of this thread was that while it was two props it only had one engine, so I would assume only one transmission.

The tests show that the boat goes from 0-36 in 80 feet rather than 190. With 3,000 lbs ballst, it takes 88 feet. Sunk to the gunnels, in the 90's. Stock boat, would not get out of the water. With one prop off, it is worse than stock, but not much. Top end is also improved, but only by a couple of mph. The real observed benefit is hole shot and speed holding. The boat is used for show skiing right now. It takes over 20 skiers off the dock at the same time without bogging down. Yes, it works. This is one motor with two shafts, not two motors. Yes, you have two props that operate at the same time, so it won't pivot like opposed engines, but it still has improved manuverability. Production models will have a single tranny with two output shafts. The prototype pictured here does have three rudders. The kept the central rudder and bracketed off the other two. Production boats will only need two rudders since the water pushed by the prop provides the steering; the middle rudder does not do too much except at speed. This is real and it works. While Rod does have a point with extra gears, friction, etc., the extra traction makes a profound difference in how the boat performs on the low end. Between the reduction gearing and the extra surface area, the benefits outweight the penalty. If you get to demo one, it will make a believer out of you.

i have a picture of it, it is used in ski shows. It can pull a ski pyramid off the peir like NOTHING!<img src="http://www.wakeworld.com/MB/Discus/messages/65921/360614.jpg" alt="Upload">

Nice (Message edited by elantz on August 23, 2006)

Can we discuss retrofitting the magnetohydrodynamic drive in my SAN now? So far I have scrounged up some hose clamps, a bicycle chain and some rare earth magnets...

Possible someone did a photoshop job on the bottom of a 190?

No, Todd. This is real. If you are in West MI, you can see it with your own eyeballs. If you look closely, the hull and trailer are both modified. Lots of glass and welding, no photoshop.

"There might be a lot less "slip" (which is NOT an energy loss) between the pitch of the prop and the motion of the boat, which might make RPM based speed control a lot better. If anything I would expect it to hurt the hole shot rather than improve it." So you're complaining about the "energy loss" of a direct drive, single speed gearbox (practically nothing), then you claim that prop cavitation is NOT an energy loss? Are you kidding?

Bocephus: I think you need to talk to Mr. Clancy about your drive update. It would be best if the hull was red and you named it October.... Joe: By "slip" I did not mean cavitation. Cavitation is something that is pretty much unavoidable on any high speed prop working near the surface (anything less than 60 feet is "near the surface"). A prop has two surfaces of interest: the "front" and the "back". The back side of the prop is pushing water. Since water doesn't compress the back side can generate a lot of force to push the boat forward. The front side of the prop is trying to pull water towards it. Unfortunately, the water molecules are not connected to each other, you can't pull water. All you can do is create a lower pressure area and let the water flow in. The maximum pressure that the front side of the prop can generate is a function of the abolute pressure around the prop, which is atmospheric plus water depth. While the back side of the prop can generate thousands of PSI the front side can generate, at most, ~15 psi. Get the prop 32 feet down and it can generate 30 psi. Get it down 60 feet and it can generate 45 psi, etc. Until the cavitation get severe enough that it causes the prop to lose its bite on the water it does not significantly effect the performance or efficiency. "Slip" is a poor term for what I meant, but I can't seem to come up with the proper term. If your prop has a pitch of 13 inches, and it turns in an infinately viscous medium and somehow manages to have zero drag and the boat has zero resistance to moving through this medijm then it will propell the boat forward 13 inches for every revolution. In real life, things don't work so well. At any given speed the prop will be pushing water back to make the boat go forward. The boat moving forward is what you want, the water moving back is a necessary evil. If you calculated the theoretical speed that the "perfect" system would provide and compare that to what the boat is actually moving, the difference is what I erroneously called "slip". In general, a larger prop turning slower will be more efficient than a small prop turning fast. If you consider that the center of the prop is useless and does nothing but cause drag then it is clear that as the prop size increases you gain a lot more useable area. The dual prop would gain a lot more prop area, and thus reduce the slip. I would have expected the fact that there was twice the hub area would have caused an efficiecyy loss. I am wondering if the close proximity of the two props channels the thrust back in a more focused direction instead of having it fan out so much?

"Slip" is the correct term. Your analysis is basically correct. Cavitation can be a friend (ventillated props, surface piercing drives, etc.), it just has to be planned for. Two props too close can cause "hunting" or inconsistent thrust. You also have to also look at the space beteen the props and the hull and the props to the rudders. Lots of factors. Theory aside, it works and works well. Coming to a boat near you.