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  #1  
Old 10-11-2004, 03:22 PM
Rosati Rosati is offline
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Solid VS flex shaft

I have been running boats for over ten years, but all of mine have been tunnel hulls. I have always set up the prop with drive dog parallel to the hull plus 5 degrees and they handle like there on rails.
Now that I am running the Miss Bud hydro, I have been looking into the driveline setup for potential improvement characteristics.
I understand the flex cable with a strut will provide a vast array of adjustment angles (limited only by the design) and the fixed shaft offers no means for adjustment.
The real question is coming, I promise.

Ok here it is:
Which is better to propel the hydro, the angled down straight shaft or the adjustable flex shaft with the prop running almost parallel to the hull?
I have seen both setups on nitro's and fast electrics while surfing the web and I don't fully understand the concept of an almost horizontal prop just pushing forward with no lift. I would think hydros NEED the angled prop to help in lifting the rear but does this sacrafice speed and handling?

Signed,
Stuck in the Mud
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  #2  
Old 10-12-2004, 12:37 AM
Chris LaPanse Chris LaPanse is offline
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The horizontal prop is a better stup. There are props made that are "lifting props" by design, and therefore, you do not need the downward angle. the flex shaft gives you so much more adjustability, that there really is no better alternative (except maybe music wire drives).
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  #3  
Old 10-12-2004, 03:40 AM
Hydro Junkie Hydro Junkie is offline
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I totally disagree with you on this one Chris. Having been around the scale boats for longer than you've been alive, I can honestly say either way works well. It is possible to make a solid shaft adjustable by not hardmounting the stuffing box to the hull. Granted, it still has adjustment limitations, but I've watched solid shafts outperform flex and I've seen flex outperform solid. It depends as much on boat balance, engine used and how it was prepared, fuel and driver as anything else. Bluntly saying one way works better, WITHOUT having run or built one, is like saying a Ford is better than a Chevy while you only drive Mopars. Just so you know, the downward shaft doesn't give nearly the lift you think it does. Almost all the scale boats I've seen REQUIRE lifting props, regardless as to which shaft type is in the boat.

Getting to the Pro Boat Budweiser, in this case, I would recommend the flex shaft. The reason I say this is due to the hull's internal layout. Having the radio box in the back like it is, you're very limited on how you can run a shaft and stuffing box. A flex will let you run outside the hull and avoid the radio box all together. It also lets you use the hole in the bottom of the boat from where you cut out the existing stuffing box and bracing.
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Old 10-12-2004, 11:46 PM
Watercadet Watercadet is offline
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HJ how about this? Flex shafts have less drag on them than a solid shaft that is not bearing supported, as in most direct drives, thereby making flex shafts more efficient. The "straight" shaft will never be straight, and the total contact area of the stuffing tube is stiffeling at best. That understood, flex shafts are faster than the solid shaft.
The ease of adjustability of a flex far surpasses a solid shaft. In this case the stuffing box is glassed into the hull giving NO adjustment. The motor mounts are not adjustable either.
Out of curriousity, how many of those scale hydros you see all the time and take pictures of use a solid shaft? Any pictures of one? I am thinking that they are flex shafts.

Rosati- yes we need lift to provide us with a proper ride but, not all the work must be done by the prop. The hull is our biggest asset. In my bud with a flex setup, I am trying lifting props so I can get the heavy back end out of the water.
There my .02
Adam
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  #5  
Old 10-13-2004, 02:46 AM
Hydro Junkie Hydro Junkie is offline
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Every boat with a solid shaft that I've seen has had needle bearings, making drag minimal. Just out of curiosity, how much contact area is there in FOUR NEEDLE BEARINGS? The four bearings combine both strut and stuffing box, and since flex shafts use BEARINGS in their struts as well, drag is a mute point. Come to think of it, I've only seen one solid shaft lose a prop, due to a missing prop nut laying on the table. How many props are lost due to failed flex shafts? As I won't see any of the guy's boats again till April or May, I can't take any pics till then. BTW, have you ever seen an Unlimited with a flex shaft? Both systems have their pro and cons. Either can be used in many cases and it's more often than not owners preferance to which goes in a boat.
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  #6  
Old 10-13-2004, 03:50 AM
Hydro Junkie Hydro Junkie is offline
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Just got to thinking about this flex VS solid debate. Just for the record, ALL BOATS RACING IN E-R/CU HAVE SOLID SHAFTS AND ARE GETTING OVER 40 MPH. That's using an Astro 25 5 turn motor and 12-14 cells. An added note, flex shafts are strictly forbidden by club rules for (at least) all round nose hulls. The catch to using a solid shaft is not to put the prop too deep. If a solid shaft is used in a hydro, the center of the hub at it's furthest aft point should be the same depth as the bottom of the sponsons for an initial position.
So WC, my question to you is "if the boats in E-R/CU have nonarticulated solid shafts and the afore mentioned electric drive, how can they be doing 40+ with stiffeling stuffing tubes and all that drag you mentioned?" How can they be going faster than the SMALLER, NITRO POWERED PRO BOAT BUDWEISERS? They even compare favorably to heavily modded Pro Boat Buds, so how can this be? I think your description of the solid shaft drive needs some reworking, don't you ?
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Old 10-13-2004, 12:33 PM
Rosati Rosati is offline
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So if a "lifting" prop is used, the shaft itself really plays no role in the speed. Since stuffing tube is out of the water anyway regardless of flex or solid. But the true difference is the angle at which the prop provides the lift and thrust? Hence the flex shaft will allow you to tune this angle allowing for maximum thrust and lift capabilities?

Anyone have pics of a standard prop and a lifting prop for comparison?
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  #8  
Old 10-13-2004, 12:53 PM
Hydro Junkie Hydro Junkie is offline
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On a solid shaft, the stuffing tube is only long enough to clear the bottom of the boat, while a flex shaft needs to be enclosed all the way to the strut to prevent tangling. Beyond that, you have basically got it. Sorry, but I don't have any pics to show you the difference, but then again, I haven't built a boat that didn't require a lifting prop. Just remember to not set the prop too deep(hub center even with the sponson bottoms to start) and I'm sure you will find a performance gain. I would also recommend putting on a larger skid fin and a heavier rudder assembly to handle the increased performance

Last edited by Hydro Junkie; 10-13-2004 at 01:00 PM.
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  #9  
Old 10-13-2004, 03:00 PM
Watercadet Watercadet is offline
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Quote:
?" How can they be going faster than the SMALLER, NITRO POWERED PRO BOAT BUDWEISERS? They even compare favorably to heavily modded Pro Boat Buds, so how can this be? I think your description of the solid shaft drive needs some reworking, don't you ?
They can be going faster because of more torque and higher RPM opperating a larger prop. An Astro 25 at 14.4 volts has WAY more power and torq than my .18. Lets compair apples with flex to apples with straight shafts. My Bud goes faster with a flex than one equally equiped with a straight shaft.
How long are the needle bearings you referr to? Too long and they would be almost as much drag as a tube with just a little less contact. And what if the needles are not perfectly straight? Not all flex shaft assemblys use bearrings in the strut. In fact I have not seen a single one on several years and that is including record holders from .12 to open twins. We use bushings in the strut that are very short to reduce drag and usually made out of a self lubricating metal.

My thesis remains the same. Flex shafts are more efficient there by making them faster. The flex is rarely touching the tube that is two sizes larger than the shaft and it rides on a thick cushion of grease! That is not to mention the ease of opperation.

Lifting props take energy that could be used to move the boat forward and push the boat upward. There will always be a compromise. I will post pics tonight of the two different props.
Adam
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  #10  
Old 10-13-2004, 03:40 PM
Hydro Junkie Hydro Junkie is offline
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You're comparing a factory shaft to your flex. I'll be the first to say the factory set up is garbage(but then again , I say that about the whole boat). What do you say we put this to the test and settle it one way or the other. I'm building an electric Atlas with a straight shaft, why don't you build one with a flex? I'm building mine to meet E-R/CU rules(which you can get from their website). Are you up for the challenge? BTW, the needle bearings I use for a 3/16th solid shaft have a 3/8th case with 3/16ths long caged rollers, which has probably got less drag than your flex riding in grease.
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  #11  
Old 10-13-2004, 04:05 PM
Rosati Rosati is offline
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Not to get in the middle of the debate, because I'm not really qualified to participate.
But in a K&B outboard, the flex shaft is curved at almost 90 degrees in the lower unit. I cannot spin that flex cable (totally clean, no grease) freely because of the bend. But if I place a new flex shaft in a new tube, again, ungreased, it will spin more freely than the curved cable.
Also, a flex cable will inherently 'wobble' more in the sleeve as opposed to the more solid straight shaft. This has to rob a % of the HP from the engine as it would in say, a race car turning an out of balanced driveshaft at high speeds.
Although in the greased sleeve, this would not be measurable in the RC scale of things.
What do you think?
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  #12  
Old 10-13-2004, 04:17 PM
Hydro Junkie Hydro Junkie is offline
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Why not jump in with the old .02? It's more fun to have more opinions to mull over. What I find as interesting is the one that really started this little debate(Chris LaPanse) hasn't jumped back in to defend his point of view. WC, I think you're doing too good of job, or do you think I hurt his feelings?
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  #13  
Old 10-13-2004, 05:23 PM
Watercadet Watercadet is offline
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Rosati I always pull the shaft out (in my OB too) after the day and put it aside to prevent the perma bend. Onder load the flex shaft will tighten and be just as "live" as a direct drive but with the ability to curve. The grease is very thin interms of its viscosity to the point of dripping. Others use blend of gear lube and Slick 50 and a ton of other combos that are super slick.

HJ no, I am not up to the challenge. There are a myrad of excuses but the fact is that I don't have the patience or the skill to work with wood.
Adam
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  #14  
Old 10-13-2004, 08:30 PM
Chris LaPanse Chris LaPanse is offline
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I'm going to have to defer to you on this one HJ. I've heard a little, which I basically summed up on my previous post, but you know a lot more about it. Sorry if my opinion misled anyone.
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Old 10-13-2004, 09:17 PM
dmack dmack is offline
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I've used both, and they both have good and bad points. I have broken a solid shaft, by the way, and lost a prop, so it can happen to either one.

For me what it comes down to is flexibility, pun intended. I have run both solid and flex shafts on my scale hydros, and I have decided flex is the way to go. It is now the only thing I run on all my boats.

For example: I just rebuilt my Miss Bud 1/8 scale and took a lot of weight out of it. After finishing my upgrades, I ended up changing the depth of my prop angled the strut to compensate for prop walk, and angled the strut downward for just a little lift in the rear. All of these changes were easy due to the flex shaft. I just slightly bent the flex tube so everything lined up properly.

When I got to the pond I realized the prop was a little too deep, I raised the strut, and re-bent the flex tube and was back in the pond in minutes.

That is the "flexibility" I am talking to about. The ability to try new set ups quickly and easily.
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Old 10-13-2004, 09:33 PM
dmack dmack is offline
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Lifting prop vs Non-lifting prop

Attached is a pic from the CMD website that shows both lifting and non-lifting props. The prop pictures in the middle is a lifting prop. The tips of the prop are rounded and flatened to throw water down as well as backward.
The other two props are non-lifting. They are designed to only throw water backward.

Lifting props are usually only used in scale hydros or outriggers that are a little heavy at the rear. The lifting prop helps to get the back end out of the water and put some pressure on the front sponsons to keep them on the water.

On my scale, the weight ballence is perfect and I don't need a lifting prop. I usually run it parellel with the hull, or with the slightest amount of lift I can dial in to keep a little pressure on the sponsons.
Attached Images
File Type: jpeg custom_props.jpeg (15.9 KB, 114 views)
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  #17  
Old 10-14-2004, 11:41 AM
Rosati Rosati is offline
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Thanks for the pics. I've never had to run a lifting prop since outboards have to keep the prop in the water. My props tend to run similar to surface drives when the hull is on plane but the engine is almost always tilted back to keep the hull from blowing over.
As I have said before, hydros are new to me but iI have always wanted to get one. Now that I have one, I think I may be focusing more on them in the future.
If I were to build one at this point, I would have to say it would be from scaled plans, with an adjustable flex setup, as peer the info here.
What would be a reasonable estimate of build cost? $1000-$1500?
Do the plans provide a detailed materials list or just the 3 plan sheets?
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Old 10-14-2004, 04:01 PM
Hydro Junkie Hydro Junkie is offline
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Cost is what you want to put into it, in all actuallity. Here is a rough breakdown of what it will cost to build an 1/8th scale boat:
A) $35.00 for plans, this includes frame sheet, layout sheet and color sheet
B) $5.00 for dummy engine plan, for if the boat had an exposed engine
C) $300.00 for plywood. This is aircraft grade from the LHS or mail ordered from Sig
D) $300.00 or more for engine
E) $100.00+ for hardware. A driveshaft and stuffing box/tube, strut, rudder and bracket, skidfin and bracket, engine mounts(preferably rubber damped), as well as nuts, bolts washers and any other pieces required.
F) $150.00 for Radio. It must be a surface band with a heavy duty rudder servo. An FM or FMPCM would be prefered as they are harder to get "hit" by stray RF
G) $100.00+ for fiberglass parts. These include cowlings and tail sets for most boats
H) $50.00+ for painting. If you can do it yourself, it's much cheaper. A custom professional job can cost well over $1,000.00
I) $75.00+ for decals. If you don't have to have them custom made, the average is about $100.00
J) $50.00+ for epoxy. Hobby shop epoxy isn't strong enough(so I discovered). I would recommend West Systems Epoxy. It's made for marine use and has a wide range of hardeners, fillers and who knows what else formulated to work with their base resin

There you have it. I left some areas generalized as you may pay more or less than someone else to build a boat. Some words of advice are:
1) Don't skimp on the plywood, hardware or epoxy. To hold up, the ply needs to be aircraft grade, with anything 1/8th inch and thicker being 5 PLY. Hardware should be a no brainer to the experienced boater, and epoxy I gave my recommendation above
2) Radios need a failsafe of some sort and a 100 inch/ounce or stronger rudder servo. Anything lighter won't be strong enough or last
3) Don't plan on a 2-56 or 4-40 pushrod to be able to handle the rudder. Depending on radio box location(usually in the front), most here in Washington use arrow shaft tubing from an archery supply house, with SHORT sections of 4-40 rod to connect each end to the rudder and servo. Also, the rudder arm needs to be on the right side of the rudder, so during the hard righthand turn, the rudder is pulled, rather than pushed

If you still want to build a boat and have more questions, give me a yell
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  #19  
Old 04-18-2012, 07:03 PM
aprelev aprelev is offline
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HJ,
I followed this thread and all you are saying here make 100% sense to me.
Would you please help me to find a source for 3/16 needle bearings, solid shaft and may be other stuff I need . I am building deepV /surface drive/ CMB 0.46/solid shaft. That kinda unusual as I see. Google can not help me .
I use to build FSRV in Europe.

Thanks a lot
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