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Height of prop in water for hydro?

Old 11-29-2011, 05:20 PM
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vasek
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Default Height of prop in water for hydro?

Hey guys, I"m ordering some hardware, thus doing some sketching on the plan (Newton Renault, no hardware drawn). I'm going with the prop sticking behind the transom (see pic). How high should it ride? (approx)

In the "middle" of the strut adjustment, I've got the highest point of the prop aligned with bottom of the boat. Is that a good starting point?

Any info / links on the subject would be great!

Thanks
V.
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Old 11-29-2011, 07:33 PM
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Default RE: Height of prop in water for hydro?

Maybe posting the sketch will help. I haven't drawn in the prop yet when I took it, but the lower shaft is the correct height for having the tip of the prop at the height of the lowest portion of the transom.
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Old 11-29-2011, 09:14 PM
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Default RE: Height of prop in water for hydro?

Most set up the strut so that the middle of the shaft is even with the bottom of the sponson for an initial setting. From that point, there is NORMALLY very little adjustment needed to hit the ideal prop depth
Old 11-29-2011, 11:10 PM
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Default RE: Height of prop in water for hydro?

Thanks HJ! That's what I needed to know. BTW am using 1/8 scale hardware, the pic was just for illustration. Just forgot to mention that.

Since you're here HJ, my angle of the shaft (going through the hull) @ 20 deg angle to the horiz 0 deg datum line. Works good on the plan. Is that the standard or close to it? I'm electric powered (the motor is the size of a Coke can) and have it's quite close to the transom due to scale location of the "fake" engine on deck ( to hide it . motor's poking out a bit). The reason I'm posting here is the boat & hardware are all from nitro setup, so you guys know this stuff better

Thanks,
V.
Old 11-30-2011, 01:28 AM
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Default RE: Height of prop in water for hydro?

The angle through the bottom isn't what is important, it's how sharp the bends in the stuffing tube are. If you have to go with fairly sharp bends, you're going to add drag and wear to the cable and stuffing tube. This, in turn, will cause higher amperage draw and the associated wear and additional heat to the motor, batteries and speed controller. Over the long run, it can even cost you the prop and all the associated hardware if the cable breaks due to the excess drag. What you need to do when you get your boat partially built and before you attach the bottom is to set up your drive train as it will be in the boat when done. Next, spin the flex cable and feel how much drag there is WITHOUT CLAMPING THE CABLE TO THE MOTOR. If you feel a considerable drag, you need to make the curves shallower and move the motor forward , thus sacrificing the total scale look for performance. Another option would be to install a belly pan so the motor can be mounted lower, thus allowing you to move the motor forward and down to help eliminate the drag to the flex cable without sacrificing appearance. Something you should consider is that moving the motor forward may be required to balance the boat so installing it further forward, even if visible, may be a neccessity you will have to live with
Old 11-30-2011, 04:45 AM
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Default RE: Height of prop in water for hydro?

All good points! I'll check it as you suggest. Since I've moved the strut tube up a bit, the angles gets better. It's pretty crowded with the batts up front, 6x 3S 5000mah, it gets busy fast. It's a shallow space between the rails for this boat. If the controller fits alongside the motor, there'll be a couple of inches left for the motor to be moved to the front if needed but not much. I'm starting to be happy with the mock up, making some headway

One think I couldn't locate on the plan is the COG. What's the rule of thumb on that?

Thanks,
V.
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Old 11-30-2011, 08:46 AM
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Default RE: Height of prop in water for hydro?

Your hull must be legal. I don't keep up with the rules IMPBA or Namba. My thought is the strut must come out the bottom of the hull. Where you live may be different. Just a point to make. I like the ideal of getting at the strut for adjustments. My fat fingers can't get inside. You can use a setup board. Just a flat board with holes or slots for the rudder and trunfin
Old 11-30-2011, 09:23 AM
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Default RE: Height of prop in water for hydro?

AB, if he was living in the US, I would have made that point however, being in Europe, I wasn't going to get nit picky. AB is right however, if you have plans to ever race the US, the strut does need to come through the bottom of the boat forward of the transom. As for the CG, you should be in the range of 4cm, +1 cm behind the sponson transom to start with. This is where things get interesting however. This is a rough starting point that will most likely change with testing. Depending on how your boat turns out, you may need to add weight to move the CG forward or move your batteries or radio gear aft to get the boat to run well
Old 11-30-2011, 09:38 AM
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Default RE: Height of prop in water for hydro?


ORIGINAL: vasek

All good points! I'll check it as you suggest. Since I've moved the strut tube up a bit, the angles gets better. It's pretty crowded with the batts up front, 6x 3S 5000mah, it gets busy fast. It's a shallow space between the rails for this boat. If the controller fits alongside the motor, there'll be a couple of inches left for the motor to be moved to the front if needed but not much. I'm starting to be happy with the mock up, making some headway

One think I couldn't locate on the plan is the COG. What's the rule of thumb on that?

Thanks,
V.
Hey V, looks like you are really coming along nicely with your progress. A couple things I would like to mention and or suggest as you move forward. You have two threads going for your build in two seperate forum categories fast electric and now nitro. If you want to keep contributors and yourself focused you should try to stick to one thread or at least one forum category. Again, I am just making suggestions, but have you ever heard of Rum Runner Racing Forum? Not sure I can post a link in the open forum but you would be wise to check it out. There are a very knowledgeable group of modelers on there who do nothing but scale FE hydroplanes in 1/8, 1/10, and 1/12 scales. Not trying to poopoo the people in here but the guys on Rum Runner are really hooked up with reliable parts suppliers, proven parts combos, scale accessories like drivers, dummy engines, and cowlings...the whole sha-bang.

Hope this helps, enjoy your build.
Scott
Old 11-30-2011, 11:07 AM
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vasek
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Default RE: Height of prop in water for hydro?

A little teaser pic for you guys

Scott, the one in the electric forum didn't catch on, I'm using nitro designed boat, nitro designed hardware... I'm in the right place!

I did post at RR but didn't want to steal the thread. I've also been at Offshore Electrics Forums, that's where I've got the basic setup help. Good knowledgeable guys there, but since I'm a newbe at this I'm asking some basic (and sometimes dumb) questions & it's to novice for them to get involved ... So here I am, getting solid info here!

Cheers,
Vasek
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Old 11-30-2011, 11:10 AM
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Default RE: Height of prop in water for hydro?

OOPS, wrong pic.... I keep posting this & don't know why )))

this is the one:
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Old 11-30-2011, 11:19 AM
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Default RE: Height of prop in water for hydro?

I have a question for you. Did you already order/receive a plan sheet for the dummy Turbo Allison? It's possible to get many of the parts needed to build the dummy engine premade from several sources here in the US, if you're interested
Old 11-30-2011, 12:15 PM
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Default RE: Height of prop in water for hydro?

We have a few http://www.genuinehotrod.com/search/.../Model-Engines
I like ice-cream
Old 11-30-2011, 12:47 PM
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Default RE: Height of prop in water for hydro?

HJ, no I didn't know. Where can i get me a 1/8 scale Allison V12 turbo for my boat, pls post a link! Thanks!

V.

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Old 11-30-2011, 01:39 PM
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Default RE: Height of prop in water for hydro?

Since the person I deal with is a friend, I sent him a PM in another forum to get his okay first. I also asked for updated contact info so that, if he agree's, you won't have any problems reaching him
Old 12-02-2011, 06:08 AM
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Default RE: Height of prop in water for hydro?

more of newbe questions:

1) The rudder; what side? I've seen on both sides, left and right. What's theory?

2) Fin; I've seen right side only & both sides. Theory?

anyone? links are welcome!
Old 12-02-2011, 06:31 AM
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Default RE: Height of prop in water for hydro?

BTW
http://www.tdrcatalog.com/servlet/th...-engine/Detail [X(]
Old 12-02-2011, 05:03 PM
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Default RE: Height of prop in water for hydro?

RUDDER: Your choise. I prefer to install the rudder at the back of the left side engine bay wall. The main reason for this is you're pulling the pushrod to turn the normal direction, being to the right. To push the rudder can, and often does, cause the pushrod to flex. A second reason is that you're putting the rudder in a place where it's supported by the engine bay wall, the transom, the deck and the bottom of the hull

TURN/SKID FIN: Right side only. Having a fin on both sides will adversely affect handling and since you're only going to turn right at speed, a fin on the left side isn't needed.
Old 12-08-2011, 03:58 PM
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Default RE: Height of prop in water for hydro?

"Since mine is from plans only, I was trying to figure a way to replace the hard wood leading edge between the 5" rails shown on my plan & span a cf tube all the way in the sponsons & "foaming" it in the tips."

Could you show me, either on the plans or with a picture, where you are trying to remove this hardwood so I know where you're referring to?
Old 12-08-2011, 07:56 PM
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Default RE: Height of prop in water for hydro?

Honk, Honk..............
Old 12-09-2011, 10:35 AM
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Default RE: Height of prop in water for hydro?

HJ, not sure if you can see on the light prints, but the wide hardwood bloc shown in plan would be replaced with tube extending into sponsons & narrow hard wood leading edge @ front .
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Old 12-09-2011, 09:00 PM
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Default RE: Height of prop in water for hydro?

I prefer to use the solid wood bow block. It's easily shaped and easily repaired if damaged. To use tubing in the way you are showing can be done BUT it does have problems:
1) You almost have to wrap the front with glass to hold the deck in place
2) A hard strike and the thin wood shatters and the whole front of the boat has to be reworked, not an easy fix without taking the deck off
Old 12-11-2011, 01:46 AM
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Default RE: Height of prop in water for hydro?

OK I'll glass the bow. Since I'm not going to race the boat, there's not much danger to the front end + it's hard to get a hard wood block that size here [:@]

Thanks HJ
Old 12-11-2011, 07:04 AM
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Default RE: Height of prop in water for hydro?

We all started out saying I will never race that hull. Then one day it hits you You say I want to see what my boat will do against another hull. So build the hull legal. Even if go to sell the hull years from now, make it legal. Do you have clubs in Czech R? they may help. If no clubs to race with then do what you want.it's all legal
Old 12-13-2011, 01:00 PM
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Default RE: Height of prop in water for hydro?

Hey guys regarding "tail weight" of a 1/8 hydro , does 1.5 lbs sound about right? Read some stuff about tail weight being more important than CG. Any thoughts?

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