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Scale Hydro Board This board is for the Scale Hydro fans!! Scale Hydros of all sizes - 1/16, 1/12, 1/10, 1/8, and even 1/6th scale.

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  #181  
Old 12-11-2010, 12:49 PM
mbarbee's Avatar
mbarbee mbarbee is offline
MarkB
 
Join Date: Jul 2007
Location: Colorado
Posts: 68
tail hop

Hi Capt!
Tail bounce with these under-hull, angled setups can be hard to figure out. There are two scenarios here and they require different solutions. First if your boat is bouncing on the straights at speed then you need to adjust the propeller weight. You measure this by balancing the hull (ready to run batteries, tape, everything) on the aft edge of the sponson. I've attached a picture of the rig I use. Under the prop place a postage scale. Make sure the boat is sitting in the running attitude. Generally this is slightly bow high. My boats run well with no hop at around 14.5 oz prop wt. The CG's are in the range of 2 - 2 3/8" aft of the sponson. There are lots of theories out there on rigging these hydros. This setup works for me.

Some theory..
As the boat bounces over the waves the prop will sink a bit. If the tail is too light it gets thrown up out of the water, the bow sinks a bit and that throws the tail back down again and the cycle repeats. This is particularly true of our scale angled drives where a portion of the prop is under the hull. The force of water against the bottom and the drive angle produce significant vertical forces. As Teach "teaches" us narrowing the cone of thrust can help minimize the amount of water being thrown in the vertical aspect as well as against the bottom of the hull. All these can contribute to hop. Weight can help counteract this inertia.

The other "hop" scenario occurs only in the turns. There is A LOT going on here... The geometry of rudder placement to prop, prop thrust cone angle, boat roll in the turn, the fact that you are slowing in the turn causing the tail to settle, and rudder angle all play a part. Reconciling all of this can be difficult. There are too many variables.
First check the angle of the rudder (fore and aft). If the rudder is angled so it's lower end is too far aft it will lift the stern up out of the water during a turn. The opposite is true when the rudder is angled forward. Very slight changes in this angle will make big differences.

So to fix your hop... Try changing the CG a bit more aft - get that prop weight up. Try a prop with a bit more cup at the tips to narrow the thrust cone. Check rudder angle. Move the prop a bit further back. Also one last thing. Solid, hard drive shafts tend to do this more that flex and thin wire drives do. The flex shafts tend to be more forgiving as they can "wind-up" a bit and absorb energy.

Good Luck!
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File Type: jpg IMG_1967.jpg (60.2 KB, 120 views)
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Rocky Mountain Hydroplanes
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  #182  
Old 12-14-2010, 03:52 PM
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Capt. Crash Capt. Crash is offline
Racer
 
Join Date: Jan 2009
Location: Millbrook, Alabama
Posts: 138
Thanks Mark...that explains a lot....and that is a fine looking boat you have there...:thumup:
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  #183  
Old 12-15-2010, 08:05 AM
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Capt. Crash Capt. Crash is offline
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Join Date: Jan 2009
Location: Millbrook, Alabama
Posts: 138
Here are some pics of the cooling fan and switch. Also note the suction tube, it ends at the bottom of the transom to allow a turkey baster to suck water out of the boat. It works really well.
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File Type: jpg P1040938.jpg (58.4 KB, 127 views)
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  #184  
Old 05-13-2011, 01:32 PM
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Capt. Crash Capt. Crash is offline
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Join Date: Jan 2009
Location: Millbrook, Alabama
Posts: 138
As for the turkey baster in the post above...it has been replaced with a hand cranked (fuel) pump and works faster at getting a lot of water out of the hull.

Here is a pic I took this weekend. The boat now has over a year of service and many miles of fun with no prolems. I am getting 40-45mph out of her on a pair of 5000 2s 40C Zippys...
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  #185  
Old 06-01-2013, 09:57 PM
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ron2010 ron2010 is offline
Racer
 
Join Date: Oct 2010
Location: brandon ms
Posts: 180
should have built 2 at the same time and sold me one lol good way to pay for your time
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  #186  
Old 06-21-2014, 08:12 PM
blowbuggy blowbuggy is offline
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Join Date: Feb 2004
Location: Dunnellon,Fl.
Posts: 28
cowling

Hey Capt. Did you build the driver and tail cowling or is there a prefab available? I need one just like it!!!! THANKS John jabullis@embarqmail.com
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  #187  
Old 07-02-2014, 03:37 PM
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studioRS studioRS is offline
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Join Date: Jan 2009
Location: Vermont
Posts: 176
1/10 scale hydroplane driver figure available from Classic Hydros.
http://classichydros.com/#!/~/produc...13&id=27252050

Rear cowling here
http://www.hydroscalecreations.com/C...s/Cowlings.htm
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1/10 1954 Breathless U-22, Tahoe Yacht Club | 1/16 1958 Dumas Thiftway Too, built in '92
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