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Props

Old 11-29-2003, 01:05 PM
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pro27
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Default Props

What is the better way to go.........
a 2 blade prop or a 3 blade prop?

Maybe we can list suitable engine / prop combos...

What has worked well for you all?

Also list approx weight of hull , as this plays an important factor.
Old 11-29-2003, 01:28 PM
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TERBObob
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Default RE: Props

Well , for the RYOBI pushing a weight of almost 25 #'s (RTR) , I found that the MASTER AIRSCREW 16/10 3 blader worked better than an APC 18/10 2 blader and also the APC racing 16/10 2 blader .
Not being a airplane fanatic , or honestly knowing that much about them , I seeked out some info from fellows who have 30 to 40 years experience and they basically told me that if you choose a 3 blader , then you drop in size two inches . If you need to drop a regular 2 blader prop down in size , then you need to increase the pitch up a number or two . And also , was told do NOT use a straight size wooden prop . If you DO use a wooden prop and say for example you need a 18 incher , do NOT buy an 18 incher , but buy a 20 or larger abnd cut it down to the size you need - reason - the smaller wooden props will splinter easier under all that load and getting wet and all . ( sure don;t want a chunk of splintered wood flying at you at 7000 ( or so ) RPM's )
Old 11-29-2003, 02:56 PM
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pro27
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Default RE: Props

As a general Safety rule, WOOD props should be avoided at all costs on an Airboat. The risk of them destructing or recieving unseen damage from water spray or splash is too great a chance. They can do severe damage to the engine should it destruct while under power on the water. Wood props subjected to severe humidty (spray & splashes) can easily develope cracks that go unseen, until you put your starter to it.
I've had the opportunity way too many times in the old days of U/C racing and combat to have props destruct near my face. And this was under normal use.

There is an abundance of plastic, nylon and composite props out there that can make selection mind boggling.

Lets keep SAFETY in mind when choosing our props.
Old 11-29-2003, 10:20 PM
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rsieminski
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Default RE: Props

Right now I'm using an APC 10x4 chopped down to 9.5 inches with a leo .37. I had a 3 blade 9x7 but it just didn't have the acceleration. Top speed's gotta be around 40 mph. It's made out of a 36 inch boogie board and I don't know the weight right now, but I'll weigh it tomorrow. It's a lot of fun!

--Rick
Old 11-30-2003, 07:21 PM
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TERBObob
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Default RE: Props

40 MPH is a VERY respectable speed for an airboat . [8D]
Old 11-30-2003, 08:08 PM
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rsieminski
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Default RE: Props

I put a full width horizontal fin on it tonight to try and keep it down, i don't know if it helped or not. It still flipped over into the wind at full speed. I stripped the servo gear today?? I've never done that before on an airboat. Speed os more like 30 to 35. I was keeping up with traffic in the grass parallel to the road, and the speed limit is 30, but most do 35. The problem is, it's hard to keep going for any length of time in a straight line. I was thinking of putting 3 rails on the bottom. Maybe 1/8" high x 1/4" wide x 1/2 the hull. I don't know what to use though?? Any ideas??


Weight is 5# right on the nose, hull is 36 x 18.5
Old 12-01-2003, 01:06 AM
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pro27
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Default RE: Props

I do not normally add bottom strakes to the hull when I first built it. I like to see how it handles first. The only acception was the last Swamp Buggy I built, I went with the plan suggested strakes on the bottom. Now I will need to trim them 'cause they are too much.

What I normally do and works well for me is the following...........
I add three strakes to the bottom.
One in the center, 1/2 the length of the hull.
On both sides of the center strake, I put strakes that are 1/4 - 1/3 the length of the hull. These are positioned, centered between the center strake and the hull side edge.
All strakes end flush with the transom.
The front of the strakes are flatened to a point in front, heightwise.

Generally, I use 1/8 x 1/2 spruce and epoxy them to the hull.

I have found that using full length strakes makes the hull a bear to turn sharply. It wants to keep going straight. Half the hull length has shown me to be adequate enough to keep it running straight.
Having the outer strakes shorter, still allows me to slide under power but with enough rudder thrown in, will hook the transom enough to swing the front around for tight turns.

The most important thing though is this.............
Make sure they are straight !!! Or you will build in a pemanent turn that is hard for the rudder to overcome.
Old 12-01-2003, 09:04 AM
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Default RE: Props

Also , I noticed your from Florida , in which case , this won;t apply to you , but , for those who are going to run theirs in the snow as well as the water , no strakes . Flat bottom or you WILL not be able to turn in the snow . Grass and water are not the same as the snow . So for those that are building one to run on the snow AND the water , I would suggest flat bottomed . But if its water or grass , then as above ( PRO's thread ) is a VERY excellent idea !
Old 12-01-2003, 11:03 PM
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Mikie888
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Default RE: Props

I 'am in agrement with Terbo on the 16 X 3 blade , i have about the same set up he has,
25# to 30# boat , just a guess right now, 31cc Ryobi.....

I bought a 18 X 8 to break in the motor at Idle and about 1/2 throttle... And no wood props,
in the water may get wet an splinter...an knock a hole in the hull ,, [] good by air boat..

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