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First FE flex/strut - OK?

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Old 06-20-2011, 10:17 AM
  #1
cowana
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Default First FE flex/strut - OK?

I'm constructing my first FE boat - a 32" cat from R2Hobbies.

There are a few threads on here about this particular boat. The design is nice and the sponsons are very sharp - the only negative is that the fibreglass is very thin. I sorted that by adding carbon fibre to the hull between the sponsons.

I'm planning to use a Leopard 4074 (2000kv) on 4s, with a Hobbywing 180A ESC.

Hardware is a HOR Racing strut and rudder with a 4mm flexshaft, going to an Octura X447.

I know 3/16" flex would be stronger, but it's too late for that now.

This is my first boat with a flexshaft - I've heard that the centre of the strut should be level with the bottom of the sponsons. This is how it's set up at the moment (see the photos). However, the boat is very shallow and light - I'm expecting it to sit high in the water, and it looks like about 50% of one prop blade will be out of the water when the boat is at rest.

My instinct is to put the prop lower so it is definitly submerged, but I thought I'd check with the experts first!

So; - is the centre of the prop level with the sponsons correct for such a shallow boat?

The motor mount is currently unglued and the brass propshaft is uncut - I'll wait for some answers before doing anything major.

Many thanks

Andrew
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Old 06-20-2011, 10:28 AM
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Default RE: First FE flex/strut - OK?

You have heard correctly. You may confirm your build with the photo and setup info provided in the [link=http://radiocontrolinfo.com/ElectricBuild/catamaran.html]Catamaran Hull Setup[/link] page.

Whether the boat is heavy or light the hull will run on the very bottom face of the sponsons. The prop will be 50% in the water and 50% out in theory when on plane. This is the surface piercing setup that is commonly referenced here. When at rest it may be 75%+ submerged.

This rule is just a "get you close" value. You may have to adjust it from here. Most of the time I actually increase the height of the prop shaft. However some people finds it performs very well for sport boating at the height given.

Ryan
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Old 06-20-2011, 11:15 AM
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Default RE: First FE flex/strut - OK?

I am in the procces of building a 36 inche atlas vanlines u-1 kit #1314 and your in formation would help me.
i see in your pictures you dont seem to have a water intake line??
what speed do you anticipate for the motor that yours has??
artnewton@shaw.ca
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Old 06-20-2011, 12:04 PM
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Default RE: First FE flex/strut - OK?

That is quite a bit of prop for a 2000kv motor on 4S. You might want to try a 442 or 445 first.

Are you running 4S1p or 4S2P ?
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Old 06-20-2011, 08:25 PM
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Default RE: First FE flex/strut - OK?

BackEMF - my mistake - that's actually a X445, not a x447. I've also got some smaller props to try to.

I'm planning to run 4S1P with 4000mAh, 40C cells, although I'm pretty likely to get another set and run 4S2P to get longer run times. The 4000mAh 40C packs are much smaller and lighter than I expected.

A
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Old 06-21-2011, 03:29 AM
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Default RE: First FE flex/strut - OK?

Start with a small prop and work your way up, lest you may smoke the ESC. Ryan will tell you to run for 30-45 seconds and check temps. This is a pain but you need to know where you are and with a fresh boat you have no idea. Even if the setup is mild you could have some binding or something. The first run is never the dream run you are thinking of, but it will ensure that you'll have a second run. Start small on the prop and take baby steps.
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