Twin Cat Strut assembly on a budget -> help please ;)

[norbique]

Thanks for the pictures Graham! I don't think I can get as close to the tunnel edge like you did, since the construction doesn't allow it. I'll put them as close as possible.

[G Doggett]

Yes, like this as close to the tunnel as possible.
Graham.

[norbique]

OK got it. So struts as close to tunnel as possible?!

[shockerman80]

out meaning left to right not forward to backward. It makes it really unstable when the are farther out. think left to right teeeter toooter one prop is in the water the other isnt what happens?

[norbique]

OK, Thanks Simon!

So in my case that would translate into 102mm at least? That's a 90mm strut plus teflon trust bearings and the drive dog right?!

I don't know where, can't find it, Shockerman said I should not let the props too far out the sponsons... Can you (Shockerman) confirm this? After all it's your hull design.

Since I can't get SS tubes, I'll have to stick to what I have. Brass tube, D: 8.5mm d: 7mm. Wonder if it will be strong enough with this wall thickness? It won't be as nice and shiny as a SS would be, thus I'm gonna paint it black or somethin'

I just need to find some good bronze to make the bushings from....

[Simon.O.]

Norbert, if you are looking for the set back from the rear planing surface then I can help.
10% of wet length is a minimum and up to 15% is a good area to play in. I have one cat that is now at 15% and the new bigger cat will begin there and go aft from that.
I have it on good authority that these are solid numbers and I have water time too to show my results.
Go for 10-15% aft and allow for adjustment if possible.
Those who make thier own hardware can send a strut anywhere.

I am watching your fine work.

[norbique]

How long should the struts be? From sponson to prop edge?
Boat length from tip to back of sponson is 102cm ~ 40"

[norbique]

It's not hard to understand. I got it. But a pic is always welcome.
I will have to cut open the transom bottom to make the box, but I'll do it if I have to.

[shockerman80]

use the normal 3/16 speedmaster stingers. Then build a box on the bottom of the hull at the transom so that the upper adjustment location can fit into. I know its hard to explain and i dont have the pics here now to show you ill see if i can get them for you.

[norbique]

i run twin speedmasters on my twin drive cat they work great/

Hi shockerman80! Can you be a little bit more specific?
It would be nice, since the cat in question is your balsa cat enlarged to 166%.

[shockerman80]

i run twin speedmasters on my twin drive cat they work great/

[norbique]

Thanks Allan! I respect your opinion, and it makes sense, but let's wait a little more for others opinions.
Looking at the dimensions the 580L is roughly the same size as the KB45XL right?! That's quite huge.

[astecme]

So I guess the XL10 will go faster - thats for two reasons...

1. small design change at Feigao gives more RPM in new motors
2. The 580 is REALLY Heavy - but all round probably has more torque to give.

[norbique]

OK Thanks!

This means my cat is only 105cm long. Can I get away with a 70mm long strut + Teflon trust bearing + drive dog ~ 80mm to the beginning of the prop?

Another thing:

I don't want to hijack my own, thread but I don't want to start a new one either just to discuss this. After long searching, learning, and studying I reached a point where I decided to go with the Feigao motors instead of the KBs. Although I've seen some vids made by Germans on Youtube running the KBs both L and XL with great success. I guess they all replaced the bearings as a first step. But it's working. For them at least. On the other hand I heard a lot of people who splutter the KB's calling them cheap rubbish.

So, I'll go with the more expensive Feigaos, (tell me if I'm stupid to do so!) only one question remains, I like two motors but which one to use?!

My Setup: (twin motor cat) / 6S 5000mAh 25-30C Lipo / ESC not really important here

I'm considering the following two motors: the 580L-08 and the 540XL-10.
Both have roughly the same KV yet one is a lot bigger than the other.

Here's what FEcalc showed me, picture attached: (Feigao 580L-08 on left / 540XL-10 on the right) with x632 prop

Please tell me what you think! Will the 2x 540XL-10 be enough for a cat of this size or should I go with the 580L-08 and don't worry about the extra weight?

My goal is to reach somewhere near 100km/h, while not killing the motors at the same time.

[astecme]

Don;t get too hung up over that. You need the prop to be in free water in order for it to work properly is all.