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

[G Doggett]

Hi Norbert
From the front to rear of the sponson.
Not including any overhang or extension of the transom.
This rule of thumb applies to monos and DV hulls also, but keep in mind this is not an exact specification.
Hull or sponson shape and speed must have some effect on the ideal sweet spot for the prop behind the hull.
Graham.

[norbique]

The rule of thumb for strut length is 10% of hull length to front face of prop. So for you 110cm hull the strut should be about 100mm.
Graham.

Sorry to ask this but how do I measure the hull length? Do I measure on the bottom from tip to end of sponson, OR on the top from tip to the end of the hull?!

Norbert

[astecme]

If in the U.S., don't run metric shafts! You'll have a hard time finding the mating tubing and props

K&S do the brass tube in Metric as well as imperial. It might be easier to obtain in their 3feet lengths in the US. This is what I use in the UK - imported from the US!!

[G Doggett]

Don't bother with SS bearing, brass or lead teflon works fine with plenty of lubrication, and if you use a 'hexflex' type coupling between your motor and shaft it will be supported just fine.
You can make it as complicated as you want of course, but I support the KISS principle of Keep It Simple, less things to go wrong.
Graham.

[G Doggett]

You can run inside just the brass tube and forget the teflon unless you need it for ease of strut adjustment. Most of the 'go fast' boys are running without teflon with great success. Less drag.

The teflon tube is used so that the struts can be adjustable.
I haven't used a brass stuffing tube from the strut to the motor, just a short heavy walled teflon tube with the front end supported by a bracket.
Works for me.

Lets not highjack this thread with the teflon versus brass argument !

Graham.

[norbique]

I'm in the EU, thus it's hard to decide whether to go with the US dimensions or the metric. I'm afraid in the end I will end up with Octuras, or other USA made props, which would be easier to mate with the imperial shafts and flex shafts. Tell me if my thinking is wrong.

[crabstick]

You can run inside just the brass tube and forget the teflon unless you need it for ease of strut adjustment. Most of the 'go fast' boys are running without teflon with great success. Less drag.

I concur. Teflon is not needed. It will only cause extra driveline drag IMO.

[sailr]

yes, get the next size up brass tubing as the stuffing tube. Grease the flexshaft with good quality marine grease (waterproof grease).

Are you in Europe or the U.S.? If in the U.S., don't run metric shafts! You'll have a hard time finding the mating tubing and props.

[norbique]

Thanks M. Sailr, I've heard this somewhere before and was about to ask anyway. So just run the flex shaft through the brass tube only, right?! When doing so should I pump the brass full with grease?, oil? what kind? Or just put some grease on the flex prior to sliding it in the brass tube?

Thanks Graham, I'm asking all these questions because I've never had a factory made strut or stinger in my hands. So I can't really imagine how they work exactly. I only made my own strut for the Hydromite, but that's a very simple unit, brass shaft running in brass sleeve. I grease it every now and then, and it holds up pretty well.

Another question: maybe I'm over "refining" (read: complicating) the strut and I was thinking of adding the SS bearing on the motor side of the strut, to support the prop shaft where it mates with the flex. Is it worth the trouble?

Also how do I know the diameter of the drive dog I'm going to use? I'm thinking of using 4mm prop shaft, so tell me what outside diameter drive dog goes there?

[sailr]

You can run inside just the brass tube and forget the teflon unless you need it for ease of strut adjustment. Most of the 'go fast' boys are running without teflon with great success. Less drag.

[G Doggett]

Yes it makes sense Graham. You you basically have a brass sleeve running full length of the SS tube acting as the bushing right? Interesting approach! Do you have Teflon tubing inside the brass where the flex cable runs?

How long should the strut be for this 110cm hull? Or how do I calculate it's length?

Yep, you got it. The stainless tube is the same diameter as the drive dogs, and is sleeved down with the brass tube that is fixed inside.
The brass slotted 'bushing' is only the length of the 3/16 stub shaft and can float or spin much the same as it does in a Speedmaster stinger.
The teflon tube is pushed into the inboard end of the tube until it is just short of the stub shaft and bushing.
I think from memory in my case the teflon was a bit of a sloppy fit in the tube so I sleeved it up with some heatshrink to be a nice push in fit.
Works great.

The rule of thumb for strut length is 10% of hull length to front face of prop. So for you 110cm hull the strut should be about 100mm.
Graham.

[astecme]

Allan, do those HOR/TFL or ETTI flex shafts come in counter rotating versions as well?!

They can. I do not list the LH lay for ETTI but do have LH lay 130 cable in stock. That is probably a bit light for you.

The TFL/HOR ones can be fitted with both Lays. - I do not stock the reverse lay but HOR are selling a pair of cables on Ebay. Johnny is very good and will I am sure supply a handed pair.

[norbique]

Yes it makes sense Graham. You you basically have a brass sleeve running full length of the SS tube acting as the bushing right? Interesting approach! Do you have Teflon tubing inside the brass where the flex cable runs?

How long should the strut be for this 110cm hull? Or how do I calculate it's length?

[G Doggett]

Hi Norbert
My drives are K and S stainless tubing with mounting brackets welded ( easyflow) on the top. If you have found the pictures this should make sense.
The mounting brackets take the thrust so the tubes are just forced into the back of the sponsons through rubber sleeves that allow a bit of up and down adjustment.
I used r/h and l/h wound flex cables from OSE with 3/16 stub shafts and r/h and l/h Octura X442 props also from OSE.
The 'bearings' are simply brass tubing with lube slots cut in them running inside another brass tube that in turn is pressed into the stainless tube. Does that make sense ?
Graham.

[norbique]

Hi Graham,
I found the picture showing your SS tube drives, it looks really nice but can you tell us more of the building process? Did you make bronze bushings on both ends? What diameter flex shaft did you use and where did you get the counter rotating flex shaft from? How did you seal the part where the shaft enters the hull?

I am thinking of putting SS bearings on the motor side. Maybe bushings on the prop side. I was thinking of getting two pieces of brass and drop it in the lathe to make the right shape.

I am thinking of getting lower KV motors and use higher voltage. 6S perhaps.
The Ammos look really nice, and those 100A ESCs would be Ok if they could handle 6S lipos. On the other hand I'd have to pay $45 only for shipping these.

Allan, do those HOR/TFL or ETTI flex shafts come in counter rotating versions as well?!

Thanks!
Norbert