Square Drives

[BradV]

I am putting the last touches to the SprintCat/1.0CMB which should be in the water real soon.

I've used a square drive set-up so the aft end of the flex shaft ends with a ferrule and the stuffing tube doesn't physically connect to the strut.

Now I've been told this is the way they are set-up - but I don't see much structural integrity with the stuffing tube not having any support on the end under the boat.

If I apply only a small amount of pressure with my fingers the tube can bend quite easily.

It seems like a compromise having the flex shaft itself doing the support and there would be at the very least frictional losses and at worst the stuffing tube could come away altogether.

So has anyone considered this issue and come up with a solution? One possibility is a skeg pinned into the bottom of the hull but I don't want any additional drag and if the skeg was glued in then I don't have any adjustment.

Any ideas appreciated.

 

[gil sonsino]

Do no worry about this flexibility this is the way this sistem works without any problem.Otherwise stick to the standard flexcoupler that works for me since my very first boat twenty years ago .

Gill

 

[BradV]

I'm not convinced Gil. I'm sure your right in that it will "suffice" - but I want to take the engineering aspect a bit further for the above reasons..

 

[Big Red Machine]

Been using square drive for 15 years and am confident you can do it with high reliability. If your stub shaft is being used to achieve alignment with the strut, then you'll have trouble. Make sure that w/o the stub in place your ferrule is pretty close to laying right in front of the strut (less gravitational effects). If you feel the need, by all means make a small wedge on the bottom side between the stuffing tube and the boat bottom to add some support. A narrow piece that is thinner than the tube is out of the flow and with the cat, it's above water anyway. By small piece I mean 2 inches long by whatever depth the tube is below the boat.

With an oiler and the right thrust bearings/washers, you wont have to mess with that greasy shaft at all during the season. You can take the motor out and leave the cable in!

 

[BradV]

Big Red yeah I was thinking of something along those lines, but I need to find out if aluminium can be welded to brass - not sure myself. Do you happen to know?

Also mind telling me more about the self-oilers? I gather because of the open shaft end any lube washes out quickly.

I'm using teflon lined inner and was planning on stuffing it with marine grease each run. Maybe that won't be sufficient..

 

[Big Red Machine]

No need to weld. Just scuff up the shaft with 80 grit and the bottom of the boat and epoxy in a wedge of plywood wrapped in pieces of fiberglass cloth.

Yes lubing every run is advisable. I am in the process of building a lube unit. You can use 1/2" pvc with end caps, add a nipple to fill it and one at the bottom opposite end connected to a nipple stuck in the tube and it will siphon out as the motor turns. Just use any oil like 5W30 and you will have to fill it about every run but it is easier than removing shaft.

 

[Mike G]

No need to brace it, nobody has on any cats I have seen. Just let the brass tube float, you will need to do a lot of adjustments, I have seen the strut 1/4" below the sponsons to 1/2" above, if you brace it you will never get 3/4" adjustability.

I like to see people do new things but you have to ask yourself;

1. Is it faster??? No, bracing will not add any speed.

2. Is it more reliable??? In my opinion no, I have never had any problems associated with the floating stuffing tube.

3. Is it easier?? :blink: I think not

So why reinvent the wheel?

Riggers that run Square drives have an even longer stuffing tube only supported at one end and it works for them!

 

[westoz]

I agree with Mike you should leave it floating for adjustability keep it simple.

 

[BradV]

Thanks guys.

Well as to adjustability I would have placed the support mid way to still allow for that.

I might give it a go left floating on the advice no one has had any failures. Still seems like a compromise to me and for whatever reason I've got mixed feelings about it.

I don't mind re-inventing the wheel if it goes faster and lasts longer!

 

[catman]

anyone know how to weld/solder/join a stub shaft to the flex cable, i am looking for a way to do this myself so i can run the stuffing tube right thru my strut and weld cable to stub, ive heard of people soldering it ?? the stub is stainless.

Cheers