Strut for a direct drive shaft?

[Drobie]

I think I noticed in of one of Paul's boats that although it was set up with direct drive, he had mounted an (adjustable?) strut and bracket off the transom to stabilize the stuffing box.

Does anyone else do that on their scale hydros?

Does someone make a bracket that will hold a tube that's about 11/32" OD?

I also built a scale runabout that called for a skeg shaped fillet between the stuffing box and the bottom of the hull.

Has that been done by anyone? (I guess it would keep the stern from sliding a bit, but that slide might be desirable in a corner.)

[Andrewg]

Doug re the hydros

I think most people who run straight shafts use the hull and internal bracketing.

for an adjustable straight shaft a motor shaft connect using flex cable allow you to lift and drop the shaft. I prefer to seal the stuffing tube with a push rod seal and use a strut thru the floor of the tunnel at the transon. A bracket with a slot which is horizontal or parrallel with the floor to allow the "strut" to be adjusted more easily.

For a flex setup mount the strut bracket on the floor or on the inside of the transom.

I hope this helps

[Paul]

Hello Doug,

Check this out, I just finished putting this together. Is this what your talking about? My Spec Hydro wasn't adjustable but I did build a support off the transom that looked like what you described.

http://www.skullcaps.com/boats/micro5.jpg

Paul.

[AndyKunz]

Originally posted by Doug Robichaud
I think I noticed in of one of Paul's boats that although it was set up with direct drive, he had mounted an (adjustable?) strut and bracket off the transom to stabilize the stuffing box.

Does anyone else do that on their scale hydros?

When you say "direct drive" are you referring to a straight driveshaft vs. flex cable? or direct coupling to motor vs. gearbox?

On my straight shaft boats I found it much easier to mount the shaft using a standard strut. Then I started using the Graupner flex couplers, and voila - adjustable solid-shaft boats! Jeff Wohlt borrowed my Pocket Mechanic for a while which used this technique. It works great.

Does someone make a bracket that will hold a tube that's about 11/32" OD?

Yikes, why don't you just use plumbing fittings for that size tube?!?! When I use the Graupner 1157 setup, the large tube diameter makes it easy to build up a lifting skeg.

I also built a scale runabout that called for a skeg shaped fillet between the stuffing box and the bottom of the hull.

Has that been done by anyone? (I guess it would keep the stern from sliding a bit, but that slide might be desirable in a corner.)

The manual for the UL1 (see my site) hydroplane uses this technique with the Graupner 1157 drive system. It works well.

Andy

[Jeff Wohlt]

Have to say...the Kunz Straight shaft drive was fast and smooth. I liked that he used a typical Fuller Strut to run thru which made it solid.

Now that I have my UL strut adjusted to give max performace and know the setting, it would be much easier to run a straight shaft thru it with little difficulty and convert it. I think a person is better off running the shaft a bit shallower when installing and then propping dia size up.

Most of the adjustability on straight shafts I have seen is prop depth and not so much pos or neg thrust angle.

All I can say is after spinning a straight shaft thru bearings, you can really tell how free it runs. It keeps spinning and spinning with the flick of a finger...that has to be worth something in FE.

[Drobie]

Originally posted by Jeff Wohlt
Most of the adjustability on straight shafts I have seen is prop depth and not so much pos or neg thrust angle.

Pardon my denseness Jeff, but could you define "prop depth". Are you referring to a measurement associated with the prop size, or a way to move the prop up and down without adjusting thrust angle.

Note that I want to be able to run at Batavia, where a direct drive is spec'd (with a flex coupling not to exceed 2.5").

All I can say is after spinning a straight shaft thru bearings, you can really tell how free it runs. It keeps spinning and spinning with the flick of a finger...that has to be worth something in FE.

I'm making my own stuffing boxes with aluminum arrow shafts and bearings. I use hardened steel rod (and bearings) I get from http://www.psmescale.com. He stocks rod that is .001" short of 1/8" so it fits through the bearings nicely.

[Drobie]

Originally posted by AndyKunz
When you say "direct drive" are you referring to a straight driveshaft vs. flex cable? or direct coupling to motor vs. gearbox?
It'll be a straight driveshaft with direct coupling to the motor (using a Graup flex coupler).

11/32" Yikes, why don't you just use plumbing fittings for that size tube?!?!
I think the OD of Graup 1157 is bigger than 11/32", isn't it? I don't have my stuffing tubes here but they're a little more than a quarter inch and thinner than Graups.

It sounds like some people have the just the end of the driveshaft that protrudes from the tube held by a strut bracket that contains bearings. True?

[AndyKunz]

Originally posted by Doug Robichaud
I think the OD of Graup 1157 is bigger than 11/32", isn't it? I don't have my stuffing tubes here but they're a little more than a quarter inch and thinner than Graups.

Sorry - my brain is shorting out. I was thinking 11/16" - about twice the size.

I use glass arrow shafts or 5/32" ID brass tubing for mine. The arrow shafts are Dave Brown Pushrods. These are 9/32" to 10/32" OD and 1/4" ID - a perfect fit for the Boca SFR-144Z bearings (flanged, external) and SR-144Z (internal support).

It sounds like some people have the just the end of the driveshaft that protrudes from the tube held by a strut bracket that contains bearings. True?

Bushings for 1/8" drive.

Jeff Wohlt has pictures I drew for him a year or two ago to help him understand the adjustable straight-shaft concept.

Jim Clark should have some drawings or be able to create them from the info I've given him as well.

Jump in here, guys!

Andy

[Drobie]

Originally posted by AndyKunz
Sorry - my brain is shorting out. I was thinking 11/16" - about twice the size.
Not to worry. Because I was in a hurry, I was bit dislexic with the 11/32 as well.

My shafts are about 8/32 or 1/4", Graups 1157 is about 14/32" or 7/16.

It's good to know the Boca numbers. Their catalog gives me a headache....reading all those tiny measurements. LOL

Jeff Wohlt has pictures I drew for him a year or two ago to help him understand the adjustable straight-shaft concept.

Jim Clark should have some drawings or be able to create them from the info I've given him as well.

Jump in here, guys!

Yeah guys, jump in here!!

[Jeff Wohlt]

Doug, I don't think I still have pics of what Andy is talking about but with the flex connector it is possible to be able to tweak the angle slightly because of the flex connector but I was mainly talking about dropping the depth of the prop in deeper or shallower. Of course, you probably have to use RV sealant at the hull so it is flexible and then re-seal. Not much of a job you wanna do in between heats...that is for sure.

The main thing is after it is adjusted then you don't need to move it. You may get it close enough and then you simply use your batts to work your CG.

Andy has some good specs in his manual for depth and distance from hull that the prop should be at.

Running the UL boat with a 290/30/4 was cetainly the hoot for me! I did not even get it opened up and was already shutting it down. Faster than anything I have run.