rcbif

Ok, I'm building an 18inch boat as seen here
http://www.scale4x4rc.org/forums/showthread.php?t=35141

and soon I'll be getting to the part of installing the drive tube or stuffing tube thing. Yes this is my first boat.......I was wondering if this would be an ok shaft for my boat?
http://www3.towerhobbies.com/cgi-bin...?&I=LXCSZ1&P=7
The brass tube is the stuffing tube, with the flex shaft inside, correct? And the brass tube gets exoxied into the hole in the hull? Is there a method to the madness of creating the crazy enongated hole in the hull? Thanks for any help, this is my first boat build and I am enjoying it, and would appreciate any other comments/sugestions!

mfr02

Does it actually need a flex shaft?

pompebled

Hi rcbif,

You have a few options:

1) Underwater prop; doesn't 'need' a flexshaft, but the flexshaft can be used to make the propshaft run parallel to the keel, you'll need a strut to hold the propshaft in position.
2) Surfacepiercing prop, the propshaft exits through the transom and the prop is only submerged one blade at the time, this is the faster option of the two.A strut is optional.
Again, a surface drive on a non stepped hull doesn't require a flexshaft, a solid shaft will do nicely, provided the motor is in the front half of the boat, so a long shaft gives you a shallow propshaft angle.

Regards, Jan.

sportygreg

My Feedback: (2)

I usually cut a slot in the hull long enough to accomodate the angle of the shaft and cut the keel slot as well.Test fit the shaft then use doublers on the keel for strength.Tape the hole as best you can on the outside of hull then use epoxy to seal the slot and glue the tube in place.

rcbif

Cool, thanks. The shaft I posted earlier isnt supposed to be in stock for a while. What else could I use for a shaft and tube that is about 7inches long and under 15bux and can be coupled to a 540 motor?

toesupwa

Try one on here..
http://www.harbormodels.com/site08/m...propulsion.htm

8" long and $15... HAR2021-2023

Or

Would one of these be suitable?
http://www3.towerhobbies.com/cgi-bin...FVSEARCH=SHAFT

rcbif

Do these stuffing tubes use rubber seals to keep out water? or grease and seals?

ghostofpf1

Teflon tube inside of the brass to keep clearances fairly tight aeound the flex cable along with generous applications of marine grease is how I do it generally.
Make sure you anneal the brass tube so it's easier to put a bend into if needed.
HTH
Steve

rcbif

Should the motor be mounted at the COG? Was just wondering, cause the cog on my boat is a bit farther back than the build I'm following to build mine?

Dan S

have everything in your boat (empty fuel tank) but don't mount the engine.
than move the engine so you get your CG where you want it.
depending on hull and preference (this varies with everyone) anywhere between 30 and 35%

Dan.

rcbif

Thanks for the reply. I'm considering the aquacraft nitro hammer rudder, as no other ones are in stock, and I dont want to order elswhere to save on shipping. Is there is big diffrence between performance between an offset mounted rudder verses one mounted one in the center?

one I'm looking at, would probally have to use the bracket
http://www.aquacraftmodels.com/boats...6xxai02l-b.jpg
how done in thread I'm following
http://www.theoaks.ca/hullrear.jpg

danielplace

Steve,
The teflon tube in the stuffing box is something most builders have gotten away from. It has been proven that it actually causes more drag than running in the brass alone.
The biggest reason is that when the teflon gets a little thin or hot it will bind up around the shaft in a tight ball and make it lock up and twist off in the collet and be nearly if not completely impossible to get the flex shaft out.

Daniel

rcbif

My stuffing tube is in . Just have one more question. My transome is 1/8 thick. Some of the screws that came with the rudder, and turn fins are 1/4 long. Should I cut down the screws? let them stick through the other side? Or make anchor plate out of another peice of 1/8 ply to give the threads more wood to grab?

mfr02

Go for the anchor plate. Then the worst thing that can happen is a stronger transom.

ghostofpf1

Actually in my experience the "teflon vs brass" camps are pretty evenly divided and I for one would only run bare brass (with a ton of grease to keep water out )is if I was SAWracing. In SAW racing (Straight A Way) the boats are only in the water relatively briefly so any water intrusion is at a minimum.
For sport running or even running ovals I will continue with the teflon as water intrusion can affect a boats handling during a prolonged race. I have only had failures of flex cable outside of the stuffing tube but will keep an eye on things as you suggest.I normally replace the teflon every year anyway as a maintenance item and have yet to see any signs of undue wear
thanks
Steve

rcbif

Do I need to allpy any type of selant to the screws that hold the hardware onto the transome?

pompebled

Hi rcbif,

I just looked at the pictures of your build on the other forum.
The way the propshaft is positioned will give you an awkward hybrid between subsurface and surface piercing drive, which will most likely not work well.
The propshaft angle is too steep for a surfacepiercing drive, which will force the bow down, making the boat run very wet, which in turn will draw a lot of current as the motor will struggle to get the hull on the plane.
Overheating will be an issue.

Using a solid shaft for a surface piercing drive requires a long shaft, so the motor sits in the front half of the hull and the propshaft exits through the transom, not the bottom.

A slightly shorter shaft would work fine for a subsurface drive, motor way up front and the propshaft would have to exit the hull in the last half of the hull, the prop would sit under the hull, not behind it.

You may have to rebuild the drive system, as I fear this will not work, at all...

I use thin self adhesive rubber foam between the hardware on the transom to make a watertight seal, silicone will work aswel, but the foam allows removal without breaking the surface of a wooden hull.

Regards, Jan.

rcbif

Nope, not a problem, got the final assembly done and it worked great! I used some clear silicon to seal up the screws. I just need a new drive dog, as I enlarged on with a drill but it's slightly off centered. I'll have to find one pre made to the correct size. I tried it out with a dead plane battery and got maybe 8-10 mph at the most. My lake is a maze of seaweed however, so I didnt go crazy with it. Once I get the drive system fixed and secure all the electonics it should work great

pompebled

Great!

Let us know how it runs on a fully charged battery when you've got the drive-dog sorted out.

Maybe a small video?

Regards, Jan.

rcbif

whoops, I meant the universal drive. I need one with a 4mm inner diameter. Cant seem to find one.

this part but in a 4mm inner dia.

http://cgi.ebay.com/CEN-GS093-DRIVE-...ayphotohosting

pompebled

If your motor is properly alligned with the propshaft, a solid coupler is a better solution, quit and more stable.

Don't go drilling these things without at least a drill press, or better, a lathe.

Regards, Jan.

223nbecker45

I'm building the same boat and would like to make it surface.
How far up the transom would you put the prop on a surface piercing drive?
quote:

ORIGINAL: pompebled

Hi rcbif,

I just looked at the pictures of your build on the other forum.
The way the propshaft is positioned will give you an awkward hybrid between subsurface and surface piercing drive, which will most likely not work well.
The propshaft angle is too steep for a surfacepiercing drive, which will force the bow down, making the boat run very wet, which in turn will draw a lot of current as the motor will struggle to get the hull on the plane.
Overheating will be an issue.

Using a solid shaft for a surface piercing drive requires a long shaft, so the motor sits in the front half of the hull and the propshaft exits through the transom, not the bottom.

A slightly shorter shaft would work fine for a subsurface drive, motor way up front and the propshaft would have to exit the hull in the last half of the hull, the prop would sit under the hull, not behind it.

You may have to rebuild the drive system, as I fear this will not work, at all...

I use thin self adhesive rubber foam between the hardware on the transom to make a watertight seal, silicone will work aswel, but the foam allows removal without breaking the surface of a wooden hull.

Regards, Jan.

pompebled

Hi Becker,

Welcome to this forum!

Will you be using a flexshaft or a solid shaft?

With both shaft types you'll want the angle the propshaft makes with the keelline as small as possible.
With a flexshaft this is easily achieved, as it's adjustable.

With a solid shaft it takes a bit more planning:

Rule of thumb is to have the propnut at 10-13% of the boat' length from the transom.
To get the propshaft angle as small as possible, a longer shaft is better than a short one, as it allows the motor to be further to the front of the boat.
Drill a hole in the center of the transom, the size of the stuffing tube with the center abour 7-8 mm from the bottom.

Attach the motor to the propshaft with a solid coupler and slide the combination into the hull, feed the stuffing tube through the hole.

If the motor is going to be watercooled (yes!) slide the coil over the motor first.

With the propnut at 10-13% of the hull length, put the boat on its keel on a flat surface.
There should be 2 -3 mm of air between the propnut and the surface.

Adjust the hole in the transom to get this right.

Make a motormount, so the motor is fixed in position and glass in the stuffung tube (roughen and degrease the stuffing tube where the glass will sit).

Regards, Jan.

223nbecker45

Thank you for the reply!
With the info you gave me I will use a flexshaft so I can adjust it.
And yes it will be water cooled.
Were should the balance of the weight be in the boat?

pompebled

Rule of thumb is between 28 and 30% of the hull' length, measured from the transom.

Regards, Jan.