Straight shaft BBY SC21

[RPC1]

So the plan is to use a non adjustable 7.5* strut mounted to the bottom of the hull. The shaft will be a precision ground 1/8ss running through ball bearings in the strut an in my custom made stuffing box(5 total). I am putting 3/32" ride pads on the bottom to help get the prop out of the water more, then I can use longer drive shafts to adjust the depth of the prop if needed. It will be powered by a 500 watt outrunner motor on 3s2p A123 cells, if no good then I will put the right motor in it later. I will try to post pics later this evening.

[Simon.O.]

I am interested in how this one turns out.
I have used straight shafts before and had a lot of fun with them.
If set properly they have near zero resistance / power loss....this is good !!
Prop placement is critical and I can see that you have a similar mindset to to me in using a long shaft so that you can move the prop to find the optimum place for the prop.
I did this with my home-brew hydro and then went to a wire drive to get the tail shaft flatter.

Work with solid shafts, I have and so have a lot of others here. They are a lot of of fun to work with.
How many full size hydros do we see with flex / wire drives.

A WELL set-up solid shaft drive is awesome.

[Avanti]

I was just thinking and if you gear drove it you could get the shaft flatter. (not sure that is the way you want to go, just putting it out there, & subscribing to the thread)

[RPC1]

Here are some pics. The hull is trimmed and laminated with fiberglass wicked with thin ca, and a 2nd layer of 4 inch fiberglass tape down the center to help strengthen all the mounting points(and twisting). The doublers are 1/8 balsa sheet laminated with fiberglass and thick ca(stronger than I thought it would be). 3/32 epoxied balsa ride pads(not in stalled yet).
I recessed the strut mount to get it out of the water more. I aslo took 1/16-3/32 off the base, with a mill, to shorten it. To recess, I heated the strut with a torch and slooooowly placed it and applied slight pressure. When i got the depth and position I wanted, I took a wet rag and squeezed water on the strut an hull to cool it so that I could remove the strut.
The transom doubler was installed with plastic epoxy from OSE.

[Jeff Wohlt]

It will work but not for higher speeds. Why not just put a strut on it and get it running well to begin with...fewer problems trimming and it would then be ready for high speeds.

I had a SC 21 and ran a 8.4 700 and 12-14 cells...it was fun but a ton of weight. Now a little BL set up with 3s would be a hot ticket.

I also put ride pads on all of my SC cats....it helped the 32 the most. Makes it run cleaner and faster. You could even integrate some small steps on it. They need sharp edges.

[RPC1]

It will work but not for higher speeds. Why not just put a strut on it and get it running well to begin with...fewer problems trimming and it would then be ready for high speeds.

I had a SC 21 and ran a 8.4 700 and 12-14 cells...it was fun but a ton of weight. Now a little BL set up with 3s would be a hot ticket.

I also put ride pads on all of my SC cats....it helped the 32 the most. Makes it run cleaner and faster. You could even integrate some small steps on it. They need sharp edges.

I don't know if anyone has done this before, that is kind of why I like the challenge, plus I think it is cool. The ride pads are for sharp egdes and prop depth. This is all fun for me, lets see how it woks, I may have to do it the right way in the end.

[RPC1]

Here is the prop shaft, the prop is a little deep without the ride pads. The Marine Specialties 3 3/4" rudder needs a 1 1/2" extension, maybe I can make that today. This is a first try on modifying a prop(Y535). The stuffing box I made on a mill. It has a .125 x .250 bearing a flanged .125 x .250 bearing and a .125 x .375 bearing at the the exit point towards the motor.

[Avanti]

wow that is a ton of shaft angle that boat looks like it will ride very wet and stuff the front end

[RPC1]

I believe straight shafts like this provide thrust at the motor not at the transom with a transom mounted drive. In this case it should create a lot of bow lift, and tune the transom lift with the prop and CoG. I know thrust angles and such are highly debated, I guess I will find out the hard way. All I know is on a full size v-drive boat the thrust is taken at the v-drive because that is where the solid prop shaft with the thrust creating device(prop) is directly mounted, but I'm probably wrong

[Avanti]

I'm no expert, so we'll just have to see what your efforts show us all. keep the pics coming. are you going to add any bulkhead to stiffen up the boat like drjet did with his bby-hydro?

[RPC1]

Yes. In post #4 there is a pic of the bulkhead that will be in front of the motor. The motor is mounted with the OSE motor mount, very nice mount.

[RPC1]

Here is a pic of the servo mount. Adjustable and able to use larger servo if needed(probably). I am going to try and make the rudder standoff bracket today.

[Dr. Jet]

I believe straight shafts like this provide thrust at the motor not at the transom with a transom mounted drive. In this case it should create a lot of bow lift, and tune the transom lift with the prop and CoG. I know thrust angles and such are highly debated, I guess I will find out the hard way.

I'll be watching this build closely for ideas on my next straight-shaft (read: CHEAP) project.

[Simon.O.]

I think we all agree that the shaft angle is steep, however the prop is nice and close to the transom so its lifting moment is reduced.
I have played with a solid shaft in my bigger ( now shelved) cat and did a lot of learning. If the prop is behind the transom the front will run wet.
You are correct that there is a debate as to thrust locations with straight shafts, been there, argued that one out for hours.
At the moment so far as I can see you have nothing to lose.
Try your setup and play with any adjustment that you have and that includes CoB changes.
If it is not all you want it to be you can always make and fit a wire drive later.
This is what it is all about. Trial and error.......I do lots of the error so others can sidestep that part and go straight to the trialing

I was just thinking and if you gear drove it you could get the shaft flatter. (not sure that is the way you want to go, just putting it out there, & subscribing to the thread)

Been there too and it is effective. the agrument is that there are transmission losses through the gears but I believe that is offset by having the shaft flatter.This is only economical if you have some gears sitting around. otherwise I would not spend the coins on them and instead go straight to a flex or wire drive.
Given the cost of my home-made wire drives I will only fit these now.

Many of us are keen to follow this one and see how it goes.

[Jeff Wohlt]

If you balance it correctly it can work but your cg will have to be back far. It will lift the front from weight and the prop will push the transom up...if right it can run very light...fine line on that but give it a try