Flex shaft question. Building first boat

[Ham Sammiches]

I am building a balsa and fiberglass 25" Wild Thing. I have built the hull but now it is time for the hardware so I am doing some research and shopping. This is my first boat so I am learning all the basics. My question is what all do I need in a flex shaft assembly? Better yet, what do I need to connect my motor to my prop?

from what I know I need, in this order:

• Shaft adapter
• Flex shaft
• Teflon tube
• Brass tube
• Shaft bracket
• Drive dog
• Prop
• Prop nut

Is there anything I am missing? I have never seen a flex shaft set up so I am trying to understand how they work. Do I need any grease or washers?

[Chilli]

You're close. Just a few corrections for terminology. By shaft adapter you probably mean a coupler which attaches the flex shaft to the motor. Not sure if the shaft bracket you are referring to is something that steadies the brass tubing inside the boat or the strut that gets mounted on the outside of the boat. The one item you left out that you might want is a thrust bearing which goes between the coupler and motor. This takes the stress off the motor bearings. Teflon tubing is optional. Just make sure you get the appropriate diameter brass tubing. You do have to grease the flex shaft every couple of runs. Just about any waterproof grease will work. I use Mercury 2-4-C and a tube last me a couple years. Good luck. Plenty of people here to help if you run into any snags.

[Ham Sammiches]

Okay thanks, yeah I meant the strut mounted on the outside of the boat. I have a few questions regarding the brass tube. Is the brass tube supposed to have a curved bend? And does the brass tube go outside of the boat or end at the transom?

[Ham Sammiches]

Would this 4mm shaft be suitable for my boat? It seems that it comes with the shaft and brass tube but no teflon tube. Will I need a teflon tube set up if I will be running at 25-30,000 RPM? I'm having a bit of trouble getting this whole drive shaft thing sorted out

[kfxguy]

I don't use Teflon. Some do. Also, say you use a 3/16 shaft....don't use a stuffing tube that just slides over it...you need one size up from that. Personally I don't use the 4mm ones because it's an odd ball size but it'll work for you.

[kfxguy]

Okay thanks, yeah I meant the strut mounted on the outside of the boat. I have a few questions regarding the brass tube. Is the brass tube supposed to have a curved bend? And does the brass tube go outside of the boat or end at the transom?

Yes it should curve. Can you post some pics? I'll help you best I can. My suggestion is to look through the build threads and get some ideas. You'll learn a ton. I did. Check some of my build threads, there's a bunch of little tips I used in them to just make things better.

[Ham Sammiches]

Sure, here are some pics of how she looks right now. The strut I had picked out was 4mm but I think I found a better strut that is 3/16 which is easier to find props for. I appreciate the help!

I am just about ready to order, but I still need a 1/8" to 3/16" motor coupler, which I can't seem to find. Any suggestions? Is there a way to make my own coupler?

[Ham Sammiches]

Update: I found a coupler, and ordered the Straight Shaft 10.25" (260mm) Long. I was thinking the shaft would flex but it is quite stiff. I notice now that it says "straight shaft" therefore meaning it is not supposed to flex, correct? Can I still use this shaft and have the prop angled a few degrees downward or is it best to get a flex shaft so the shaft would be coming perpendicular out of the transom? What effect does a slight angle have?

[kfxguy]

Flex. Allows you to bring the nose up or down to get you hull to plane out properly. What you do is drill a big hole in the bottom rear. Probably 1/2" or so. Then build a rectangular box about 3 to 4 inches long and 3/4" wide and maybe an inch tall. Seal that off so the hole you drilled doesn't leak into the hull. Then your brass drive tube goes through it and connects your strut to the inner of the boat. If you can picture what I'm saying I can find you some pics. I think they call it a flooded tube or chamber. The reason behind it is to let you move the strut up and down and the tube can move inside the chamber.

[Ham Sammiches]

I don't think I've seen something like that before, I'll have to find some pictures to understand completely. It makes sense though. Before I abandon the shaft I bought, I'm correct to assume it is supposed to stay straight or should it flex?

[kfxguy]

I don't think I've seen something like that before, I'll have to find some pictures to understand completely. It makes sense though. Before I abandon the shaft I bought, I'm correct to assume it is supposed to stay straight or should it flex?

That's just a straight shaft. Non flex type. You could go that route but you will have no adjustability

[dahodevil]

Angle of the shaft is very important. You will do better to get a flex. Start with the shaft at the prop set parallel with the bottom of the boat and gently curved it up through the bottom of the boat to the motor. Most boats run with the center of the prop even with the bottom of the transom. Half of the prop will be running out of the water (surface drive). You can make small adjustments to see what works best.