next dumb question

sunnybob · 01-02-2008

Ok, I am almost ready to load all the gear into the boat, and float it to get the water line, but, heres the dumb question.
How do I stop water coming back up the propellor shafts and sinking the boat?

I have two brass tubes, with brass rods inside them, they are a fairly tight fit but as far as I can see, they will be below the waterline inside the boat.
The twin rudders are similar, but I think the top of the shaft tube will be high enough to be no problem.
Bob

alan2525 · 01-02-2008

On a real boat, theres something called a "Stuffing box", greased rope is packed around the propshaft and compressed into place. On a scale model grease is normally sufficient to keep out the ingress of water.

**Bunkerbarge** · 02-02-2008

It depends on what propulsuion system you are using as to what you use to fill the stern tubes. On my larger boats which use quite a bit of power I have grease in the stern tubes but in my modified Revel U-boat model which has two 12" shafts running in two 10" tubes driven by two very small servo motors when I filled one with grease it wouldn't even turn!!

Consequently that one is filled with a light oil, which works fine. There is a very small amount of oil leaks out when I first put it in the water but it seems to be fine after that.

The best stern tubes have ball bearings fitted at either end which reduces the clearances considerably and you should always have an oiling tube fitted at the top to enable you to be able to top up whatever lubricant you are using.

On my steamer I will use a syringe filled with grease to add a spot of grease every now and then through the oiling tube.

Rudder stocks also need to be thought about because even if the top of the tube is above the water a choppy sea can allow water to enter the hull. Some form of lubricant to prolong the life of the bearings and to seal the tube is usually a good idea.

sunnybob · 02-02-2008

thanks for the reply, I was hoping it would simple. Grease is simple! (G).

sunnybob · 02-02-2008

I've gone with the electronize 545/12 motors, only time will tell if they are suited or not. These props are the 50 year old originals, brass tube with brass rod inside. No room for any kind of bearing or even stuffing box. I had already greased the rods, but wondered if anything else was used. Just have to wait and see I suppose (motors should be here monday, but I'm away from home till tuesday night, so round about thursday I might have some more questions (G)

**Bunkerbarge** · 02-02-2008

As long as the tubes are not very long I'm sure 545's will turn them with grease in no problem.

I would give the set up a really good test in the bath though. You don't want the grease to creep out after an hour and suddenly water can get in.

Maybe even an "O" Ring rolled up the shaft up to the end of the tube might offer a bit of security.

sunnybob · 03-02-2008

I dont think theres any room for an O ring. The prop blade is snug to the tube, and there not a lot of extar shaft at the motor end. the shaft is a good fit inside the tube as well.
If the grease does not work out, its gonna be a pig making stuffing boxes for the ends of the shafts.

Still, thats what the thing is all about isnt it? making something bend to your will. (vbg). roll on wednesday.

The Fat Controller · 03-02-2008

The shafts should be packed with grease, this will prevent water getting into your boat

Aquarama · 04-02-2008

Hi Sunnybob, I use a low viscicity grease, you need to be careful what grease you use as some can cause drag on the drive and consequently increase you motor loading, this is worse in cold weather when the grease thickens, I have some grease that is used on the pumped lub system for CNC machinery, if you want a hypo full e-mail me on vic.hanson@blueyonder .co.uk, regards, Aquarama.

sunnybob · 05-02-2008

Thanks for the offer Vic. But to save the trouble, I have a couple friends who work with cnc lathes, so I'll have a talk with them.
I put the shafts together using some wheel bearing grease, but realised pretty soon that that is too thick, its hard enough for me to turn them by hand! I was considering vaseline, with a dab at each end of the tube (they are almost a foot long).

My motors have arrived, so now its time to make some platforms for them, and get the tubes on and connected.
Bob.