Prop Shaft Assembly

[Tony FentonParticipant @tonyfenton32936]

Just got a really silly question about fitting a prop shaft and propeller into my Riverside Models narrowboat. The supplied prop shaft is a Caldercraft 7" m4 which has a washer and nut on each end of the shaft itself.

The stupid question is : do I need the washer and nut on the propeller end as well as the propeller? I can't see that a nut and washer at the propeller end would serve any purpose?

The reason for asking is that with the washer, nut and propeller the whole lot sticks out too far and would interfere with the rudder. If I just have the propeller and washer then it would clear the rudder ok.

Many thanks for any help and advice!

[Tony FentonParticipant @tonyfenton32936]

[Colin BishopModerator @colinbishop34627]

Basically, yes you do need both. The nut is there to lock the propeller to stop it unscrewing while the washer butts up against the end of the tube to minimise water entry into the boat.

There are some possible solutions or a combination of them.

It might be possible to get hold of a thinner nut and washer.

Trim the the boss of the propeller by taking the point off to increase the clearance.

If it is just the propeller boss that is interfering with the rudder can you make a small cutout in the rudder to accommodate it?

If the rudder is mounted on the back of the boat is it possible to move it backwards slightly?

Use a smaller propeller which doesn't protrude so far, it will run faster so speed will probably not be much affected on a narrow boat.

Good luck,

Colin

[Tony FentonParticipant @tonyfenton32936]

Hi Colin and thanks for the fast reply. I see what you are saying, it may be possible to move the rudder slightly more toward the stern, giving room for the completed prop shaft assembly, I'll have to have a play around and see what I can do. At least I now understand why the nut and washer are there so I know it is necessary to make some modifications!

[Dodgy Geezer 1Participant @dodgygeezer1]

I never felt the need for a lock-nut on boats which did not have a reverse – I/C motors or fast one-way electrics. But I always used a teflon washer to take the thrust…

[Tony FentonParticipant @tonyfenton32936]

Just taken another look and believe the best option is to move the rudder slightly further astern. It only needs about 3-4mm so will mean a slightly oval hole, but after remounting the rudder tube I should be able to seal around it then repaint. How I wish I'd set it all up before the painting! Oh well, that's a bit of inexperience for you!

Thankfully the hole on the upper deck will be ok as the tiller has a nice large brass collar at its base which will easily hide the enlarged hole I'll need to make.

[Colin BishopModerator @colinbishop34627]

Tony,

What you are suggesting is the best option if you can make it work OK. It's quite normal to find you have to make adjustments like that. On one of my models the original prop didn't give enough thrust but a bigger one wouldn't fit as it fouled the rudder post. The solution was to change the prop from a 3 blade to a 4 blade to get the extra power without a physically larger prop.

Colin

[Malcolm FraryParticipant @malcolmfrary95515]

The useful side effect of close clearance between prop and rudder is that when the lock nut is not properly applied, the prop is unable to unscrew itself fully without making a horrible rattling noise as it hits the rudder before finally unwinding itself and heading for the pond bottom. A dab of thread locking compound rarely comes amiss.

[Tim CooperParticipant @timcooper90034]

Tony

I had a similar problem on a Revell Snowberry conversion. The plastic prop wouldn't fit so I removed the nicely shaped bit on the front of the prop boss.

If you enlarge the rudder hole use a square of styrene on the inside with tight fitting hole for the rudder shaft, then seal this to the inside of the hull.

On the subject of checking before you have finished the model, it always seems to be different when you try the first time in the pond. I took a small daughter boat for it's first sail this am, to find it won't steer in a straight line and so much rudder throw that it turned almost in it it's own length.

But I did get it back without wet feet or using waders.

Tim

[Tony FentonParticipant @tonyfenton32936]

Well I managed to move the rudder tube further astern and sealed the enlarged hole both inside and outside the hull. The tube passes through a square of wood anyway before a washer and nut, so with a bit of glue it is now all sealed and in the right place. Once the glue is fully cured I will be able to paint over it so all should be ok!

Malcolm – thanks for the heads up on using a thread locking compound!

Tim – I guess my next hurdle will be when I launch it. I can't imagine how it will sail, let alone not sink! Glad you managed to get your boat back without having to wade in! I'm planning to find a nice deserted bit of canal to try the narrowboat out on as a fitting place for a maiden voyage, but definitely wouldn't fancy having to wade in!

I think I know what I'm doing with the radio control, but still puzzling over the ballast. The instructions state somewhere between 10 and 12 pounds is needed. Anybody got any ideas of what to use for this amount?

[Malcolm FraryParticipant @malcolmfrary95515]

Is that the all-in sailing weight or extra to be added after the rest of the build is considered? In many narrowboat models, SLA batteries do the ballasting job nicely. Just as long as the weight is kept low.

[Colin BishopModerator @colinbishop34627]

If you need to keep the weight low then you can buy lead flashing in sheet form from builder's merchants. It is easily cut and can be shaped to fit the space available. There is no need to melt it, you can form it into lumps if you need to by folding it and bashing it with a hammer!

Colin

[Tony FentonParticipant @tonyfenton32936]

Hi Malcolm, I'm not sure if that's the total weight or not. I've got an SLA battery which will certainly add some weight, but as it's at the stern of the 50" model I'm guessing I'll need some extra ballast towards the bow as well. The first trial in the bath will reveal what and where I need to ballast!

[Tony FentonParticipant @tonyfenton32936]

Thanks Colin, I had wondered about flashing and will now look into that. I like the idea of bashing it rather than melting !

[Ray Wood 3Participant @raywood3]

Hi Tony

Fullsize narrow boats commonly have a layer of bricks under the floor to add stability, I've just completed a 30" long narrow boat which required 5lbs of well painted steelplate laid in the base of the hull + the NiCad to achieve the scale waterline. So your suggested 10-12 lbs would sound about right. I would suggest casting some small blocks from fast setting cement with some wire reinforcement in as a cheaper solution ?

Ray

[Colin BishopModerator @colinbishop34627]

I did try cement myself once as a cheap solution but it is nowhere near as dense and heavy as lead or iron/steel and takes up more room for the same weight.

Colin

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