Hi Heners2332,

You could support the underwater exposed length of the propeller shaft by making or fitting a "P" bracket (with a bearing) just in-front of the propeller.

This would give the shaft some good support that could help to reduce (or prevent) any vibration that would in turn extend the working life of the prop shaft bearings, if you are wary about replacing the shaft with a replacement that has a longer outer tube to support it properly.

I have restored a lot of model power boats over the years, and most of them have benefitted by fitting a brand new prop shaft assembly..

As robbob has suggested, propeller shafts can be removed from any glass fibre or wooden hulls without too much trouble.

My technique is to remove as much material as possible that is surrounding the shaft tube (such as old dried adhesive and filler) that can be removed using a file or a chisel etc.

After removing the "inner" shaft (and any coupling and motor etc), the end of the "outer" shaft can be hit with a hammer to produce a shock that is often enough to break any bond between the hull and the outer shaft.

The shaft can also be gripped firmly with pliers or a wrench and twisted back and forth to twist off any remaining bonded areas.

Once at this stage, the outer shaft tube can usually be turned and twisted out of the hull - sometimes after chipping away any large lumps of hardened glue or filler that expose themselves during the fracturing away from the hull.

A replacement shaft can be accurately aligned with the motor using a solid coupling of the same length as the intended (and advised) flexible coupling whilst it is being bonded into the hull.

A good epoxy resin (such as Araldite 24 hour) gives enough time to align everything before it sets, and masking tape fitted on the underside of the hull can be used to stop it "leaking" during its lengthy curing process.

Once the epoxy glue is set (I usually leave it over-night), a good glass fibre filler paste can be used to fill any gaps and to repair any minor damage that may have been caused when wrenching out the old shaft.

I usually also take the opportunity to fit (and blend-in) a triangular shaped piece of plywood between the underside of the hull and the new shaft outer.

This "fillet" gives the most solid shaft fitting that will not only look good but also help to reduce any vibration and noise that an unsupported shaft could give.

Bob.

Hi robob,

That is a really good video of the full size RAF Crash Tender in action that I have viewed several times. Thanks for sharing it with us Rob.👍

The RAF Fire and Rescue boat is very much a classic power boat that demonstrates its excellent performance that can be just as rewarding to enjoy when driving our Classic Model Power Boats at a similar speed.

Bob.

I have my twin Lipo batteries mounted under the stern deck. If you look at the original boats all the motor pumps, etc are at the stern of the boat.

Thanks very much, it might be a project that is putting to the side for now as I have a Kit for a Krick Paula to do for the New Year and shortly. I will be documenting this as I build it and then after that’s done I may alter the Crash Tender, it depends whether I should or not, I don’t know whether to keep as is ( because I know it doesn’t leak and works ) or change some stuff and have the risk of further leaks.

Hi Heners2332,

With some careful cutting snd grinding with a dremmel tool you should be able to cut the shaft out of the boat.
Even some gentle taping with a small hammer on the prop tube will loosen it without much damage to the hull.

There is never a prop tube that's fitted that cannot be removed and that will NOT kill the hull.
I have bought 3 or 4 second hand boats and alway been able to get the shaffts out.

With the amount of glassing in I have done on a wooden hull I have always been able to remove a shaft tube. Acetone will loosen the fibreglass resin and not damage the wooden hull.

It would only damage a fibreglass hull and that's a wooden hull, so you should be able to remove it.
Even slowly chipping away at the glue on the shaft with a sharp chisel ??

Somebody at the boat club should be able to come up with a way of removing the shaft and it should be easy enough to remount the motor by the way it looks in the pictures. simple packing and adjustments should suffice.

Sadly I live too far away to be able to help you, I'm in Dartford area a long was from Matlock Derbyshire.

Hi Heners.
OK, now I understand the problems that you face 🤔.
Good to know that the water leak is fixed though.
I think the excessive vibration you experience is because of the bad shaft alignment which will also be responsible for a great deal of power loss from the motor and possibly why the boat has insufficient power to 'plane'.
The gearbox 'thingy' you describe is totally new to me !
Rob.

Hi Robbob,

The leak has now been solved and it was identified to have been coming in through a very small crack that opened as the boat vibrates, this has now been sealed and the leak has been fixed.

Sadly the prop shaft cannot be removed without tearing out most of the hull where the shaft is, this is because when we purchased the boat the builder had installed the shaft in a way that is is impossible to remove without having to replace 1/4 of the hull.

We purchased the boat as a project that needed a lot of work so it’s not too perfect, just working order. Adjusting the angle of the motor and couplings is also not possible as to remove the motor block the internal wall it’s next to would need to be removed
, this is epoxied onto the hull walls and would cause damaged if removed.

So all in all there is not much that can be done but what is currently there.

The red unit is, as far as we can work out, a gearbox or a unit to adjust the length of the shaft by a few mm. It has a servo mount on it so our thinking is you could control a servo that would change the gearbox to differ the speed. This is what myself and the boat club I go to presumes.

Thanks.

Hi Henners.
Looking at the underside of the hull it's apparent that the prop-shaft tube is far shorter than the shaft itself so the shaft is not supported at the outboard end as it should be. This might cause the shaft to 'whip' or run with excessive movement and resulting end bearing wear. This may be why water is coming up the shaft tube, assuming that the tube is not packed with a suitable grease?

Also the alignment of the shaft with the motor isn't ideal and the use of a double coupling could be putting stress on the motor end bearing and the inboard shaft bearing too.
I can't make out what the red 'thingy', for the want of a better description, is at the inboard end of the propshaft. What is that?

The water pickup is facing backwards, which is not normal, but you don't need it anyway, but make sure it's fully blanked off internally.

In my humble opinion you need to install a new shaft of the correct length, with a new single coupling and make sure that it is all in a direct straight alignment and the shaft tube filled with a suitable marine grease.

I attach a pic of my 47" RAF Crash Rescue Tender in construction showing the motor position and alignment in my model.

I hope that is helpful.
Rob.

The prop size is M4, we had a leak but that is now mended. I shall attach an image of the underside.

What size prop are you using on her? and is that water coming up the prop tube inside the boat ? is that whatnthe sponge is for?
Have you got a picture of her underside?

Battery is currently located in the forward cabin where we have made a slot for it to sit nice and snug inside.

Hi All.
Here's a video clip of the real boat running at speed and in action putting out a fire.
Rob.

That's quite good, Where do you have the battery at the present in her though?

Yes I shall attach one, we are still fiddling with weight distribution and need to get more lead for the rear. Should plane nicely once done.

The other possible battery location is the receiver compartment as pictured, we would have to install a battery stand.

Ignore the sponge!

The reason I asked was she just didn't seem to get up on plane very well??
Have you tried her with a lighter weight battery, maybe a LiPo batery??
I and a biggest fan of the Crash Tender and have been since a boy, it was my first boat, the Aerokits 34" kit when I was 9yrs old.
I think they look great when they are running around up on the plane.
YES I am a speed freak I also love the MTB's running like it.
Have you any other video of her running please.
Happy boating Regards Tom, (BOATSHED).

She was running at around 3/4 throttle. The battery I have in her is a 12v Lead Acid, gives plenty of run time and is easy to use and charge.

I am curious was she at full throttle on that bit of video? and what size battery are you running her on?