BRUTUS MK 11

[Bob Abell 2Participant @bobabell2]

Good lad, Paul

Now working on the super structure and I notice that the plan does not really look like the opening photograph?

I`ve just cut out the side wall and matched it to the deck top surface, using a 5 thou feeler!

Rudder question….

If I were to add 6 " of hull to my Lady Joyce VGC, I reckon the boat would still sail as normal

See what I`m getting at?

Bob

[Paul TParticipant @pault84577]

Captain Bob

The plan that was issued with the magazine is different to my original design.

I doubt that anymore than 30% of the readers know what a 5 thou feeler is and are probably thinking about an obscure 1980s Swedish film for discerning gentlemen.

Lady Joyce is a typical displacement hull and you could easily add 6ft to it without changing its ability to sail.

Brutus is a hybrid hull and specifically designed to be the size that it is, adding or removing 6in, without redesigning everything else, would significantly change its sailing characteristics and to use an analogy, instead of having a Gazelle you will end up with a Hippo.

The length and width of the hull along with the positions of the motors, batteries, propellers and rudders were carefully worked out to ensure the boat performed in the way that was intended.

You could use thrust tubes as rudders, similar to kort nozzles they fit over the props and move like rudders, not only steering the boat they will also contain the prop wash and increase the thrust.

Paul

[ashley needhamParticipant @ashleyneedham69188]

Paul. I have no doubt that adding 6 foot to Bobs model will make will make absolutely no difference whatsoever.

Yes, my copy of 5 thou` wore out years ago.

Interesting idea regarding Kort nozzles. The Mintanic dies not steer when power has been cut off, she stays on the last heading, presumably the rudder is blanked off too much by the relatively severe rear cut-up….this is not a problem as such, but is a nuisance for instance when coming alongside, you cant drift nicely in, you have to blip the throttle. The point of this statement is….would Kort nozzles have the same lack of effect when there is no power??

Ashley

[Bob Abell 2Participant @bobabell2]

Hi Paul

The Kort Nozzles sound interesting and maybe the answer

How much clearance around a 2 inch prop would you say?

How long would the tube be?

Bob

[Bob Abell 2Participant @bobabell2]

Now we`re talking!……..Looking like a Brutus now

The side wall is not down to it`s final size yet……..Just in case

I`m really enjoying getting back into the swing of things after a 3 year absence

Pity I disposed of most of my old junk?

Bob

[Paul TParticipant @pault84577]

Ashley / Bob

The thrust tubes would act like tubular rudders and providing the rudder servo is still active they should give the boat limited manoeuvrability whilst the hull still has momentum.

Bob

The length of the thrust tubes depends upon the depth of pitch on the propellers, I estimate that 25 to 30mm would be the optimum.

Clearance around the props depends upon the position of the rudder shaft in relation to the propeller but I would guess that an all-round clearance of 10mm should allow the tubes to move without fouling the props, if my guess is correct then the tubes require an internal diameter of not less than 70mm.

Please bear in mind that these are only speculative estimates and will need confirming by accurate physical measurement and corresponding calculations, there are many factors involved in these calculations all related to the length and angle of the propshaft and the exact position of the vertical centre line of each propeller (+/- 1mm.)

Meanwhile the build is looking very good and, as Jane was heavily involved in the design, is bringing back lots of bitter/sweet memories.

Keep on building Bob and we will sort out the details when you are ready.

Paul

[Bob Abell 2Participant @bobabell2]

Thank you Paul

What scale do you reckon the model is?

The hull sides look a bit bland and think steps may look nice, going down to the water line etc?

Or several rows of port holes etc

Bob

[Ray Wood 3Participant @raywood3]

Hi Bob,

Kort nozzles ???? Are you sure your not building a tugboat 😀😀😀,

They must be great for directing the thrust, but never seen them on a fast boat?

Don't forget to put a rubber tyre on the bow !

Regards Ray

[Paul TParticipant @pault84577]

Bob

The scale was deliberately never given however if you take the height of the deck mounted rail gun as being 2m you will be able to form your own opinion.

Sorry to say this Bob but due to radar profiling things like steps and portholes wouldn't appear on future warships.

Ray

I only used the term kort nozzles as a reference point to demonstrate the approximate shape and location of where the thrust tubes would be fitted.

Thrust tubes are commonly used in aircraft jet engines and the technology can easily be transferred to be used in a different medium, water jets already use moveable thrust tubes for steering and I can see no reason why directional tubes cannot be applied to sub-surface propellers

[Ray Wood 3Participant @raywood3]

Hi Paul,

I'm familiar with the technology, but the complication would seem extreme for a model boat ?? Especially as none of this will be seen when it's On the water.

Bob the picture on the beginning of the thread has 2 levels of portholes, is that what your trying to create?

Regards Ray

[Bob Abell 2Participant @bobabell2]

Hi Ray

I just thought the hull flanks looked a bit too plain and ladders down to the water would be instantly recognisable

We'll just have to see later on in the build

Bob

[Dave MilbournParticipant @davemilbourn48782]

These are screen grabs from the plans I drew of Vliestroom, a kit by Model Slipway which was designed in 2002. The twin props are fixed but have thrust tubes (or nozzles, if you prefer) with a rudder fixed vertically to the rear edge. The centre-line of the nozzle shaft coincides with the middle of the prop so that when the nozzle rotates the clearance between it and the prop remains more or less constant. In this case the props were 30mm diameter and the ID of the nozzle was a tad shy of 32mm. The model was very manouverable.

[Paul TParticipant @pault84577]

Nice one Dave

Glad that you were watching as I didn't know about this, and its all the way back to 2002, bang goes my patent.

You have just saved me hours of work as I was about to produce a set of drawings and calcs to back up my theories.

Paul

[ashley needhamParticipant @ashleyneedham69188]

I like what DM has shared with us, but for a workboat, yes,for a high speed warship…no.

A lot of work Bob, going that way for, in this instance, questionable benefits.

HOWEVER….you are a man who can, and who likes to up-engineer everything so this would be a challenge.

The stern is very shallow and I would wonder about getting an adequate bearing tube in there?

Ashley

[Paul TParticipant @pault84577]

Hi Ashley

You are correct about the shallow stern and by extension the shallow angle of the prop shaft, this is why accurate measurements of the as built model is necessary before any design work can be undertaken.

Yes it is a lot of work but the reason for suggesting this solution in the first place was to help Bob with his problem regarding the existing rudder design

Theoretically thrust tubes can increase the performance by 7 to 12% and would work perfectly well on high speed boats, is the gain in performance worth it? that is up to the builder.

Paul

[Dave MilbournParticipant @davemilbourn48782]

I didn't post the drawings as a suggestion for Bob's model – just by way of an explanation and an example of what has already been done on one model. Bob – as always – will make his own choice for his own reasons and I wouldn't presume to offer him any advice unless asked directly.

Regarding the increase in efficiency, that would be much easier to achieve by fitting brushless motors and not those horrible MFA throwbacks to the Dark Ages. If you posess one of these 850 motors then, to quote the sleeve notes on Tubular Bells, "you should hand it in at the nearest police station". While you're there you can also hand in any resistive-board/coil speed controllers and any devices contrived from a servo and microswitches. The rozzers might also appreciate any SLA batteries which they can use either as doorstops or "restraints"…… Come on, people – we're already into the third decade of the 21st century.

Dave M

Edited By Dave Milbourn on 03/07/2020 18:43:35

Edited By Dave Milbourn on 03/07/2020 18:51:36

[John W EParticipant @johnwe]

if Bob wanted too and used the propulsion similar to nozzles – I suppose he could use the same propulsion system as was used on the Virgin Atlantic boat. Horseshoe shaped rudders – which are wrapped around the props – and give you the best of both worlds.

[Bob Abell 2Participant @bobabell2]

Thank you John

The main problem that started all these weird and wonderful alternative rudders etc is that the rear end of the model is too shallow to fit rudders with sensible shaft lengths

I am only looking for a simple solution

Bob

[Ray Wood 3Participant @raywood3]

Hey Bob,

Let's go traditional how about Lee Boards ?? With a twist in them 😀 drop the left one for left turns etc etc

Only a thought ! Everything else has been suggested 😯

Regards Ray

[Bob Abell 2Participant @bobabell2]

Keep these good ideas coming Ray

It is similar to the rudder up front idea?

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob. What was the ruddering arrangement on the original?

Another thing to consider would be an external arrangement…bracket on the back etc, although this would not be very warshippy.

OR howabout a bearing in the removable deck, to support the top of the rudder shaft in conjunction with the bottom bearing? (Nice engineering solution!)

 

Ashley

Edited By ashley needham on 04/07/2020 08:40:14

[Bob Abell 2Participant @bobabell2]

Hello Ashley

The external rudder idea has already been suggested by Ray, but was poo poo`d by El Maestro

On the drawing there is a large block of balsa shown above the rudder area. I was hoping to use that as a cover for the rudder mech, but disguised as a gun of some sort?

We`ll just wait to see El Minio has to say about that

The MFA 850 motors have already been poo poo`d too by El Magnifico

Shortly, I shall jump in with both feet and that`ll be that

The comments by the Design Committee make amusing reading

Bob

[Bob Abell 2Participant @bobabell2]

A blast from the past

Here we are at Lyme Park near Stockport, which the club used to visit and have a display twice every year

That`s my old friend Duckie feeling very pleased with himself

My models on show….SloMo 2, Paul`s Broads launch and Paul`s Brutus mk1

Happy Days indeed

Bob

[Paul TParticipant @pault84577]

Bob

As I remember the problem with water getting in wasn't due to the ruddershafts but sealing the access hatch, as a suggestion you could make a simple neoprene gasket to seal this hatch.

Paul

[Bob Abell 2Participant @bobabell2]

Hello Paul

Just had a look at the space available and there is plenty of room now, I raised the stern covering somewhat for one reason or another. Got about 2 1/2" to play with now

So we can proceed as normal

Now working on the superstructure and is quite tricky at the moment, since the side walls lean inwards and I`ve made the front windows with straight sides at 45 * instead of curved

Have a nice day, my mate

Bob

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