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Member postings for Paul T

Here is a list of all the postings Paul T has made in our forums. Click on a thread name to jump to the thread.

Thread: Hell Boats
12/07/2020 17:26:33

Dear All

The film Hell Boats is on Sony Movies Action tonight at 9pm, not a very good film but some nice shots of MTBs, both model and real (although they are really RTTLs)

hell-boats-3.jpeg

hellboatslobby.jpg

Thread: BRUTUS MK 11
12/07/2020 16:01:10

Hello Bob

At the moment Brutus MK 2 is 2oz overweight, which is remarkable when you consider the extra material that you have used.

Your selective trimming of the major parts has paid off as you have produced a far stiffer hull for a negligible weight gain.

Paul

11/07/2020 16:04:05

Captain Bob

Sorry to ruin your fun as I am sure that you have had many members scratching their heads and reassessing their views on MFA motors.

As for being qualified and for those who dont know me I will just say that I am retired and have no intention of resuming work.

Paul

11/07/2020 15:21:13

Captain Bob / Ashley

I suspect that as experienced model builders you are both having a bit leg pulling at our expense but, for Kevins sake, I think it is time to explain why four 850s are 'overkill' for this boat.

As Bob pointed out this hull is designed to slide through the water and as such weight becomes an important factor as the hull has to float high in the water.

Four 850s are simply to heavy for this boat as the motors and ancillaries will weigh the thick end of 2.5 kilos which is 1 kilo over the design weight for the power plant, escs, batteries, shafts etc.

By using four 850s there is a negligible gain in power output but when you consider that all four will only produce 320w then this combination falls well below the power to weight threshold for this design.

Using two 850s just meets the power to weight threshold for this hull as they will provide sufficient thrust for a decent scale speed without having the hull to deep in the water.

The result of using four 850s will be a significantly heavier boat with a slower performance.

In other words it is a classic Jeremy Clarkson case of power not equalling performance.

Getting onto X60 props, the design angle of the propshaft would mean that the X60s would either foul the hull or be rotating so close to the hull as to cause excessive cavitation. I hasten to add that this is based upon the design angle of the propshaft and that the ultimate choice of propellers is down to Bob who, as an expert model builder will have considered all of his options.

Now I feel like a spoil sport but I would hate for Kevin to invest in equipment that he doesn't need.

Paul

09/07/2020 19:42:13

Hello Bob

Are you keeping the rear hatch surface mounted, as in your photo, or will it be flush fitted like MK1? any thoughts about the final paint job.

Paul

06/07/2020 11:51:09

Yes Bob it is looking fine yes

04/07/2020 20:32:59

Bob

Its looking just fine

Paul

04/07/2020 19:55:47

Captain Bob

This is good as the rudders can be fitted in their original position but I would advise fitting a neoprene gasket to the access hatch to prevent flooding.

As I remember the hatch seal was the problem, as when the boat was reversed the water washed over the hatch and leaked in through the gap between the hatch and deck, a simple seal would prevent this problem from occurring.

Paul

04/07/2020 11:02:21

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

03/07/2020 18:12:31

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

03/07/2020 17:31:54

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

03/07/2020 15:15:47

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

Thread: My Time Media. Model Boats Magazine.
03/07/2020 13:08:33

Does a Midshipman have to stay in the middle of the ship is it something to do with moveable ballast?

Thread: BRUTUS MK 11
03/07/2020 13:05:19

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

02/07/2020 21:14:01

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

Thread: My Time Media. Model Boats Magazine.
02/07/2020 19:15:28

And the winner of the life time subscription is...

Thread: BRUTUS MK 11
02/07/2020 19:13:31

Bob and Ashley

The 850s sound like a good solid answer to the question of motors as for rudders you could fit moveable kort nozzles around the props.

Paul

02/07/2020 12:09:08

Bob

It was a very addictively demanding hull to design as it was neither traditional planing nor displacement but a hybrid of both with a lot of aerodynamics thrown in.

Paul

02/07/2020 11:42:54

Bob I honestly don't know how the performance dynamics will be effected by moving the props and rudders so much further forward.

As you will remember a lot of time was invested in designing the hull around the motors/props/batteries/rudders in their current positions which equated to a very finely calculated centre of gravity, moving everything forward will significantly change this critical point and it is very possible that the model will become nose heavy and 'dig in' as opposed to gliding over the water.

Extra ballast would re-trim the boat but the extra weight will only compound the problem as the hull would sit to low in the water

I'm sorry to say that I don't think that it is a good idea however this is your build and you are free to do whatever you want, I might be wrong about how the change will effect the boat but if you want to try then I am happy to re-do the calcs but this will take a couple of days.

Rays idea has certain advantages but from the original design perspective it would ruin the hydrodynamics of the stern by introducing a surface piercing element in an area intended for smooth water.

Another soloution to your problem would be to fit azipods with full 360deg rotation, this would have the advantage of lowering the C of G without moving it further forward.

Paul

 

 

Edited By Paul T on 02/07/2020 11:51:40

Thread: My Time Media. Model Boats Magazine.
01/07/2020 17:36:54

Hello Charles

Yes it is very good news and all joking apart it will be comforting to have the magazine back.

But with the new editor being a lady do we have to be smart and shave before we read the magazine

Paul

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