BRUTUS MK 11

[Paul TParticipant @pault84577]

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

[Bob Abell 2Participant @bobabell2]

Thank you, Paul for your technical explanation

I hasten to add for the benefit of members who don't know Paul, and I know he won't thank me for this but Paul is very well qualified on such matters…..and then some!

Well done my mate

I'll weigh the hull shortly and let you know.

The birch ply is quite heavy compared to the cheap stuff that you can get from the local wood shops

As Paul says, I've not built a speed boat, just a futuristic scale model, to cruise sedately around the Etherow Lake

Bob

[Paul TParticipant @pault84577]

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

[ashley needhamParticipant @ashleyneedham69188]

Of course I was pulling Kevin’s leg. 4x 850s weigh a serious amount and anyone contemplating something fast would choose a 35mm brushless (pair, possibly) developing twice as much power and weighing probably only 1/3 the weight.

However Bob doesn’t want to go fast and if he has a pair of 850 motors they would do…?

Our Trevors current project has a 28mm 2200Kv outrunner developing 342 watts, according to spec..for something the size of a 300 can sized brushed motor.

Ashley

[Bob Abell 2Participant @bobabell2]

Hi Paul, I have just weighed the model as shown on photo, and it comes to………. 8 1/4 lb

Any comments, Prof?

Bob

[Paul TParticipant @pault84577]

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

[Bob Abell 2Participant @bobabell2]

Thank you, Paul

That is a nice surprise, as the model feels very heavy to my way of thinking

I will examine the build and try and remove any unnecessary weight where possible

Bob

[Paul TParticipant @pault84577]

Bob

2oz isn't worth bothering about, you have built a lovely model and there is no need to alter it.

Paul

[Bob Abell 2Participant @bobabell2]

Hi Paul

I`ve removed about 2 oz of surplus wood already, for the rest of the superstructure, I will try card construction

Bob

[Bob Abell 2Participant @bobabell2]

Fitting the hull rubbing strips using the weighted string idea, which is ideal for working on large model hulls

The trick is to have plenty of strong string and plenty of weighty things to dangle on same

Bob

[Paul TParticipant @pault84577]

Hello Bob

The rubbing strake is an interesting addition to the design and something that I considered on MK1.

You will remember that there was some discussion about spray rails on MK1 and if you follow the chine on MK2 your rubbing strakes will meet half way up the bow and become very effective spray rails.

Paul

[ashley needhamParticipant @ashleyneedham69188]

Bob. I like the string idea, it’s much better than using tape which I find tends to pull or lose tension. With the string you have good tension all round.

Did the original look like it needed spray rails? I must say that having the rubbing strip become a spray rail is an ingenious idea.

Ashley

[Bob Abell 2Participant @bobabell2]

Thank you, Paul and Ashley

How wide do the spray rails?

Ash, the original needed a water deflector on the deck, such was the spray with tight turns using brushless motors!

I`m pleased you like the string idea, Ash, I quite enjoy using them myself

I`ve got them all hung up on nails on the wall

The problem at times is finding enough weighty bits

Bob

[ashley needhamParticipant @ashleyneedham69188]

I would have said at least 4mm deep for the rails? it is a big boat and the hull sides can take a wider rail without it looking too wide.

I would err on slightly too wide and deep a rail rather than too small, as adding more to the rail afterwards (if it needs it) would be difficult later on.

Bob…surely you must have LOADS of tools to use a weighty bits!!

Ashley

[Bob Abell 2Participant @bobabell2]

Thanks Ashley

My fertile mind has been at it again……….Got an idea and it`s just up your street!

The spray rails could be Spray Wings!

Wide enough to take advantage of the ships speed?

Come in Prof Paul with his trusty and probably rusty………Slide Rule

Not really serious, but 12mm wide would be a novelty.?……A bit like an MG model TC mudguards

I really don`t know how I can do it for the money!

Bob

[Paul TParticipant @pault84577]

Captain Bob

I don't know how you do it either but you do have a very fertile imagination.

Yes wings would be a novelty but my rusty slide rule informs me that to provide any lift each wing would need to be 150mm long and 100mm from leading to trailing edge and you would need some very serious motors to reach 'flying' speed.

Oddly enough your imagination isn't far off the mark.

You might find the following pictures interesting, MK1 had two bow mounted torpedo tubes mounted within the small wing fitted just above the waterline, although it didn't provide any lift this fixture also doubled up as a very effective spray deflector.

Paul

[Bob Abell 2Participant @bobabell2]

Thank you, Prof

Or do you prefer the name……..Prof Poo Poo?

For Kevin`s information this is a lash up of what I was suggesting

A pair of small wings mounted at the front to deflect the spray and possibly provide some lift and perhaps look very pretty and a hint of Sci Fi?

Afterthought for the Prof…….If there is enough water spray, then the wings may make a difference?

Come in our inventive representative form the Home Counties…….Mr Ashley Needham

Bob

PS …….Motors and stuff now ordered and awaiting delivery

[Paul TParticipant @pault84577]

Hello Bob

I don't like pouring cold water on your ideas as its not the way that friends act especially as you have such an amazing imagination, I had envisaged wings looking like a USA submarine dive planes being fitted midway on MK2s bow.

The mockup that you have done is very similar to what I did on MK1 so it goes to prove that great minds do think alike, I actually prefer your version as it does look very futuristic.

Its a little late now but after your rudder comments I have devised a bow mounted rudder that would fit below where your rubbing strake is.

Paul

[Bob Abell 2Participant @bobabell2]

Hi Paul

I don't mind you poo pooing my crazy ideas, I just do it to get your comments

That's what friends are for

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob, as Paul says, the deflectors you have mocked up look just like those fitted to the mk1 and from the photo seem to be working as they should.

Ashley

[Bob Abell 2Participant @bobabell2]

Thank you Ashley

I don't remember the MK 1 having deflectors?

Have you been drinking that Vintage Pond Water again?

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob, see the last pictures Paul posted. The boat was fitted with torpedo tubes and deflectors that doubled as a front spray rail. Almost exactly the same as you propose.

Ashley

[Bob Abell 2Participant @bobabell2]

Thanks Ashley

I`d forgotten about Paul`s modifications

Good news……The motor stuff has arrived this morning……Christmas hath come early this year!

Such good service from Howes Models Ltd, only ordered the stuff last Tuesday!

Spot the cannon

Bob

[Paul TParticipant @pault84577]

Arr! Capt'n Bob

Avast ye lubber, yo ho ho and a bottle of sanatogen, with this talk of cannon you make it sound like a pirate galleon instead of a 2050 warship, mind you I do like the shape of the turret.

As we live in enlightened times here is my version of a pirate flag ..

The Jilly Rodger

Paul

 

Edited By Paul T on 16/07/2020 14:31:06

[Bob Abell 2Participant @bobabell2]

And for my next trick…..

I`m also having a few Rockets protruding out the bolt holes…eh?

And a few lids open etc

Etc

Bob

[Author]

Posts