ScaryKat By Paul Thomason

[mike farrellParticipant @mikefarrell21522]

Now then Dave That's not a Bakewell Tart is it . Paul will pull it off as with many others in the past ,I still do not know how but will wait and seeMichael

[Paul TParticipant @pault84577]

Michael:

Thank you for your vote of confidence.

Dave:

 So the gauntlet has been thrown and the challenge made, honour demands my response.

As its my choice of challenge I choose the design of a 1m long high speed model boat capable of reaching 40mph. So Mr M will you accept the challenge or will your pie in the sky end up being humble pie? 

 

The principal of the tilting hulls is based upon the way a skier turns during a slalom.

Paul

 

Edited By Paul T on 31/08/2014 18:39:44

[Dave MilbournParticipant @davemilbourn48782]

If that thing has a turning circle smaller than Titanic's then I'll happily make the custard, Doc.
DM
(You cheated and added a bit while I was posting!)

and no – duells have been illegal for centuries and I've two models on the go already – with no elves to help me.

Edited By Dave Milbourn on 31/08/2014 18:40:21

Edited By Dave Milbourn on 31/08/2014 18:42:33

Edited By Dave Milbourn on 31/08/2014 18:43:40

[Bob Abell 2Participant @bobabell2]

Hello Paul…..A few questions

Why have you opted for this strange parallelogram arrangement?

What prevents the shape flopping about on the straight?

Why the obsession with turning corners?

Why are the rudders not behind the props?

I'm sure we all would like to know the answers to the above questions?

Bob

[Bob Abell 2Participant @bobabell2]

If you don`t mind me saying so, Paul and Dave, I don`t like the present name for this controversial model, it`s not quite right

How about…….."Thom Kat" instead?……..Not bad?

I think it needs Pauls name on it, because the design is pure Paul Thomason

If Paul likes ScaryKat, then that`s the name

Bob

[lnvisiblemanParticipant @lnvisibleman]

Mr P T

I have a hankering to use a pair of these

**LINK**

What do you think ?

Mike

Edited By lnvisibleman on 31/08/2014 23:42:56

[Paul TParticipant @pault84577]

Hi Bob

Why have you opted for this strange parallelogram arrangement? Its the easiest geometry to maintain the positions of the superstructure and hydrofoil whilst the sponsons are banking.

What prevents the shape flopping about on the straight? The sponsons will be held in the correct position with either heavy duty servos or, and more likely, high torque geared motors. If you visualise the parallelogram these motors would be fitted on each of the top corners. 

Why the obsession with turning corners? Obsession? If the boat can turn tighter corners then it will be quicker around a course.

Why are the rudders not behind the props? Given that the sponsons tilt the best position for the rudders is behind the superstructure as this will have far less of a tilt letting the rudders be far more effective.

Re the name

There is a commercial range called Tom Cat and whilst I appreciate there is a difference I'm not over bothered about having my name on every design so we will stick with ScaryKat

Mike

To make this thing live upto your expectations we will need a minimum of 25000rev which I suspect is only achievable with surface piercing propellers and some high tec transmission.

Paul

Edited By Paul T on 01/09/2014 15:28:53

[lnvisiblemanParticipant @lnvisibleman]

Paul

this seems to be where the brushless mystery deepens. 25,000 rpm is very easy to achieve ( I have found some that will get up to 40,000 on 3s lipos  http://www.hobbyking.co.uk/hobbyking/store/__21483__NTM_Prop_Drive_28_36_3000KV_755W.html&nbsp  but those motors that will deliver the revs all seem to be of quite a low relative power ( watts ) compared with the slower reviving high wattage units.

Which is more important when trying to achieve high speeds ? Power or revs?

Mike

Edited By lnvisibleman on 01/09/2014 15:27:26

Edited By lnvisibleman on 01/09/2014 15:30:13

[Paul TParticipant @pault84577]

Mike

Try looking at your problem from a different perspective…………….the power to weight ratio.

Paul

[Diede van AbsParticipant @diedevanabs87670]

Hi Paul,

that looks like a very interesting concept, I am very curious as to how this will work out… I think you do need some very heavy duty stuff to keep the hulls in check, though. At high speed there is a lot of forces working on the hulls.

Second; you will need to move the props more to the rear, to prevent them from hitting air when the speed picks up – aim to extend the propshafts 10% of the hulls length.

As for the revs: 25000rpm should be a good target, you could go a liiiitle over. the 40k Mike is referring to, however… don't do that. You'll just stir up the water without much forward thrust.

[lnvisiblemanParticipant @lnvisibleman]

. the 40k Mike is referring to, however… don't do that. You'll just stir up the water without much forward thrust.

That's a shame !! I like stirring,

Mike

[Paul TParticipant @pault84577]

Hi Diede

The forces on different sections of the boat are immense and are constantly changing as the hulls move independently of each other but the biggest design problem isn't resisting the force on the hulls, the main problem is finding a non exotic material to construct the cross hull connections such as the hydroplane wing from.

I cant use carbon fibre or titanium so at the moment I am looking at epoxy laminations reinforced with stainless steel wire.

Paul

[lnvisiblemanParticipant @lnvisibleman]

For why can we not use carbon fibre? or GRP ?

Or multiple layers of 1.2mm plywood even ?

Edited By lnvisibleman on 01/09/2014 16:19:24

[lnvisiblemanParticipant @lnvisibleman]

Could it be that the " rudders " are above water ? More like an aeroplane rudder ?

Mike

[Paul TParticipant @pault84577]

Mike

For why can we not use carbon fibre?… to expensive or GRP ?… to fragile.

Or multiple layers of 1.2mm plywood even …to fragile

Could it be that the " rudders " are above water ? More like an aeroplane rudder .. Yes

[lnvisiblemanParticipant @lnvisibleman]

For why can we not use carbon fibre?… to expensive

**LINK**

[Paul TParticipant @pault84577]

Mike

I appreciate your enthusiasm but some things are beyond the average model boat builder, Carbon Fibre is an exotic material and the pieces are critical parts and have to be correctly manufactured, The cost of production in an autoclave would outweigh the advantage of using the material as opposed to wire reinforced epoxy which falls comfortably into the DIY category.

Paul

[lnvisiblemanParticipant @lnvisibleman]

OK, I'm off back to my thumb twiddling corner

[ashley needhamParticipant @ashleyneedham69188]

What about Vacform?? shouldnt be too difficult should it?? just got to make wooden patterns and take it to a vacform/plastics setup. Its something I might try later on, and also as a plus the styrene glues very well.

An alternative is to make two hull parts from styrofoam and have the shell moulded over this, but leave the styrofoam in place and carve out the space you need. Can use thinner styrene then.

Hull could also be made of slightly thicker stuff than the normal kit for durability…?

Ashley

[lnvisiblemanParticipant @lnvisibleman]

I have started on the frames, all credits to PT for inspiration.

Power will be supplied by twin water jet units powered by brushless motors, Total power supplied will be approx.2,600 watts and weight will be around 3.2 Kg.

build will be from 1.5mm ply with grp reinforcing and ( just for the hell of it ) the bow foil will be Carbon fibre composite.

[Paul TParticipant @pault84577]

If only you had asked me first I could have saved you so much time and money.

Firstly I would have told you that jet units wont work in a tilting hull because, as the hulls tilt, the intakes rotate out of the water.

Secondly, and far more fundamentally, the original tilting hull design that you plagiarised simply doesn't work as when the hulls tilt greater than 10deg in a tight corner they flip over.

The problem that designers have with inspiration is that the original flash of thought might look good on paper but it can take many months and many changes to bring that brilliant thought to life. ScaryKat is now in its 7th reincarnation and has changed quite a lot since our early discussions. for example the centre of mass has moved down to below the waterline (this stops the hull flipping over) and the bow has increased in depth to 120mm. But then I suppose that you, being a self confessed Phd will have already figured this out for yourself.

You were offered the hand of friendship and you have repaid it with unkind words, this aspect of the whole affair is the part that has saddened me most of all.

[Colin BishopModerator @colinbishop34627]

Invisibleman has left the Forum.

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Colin

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