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[RipSlider]

Hello all.

Before I get start this subject, please have a look at the photo's that are attached to this thread.

They show the EarthRace Wave Piercing Trimaran, which, for the rest of this and any other thread, I will just refer to as the ER boat.


As you can see, it is VERY different to the "normal" shape of a boat, what ever that might be defined as.

Here is my question:

"from a mechanical point of view, how do I build it?"

Let me explain. This is not specifically a thread about a specific modelling technique, it is more about now I build a scale model of it that won't tear itself apart.

There are two purely mechanical problems that I am facing, before I even think about build method. Both centre around the fact that it is a wave piercer. Essentially, the boat is designed to go straight through the waves rather than up and over them. When the boat has penetrated the wave to the level of the top of the cabin, the "wings" at the top of the boat apply hydrodynamic lift, causing lift which, when combined with the buoyancy of the boat itself, keeps the boat from penetrating any deeper into the water. The boat therefore drives straight through the waves, rather than going over the top of them or diving like a Sub.

visulisation is here:

http://assets.earthrace.net/vid/waves%20web%20H.wmv

Mechanical issue number 1: The pressure on the "wings" at the top and on the flying arms linking the floats to the main body are is going to e pretty strong. Unless it's utterly perfect in build, which, knowing my level of skill, it won't be, there will be some amount of force trying to pull the two floats either into or out of the boat. When the boat is at speed, and goes through a wave, there will be a large amount of upward force generated.

What sort of factors do I need to build into the design of the scale boat to allow for these forces? What is the best way to accommodate them? Do I just over engineer everything, or just add strength to certain properties? If so, which properties would these be? I'll give you an example: In the real boat, the arms, along with the first 1.5m of nose of the main hull, are solid carbon fiber. This is not something I'm going to be able to replicate, so I'm looking for alternatives.

Mechanical issue 2: I will need to get at the radio gear, just like in any other boat. However, unlike most other boats, this will be driving straight through waves at 20MPH+( power train will be an 800 sized motor or something similar brushless ). The cabin will be placed under a lot of stress, and a lot of pressure. So how do I attach it to the hull in such a way that it doesn't come off, or let in water, and still remain in scale. ( I.e, not have large bolts stiking out of the top?)

The choice of glazing material is also a consideration....


Your thoughts most gratefully appreciated.

Steve

[Umi_Ryuzuki]

Hulls are simple enough,...
Just treat the struts as you would a model airplane build and work out the "wing structure".

 

[RipSlider]

Hulls I agree are going to be pretty normal.

I was thinking along the lines of Frame and Stringer build for the struts, but not sure I can get the curves. Other option is a total loss moulding around foam plugs, but that would have little strength ( I think ).

Steve

[Umi_Ryuzuki]

The core or center line, top to bottom, of the strut can be rigid flat plates, and angular.
once you put the air foil frames on top and bottom of that form, you can fill the between with
rigid insulation foam, and shape it to a nice curve.  :)

[OMK]

Your thoughts most gratefully appreciated.

Steve

Aw, thanks. Well, in that case, I think photo #5 is sleek but spooky, and I'd wager a farthing to a groat that photo #5 could indeed be the root cause behind your insomnia
Man, that is a nightmare'y-looking vessel, is it not?

[HS93 (RIP)]

One way to go about it would be to make the Link arms from aluminum sheet bent to shape, you could use heavy gauge but drill largish holes to lighten it , this prob give you the stiffness req to take the battering it would get. It could then be padded out to give the shape req, it would also enable you to run wires cables to the sides , and you could test and adjust angles before the detail work has to start .

peter

[tigertiger]

First I would like to say that I don't know what I am talking about here. But a thought springs to mind.

Carve the outrigger arms out of that blue foam stuff.
The skin them with fibreglass for rigidity.

You may need to use some farly light weight fibreglass coz of going around such an odd set of curves, but you could do several layers.

You could allow for the thickness of FG when you carve/shape the blue foam.

In addition the core of the riggers will add bouyancy if the worst happens.
Thinking about it outriggers could be the same, perhaps assembled to the arms before fibreglassing, this would avoid a weak join.

Like I said, I don't know what I am talking about, just a few thoughts though.

Good luck.

[Arrow5]

Tiger has it  about right but add a carbonfibre centre strip. Laid-up at diagonal angle over suitable diameter same as sweepback of strut (with flat plate to sink into outrigger float) then blue foam and skin with lightweight glass. Stronger, lighter, easy obtainable aeromodelling shop materials. BTW I can email you close-up photos of the real boat as it passed through the Caledonian Canal this summer.

[wombat]

My thoughts on this - the struts holding the outer hulls are pretty bulky looking at them - the cross sectional area is pretty large. You could be a bit radical and see if you can get something like a honeycomb composite. How about doing some sort of lost wax casting - form a plug of some low melting material in the shape of the  struts - lay up on top, remembering to include internal bracing then melt out the former. This will give hollow struts so you can put stuff inthe outer hulls.

For the canopy - force is likely to be pushing the canopy sternwards, so rig up up the seal and locking arrangement so you push the canopy bow-wards to release it and stern-wards pushes it harder into the locks and onto the seal.

Wom

[RipSlider]

Arrow5.

I think I'm being thick, not quite sure what you mean, although it sounds good. Can you explain further?

Pics would be greatly appreciated. Will PM you my e-mail address.


OK, this is what I'm think of for the struts at the moment. It's sort of a combination of a few of the idea's on here.

1) Produce a frame of a vertical section through the middle of the riggers.
2) To this, add some horizontal frames to get the shape of it.
(Not sure whether to do these in ply or carbon sheet)
3) glue in blue or orange foam into the spaces, and then set to work with the surform and then sand paper
4) make it smooth with car body filler and lots more sanding
5) skin it.

For the skinning, do you thik Fibreglass will give sufficent strength? If so, what sort of weights/types of glass should I use? The other option is to use carbon fibre, as I can get hold of a Vac-bagging set up, but not sure if this is overkill with the structure that's in place


OK, a few more questions along the same sorts of lines

1) Any thoughts on the best way to make the sponsons/outriggers identical?
2) Any thoughts on how I would make a jig to get everything in line
3) The 1:1 sized boat is a monocouque. One option is to have the sponsons and struts removable, the other is to build then seperately, glue them all together, and then glass/carbon then to the main hull as a single entity. Which would you think is best approach?

Lastly, Does anyone have any thoughts on the water proof cabin? I'm thinking of using 4mm glass held in place with silicone sealant for the glazing, as it is similar to the real thing.

Many thanks for all the thoughts so far.

Steve

[RipSlider]

Wombat,

re: canopy, how would you go about making something like that? Your right in what you say about stern-wards force, had not really thought about that. I need to find a mechaism that I can hide on the inside of the boat, as the 1:1 boat is very flush around the canopy.


Question for the group:

What are the proper names for the various different parts of a trimiran called? I've used Riggers/Struts, Sponsons/floats and Canopy/cockpit. Not sure what the correct wording is.

Many thanks once again.

Steve

[wombat]

Hi Steve,

Simplest way I can think of is to have pegs or similar on the canopy, positioned inside the canopy. These mate with slots in some support structure. If you have the slots angled at 45 degrees downwards and towards the stern, any sternwards force on the canopy will be transferred to downwards force pushing the canopy harder onto the seal. To remove the canopy you would have to pull it up and forwards.

Will try to do some sketches at some point.

[Welsh_Druid]

Steve  re the canopy.

You might like to think about making a one piece plastic canopy by the vacuum moulding process and just paint over the non transparent areas- this would be very strong. 

A company by the name of Sarik Vacform near Bristol will make one off mouldings from your own plug. They make canopies for very large ( 1/3 scale) model sailplanes and can produce them in  various thickness.

Don B                                     http://sarik-vacform.com/home.html

[tigertiger]

Hi I have have some more thoughts.

Canopy, looks like it could be windscreen on commerial aircraft. As there are spereate panels.. Depends how scale you want.
also go to a model shop and see how bigger canopies are fixed on buggies, choppers etc.
It might be best to fix permanently and seal.

Floats/outriggers. These may not be symmetrical but may mirror each other.
Getting them the same will mean designing your profiles and using two sets. So a bit like making two identical boats, perhaps mirror images.

Attaching floats.
If the booms and floats are done as one assembly that fits onto the main hull. This would make transport a bit easier and the boat would only be in two pieces so stronger. Also in the even of a crash the whole lot can separate easier. A bit like some model aircraft wings.
It would also give a reasonable size hoe for access to RC gear/motors etc. Have you thought about access?

See figure.

[tigertiger]

Second thoughts

It might be better like this.
Cannopy built in to top half.

Sealing will require more thought. But the size of the opening could be smaller than the overlap of the structures.

It might be worth seeing if there are any other fast trimarans around and see how they are constructed.

[HS93 (RIP)]

I would have thought that whatever way it's built it would prob need to be adjust as you test to get it to perform. the origanal would have eather been computer modeled or put in a test tank to get the optimal set up.

Peter

[John W E]

hi there all,

My first approach on this model would be to try and contact the people who are actually running this show and to see if they can supply a set of drawings; or some good photographs.  This is because we really need to know what the hull shape is on the bottom.  We are taking it for granted that it should be a 'rounded' hull, unless we can see some photographs or some plans, even from the builders of the hull, it is only going to be guesswork.

If it was me who was building this project; the way I would do it would be;

I would make the 'outriggers' from aluminium, (see 'B' below)   balsa wood and ply-wood, covered with a thin tissue mat.  I would then put polyester resin over the top of that.  These would be bolted to an aluminium frame (see 'A' below) which would be bonded into the hull.

I would make the hull plank on frame and I would incorporate three keels; the centre keel and two outer keels.

On the two outer keels; I would bond 'A' to; and, this in turn would transmit all stresses caused by the outriggers to the outer keels; the outer keels could also carry the motor mounts.

I have included a few scribbles to try and explain, but, to be honest with you though before I proceeded further with this project I would try and locate some drawings to which I could work from.

GOOD LUCK with this project it does look very interesting 

aye
john e
bluebird

[Shipmate60]

How strong would the outrigger mounts HAVE to be.
What is the most likely conditions you are going to run her in, and are you likely to find such large waves as to submerge the main hull.
Once you have decided on the design parameters you can then decide how strong you need it to be.

Bob

[RipSlider]

Gentlemen and lady,

Firstly, thank you for all the input so far. There is a lot to think about, but my confidence levels are increasing that this is a do-able project.

This is my thinking so far:

build the main hull along the lines drawn in TigerTiger's second image, with a fairly large opening. One issue I am struggling on is that I can't currently find any information size/shape/position of the rudder, but I'm sure it will be do-able,.

next, as suggested my Bluebird, create formers using aliminium. These will have a series of slots cut into it. These will have some form of good quality plywood templates passed through them. these will effectively befome templates/formers.

At this point, I'm not sure whether to add in additional stringers, but I'll then pack out all the holes with blue or even orange foam. Lots and lots of work with knife, surform and sand paper. then the lot will get covered with car body filler and sanded to loveliness. lastly, it then gets either glassed or carboned using a vac bagging method.

Because I want to stay fairly close to scale, for the cockpit windows I think I'm going to use 6mm reinforced DiaMant glass, which is hugely strong. I'll then build these in using black aquarium silicone sealent. The add some metal strip over the outside to make it look scale.

Having spent the day researching, I've found that the stern of each of the three sections must have NEUTRAL buoyancy and be increbibly strong, in order to make the wave piericing action work. Effectively the first 1/4 of a wave pieircing boat needs to be solid and either neutral or even slightly negative in buoyancy.

Thinking here is that I build "plugs" in either solid oak, mahogany or something similarly dense and solid. This is then just going to be glassed over/carboned over.

How does all of this sound? Any issues raising eye brows?

Once again, thank you for all the advice so far.

Steve

[Shipmate60]

Only with 6mm glass, how big is she gonna be?

Bob

[RipSlider]

1meter long, at a scale of 1:24.

6mm toughened DiMant will happyily handle 20kg/inch at this kind of area, which is enough for this purpose. I can get hold of 8mm glass, but would use this only if it looks better from a scale point of view.

[John W E]

hi ya Ripslider

Just been having a good look on the other thread at the line drawing put on by Telstar.   Although this drawing seems to be just an 'approximate' drawing of the general layout.   It does give an indication of the whereabouts of some vital components.  She looks as though she has three ballast tanks right up in the bow.  I suspect these would be filled with either salt or fresh water, to aid trimming and forward motion of the vessel.   Underneath in the centre area, there seems to be her fuel tanks in the central location as stated.   They will be here because this is known as a variable weight factor e.g. as we use fuel, she does not affect the trim or the centre of gravity.     I think also that she will be twin-engined because if you have a look at this drawing, what seems to be are rudders mounted on the aft of her outriggers.

Now.....we would only mount rudders on the outriggers as an 'aid' to steering.

On your model, you are talking about making the outriggers solid.  Therefore it would be extremely difficult to have the rudders operating and you would have to rely on motor movement for steerage only.

The other thing is; with the size of model you are building, there will only be a very few times you will come across scale waves to actually see her perform wave piercing.   So, having the cockpit opening 100% waterproof I would not have thought it would be that critical for the time being.

aye
john e
bluebird

[Arrow5]

 Rip, Did you get my PM ?

[Arrow5]

Pics,this is a test. Nope cant get the rest on yet.

[RipSlider]

Thought I would give an update on where I've got to on this build.

Working with a friend of mine, who is more than a little clever when it comes to physics and engineering, we took some rough plans t the pub, along with a calculator and pad of paper.

what we came out with is that, as I'd already guessed, the part of the boat that is under the most stress is the rigger arms tlinking the sponsons to the floats. discussion then turned to the mechanism of construction, particularly the alloy centre, followed by foam, and then glass, and there would seem to be a problem.

Essentially, the forces acting on the outriggers are constantly changing, with lateral, axial and torsional forces acting in all directions, in all three planes.

how to embed the alloy into the foam without it tearing the foam to pieces was discussed at length. To this end, I now believe that, while it is a very good idea, it may not be suitable for the purpose of the riggers.

this leads me back to using a lost foam method of creation, where the moulds are created, then glassed or carboned, and then the foam disolved. I'd rather not go along this path, but it should lead to a stonger construction. I'm currently looking at the different types of glass cloth, but it would seem, currently, that I will have to use either 6 or 8 layers of carbon, or possibly a carbon,amarind mix to give strength. This is a real pain in both the backside and the wallet, and is putting me off the idea.

Second issue is that this boat does really need to be designed to work submerged, and so be designed in a similar mechanism to a submarine. The boat will pierce any wave that is around 1/2 meter high or less, and this could mean that the boat travels effectively fully submerged, apart from the top wings, for up to 2.5 meters.

This means that the construction will need to be similar to a model sub, with everything contained in a waterproof tube. This will, i expect, be another pain, as thinks like how to handle the rudder etc I've not yet worked out.

Off to post a thread in the subs section...

Steve