michlet/rocker

HC hull

The HC idea is the better approach, you are right.

Do you expect the HC hull to behave more or less alike to the NC hull, especially in the surf ?

Ease of take off, glide, pitch/roll control and control are the main issues.

In other words what will I be able to learn from the HC hull that can be used to determine if a NC hull would be worthwile to be built ?

 

ship_ouput_speed NC 7.28

Rick,

I do not have the Excel spreadsheet, so for me it is a little hard to read.

 

What I would do is model the existing hull. I know at my power level the Yellow OC1 is about 2kph slower than my optimised black boat. However I can only get about 1kph faster at full power from the black boat. I think if I optimised for 5m/s instead of 3.3m/s the result might be more in favour of Godzilla.

You may in fact find that the HC hull actually works better than the NC because it has a flat bottom. It will eventually plane. It will have some damping in the ends. It will have some intrinsic roll damping in the main hull although this will be tiny compared with the outriggers.

Designing for flat water is easy as the Michlet model perfectly matches real life. Handling waves is another matter.

You will have an easily driven hull that should rise and take off quite early on a wave. In the end it gets down to comparing different hull forms both above and below the surface.

You will have a good base to get the footwell and seat exactly as you want. You can easily make different outriggers to trial.

If you found the HC did not outperform your existing boat then I would not recommend making the NC as you would conclude the design constraints have not been selected well.

The biggest difference I see is the very low KMT. In a pinch you can balance a typical OC1 with the paddle. You may find that more difficult with either the NC or HC. The twin outriggers should make a secure platform that is well ballanced thereby enabling relaxed power paddling. If you never have to really worry about capsize you can concentrate on moving the boat through the water.

So two things - model existing hull in Delftship as best you can, export to Michlet and compare with HC. Make the HC model so you work out how to develop from Delftship and see that it looks right.

Also post as you go so you keep us interested.

Rick W.

 

isolated plates

The plates have been isolated, see attachment.

I think I can load them individually and save them from the lifeplan view.

I have a plotter available that should be able to print the plates in their entire length.

In which format should these plates be saved so that the plotter can read them ? Would that be .dxf or should I go through gnuplot ?


Eckhart


PS I have not figured out how to load them into a layer; iow I have not arrived at a model where I can switch layers off and on.

PS: file name should be bottom not buttom

 

outrigger

Rick,

my current outriggers have a flat bottom that rises towards the bow; they are not piercing at all. We try to get them on top of the water. They are ~ 6 1/2 inches wide and getting wider.

Do your outriggers have a specific displacement volume and how far do you set the lateral distance to have them ride the bow wave at design speed ? Length/beam ?
Outrigger baseline compared to the baseline of the main hull ?

How do I approach the buoyancy in the stern through the outriggers ?


Eckhart

 

You need to get into the layer properties. You need to nominate each of these parts as "Developable". You can then use the development function of Delftship to give you the shape of the cut out on a flat surface.

Also when you import a part to a file it automatically goes to a new layer. You can rename the layer. You can have different colors for layers and many other features. You need to have a look at the layer control.

You can have a single file containing the original hull on one layer and all the parts of the hull in separate layers.

It is worthwhile taking the time to learn how to operate the layers.

It is also important to understand that you want the flat projection of hull parts and that is what development does. Makes it very simple to cut out.

Rick

 

The layers and plate development are working now. I think that the free version of DelftShip does not allow to save the developed plates.

Is there a way to export the offsets/coordinates of the plates ?
I could then feed them into gnuplot and arrive at the target this way.


"Save as" does not seem to work.

Can you save the HC hull in a down-compatible version ?

 

I like the outrigger I have on my OC1 for a single sided outrigger as it is always loaded so it needs to plane. If you have two you can balance them so they operate above normal water level. My requirement is to have them generate uplift quickly so they have a flat rocker with a long pointy nose and stern.

This video shows the cone type in operation on the yellow boat. You will see they are mostly unloaded in calm conditions. In waves they drive though with very little added resistance.
http://www.youtube.com/watch?v=ckWqIgmVM4Y

The outriggers on the black boat are slightly different in design. They work on a torque arm and roll over waves. The bow lifts rather than plough. They submerge in the middle and the stern lifts as the wave moves under. You would not be able to do this with the limitation of two iakos.

For twin outriggers I would first try the conical type. Say 6ft long bow and 4ft long stern - so 10ft overall. The mid section diameter around 4 to 5 inches. The cones are tilted downward so they have a flat rocker. For ocean use where there will always be some wave they could have in-line axes.

The front of the outriggers would be aligned with the front of the cockpit and the stern just ahead of the stern of the main hull. You need calm conditions to get advantage of the bow wave as it is very small. I normally set the outriggers about 10mm above the water level when I am on the boat. I doubt that you would detect any benefit from doing this.

I find outriggers displacing around 15l placed about 1m out work well. You need to elevate the iakos with faired struts to prevent them from clipping waves. I suggest at least 1ft above water level. You rolling moment will not be very high because you are sitting low. If you have a preferred side to paddle on you might want to create some initial roll so that the boat sits balanced when you stroke. It might pay to get the set up efficient in calm water and see how this translates to rougher water. (By the way I hate paddling. I can pedal at twice the speed I can paddle. Hence I am not the best person to discuss paddling set up. Although I agree that sitting low has merit on a number of fronts.)

Long slender outrigger hulls like those described will just rocket through waves and the roll is controlled mostly by buoyancy rather than induced lift. Set slight bow up so the stern hits first and they do tend to lift than dive. Remember induced lift will add drag that more than offsets any benefit from the lift.

You only need say 3mm thick corecell to form the cones and then glass over the outside with say 400gsm total. Weight of each should be less than 1kg.

You can use the cylinder function in Delftship to create the outriggers. Also make sure you place them on a separate layer. These will be easily developable. On the other hand diving can be nasty as it can tip you at speed.

Rick W.

 

There should be an icon on the menu bar of the Plate Development window that allows you to save the coordinates for each plate in a txt file.

Rick W.

 

FreeShip can't read DelftShip files; DelftShip free does not allow to save the plates.

I will try to reengineer the HC hull in FreeShip so that I can save the plates.


I'll rest my case for now until I have figured all this out.

Thank you very much, - thanks to you my plans are more concrete and realistic now.

The key issue will be how the boat responds in the wave.

 

My version of Delftship allows you to Save As in FreeShip 2.6. I have attached HC including outriggers.

Rick W.

 

developments

Rick,

There is actually a way of using a delftship file in freeship; it is probably not intended use, so I will hold on posting it here.

Thank you for the other file.

Next I will create some stations and see that I can print them. I will report back once I have worked out the plotting of the plates.

I am happy - it is just the beginning, nevertheless, I think I learned a lot and we were able to clarify the concept.

The video is nice; the yellow outrigger looks like a Pahoa. The double-conus outriggers scare me a little bit - they look very different from what we have in use here.


Eckhart

 

You can turn each piece off in the Development window so you only get the one piece at a time. This means you can create a coordinate file for each plate (composite piece).

I usually mirror the pieces that cut along the centreline so I get a single piece in the development. You can choose each layer to be symmetrical or not. Does not make much difference if you loft manually but if you want to plot a cutout it makes it a bit easier.

I think I mentioned earlier that the yellow boat is a Pahoa. I have tried the original outrigger and the two pointy ones. The two pointy ones are superior on many counts. They really do just slice through the waves. A planing type with a flatter ski-like nose causes a lot more drag.

If you get some thin corecell or PVC foam you should be able to make a couple of pointy outriggers in a day. Form up two cones for each outrigger with the foam and glass over. Worth a trial.

Rick W.

 

Open ocean concerns

Rick,

we have discussed the design in its current stage with regards to Hawaiian open ocean conditions.

Two points of interest came up:

1. A hard chined boat would be too 'stiff' allowing no lateral glide/movement of the hull.
This becomes an issue while paddling in sections where ground swell, wind swell an backwash cast waves at the hull from at least three directions, such as close to island shores/cliffs.

The same is true for boats that are too narrow, beam to draft.
It leads to an uncomfortable, not efficient ride and back pains.

My current boat has this problem, there are sections in local races where it has a terrible time.

Our thought, the chines have to be at least soft, or the hull should be rounded with a higher beam to draft ratio. The ideal number is generally 2.8.
We don't want the boat deep in the water.

2. There was a concern that a two outrigger layout would break in the ocean.
Examples for Trimaran failures were given. I do not have an opinion on this concern.

One main ama and a rescue ama would be an approach to consider.


Eckhart

 

The first point makes sense. To get sideways glide you need a lifting bottom when pushed sideways. The current hull will dig in.

The idea of the single hard chine was to make simple construction. Adding another panel to soften it as well as Veeing along the keel adds complexity and the foam mould becomes more attractive. I think you will find it is not the beam to width ratio so much as having a shape that lifts when pushed sideways.

I have capsized a hard chine dinghy driven by an outboard. I have cornered much faster in Veed bottom boat without tripping up. I believe lift is achievable without going to the 2.8 ratio and getting into the pack. The way you will go faster is to keep it narrow.

On point 2, the long slender outriggers work well in waves. They do not generate uplift other than buoyancy so the force can be easily determined. You do not need strong iakos to take the loads. I am recommending around 15l of displacement volume total. Maximum force is therefore 150N - peanuts.

Rick W.