michlet/rocker

A boat with rocker will certainly turn easier but it will be less efficient going straight.

I find that V11 is very responsive to rudder for stability. It will turn 5 to 10 degrees easily. After this it is like turning the Queen Mary. So it is easy to use the rudder for dynamic stability once at speed. A long hull tracks very well so if it lifts the nose when surfing down into the back of a wave it should be very controllable. I think flare and buoyancy in the bow will help this.

If you change the optimising speed to 5m/s in the in.mlt file you will see that the hull length is reduced while the ends get fuller. There is not much difference in power level at any speed compared with the hull optimised for 3.5m/s.

So this might be a better hull. The 8m long hull will have very thin ends below the water and I often cut these off as they offer little for the extra length.

I also fair the hull in Delftship before moving forward and then check the result in Michlet.

There was no linesplan attached. You need to choose the file and then upload to get the attachment.

Try the 5m/s hull and post the lineplan and we can discuss the merit of various changes. Godzilla will certainly produce the best hull for calm water performance. This translates to good performance in small waves but I do not have experience in ocean conditions on one of these boats. I would be tempted to leave the underwater shape and just work with shape above the waterline. With models I have made, I found that if the hull is easily driven it tends to ride waves very easily.

Rick W.

 

Linesplan

The linesplan at 5 m/s has less rocker.

Waterline length 7.28, beam 0.255, draft 0.105.

KAPER did not work in Freeship, not sure why.

Cb 0.56, Cp 0.69

LCB positive 0.014; shouldn't it be negative ?

S slightly improved with 2.21 m square

 

Now all that has to be done is work out the 'minor' detail of what sits above the waterline.

By the way I have found drag data from Freeship next to useless. This is partially recognised by the software in that it bombs out if Cp is higher than 0.64 (from memory).

If you think about what has evolved it makes sense. The wave drag is very low in any case with these hulls so as the design speed increases you find they tend to get higher Cp. The ends are fuller resulting in lower wetted area.

I would not worry about detail in the stern too much. Buoyancy in the stern can be achieved with placement of the outriggers. I am assuming you will go for two outriggers as this is by far the best if rules permit.

In a pedal boat you do not have the use of a paddle to help stabilise the boat. Hence you are totally reliant on the effectiveness of the outriggers. I find that a single outrigger induces a lot more roll than having two. If you are powering down wind in a chop then the boat rolls badly each time you cross a wave. This does not happen with two. In a beam sea you constantly have to lean into the roll if only one outrigger. With two you get snap roll but no risk of capsizing.

I also place the outriggers so they ride the bow wave of the main hull when at design speed. The back end of each just sits on the bow wave - although it is not very big. This means you can sit the outriggers above the water level and they will just sit on the wave once moving. Same thing happens in a chop. They just ride on crests. Not sure if you will be able to make use of the bow wave at 5m/s as they will be close to the main hull and a long way back. You might choose to set them to ride at say 3.5m/s - roughly sustainable calm water speed.

Taking the hull above WL, I would now provide a gently flare in the bow with a nice wave piercing shape and rising buoyancy in the first few metres to the footwell. This can also provide some wind fairing.

In my view there is not a lot of value in using carbon fibre for these hulls. Glass will provide a harder wearing finish and the shape is inherently strong. If you do the numbers, a single layer of 200gsm CF will handle the bending loads but is hopeless for puncture resistance. I find a total layup of around 700gsm is adequate. I have a flat deckline and this adds to the strength. The detail around the footwell and seat on yours needs careful consideration as this is where bending stress is highest. This area is a candidate for adding some sandwich core inside the initial layup.

You may find that this hull is too narrow at the footwell to comfortably fit your feet for good leverage. I have seen wells that provide support up the sides of the legs.

Unless you have proven reasons to move from this design I would recommend you try it out and aim to correct any disappointing aspects in version 2. Evolution, as seen in current boats, usually gets close to best after many years but remember Godzilla did maybe 30,000 iterations to get that shape. You would want to be really confident in your knowledge of what is good and bad to vary the underwater bit.

To make the deck you just keep extending the top edge and shaping to suit. It will get complicated around the footwell but is quite doable in Freeship. I could do it in a few minutes so if you are having difficulty just post the fbm file and I will modify. Keep posting the evolution of the deck and any changes you make below the waterline. Once you are happy with what is below the water it pays to export a mlt file from Freship and check the numbers.

Rick W.

 

Eckhart
There is one option worth considering. It is hard to beat a hard chine for ease of construction using a flat panel method. With this method you save a huge amount of time for a one-off construction and it is easy to get a nicely faired hull that requires little work to finish.

If you look down the in.mlt file you will see the parameter that sets the chine is noted. If the maximum is set low - (even zero) and the starter zero as well, you will get the optimum hard chine hull. I usually set it al little above zero and then make a hard chine in Delftship with sides splayed rather than vertical to approximate the shape. You will find the resulting hull will not have much higher drag than the NC hull. It will be much easier to make though using thin sandwich panels.

Rick W.

 

Design details

Rick, thank you very much.

To have the ama ride on the bow wave is a very good consideration, I never heard about it. Great.

Buoyancy in the stern with the help of the ama makes a lot of sense to me.

Do the amas have to be symmetrical or would a main ama on the left and a smaller ama on the right, such in a trimaran, be feasible ?
This would allow to 'fly' the main ama while surfing, reducing drag.
The rules require that the main ama has two iakus and that the paddle is being used between those two iakus. That is diffferent from your V11 with only one iaku. Not a big issue, the forward iaku could be rudimentary.


Using glass for the hull would be much easier; if a core would only be needed in the midsection - so much better as core is always susceptible to being soaked.

To make an initial version with hard chines is definitely a good idea. The chines would help 'carving' the turns on the wave face.
According to the study from Lazauskas it does not make much of a difference re drag.

Today I talked to one of our main boat builders. The OC started with 27 feet, went down to 19, went up to 23 and are now in the 21 - 22 ft range. All this over the last 20 years here in Hawaii. The argument is that they do not fit well into the trough when to long.
On the other hand they are not built to a displacement of 0.11 tons.

At this point I hope that the 7.28 m = 24 ft may work.

I have experience with the footwell and would like to improve on my design.
The gunnels at the feet would be narrow and have little volume, if needed I would flare the shape of the deck outside to accomodate the forefoot in a transverse direction.

I need about 0.28 m inner diameter for the forefoot, 0.27 m would do.
At the heels the transverse diameter needs to be 0.24 m, 0.23 m would also do well. The shape of the bottom of the foot well would follow the outside hull, at the very bottom it would follow the heel contour.

Currently I have a small midsection at the bottom for extra strength, it contains a stringer.

The foot plate allows full contact with the entire foot up to the palms, the angle is about 60 degrees. Higher up the angle is lower, the toes extend over that edge and operate the t-bar steering.

The cables for the steering run inside the gunnels.

The surface for the seat should be 0.12 m above the level of the heels. I asume it would end up about 0.18 - 0.20 m above the bottom of the boat.
The lateral aspects of the hip will extend over the gunnels, I was planning to create a recess in the gunnel to allow for that.


Currently I am trying to fair the hull. How many lines and sections should I import to make this effective for this length ? I have designed in Blender and in Cinema 4 D before but not much in FreeShip. So that may take a while. If you find time for a rough scetch of the deck it would definitely speed up things.

Your help is very encouraging.

 

If you are going to consider the hard chine you should look at that now with Godzilla before you put too much effort into the NC hull with fairing and the deck.

If you choose the NC hull with round chine then you need to be thinking about a foam plug to mould it on. I expect the hard chine hull will be narrower than the NC so you might struggle for room in the footwell.

I have set the number of waterlines and stations in the in.mlt file to give good hull resolution. You should import all of these and not cut any out. From memory it is 17 stations and 9 waterlines. You can check the in.mlt file.

The version of Delftship I have has auto fairing but it is not all that good. I usually just persist with the points until I get any bumps removed. It does not take too long and it gives you a good feel for the shape.

When I make the plug I loft from waterlines at 1" for the underwater section and this relates to 1" thick foam. It will take for 1" layers. Above the waterline I go to 2" sheets. I then glue the layers together and just fair out the steps in the foam. This means if there are some bumps in the model they can be faired out at the foam stage. The plug for V11G was milled from full thickness foam and I faired these thoroughly. I find making the plug from 1" and 2" foam sheets can be done in a day so having the plug milled is really an expensive luxury - unless you have a tame shop nearby. The sheets we get here are metric and are 2.5m long so work well for 7.28m hull - 8ft sheets could mean you want to reduce the length a tiny amount. If you plan the cut out you can save material.

There are a few tricks to making life easy with Freeship. Moving the image about and zooming in and out with the mouse are essential features for doing fine work. I also work between view windows. The 3D view with shaded rendering is very helpful to identify where things may be going wrong.

Rick W.

 

First attempt

I think that I will stick with a round hull.

I like the idea of flat chines in the forship , but I rather add them in case they are needed for lift.

My feeling is that the reduction of the pitching is more important than the question whether the deck is wet or not.
The speed is going to be higher in the surf and gravity is pulling so there should be enough energy to keep moving.

 

If you want to try the hard chine you should set that as a constraint in Godzilla and have it optimised with the chine.

I did a run and produced hull. I have modified it substantially so it should be rechecked in Michlet and compared with the NC hull to see how it compares.

I have tried to open the fbm file with two versions of Freeship and Delftship. None work. It is easier for me if you use Delftship. It also has a free version and is almost identical to Freeship.

I have done a hard chine version. It requires 6 panels for construction. See lineplan.

If you make this one you do not need foam. I will explain how you make development from this if you want to proceed.

I have the Delftship fbm file attached.

Rick

 

If you are keen on the NC with the rounded chine then it is easy to set waterlines at 1" (25mm) to get cutting lines for 1" foam sheets. This is done using the intersections function in the view menu. You set the start to 0 and the end to the gunwale height and then set the spacing to 0.025m.

You can then printout the waterline coordinates. These are lofted to the sheets for cutting lines.

Rick W.

 

Construction

Rick,

meanwhile I had a chance to open the file in DelftShip; the boat looks nice.

My file was made with FreeShip plus 2.9 - Delftship opens earlier files from Freeship 2.6 - but not from 2.9.



Developing with hard chines: how many stations would be needed; would you need a strongback ?

The plates would be made out of saturated fiber glass and then cut to fit ?


Performance: would you expect the hard chined boat to behave similar or different form a soft chined/ round hull boat ?


For soft chines: could a strip-plank approach with cured fiber glass strips be successful ?

 

I usually use stations at 1m. I would suggest a strongback or nice long flat surface for reference. I can fit the 7.5m on my garage floor and it is nice and flat.

I did not check the performance of the faired HC hull. You should export a Michlet file from Delftship and run the numbers (post them for me to look through). Then compare with the No Compromise hull. If it gives away a lot then go for the NC. The Godzilla HC was actually better than the NC before I did the fairing.

You can make panels from glass and a good PVC or Corecell foam. I would suggest say 200gsm on either side of 1/4" core. You might want to add say 100gsm of smooth finishing cloth on the outside of the panel to reduce effort in surface finish. These panels will be stiff with adequate strength once layed up.

I am only starting to learn about this sort of construction and making joins at the chine and deck but there are others here who can give better advice.

I have very little reserve buoyancy in the stern of HC. The intention is that you play with outriggers to get the stern to lift as you would like. You could easily add foam to the flat deck to add buoyancy. I have ideas on outriggers but not sure if they are the best. The ones I like the best for rough water are back-to-back cones. These just knife through waves without upsetting trim but they have enough buoyancy to give good long-term stability.

Rick W.

 

Michlet run HC hull

This is the 'out' file from the Michlet run.

I will run the NC and post that out file for comparison.
The limitation here is that I do not know how to properly fair the hull.
It looks pretty clean to me.


What I can see so far is that S is about 1.8 in my current OC 1,
in the NC version with 7.28 it was 2.17, in the HC hull it is 2.34.

 

Eckhart
I normally use the ship_output_by_speed.mlt file. The reason being that it is easy to import this whole file into Excel as a text file and do comparative graphs and play with units. Irrespective the drag data you got is a fraction higher at 5m/s for the faired hull than the NC. Something like 84N v 81N at 5m/s.

I think you will find other issues will be more significant than this so the HC might be a good starting hull for first round - maybe the last one of it works well. It will be quick to build if you have the materials and a good place to work.

You can make nice flat surfaces using ply with plastic stretched over them. Epoxy will readily release from the plastic.

By the way the value of surface finish is usually overstated. For long hulls like these most of the hull operates in a well developed boundary layer. If the boat feels smooth to touch then that is good enough. Achieving a mirror finish gets very little return on effort.

Rick W.

 

Michlet run NC - 7.28 m

Attached is the out file for the
7.28 m hull, derived from the NC.

The hull lools reasonably clean in shaded and gaussian views.

I am not sure that I faired it very well.

I will try to make the file DelftShip readable.

 

The HC hull is probably reasonable for developing from.

I do this by exporting the entire hull as a part and then import the hull to layers set up for say bottom, side, aft_deck and front_deck. I then strip out all the rest of the hull in each layer apart from the nominated piece. If all layers are turned on the boat will look the same. You then develop each layer using the function in Delftship.

You could make a model out of cardboard or balsa to check how it works. You might make some changes after you see the model.

As far as surface area goes it is what you get out of Michlet that counts as it looks at all significant causes of drag. Surface area is only one component. I have numerous examples of the accuracy of Michlet.

The lowest surface area is half a sphere but it makes a lousy boat.

Rick W.