Hull for small autonomous ocean crossing boat

[elkroketto]

Hi everybody,

my name is Elias, I am a software engineer from Germany. For the last seven months I have been working on a software controlling the systems for an unmanned and autonomous boat which is supposed to travel through the oceans. The software is making great progress when it comes to navigation, power management, and communications. Unfortunately my skills in designing mechanical structures - especially when talking about water vehicles - are very limited. Therefore I hope to find some advice on this forum.

A very popular hull design used by different robot sailing teams is the so called MaxiMoop developed by the US Naval Academy. In a 2014 published paper they show two design approaches:

The original design, built and tested in 2014

Improved hull design​

Although this design is intended for sailing boats I think it is great for stability reasons: The ability to safely flip over after capsizing is crucial for a boat out on the sea far away from any human help. On the downside the deck does not offer lots of space for solar cells and every inch counts when harvesting energy. I do not intend to add any sails, only solar cells and a (small & max efficiency) motor. The overall length is going to be around 1.7 meters.

What hull design do you think would be the best for this project? Should I stick with the MaxiMoop, and resize the deck for the maximum flat area? Or dou you have any other design ideas on this special topic?

Your help is much appreciated! Best regards
Elias

 

[TANSL]

Welcome to the forum, Elias.
You have shown us the original design and the improved design. Could you tell us what each change in the hull has meant to improve. In short, why is the improved hull better than the original? What performances have been improved and how?
Maybe the answers are obvious but I am not able to guess them. Thank you.

 

[Stumble]

I would suggest that neither of those are particularly good. They have lots of wetted surface, increasing drag.

My first thought is that since human comfort isn't required a near cylinder with a thin light keel would be close to ideal. It would be uncomfortable as all heck to live on, but that isn't a real concern here.

But what is the full design brief and SOR? Does it need to carry a lot of weight, how big is it, how stable does it need to be, how fast, what's the propulsion, etc?

 

[upchurchmr]

If you are not going to have a sail you don't need a large keel area as shown above.
The rudder might not need to be so deep.

But you do need a fairly deep ballast, which you could support on the smallest sized keel. Meaning something shaped like the rudder not so long fore and aft like the keel shown.
You also should not have anything which would collect seaweed or other debris - plastic?

Perhaps something like the keel on a Flying 15 would work.

Hard to see, but most of the weight is at the bottom where it widens out.
The raked leading edge will "tend" to shead debris.
Just don't have any part of the ballast protrude in front of the leading edge of the keel.

Will it hurt power production to have the solar cells get wet? You might need to have them raised off the deck. Too much and you might need to make the keel deeper.

Longer will be more stable in the waves. Wider will get the boat thrown around more. Will motion of the solar cells be a problem?

Interesting problem, but you might need to study up on boats as much as electronics and programming.

 

[elkroketto]

@TANSL: That's a legit question. Let me try to summarize the advantages and disadvantages of the original and improved MaxiMoop design:

Paul Miller, a researcher at the US Naval Academy in Maryland, re-engineered the very basic Moop-hull that was meant to be a small (approx. 70cm length) universal ocean research platform. Due to it's lack of storage space, the first MaxiMoop design was enlarged in all three dimensions. Other requirements were: easy to build, transportable in an everyday car, cheap to build (material costs are less than 250 US$) and deployment by one person. The keel is shaped to avoid attachement of sea weed and to provide maximum stability / self erecting after capsizing.
The improved MaxiMoop is shown in the second picture of this thread's first post. Draft and Freeboard were further increased, what results in an additional payload. The revised keel has a better streamlined shape, so that the overall performance of this improved design is supposed to be higher.

I think the MaxiMoop can be a good point to start my attempts from. I just wonder if a sail boat's design is suitable for a motor boat as I am planning to build. Any opinions on that?

@Stumble: Human's comfort is indeed not an issue here. What would be the advantage of a cylindric hull? I imagine it to have way more wet surface than a flat shaped boat? Furthermore flexbile solar panels are less effective and more expensive than conventional rigids. Could you please tell me a little more about your idea? Maybe a sketch will help me to understand. Thanks

@upchurchmr: I love the Flying 15's design! The short keel probably collects less seaweed and other stuff as the MaxiMoop does. But one of my concerns is that the solar panels have a higher weight than this keel could counterbalance. I was thinking about mounting the motor and screw at the bottom of the keel. This way smaller and medium waves would not lift the screw out of the water which could improve the propulsion.
Wet solar cells are not too problematic, even though the salt (after the sea water condensed) will reduce the efficiency dramatically.

I'm looking forward to hear about your thoughts on my ideas. In the meantime I'll try to translate my ideas into the DELFTShip software.

Elias

 

[upchurchmr]

The Flying Fifteen is just an illustration.
A "similar" keel could be deeper and balance more weight on deck.
But if you have no sail rig, what is it that is causing the boat to be unstable?

If you want a motor deep in the water, you could look at a Swath design - small area waterplane. It also provides lots of deck area for the solar cells. No idea how it would work in a small size boat and ocean sized waves.

 

[TANSL]

Elkroketto, I appreciate your explanations although I do not agree with most of them. I'll give you some of my opinions. For me, for example, increasing the storage space is not an improvement but a transformation to adapt it to the new needs. An improvement would be to get more usable space without changing the dimensions. A bigger keel will only give more opportunities to seaweed. A more hydrodynamic keel does not have to increase the overall performance of a boat. This is obvious but it is clear that a hydrodynamic keel larger than necessary, heavier or poorly placed, can worsen the final result. And finally, the design of a sailing boat, in general, I repeat in general, has little to do with a motor boat.
For my part, just advise you to study a little more theory of the ship and have a lot of luck in your plans on shipbuilding.

 

[upchurchmr]

If you already decided, please let us know.
You can just say you are making a boat in a certain way and give us updates.

If you want everyone to tell you that your idea is wonderful, this is probably the wrong place. Especially when you clearly say you don't know much about boating.

Good luck

 

[Stumble]

Determin the radius of a circle with an area of 1ft^2, determine the perimeter of a square with an area of 1ft^2.

A cylinder has less wetted surface for the same reason the circle has a smaller perimeter.

 

[elkroketto]

@upchurchmr: I was hoping to discuss my thoughts on this project with experienced boat designers like you are. I don't know what parts of my post were the reasons for this misunderstandig. I am sorry if you felt offended.

The boat is supposed to cross the Atlantic ocean (hopefully, one day) from East to West. Speed does not play a big role - I think 2-3 knots will be sufficient as long as the vessel is making a tiny progress every day. Do you think that my thoughts on this part are correct or do I need overthink this again?

I read more about the Flying 15 design and I think it's quite useful for my plan. boat-ed.com tells me that the round bottom-hull moves through the water with little resistance. Due to the large keel any capsizing-situations should be handeld very well. I tried to model the hull in DELFTShip and would love to hear opinions on this hull:

@Stumble: My apologies, due to my insufficient English skills I misunderstood the term "wetted surface". I thought you were speaking of the top area of the boat, not the bottom. You are absolutely right that a cylinder has a smaller under water surface than a rectangle / square. This approach is definitly something I am going to think about - thanks for this new input.

@TANSL: As a professionnal software developer I am used to ask in forums if I am stuck in a situation. I was hoping to get help here on this topic which is completely new to me. I already have learned many interesting things on the theory of boats and currently I am trying to get everything together. Maybe you're still willing to support me on this project?

Thanks
Elias

 

[upchurchmr]

I'm not offended.
Everyone who comes here has different desires, and generally it is difficult to understand what they actually mean.

I didn't realize you were not a native English speaker, that always presents difficulty in communicating ideas and questions.

Many times people start a conversation with a definate concept in mind, but it does not become apparent until later.
There are few actual designers on this or any forum and I am not one.

The model above does not seem to match the flying fifteen, in that it has a concave bow where the fifteen has a convex bow. It is really difficult to recognize other issues without hull sections shown.
Please remember as another said above, you are looking at sailboat hulls, when you will not have a sail. Motorboats are completely different. Uffa Fox (designer of the flying fifteen) also designed an aircraft dropped life boat, used in WW2. You might look for this design since it is intended to be unsinkable and self righting in the case of heavy waves.
All boats either motorboat or sailboat will travel faster and with less energy if they are long and narrow.

 

[TANSL]

Elias, of course I will be delighted to help you in everything that is in my hand, within my knowledge.

 

[Stumble]

Elk,

No hard feelings, and perhaps I was a bit testy for which I apologize.


If the plan is to cross an ocean than a completely sealed structure would be preferred. But I am still not sure what the goal of this project is. If it's just to get a drone across the ocean then a round boat with a simplistic hull, sail, and rudder would be pretty close to ideal. It doesn't take much.

My initial thought would be a long cylinder, with a rig called a Cat (one sail in the front), with a fixed boom. The round hull being matched to a flat (across the top) set of solar panels. A deep keel (say 300mm long) with an L shaped bulb (for stability and weed shedding).

The entire mast turns, without any lines, just a small linear drive motor pushing against a mast pivot arm. Basically a very simplified Cat rig, deck stepped into a bearing.

The rudder would be transom mounted with a linear drive actuator attached to the tiller (basically a very small tiller pilot).


All of the brains, batteries, and scientific equipment would then be stored inside the hull. With the deep keel the AVS would be very high, and the force needed to re-right the ship would be almost trivial.


I am envisioning about 1.1m long by 100mm wide, though within reason the size could be pretty variable. And if you use a reasonably strong tube material (say fiberglass) I doubt it would need any internal framing or structure.


But I would be very interested in what the mission statement for the design will be.

 

[Tenedos]

I am also looking for a similar hull.

BTW, not sure if everyone knows SeaCharger:

http://www.seacharger.com/

It certainly was successful in what it was doing.

 

[Mr Efficiency]

This drone boat thing, which pops up around here periodically, seems to be some kind of ego experience, look at me, I sent a tiny little boat across the ocean ! Does it serve some useful purpose ? I doubt it, pump your own tyres up by actually doing something that serves a worthwhile purpose for someone, it ain't as bad as shining laser lights in pilot's eyes down at the airport, but is pretty damn useless so far as I can see.