[freeztar]

I have a friend that is looking to build his own boat. His basic concept is a two person pedal boat that is capable of calm sea travel. Here are some of his plans:

* the boat is to be entirely self sufficient
* generators on the pedal gears and PV cells on top of the covering will charge batteries
* an electric motor can turn a "waterwheel" near the rudder when not paddling
* the boat frame will be made of cedar and filled with flotation foam for bouyancy
* he also mentioned making a small wind turbine up top, but I don't think it's possible for him to create much energy with it
* a solar still design to create drinking water


I'm probably forgetting some stuff, but I'll amend as needed and feel free to ask questions. I've got a few of my own...

Is there an easy calculation for determining how many watts it takes to push a boat through the water? (eg 10W can carry a 500kg boat 1km, or something like that) I realize the design of the boat factors in (as well as environmental conditions etc.), but I'm just looking for ballpark figures.
Is it better to make the generators, or can they be had cheaply enough?
Would it make sense to use a car alternator in this situation?
What materials are susceptible to brackish waters or should otherwise be avoided?

Any ideas on general design and building are greatly appreciated as well!

[Cedars]

Originally Posted by freeztar

I have a friend that is looking to build his own boat. His basic concept is a two person pedal boat that is capable of calm sea travel. Here are some of his plans:

* the boat is to be entirely self sufficient
* generators on the pedal gears and PV cells on top of the covering will charge batteries
* an electric motor can turn a "waterwheel" near the rudder when not paddling
* the boat frame will be made of cedar and filled with flotation foam for bouyancy
* he also mentioned making a small wind turbine up top, but I don't think it's possible for him to create much energy with it
* a solar still design to create drinking water


I'm probably forgetting some stuff, but I'll amend as needed and feel free to ask questions. I've got a few of my own...

Is there an easy calculation for determining how many watts it takes to push a boat through the water? (eg 10W can carry a 500kg boat 1km, or something like that) I realize the design of the boat factors in (as well as environmental conditions etc.), but I'm just looking for ballpark figures.
Is it better to make the generators, or can they be had cheaply enough?
Would it make sense to use a car alternator in this situation?
What materials are susceptible to brackish waters or should otherwise be avoided?

Any ideas on general design and building are greatly appreciated as well!

Ok I am not familiar with ocean travels. #1 Cedar (or any wood) is going to be heavier than something made of aluminum or fiberglass resulting in more power needed to push it around.

I looked into generators for home (diy types). Car alternators take more input power to generate electricity than was acceptable for me. Look into motorcycle generators, they are smaller, they run 12 volt, you can find them at junk yards and swap meets, and motorcycle batteries are smaller.

Another aspect you might want to look into is electric chainsaws or weed wackers for your motor ideas.

Hope this adds something to the idea!

[CraigD]

Originally Posted by freeztar

Is there an easy calculation for determining how many watts it takes to push a boat through the water?

Here are some useful designing steps and formulae for low-power boats:

1. Determine the boat’s water speed requirement, V. This is very application-specific – for a boat intended to tool around a large indoor swimming pool, it can be miniscule. For a commercial vessel where time is money, it can be pretty high. For a boat intended for a stream or costal ocean, it must be at least as fast as the current or tide, or it will be good only for one-way trips.
2. At this point, you can determine how long you boat needs to be at the waterline (LOW), , where C is a “magic” number known as the speed/length ratio. In the traditional English units of knots and feet, C=1.34. In MKS units, it’s 1.13.
   
   For example, if you’re boat must go 2 m/s, it need be only about 3.2 m LOW. To go 3 m/s, it must be about 7 m LOW.

The “magic” of the speed/length ratio has to do with wave propagation speed. A low-power boat has far to little power to “climb its own bow wave”, or plane, so once it reaches its limiting speed, that’s as fast as it’ll go without a lot more (about 3 times) power.

1. Now that you have some idea how long you boat must be, you should be able to determine its mass M (usually called “displacement” in boat design). In addition to the mass of its hull materials, engines, passengers, and everything else in it must be included in this calculation.
2. You can now calculate your boat’s required power, . If you’re using old-fashioned units of tons, feet, and horsepower, K is 1. For MKS, it’s about 0.3687
   
   For example, for a 7 m, 2000 kg boat, you’d need about 5200 W. A stripped-down, single-person 3.2 m boat massing only 150 kg would need only about 180 W – well within the capability of even a non-athlete pedal-spinner.

Note that all this ignores a very important consideration – wind. Minimizing the above-waterline surface area of everything is pretty essential on a low-powered power boat, or it can wind up being unmanageable in a strong wind. This is also a strong design argument to have some wind power of some sort – either a large wind turbine (vertical axis like the Cousteau society’s 32 m Alcyone is a good design), or conventional sails

Originally Posted by freeztar

Any ideas on general design and building are greatly appreciated as well!

Keep it light and make it long. Use a twin-hull catamaran design, for long, thin hulls with good stability. Use a high-efficiency prop, rather than a paddle wheel.

For convincing of the goodness of these suggestions, rent a small 2-person pedal boat, and try getting somewhere in it – these recreation vessels are just that – large toys, not suitable for serious cruising.

Be an excellent mechanic before getting into any sort of open-water conditions with such a boat. Have a rescue plan, and a good radio and/or satellite phone.

Not to rain on your friends preliminary design criteria, but consider not “reinventing the wheel”, and simply building or outfitting a conventional monohull sail boat with an electric auxiliary engine, and the other goodies you describe. If money is no object, or you’re really good high-strength composite designers and fabricators, an exotic multihull can be much faster, though the possibility of catastrophic breakup or capsize remains with these high-performance beasts.

[freeztar]

Originally Posted by Cedars

Ok I am not familiar with ocean travels. #1 Cedar (or any wood) is going to be heavier than something made of aluminum or fiberglass resulting in more power needed to push it around.

I looked into generators for home (diy types). Car alternators take more input power to generate electricity than was acceptable for me. Look into motorcycle generators, they are smaller, they run 12 volt, you can find them at junk yards and swap meets, and motorcycle batteries are smaller.

Another aspect you might want to look into is electric chainsaws or weed wackers for your motor ideas.

Hope this adds something to the idea!

Definitely! Thanks!
It seems that golf cart batteries are well-suited for the task, but I haven't researched the prices (mainly because I'm pretty sure they are pricey).

[freeztar]

Originally Posted by CraigD

Here are some useful designing steps and formulae for low-power boats:

1. Determine the boat’s water speed requirement, V. This is very application-specific – for a boat intended to tool around a large indoor swimming pool, it can be miniscule. For a commercial vessel where time is money, it can be pretty high. For a boat intended for a stream or costal ocean, it must be at least as fast as the current or tide, or it will be good only for one-way trips.
2. At this point, you can determine how long you boat needs to be at the waterline (LOW), , where C is a “magic” number known as the speed/length ratio. In the traditional English units of knots and feet, C=1.34. In MKS units, it’s 1.13. For example, if you’re boat must go 2 m/s, it need be only about 3.2 m LOW. To go 3 m/s, it must be about 7 m LOW.
   

1. That's incredibly useful info. (sorry for the outline break )
   

The “magic” of the speed/length ratio has to do with wave propagation speed. A low-power boat has far to little power to “climb its own bow wave”, or plane, so once it reaches its limiting speed, that’s as fast as it’ll go without a lot more (about 3 times) power.

1. Once again, great info. Are you a sailor perchance?
   

   Now that you have some idea how long you boat must be, you should be able to determine its mass M (usually called “displacement” in boat design). In addition to the mass of its hull materials, engines, passengers, and everything else in it must be included in this calculation.

   Eureka!
   
   

   You can now calculate your boat’s required power, . If you’re using old-fashioned units of tons, feet, and horsepower, K is 1. For MKS, it’s about 0.3687
   
   For example, for a 7 m, 2000 kg boat, you’d need about 5200 W. A stripped-down, single-person 3.2 m boat massing only 150 kg would need only about 180 W – well within the capability of even a non-athlete pedal-spinner.

Note that all this ignores a very important consideration – wind. Minimizing the above-waterline surface area of everything is pretty essential on a low-powered power boat, or it can wind up being unmanageable in a strong wind. This is also a strong design argument to have some wind power of some sort – either a large wind turbine (vertical axis like the Cousteau society’s 32 m Alcyone is a good design), or conventional sails

Thanks Craig.

Keep it light and make it long. Use a twin-hull catamaran design, for long, thin hulls with good stability. Use a high-efficiency prop, rather than a paddle wheel.

My friend mentioned using a similar design.

For convincing of the goodness of these suggestions, rent a small 2-person pedal boat, and try getting somewhere in it – these recreation vessels are just that – large toys, not suitable for serious cruising.

I've taken a double paddle boat on a lake and in the ocean. It's a very tiresome affair in the ocean, but can be paddled long distances with relative ease in a calm lake or pond.

Be an excellent mechanic before getting into any sort of open-water conditions with such a boat. Have a rescue plan, and a good radio and/or satellite phone.

A radio is essential imo. I don't know of his rescue plans and such, yet.

Not to rain on your friends preliminary design criteria, but consider not “reinventing the wheel”, and simply building or outfitting a conventional monohull sail boat with an electric auxiliary engine, and the other goodies you describe. If money is no object, or you’re really good high-strength composite designers and fabricators, an exotic multihull can be much faster, though the possibility of catastrophic breakup or capsize remains with these high-performance beasts.

I'm going to direct him here and hopefully he'll join in. He started with the idea of a fiberglass frame, but abandoned it because of technicalities and expense.

He wants to build this thing REALLY cheap, but sturdy. A real DIY Viking-mobile.

[CraigD]

Originally Posted by freeztar

That's incredibly useful info.

Glad you found it so.

I should have cited its source: “Designing Small Craft” by John Teale (1976). He’s written several books on the subject – see this google search

This book was a given me on my 16th birthday by an uncle, and avid sailor and boatbuilder who designed small craft for Mossberg, a company best known for shotguns. In the 1950 and 60s, they made a brief foray into boats of various descriptions, their most successful being a line of fiberglass canoes. AFAIK, none of their sailboats were ever sold, but I had access to a couple of my uncle’s prototypes.

Originally Posted by freeztar

Once again, great info. Are you a sailor perchance?

When I can be. The old adage about a boat being a hole in the water into which you throw money is one of the truest ever spoken. My largest and best boat, a 30’ sloop based on a wrecked 26’ one I finished in 1979, I sold less than a year later. Since then, it’s been other people’s boats, and a wonderful little 12.5’ sailing dingy I’ve managed to hang on to since 1974. This last needs a new swivel main sheet cleat (a bump getting it off a car top late this summer) and new wood parts (some invisible or very sneaky bug in Maryland actually eats mahogany, something I’ve not encountered in the several other states I’ve had it), but nothing like the wear and tear and storage and marina fees on a larger one.

Originally Posted by freeztar

He wants to build this thing REALLY cheap, but sturdy. A real DIY Viking-mobile.

For cheap, sturdy, and low-ish build effort, I recommend a hard-chine (no major curves) hulls built of plywood, lumber, and deck screws, then completely covered (inside and out) in fiberglass. Expensive “marine” plywood isn’t necessary – even construction scrap can be used, though not the heavy 3/4" stuff, if you hold any hope of keeping your mass reasonably low - and while I wouldn’t trust them to last a 50+ years, ordinary blue coated deck screws appear to be good for at least 20 of exposure to salt water. Though initially sealed, you can count on some mishap eventually holing the fiberglass and wetting the wood and screws. Unlike the thick, many layer lay-up of a true fiberglass hull, a few layers over wood is almost certain to need an occasional fiberglass repair.

It goes without saying and can’t be said to often: even when doing fiberglass work as small as minor repairs, mask, glove, and be careful, or you may sorely regret it – improperly handled, fiberglass can make a blood mess of you, outside and in. Doing large work like building an entire boat, change “may” to “will”. If you’ve not already, or even if you have, read a good book on fiberglass fabrication and safety before touching the stuff.

This sounds like great fun. Please post pictures

[freeztar]

Well, my friend lives in Mississippi right now, so I will not be participating in the building. I might be able to get some pictures from him when he starts, but right now he's still in the design phase. I'm sure he'll be happy to hear that you concur with his idea for a wind turbine as I tried to convince him that it would not generate enough electricity to be useful. The last email he sent, he said he had a sketch for the basic design. I'll post that here (with his permission) once I get it.

[freeztar]

Here's the latest info I got from my friend. He says he plans to join the forum tonight, so the discussion should pick up at that point.

I checked some of this stuff out and it is some good info. I read that person who said the paddlewheel is no good, but the system becomes much more complex when I have to change the 'wheel' motion to the rotary prop motion, although I admit that the prop would be better. For starters it's much lighter.
The info on where to get electric motors rocked. I am already on the golf cart thing, but I just don't know about finding junked golf carts. I saw used motors on ebay for around 80 dollars. There might be a golf cart junk yard in Hotlanta.
I am not going to use cedar at this point. I am looking at pvc. I am going to use pvc to make a frame, then rubber coated chicken wire (tool grip stuff) to make the hull. Then I will use some type of material like hyphalon (raft materail) to cover the hull. Then I will put flotation foam in the bottom of the boat, which in sufficient amount will make the boat unsinkable. Also, the hull will be completley wired (with rubber coated steal cable) together and along with the chicken wire will make it virtually imposible for the hull to break apart. Basically the flotation foam will keep the boat afloat so the hulls task then becomes to make the boat slip through the water effieciently and to keep the inside of the boat dry. I am using PVC because it won't corrode and I will seal the pipe, which if the weight ratio is correct should create more bouyancy. This design should be very light.
Also I am going to put some flotation foam on the roof of the boat which should keep it from capsizing in ANY conditions. Drawing to follow.
One reason that I want to go with a water wheel, besides the gearing system to transfer pedal to prop, is the superior performance in very shallow water and the ability to effectively 'change gears' by simply lowering or raising the water wheel in the water. I would like the boat to perform in very shallow water (perhaps less than a foot) so a prop could inhibit that, although I am willing to sacrifice some shallow water performance for efficiency.

[LaurieAG]

Originally Posted by freeztar

Any ideas on general design and building are greatly appreciated as well!

Hi Freeztar,

Have you given any thought to Ferro Cement?

If you used curved surfaces you can gain much strength with relatively little weight and cost. I have seen Ferro boats built of varying lengths from 18, 25 and 42 foot (trawler), all on the same displacement hull design.

[freeztar]

Originally Posted by LaurieAG

Hi Freeztar,

Have you given any thought to Ferro Cement?

If you used curved surfaces you can gain much strength with relatively little weight and cost. I have seen Ferro boats built of varying lengths from 18, 25 and 42 foot (trawler), all on the same displacement hull design.

Interesting, I'd never heard of it before. It seems like overkill for a pedal boat, but seems like a great material for making a medium sized "traditional" boat on a budget.