Tiny boat

Hey folks.

By way of introduction, I am an A&P mechanic, have previously built a wooden biplane, and am presently starting up a composites shop building custom car parts. In college, I used to sit in on my girlfriends aerodynamics classes and do her homework. I love engineering, but never really felt the urge to take the tests. I dabble in a lot of things. Presently, I have been designing an aircraft which uses some little "tricks" that I've discovered or learned about composites while in the process of manufacturing items. I've been involved in aviation since I was 12, so much of that is almost instinct to me. And before I even start a project, I learn enough so that I will know how to know when I don't know enough. And then I start reading and asking questions.

What I came up when designing the aircraft was a unique method of fuselage construction. Structually, I know it will work, but I need to see how easy it will be to build for an average builder. Basically, it's a wet-layup vaccum-bagged system on a ridiculously easy-and-cheap-to-make male mold. Of course, female molds are better for this sort of thing, but for my purposes, the male mold will be more appropriate... just take my word on that. And this brings me to my boat question. I need to build something hollow and 3 dimensional out of foam and fiberglass in order to test my construction system. I wanted something other than an aircraft fuselage though- specifically, something that I can enjoy when I'm done. A boat.

I haven't been in any boats since I was a kid. My knowledge is, admittedly, limited, but this is somewhat offset by the fact that I am willing to learn and I will be perfectly happy if the boat is less than amazing. Afterall, this is mostly going to be a testbed for the type of construction. I have a small place up in Michigan, about a block from Lake Michigan. I have a need to test out my fuselage design system. What the heck? Once I'm done, I might as well put a motor on it! But, I don't want to spend a lot of money. It will mostly be for short jaunts along the shore. I'm not talking about some seaworthy beast.

I'm thinking- a 5hp motor, an 8 foot length, enough foam to keep it afloat and upright regardless of conditions, and 400lbs with a single occupant on Lake Michigan. A fair-weather putter-about.

What I'm asking is... would such a boat be fun? I know it wouldn't be fast. I know it wouldn't be impressive. But could it be fun? I'd imagine you'd probably need to get a little bit wet from time to time and the ride would be rough as all heck. But could it be a fun machine to operate? I don't want it to feel like a ride for 5 year olds at Disneyland, nor do I want something that would be an outright hazard.



Or should I just build a kayak to test my theory and then toss it in the trash when I'm done?

 

http://www.angelfire.com/ego/lewisboatworks/Plans/LilJonboats.doc

Feel free...probably 10 have been built here and there.

Steve

 

Very cool. Very inspirational. The thing is, I need a ship with a hull and deck as a single piece in order to approximate the building conditions for the aircraft. Imagine one of those roto-molded kayaks... it would be made sort of like that- in one piece- only with foam and fiberglass. It could be done with or without extra bulkheads for support, but I have to stick with foam and fiberglass as the building material.

What I like about your designs is that they are simple and that's really encouraging. I will probably use your pictures for reference when I try to envision the way things work on a boat. Because I need to build a hull and deck as one piece, I'm guessing I'm more or less doomed to design my own. It's a lot of work, I know. And I'm trying to decide if it's worth it. Will the boat be fun? Or will it be an underpowered dog for puttering about for an hour or two at a time on the Great Lakes? To give you an idea, I'm imagining something that's sort of a cross between your Podyak and your Fisher 8... but with more of a planing hull.

What I'm fantasizing about is something sort of a cross between a sea kayak and a small hydroplane. Something that can take a little water, be self-righting, and fast enough to give you a punishing ride to give the sensation of a little speed and excitement. It's a bit perverse, I suppose, but I'm imagining something that can jar your molars out without being an absolute hazard. I'm thinking that an 8 foot hydroplane would be brutalized by the waves on a large lake, but if the boat were self-righting and you weren't going across the lake or far from land, then it might be fun and exciting.

What got me thinking about this is the new Briggs&Stratton 5hp motor. I'm guessing 15mph would be within the state-of-the-art. Would anybody dare suggest I could get such a boat going faster? Would the speed be sufficient for a little excitement? Or do I need to step up to a larger engine and greater costs to achieve my goal?

 

I want to go into a little more of an explanation of what I'm pondering and why I'm looking at boat construction.

Basically, my idea is for a reusable and collapsible form. It would allow someone to set up their entire plug in an hour or two and permit them to make the entire shell of their boat- all 4 sides- at once. It would work such that multiple people could make one-off foam-cored boats without the cost of a plug. No framing, etc. Here's how it would work:

Imagine I'm building an 8 foot boat. It's going to be built in one piece.

You would have, say, 20 metal(?) U channels, ~ 3/4" in all dimensions with the open side facing outward aligned radially. Into the channel you would screw in (or otherwise secure) a piece of wood which would serve as the stringer. This wood would be shaped to give the appropriate dimensions. Attached to the base of the U-channels would be a threaded rod and butterfly hinges. When collaped, it would be 8 feet long with perhaps 24 inches in diameter.

Now, you want to get those stringers out farther than 24 inches because the boat is going to be wider than that... so you start turning the threaded rod and this pushes the stringers outward. Then you turn another threaded rod... and another... with each threaded rod pushing different stringers out to varying degrees. I would provide a measurement describing how many inches each rod is to be extended.

When all the rods are extended, you now have the shape of the boat, as provided by the wooden stringers. You lay the foam on the stringers, fasten it by, say, wrapping roving around the foam pieces and epoxying it into place. Then coat it in a slurry. Then you lay up the layers of fiberglass all around the boat (obviously, this would have to be done in multiple steps as it would be impossible to glass a structure upside down).

Finally, once the outer shell is complete, you reach in from the passenger compartment or other provided access areas (which had no foam covering), and collapse the entire supporting structure by turning the threaded rods and pull it out the entire assembly through the transom area.

You now have a complete 4-sided one-piece structure. The form can now be shipped to someone else- in its collapsed condition to save shipping costs- to build their boat. You then proceed to glass the interior of your structure.

Of course, you would probably also want to slide in premade bulkheads and bolt them to the frame in order to stiffen up the structure a bit more before building your hull. The point is that, instead of using glue and nails and whatnot to create the male part of the mold, you are simply using threaded rods to provide tensile strength and the bulkheads for compressive strength and the "mold" is collapsible and reusable and allows you to build all four sides at once.

Admittedly, a lot of you boat people are probably reading this thinking, "Why would I want to build all four sides at once?" I confess that this would probably be much more desirable in aircraft construction than boat construction, but as I said, I'm just looking for a little project to do a proof-of-concept.


ISSUES:

Obviously, this would work great for very smooth, convex shapes. Concave shapes or anything other than gently curving foam shapes may pose a problem. Let's say you want a sharp edge along the side of the boat. Well, the bulkheads can have slots in them. You can make the desired shape in a piece of foam and then mechanically attach it to the bulkheads in order to get a sharper edge or different shape... such shapes can even be premade on a type of router for inclusion with the rest of the core. So you aren't quite as limited in shape as it might otherwise seem. You can, for example, rout out a particularly unusally shaped top for the boat and then attach it to the form. In other words, more complex shapes are possible, they will just require preplanning.

 

Same idea, different method of construction-

Make the frame into 5 pieces, each running the length of the ship: A right side, a left side, a top, a bottom, and a middle.

Once the foam is secured and the exterior is glassed up, unbolt the middle section and pull it out through the transom. This will cause the top piece to fall down and you can then pull it out as well. Next pull out the two sides, followed by the bottom.

Voila! a 3-dimensional plug that can be removed through an opening which is smaller than the plug itself.