Ferrocement Dinghy

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This topic contains 81 replies, has 13 voices, and was last updated by  shredder7753 3 years, 5 months ago.

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• #1480

elspru
Participant

70cm*110cm*180cm or 2.3ft*3.6ft*5.9ft big enough for 1 person dinghy.

Got supplies for making the ferro-cement dinghy,

bolt cutters for cutting rebar

wooden float for applying concrete

styrofoam to make it “unsinkable” float even with major breach.

68feet or 20 meter rebar for skeleton of boat,

100m galvinized wire for joints of boat,

1″ or 2.54cm hexagonal 48″*25′ or 18.6m^2 galvanized fencing.

All together that cost me \$200

there is about 33kg of portland cement left

this is the cement mixing bucket and mixing stick I’ve been using,

actually used a larger bucket for most recent boat,

might use my 5 gallon bucket for the boat.

I’m starting with the keel.

Though now I’m not sure what length it needs to be.

I had calculated the lengths based on a rectangle.

#13251

elspru
Participant

okay so I figuered out how to calculate the perimiter of an ellipse! w00t w00t!

upon realizing inability to perform integration decided to order some math reference books.

# Practical mathematics : a complete course for students in technical and trade schools, evening classes, and for engineers, artisans, draughtsmen, architects, builders, surveyors, & c. (1912)

I a simple formula to calculate ellipse perimiter by google found

source of formula http://www.mathsisfun.com/geometry/ellipse-perimeter.html

pi(a+b)(1+(1/4)((a-b)^2/(a+b)^2)) = accurate to within 0.25% which is enough for my purposes at the moment.

here are the formula’s diagrams, descriptions and calculations that I wrote in my book:

quite fortunately seems that the ellipse has fit into 6ft 182.8cm and 8ft 243.8cm rebar that I attained.

231cm gunwale, 217cm keel, 157cm beam, I’m gonna have 2 beam rebars, one for the hip, one for the shoulders, that’s 8ft*3+2*6ft=36ft 10.97m of rebar

in the follow photo rebar with white tape at measured distance applied

future construction plan, support cross hybrid lashings made of galvinized wire, binding the rebar at the beach.

am getting ashley’s book of knots, perhaps it will have some interesting additional lashings and insights.

also though likely before then, planning on bringing the chicken wire outside, so it can become “dull colored” to adhere to cement better.

I could calculate how much chicken wire it is that I expect to use, perhaps by elliptical sphere.

hmmm, could just bring the pyramid area times two or three and have extra …

can I simply bring all of it outside to leave in forest somewhere to dullen, what do you think?

calm aware desire choice love express intuit move

#13281

elspru
Participant

here is video of me rolling around the galvinized mesh in the river to make it oxidized:

here I made a rocket stove to make wood potash with:

unfortunately I’d have to burn approximately 120kg of wood, to be sufficient ash for a 40kg of cement.

so I’ll likely search for alternative sources of ash, there are some smoke-stacks near my sailing club, could try there.

if any of you know where I could get ash for the concrete would be a great help

calm aware desire choice love express intuit move

#13282

shredder7753
Participant

lol, he’s a character. “ash has many uses… it can be used as soap…”

____________

My work

“Leadership and do-ership are not the same thing”

#13283

OCEANOPOLIS
Participant

Who told you that you need wood ashes? For what?

The mortar for ferrocement is 1 part Portland cement, 2 part sand and water. That’s it.

http://www.scipub.org/fulltext/ajeas/ajeas34643-649.pdf

Also, it looks like the rebar you are trying to use is way too heavy for such a small dinghy, LOL. Keep in mind you will have to make framing of it so you can cover it with few laters of chicken wire and then plaster it. Use 1/4 ” rebar. Check out this site. Scroll down and see that those concrete canoes hulls are pretty thin. You really don’t need more then 3/4 ” hull thickness for your dinghy,…

PS. The only “ashes” might have been pozzolan, which is a “volcanic ash”, used as an additive to concrete.

http://en.wikipedia.org/wiki/Pozzolan

PPS I would suggest you go to http://www.ferrocement.net, register, post and discuss your project with the guys there before you start. You might get valuble feedback.

#13284

elspru
Participant

OCEANOPOLIS wrote:

Who told you that you need wood ashes? For what?

sulphate resistance.

Ferrocement boat book I have recommends sulphate resistant cement, which is basically cement with ash in it.

The mortar for ferrocement is 1 part Portland cement, 2 part sand and water. That’s it.

http://www.scipub.org/fulltext/ajeas/ajeas34643-649.pdf

ya, that’s fine for land based applications..

however in a marine environment there are many sulphates..

Also, it looks like the rebar you are trying to use is way too heavy for such a small dinghy, LOL. Keep in mind you will have to make framing of it so you can cover it with few laters of chicken wire and then plaster it. Use 1/4 ” rebar.

even half inch rebar bends pretty easily,

though it is rather heavy.

it was the only rebar available at home-depot.

guess I could go down to canadian tire get some of the thinner rebar.

maybe they have 1/2 inch chicken wire *hopes*.

though I can still use this 1/2 inch rebar for the larger boat correct?

actually now I think I’ll just go ahead and use the half-inch rebar,

it’s okay if the reinforced areas are protruding a little.

and based on my calculations amount of rebar I’m using is only 10kg,

considering that the concrete itself will likely weigh 60kg at least, it’s okay.

Check out this site. Scroll down and see that those concrete canoes hulls are pretty thin.

which site are you refering to?

You really don’t need more then 3/4 ” hull thickness for your dinghy,…

that’s actually much thicker than I was aiming for, I was thinking half inch tops.

PS. The only “ashes” might have been pozzolan, which is a “volcanic ash”, used as an additive to concrete.

http://en.wikipedia.org/wiki/Pozzolan

“With proper proportioning and material selection, silica fume, fly ash, calcined shale, and ground slag can improve the resistance of concrete to sulfate or seawater attack.”

http://constructionz.com/articles/fly-ash-slag-silica-fume-and-natural-pozzolans.html

I read that any more than 10% admixture could be detrimental in freeze unfreeze environments i.e. eastern canada.

though I guess you’re right in the sense that it “improves sulfate resistance” it isn’t mandatory,

and considering that it’ll likely be on a fresh water lake at least for a while, should mean the sulphate attack to be minimal.

PPS I would suggest you go to http://www.ferrocement.net, register, post and discuss your project with the guys there before you start. You might get valuble feedback.

K i sent in my registration forum.

so how many layers of 1inch chicken wire should I use?

calm aware desire choice love express intuit move

#13286

elspru
Participant

here are some more pictures from the galvinized chickenwire experience.

the zeroth thing to do is to make it safe, such as folding exposed sharps to minimize occurence

to tie it together I used an 8 knot, which is easy to untie,

then when wire came around from the other side I fed it through the same 8 knot.

I had tied three wires around, unfortunately one of the wires was too short, so I connected it with a sheet bend.

I hid the galvinized chicken wire to oxidize, behind a fallen tree, covered in bark and sticks.

calm aware desire choice love express intuit move

#13290

OCEANOPOLIS
Participant
#13291

elspru
Participant

Only managed to get to the construction site an hour before sunset, street lights were a help. also full moon in two days.

here I layed out the rebar in the manner that I would be attaching them.

here is a constrictor knot, looks like a jolly-roger, I like to start and end my lashings with it, as it has a very firm grip.

I used both square and cross lashings

here is the seizing knot that I used on the transom nearing completion.

here the frame is complete, we’re looking at it from the starboard side.

portside view upside down, on upper beach, just before I hid it in the forest.

I was in a rush and have better ideas for some of the lashings can redo it or adjust it later.

in particular the bow lashings and one of the beam lashings could use some work.

also might spend a little more time straighting out the shape,

likely will have to do it on the lower beach as it’s flatter.

for reference here are the lashings from Ashley’s Book of Knots:

2114 is the square lashing

2115 is the cross lashing

3388 the round seizing I used for the transom gunwales.

3385 finishes off the round seizing lashing.

calm aware desire choice love express intuit move

#13293

shredder7753
Participant

holy moly

what is he attempting to prove?

____________

My work

“Leadership and do-ership are not the same thing”

#13298

wohl1917
Participant

What Spru IS proving is that the first step in an around the world trip begins with the first step. He’s doing it. And it’s a more than some of us have done. I’ve bought a boat: a MacGregor 26D. I’m still outfitting her in preparation for the shakedown cruise but I have plans…

elspru
Participant

shredder7753 wrote:

holy moly

what is he attempting to prove?

Well I was actually thinking of this as a tutorial for those that come after me,

so they could build their own models, dinghy’s and seasteads.

I believe in open-source and freedom of information.

but in terms of “proving something”.

As explained in Patri’s book on seasteading.

The most general area in which we must be incremental is the size of each project, in terms of cost and number of people. For these reasons, our plan includes a series of distinct stages, each involving a greater number of people.

First we complete a design, and build an aquarium-sized model. Then a pool-sized version. Next we build a habitable Baystead prototype for 5-10 people, anchored in sheltered waters

here is my aquarium size models:

I also made tub sized models:

And now I’m working on “pool sized version” or a dinghy. we happen to have a pond nearby we could try it out at.

Oh and btw the galvinized chicken wire wasn’t oxidizing fast enough, so I dumped it in a shallow pool part of the river, with a string attached to a stick to retrieve it.

Next would be two person and a child seastead.

290cm*470cm*760cm that’s 9.5ft high, 15.5ft wide, 25ft long

calm aware desire choice love express intuit move

#13300

OCEANOPOLIS
Participant

to the oar(s) from the other thread. I wasn’t trying to tell you what to do, Spru,…. just trying to save you some time since you can buy good oars really cheaply on craigslist or at the local chandlery.

Also, I have noticed from your design that you are building a “canoe stern” dinghy. If one day you might want to fit a small outboard there you might have a hard time doing that due to the round shape of your transom. Most of the dinghys are built with a straight transom so an outboard can be mounted there. Something for you to consider.

http://www.aluminumatstudio-k.com/boat022_614x600.jpg

#13301

elspru
Participant

OCEANOPOLIS wrote:

to the oar(s) from the other thread. I wasn’t trying to tell you what to do, Spru,…. just trying to save you some time since you can buy good oars really cheaply on craigslist or at the local chandlery.

Also, I have noticed from your design that you are building a “canoe stern” dinghy. If one day you might want to fit a small outboard there you might have a hard time doing that due to the round shape of your transom. Most of the dinghys are built with a straight transom so an outboard can be mounted there. Something for you to consider.

http://www.aluminumatstudio-k.com/boat022_614x600.jpg

USD may be the petrodollar but gasoline/diesel is unsustainable, can’t get it ourselves so there is no point in using it.

honestly, I think this whole burning of subteranian oceans of oil thing is of questionable ethical standing to say the least.

Though I am of the opinion that using it for clothes and plastics is relatively renewable and thereby okay.

I was mainly contemplating using it as a sailing dinghy.

Also square transoms aren’t particularly ocean worthy.

though I may later install a wave action pump for an extra boost,

not really sure when that would be.

I’m thinking of making a keel with some semblance to a fish’s fin,

in terms of that it’s retractable, has a few ribs, with soft connective tissue.

though who knows, maybe I’ll go with daggerboard or centerboard.

calm aware desire choice love express intuit move

#13302

OCEANOPOLIS
Participant

you say so.

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