making a hull model, or two

[Alan H]

I've worked out two rather different variations on what I'll be building, which is basically a 15 foot double-ender with 66% emphasis on sail and 34% emphasis on rowing. It'll be stitch and glue plywood.

Anyway, I've now stared at the lines for untold hours and I think each version is reasonable, each has its pluses and minuses. I'm thinking about building 4-5 foot models of each. This is partly to gain experience in the process before biting off "the real thing" and partly to decide which version to build. I'll be making them out of 1/8 inch doorskins ply. I figure that if I can build the model then I can build the real thing. If I've made some horrendous mistake, it'll show up in the model, when I only have two, ten dollar doorskin panels at stake (which I already have in the garage).


Couple of questions...

1.) am I gonna run into problems bending doorskins around a 4-5 foot model? I could up the size to 6 feet easily enough but that's getting pretty big for a model. Maybe I could make the models 6 feet and a little bit, call them a kids canoe and give 'em to my nephews...:lol: NOT!

if the answer is yes, I'm gonna have problems bending the doorskins then I will go buy some hobby balsa or veneer and make a 2-3 foot model, which will sit neatly on my shelf, or something.

2.) You boatbuilders out there...does comparing model hulls help you in the decision-making and design refinement process? Could you elaborate on that?

Thanks.

[donald branscom]

Answer to both questions. YES... elaborate- It helps you figure out how much you can bend door skins.

[Alan H]

Originally Posted by donald branscom

Answer to both questions. YES... elaborate- It helps you figure out how much you can bend door skins.

I kind of wondered. I made a hard companionway cover for my old 30-footer out of doorskins epoxy sandwiched around foam and I was shocked at how tough the doorskins were to bend. I mean, I had 75-80 pounds sitting on a roughly 18-inch-square sandwich suspended at the edges and I might have gotten 3/4 of an inch deflection. Once the sandwich was set up, wow, was that thing ever rigid. I could easily have jumped up and down on it, and it wouldn't have budged.

OK...likely I'll be moving to balsa or veneer, then.

[perldog007]

Can't really call myself a boat builder ( yet ) . When I made my box punt modeling helped me settle on dimensions and a particular design. Now looking to make a car top row/sail boat, again making models is proving helpful in deciding what is desired and what ain't.

I have been working on an 1/8 scale, mainly because that's what Dynamite Payson recommends. The Bolger Cartopper and Michalak Piccup Squared were made Dynamite style, by copying 8:1 scale plans and cutting them up for patterns.

The dory model is Gavin Atkin's Doris the Dory, and I made it by measuring plans from his book and extrapolating those numbers to a 1/8 scale model.

One advantage to these smaller models is that you can mill your owm stock with a table saw or buy thin stock at a hobby store. The models shown contain both kinds of wood.





Have to admit though, a five or six foot model sounds pretty cool.

[TerryLL]

I've built several models and I would highly recommend the process as an excellent learning aid to the full-size build. If you're working from a table of offsets in feet and inches, then a 1/8th model is an easy scale to work with.

A foot on the boat will be 1.5 inches on the model, an inch will be 1/8-inch, and so forth. For a 15' boat, the model would be under 2' long and could easily be done in balsa. Nice thing about hobby shop balsa is that most of the stock will be in thickness increments of 1/32-inch, which matches the scale of the model. An X-acto knife, a box of T-pins, and a tube of glue and you're good to go.

[W Grabow]

1.) am I gonna run into problems bending doorskins around a 4-5 foot model? I could up the size to 6 feet easily enough but that's getting pretty big for a model. Maybe I could make the models 6 feet and a little bit, call them a kids canoe and give 'em to my nephews...:lol: NOT!

if the answer is yes, I'm gonna have problems bending the doorskins then I will go buy some hobby balsa or veneer and make a 2-3 foot model, which will sit neatly on my shelf, or something.

2.) You boatbuilders out there...does comparing model hulls help you in the decision-making and design refinement process? Could you elaborate on that?

1. I used the thickness of the sheathing to help determine the scale of my models. If I can't bend it around the model, it will also be a problem with the full size design. Soak your doorskin in a bathtub before bending it and it will bend easier. You can also create a basin for the full-size ply panels to ease their bending. I used 1/5 scale for an 20' full-size design and sheathed the model with 1/8" doorskin. I also created scaled dimensional lumber for the frames, keel, etc. in the model. It is wonderful to solve all your problems on a model before attempting the full size.

2. I created four sequential models before starting the full-size build and still made some changes between model #4 and the actual build. It really helps to see your boat in three dimensions. I also was able to float the model in a tub and check displacement calculations and the anticipated distribution of loads.

[donald branscom]

I like using 1 inch = 1 foot. The reason is that for boats that we can build at home the model ends up being a nice size and all the wood for the model can be bought from a big box store. Once you have to start buying the wood from a hobby shop the price gets VERY expensive.

Here is my model of a 36 foot boat . The model is 36 inches.

[Ed Armstrong]

Beautiful model Donald. I've been working on a 1-1/2" = 1' model of a 22-foot Gartsides cutter. It's been fun and educational.

Ed

[MountainMan]

How do you calculate weight on a scale model? Is it the same as length? I was just wrestling this idea. I have a hull model of a 14ft row boat, built at 1:12 scale. So I have a model 14 inches long. I want to test loads in the model. I am 6ft tall, 250lbs. If I scale my self by the same ratio, I would be 6 inches tall and over 20 pounds. That doesn't seem possible. Am I calculating this incorrectly? Oooohhh I knew I shoulda paid attention in algebra!

[perldog007]

Originally Posted by MountainMan

How do you calculate weight on a scale model? Is it the same as length? I was just wrestling this idea. I have a hull model of a 14ft row boat, built at 1:12 scale. So I have a model 14 inches long. I want to test loads in the model. I am 6ft tall, 250lbs. If I scale my self by the same ratio, I would be 6 inches tall and over 20 pounds. That doesn't seem possible. Am I calculating this incorrectly? Oooohhh I knew I shoulda paid attention in algebra!

Some things just don't scale easily. Remember that your model is 1/12 length, 1/12 beam, and 1/12 draft. To me that suggests 250/12/12/12 roughly .14 pounds I think that's roughly two and a quarter ounces.

I ain't no engineer - mebbe one could chime in?

[wizbang 13]

I've built many small stitch n glues' to my own "design" using cardboard @ 2" to the foot. Cardboard for matting artwork, bought from art framing shops. Build models for 2 dollars in cardboard,10 dollars in balsa.Every problem will show up in the model. I stopped using glass tape on the seams years ago, just use a bigger filet of 403 (west). Most recent is a 13 footer of quarter " ply with a (gasp) 40hp merc, goes 50 mph.

[perldog007]

Originally Posted by TerryLL

I've built several models and I would highly recommend the process as an excellent learning aid to the full-size build. .....

From my newbie perspective, models would not mean so much if my skills were sharper. When I look at my poor twisted models, I can easily see where the trouble starts.

The next round of models will be better and there will be another batch of mistakes i find out about at near zero ( disposed cardboard) or as much as ten bucks or so a hull when i buy wood instead of milling it myself with a table saw.

I have asked folks with skills if their models are important to them, and they insist they are for alerting them to possible trick bags in the "live" build.

[TerryLL]

Originally Posted by perldog007

I have asked folks with skills if their models are important to them, and they insist they are for alerting them to possible trick bags in the "live" build.

The models I built were from plans of dories and dory-skiffs, and I used the offset table to build an exact 1/8 scale model. The process involves lofting the plan at 1/8, constructing the frames, setting them up on a strongback, and planking the frame. Pretty much the exact process you would use building the actual boat.

As a nube back in the day, this process definitely taught me how to loft the hull from the table and fair the lines. I was able to experiment with many different interior layouts and rig options for minimal expense.

It occurs to me that some folks take an entirely different approach to model making. They start with an idea for a hull and go right to cutting plank and gluing or taping the pieces together. This produces a quick 3-D look at the hull, but turning that unique model into a table of offsets for the full-size build is not a simple task. This method is akin to carving a half-model and then taking the lines off the model, and then generating the offset table from the lines.

I've never considered my design skill sufficient to start from scratch with an entirely new hull. So I pick a design that's close, tinker with the lines on paper, develop an offset table from the lines, and then build the model. Most end up in the woodstove. That's the most valuable aspect of model building, you get to burn your failures and move on.

[wizbang 13]

Offsets for a stitch n glue? Whats wrong with taking apart a "good" model, taking some measurements from it and scaling up to the full size?

[perldog007]

Originally Posted by TerryLL

The models I built were from plans of dories and dory-skiffs, and I used the offset table to build an exact 1/8 scale model. The process involves lofting the plan at 1/8, constructing the frames, setting them up on a strongback, and planking the frame. Pretty much the exact process you would use building the actual boat.

As a nube back in the day, this process definitely taught me how to loft the hull from the table and fair the lines. I was able to experiment with many different interior layouts and rig options for minimal expense.

It occurs to me that some folks take an entirely different approach to model making. They start with an idea for a hull and go right to cutting plank and gluing or taping the pieces together. This produces a quick 3-D look at the hull, but turning that unique model into a table of offsets for the full-size build is not a simple task. This method is akin to carving a half-model and then taking the lines off the model, and then generating the offset table from the lines.

I've never considered my design skill sufficient to start from scratch with an entirely new hull. So I pick a design that's close, tinker with the lines on paper, develop an offset table from the lines, and then build the model. Most end up in the woodstove. That's the most valuable aspect of model building, you get to burn your failures and move on.

I plan on learning lofting exactly that way. I don't know that I will ever build a boat that way, but it's something I would like to know how to do.

All in all, from my limited perspective I can't really see a good reason for the home builder not to make at least one model of any design before "going live".

[Alan H]

Originally Posted by wizbang 13

I've built many small stitch n glues' to my own "design" using cardboard @ 2" to the foot. Cardboard for matting artwork, bought from art framing shops. Build models for 2 dollars in cardboard,10 dollars in balsa.Every problem will show up in the model. I stopped using glass tape on the seams years ago, just use a bigger filet of 403 (west). Most recent is a 13 footer of quarter " ply with a (gasp) 40hp merc, goes 50 mph.

Matting board. Brilliant. THANKS!

[bwd]

Maybe get the gougeon bros. epoxy + wood boat building book (aka the Bible of the Epoxy Church).
It has a little table giving scale plywood thicknesses for 1":1' models, for full scale plywoods 1/4" and up -the model plywood needed is quite thin. I think 1.5mm models for 1/4."
IMHO the book is well worth the price, since it has 30-40years of experience as its basis.

Aircraft spruce has an ok price, hobby shops usually a rip off. But yes, cardboard is cheaper!

[TerryLL]

Originally Posted by wizbang 13

Offsets for a stitch n glue? Whats wrong with taking apart a "good" model, taking some measurements from it and scaling up to the full size?

Sam Devlin wrote a great article about converting a conventional design to S&G developed panels without the use of a computer. The process involves making a very accurate S&G model, transferring the developed shapes to mylar, then scaling up to full size.

WB #106, p. 80-89.

[Alan H]

'allo??? I must be on the right track, as my preferrred design appears to be essentially identical to the Chesapeake Light Craft 15 foot skerry, except for the rig. i was going to use an unbalanced lug. OK, there are a few other details that are different, like how I was going to set up the center thwart and the daggerboard, and details of the fore-aft flotation tanks. Aside from that.... Looks like the CLC Skerry is designed by John C. Harris, who apparently is the CEO of CLC..

http://www.clcboats.com/shop/boats/b...inghy-kit.html

Pretty boat, to my eyes...

I must not be TOO far off the mark.

[StevenBauer]

There are a few others that have designed 15' double enders.










Steven

[Alan H]

Originally Posted by StevenBauer

There are a few others that have designed 15' double enders.










Steven

Lovely boat! Wonderful! More pictures, please!

[StevenBauer]

I guess you missed all the threads of building this Faering, Alan. I suppose it was a few years ago. My son and I built her starting when he was in middle school and finishing when he was in high school. She is an Iain Oughtred designed Elf. Her maiden voyage was at the Small Reach Regatta in Brooklin in 2007. Most of the pics from the early threads are broken from the Imagestation debacle but I've fixed most of them on this one:

www.woodenboat.com/forum/showthread.php?t=23

Gavin is still using her, he did some island camping on Casco Bay in her this past summer. Feel free to ask any questions you may have.

Steven

[Alan H]

Originally Posted by StevenBauer

I guess you missed all the threads of building this Faering, Alan. I suppose it was a few years ago. My son and I built her starting when he was in middle school and finishing when he was in high school. She is an Iain Oughtred designed Elf. Her maiden voyage was at the Small Reach Regatta in Brooklin in 2007. Most of the pics from the early threads are broken from the Imagestation debacle but I've fixed most of them on this one:

www.woodenboat.com/forum/showthread.php?t=23

Gavin is still using her, he did some island camping on Casco Bay in her this past summer. Feel free to ask any questions you may have.

Steven

Excellent, and thank you! The construction pictures answered two of my questions, but take a look at your message in-box!

[Alan H]

OK, I now have an inexpensive t-square, an x-acto knife, a piece of 36 x 40 single layer matting cardboard and a nice 20 inch s.s. straightedge. Oh, and 4-5 really sharp pencils.... And a hot glue gun and glue stix. I spent $30 and I don't really need the straightedge, which was $10 of that $30 but it called to me. I have some small-gauge brass wire in the garage for stitching the panels together.

1. Plot the panels from the coordinates from the Hull program. Stick pins in the plot points. I can push the fairing batten up against the pins.
2. Fair the outlines with a batten, draw the panel outlines
3. cut 'em out
4. punch a mess of holes along the edges with little pins to "stitch" through
5. stitch the panels together
6. hot-glue in the three frames/bulkheads
7. hot-glue the chines.
8. trim the wires
9. tape the outside of the chines with masking tape
10. take pictures, upload, post on web
11. put URL of model pictures on Wooden Boat forum
12. drink whisky, placate wife, go to bed
13. arise next morning, check for comments, insights, insults and flattery (highly unlikely)

I've taken the panel layouts from Carlson Designs Hull program, and shrunk it down to 1/6th scale. This gives me a model that will be 31 inches long. We shall see. I have all afternoon, tomorrow. Kudos to wizbang 13 for the matting cardboard idea. The whole piece cost $4.25

[wizbang 13]

And in your favorite color! Hey now!

[Alan H]

Originally Posted by wizbang 13

And in your favorite color! Hey now!

Yeah, white! LOL

Anyway, I'm about three, maybe four hours into it, spread over two evenings and a morning. I found that a sharp box cutter did a better job cutting the cardboard mat than an x-acto knife. Anyway, I know this thread is kind of dumb for many of you, you're far far beyond this stage. Still, I expect that someday, someone will come along who wants to make a design model, and not spend a mint doing it, so I'm going to toss details in here as I go along.

The design is a 15 1/2 foot double ender, figured out by using Carlson Design's "Hulls" program. It's a three-panel-per-side boat, and of course, no transom. There are three frames/bulkheads. The center one is pretty much right at the center of buoyancy of the hull, which also happens to be really close (according to the computer) to the center of lateral area. Three-four hours has gotten me through plotting all the panels, cutting them out, and I'm almost done poking little holes in the edges with a push-pin for the stitching wire. I have one last panel to do, then I can start stitching.

I think I'm going to stick a rig in this thing, just to see how it looks. Maybe I'll fudge together a rudder, too. I figure a quarter inch dowel and a sheet of construction paper should do it for the rig and I can cut something like a rudder out of the cardboard mat stock.

One limitation of the Carlson program is that it makes everything straight lines...it creates curves by generating lots of straight lines that change direction. This is fine for the sheer and chines, as the bending of the material, when you get to construction, make a nice smooth curve. However, unless you use lots and lots of panels, which means cutting them out and stitching them up (read: a lot more work), when you get to the bow and stern profiles, you'll discover that you're a bit limited in the shapes you can generate. While I would absolutely love a nice, curved bow profile like an Oughtred boat like "Elf" or "Tirrik", or François Vivier's "Youkou-Lily", or a nice American peapod it ain't gonna happen unless I make several models, working out the details of how the panels curve by trial and error. I *might* do this, but I can forsee that this will take me at least three tries and maybe four, and I'm not sure that I have the patience. We'll see how the straight bow profile works. If anyone knows a "computer" way around this, meaning another computer program into which you can import Hull files, and you have a bit more flexibility with panel shape, please share!

There will be folks who will say "if you want a boat like an Oughtred boat, then why not build an Oughtred boat?" The answer to that is that for a long time I've wanted to build a boat to MY design. Sure, that design might be influenced, even heavily influenced by looking at what other designers have come up with. But the point of this exercise is that what I make is MINE, even if it has some compromises. I originally wanted to build a 24-26 foot cruiser-racer,a nd sail it solo to Hawaii, but common sense prevailed. Then I though I'd design and build a low-tech mini 6.5. Again, common sense prevailed. Thus....going along with my current thoughts about downsizing my boating costs and general grief/fun ratio.... a pretty 15.5 foot daysailer and camp cruiser. It's gonna be called the "Herron Island 15 1/2" after the island in South Puget Sound that I've spent many summer weeks on, with my in-laws over the past 15 years.

BTW, what really started me thinking this way was the 2009 Wooden Boats "Small Boats" magazine. "Harrier" jumped off the page at me, and that got the juices flowing. Thanks, Ben!

Finally.....This is fun!

[S B]

I have made half models, some my design, some not. I used a half sheet of 3/4" fiberply or plywood as the base,for the constructed ones. Working 1/2 or 1/4 scale you get to use the same type fastner and material,smaller of course. I worked the design on a 2'x8' panel and built the model on the actual drawing. The closer to lifesize you work the better.

[bucheron]

Originally Posted by MountainMan

How do you calculate weight on a scale model? Is it the same as length? I was just wrestling this idea. I have a hull model of a 14ft row boat, built at 1:12 scale. So I have a model 14 inches long. I want to test loads in the model. I am 6ft tall, 250lbs. If I scale my self by the same ratio, I would be 6 inches tall and over 20 pounds. That doesn't seem possible. Am I calculating this incorrectly? Oooohhh I knew I shoulda paid attention in algebra!

Sorry I should have contributed to this superb thread a bit quicker.

Height is a length dimension. Divide lengths by 12 to get the scale length. So the model of you is right at 6in tall.

Weight is a function of volume. Volume is found by multiplying 3 length dimensions together. Each of those lengths must be divided by 12 to get the scale volume. Therefore weights must be divided by 12 cubed or 1728, to get the scale weight.

250lb / 1728 X 16 = 2.3 oz is the scale weight of your body.

Weston Farmer was a keen user of models for boat design. There is a chapter or more about it in his book "My Good old Boat Yard" I think is the name.

BTW, areas need to be divided by 144, but usually you are making an area by plotting it out with lengths, so the calculation does not arise.

[perldog007]

Originally Posted by Alan H

There will be folks who will say "if you want a boat like an Oughtred boat, then why not build an Oughtred boat?" The answer to that is that for a long time I've wanted to build a boat to MY design. Sure, that design might be influenced, even heavily influenced by looking at what other designers have come up with. But the point of this exercise is that what I make is MINE,

Alan, I can't fault your talent of design ( I still wear my X-Kilt all the time) and I am envious of your sailing ability. If I was going to sail for Hawaii I would want that freestyle cruising deal where you don't have to sit with the same folks at dinner every night....

But maybe for your first build you should go with a proven design by a celebrated naval architect and just to be safe, paint it so's as it's visible in case of emergency - like this model...



Sorry, I couldn't help myself I really meant to make it to my @$$0#0L1C$ anonymous meeting tonight but I fell off the wagon....

Seriously, I am reading John Gardner's book and the double enders are extremely beautiful and interesting. Can't wait to see the model.

[Alan H]

Originally Posted by perldog007

Alan, I can't fault your talent of design ( I still wear my X-Kilt all the time) ...

I thought that picture looked familiar!!! LOL

[Alan H]

OK, here we go. I am REALLY glad I made the model before butchering $150 worth of Hydrotek!

layout... The sheets of paper are the panel dimensions created by the Carlson Design Hulls program. You can see my cheap T-square.



And here are the panels and three frames all cut out and looking nice on the dining room table (also the site of all X-Kilt sewing!).

[Alan H]

FINISHED MODEL

uh-oh. I see problems already!! The sheer is all wrong!!



Above the bow...

[Alan H]

Above the stern...



head-on forward sections, sorta.



And this one that I took to illustrate the one really big problem.

[Alan H]

What did I learn?

1. I CAN make a model and learn stuff from it. So now I'm going to make some changes and make another one.

2. Nifty ideas which seem good on the computer very well may not work out so great in real life.

3. Little changes on the computer screen translate to big changes in the model and probably HUGE changes in the real boat.

4. Even a little error in where the bow and stern frames go makes a gigantic difference in the shape of the boat. In contrast, a little mistake in the middle doesn't have such a huge effect. (if you look slosely at the pictures, you'll see where I had to cut out the fore and aft frames, because I'd but them in the wrong places.)

5. Hot glue is nifty stuff, but it's kind of messy. I've never used it before!

****

BTW, I hot-glue'd in the "frames". The little glue gun cost all of $4.50.

I thought I'd designed this boat to be slightly asymmetrical. I wanted the stations aft of the rowing seat to be a bit more full (and more buoyant) than up forward, because I knew I'd be spending more time back there. Also, if I take the Mrs. out for a nice row on the Estuary, she'll be sitting back there, and I need the buoyancy so that the boat doesn't dog along, butt-down.

However, what I thought was a fairly subtle difference on the computer screen is a HUGE difference in the model. I will be making model #2 a lot more similar fore-and-aft.

Also I tried to make the aft sections flatter than up forward. Again, this was to be a subtle difference. Subtle? NOT!!!!

I also think that I might try my hand at some freehand stuff. I do so like the pretty, sweeping faering bow. So I'm gonna tweak this thing and see if I can't freehand the front edge of the middle panels to work some curve into it. I don't mind the straight stern...makes it easier to attach a rudder, anyway.

This was a *very* valuable exercise, and I have enough mat board to do another one. Besides, it's so cheap that really this is just an investiment in time. I can forsee that I may very well make three models before I move off into plywood.

[Alan H]

Originally Posted by perldog007

...........

But maybe for your first build you should go with a proven design by a celebrated naval architect and just to be safe, paint it so's as it's visible in case of emergency - like this model...

Honestly, I've been tempted to make a three-sheet (approx. 11 foot) v-bottom, single chine, stitch-and-glue skiff out of exterior AB ply for practice. That's pretty simple and it wouldn't cost much. I've got a line on a used 14 foot aluminum mast and could cobble together the rest of it pretty easily. Then I'd give it to my nephews and chalk it up to a learning experience. I could also haul it up to the in-laws place up on Puget Sound so the whole family could use it.

I still might do that. BTW, I scored a free 14-foot boat trailer off of Craigslist today. Yee-ha!

[wizbang 13]

Hi Alan,I've not used a computer for designing,wouldn't even know where to start. Here are a few thoughts.. pull those station molds outta' there and see where the "wood"wants to go. Try using cheap paper tape to put it together, easy on and easy off for "adjusting" ."draftsmans"tape is very weak and will not tear the mattboard apart if you try to pull it off.Design wise, and I'm no designer"try the center plank smaller and top plank taller. Bet 'cher gettin' a feel for it real fast. Make a freakin dozen, these models aren't for decorating the hearth,(build one of balsa when your done if you want one of them). Building a "dirty" (cheap ply) boat will still cost in adhesives and abrasives. You'll get what you want, your very close!

[Alan H]

Originally Posted by wizbang 13

Hi Alan,I've not used a computer for designing,wouldn't even know where to start. Here are a few thoughts.. pull those station molds outta' there and see where the "wood"wants to go. Try using cheap paper tape to put it together, easy on and easy off for "adjusting" ."draftsmans"tape is very weak and will not tear the mattboard apart if you try to pull it off.Design wise, and I'm no designer"try the center plank smaller and top plank taller. Bet 'cher gettin' a feel for it real fast. Make a freakin dozen, these models aren't for decorating the hearth,(build one of balsa when your done if you want one of them). Building a "dirty" (cheap ply) boat will still cost in adhesives and abrasives. You'll get what you want, your very close!

Yeah, you know, I almost did that. The aft frame isn't bad. If it were 5% wider with a little more flare, I'd have it.

Your comment like this: "pull those station molds outta' there and see where the "wood"wants to go"

is EXACTLY my first thought after I glue'd it all together. I was saying....If I just set up the center frame and then let the panels fall where they wanted, this would be pretty good. That's true except for the fact that I'd have wound up with a really flat forward section. But in principle, I think you're right.

I also thought I'd pull the front frame out and make it a bit differently...basically, wider....and toss it back in there. But there are a few other things I want to change. The sheer isn't right, for example. But I can see that I'm close, I can get something out of this process that's going to work.

[StevenBauer]

If you slide the forward frame towards the bow a little it will fix some of your problems, the bow will be fuller and the sheer will look better. Keep at it.


Steven

[Daniel Noyes]

Yikes!
this highlightes the brilliance of the traditional "dory built" technique that produces a fair hull without lofting

[TerryLL]

A second yikes.

I'll stick to my fairing battens, spline weights, and offset tables. All that old worthless stuff that is so last century (literally).

A prime example of the kind of weird result a design program can produce.

[Alan H]

Originally Posted by TerryLL

A second yikes.

I'll stick to my fairing battens, spline weights, and offset tables. All that old worthless stuff that is so last century (literally).

A prime example of the kind of weird result a design program can produce.

Whoah, wait a minute.

I purposefully made the bow section smaller. I wanted a thinner profile up forward than aft, as I wanted more buoyancy aft. This is exactly what I got, just that I got a bit more of it than I thought I did.

This is not something that the computer did that was "wrong". It was something the designer tried out that didn't work. I need to emphasize that. The computer did nothing WRONG, here. The designer made a mistake. Also, because you're working in a smaller scale...the size of your computer monitor... you don't see things quite as well. That's why I'm going through the model making process. Also, I've never made a hull model before. This is a total, rank amateurs first shot at the whole process.

I would *STRONGLY* urge against condemning all computer hull design programs, outright, on the basis of this model and what you see. In fact, if there were one single, simple, intuitive computer hull modeling program to try out, this is it. Carlson Design "Hulls". One wonderful thing that this program allows you to do is make changes, radical changes and view them instantly. Yes, the scale is small so you'll miss details (obviously) but if you tried that with your battens, etc. it'd take ten times longer. "Hulls" is a free download, and it runs on Windows 98, 2000, XP and presumably Vista as well.

http://www.carlsondesign.com/#Fun_Shareware

If you have traditional boatbuilding experience, then you can make more educated judgements about what you see on the screen than I can, so you probably won't make mistakes like the one I just made up there.

I'm not knocking the traditional way of doing things at all, those methods worked just fine for a long time and they still work. I'm just warning against judging too much about "computer aided hull design" by what you see in this model. Besides, the second revision is done, and I made significant changes. Also, the second revision will have...*gasp* a freehand drawn line in it. Yup, I'm going beyond what the computer can do. I bet I'll not get the curve quite right the first time. Thus, I bet dollars to doughnuts I'll be making a third model to refine it.

[TerryLL]

Alan,

Apologies are perhaps in order, but I meant no offense.

With a design program it is quite easy to get results like yours, a model with significant unfairness, hollows and bulges.

Dan mentioned traditional dory construction that relies on the stiffness of the planks to insure a fair hull. I mentioned fairing battens as a traditional method of insuring a fair curve. Using either of these methods would make it very difficult to get the type of unfairness that you got with your design program. That was the point I was trying to make, but didn't express myself at all well.

Your program will certainly do exactly what you tell it to do, and if you program it to produce an unfair design, an unfair hull is what you get. Design programs can be incredibly productive in the hands of an experienced designer, but I wouldn't recommend them as a starting point for a new builder. I've played around with a couple different programs and agree with you that they are fast and easy to use. But when it's time to fair the lines for the model, out come the battens and the spline weights.

[perldog007]

I don't know Alan, my money is on you pulling it off. After all folks designed their own boats for more of human history than they haven't . But a lot of them did drown in the process. Discretion, safety, prudence, and all will be well. I really like double enders and planking, but my skills are far from that goal. I will be happy for a plywood one or two chine rowboat that does not suck.....

[Alan H]

Originally Posted by TerryLL

Alan,

Apologies are perhaps in order, but I meant no offense.

With a design program it is quite easy to get results like yours, a model with significant unfairness, hollows and bulges.

Dan mentioned traditional dory construction that relies on the stiffness of the planks to insure a fair hull. I mentioned fairing battens as a traditional method of insuring a fair curve. Using either of these methods would make it very difficult to get the type of unfairness that you got with your design program. That was the point I was trying to make, but didn't express myself at all well.

Your program will certainly do exactly what you tell it to do, and if you program it to produce an unfair design, an unfair hull is what you get. Design programs can be incredibly productive in the hands of an experienced designer, but I wouldn't recommend them as a starting point for a new builder. I've played around with a couple different programs and agree with you that they are fast and easy to use. But when it's time to fair the lines for the model, out come the battens and the spline weights.

OK, it's all good!!!

I'll say this... that model would look at LOT better if I ditched the forward frame and just let the cardboard planks find their own way. It wouldn't be what I designed, but it would be a better boat!! Unfortunately, it wouldn't have had the "V" in the forward section of the bottom planks, either. On the other hand, the sheer looked an awful lot better!

The principle of not forcing the materials into unnatural shapes they don't want to go into, seems like a sound one at this level of boatbuilding. If a batten doesn't look right, then it probably isn't right, eh?

Let's see how version #2 works out.

[Alan H]

Originally Posted by perldog007

I don't know Alan, my money is on you pulling it off. After all folks designed their own boats for more of human history than they haven't . But a lot of them did drown in the process. Discretion, safety, prudence, and all will be well. I really like double enders and planking, but my skills are far from that goal. I will be happy for a plywood one or two chine rowboat that does not suck.....

Oh, even that disaster I modeled up there wouldn't flip over!

If I had blown off the model-making process and just cut out the parts and starting stitching plywood together, I would have figured out mighty quick that something wasn't quite right. I'd have moved the center station forward about a foot, and re-made both the forward and aft stations. Now, it might have been a bit of trial and error, but I would have come up with something that would have built up a reasonably natural hull form. It would have floated right side up! ...would have probably rowed OK, too. Now, it probably would not have had anything like the designed stability, but it wouldn't have been *grossly* off. I don't think I'd drown in it, paddling around the Estuary!

It just wouldn't have been the boat that I wanted to design.

It seems to me that when you design small boats, there's a LOT of leeway that will *work*. I mean, look at the difference between Elfyn and the Puddleduck Racer or the Bolger Brick. I mean...wow. But you know what? They both float, they both move in a forward direction when you row them, and when you put up a sail and there's wind, they both go. Now, *work* is not the same thing as *optimize*. The Bolger brick "goes" and it "floats", sure...and people have fun with them. But it's in no way an optimized sailing form. It's optimized to be really easy to build and sail "good enough". Hey, there's nothing wrong with that.

So my point is this.... To get a really incredibly superb boat performance and looks-wise, in the unballasted 8 - 18 foot range, you probably need an experienced designer to optimise hull shapes and so on. But I think that an amateur, if he/she has stared at a lot of boats over a number of years and pays attention to basic design principles and doesn't stray too far off into the weird can design a perfectly workable small boat. I mean, if folks build one-station, "done-by-eye" skiffs and get them across the Bay, then why can't I design a small boat that will get me across the bay, too?

To keep it close to home....compare the Bolger Windsprint to the Oughtred Elfyn. They're both the same size. They use similar rigs. They both *go* just fine...the wind blows, the sail is up, they GO. You can row both of them. And yet those two hulls are wildly different from one another even though they're 16 foot double-enders. I want a double-ender. As long as I stay within the parameters of length/beam for enough stability, and keep the boat some sort of symmetrical, and give it enough, but not wildly too much freeboard, how far wrong can I go?

Now, designing 50-foot steel powerboats with three decks and gadzoogles of widgets and horsepower...that's different. But designing and building a 10-15 foot plywood punt or skiff? I don't think I need Nathaniel Herreshoff or Joel White to put together a reasonable boat.

Step 2 is on its way, including a freehand bow profile because...well....because I want a pretty faering-type bow profile and "Hulls" won't do it with the number of chines I have. So I gotta freehand it. OK, I'm down with that. I'm gonna learn something.

[paladin]

One neat thing about Plyboats software is that you can calculate the panel flats to make the curved pieces lay flat on a piece of ply, then cut it out an assemble. I use a scale fiberboard, and a 11 X 17 printer......print the panels for a 21 foot boat at 3/4 inch to the foot, making the 21 footer to scale at 15.75 inches....print the color version as desiered on printing/photo paper and bond it with portholes/lights, planking lines and all else drawn on the paper, cut out and glued to a pice of thin veneer, then assembled. I just did the strakes for a 9 1/2 foot dink that way to make a lapstrake dinghy for my proposed retirement boat.

[lumberjack_jeff]

Originally Posted by Alan H

OK, it's all good!!!

Check out Hannu's boatyard.

His site is a great start for someone using the carlson program to design hull shapes. It'll give you the courage to try and some ideas to adapt.

Originally Posted by Hannu

Is there any point in building something as useless as a 4 ft dinghy?

Yes, of course there is! Someone has to do the stupid things in the world. By doing something really stupid one pushes the whole stupidity-sensibility scale up a bit. After this building project, things that seemed stupid yesterday, may seem sensible tomorrow, compared to this :-)
So, by building a 4 ft Halfpea dinghy I'm increasing the total sensibility of the whole world affairs. Whey! (Some might argue, that all I'm doing is infalting the scale...)

I've made a couple of quarter-scale s&g models lately. The fullsize boats utilize 3/4" ply for bulkheads and 1/2" ply for the hull panels. Thus, 3/16" underlayment worked nicely for bulkheads and 1/8" ply worked great for panels.

They came out very nicely and were easy to work.