What's the best sequence to alter a plan's lines?

[LarryR]

I've read Vaitses' "Lofting," but it focuses (naturally) on layout from an existing plan. Is there a sequence that's better than others if you want to alter the plan?

For example: I like the lines of "Wee Lassie," but, at 290 pounds, I'm a full sized adult -- and I've not found plans for the "Lard Assed Laddie." Culler's "Butternut" is a 13' double-paddle canoe, and the plans are available from Mystic. I'm considering it as a first project to learn something about the boat-building process. But I'm thinknig of adding an inch or two to the width to increase the load and stability, and rolling the upper planks in for a bit of tumblehome to keep the additional witdth from obstructing paddeling. Is there a sequence to enter the changes that would make it easier?

Very respectfully,
Larry

[Bob Cleek]

Well, it's one thing to judiciously stretch or compress the distance between station lines (within limits) to alter the length, but you will reach a point where the differences affect the performance characteristics of the boat in pretty short order. As for the sort of modifications you are suggesting, it is more complicated. These changes can be made on the lofting floor, or you can redraw the lines and take off your own offsets. However, it is pretty hard to make any change like those you mention without changing the intended performance parameters. I realize that is your objective, but if you intend to alter the stability parameters, the changes necessary will, I belive, be "pushing the envelope" of what limitations the designer was dealing with in the first place. Short of fudging a bit on length, I wouldn't mess with a proven design at all, and if I did, it would only be in a rather small boat at that. I think you'd be better off finding another design that "fit" rather than trying to modify one that didn't. You know, even a small change in the shape of a hull can wreak havoc when it comes planking time. You'd likely wish you'd have relied on the designer's own experience and the subsequent builders' experience with the design before going off on your own adventure.

[mmd]

Very respectfully, do not attempt this with your first build project. However, if you do, it is fortunate that you have selected a very small boat to attempt it upon. That way, you won't be burning very much money...

What Bob is trying to gently tell you is that messing with a design is a minefield of subtleties upon subtleties. A minor change in the lines - even only an inch here and an inch there - can possibly mess up the stability, make it difficult to propel, make it look funny, or make it difficult to build. Or all of the above.

This is not to say that it can't be done - it has, many, many times. That is how a traditional design evolves. But the messing about with the lines is usually done by builders who have a lot of experience building boats in general and often with extensive experience building & sailing the design in question.

The best analogy that I can come up with is, would you let a fellow who has never done mechanics before, but has read several books on the subject, alter the suspension geometry and brakes of your family car?

Please do not take offense to my comments. I am not meaning to be rude or belittling. Building small boats should be fun, and I can assure you that designing them is (in my opinion) even funner. But the the impact of even subtle changes can be profound, and to understand and anticipate the consequences of such changes requires more experience than you presently have. Please do not give up; find a design that suits and build it verbatim. The time you spend engrossed in building will provide time to think about why the designer made the decisions he did and allow you to understand why a boat is the way it is. Trust me (and Bob, and many other very gifted people who haunt this place), the time will be well spent and will prepare you for the hobby that can last a lifetime.

Don't risk discouragement by rushing in to the deep end before you learn how to swim.

[LarryR]

Bob, MMD,

Looking at canoe designs that are available, there are some that are markedly shorter with the same beam, and modestly shorter with markedly wider beam. So, it's not clear that my desired changes would exceed acceptable performance parameters. But your real question is harder to answer -- am I able to tweak the lines within those parameters and get an acceptable result? Maybe. Am I willing to gamble 200-300 hours on it for my first try? No, I'm not.

Thank you both for your candid replies; and no, no offense taken.

VERY respectfully,
Larry

[openboater]

everything Bob and MMD said is true.

But I say 'go do it'. just don't try to make an heirloom piece, and keep a box of matches handy. I tried building a dory by eye 4 years ago and ended up burning it. But I sure learned alot.

Designed and built my own cedar strip c-1 for stock class racing and love it.
modified the molds a little and built another that was even better.

Just don't spend a fortune on materials . (and keep the matches handy just incase)

[Steve Lansdowne]

There is a Wee Lassie Two for larger folks that Mac mentions in his book. Off hand I'm not sure what the capacity is, but you might check it out.

[JimConlin]

There is a Wee Lassie Two for larger folks that Mac mentions in his book. Off hand I'm not sure what the capacity is, but you might check it out.

I built a Wee Lassie II which was certainly OK for my 225 lbs. IIRC, it was something over 12' in length.
You might ask the designer (http://www.feathercanoes.com/html/wee%20lassie%20two.html) whether it'd be OK for your weight.

[Steve Paskey]

I've read Vaitses' "Lofting," but it focuses (naturally) on layout from an existing plan. Is there a sequence that's better than others if you want to alter the plan?

For example: I like the lines of "Wee Lassie," but, at 290 pounds, I'm a full sized adult -- and I've not found plans for the "Lard Assed Laddie."

I agree with the folks who say you shouldn't try to alter the lines. And if you like Wee Lassie, it isn't necessary.

Have a look at the Wee Two from Laughing Loon canoes. Maximum capacity is 400 pounds.

http://www.laughingloon.com/wv.wt.html

[Steve Paskey]

Below is the web site for Mac McCarthy. Mac has a boat called "Big Mac," which he says is suitable for people over 200 pounds. (No maximum given.)

http://www.feathercanoes.com/html/Big%20Mac.html

[Ray Frechette Jr]

Maybe, the best sequence is to contact the designer. If you like Wee Lassie and want Lard bucket Laddie, perhaps the designer would be willing to accomodate figuring future sales might be forthcoming....

[S B]

Well, it's one thing to judiciously stretch or compress the distance between station lines (within limits) to alter the length, but you will reach a point where the differences affect the performance characteristics of the boat in pretty short order. As for the sort of modifications you are suggesting, it is more complicated. These changes can be made on the lofting floor, or you can redraw the lines and take off your own offsets. However, it is pretty hard to make any change like those you mention without changing the intended performance parameters. I realize that is your objective, but if you intend to alter the stability parameters, the changes necessary will, I belive, be "pushing the envelope" of what limitations the designer was dealing with in the first place. Short of fudging a bit on length, I wouldn't mess with a proven design at all, and if I did, it would only be in a rather small boat at that. I think you'd be better off finding another design that "fit" rather than trying to modify one that didn't. You know, even a small change in the shape of a hull can wreak havoc when it comes planking time. You'd likely wish you'd have relied on the designer's own experience and the subsequent builders' experience with the design before going off on your own adventure.
And you permit fellow designers to bastardize traditional designs and applaud the results, without thier experiments ever proving themselves.

[Thorne]

SB -- Is there a point, or just the sound of an axe being ground? Trad designs are great, but not sacred in my book...

Traditional designs built from traditional materials are great -- I have restored one and actively sail and row it -- do you?

Traditional designs build from modern materials are completely different, which is where modern designers come in to the picture. Boats that were 400lbs built from pine and oak and wet-sailed are now 150lbs built from marine ply and dry-sailed - don't you think that calls for some minor re-design work?

But boat design (and re-design) calls for a lot of experience and skill -- something the average first-time builder doesn't have. "Bad boats" and/or a waste of time and money can easily result.

[kengrome]

Is there a sequence that's better than others if you want to alter the plan?I create a model of the boat at its actual size in my design software, then I scale it, then I make adjustments so the final model 'makes sense' according to the design parameters as I understand them or as I want them to be.

I am still amazed sometimes at how much I have to adjust things after scaling, but this requirement simply reinforces the fact that most designs cannot be scaled more than a couple percent without dramatically affecting some very important performance characteristics.

[S B]

SB -- Is there a point, or just the sound of an axe being ground? Trad designs are great, but not sacred in my book...

Traditional designs built from traditional materials are great -- I have restored one and actively sail and row it -- do you?

Traditional designs build from modern materials are completely different, which is where modern designers come in to the picture. Boats that were 400lbs built from pine and oak and wet-sailed are now 150lbs built from marine ply and dry-sailed - don't you think that calls for some minor re-design work?

But boat design (and re-design) calls for a lot of experience and skill -- something the average first-time builder doesn't have. "Bad boats" and/or a waste of time and money can easily result.I am not trying to grind an axe, but I do have 2 questions that only the designers, engineers on this forum could answer and I was trying to hook one's attention. First ,any time there is a request for help on modifying a design, there is a line up of forumites, to tell you you can't handle the task and leave it to the pros. There was nothing in Larry's thread to suggest he was unable to follow instructions. Telling him which book to read might have been a more useful response. Is this attitude the norm for the trade? Second ,in any other profession ,I can think of,the practise of trying to piggyback the reputation of someone elses work onto your own ,to make it more marketable, is despised. Even though their names have been lost to history, traditional designs are someone elses work. Why is this not a problem for wooden boat designers.

[David G]

Larry,

Step 1 - consult designer, or naval architect

Step 2 - abandon notion of design changes

JUST KIDDING! But just barely.

I agree that one can learn a lot by making changes and trying out ideas. That's one reason I like the Puddle Duck Racer class. There's lots of room for experimentation and it's a small, cheap, very simple boat - so mistakes are not devastating in time or money.

I also like the idea of making models incorporating the proposed changes. Hull modeling software would be useful in the same way, I'd imagine. I've yet to add it to my toolbelt.

However -- I very much agree that serious boat design is a far more complex subject than you'd imagine at first glance. What mmd said in post #3 is very true - most successful mod's are accomplished by designers or builders (not necessarily formally trained) - With A Lot Of Background.

My perspective: I grew up on & around boats. I've been a professional woodworker for 35+ years. I've designed some fairly elaborate residential & commercial cabinetry, furniture, and millwork. Some projects with total values in the $millions. I started building boats about 5 years ago. I've built half a dozen small boats now. I've also been reading steadily on building and designing for the last 6 - 7 years. I initially thought that my background would give me a very large head start toward designing & building my own boats. The more I learned, the more I decided I was quite wrong. Can you say "hubris"? At this point, I don't feel even close to being capable of designing a boat for a client. I don't have the technical stuff down - and probably won't ever bother. However, I think I am beginning to understand the rudiments of hull shape & lines that affect the overall handling traits. I'm about to a place where I'd venture a design for a small, open, plywood skiff. I'd regard it as experimental... and likely disposable. My mob of boating/boatbuilding buddies has an annual New Years boatburning ceremony to take care of such ventures. :p

If you want a boat that is likely to perform well, I'd suggest finding a plan you like & building fairly strictly to plan... at least for the first boat. :)


"Design can be art. Design can be aesthetics. Design is so simple, that's why it's so complicated" -- Paul Rand

[htom]

You could try

Repeat
First, multiply the length by 1+((phi^3)/100),
then multiply the breadth by 1+((phi^2)/100),
then multiply the depth by 1+((phi^1)/100),
Until new displacement is acceptable.

If I had no other clues or help. The factors are roughly 1.04, 1.025, and 1.016; each trip through the loop adds about 8.5%

[Thorne]

I am not trying to grind an axe, but I do have 2 questions that only the designers, engineers on this forum could answer and I was trying to hook one's attention. First ,any time there is a request for help on modifying a design, there is a line up of forumites, to tell you you can't handle the task and leave it to the pros. There was nothing in Larry's thread to suggest he was unable to follow instructions. Telling him which book to read might have been a more useful response. Is this attitude the norm for the trade? Second ,in any other profession ,I can think of,the practise of trying to piggyback the reputation of someone elses work onto your own ,to make it more marketable, is despised. Even though their names have been lost to history, traditional designs are someone elses work. Why is this not a problem for wooden boat designers.

Sb -- it is very simple.

To answer your first question:
The "line up of Forumites" are saying it because it is true. No amount of wishful thinking or rebellion against the Oppressive Forces of Naval Architecture can change that fact. And any of the books that might tell him how to change lines will also be the ones telling him how to create those lines in the first place.

To answer your second question:
All design works the same way, making changes to what has gone before or combining same -- clothing, automobile, homes, hair, and boats. That is why it is not a problem for wooden boat designers.

The reason why I mentioned that you seem to have an axe to grind, is that you have multiple posts all saying the same thing as question 1 above. It has been answered by a number of us, but you don't seem to be listening...

Designs for earth-bound objects are easier for people to understand than designs for air or water based objects. Whether the laws of physics are easier or we are just more experienced with them I can't say.

Few people would consider riding across the US on a home-built bicycle with 12" wheels == we seem to understand that larger wheels (up to a certain point) work better than small ones.

But many new builders will take a 17' boat and shrink it to 12' -- and then wonder why the damn thing is so slow! Same basic physics but different ability to understand.

I once spent a year restoring a lovely old pine over oak Banks dory, built exactly to Gardner's plans with one small change -- the beam was aprox. 4-5" narrower across the bottom, probably some builder's clever plan to make it row better.

But that 4-5" on bottom translated to 10" narrower at the gunwales (1/5 of the beam), and turned an already tender design into a real problem boat. With 300lbs of wet sand in burlap bags, two experienced oarsmen could operate the boat in calm water - but with no balast the boat was unusable by a single rower.

So you are welcome to any opinion you may have on the wisdom of modifying proven and/or commercial designs -- but you will keep seeing the same advice given over and over by other Forumites.

Here's an extreme example of "doing it yourself". This 'designer' is a friend of mine and had all sorts of experienced and active boatbuilders to work with, but he knew better -

http://www.luckhardt.com/ST07/images/7.jpg

When the 'floating coffin' proved to be unable to sail against the wind or even carry canvas, some lovely plastic plumbing pipes and pine crossbeams bound with hoseclamps were created to add amas. He also rows facing forward without using any of his upper body other than his arms -

http://www.luckhardt.com/coffin08-1.jpg

[Steve Paskey]

You could try

Repeat
First, multiply the length by 1+((phi^3)/100),
then multiply the breadth by 1+((phi^2)/100),
then multiply the depth by 1+((phi^1)/100),
Until new displacement is acceptable.

If I had no other clues or help. The factors are roughly 1.04, 1.025, and 1.016; each trip through the loop adds about 8.5%

Each trip adds 8.3 percent. Most designs wouldn't survive two trips through that loop without problems, and many couldn't handle even one. In this case, getting the necessary displacement would require quite a few trips through the loop. Not a chance.

Mac McCarthy's Wee Lassie II is not just an enlargement of the original Wee Lassie. The same is true for the two Laughing Loon boats (Wee Vera and Wee II). And Big Mac is a very different hull altogether. The designers did not do all that extra work on a whim -- there's a good reason for it.

[htom]

Each trip adds 8.3 percent. Most designs wouldn't survive two trips through that loop without problems, and many couldn't handle even one. In this case, getting the necessary displacement would require quite a few trips through the loop. Not a chance.

Mac McCarthy's Wee Lassie II is not just an enlargement of the original Wee Lassie. The same is true for the two Laughing Loon boats (Wee Vera and Wee II). And Big Mac is a very different hull altogether. The designers did not do all that extra work on a whim -- there's a good reason for it.

I agree. I was trying to point out how boats seem to grow (in length first and most, depth last and least.) Two complete trips adds about 17%, rough for most designs, three about 28%, and there almost any will have problems.

[LarryR]

Oh dear. I really didn't intend the question as a torch.

David, I can say hubris, but I have a heck of a time spelling it. :)

Actually, the light came on with MMD's comment that I should use inexpensive material to build my modified design because "that way, you won't be burning very much money..." It's not that money doesn't count, but I'll be doing this for fun, and my most significant limitation is time. I'd wanted to do the design mod for fun, too; but Bob's and MMD's comments clarify that doing so put the outcome at risk. So I accepted their advice and will identify and purchase a design adequate to my needs.

S B, I am fairly sensitive to intellectual property. But my impression is that many, if not most, of the canoe designs are derivative; and I think that, after purchasing copy of the design and the rights to build one, modifying the design for my one-off personal build would be fair use so long as I did not then identify the craft as his design.

Thank you all for a very interesting discussion.

Very respectfully,
Larry

[Ray Frechette Jr]

Why do I suggest having a NA redraw lines to suit?

I guess it is because I realize I am not smart enough to do it myself.

I am smaert enough to realize the issues involved and smart enough to know I ain't spending the time or money to build a boat I didn't have a recognized NA draw up and design right.

Even NA's have jokes about designing right. Like an NA should always wear ru8nning shoes to a boat launching.

If someone thinks they can redraw lines to suit after reading a few books on lofting and such. Good Luck.

But I am not building that desing for anyone untill it is proven, or untill an NA does the numbers on it. Even if it looks real nice on paper.

[S B]

fair use so long as I did not then identify the craft as his design.
I rest my case.

[LarryR]

S B,

I am totally ignorant of acceptable practices in the trade and use of off-the-shelf boat designs. So I mean this post as a question, not a challenge:

Assume that I want to build a canoe and that you have a successful business selling canoes and canoe plans. I purchase a copy of your very popular "Wet Lassie" plans, which show how to build a Rushton style canoe using modern plywood.

If I wanted a boat a tad longer and put an extra inch between each of 5 stations, I would not expect that the result would damage your reputation as a designer. The discussion above suggests that going beyond that could result in an undesirable boat -- a boat that you might not want associated with your name.

If I take your "Wet Lassie" design, lengthen it, widen it several inches, and add tumblehome; the extra width might degrade performance and the tumblehome would change the aesthetics. If so, it's no longer a fair representation of your work as a designer. In my (ignorant) opinion, I *should* be permitted (I don't know if I actually *would* be permitted) to modify the boat that I build from the purchased plans so long as I not market the resulting design (it's derivitive) and so long as I not identify the resulting boat as only your work.

So. . . I've bought your plans and they arrived in Friday's mail. Because I'm still trying to master my new screwdriver and hammer, I improve your design to make it easier to build. Later that weekend I launch my "Black Beauty" (very similar to the boat that Thorne has already posted).

Consider a continuum from an exact build (if that's possible), through that "tad longer" canoe, through the wider/tumblehome canoe, to my "Black Beauty."

My questions:

Does my right to change your standard design to build my one boat end anywhere along that continuum?

If so, how will that limit be communicated to me?

Is there a point along that continuum beyond which I should no longer identify the result as your design? (That is, would you want me to tell the Coast Guard's rescue pilot that my "Black Beauty" was an "SB Wet Lassie"? If I no longer need "Black Beauty," would you want me to nationally list it on eBay as an "SB Wet Lassie"?)

If so, as a builder, how do I know when I've reached that point?

VERY respectfully,
Larry

[S B]

S B,

I am totally ignorant of acceptable practices in the trade and use of off-the-shelf boat designs. So I mean this post as a question, not a challenge:

Assume that I want to build a canoe and that you have a successful business selling canoes and canoe plans. I purchase a copy of your very popular "Wet Lassie" plans, which show how to build a Rushton style canoe using modern plywood.

If I wanted a boat a tad longer and put an extra inch between each of 5 stations, I would not expect that the result would damage your reputation as a designer. The discussion above suggests that going beyond that could result in an undesirable boat -- a boat that you might not want associated with your name.

If I take your "Wet Lassie" design, lengthen it, widen it several inches, and add tumblehome; the extra width might degrade performance and the tumblehome would change the aesthetics. If so, it's no longer a fair representation of your work as a designer. In my (ignorant) opinion, I *should* be permitted (I don't know if I actually *would* be permitted) to modify the boat that I build from the purchased plans so long as I not market the resulting design (it's derivitive) and so long as I not identify the resulting boat as only your work.

So. . . I've bought your plans and they arrived in Friday's mail. Because I'm still trying to master my new screwdriver and hammer, I improve your design to make it easier to build. Later that weekend I launch my "Black Beauty" (very similar to the boat that Thorne has already posted).

Consider a continuum from an exact build (if that's possible), through that "tad longer" canoe, through the wider/tumblehome canoe, to my "Black Beauty."

My questions:

Does my right to change your standard design to build my one boat end anywhere along that continuum?

If so, how will that limit be communicated to me?

Is there a point along that continuum beyond which I should no longer identify the result as your design? (That is, would you want me to tell the Coast Guard's rescue pilot that my "Black Beauty" was an "SB Wet Lassie"? If I no longer need "Black Beauty," would you want me to nationally list it on eBay as an "SB Wet Lassie"?)

If so, as a builder, how do I know when I've reached that point?

VERY respectfully,
Larry
Here is how I see it. Correct me when I am wrong. You buy a set of plans to help you build a boat, They are close ,but not exactly what you want. You change the plans ,build the boat you want, you are happy, the designer is happy that he sold his work. You decide to sell the boat on ebay, as a wet lassie. Now you are not being honest to the buying public and giving unwanted responsibility to the designer of the plans. If you list the boat as Larry's version of a wet lassie, you are both telling the truth and relieving the designer of any responsibility for what you have done.
The boat was invented a long time ago and all new designs are the reworking of someone elses ideas.In the selling of Larry's version of the wet lassie,it usually takes legal action to decide if Larry's version is inovation or plagarism. If you make significant changes to the wet lassie ,market the plans under the same name, take credit for it, claim the same performance as the original and nobody sues you, IMHO you should not get away free ,your peers should protect the integrity of their trade.

[LarryR]

S B,

Thank you for your reply; I can easily understand and agree with it. And, now that it's pointed out, I recall seeing that "Larry's version of . . ." label on designs derived from or evoking classic (public domain?) designs.

Very respectfully,
Larry

[Grizz_]

I had some left-over aluminum to play with. I converted the lines of Bolger's Nymph to metric system and enlarged all dimensions by a percentage that expanded the length to ten feet.

The boat isn't finished for sailing but I've had it out in a choppy harbor westerly to get a sense of her. Good boat. The original would fit comfortably inside the metal one, but I couldn't fit comfortably inside the original.

I say, if you have an idea and desire to do it, do it. You will learn something, a lot of things actually.

Aluma-Nymph? She floats in about an inch of water with enormous reserves for occupants. I'm going to make her self-bailing and go salmon fishing...,


http://www.empresspublications.com/stuff/CIMG1284.JPG


This won't please the wood-only crowd, but it does make the point that you can enlarge a design and still have a boat. A very different boat, but one that is also very useful and suits you to a T.

Everyone can say what not to do, or why it can't be done. I look for counsel that tells me how to accomplish my objective. I hope you do too. After all, every boat is experimental at some stage, or it's just a reproduction....

Regards,

Grizz

PS: As regards the discussion above about whose design is it anyway, etc. I don't claim this boat is Bolger's Nymph. That would be stupid. I only say I started with Bolger's design as the idea for the boat I built.

I don't plan to sell this boat. It's too much fun to play with to let her go. But my heirs might. They can truthfully say that it is a home made pram. That's all they need to say. They can let a prospective buyer sail and row until they're satisfied they do or don't want it. No harm, no foul; vessel sold as is with no guarantees. It's unsinkable, so it's gonna be around until the scrap value of aluminum is greater than the replacement cost for that particular displacement.

[Canoeyawl]

This is a reasonable approach. It is after all your boat, your project. Build it the way you want to, Build it now.
Some very simple water plane calcs will give you the needed extra displacement.
(see, From My Old Boatshop, Weston Farmer)

It is a simple thing to set the stations a bit further apart. Many boats have been modified this way successfully.
Another approach that comes to mind is for example the Drascombe Long Boat. They took the lofting for the Lugger, cut it in half, added three feet to the center, faired it and it is the better of the two boats in my opinion. This method of modification has been done successfully on finished vessels.
I have modified several designs; some did not achieve everything I wanted and I learned. But this was more about the original choice of hull form than the modifications.
I recommend making the changes on a building form, this way you can see it full size, sort of a three dimensional lofting. I have made up a temporary full size half model mock-up of the boat with molds and battens from cheap lumber and changed things as I wanted with no consequences other than creating a bit of extra kindling, All in all a rewarding exercise.
Having suffered the indignity of being publicly accused of Victorian Vandalism – LOL I say, It’s a tempest in a teacup – go build your boat, have fun.

[W Grabow]

You can make the alterations or develop your own design, but realize the risks involved. I agree that re-spacing the frames is probably the safest change to make, and that alteration should not be more than 10%. Study the proposed design closely to understand what elements of the design are essential. Think about how and where you will be using the boat.

I've never altered the lines of an existing plan. I have designed and built six of my own boats. First, I studied traditional designs to discern the important characteristics which make them perform the way they do before attempting something of a similar type. I also restrict myself to smaller, less complex, less expensive boats. One of my designs turned out to be a failure: too much rocker made it track poorly. It became a sandbox. In other boats I have built, I recognized in retrospect improvements that could have been made. But for me, the satisfaction from experimenting in design is as great as that from actually using the boat. It all depends on what your priorities are.

[john welsford]

This thread, like many, has strayed well away from the original question. Sometimes thats interesting and fun, and sometimes counterproductive. In this case your question is pretty much unanswered, so heres my attempt.

To achieve what you want will require a new design, very similar to the original , but new.

I'd get a copy of Cyrus Hamlins " Preliminary design of Yachts and Boats". There are plenty of other books on the subject but that one explains the methodology better than most.

Then, using your original Wee Lassie line drawing as a guide, draw a profile and a midsection thats a little bigger and to the shape you want. Measure the underwater area of the cross section, multiply that by the waterline length, divide that by a suitable prismatic coefficient, say 60% and that will give you an approximation of the displacement ( this is a piece of cake when done in metric) which will tell you if you have to change the profile and cross section to get your target displacement.

Use the originals as a guide as to shape and proportion, note that copying a design is legally fine as long as you dont use that for commercial gain, and there is no need to reinvent the wheel.
From there follow the line drawing process that you can get from the book until you have the new line drawing done.

Do a curve of areas and check the centre of bouyancy.

THEN BUILD A SCALE MODEL! That will tell you if you have it right, or if you need to start again.
I use model airplane balsa and cyanoacrylate glues and can have a fairly complex model that is quite adequate for its purpose of checking fairness of lines and shape all done in a couple of hours

Good luck, have fun.

JohnW

I've read Vaitses' "Lofting," but it focuses (naturally) on layout from an existing plan. Is there a sequence that's better than others if you want to alter the plan?

For example: I like the lines of "Wee Lassie," but, at 290 pounds, I'm a full sized adult -- and I've not found plans for the "Lard Assed Laddie." Culler's "Butternut" is a 13' double-paddle canoe, and the plans are available from Mystic. I'm considering it as a first project to learn something about the boat-building process. But I'm thinknig of adding an inch or two to the width to increase the load and stability, and rolling the upper planks in for a bit of tumblehome to keep the additional witdth from obstructing paddeling. Is there a sequence to enter the changes that would make it easier?

Very respectfully,
Larry

[LarryR]

John,

Thank you for the cite to Cyrus Hamlins; I'll try to find a copy.

Very respectfully,
Larry

[sailing canoe]

Just do it! We are not talking about a large boat with fixed weights here. If the balance is off a little scoot your butt forward or back a little. Thats what you do in a small boat anyway to account for waves and wind. Pete Culler said so and he's dead so it must be true. You are not talking about making it hugely bigger any way. If you were to enlarge the lines by 25% at kinko's -and remeasure to create new offsets - the boat would only be 25% longer but would have twice the volume - way more that you need. Very low tech and you may, as many have said, not like the results but it would be fun - matches are cheap!