modifications

[dennyplane]

Hi everybody
My name is Denny and just joined the forum. Before anything please forgive me if my spelling or composition is wrong but after 30+ years here, The foreigner in me still slips out sometimes.
I have been reading this woodenboat forum for a while and have not seen yet about mods to designs. What I mean is enlarging or making designs smaller. Using diferent rigs and so on. One sample
that stands out is the infamous weekender. I have read lots of discouragement towards choosing it,but what if you were to choose a diferent hull and build the weekender on top of it. Like the glen-l
minuet.(almost same size).Or a 16 foot pooduck skif?
I really like to experiment with ideas. Several years ago built a bull's eye from glen-l and enlarged all dimentions by a factor of 1.3. Ended up with a little over 15 foot loa and little over 6 foot beam.
Sails were a pain to get but sailed good. After a year me and my better half were sailing fast close to shore in lake mead and the daggerboard hit something causing mayor damage.
Of course cl and ce will have to be calculated and also position of the centerboard or keel. No perfection intended.
Would like to hear opinions.
Thank you

[daniel gross]

If you like the look of the Weekender, look at Glen-L's Fancy Free no mods needed.
This coming from someone who built and sail a Weekender.

Just a thought.
Dan

[Cuyahoga Chuck]

The Glen-L Bullsye is 11' x 53". The rule of thumb is ±10%. When you go beyond that you are essentially designing your own boat. Even though you have done it and like the result there is no guarantee you can keep being successful. A 30% increase in size should result in a significant increase in weight and possibly heavier scantlings are needed along with a lot of hunting around to get the mast and daggerboard right so it will sail properly. Personally that woud involve too much hair pulling for my taste.

[karl kirkman]

Denny,

I am writing this from the viewpoint of a Naval Architect trained to design boats. Whether you modify an existing design, or draw up an entirely new one, there are certain supporting analyses that Naval Architects are trained to utilize, and it is important to understand that a set of plans is not all there is to a design. That does not mean you cannot build a boat to just a set of plans, or even with no plans. What it does mean is that if you do so without doing the amount of analysis that is appropriate to the boat to go along with the drawings, you run the risk of a failure; poor performance or maybe even danger. Part of the skill of an experienced designer is to know how much and what analysis is needed. The kind of things that Naval Architects often check as part of preparing plans are things like weights, stability, strength, resistance and power, controlability, and seaworthiness.

Karl

[JimD]

I have a Glen-L Minuet that no longer looks much like the original. The cabin is gone completely and the rig is now very different. You can play around with aesthetics and sail plans quite a bit as long as you have a good understanding of what effects the changes will have. I make no claim to my changes having improved the performance over the original. More likely I've made it a somewhat worse boat from that point of view. But I like the boat better now and that's what's most important to me.

[dennyplane]

I thank everybody por your replys. I do agree that mods are not recomended for several reasons. I do not know if I would be allowed the space to write everything that I needed to change with that bull' eye design that I enlarged from thickness material
to bigger hardware to reinforcements to finding cl vs ce and on and on and on. I did it for the challenge and cause I personally like building stuff but I would not recomend it myself unless the person willing to do it understands that it will take more time,effort and money.
Jim, as long as you are happy, that is what matters.
I got a more comfortable boat size wise but that was it.
Never the less, size up as long as EVERYTHING IS PROPORTIONAL doesn not have adverse effects. I would never go smaller. Doesn not seem to work at all that way. Do not know why.

[dennyplane]

Karl. I totally agree with you. Any change should be done with research and brains first. And when something pops in my mind I go to the libray or web to find if ok or not.
I am just a total "what if" person.
I would love to have naval and aeronautical engineers to ask questions to.

[Wayne Jeffers]

. . . Never the less, size up as long as EVERYTHING IS PROPORTIONAL doesn not have adverse effects. . .

I’m no naval architect, but I know this is wrong.

If you increase all dimensions proportionally, say by a factor of 1.3, you increase displacement by the cube of 1.3 and the sail area by the square of 1.3. The result is a displacement that is 2.2 times the original and a sail area about 1.7 times the original. This will affect performance. There are a number of ratios affecting performance and safety that do not change in linear proportion as dimensions are changed.

If the increase in dimensions is 10%, the displacement increases by 1.33 times the original and the sail area increases by 1.2 times the original, not enough in most cases to drastically alter performance, or move the boat outside the margin of safety the designer designed in to the original plan.

The changes needed to scantlings, etc., to maintain the original margin of safety I will leave to the NA’s.

Wayne

[dennyplane]

Thanks wayne.
That explains why I needed a very heavy daggerboard and why it felt overcanvased.
One single mod starts a domino effect.
Still it was interesting to do it.

denny

[Gerarddm]

On certain small boats, one can simply extend the distance between the stations a bit, such as I am doing on my 15' Lincolnville Salmon Wherry, stretched from the original 14' lines.

[dennyplane]

Thanks Gerard.
I have heard and read that is ok to do that. Also that the longer it is the better it rides the waves.
Seems that the deep round bottom hull works the best in most cases.
My luck usually, most designs I like do not have it.
Basic reason for trying to change them.
Daniel suggested the fancy free but, flat bottom.
Looking for something like that but round hull.

[Wayne Jeffers]

Denny –

By increasing all measurements 30%, your hull’s volume (amount of water displaced) to the proportional equivalent of the designed water line would have increased by a factor of 2.2, far more than the increase in the weight of the bare hull. It would have needed a lot of ballast to pull it down to the proportional equivalent of the designed water line. Without ballast and therefor floating too high, it figures to be a bit “tipsy,” even though the sail area was increased less than the volume of the hull.

Changing only distance between stations by a modest amount, as Gerrard suggests, produces proportional changes for the most part.

Wayne

[dennyplane]

You are right Wayne.
I remember putting a lot of weight in the daggerdoard and rolling the sail around the boom to make it shorter.
As I posted before, all I got was a bit more comfortable size. The original bulls' eye size at 11' was too cramped for two.
Live and learn. Took waaaaaaay longer and more money not to mention that there were things that needed to be
changed after every sail trial. The construction process was worth it, the rest was not.
If I still had it,I would probably still be messing with it instead of sailing it.
But, what is the solution when you like a design but the size or something else does not appeal?
denny

[Wayne Jeffers]

. . . But, what is the solution when you like a design but the size or something else does not appeal?

If you figure out an easy answer to that one, I'm sure a lot of us here will be interested in knowing!

Wayne

[Todd D]

I am not a naval architect. However, in my experience the calculations required to modify a set of plans are actually very simple to do. Dpn't let the people scare you away from making revisions to plans by waving the calculation flag in front of you. None of the things that need to be done are what I would call difficult. just work at it and be thorough. Don't be scared off by the arithmatic.

[paulf]

Hi Denny,
Perhaps a couple of books on vessel design, and a cad program to allow you to "tinker" would allow you to modify a design.
Once you know the CB, CG and some other things you could gain confidence in an soft-ware environment, no harm done.
Then when you feel you are on to somthing, ask the designer/ N/A To check your calculations and OK your changes.
At some point you will be ready to go it alone.

[dennyplane]

Hey, many thanks paulf and todd.
Here is the deal. I would like something that is coastal cruise capable in a small size. The reason for the size is that when island hopping in the caribbean, nobody pays attention to you in anything smaller than let's say 16 feet.
Cabins in that size boat are really impractical but you can carry way more than camping on foot To get in and out of and island without having to bother with the marinas. You know, just pull on the beach at sunset, set your tent
and be gone early the next morning towards another one. I personally really like the gaff rig, either cause it reminds me of a friendship sloop or who knows what. I would mostly sail in lakes but I want to know if I decide to go coastal,
I will have something able to do it with. As you can see, there are really no designs(as far as I know)that have that. Either fancy free(glen-l design) or weekender(stevensons projects)aproach what I would like. Rather go for the
weekender cause its size. But both are flat bottom. I have read that a round bottom(Does noy have to be full keel)is just more capable in a wider envelope of water conditions. Be able to build it myself is a prime factor. Several times got stranded
away from home port and was able to repair with local wood and that was a very big plus.
I would like to hear anybody's suggestions.
Denny

[paulf]

Well there you go,
You have definate goals! read all you can and then go there!
"Some" set of plans will get you there!

[Wayne Jeffers]

. . . in my experience the calculations required to modify a set of plans are actually very simple to do. . .

True enough. My point was that increasing everything proportionally in a design, by something on the order of 30%, does not simply result in a larger version of the same boat with the same performance and safety characteristics. At a minimum, you or someone has to do the calculations and make appropriate revisions. At some point in the process of enlargement and revision, it becomes a new design, bearing little resemblance to the original.

Dave Gerr's The Nature of Boats is a good primer on the necessary calculations.

I've also found it useful in developing information about a set of plans where the designer did not share his calculations, e.g., approximate hull weight if built as designed, displacement to LWL, SA/D ratio, etc. These are numbers that are of interest to me, yet designers don't often provide them for small boats.

Wayne

[JimD]

This website on micro cruising in the Bahamas and the boats of Matt Layden would be a very good place to continue your research. http://microcruising.com/






etc..

And for Gawd sakes don't build a Weekender. Good luck.

[dennyplane]

Thanks jimd. Already went to that web page. Very interesting. Could not help but laugh because your last comment.
I would like to hear the explanation of why is the weekender so bad.
I promise you I will try my best to find a design that suits what I want and only if there is absolutely no hope, then and only then
will I go for it but I give you my word it will be heavily modified.
denny

[dennyplane]

thanks wayne.
I will get that book.
denny

[JimD]

Thanks jimd. Already went to that web page. Very interesting. Could not help but laugh because your last comment.
I would like to hear the explanation of why is the weekender so bad.
I promise you I will try my best to find a design that suits what I want and only if there is absolutely no hope, then and only then
will I go for it but I give you my word it will be heavily modified.
denny

denny, wish I could be more helpful, but the Weekender has been raked over the coals on this and other boards many times. I just don't have the time or interest in rehashing old hash. Could you recap what you're after at this point? Round bottom, shoal draft, centerboard/daggerboard, more or less? There are lots of proper little boats out there far more seaworthy. John Welsford comes to mind. http://www.jwboatdesigns.co.nz/index.html A number of builders have put small cabins on his open designs. Have a look at Navigator and Pathfinder.

[dennyplane]

Thanks jimd.
I went to duckworks website and they have all of welsford's designs. Houdini or navigator would be ok, definitely centerboard. But none are gaff rigged. A cabin or lack of is of no importance.
So,coastal capable, 14 to 15 feet,gaff rig,bowsprit,kick up centerboard,kick up rudder,5 to 6 feet beam,and most important,I want to build it with wood.
Most of the time solo with full camping gear,very seldom would I forsee taking one passanger.
Basically that's it.
denny

[JimD]

I understand the attraction to the gaff rig but a lug rig is so much more practical on a small boat. Either way, you could switch to the gaff if you really insist. Bow sprits have that salty look but they can be a bit of a pain on a small boat. My boat plan came with a bowsprit with a jib that was originally hanked on to a forestay - a really inconvenient arrangement. So now the jib can be taken in or set with an outhaul from the cockpit. Much better. Here is what our Glen-L Minuet looks like now. Unstayed mast, balanced lug main, jib on an outhaul, centerboard, kick up rudder, and cabinless. Going to get a little mizzen on the back soon, to complete the deal:

Main only



And with jib

[JimD]

A gaff rigged Navigator:

[dennyplane]

Thanks Jimd.
I think that a boat that I am gonna build has to be something that when I'm done sailing for the day,once on the trailer, makes me look back at her and say: I like you a lot.
Many very good designs out there,but you have to fall in love with it. You will take better care of it and sail it more often. It has to be kind of personalized. I do not know if you get
what I am trying to say. To have a boat that you like partially is no "it". Much less to have one just to have it.
I know I am a pain when choosing, but that is how I am with cars, bikes and planes. Can't help it.
That mizzen is so out of optical balance.
But we go back to point one. The hull is ok. There has to be a way to put the sails and deck that appeal to me on top of it.
When done it has to look right.
Aweekender with a different hull or a smaller fancy free.
denny

[JimD]

Yup. No point going to all the trouble of building a boat you don't like looking at. You could buy the Weekender sail kit and adapt it to a lot of boats in that size range. You can add that clipper bow to almost any design, too, and play with cabin shape. But if you don't start with a seaworthy hull in the first place you could end up very sorry. A couple ideas from Selway Fisher:





They're not intended for the sort of sailing you have in mind but they've gotta be better than a Weekender.

[JimD]

Sam Devlin's Nancy's China could be worth a serious look:

[JimD]

One of the shippiest pint sized gaffers ever drawn:

http://www.atkinboatplans.com/Sail/Pocahontas.html



You could trade in the leeboards for a centerboard.

[dennyplane]

Thank you so much guys.
That was the initial idea. To get a good hull in the size I wanted and put that gaff rig and bowsprit on it.
As long as ce is in the proper place with cl, and the centerboard, should be close enough to work.
Also I am assuming that the weights should be close too.
Now. That leaves to too many hulls to choose from. I am inclined to a welsford design because most of his designs are basically made for coastal waters.
Am I right?
I think with your help and a few more answers and suggestions I will finally make a good choice.
Jimd , I still think round hull. Your opinion?
denny

[JimD]

Jimd , I still think round hull. Your opinion?
denny

denny, I almost always have opinions but not always the expertise to back them up. Yes, I'd say round. But there's a lot of different rounds. Myself, I really don't like to heel, and I hate tender. I like a reassuring stiffness, especially in a very small boat far from shore.

[StevenBauer]

I find it hard to believe that none of the thousands of boat plans out there fit your desires. Between the two Atkins, Iain Oughtred, John Welsford, Selway-Fisher, Francois Vivier alone there are dozens of boats that meet your design brief. Not one has the looks you want? I'd think your best bet would be to build a hull to the designer's specs then play with the rig until it suits you.

[dennyplane]

Thank you steven.
I think that would be the best solution too.
denny

[Ian McColgin]

"I have been reading this woodenboat forum for a while and have not seen yet about mods to designs." [OP]

A remarkable statement given the great number of threads on various notions of changing designs. One hopes that folk can understand why you can't run a Glouster Gull through the xerox at 140% and get a boat that worth doodly.

[JimD]

... get a good hull in the size I wanted and put that gaff rig and bowsprit on it.
As long as ce is in the proper place with cl, and the centerboard, should be close enough to work.
Also I am assuming that the weights should be close too... I am inclined to a welsford design because most of his designs are basically made for coastal waters. Am I right?
denny

I'd say you're sort of right but its probably easier to screw up the balance and performance of a boat by switching sail plans than you might imagine. John Welsford posts on this board quite often and I wouldn't be surprised if he had a few things to say about the idea of doing so with one of his boats. I'm hoping that with a little more time you will change your mind as to what you want this boat to look like and come to appreciate the aesthetics of other designs. I know I have done so many times.

[dennyplane]

People have been modifying cars and airplanes since the start. Some succeded, some did not, but we got to this point because of the ones that tried new stuff. Boats are not different. With the amount of knowledge that is available today,can not be
hard to do. Some choose to live with limits and some not. Nothing wrong with that. Years ago a guy asked me if I could put a 460 in a 68 mustang. After two years, he got the car that he wanted and I got the satisfaction of being able to say " I did it"
What I want is out there, somewere, either as one or pieces. Just takes time to find it. I do not limit myself. I will get what I want and how I want it.
I have to say that there is absolutely no intention in this words to offend or fire anybody. Just the way I think. There is a lot of knowledge from people in this forum and that is what I am after. Knowledge is power.
I will always welcome and thank all responses, positive or negative. The exchange on info is a powerfull aid.
denny

[John Bell]

Modifying is fine is you are not risk averse. But if you aren't careful and prudent it's very possible to make a boat worse than a Weekender. The mind boggles at the idea!

[Ian McColgin]

Putting a 460 in an old Mustang makes for a bit of muscle, not unlike my recent boosting of Marmalade's sail area from 535 square feet to 625 - a nearly 16% boost all on the same spars. Another cat I can think of had her boom cut down by a good 8' - underpowered for racing but rather genteel for sailing about. In Marmalade's case, the extra HP is well used and the handling not harmed. I don't know about the old Mustang, but I do recall the older Sunbeam Tiger that was the real first put a big US mill into a small English car - hot but really poor balance and not enough friction between rubber and road.

Boosting a boat by 30% all around is another matter. The OP does not say but implies that the sail plan was just run through the xerox enlarger with the rest, but if that's what was done, the SA to displacement was radically lowered and the notion that she sailed well is not founded on any rational comparison. Owner satisfaction is fine as a subjective experience but means little to other sailors.

And you bet people modify airplane designs. And they get a pretty rigorous FAA evaluation before they get the airworthiness cert. The rather numerous "Mustang" fighters that are really somewhat shrunk versions also have important and interesting changes in air foil and other porportions to make them work well.

Just noting all this to help people who think they are introducing a novel subject that's actually extensivly discussed already and who might or might not be making for novelty. We all benefit from taking seriously the reality that "Knowledge is power" [#37] by listening before dismissing.