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Thread: Making my own Sailing Dinghy Plans: questions

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    Default Making my own Sailing Dinghy Plans: questions

    Hello everyone. I am new here and I may as well say it outright; I know very little about building or designing boats. Anyway, me and my buddy decided to design and build our own boat last weekend. This won't be anything like the boat that Fancy was thinking about building at the beginning of the year. For me, the purpose of this project is to a) get a boat and b) figure out if I want to go to NWSWB... So I'm... testing the waters!!! *ba-dum-tsssss*

    I apologize for the bad pun, thank you for reading past it...

    We want a sailing dinghy to learn on. We decided on a range of between seven and twelve feet long, because we are students and have very little time outside of our studies and we want to be finished by the end of summer.

    We chose to use traditional Lapstrake construction because we liked the way it looked and it seemed like the easiest method to us... I am not sure if it is, but either way, we are quite set on it, so unless any of you have any major concerns, I hope to keep it...

    So... I have some a bunch of questions, but first, a little background info: the boat is not meant to be a record breaker for speed... We want it to be able to carry some camping gear, a cooler... enough for a weekend somewhere, but not anything crazy.. It would be a sailing skiff with a daggerboard... We were planning on putting plywood ribs into it... We went back and forth over an all-nighter on Saturday and eventually settled on 7.5 feet long and 5 feet wide at its' widest point... This seems outrageously wide to me...That's all I can think of right now...

    I am going to number the questions so that if and when you guys answer them you have an easy way to reference whichever ...

    On to the questions: 1) What type of wood should I use? I think I can get my hands on some Port Orford Cedar... Is that a good wood for this type of project? 2) What dimensions should the planks be... I was thinking of getting them milled to 1/2 inch by 6 inched by 10 feet... Is that standard? 3) What is the depth for a boat of this size? 4) how do I calculate Waterline? 5) Is the bottom of the boat a semi circle, or does it have a different shape? 6) What is the name of that board that runs up the bottom middle of the boat and up to the bow? What dimensions is this usually? 7) Do we need the ribs because I read somewhere that lapstrake doesn't need ribs a lot of the time.. is that recommended? This part is giving me a little bit of anxiety... We are making our own sail... and Mast... And basically everything.. but that's not the point... 8) What size of a mast should go on boat of this size? 9) what types of wood are masts made out of? 10)How long should the boom be in proportion? 11)What material should I use for the sail? 12)what type of sail should we make? 13) What type of rigging? Also... the width of the boat that I mentioned earlier... 14) am I correct in my apprehension to have a boat that wide in proportion to its' length? 15) Is 7.5 feet a safe length for learning how to sail on? also, I live in Arizona so this boat would probably go on pretty calm water... I may eventually take it out to the Puget sound if I go to NWSWB... 16) Is this type of boat something that could handle Puget Sound Conditions? I know that the water there can change at a moments notice... will a novice sailor be able to survive in such a boat? Last question... 17) Is this a reasonable idea: two people build and design a small boat in one summer with no prior knowledge?

    Thank you all so much for dealing with my ignorance and reading to the end of this very long discourse. I would appreciate it a lot if you could possibly answer some of my questions and maybe raise any concerns that I might have missed. Once again, thank you for your time and consideration.

    Kind Regards,
    Gabriel Partridge

  2. #2
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    Default Re: Making my own Sailing Dinghy Plans: questions

    Hi Gabriel.
    Welcome to the forum.
    Now have a look at the plans on here https://www.woodenboatstore.com/cate...ling_-_pulling
    and make notes of the length breadth depth, sail areas and so on. Study the plans to get some idea of what works. For two and camping gear 7' 6" is too short. My boat is 18 foot long and 5' beam, so your proportions are way off.
    You want lapstrake? Borrow or buy this book https://www.amazon.co.uk/Clinker-Boa...40_&dpSrc=srch to study how. That will show you that you will need wider boards than 6 inch to accommodate the sweep of the plank. Boatbuilders usually have a tree sawn through and through to obtain boards wide enough. Ply wood frames are only used in stitch and glue plywood boats, not traditional clinker.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    Puget Sound? Please do not think of building a 7 1/2 foot boat for the puget sound, unless it is to be towed behind a 20 footer.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    You can realize all of your objectives on time right here and do so without becoming so terribly disillusioned that you give up on the dream entirely.

    https://www.woodenboatstore.com/category/white_designs

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    Default Re: Making my own Sailing Dinghy Plans: questions

    Thank you all so much for your feedback.

    Mr. Wizbang:

    I will be very careful while on the sound, and I will probably not use this boat for it unless I am within swimming distance of shore. I did some more research on it and.. I agree with your worries. Thank you for your concern.


    Thank you Mr. Maa:

    I have ordered a copy of the book and look forward to its arrival. I also took a look at the boats that were shown in the link. I am wondering what you suggest I do: revise the plan to be a narrower beam, or a longer boat? Which would be safer/better to learn on?


    Thank you Mr. Etheridge:

    I appreciate you going out of your way to send those plans my way, although I am loth to use them. Me and my friend want to have a boat that is wholly ours. We need a challenge, and this seems like a good one. If by the beginning of May, we have not come up with a substantial plan, then I look into purchasing the plans for the Auklet by Iain Oughtred.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    It all comes down to your budget. Building something totally self-designed will be a great learning experience, but can be quite costly in terms of materials, time and possibly gear (if it capsizes). I have several friends that have insisted in building their boats their way -- but the results were often frustrating for them when things didn't work, broke at critical times, or performed very badly; and also frustrating for their friends who were trying to row or sail along with them, but kept having to wait and wait and wait until we gave up and left them behind.

    Many boats have simple plans for sailing rigs, so you'll have lots and lots of room for self expression building the spars, supports, centerboard and rudder, steering system, etc. If you keep function in mind you can add all sorts of things and still have a very functional craft.


    My Chamberlain Dory Skiff was just a pulling boat when I started restoring it. I moved the mast forward from the position in the plans, then had to add a bowsprit to get the sail rig to balance (heavy weather helm). Even though it is far from the original sail plan and spar design, it works and lets me carry three crew or a full load of camping gear.



    Here's a highly-modified Catspaw dinghy built by Ed Frey in Fortuna. Despite the extra sheerstrake and decorations, it sails and rows very well.


    Here it is with a new paintjob and sails -


    Here's a boat designed and built by a very stubborn friend of mine. We nicknamed it The Floating Coffin, and it couldn't be sailed upwind or rowed very far, and he had to add plastic outriggers to get it to sail much at all -


    the small boat with the lateen sail (a tent rainfly) was built by another very stubborn friend, and it sank with him and his gear three times in two different trips. It also couldn't sail...but that didn't stop him from trying. He's now bought or built three more boats, all nearly as bad and some slower than this one. When we row or sail to a lunch spot, he always shows up just as we finish and are heading back...sigh
    Last edited by Thorne; 03-07-2018 at 01:35 AM.
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    Default Re: Making my own Sailing Dinghy Plans: questions

    Buy an old fixer upper boat before jumping in to the expense and time of a whole build. Depending on what you buy you will still learn a lot and get great satisfaction. Depending on the finish you want most boat building is sanding and you can do that just as easy on a old boat.

    The fixer upper will help you understand your requirements and you and modify and experiment quickly and cheaply. Unless you are a great builder your new build, especially to your own design, won’t be worth a great deal so if it doesn’t meet your requirements you have lost lots of money.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    I like your attitude and that you want to build traditional, but Why do you need to build it that small Badgerbuilder? Shop space? Money?

    How about building a flat bottomed skiff like this: http://www.atkinboatplans.com/Sail/Nina.html I believe this is less complicated than clinker lapstrake with bent frames.

    If you watch all the videos in this series https://youtu.be/0vIVSfXg61I you learn a lot about building flat bottomed skifffs (ps: I have never done it myself)

    Good luck!

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    Default Re: Making my own Sailing Dinghy Plans: questions

    Quote Originally Posted by Badgerbuilder View Post
    Thank you all so much for your feedback.
    Thank you Mr. Maa:

    I have ordered a copy of the book and look forward to its arrival. I also took a look at the boats that were shown in the link. I am wondering what you suggest I do: revise the plan to be a narrower beam, or a longer boat? Which would be safer/better to learn on?
    7'6" is only fit for a dink going from the beach to a mooting, 10' will be too cramped for two up, for two and gear I would look at a 12' design. Use the proportions from the study plans and copy the form of the midship section (definitely not a semi circle).
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    To clarify my post, I recommend building a stock design to meet your requirements (two crew and gear), as you'll have plenty of room to experiment and do a lot of headscratching over the non-hull elements. Another big advantage of building a standard design is that if you then decide you like building and want to make something bigger / stronger / faster -- you can sell the first boat to pay for materials for the second boat. Trying to sell something home-designed will be more difficult and bring in less money.

    Our kind hosts here sell plans for all sorts of traditional lapstrake boats -- here's the Catspaw, which will just barely hold two active sailors and some gear - https://www.woodenboat.com/boat-plan...catspaw-dinghy

    They also sell the book, which is a huge help to new (and old) builders - https://www.woodenboatstore.com/prod.../boat_building

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    Default Re: Making my own Sailing Dinghy Plans: questions

    Sounds like an excellent adventure in design and building! If you're heart-set on staying small, you may want to think of a pram-style design with a flat bow. I think you'll get more usable volume and buoyancy out of that type design for the length you're restricting yourself to. Usually also requires less extreme bends on your materials which could simplify your build.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    About this time of year many sailing clubs start to offer beginner courses, these are a great way to meet like minded folks and learn the basics of sailing...

    Useful skills once the boat needs launching.
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    Default Re: Making my own Sailing Dinghy Plans: questions

    Over the years of forum viewing, I've seen numerous threads from first time builders who also firmly state they are going to design their own boat. I'm curious to know if anyone here has ever encountered someone who has actually done this. I'm talking about stone cold beginners who have designed, built and sailed/rowed/motored a successful boat. Seems to me that these folks post their ambitious, grand plans and then accomplish....nothing. I can't recall ever seeing a post where someone has done this. Invariably the OPs are never heard from again.
    Last edited by Dusty Yevsky; 03-07-2018 at 07:49 PM.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    Quote Originally Posted by Dusty Yevsky View Post
    Over the years of forum viewing, I've seen numerous threads from first time builders who also firmly state they are going to design their own boat. I'm curious to know if anyone here has ever encountered someone who has actually done this. I'm talking about stone cold beginners who have designed, built and sailed/rowed/motored a successful boat. Seems to me that these folks post their ambitious, grand plans and then accomplish....nothing. I can't recall ever seeing a post where someone has done this. Invariably the OPs are never heard from again.
    I think we've had a few successful builders. Some post after the fact -- avoids people like me raining on their parade -- and many seem to have designed and built some quite nice boats. But in general it can be difficult steering builders towards designs that meet their requirements, when the requirements need some serious rethinking. I completely respect building on a budget, and have friends that have had both successes and failures -- see my photos above. ;-)

    Photo of a "boat" constructed from the remains of the Floating Coffin by friends who know better, but just can't help themselves, or so it seems. Nobody drowned, so yay!
    Last edited by Thorne; 03-07-2018 at 09:38 PM.
    "The enemies of reason have a certain blind look."
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    Default Re: Making my own Sailing Dinghy Plans: questions

    Thank you all for your support and consideration. It means a lot to me to know that so many people are interested enough to leave a comment. I am going to meet with my co-conspirator soon and we will go over and make changes to our plans. I know it may not be the easiest option, but we never were interested in doing things the easy way. Thank you all for your care and advice, and if it turns out to be too complicated for us, I think we will seriously consider the Catspaw. It looks like a very capable and handsome boat.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    Over the years of forum viewing, I've seen numerous threads from first time builders who also firmly state they are going to design their own boat. I'm curious to know if anyone here has ever encountered someone who has actually done this. I'm talking about stone cold beginners who have designed, built and sailed/rowed/motored a successful boat. Seems to me that these folks post their ambitious, grand plans and then accomplish....nothing. I can't recall ever seeing a post where someone has done this. Invariably the OPs are never heard from again.



    Probably because people that take 7 1/2 foot boats, two up onto Puget Sound rarely live long enough to report back.

    Judging by the original set of questions about basic things, they haven't got a clue (and they admit that this was a "Hold mah beer and watch this" idea on a Saturday night) and if they REALLY want to do this, then suicide by boat isn't something that I'd want to encourage. The "Something must be done!' reaction of the bureaucrats is likely to impact us all with rules, regulations and licensing for any boat design and build.

    However, if they are determined, nothing that anyone contributes will change their mind. I only hope that they take the advice and build from an established, tried and tested design.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    Quote Originally Posted by Dusty Yevsky View Post
    Over the years of forum viewing, I've seen numerous threads from first time builders who also firmly state they are going to design their own boat. I'm curious to know if anyone here has ever encountered someone who has actually done this. I'm talking about stone cold beginners who have designed, built and sailed/rowed/motored a successful boat. Seems to me that these folks post their ambitious, grand plans and then accomplish....nothing. I can't recall ever seeing a post where someone has done this. Invariably the OPs are never heard from again.
    Not quite sure I was a first time builder, I had built a couple of proas but of simple box form. I posted my ideas for a twelve foot canoe on this forum and received help and advice from the furum and built what I consider a fantastic little craft. The design evolved heavily due to the help of this and a canoe forum but I get great pride in having designed it myself.

    Your point is valid however which is why I in a earlier post recommended buy and old boat to fix up. I know a hot shot young laser sailor who fixed up and old mirror and it is his pride and joy. Over here you can pick up old woooden boats for less than £200 even for £100 if ypu want. a challenge.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    Gabriel ,
    Lucky man having access to Port Orford Cedar. Great stuff.
    I have built a 30 foot launch from Port Orford Cedar (Lawsoniana down under). Two skins on the diagonal with fibreglass covering. 15 years old and still going strong.
    Pict0013.jpg

    If I was you and your mate I would suggest a minimum of 12 foot and if need be go to 14 feet.
    This thread is on this website and is for Hartley 14. http://forum.woodenboat.com/showthre...8-More-Hartley
    Use the Port Orford Cedar for framing and stringers and cover with plywood.
    I did this when building this Hartley 16 about 10 years ago.
    DSC02710.jpg
    I am using left over Port Orford cedar for framing a Pelin 12 footer outboard dinghy this winter.
    http://forum.woodenboat.com/showthre...ot-Nomad-build

    I would also look at Paul Gartsides sailing dinghies. https://store.gartsideboats.com/coll...and-daysailers
    Prettiest boats I have seen drawn and can be built in clinker/lapstrake. He has some beautiful 12 foot to 16 foot designs.
    Plus his boats sail really well.

    The other option I would recommend is have a close look at what wooden boats your local sailing club sails.
    Join the club, go for some practice sailing as crew then start building a new one for the class. You might have some excellent helpers from the club.
    Plus when not building on fine weekends you can go sailing. And there might be a buyer in the club if you and your buddy can never see the finish of the project.

    This project for you and your mate will take at least 2 to 3 years - depends how much spare time you have to put into it.
    If you are cutting and milling green Port Orford cedar it will take some time to dry out before use. Depends where you are?
    I would get the Port Orford Cedar milled by a miller who has supplied boat builders in the past.
    Ask him to mill the planks long - I would expect a 5 to 6 metres as normal. Much easier to cut to length than join to make longer.
    Those are full length stringers on the Hartley 16.
    For your first cut timber, I would expect most planks to be (width)100 to 250mm X (depth) 50 to 100 mm as a minimum.
    Then once the timber has dried you can cut these down and dress them to required plank size of say 12mm.

    You are very lucky to have a good source of excellent boat building timber.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    I'm one of those people who thinks that folks should design their own boats and go sail them. However, there's a big caveat.... you need to know SOMETHING about boats to do this. Seriously if you know ABSOLUTELY NOTHING about boats, have never sailed, never been on one, never wandered around a boatyard or storage field staring at designs, then the odds are good that your results will be less than sparkling.

    Nobody is saying that you absolutely no way should ever, ever, ever design your own boat. But what says that the FIRST one has to be all yours? Why not build a simple boat designed by someone else and sail/row it for a few months? Maybe build two....a simple 8-10 foot sailboat and a simple flat-bottomed rowing boat.

    After you've done that, you'll know something. THEN, break out the software and do your stuff.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    Also, to seriously oversimplify, your beam should be something like 1/3rd of the overall length. Sure it could be a little more or a little less, but "more or less" 1/3rd.

    A couple more comments... lapstrake construction is a stinking lot of work. Yes, it's beautiful, but you know next to nothing. Your design process may very well produce an abomination. Do you want to spend hundreds of hours creating an abomination? For someone in your situation, build a simple plywood skiff. You still might create an abomination, but at least you'll have spend $200 and sixty hours, not three hundred hours and a thousand dollars in materials.

    Look, a standard piece of plywood is 4 feet wide by 8 feet long. If you join two pieces together, you get a piece that's 4 feet wide by 16 feet long. You can build a very nice 14-15 foot skiff with 4 1/2 feet of beam out of four pieces of plywood and some 1 x 2's. Add in a mess of copper nails and a few tubes of PL Premium glue and you are on your way.

    http://www.simplicityboats.com/LCB.htm

    That thing will carry you and your friend on great adventures. It's cheap to build, and while it's pretty big it should probably row OK. If you think it's too big, apply the same principles outlined on that site to making one that's a bit smaller.

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    Default

    Whatever you build the main sheet and few blocks will set you back more than this

    When you meet with your friend draw up a FULL budget, trailer, trolley, cover, sails, mast, hardware etc etc



    I am sure you can find similar near you. No disrespect but based on how much you know about boat design I think an old boat is a good route


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    Default Re: Making my own Sailing Dinghy Plans: questions

    Designing and building your own boat and then doing some gunkholing with a ate is a lovely idea. Plenty of people have done it. Many more have failed. At this stage my money would be on you failing. You don't k ow what a keel is. You want to use ply for ribs on a traditionally planked clinker dinghy. You haven't picked up the difference between glued lap strake ply and traditional clinker planking. You have no understanding of even basic hull form and dimension. A few weekends in you will have started to understand how much you don't understand, and if you are lucky or wise will then cut your losses. Sure, keep the dream alive, but understand that you have a lot to learn before you draw your first line on a bit of paper, let alone cut any wood. Good luck with it.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    Building a boat is one thing (go for it!), but - having admitted "I know very little about building or designing boats." - why do you feel the need to design one?

    Assuming you have already examined the dozens, if not hundreds, of existing plans for small sailing boats - many of them designed by people who know a great deal about designing boats - why would you reject those in favor of your own design?

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    Default Re: Making my own Sailing Dinghy Plans: questions

    ^ Especially considering that you want to get it done in one summer. You are underestimating the amount that you have to learn, including woodworking, and the amount of time it takes to do something like this, perhaps the expense as well. Swallow a bit of your pride and take advantage of other's experience.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    There is no safe distance from shore in the Puget Sound. Out side of the few protected harbors , even right in front of the port Townsend place, currents are dangerous and the coldness of the water is more dangerous than any shark.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    Quote Originally Posted by Alan H View Post
    Also, to seriously oversimplify, your beam should be something like 1/3rd of the overall length. Sure it could be a little more or a little less, but "more or less" 1/3rd.
    For traditional craft (not modern "scale up a Lazer dinghy until you have full standing headroom" types) a better rule of thumb is to take the square root of the beam and multiply by beam to give either LOA or LWL or take the cube root of the length and square it to yield the beam. For example:

    8 foot yacht tender gives a beam of 4 foot - perfectly normal and no one would bat an eye at that.
    9 foot beam gives a 27 foot long yacht - a normally proportioned yacht.
    16 foot beam yields a length of 64 feet.

    etc. etc.

    I have come to this rule of thumb by analysing the many designs in many of the books I have on yachts and small boats designed by Alden, Philip Rhodes, Maurice Griffiths and many others. It works to within a few inches except on specialist boats like Cape Cod catboats. Five minutes with a pocket calculator will demonstrate this.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    I have heard reference to previous threads that are essentially what I am attempting to do. Can anyone point me in the direction of those threads? I'd love to read them.

    Wizbang, I will keep that in mind. thank you.

    We may decide to change building methods in favor of an easier one. We meet about once a week to discuss this project but will most definitely increase our meetings as soon as the semester ends. That is why it is taking so long for me to make solid changes to the plan. Solid changes will be made though. I would like to thank Phil and Alan for helping me with the proportions. I will be loosely using those suggestions. Mr. Tink: I may very well abandon this project in favor of a fixer-upper. The only problem is that I am having a lot of trouble finding one. If anyone is able to help me find a wooden sailboat for sail in the heart of the desert... I live in Phoenix and if anyone knows anything... All I can find is ugly fiberglass... Maybe I'm looking on the wrong websites...

    Anyway, once again, thank you all for your kind posts and encouragement. I appreciate all the feedback I'm getting and I want to let you guys know that it is making a difference in my plans.

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    Default Re: Making my own Sailing Dinghy Plans: questions

    https://lascruces.craigslist.org/boa...478762358.html

    This is a rowboat, I donít know anything about the design, if it can take a sail. My guess is it might be able to handle a sail and leeboard better than what you are planing on building. Itís in Las Cruzes, a little drive from PHX but not bad, easier than building.


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    Default Re: Making my own Sailing Dinghy Plans: questions

    Phil B - just for kicks, could you work your formula for my Lightning? Total length is 19 ft and max beam is 6'6". Not sure if I am doing it right, but, when I try the formula starting with the beam, looks like it should be more like 16 1/2 ft. And, when I start with the length, it comes out to 6.25 for the beam, which at least is pretty close. Either way, it looks like the Lightning is a little narrower than your formula would call for. But it seems most folks agree that it sails quite well, so I guess there are a lot of other factors in play.

  30. #30
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    Default Re: Making my own Sailing Dinghy Plans: questions

    I just re-read your opening post. The answer to each and every one of your questions is "Depends". Hope that helps.

    PS... PLEASE just build the Catspaw, and follow the plans exactly.


  31. #31
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    Default Re: Making my own Sailing Dinghy Plans: questions

    Quote Originally Posted by Badgerbuilder View Post
    I have heard reference to previous threads that are essentially what I am attempting to do. Can anyone point me in the direction of those threads? I'd love to read them.

    Wizbang, I will keep that in mind. thank you.

    We may decide to change building methods in favor of an easier one. We meet about once a week to discuss this project but will most definitely increase our meetings as soon as the semester ends. That is why it is taking so long for me to make solid changes to the plan. Solid changes will be made though. I would like to thank Phil and Alan for helping me with the proportions. I will be loosely using those suggestions. Mr. Tink: I may very well abandon this project in favor of a fixer-upper. The only problem is that I am having a lot of trouble finding one. If anyone is able to help me find a wooden sailboat for sail in the heart of the desert... I live in Phoenix and if anyone knows anything... All I can find is ugly fiberglass... Maybe I'm looking on the wrong websites...

    Anyway, once again, thank you all for your kind posts and encouragement. I appreciate all the feedback I'm getting and I want to let you guys know that it is making a difference in my plans.
    You sure do have slim pickings over there, looked on Craigslist and very poor choice and very pricey. Looked at San Francisco Bay Area just for reference and nothing would appeal to me there either. I think we are lucky here in the UK in that we had the whole homebuild / plywood thing going on in the 70s and with many clubs dedicated to racing we have a lot of old boat people don’t want just because they are perceived as uncompetitive. Good luck with your search if you go that route.

  32. #32
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    Default Re: Making my own Sailing Dinghy Plans: questions

    Quote Originally Posted by Phil_B View Post
    For traditional craft (not modern "scale up a Lazer dinghy until you have full standing headroom" types) a better rule of thumb is to take the square root of the beam and multiply by beam to give either LOA or LWL or take the cube root of the length and square it to yield the beam.
    This is also the approach that I use. Stability is correctly adjusted as boat length changes since the design wind velocity is not typically scaled up and down with boat length. For typical dinghies less than 18 to 20 ft, I start with a length to beam ratio of 2.57 and adjust from there. Live ballast has a big influence as the boat length is decreased, so length to beam ratio does not need to scale to L^(1/3) on the shorter boats.

  33. #33
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    Default Re: Making my own Sailing Dinghy Plans: questions

    Regarding beam, lets just for giggles compare two very successful but very different boats.

    Here's a Lido 14, a monstrously successful 14 foot fiberglass knockabout dinghy, which has had something like 2,000 of them made.


    LOA is 14, beam is 6. It's a chubby little thing, but a great, stable daysailer. Obviously the beam is a lot more than 1/3rd of the LOA, but I would like to suggest that this ratio, unless our friend knows a lot more than he indicates he does, it about the upper end of beam/LOA that he should be thinking of.

    Here's something different. Here's Ian Oughtreds lovely Elfyn



    derekthompsonlaunch13061282web.jpg

    Elfyn is very narrow, being intended for both rowing and sailing, perhaps with an emphasis on the rowing aspect? Elfyn is 16' 6 LOA with a beam of 4'9"

    So the length to beam ratio of the Lido is 14 / 6 = 2.33
    The length to beam ratio of Elfyn is 16.5 / 4.75 = 3.47

    without getting into square roots, cube roots and so on, I would suggest to our first-time builder and designer, that he stick to a LOA /Beam ratio between those two things. If He wants to sail, primarily, then build a wider boat. If he wants to row, primarily, then build a narrower boat.

    cheers!
    Last edited by Alan H; 03-09-2018 at 03:31 PM.

  34. #34
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    Default Re: Making my own Sailing Dinghy Plans: questions

    On a larger scale, Google flyin Hawaiian.

  35. #35
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    Apr 2017
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    Nelson, New Zealand
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    Default Re: Making my own Sailing Dinghy Plans: questions

    Quote Originally Posted by Mike Seibert View Post
    Phil B - just for kicks, could you work your formula for my Lightning? Total length is 19 ft and max beam is 6'6". Not sure if I am doing it right, but, when I try the formula starting with the beam, looks like it should be more like 16 1/2 ft. And, when I start with the length, it comes out to 6.25 for the beam, which at least is pretty close. Either way, it looks like the Lightning is a little narrower than your formula would call for. But it seems most folks agree that it sails quite well, so I guess there are a lot of other factors in play.
    Yep - I get the calculated length to be 16.57 feet (16 feet 7 inches) from the beam and the calculated beam from length to be 7.12 feet or 7 feet 1 inch. But there again, I did stress (or should have stressed) that it was for normal cruising boats and there would be exceptions such as shallow draft, beamy centreboarders which will have a greater then average beam, racing craft and other specialist types.

    It is easy to set up a spreadsheet to calculate the beam from the length in 1 foot increments. Print it out and look at the plans offered by Woodenboat from 8 foot yacht tenders (no one would bat an eyelid at an 8 foot tender with a 4 foot beam) to big yachts and you are likely to find that they are within an inch or two of the predicted result. I use this rule of thumb when sketching out the parameters of a boat I try to design and/or use it to screen boats for normal, healthy proportions. Which isn't to say that your Lightning isn't well suited for its designed purpose. Just if you want a cruising design that isn't too extreme it is on the slim side of the equation.

    As I remarked, checking out designers like Alden, Philip Rhodes and others who designed cruising yachts gives remarkably good agreement with the formula. Modern boats, not so much ...

    Here is a part of such a spreadsheet. It might give a better idea of what I mean (or there again ...).

    Beam LWL LWL-Beam ratio LWL Beam LWL-Beam ratio
    1 1.00 1.00 1 1.00 1.00
    2 2.83 1.41 2 1.59 1.26
    3 5.20 1.73 3 2.08 1.44
    4 8.00 2.00 4 2.52 1.59
    5 11.18 2.24 5 2.92 1.71
    6 14.70 2.45 6 3.30 1.82
    7 18.52 2.65 7 3.66 1.91
    8 22.63 2.83 8 4.00 2.00
    9 27.00 3.00 9 4.33 2.08
    10 31.62 3.16 10 4.64 2.15
    11 36.48 3.32 11 4.95 2.22
    12 41.57 3.46 12 5.24 2.29
    13 46.87 3.61 13 5.53 2.35
    14 52.38 3.74 14 5.81 2.41
    15 58.09 3.87 15 6.08 2.47
    16 64.00 4.00 16 6.35 2.52
    17 70.09 4.12 17 6.61 2.57
    18 76.37 4.24 18 6.87 2.62
    19 82.82 4.36 19 7.12 2.67
    20 89.44 4.47 20 7.37 2.71
    21 96.23 4.58 21 7.61 2.76
    22 103.19 4.69 22 7.85 2.80
    23 110.30 4.80 23 8.09 2.84
    24 117.58 4.90 24 8.32 2.88
    25 125.00 5.00 25 8.55 2.92
    26 132.57 5.10 26 8.78 2.96
    27 140.30 5.20 27 9.00 3.00
    28 148.16 5.29 28 9.22 3.04
    29 156.17 5.39 29 9.44 3.07
    30 164.32 5.48 30 9.65 3.11
    Last edited by Phil_B; 03-10-2018 at 05:21 AM. Reason: Added spreadsheet.

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