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Boat Forum / Building / August 2006Lengthing an 11 foot Sailboat
If I added 2 feet to an 11 foot sailboat with a 5 foot beam, what else would have to be changed in addition to adding an extra frame. Thanks, Ted in Mich. Ted, Nothing..... It will be longer. But there are couple of things here..... When this is done to ships, it is easy because most ships have what is called parallel mid-section. No sailboat that actually sails has this feature. Next - Are you planning to build this boat or are you thinking of this as a modification of and existing hull? And - What materials are you planning to use? Finally - Why are you doing this? Matt Colie - > If I added 2 feet to an 11 foot sailboat with a 5 foot beam, what else > would have to be changed in addition to adding an extra frame. Thanks, > Ted in Mich. > Thanks for your response Matt. Does "parallel mid-section" refer to the flat mid-section of the bottom of a ship? I have plans for a v-bottom boat (I like the lines of this particular boat) which I would like to lengthen. It would be fibre glassed plywood. Thanks, Ted. It means there is not a lot of curvature in the middle of the boat compared to the ends. Designers think of a boat in cross sections of (equal) length so the mid-section is the one amidships. The ends of the sections are usually called stations in case you ever come across that term. :) What I imagine you are going to get is a shift aft in the centre of balance of the boat due to the added weight of the extension. The boat will float a little differently in the water which will unbalance the sail and daggerboard(centreboard?). In a boat that small you can counteract any directional instability with the rudder or by shifting your weight to compensate. I doubt it would be a problem. > Thanks for your response Matt. Does "parallel mid-section" refer to the > flat mid-section of the bottom of a ship? > I have plans for a v-bottom boat (I like the lines of this particular > boat) which I would like to lengthen. It would be fibre glassed plywood. > Thanks, Ted. Ted, The parallel mid-section is more than just flat bottom, typically it is a portion where the bottom, deck and both sides are straight for some distance. This is not an effective hydrodynamic form, but if you have limits on draft and beam then you do what you have to do to carry cargo. Back to your situation. Assuming that what you have are plans for a straight frame "plywood and tape" design (meaning that the stations and frames are made of straight lines and the skin is wrapped or twisted plywood), you should be able to loft (layout) an intermediate station that will be fair. As you are not currently a boat builder or a loftsman, I stongly suggest that you build a very accurate scale model in balsa or foam core. This will give you the opportunity to both loft your additional station and get a preview of the result. Will this effect the almost every aspect of the boat's characteristics? Yes - for better or worse? I can't tell you without studying the plans and the changes. The boat's load and trim lines will change as well as the stability characteristics. The sailplan will change some because the relative locations of the centerboard, mast and rudder will change. What do you hope or expect to get for the extra 2 feet? Does the designer of this boat you like have a set of plans for the larger sister? (This is very often the case, and if they are a purchased set of plans, the plans and included rights can be sold.) If these plans were purchased from the designer, he may be able to point you to a good alternative. Short answers - Can you do this? - Yes Will the result have lines you so appreciate? - Maybe. Will you get what you want from it? - I can't tell you. Matt Colie > Thanks for your response Matt. Does "parallel mid-section" refer to the > flat mid-section of the bottom of a ship? > I have plans for a v-bottom boat (I like the lines of this particular > boat) which I would like to lengthen. It would be fibre glassed plywood. > Thanks, Ted. Thanks again Matt for your extensive reply to my post. The plan I have is a plan from the 1940's which I printed from the internet. The boat which I really like as far as lines and size is (13' by 5'). This plan is also from the 40's from the Eddy Ship Building Co. of Bay City, Mi. now out of business. The designer was Douglas Van Patten who also designed the "Canada" unlimited hydroplanes in the early 50's. This url: http://boatdesign.net/boat-plans-archive/ is a scanned sheet of construction drawings posted on a boat discussion/forum web site. The problem is that some of the lines are too faint to make out. Would a blueprint service be able to correct this problem? Thanks again, Ted. ps- I do know how to spell _lengthening_! Thanks for the link! surfnturf > Thanks again Matt for your extensive reply to my post. The plan I have > is a plan from the 1940's which I printed from the internet. [quoted text clipped - 9 lines] > > ps- I do know how to spell _lengthening_! Ted, The construction plans as posted at http://boatdesign.net/boat-plans-archive/13-eddycat-plan.htm and http://boatdesign.net/boat-plans-archive/13-eddycat-plan.htm are incomplete. The information required to construct the frames is not there. Some of this could be scaled off the drawing, but the sides above the chine will be very difficult to get correct on the first try. If you are not a very experienced boatbuilder, this would not be a good place to start. (I am a naval architect and marine engineer and have been building small boats on and off for most of my near sixty years and I would have a very hard time working from the posted material.) Yes - Some blue print services could bring out some of the faded lines somewhat, but blue print services (very rare these days) largely just print a copy of the drawing you give them. If you are diligent, you could do as well to get large prints of your files and recreate the lines with a batten. I did have a local office that I did use, but they have disappeared with the advent of electronic drawing handling (now a days offices set up an FTP where you can get to and download the IGES file you need.) It does look like a pretty little boat, and if you really want to attempt this, then the very scaled build would be the only place to start. Keep complete notes of your measurements and corrections (make a few small changes and sell the design as your own). If you do add a couple of feet to the LOA then it is your design. Good Luck Matt Colie Ted, I came into this 'discussion' a bit late, so bear with me. I have read all the correspondence to date - 08-20-2006 - and I'm a little confused. Your initial Q was . . .' > If I added 2 feet to an 11 foot sailboat with a 5 foot beam, what else would have to be changed in addition to adding an extra frame. . . .'. There then followed a lot of back-and-forth, and finally a reference & drawing. BOTH refer to a 13 FOOT BOAT !! ?? Anyhow . . . based on the initial Q, you wish to extend the LOA by 18 percent. That is really on the cusp of a 're-design', but within margins. The Drawings give you some good, and basic, data points to do a 'take-off'. They also give you 'station lines'. A 'legitimate' process would be to take that 24 inches, divide it by the number of stations, then ADD that dimension to the separation BETWEEN the present lines. THEN . . . LOFT the plan and 'check & correct' for fairness with a batten. Use a 20ft x 4ft piece of white 'butchers paper' or similar. If it were me, I'd get a couple of 4x8 sheets of 1/8in Hardboard, butt them together, tack in place, and roll on a couple of coats of water-based white primer. This is what I do to make parts templates. There are a number of books on lofting & building. Many illustrate how to use the information you already have. I just read through one by Chappelle which seemed to be 'contemporary' with this drawing. Also, take a look at a re-print of a book by Edwin Monk - 'How to Build Wooden Boats' - from the '30's. Regards & Good Luck, Ron Magen Backyard Boatshop Thanks to Matt, Ron and all who responded to my question on lengthening an 11 foot sailboat. As Matt pointed out the plans for the 13' Eddycat were incomplete and could not be used to build the boat. The 11' foot boat "Conga" was a complete plan I found later @ http://members.aol.com/polysail/HTML/conga.htm that is very similar to the Eddycat design. That link won't work with webtv, but it will with a pc. Thanks again for the useful info which I will use. Ted in Mich. p.s.-Both the Eddycat and Conga are plans from the 1940's. Ted, That is a set of drawings that you should be able to use. The statement about them being usually complete is correct as there is more information there than one would expect to find, but there is no problem that this could cause. Did you say where in Michigan? I am in the south east and sail on Lake Erie. Matt Colie > Thanks to Matt, Ron and all who responded to my question on lengthening > an 11 foot sailboat. As Matt pointed out the plans for the 13' Eddycat [quoted text clipped - 5 lines] > > p.s.-Both the Eddycat and Conga are plans from the 1940's. No, I guess just signed, Ted in Mich. I live in the village of Spring Arbor which is about 8 miles west of Jackson. Ted. > If I added 2 feet to an 11 foot sailboat with a 5 foot beam, what else > would have to be changed in addition to adding an extra frame. Thanks, > Ted in Mich If your download that has the very light lines can be loaded to a program like Elements 2 from Photo Shop you can darken them up. If you can't do this send me a copy of your drawings and I may be able to help |
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