View Full Version : Stretching lines, again
12-15-2002, 09:39 AM
Yes, I've run a search, and I understand the pros and cons of making an existing design longer and the percentages. Here's a little different situation.
My dad built many boats, among them a 12' bateau, flat-bottomed, outboard powered, which I still have. It's 40 years old and sound. I love the little boat, and I'd like to have one just like it, but 14, maybe 16 feet. I want it to be the same design as dad's, both out of nostalgia and as a tribute, as well as the fact that he had a certain way of building which I've not seen in other bateaus. It's probably why people would come from all over the south to have dad build bateaus for them. There's something about his lines, which were never put on paper, that make for a sweet, pretty little boat.
Here's my questions, please:
1) I'd like to "taker her lines" and put them on paper as she is, for posterity, so to speak. Would the baseline to measure from on a bateau be the bottom? I am thinking I could do a fairly good job with careful measuring of her dimensions and shape, and transfer it to paper.
2) I have access to Corel Draw and Adobe Illustrator, which I understand are not CAD programs, but that's what I got and understand fairly well already from my work at the newspaper. Think I could generate a decent set of plans with these? I'm not going to sell them or anything, just like I said, preserve the design.
3) Enlarging: If I go to 14 or 16 feet, would I establish a percentage number which represents the enlargement, and apply that number across the board? I.e., the same number to length, beam, freeboard, etc.?
4) The boat is plywood. With the increase in size in mind, does she need more frames, or just an increase in the spacing of the existing number of frames? There are six frames between transom and bow. The rear two are closely spaced to form a seat and storage bin, then forward there are two frames in the same fashion to form a seat and livewell. There is one frame between the two seats and one where the bow curves up to the head block.
What ya think?
Regards from the Rez,
[ 12-15-2002, 10:41 AM: Message edited by: Roger Stouff ]
David Tabor (sailordave)
12-15-2002, 09:56 AM
Well, you *can* stretch the lines to a degree. I "stretched" my stripper canoe HIAWATHA from 15' to 15'6" by increasing the spacing of the middle third of the boat where the shape of the hull didn't change as drastically as the ends. And I paid special attention to making sure my fairing battens laid fair when I set the molds up on the strongback. That said you could probably stretch the boat 6-8 inches in length w/ no real worries about additional frames or increased planking scantlings... I'm no expert but what you're talking about is a 17% increase in length (12 to 14) so I would probably increase beam by 10-12% and maybe 5-8% in the freeboard department. Those are just rough numbers based on what I've thought "LOOKS" good in comparing various designs over the years but I'll wager that if you compare dimensions of several similar type boats that would be close. IMHO of course! :D Sounds like a neat project, keep us posted.
Mr. Know It All
12-15-2002, 10:06 AM
Good morning Roger. I can't help much in the way of advise but wanted to comment on what you're trying to do. I think it's a great idea to preserve your fathers way of building and following him in building a bateau. You're a good son. smile.gif How's the Thompson coming along?
Kevin in Ohio
12-15-2002, 10:08 AM
Not too good. I shoulda listened to my pal Scott Rosen's advice on this forum. It's gets worse the deeper I go into it, and I'm undecided now if I should continue.
12-15-2002, 10:53 AM
Without making any claims to being any boat designer, I would enjoy taking a look at what you are doing and what you are working with. We have always done our scows in the past just the same manner that you are attempting to do with this boat, dealing with needs and desires. If you would post a picture or two, maybe amoung some others here, we can work this out for you. Just a thought.
12-15-2002, 11:35 AM
Here are some photos I took today:
[ 12-15-2002, 06:50 PM: Message edited by: Roger Stouff ]
Mr. Know It All
12-15-2002, 08:06 PM
Roger.....Sounds like you're entering the "Oh no,what have I got myself into" phase with the Thompson project. I would say (speaking from experience) it's progressing normaly. :D Hang in there.
Kevin in Ohio
The baseline is usually below the lowest point of the boat; this allows all of the measurements to be positive. Sometimes they're some other way placed and the location of the line noted (I don't remember what it was, but the baseline was 3" above the top of the strongback, and the figures were given as if the boat were to sail upside down.)
You're not required to stretch the same amount in all dimensions (and in going to either 14' or 16' it would probably not be a good thing.) Twenty percent in length would get you to 14'6" (adding 30" in length; an inch more in depth, maybe two or three in beam, might be nice, depending on what you want.)
That is a great boat. It is closer to what I am looking for in a river boat than anything I have seen so far.
How does it do in a bit of a chop.
Peter Malcolm Jardine
12-15-2002, 11:46 PM
thats a really neat boat... We don't see that design up here that much. I bet it goes like a rabbit with a fifteen on it. Sure beats the hell out of those ugly glitter bass boats.
12-16-2002, 05:57 AM
I could draw it with Rhino if you want and then you could import the lines into Corel draw.
try to level your boat with the waterline. And measure it station wise start from the bow and measure every 3 fot or similar.
Make an table with excel or similar program
The nice thing if you draw it in Rhino is that you can makes the lines smoth with Rhino. Another bonus is you vill get panel layouts also
Intelicad is free exelent cad program that you can use if you want to makes plans. But you can also us Corell, with Corell you can make more "fancy" plans
For a larger boat I would chose to make the bottom laminatet out of two sheets otherwise you could have som problems with bending of the plywood
12-16-2002, 07:52 AM
Thanks for all your kindnesses and thoughts.
Howard, in a mild chop, it's fine; when things get a little heavier, it tends to batter pretty good on the bow, but slowing down and letting her ride with the swells works wonderfully. You might be interested in reading one of my favorite memoirs regarding this boat, my dad and rough water: Parables (http://www.banner-tribune.com/ftos/Columns/ftos8-29.htm)
Peter, by myself, it zips along great. With another person, it's still real respectable. Dad used it with a 9.8 Mercury, which also did very good. It was a 1963 model, I still have it.I took it off in 2000, was still running good, but I wanted to do the cosmetic restoration, which is still pending.
Hans, thanks for your generosity as well. I'm still weighing my various options and as soon as the Christmas season is done, I hope to get down to the nitty-gritty on it.
John of Phoenix
12-16-2002, 08:38 AM
I really love your writing Roger. Thanks for the story. Don't worry about your new boat. Your father will help you design it.
12-16-2002, 09:05 AM
I'm counting on it, John. smile.gif
Hi, Roger. Sorry to take so long to reply – I wuz doing “domestic engineering” (putting up Christmas decorations) all weekend, so I sorta ignored my buddies here on the forum.
Yes, by all means, lift the lines of your father’s boat. Preservation of indigenous small craft is something that should be done whenever possible. Keep as much info as you can about the vessel such as who built it, where, out of what, describe any special building techniques, common paint schemes, colours, scantlings, etc. etc. Take lots of photos of every detail. Store the gathered info in a safe place and make arrangements to donate the info to the nautical museum of your choice, and stipulate whether and how you want the plans disseminated after you’re gone.
To lift her lines, it is common on a boat this size to turn her over on two sawhorses and level her to her static waterline. The baseline is parallel to the waterline at the deepest point of the boat, usually the aft end of the keel, but that is dependant on the boat shape. The bateau is a pretty simple – tho’ subtle – hullform, so you can probably describe her pretty adequately by defining the keel profile (if there is one), rabbet line, chine line, and sheer line. If there is a lot of shape in the rise of the bottom and inward sweep of the topsides strakes, you may want to pick off two buttock lines at, say, 1’ and 2’ off centre, and a waterline about 6” above LWL. Usually this type of boat didn’t have a specifically defined bow shape – it was dependant upon the sweep that the planking naturally took, and was only influenced by the builder by where he set up his building mould in relation to the stem. The uniqueness (and the devil) is in the details of HOW the boat is put together. A linesplan without a detailed investigation of the scantlings, materials, and building method is only a partial document. If you would like a description of how I set up to lift lines, shoot me an e-mail to my private line.
Given that you are not currently familiar with CAD or 3-D modeling software, I would suggest that you abstain from creating the lines on a computer. Corel & Adobe are great programs, but lacking features that are required for accurate technical drawings. Use pencil & paper, battens & weights to hand-draw the hull. It is a rewarding exercise and your accuracy will probably be better. Battens can be made from close-straight grained wood or cut from lexan, and weights are easily made from scrap lead and nails. If you do this once and like it, you will use these tools over and over again. Chapelle’s “Yacht Designing & Planning” gives and excellent description of how to create a lines drawing. If you wish to later have the lines transferred to CAD or 3-D, it can be easily done from your drawing with a digitizer and faired with plate developments in an hour or two.
To enlarge the boat, you first have to decide whether you want it bigger all ‘round, or just longer. Given what little I know about the local boats in your area, I will presume that you are interested mostly in longer, not appreciably deeper or wider. I would do this by creating a table of offsets for each of the stations of your newly-created linesplan, then lay out a new drawing sheet with the station spacing AFT OF THE BOW SECTION (i.e., in the area aft of about 1/3 of the length of the boat from the bow) increased by the proper percentage to achieve the desired length. You don’t want to mess with the shape of the bow if it works well in its original form. Draw the rabbet, chine & sheer lines on the new station spacing in plan and profile (the sections will remain the same as the original), and – voila! – your new & improved boat lies before your very eyes. This will work well for a hull type like a bateau due to its constant section shape, but not well with more shapely hull forms such as sailboats. Note that you have just increased the buoyancy of the hull by much more than the extra hull material will counter, so she may not float on her lines as before. For example, a 2-foot extension in a 5-ft wide bateau hull with 3” of draft will add 150 lbs of buoyancy, but the materials to add this length will weigh only about 30 lbs. She will float higher, but in a simple bateau hull form this will translate into more carrying capacity without serious side effects. The increase in wetted surface area will create a bit of extra drag, requiring a bit more horsepower to push it along, but you want a bigger boat to carry more stuff, so you already know that you want a bigger motor, right? If you want to widen the boat, I would recommend that you do it on a much smaller scale than lengthening. A ratio of about 3:1 would be reasonable. For example, taking your bateau to 14 feet from 12 feet is an increase in length of 16%; a proportionate increase in beam would be too much, so apply the suggested ratio – 16% x 1/3 = 5% - and your 5-foot beam becomes 5’-3”, which is more reasonable. Remember that frictional penalties for beam are much greater than for length.
Finally, framing the new hull. Frames are spaced to support panels of plywood. Plywood has a finite strength base on the length of the unsupported panel. Exceed the optimum panel length and the ply is too weak to support the local loads, and you get tin-canning or worse, panel failure. Conclusion? Add framing to your new hull at the original frame spacing from the old. Also, note that as you lengthen the boat, you are making it weaker longitudinally. Think of it as a 2x8 plank spanning a ditch: If the plank at six feet long is easily capable of supporting you as you walk across it, will a ten-foot long plank of similar size be as strong over a wider ditch? Not likely. If you increase the length of a low, flat boat by more than 10-15%, you should consider beefing up the scantlings of the primary longitudinal strength members of the boat; namely, the keel/keelson and sheer structures. A ¼” larger depth of the keel and a 1/8” thicker rubrail and inwale will add significant strength to the boat. You really don’t want to be in the boat with you in the stern and Junior & Rin-Tin-Tin in the bow and notice that the hull is contouring the water surface as you motor over the small wind-chop on the bayou.
BTW, your dad built a fine looking bateau. A good example to follow. Good luck!
Thank you for the parable.
12-16-2002, 11:15 AM
Roger, I just finished a Christmas gift using a couple of pecan boards my brother brought back from Houston and the seats in your dad's bateau look to have identical grain. Could this be? You are one fortunate guy to have something as elegant as this bateau, made by your dad, to cherish.
John of Phoenix
12-16-2002, 11:41 AM
Between Roger's story and mmd's tech bulletin, I'm having a great day. I love this place.
12-16-2002, 11:42 AM
Thanks for the look into your life Roger... the boat is a beawdy and yer old man a terrific man no doubt would have been a pleasure meeting him...
mmd youve just answered a few questions Id been wondering over the last few days thanks!
Cecil... Gidday mate! :cool:
Thanks for givin me this opportunity to have me say Roger right neighborly of yer mate! ;)
Take it easy
12-16-2002, 11:44 AM
"Preservation of indigenous small craft..." is something I certainly have in mind. If I can generate some good sheets, I plan to give them to the Center for Traditional Louisiana Boatbuilding at Nicholls State University in Thibodaux, as well the Chitimacha Cultural Department.
The boat has no keel. The plywood bottom is flat and seems to be scarfed 8' from the bow, to relieve the pressures of pouding on the scarf at the point where she curves upward, I assume. Having no keel, then, I guess that negates your comments about the rabbet?
I had intended with the lengthening to add battens as for forward as possible. Would this be advisable?
I do want a proportionate amount more beam and freeboard, as with the ratios you provided.
And thanks for the compliment to dad. smile.gif
12-16-2002, 11:47 AM
Howard, Shane and John, the pleasure is all mine.
Cecil, actually, that's new-cut cypress, which has a wide, long grain as opposed to the antique stuff, which is so much better.
12-16-2002, 12:51 PM
Why hasn't Roger won the Pulitzer yet? Has his paper nominated him? No joke here, I am serious.
12-16-2002, 03:07 PM
*blush* Thanks. No Pullie yet, but consecutive first and second place wins, Louisiana Press Association, Best Regular Column in 1998 and 1999. smile.gif
Thank you, really.
Roger - yes, battens are good. With no keel, measure the bottom profile on centreline. To beef up longitudinal strength, make the chine logs 1/4" taller. Basically, you are creating two I-beams (boat sides) to support a floor panel (boat bottom), so an increase in the volume of the material at the top and bottom of the beam will increase it's load-carrying capability. It is always nice to arrange a bottom scarph so that it lands at a frame or bulkhead, so as to minimize stresses in the joint caused by the panel flexing. Not supposedly necessary, but why not use the "belt & suspenders" approach when the suspenders are so easy to slip on?
Just thinking out of the box here, but couldn't a person achieve greater strength on the bottom by cold molding out of say two layers of 1/4" ply rather rather than worrying about the scarf.
Theoretically, no. Properly done scarphs in plywood with epoxy supposedly possess around 97-98% of the strength of a piece of uncut ply. Butt joints, no matter how tight and what googe, are still end-grain joints that allow discontinuation of stresses in the panel. This means that if the panel is overstressed, the stresses build up at the butt joint and the panel will fail at the seam. Butt jointed panels can be assumed to have about 60-75% of the strength of a continuous panel of similar thickness. Scarph joints have more parallel fibre alignment in the epoxy matrix between panels and are therefore able to transfer stress from one panel to the next more efficiently.
But for most folks the precision joint of a lab test sample is unlikely to occur in their shop, so 85% strength of a scarph joint is more reasonable. When butt joints are sheathed in 'glass, their strength moves up to about the same strength range, so the decision becomes one of labour and cosmetics, rather than strength. The problem with two layers of thinner ply bonded together on the hull during construction is getting a fair curve in the skin at the butt point. I usually look at it from a cosmetics viewpoint - if appearances of the hull is worth the extra manhours to prepare scarphed stock and the client is prepared to pay for that extra level of cosmetics, I'll spec scarphs; if cost is more important than appearance, I'll spec butt seams. Strength is easy, flawless topsides are much tougher. If light weight is optimum, such as for racing dinghies & shells, scarphs win hands-down.
Of course, to eliminate unfairnesses in the topsides panels but still use butt-seam panel construction, one could always butt-laminate sheets of thin ply into the lengths required prior to cutting to shape by vacuum-bagging them together. Hmmm.... ;)
12-16-2002, 07:35 PM
Roger, I've always loved that boat.
Stretch it in the middle by a foot.
Add an extra frame at six inches of that
foot. It shouldn't be a problem with all
the extra support you have as a deck.
I've been in twenty foot flat bottom wooden
trout boats on the White River that aren't
built as well.
12-16-2002, 08:39 PM
Thanks, Roger for sharing with us!!
Along the lines (no pun intended) of stretching lines...
Wasn't it fairly common in wooden lobsterboat construction (and maybe other types of plank over molds construction) to significantly stretch the mold spacing? ie. using the same set of molds for boats that were anywhere from maybe 28 to 35 feet long.
That all said, what do you think would happen if you took the station molds for something like an Ocean Pointer Skiff and stretched it out to 23', 25' or 27' feet with out adding to the beam?
Hello, RCL. I hope you and Roger won't mind my stepping up to the plate to answer your question.
I can't speak for the construction methods used "Down East" in Maine and other New England states, but can speak with some knowledge about the lobsterboats built in Nova Scotia and Prince Edward Island (two very distinct types of boats, I might add). In the simplest response to your question about "Wasn't it fairly common in wooden lobsterboat construction to significantly stretch the mold spacing?", yes, it was, but the builders that did this had tremendous experience with these types of boats and knew pretty much intuitively what the effects of the changes they were making would be. They didn't apply the increase in mould spacing equally over the length of the boat; rather, they kept some moulds fixed and moved others so as to control where on the hull form the extra length was added. If one attempts to make radical changes in the form of a hull without a good understanding of the overall impact of these changes to the hull strength and performance, one can be heading down a path to some terribly expensive and possibly dangerous surprises. Stretching a box-like skiff to go out on the pond is one thing, altering a complex form hull to go out to sea is quite another.
The primary problems with lengthening a hull are 1.) longetidinal strength is reduced if structural scantlings aren't adjusted accordingly, 2.) buoyancy is increased dramatically, although (depending on hull form) not equally distributed over the length of the hull, so adverse trim can occur, 3.) centres of gravity, LCF, LCB, and longitudinal metacentric height - all factors that affect stability and seakeeping - are altered, 4.) wetted surface area is increased, resulting in greater power requirements, and finally, 5.) directional stability is enhanced, which may require resizing of the steering gear to compensate. None of these are insurmountable problems, but if one is unaware of their consequences, one can be rather disappointed with the results of lengthening the hull.
If one arbitrarily re-spaces the building moulds equally, you are significantly altering the shape of the bow. This can have a profound effect on how the boat moves through the water. Where once the bow rose easily to a swell, the stretched waterlines will now slice through the waves, making for a wet ride. Possibly the location of the maximum bow flare was originally located to intercept the catenery of the bow wave and knock it back to the sea surface, but is now further aft, allowing every wave encountered to leave a calling card on deck.
I am not opposed to altering the length of a hull design by stretching the spacing between building moulds. I am, however, very worried that sometimes this is done without full appreciation for the multitude of effects that this will have on the performance and structure of the hull. When you are making such changes to wee boats that you play with out on the pond, where you can easily swim to shore if the unthinkable happens, that is no big deal. It does become a big deal when you are considering altering a boat large enough to take unwitting friends and loved ones out on waters big enough to be unpredictable and dangerous.
Please, if you are considering altering a hull form while building, research to effects of what you are about to do, or consult a naval architect or designer. Don't build what looks good and hope for the best. It can kill you.
12-17-2002, 10:01 AM
Some further details, just for grins and giggles, and since I just love talking about this old girl.
I believe the frames are oak, but they may be cypress. My confusion is a result of 40 years of paint covering them. I know the dash beam is oak, so I would assume the framework is, too.
It's fir plywood, might be marine, but I doubted. Probably exterior. In '62, dad wasn't making much money, and while he used the marine stuff for customers, he might have used exterior for himself to pinch pennies. The bottom and about four inches up the sides has a layer of polyester fiberglass and cloth. As dad also repaired fiberglass boats for extra money, he was quite good at it. It has no cracks or peeling throughout its lifetime. The livewell is also fiberglassed and has never leaked.
There are to runners on the bottom to keep her from sliding. They run completely from the transom to the headblock. With a 15 hp outboard on it, she does still want to slide at moderately high speeds, so it's always best to throttle down in the turns. The transom appears to be laminated from 3/4 ply, with an extension in cypress atop it. She draws about 3-4 inches of water loaded and I can take her just about anywhere. On step, she'll get through 6-8 inches of water as long as I don't slow down.
I grew up in this little boat. I learned a lot of life lessons between those rails. It was the best classroom I've ever known.
By the by, should I be able to generate a good set of sheets for her, I'll be happy to make them available to anyone who's interested. I'm not interested in charging for them at all, I'd just like to see it persevere.
[ 12-17-2002, 11:05 AM: Message edited by: Roger Stouff ]
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