The game is afoot

Discussion in 'Boatbuilding' started by Boston, Apr 20, 2011.

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  1. Boston

    Boston Previous Member

    I've got a set of prints for the Bronco and we've discussed changing the hull from a plank on frame to a cold molded type, the suggestion came up of a strip planked core which seems like a popular technique so I thought I'd try that. Not sure what you mean by poor materials. Black walnut has excellent rot resistance good dimensional stability, bending strength and is generally pretty tough stuff and its reasonably light. Same holds true for Cherry ceder and oak; the original design calls for cedar over white oak so I'm not deviating that far except on the skins. I don't get how you think I'm cheeping out on materials. Those are all pretty high quality woods and I'll be buying all select grade, I just get good prices, its not like just cause it doesn't cost much that I"m buying off the bottom of the barrel.

    Glue is a purely environmental issue, I have it on some pretty good authority that I can probably get 25+ g of epoxy from a local formulator for about 1k or so. and my consideration of the Elmers product or the TB-3 ( in the same family and nearly identical is a lot of ways ) and used in the same way as Guzzwell did in his builds seems perfectly reasonable, it was your suggestion after all. So again I'm a bit baffled about what I'm screwing up

    its just a few mechanics and some dimensional questions to go as far as I can see. I'll keep the weights similar ( engine estimated at something like 450lbs, tanks are pretty well defined on the prints ) and aim a bit strong on the structural and light on the weight, how do you mess that up.

    I asked about the remaining big unknowns, the keel and if I should go with the same material as is used in the skin or if I should stick with the white oak they suggest. That question is based on the skin now being stronger than original ( diagonal planked over strip core vs old school carvel ) engine beds and whatever that kinda stuff we can work out over the next few weeks and be ready to let them into the molds along with the apron bulkheads and whatever else I gotta have once the molds are in the air.

    Maybe its cause I've been building odd ball stuff for so long but I'm just not seeing where I cant start lofting some stations and getting a mold set up. I guess maybe we miscomunicated cause I have a set of prints which define the original boat. We've been discussing hull strength and configuration or at least I have for almost two years. This cold molded or double diagonal thing seems the best way to go. Several folks including yourself if I remember mentioned that it eliminated nearly all interior framing. Perfect, so I draw out the lines and mold up a hull.

    I'll be using an engine of significantly less power than the VB ( again as per suggestion ) and a construction method aimed at getting the same waterline so all in all I may be strong and slow but I cant see a danger of the boat being unsafe unless I develop a bunch of weight up high. Not happening. I'll squeeze everything low every chance I get and aim to keep it balanced

    I just don't get how those materials are inferior, or how Im flying without a net. I'm not sure how you think I'm going to hodge podge anything together, I'm making the final decision as to methodology right now, and its looking like what Rassy Viking and Par all suggested is the way to go, a strip core. Seems pretty easy actually. I can see where a purely cold molded hull is more difficult to keep fair when laying up the veneer's so it seemed like a good idea.

    the homogeneous nature of the double diagonal method seems distinctly similar to the cold molded method and marrying the two has been suggested many times, is that where you think I'm screwing the pooch? I'm way baffled as to how I'm doing something wrong over here. I have prints, I have a methodology, I have a materials selection that is superior in strength, equal or better in rot resistance and no heavier than original, and I'm considering all type 1 glues. What did I do wrong ?
     
  2. Boston

    Boston Previous Member

    are you suggesting that I have to draw up an entirely new set of prints that reflect the changes in hull planking and engine choice?

    Having reread my previous it sounds a bit short and it wasn't intended to but I'm lost as to what I'm doing wrong. I been overthinking every element of my first build for a long time and I'm just not sure what I've missed.

    how is this not a homogeneous design and what am I hodge podgeing together
     
  3. Boston

    Boston Previous Member

    My thinkin on the hull thickness was based on what we discussed over on the diagonal planking thread, something like a 25% reduction in hull thickness allowed by loyds for cold molded and something a bit less but similar for cold molding. So I guesstimated the weight of the frame I'd be loosing and added that to the thickness of the hull and I should end up with a really strong hull that floats on its water line, no. Only thing I was concerned about was matching the stiffness of the hull to the stiffness of the keel, which is one of my outstanding questions.

    only thing I can think of that might have led to your thinking I was butchering anything together is that maybe your opposed to the strip planked core. In which case I'm all ears.

    anyway when you get a chance get back to me cause I am anxious to get started and the space is already rented, so I want to make some hay while the sun is still shining.
     
  4. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    B.....I did not mean to upset you.....only to urge some overall consideration before plunging ahead.......

    Framing......if I mentioned the elimination of framing by using cold-molded skin it was in the context of a full displacement powerboat or a moderate weight sailing cruiser....not a high-speed powerboat.....

    Loading on the hull of a small (<80') high-speed powerboat is different than that imposed on a sailing hull or a displacement powerboat. The major loads are generated by the speed of the hull slamming over and through waves....these are not global loads but point loads limited to a fairly small area of the skin. These point loads might reach 15-18 psi at 25 knots in this little boat....that's over 2000 pounds per square foot........

    Typical skin support in a small powerboat consists of transverse bulkheads supporting stringers to which the skin is attached. The stringers are a reasonable solution because engine beds run fore and aft and thus become the stringers in the middle of the boat.....efficient and continuous structure......stringers can vary in depth to suit the load and they are easy to build fair being nice long pieces.....

    A series of bulkheads with stringers splits the skin into longish narrow panels with the long dimension running fore and aft.....As wood stiffness is dependent on grain direction it's better (stiffer) if the grain direction in the panel runs across (shorter dimension) rather than lengthwise (longer dimension)........as testing shows that an angle of about 45 degrees off centerline is still very stiff, bottom panels can be all +/- 45 degrees and topsides all +/- 45 degrees of vertical (a deep web frame supporting the bottom)....planking is in short lengths except the last one in the topsides can be longitudinal if you are worried about print-through of planking lines.....

    I would suggest perhaps 3 layers of planking, all diagonal......slightly thinner in the topsides than the bottom.....

    So strip planking a high-speed powerboat is not the most efficient use of the wood's properties....but that depends on the framing system......

    My understanding is you are changing from single to twin engines? This changes a great deal as well......So yes, I want to see a new drawing showing the engine beds (stringers) and bulkhead locations so we can see the size of your bottom panels....then the loads, wood species, and thickness required can be engineered to meet those loads.......
     
  5. Boston

    Boston Previous Member

    no worries I was just kinda surprised, not really pissed off or anything. Couldn't figure out what I'd done wrong.

    Those transverse bulk head over stringers are exactly what I'm talking about, but the stringers are acting as engine beds as well. I think I mentioned combining stringers and engine beds in my previous somewhere. The bulkhead placement can be seen in the image on the 2nd post. The engine beds were about to be defined but then I discovered I cant get those engines at that price any more so I'm looking for something new. I had considered using an adapter plate and spacing the beds in the most structurally advantageous place, not sure I mentioned that one yet. My thinking is that the prints show only two beds and no stringers over 7/8 x 1 1/2 frames with floors over. So the plan was to loose the frames and loose the floors but have four engine beds acting as stringers along the bottom.

    As long as I keep the total weight the same and the shape I should end up floating on the lines, after that its just spreading out the weight properly as far as I can see.

    The speed of the original boat was estimated by Hand to be about 20 knots, My prop calculator shows at 29', 20 knots and 4500lbs ( my original estimate of this things weight ) I'd need about 200hp. But I don't really care to be bombing around the PNW. I'd kinda like to just cruise it, with maybe the occasional run from weather. You suggested hull speed and an efficient engine so I thought I'd go with that but use two to keep the weight up to where I needed it in the area I needed it and to give me a little security. Then I ran into the availability issue. Screwed me all up but I'm still thinking no faster than about 15 knots max and a vast majority of the time at hull speed. So again I was thinking the stress on a modern stronger hull was less than the original. Err on the side of caution.

    The original beds run about the middle third of the hull and are 1 7/8 with bearers of 1 1/8 alongside the length of the engine room, I'm thinking this is the area of greatest slamming loads so by using four stringers/beds and tapiring them out the length of the hull I'm actually strengthening this thing, while keeping the area of greatest stress fully supported. Essentially exactly what your suggesting. The widest point of the bottom of this boat is only about 5'6" so four beds spaced evenly gives me 13 3/16 inches max between plus there is the apron ( must be an old term cause I seem to remember this piece being called a false keel or a keelson ) running over a keel. Which is another question I had. 13 3/16 is pretty close and after centers are considered you end up with even less of a span. On a 1 3/16 thick hull. Seemed like it aught to work. I could go with a purely cold molded hull but then I'm building a more complex jig and run into a few other issues. I was actually kinda really liking the idea of having 5/8 of cedar to stable the veneer's into, seemed pretty easy and the extra thickness mite keep my scrawny *** from freezing on a cold Alaskan night.

    Sure you'd have to run a few numbers to divide out the load and come up with an actual section for those stringer/beds but thats just part of the game. The hull thickness I based partly on how easy or hard it is to work a veneer with the tools I have, my planer tends to eat anything less than 3/16 and even then its "dicey". If I use skins any thinner then I gotta either get some new equipment or pay someone to prep my materials, which I've always found to be a big mistake.

    I have a plan and I'm keeping to the shape, weight and weight distribution. I'm dropping 25% off the speed and altering the construction technique to take advantage of modern glues. I'd prefer to use Guzzwell's method but that question is still out there. That and I'm using lighter engines spread out over a larger area. I could "stick" to epoxy under the water line if it keeps everyone happy but since I've enhanced the strength of the structure and lowered the forces being applied, I was thinking Guzzwells approach would be ok, Elmers is not the best brand of wood glue so I mentioned TB-3.

    I can weld up something to fit the engine mounts because the beds are now more like stringers and following the contours of the hull. Shouldn't be an issue, that engine room is something like 5' long and 7' wide.

    Anyway grinding out some numbers is exactly what I'm after. That and matching the flexibility, which I'm thinking is best done with matching materials but that ones still up in the air. I just wasn't thinking that a whole new drawing would be required. I'm pretty much following the plans I have but changing the engineering some.

    Anyway its late but I can scan and post everything I have tomorrow, I gotta get up in a few hours and go earn some boat money.

    cheers
    B

    ps
    I was just baffled as to what you were thinking. If you want to try and close up some of the engineering on it and make it as light as possible then I suppose a full analysis might be in order but that would be kinda trying to fit a square peg into a round hole. This old style design is only ever going to be so efficient, and lightening the boat changes everything, I guess I never even considered making it a tightly engineered structure. I just thought I'd modify a few things to make a dryer stronger hull and keep the power down to something reasonable.

    no worries, lets just figure out those panel loadings and make sure that I'm not going swimming instead of boating.
     
  6. viking north
    Joined: Dec 2010
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    viking north VINLAND

    Boston,You are in overload back away from the big picture, take it in steps. First make a final decision on the construction method of building the hull. My opinion strip plank is the way to go and using epoxy thruout the build. Once you have her planked then go to the next step because from there all options and engineering are open, You will not have to re trace your steps, you have then reached a point in the construction where you have a solid basic hull to work from. Next make a final decision on the drive train. I still think you should reconsider the set up and go with a standard engine - transmission-shaft and prop. I know it requires the expense of a transmission but by the time you experiment with the custom outdrive/flipup unit(which is a prototype experiment that will frustrate the hell out of you with it's bugs and it will have some). The shroud idea as a prop protector by PAR is an excellent one. It acts like a cage but gives the benifits of extra trust and when applied against a rudder thats manourivability plus. You basically have the big picture pretty well planned out now drive the first nail--:) Geo.
     
  7. Boston

    Boston Previous Member

    well I don't really have the intuition to judge the full effects of the verious alterations I"m throwing at this thing. Ya I'm keeping the lines, the weight, the overall dimensions, I'm also re-engineering some stuff I've never engineered before. Ole Tads got a point about if it were a house or a fish tank or some zillion dollar conservatory up in aspen but its not. If the only way he's going to feel comfy with it is to do a drawing and work out the numbers that way then I'm not going to argue with him. I'd go with a more seat of my pants approach but to each his own and I'm not to feeling to inclined to swim ashore and then admit I needed help on something. Who knows, maybe there are other NA's out there who would just rip some numbers out of there buts and give me a nod but thats not who I'm playing with and its called delegating a responsibility and then getting out of the way. I just hope I can afford whatever he's got in mind.

    The only real variables at this point are a true cold mold vs a basterdized one like what you suggested. I kinda liked what you suggested cause what your talking about made a lot of sense and what tools I have can do what your suggesting. Thinner veneer's are way more difficult to re-saw and I'd have to order them out of house which I detest doing. Might as well just pay someone else to build it for me at that point, which isn't happening. I love those plastic staples and they'd work perfectly if I was firing through a 3/16 skin into a 5/8 core, you gotta point on that one, I liked it, didn't go over well apparently with the powers that be. Maybe there's a compromise in there somewhere but he's got a point about the grain orientation. There's a solution, don't know what it is yet but there is one.

    second big variable is those engines, I picked them cause the surplus center listed them ( Yammies ) for a great price and in the end I"m a cheap bastad. Now I'm thinking if I just look hard enough I should be able to find a similar price on a similar engine. Going to take a while tho and so I might be stuck using an adapter plate, which I probably would have ended up using anyway given that engine beds are now stringers which follow the contour of the hull, gotta leg up to a level base for the engines anyway.

    My drive idea I'm pretty darn fond of. I'll do some development on it and see if a test subject runs as planned but its got a lot going for it.

    A
    in a wreck it sacrifices the lower end but saves the hull and the rest of the drive train. I can carry a spare if I really want to.

    B
    I can flip it up clear the prop if I get tangled on anything.

    C
    It allows me to have a no through hull boat, which is about the best insurance policy I can think of, no holes, no leaks

    D
    no transmission so I'm saving weight

    E
    hugely simplified clutch ( pretty much just a tension wheel )

    F
    automatically disengages the prop in the event of a strike, lots of benefit wrapped up in that one

    G
    the whole thing is accessible from under the seating thats going to installed in the pit area, lift up the seat and the entire mechanics of the unit are right there

    its worth exploring
    I'll build a wooden mock up housing and install the guts ( inexpensive guts at that ) and see how it goes. If it doesn't work the way its expected I'll know it pretty quick

    anyway I'm just in from a run and I stink so gotta hit the shower
    cheers and thanks for all the tips and advice
    even if I don't take a suggestion doesn't mean its not appreciated
    the benefit lies in exploring all the options

    cheers
    B
     
  8. viking north
    Joined: Dec 2010
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    viking north VINLAND

    Well no argument with that, between TAD, PAR and a few more of the forum Boat Gurues you certainly can't get far astray-- Reading some of their posts i'm sure these guys could build a Mars rocket. Here, I'm waiting for the dam rain to stop so I can get on with my keel mold.Got a money making project on in the shop over the summer or thats where the boat would be, however it'll be cozy next winter. -- Geo.
     
  9. Boston

    Boston Previous Member

    I've noticed something about land based architects, at least when it comes to what I do. The vast majority of them don't know squat about building anything, I'm betting Tad knows what he's doing and I'm pretty much betting with my life and the lives of my passengers. I've read his articles and I like his designs, he also has always had respectable input. Not that he always agreed with his constituencies but at least it seemed logical to me even if I didn't like the idea. I kinda really really liked your strip plank suggestion cause it instantly clicked about how much easier it would be and more importantly it works with my existing shop tools, except maybe for the plastic nail gun. Not that I mind difficult but this is kinda a practice build and I sorta want it in the water asap. I'm kinda banking on him being intuitive enough to make a few changes with a minimal of drawings needed, but thats not something I can, nor want to micromanage, I'm pretty much stuck either winging it or not and I'm not. Remember ole George McKay I think it was, and his Blind Faith, I have none of that kinda faith. Or those guys who nearly sank several million dollars on the first splash, then ended up welding on some dam huge and but ugly sorta sponsons. I'm feeling pretty determined not to have a thread dedicated to my screwing up on every boating thread that ever existed. Its sorta one of my goals in life :D

    Now that doesn't mean I'm not going to my share of thinking out of the box, I hate being constrained by "what everyone else does" its never been my style, but I have a respect for the ocean bordering on paranoia and not asking for a bit of help on the first build or two would be foolish in the extreme
     
  10. hoytedow
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    hoytedow Carbon Based Life Form

  11. viking north
    Joined: Dec 2010
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    viking north VINLAND

    Boston, i've read and collected articles written by Tad for years and always been impressed both by his knowledge and ability to put it in laymans(boatbuilders) language. He has a past of lobster yacht designs(Novi Hulls) which tells me he reconizes a good seaboat and the ability to design based on it. Downeaster thinking i'm comfortable with it, you're in good hands---Geo.
     
  12. Boston

    Boston Previous Member

    I tend to note pad on here when I'm curious about something and since I'm off a bit early today I'm just curious how my conceptual engineering skills worked out

    ok the original drawings had a max span of about 2'6" between major structural supports (chine to engine bed). So the frames 7/8 x 1 1/2 spanned 2'6" and were spaced every 9" oc and were white oak. the hull planking was 3/4 white cedar. the boat it estimated to be able to do 20 knots. Resistance is a function of speed. not a linear relationship. I'm remembering all the times I've read about a refurbish job that included replacing a slew of broken ribs. My max speed is about 15 knots depending on what motor I put into it but I'm not going over a 55 hp rig nor under a 27 hp rig cause it puts me being able to do somewhere between 11 and 15 knots and I'm leaning towards the 15 knots.

    so dividing the ribs into the spacing I end up with about 15/16 worth of material spanning 2.5 feet on the original hull with an average strength of 4/5ths ceder to 1/5 oak.

    the new plan has the largest span between major structural support at about 1' 1" 3/16 oc. With a hull thickness of 1 3/16 made up of 10/16 cedar 6/16 cherry and 3/16 black walnut. Grain orientation is key so on the diagonal the span is 1.42x the perpendicular span or 18.73 inches span for the diagonal members which make up 6/16 of the thickness of the planking and have an average strength of x ( gotta look that up ).

    OK so

    western red cedar has an impact bending strength limit of 17 inchs at 12% moisture content and a compression perpendicular to grain of 460 lbf/in^ specific grav .32
    yellow cedar is 29 in and 620 lbf/in^ specific grav .44
    white cedar which is called for in the prints 12~13 inchs and 310~410 lbf/in^ specific grav .31
    white oak 37 inchs and 1070lbf/in^
    cherry 29 inchs and 690 lbf/in^
    black walnut 34 inchs and 1010 lbf/in^

    all from http://books.google.com/books?id=mU...page&q=cherry impact bending strength&f=false

    crunch a few numbers later and I get an average strength of

    9.37 + 6.9375 = 16.3 in

    and

    270 + 200.6 = 470.6 lbf/in^

    for a average impact bending of 16.3 inches and a fiber stress at proportional limit of 470.6 lbf/in^

    over a max span of 2.5 ft

    If I consider the double diagonal hull as a unit which it is then I would have to go through a whole set of numbers parrallel to grain so for now I'm going to forget any wood thats not got its grain oriented to cross a structural member. I end up with 3/8 of cherry on the diagonal crossing a major structural component every 18,73 inches C to C.

    3/8 x 29 or 10.875 inches

    and

    3/8 x 690 = 258.75 lbf/in^

    then I'm going to divide the smaller span into the larger span and develop a multiplier by which to compare the two materials at the two various spans

    30/18.73 = 1.6
    so
    1.6 x 10.875 = 17.4 inches (original = 16.3)
    and
    1.6 x 258.75 = 414 lbf/in^ (original = 470 )

    and remember these numbers do not reflect the 5/8 of core material ( WRC ) thats going parallel to the structural members nor does it take into consideration the 3/16 of black walnut in the same orientation.

    If I do consider those materials and I consider the inner diagonal planking as the frame members across major structural components for both core and outer skin material then my average strength of planking in the same orientation as the original is greater than original by a substantial amount which makes up for the previous 12% deficit in fiber stress at proportional limit of the diagonal members as compared to the original hull material.

    so I over engineered it
    which is just fine by me as long as I get the weight and weight distribution the same
    I should float on the lines

    I think

    my version of engineering
    most of which is done on a cocktail napkin

    cheers
    B
     
  13. CatBuilder

    CatBuilder Previous Member

    A little bit off on a tangent, I noticed your epoxy price. $1000 for 25 gallons of no-name is no special deal.

    You can get System Three for about $1500 for 25 gals. Just wanted to give you a quick heads up on that.

    I know you have more than a full plate, but little tidbits like that would have helped me save a few bucks and some time when I first started.

    Hope it helps.
     
  14. Boston

    Boston Previous Member

    If I go with longitudinal hull material strength as compared to the original I get on the original hull

    9.37 inches and 270 lbf/in^

    VS

    10,625 + 6.375 = 17 inches and 297 + 189.375 = 486.375 lbf/in^

    so the longitudinal members only ( just the cedar core and the black walnut skin have almost twice the impact bending and almost twice the fiber strength at proportional limit supported on a diagonal members that have only a bit more impact strength and about 12% less fiber strength at proportional limit

    So in the end Tad has a good point about the orientation not giving me the most bang for the buck so to speak

    course I didn't add up fiber strength parallel to grain yet which will make up a lot for those low numbers at the diagonal members

    I think the easy solution assuming I want to strengthen this thing up some is to change the inner diagonal skin to black walnut which increases the strength of the diagonal members about 15% and adds about 30 lbs or loose the core entirely and increase the three skins to 1/4 each, plan on a lot of steam bending, and only be able to fire staples into areas were the skins cross the forms or I"m going to be blowing out the back no mater what I do. Bagging gets less effective the thicker the skins so thats also a consideration.

    also there is the consideration of a laminate material over a solid one. Lloyds allows for a reduction in hull thickness for laminated hulls and I've increased the thickness so if Lloyds allows for 10% ( estimated low ) for diagonal planking and I added 34% ( for a total of 44% over what Lloyds suggests ) then it seems logical to multiply my hull figures by some relative factor and in the end I should be able to hit a tank with this thing and get away with it.

    the next consideration might be that I'm going slower. A 25% drop in speed means a 50% drop in resistance if I remember the rule to thumb correctly.

    so my hull is way heavier than I need it and I could probably save some money and try and figure out a way to skinny it up some and still get away with using what tools I have to do it.

    again in the end Tads right, My design works but its not ideal, I don't need the core at all, I could just use thicker skins and stick with a double diagonal planked hull.

    hmmm
    and build a more complex jig
    well
    plywood is cheaper than boat and I don't have to haul it around with me

    now I gotta go figure it all out again minus the core, but I'll spare you guys on that one

    ok we now return you to your normally scheduled programing

    cheers
    B

    so the weights work out this way
    958 lb the original white cedar hull ( planking only ) before take up.
    1,416 lb if 3/116 black walnut 3/16 cherry 5/8 red cedar 3/16 cherry the strip plank core idea
    1,250 lb if 3 layers of 1/4 black walnut which has bomb rot resistance and really high strength, way stronger than the original or the strip plank version
    1,146 lb if 1/4 black walnut 1/4 cherry 1/4 cherry also ends up significantly stronger than the original and about as strong as the strip planked version

    now to try and figure out what the stringer/beds size ought to be for this thing according to ole Skene a boat with a 9" frame spacing and 3/4 planking should have a stringer with a cross section of 4sq/in. The original Bronco has no stringer and the floors seem to follow the width of the engine beds which is undefined, the original chine is one inner of 1 1/8 x 4 and an outer of 1 3/8 x 1 3/4. I'm thinking that outer chine is little more than a buggy bumper which leaves the section of the inner one right about what a stringer should be in the same sized round bilge boat.

    I'm going to take a guess at the original engine bed size by scaling of at its thickest location, ends up looking like its a 13.5 inch section made up of two pieces one called a bed and the other called bearer. I'm thinking I'm going with 14/4 which = 3.5 call it 4 and I end up four stringers of 4 inches in section spread out evenly or on 13" 3/16 centers and I'll keep the chine at the ~4 inch section it has. this thing calls for Georgia pine and since I hate pine in all of its detestable forms I'm going to change that to something a bit more conducive to craftsmanship.

    Georgia pine specific gravity = .59 impact bending 34 inches and fiber strength at proportional limit of 960 lbf/in^

    so If I replace that with black walnut as well I end up with a specific gravity of .55 impact bending 34 inches and 1010 lbf/in^ which gives me a stronger lighter more rot resistive member and I'm going to spend a little of that savings in carrying these four stringers out along the length of the hull and tapir them as they get to the extremes. I'll divide out the span/cubic inch to get the tapir and go no less than say 2.25 inch section. calculate the weight of that and figure out if I'm blowing the budget or not.

    I've got four bulkheads which all weigh the same as the originals but are stronger being out of marine ply instead of mahogany staving

    I've lost all the fillers and floors as well as all the frames and replaced them with these four stringers. The frames alone weigh in at 298 lbs the floors I'm estimating at 75 and the fillers at 20 for a total of about 400 lbs, my stringers weigh in at about 96 lbs so I could spend a little of my weight savings on increasing the dimensions of these stringers or I could consider the weight I'm spending on the hull and keep the stringers at there present average sections of 3.5 inches. I'd be making up for the 200 or so extra pounds my planking method cost me and call it good on the weight budget so far.

    interesting that way that worked out, I've got a diagonal planked hull of black walnut over stringer's/beds of the same sectional area but arranged to span a shorter length, and it weighs the same as the original hull before take up.

    keel would be next on the hit parade and since I"m on a role I might as well do that out of black walnut to. I'd be using a wood that weighs in at 34.5 lbs a cubic ft vs a wood that weighs in at 42.5 lbs a cubic ft ( white oak ) so how many cubic ft in the keel, hard to say, average section of 16.25 inches. including stem over a distance of 34' or 3.83 cubic feet of material. So I'd be saving 30.7 lbs and keep the same expansion and contraction as the other major structural components.

    apron is originally Georgia pine so thats a no brainer, its outa here. 2 1/8 x 5 over the length of the hull =

    ok saved by the bell I gotta go, to anyone fool enough to actually read this rambling have a great night

    and PS
    I was wrong and Ole Tad was right, there's a better way to do this than just whats easy to build.
     

  15. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    Okay, here are bulkheads of 5/8" ply spaced 33".......The bottom stringers will be juggled to suite chosen engines........

    So loft the whole boat, then draw the big side of these new bulkheads in, reduce for planking thickness and cut out the bulkheads, set them up (upside down on a strongback).......laminate in the apron, chine log, and clamp....then we'll run in the stringers and start planking.......

    Bronchoconst.jpg
     
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