Stitch & Glue flat panel design TO 3D Cad?

[Windbag]

Hello! I've been searching around this and other forums looking for a way to take a stitch & glue flat panel layout outline and turn it into a 3d drawing (I'm most familiar with AutoCad). MOST people ask the question how to go from a hull design to S & G panels for cutting plywood, but I have some purchased plans for a 30' trawler - these plans only have the layouts for the bottom and side panels for the stitch & glue hull, plus the frames (CAD files of finished boat hull not supplied)...and I'd like to mess around with the cabin layout in CAD before starting the actual build. So in CAD I'd like to see what the hull shape look like if I "stitch" the panels together in CAD and then expand the "pouch" surfaces around the frames. I did try starting with a 3d frame layout and tried "wrapping" some polylines around the frame line to see if I could come up with a similar flat panel shape...but that was coming up with a different result for the hull shape vs panel shape. Is there a software package out there that can generate a 3D CAD result of what happens when we stitch known panel shapes together and then expand those surfaces over the frame dimensions? I'm wondering easier to just build a scale model of the hull and play with the cabin layout in a physical model?

 

[Tops]

If you have the frames drawn and located in space, it might be as simple as lofting one to the next.
I have done this in AutoCAD Inventor and Fusion, and something similar in Rhino3D. I would imagine other software can do this too.
I am not aware of something that will 'reroll' an 'unrolled' developed panel. Perhaps others in the know can reply.

 

[Windbag]

Thanks for the reply! So far I haven't found any software that will "roll" a flat panel along a "stitched" edge...If you want to laugh, have ChatGPT give it a try.

Yes, I suspect I can get sort of close in CAD by lofting some intermediate frames, but we were just doing some experiments in the shop with just the bow section and some scrap plywood sawn to shape and stitched - even between 1/2" marine ply vs 12mm okume you get a little different hull shape in between frames depending on how the first layer hull skin material wants to take to the frame shape (or not). Probably best idea is to not lean on CAD too much and just build the hull, then make any adjustments to cabin bulkheads as "build to fit" especially in places in between station mold frames where there is more curve going on. On the flatter sections the hull matches up to my frame CAD drawing pretty close using any hull material - as you'd expect.

 

[Tops]

Your boat has multiple layers of 1/2 (12mm) ply as skin? Sounds like a substantial vessel and that you're going to get a workout molding it.

If you paid for the plans and the designer is still available, it might be worth a consult to make sure that something else would not be adversely affected by the proposed modifications. They get testy if you move the bulkheads under the mast, etc...

Making a scale model might be good, if not just good fun. All the best with the project!

 

[Windbag]

Oh - not multiple layers of 12mm... Just first layer is 12mm, the other layers are 6mm. You want the first layer to set the shape of the hull and normally all the rest of the cold mold veneer / ply layers should be much thinner than the first layer. This is a Devlin Black Crown power trawler.

Black Crown 30 Plans https://devlinboat.com/product/black-crown-30-plans/

We're making some modifications with designer's blessing to add an integrated swimstep / outboard motor bracket as well. The inboard diesel this was originally designed for is kind of not practical these days now that we have to meet US EPA Tier III requirements. Tier III engines are crazy expensive, these will be high rpm with turbo, intercooler and common rail injection. A Volvo Penta 225Hp with stern drive and controls is coming in at around $65k USD (to start) with controls and commissioning cost, so this boat is going to get a 200hp gas outboard + 15hp kicker. The down side is the space we save going to an outboard means we have to add 30% more fuel tankage. She'll be traveling between Puget Sound and Alaska so we'll need decent fuel range. Gas is available at fuel stops, but not ALL the fuel stops along the inside passage, so you have to plan ahead. Diesel is easier to come by, but gasoline is becoming more available as people switch out diesels for gas outboards.

Haven't decided to build her yet but we're just doing some serious study and planning. Just playing around with some sample frames around the bow and doing some testing to see how the hull takes shape.

 

[wet feet]

I'm a bit baffled by a few things here.To begin with,you could buy a more or less equivalent Yanmar diesel for a lot less money and come out way ahead on operating costs vis-a vis an outboard,particularly with the distances you propose to run the boat.Yanmar 4LV250 Marine Diesel Engine 250 HP https://rapidoengine.com/products/Yanmar-4LV250-Marine-Diesel-Engine-250-HP.html .Yes I do realise that no sterndrive is included but I don't know of any experienced users who would take a sterndrive over shafts,or you could probably have an adaptor plate custom made and still come out ahead.

As for playing around with cabin layout,why not simply build a scale model,say 1/12th scale from doorskin or thin aircraft plywood?While juggling with potential layouts do keep in mind that your considerably increased fuel capacity will need to be centred around the LCB so that some semblance of trim is maintained as the tanks-frequently-drain.If you do arrive at a more suitable layout it isn't difficult to take patterns from a model and use the scaling features of a CAD package to convert to a full size version.

 

[montero]

I'm a bit baffled by a few things here.To begin with,you could buy a more or less equivalent Yanmar diesel for a lot less money and come out way ahead on operating costs vis-a vis an outboard,particularly with the distances you propose to run the boat.Yanmar 4LV250 Marine Diesel Engine 250 HP https://rapidoengine.com/products/Yanmar-4LV250-Marine-Diesel-Engine-250-HP.html .Yes I do realise that no sterndrive is included but I don't know of any experienced users who would take a sterndrive over shafts,or you could probably have an adaptor plate custom made and still come out ahead.

Heavy , for a 4-cylinder car engine.

 

[gonzo]

Stitch and glue has an undefined shape until you add the bulkheads and other structural members. The shape can be modified depending on where those interior members go. I mean, that no program will be able to give you the finished shape just by joining the edges of the panels. You can loft the lines from the bulkheads, etc. I assume those are provided by the designer.

 

[Windbag]

I'm a bit baffled by a few things here.To begin with,you could buy a more or less equivalent Yanmar diesel for a lot less money and come out way ahead on operating costs vis-a vis an outboard,particularly with the distances you propose to run the boat.Yanmar 4LV250 Marine Diesel Engine 250 HP https://rapidoengine.com/products/Yanmar-4LV250-Marine-Diesel-Engine-250-HP.html .Yes I do realise that no sterndrive is included but I don't know of any experienced users who would take a sterndrive over shafts,or you could probably have an adaptor plate custom made and still come out ahead.

Try ordering an engine from Rapido and see if it ever arrives. I checked with our Credit Card company last fall and they won't even process any payment to that outfit, nor will the bank wire any funds to that account. Any new US Tier III diesel that's going to be USCG documented (since 2018 for recreational) generally has to get setup & commissioned by a dealer, and the engine won't be supplied be some website with a fake or no physical address. There are dozens of those websites...the clue is if you see a new engine listed with a price, it's probably a scam. That engine you're looking at is more like $47k plus more for stern drive / straight shaft output w/ gears, prop/s, controls, commissioning, dealer fees, etc.

Can you get a used Tier III diesel? Sure. Will it be any cheaper? Maybe, maybe not in the long run. "Hurricane damaged" engines from Florida are fun....That's a code phrase for "engine submerged".

Any Tier III will typically run at higher rpm, will have common fuel rail / turbo / inetrcooler. Their expected lifetime is much lower than the really good older, slower RPM diesels. No, you can't just use an old truck or tractor engine (and marine heat exchanger) like the old days. I know, I've done a boat or two like that back in the day. I've got a stack of current marine diesel quotes from Yanmar / Volvo / Merc / John Deere / Cummins / Steyr / Iveco / Cat / Cox outboard / Oxe outboard. I feel like I have a handle on current Tier III marine diesel engine prices whether it be sterndrive, v-drive, IPS, straight shaft, diesel outboard (diesel outboards are at the extreme). Yes, cheapest option for diesel would be a 80 or 110hp Yanmar that would be a good fit for a full displacement trawler straight shaft setup (like a DIY strip-planked Robert's 29' TY, mid 30' Coaster series or similar) - maybe around $30k with engine, gears, controls, shaft, prop and $1200 commissioning fee. We also have to look at what service is available along inside passage - From that angle best options are Deere / Cummins / Cat especially if you have a legacy 2000 RPM engine in an older boat. Yanmar you can get parts for along the way, maybe...depending on what's in stock. Or you might be waiting several days at the boatyard waiting for something to get flown in. THE OTHER THING TO NOTE is all Tier III engines will require a shop to have whatever proprietary software to access the engine's control computer to register any repair or changes to tuning setup (same goes for newer outboards as well). Now your repair shop choices are more limited along the way. Diesel engines last longer but I can easily replace an outboard many times over for less money. Right now diesel costs a little less than gas, I know. There is no 100% correct answer. Would I rather have diesel? Sure. But the resell value of the boat has to still be something to consider. If you build a boat sometimes you're lucky to get half your money back at resell time, but we do it for fun anyway.

RE: Just making a physical model instead of CAD way of visualizing the real hull to plan changes: Turns out that's really the fastest simplest way. In a few hours with some posterboard, scraps of balsa and tape I've setup a basic model of the boat. 1/10th scale, so about 36" long. You really get a much better sense of the boat that way, much more than anything on paper or CAD. If I wanted to I could create a regular table of offsets from that, and generate a fairly accurate 3D CAD drawing. BUT we looked at the boat for a while and decided to cancel the project...too long and skinny especially if we add on extra length for outboards. Yes, it's a trailerable boat which is sort of what we're after but we're already setup with the means to tow up to 11' wide and 22klbs, so we'll probably look at building a boat with more beam, and just use regular cold molded technique. I think stitch & glue has it's place, but for us as the boat gets bigger other methods work better for us.

Thanks all for the advice!! - Yes just making a physical model is the way to go if you want quick results, at least for me.

 

[wet feet]

Nice to know the (very) traditional technique of creating a 3D model still has practical applications.Living in a land of $7/gallon fuel I find it hard to imagine any kind of economic case for an outboard,but then I don't have any obligation to register a boat either.

I have no affiliation with any brand of diesel but do recall a conversation I had with a long time boatbuilder a few years ago and who told me that his brother had just bought a new Toyota Land Cruiser.When the engine was revealed he said immediately that it was a Yanmar,which may have reversed the chicken and egg situation.Given the published tables of automotive reliability I can understand why the choice was made.As with so many other pieces of hardware,if you can find the version that doesn't come in a pack that has a picture of a boat on it,the price may be less painful to contemplate.The software lockout does create an effective cartel to protect the dealerships and it is rather too widespread and definitely not in the public interest.There may be somewhat legitimate ways to circumvent the system,but I wouldn't know about them.

 

[Windbag]

Ooops - I just run across this thread from 11 years ago on this same forum:
2d pattern to 3d hull https://www.boatdesign.net/threads/2d-pattern-to-3d-hull.51356/

Looks like nothing has changed - rolling a flat stitch and glue panel shape onto a framework skeleton isn't always super easy in CAD, even a decade later. At least for me: some paper, wood scraps and tape got to a quick visible result the easy way.

I know the designers don't like to put the lines plans on their Stitch & Glue construction plans, but building a model can lead you to regular lines plans and table of offsets. Then you could build the hull in any reasonable method, and relatively easy to draw up in CAD or on the lofting table.

Building the model for this boat also exposes something else about Stitch & Glue construction on a longer boat: For first layer, handling four scarfed sheets of plywood (about 32' long, 1/2" thick) between him and her would get a little challenging especially for the missus. It can certainly be done with some planning and setup, but we've done cold molding ply / veneer over longitudinal strips on a 29 footer and it wasn't very hard at all. The only thing that was full boat length and floppy were the initial cedar tongue and groove strips we used on initial layer over the mold frames - but it went pretty quick if you just let the strips run long and trim the ends and sheer to dimension after all the strips glued up. Some strips near the center keel had to get trimmed up to fit but no big deal. We tried scarfing the strips on the boat and that worked too, but we found it went faster is we scarfed a pile of strips and then stacked several in an edge-jig for epoxy coating the edges. As per Gougeon book - worked great.

 

[montero]

I've read about these diesel problems. How they achieved certifications EPA Tier 3 for these small diesels ?
https://www.yanmar.com/marine/products/engines/ym-series/
Its not possible to make 50-100hp-200hp fully mechanical engines EPA Tier 3 ?

 

[montero]

Maybe for safety reasons, at least for sailors, these standards should be changed. The owner of a larger boat does not have a reliable drive.
What if the fuel is of poorer quality or becomes contaminated with salt water. All these new wamby-pamby diesels are not so reliable .

 

[gonzo]

Maybe for safety reasons, at least for sailors, these standards should be changed. The owner of a larger boat does not have a reliable drive.
What if the fuel is of poorer quality or becomes contaminated with salt water. All these new wamby-pamby diesels are not so reliable .

Modern diesels run for many more hours than the ancient ones. They need to be maintained properly. As far as contaminated fuel, there are filtration systems that take care of it.

 

[montero]

Modern diesels run for many more hours than the ancient ones. They need to be maintained properly. As far as contaminated fuel, there are filtration systems that take care of it.

Which one do you choose for ocean going boat :
https://www.yanmar.com/marine/product/engines/4lv230/
or
https://www.yanmar.com/marine/product/engines/4lha-stp/
and why ?