Hull design for plywood boat...

[gc9773]

I need help... And not the kind one finds with therapy...

I have a very simple design for a plywood boat build. I've purchased epoxy, fiberglass, plywood, what have you. But what I cannot understand is the hull design portion. I've download "Hulls" and toyed with it, "FreeShip", and "Delftship", and yes, I am computer literate. I've coded in "C" and "Perl", administered UNIX and Windows machines, what have you. But for some reason, I cannot understand how to use these applications. I've purchased plans for various designs, but this somewhat defeats the purpose of what I am doing.

The design is for a 3 chine hull, 15.5 feet long, 4 foot beam, 30" transom. Hull depth of 23" aft of the 8 foot mark from the bow, 30" forward of that, I know, it's weird, but this is an experiment for what I do on a local reservoir. Maybe 5 frames total, including the transom.

So basically, I need to cut (3) strips of plywood to make each side of the hull. I've considered just starting by cutting the uppermost portion and seeing how I could fit the other parts, but this does not seem like the proper way to go.

Is anyone here an expert or at least seasoned user of "Hulls" or similar and can point me in the right direction. At a minimum, I would just like to get the design in the software and loft as appropriate.

Thank you!

Garry

[Clinton B Chase]

Re: Hull design for plywood boat...

Garry,

If I understand correctly, you desire to design your own boat? You have an actual 3D surfaced model of the boat? The software should have a feature that allows you to "unroll" 3D surfaces to produce 2D geometry which can then me used to cut actual wood. You need to learn about that feature. Make sense?

If you do not have a 3D model, then you need to learn how to do that by lofting the lines 2D then creating 3D surfaces from those curves. THat is beyond the scope of any thread on this Forum.

The WoodenBoat School has a class in computer design using Rhino which teaches this process. The class is full for this summer, but something to consider in the future.

~clint CHase

[John Meachen]

Re: Hull design for plywood boat...

Freeship should do it easily.Have you discovered the "add crease" function to create chines?This plus using the smallest possible number of control points across the hull should get you something to work from.the test for developable surfaces can come later.

[gc9773]

Re: Hull design for plywood boat...

Garry,

If I understand correctly, you desire to design your own boat? You have an actual 3D surfaced model of the boat? The software should have a feature that allows you to "unroll" 3D surfaces to produce 2D geometry which can then me used to cut actual wood. You need to learn about that feature. Make sense?

If you do not have a 3D model, then you need to learn how to do that by lofting the lines 2D then creating 3D surfaces from those curves. THat is beyond the scope of any thread on this Forum.

The WoodenBoat School has a class in computer design using Rhino which teaches this process. The class is full for this summer, but something to consider in the future.

~clint CHase

Thank you for your reply!

"Designing my own boat" is a bit of a stretch, in reality, it's just the sum of many designs I have found or purchased. I have a 3D surface model, the only problem, it's in my mind... I've been working out the particulars for some time now. Understand about the "unroll" feature.

What I find most interesting is "plywood boat building" and boat building in general has been with us for some time, likely recorded history for the latter, sans the ability to model an idea on a computer, hell, the Titanic was built without the benefit of any of these software packages, and modeling hull designs was done in a small tank with a prototype miniature... I remember a quote, cannot cite the source, but basically, a boat is, "just a box in the water with a pointed end", so I'm trying not to "nuke this"!

I'll sign up for the class for the summer after this one, alternatively, I'll look around and see who else teaches this stuff.

The journey continues...

Garry

[gc9773]

Re: Hull design for plywood boat...

Freeship should do it easily.Have you discovered the "add crease" function to create chines?This plus using the smallest possible number of control points across the hull should get you something to work from.the test for developable surfaces can come later.

I'll take another look at Freeship. Much of the software is non-intuitive for me, I'm like a blind man in a room...

[Peerie Maa]

Re: Hull design for plywood boat...

The lines of this model were faired and the plank expansions generated in Freeship.

http://forum.woodenboat.com/showthread.php?149296-Building-a-coble-model

This smaller six strake coble was designed in Freeship, then the lines and plank expansions were transferred to a simple 2D cad to allow patterns to be created for the structural members, and the planks nested on ply sheets.
Bow quarter (2).jpg
6 strake coble GA.jpg
6 strake developments.jpg

[sp_clark]

Re: Hull design for plywood boat...

Maybe you can start with something less 'custom', something that has a less esoteric shape? Maybe print that out - at reduced scale - then make a paper model, see if that helps you grasp what so far has eluded your understanding?

Out of curiosity what is it you want to do on a reservoir with this custom hull design that can't be done with something more 'traditional'? 15+ feet means you'll have to do some scarfing to get ply panels sufficient in length.

[Peerie Maa]

Re: Hull design for plywood boat...

I'll take another look at Freeship. Much of the software is non-intuitive for me, I'm like a blind man in a room...

I started with a rough sketch on graph paper, then created the input files in Excel using offsetts from the sketch, that gave enough to allow the fairing process to begin. Freeship allows the strakes to be checked to ensure that they are developable using one of the shading facilities. As you are going for plywood, work with the chines option, and don't worry too much about the sections.

[gc9773]

Re: Hull design for plywood boat...

I had a square stern canoe, an Old Town Discovery Sport 15, which I would drag out to Elephant Butte Reservoir and putter around in, along with my dog... It is therapeutic for me, being from the coast, spending 20 years in the Navy, and now living in the desert, to suggest I miss the water would be an understatement...

I can actually now afford to buy a fairly nice boat, but that would take away from what I am trying to accomplish here. Additionally, I've been interested in sailing and the idea of building a boat.

Several issues with the canoe:

- Stability. The Discovery Sport 15 was fairly stable, but conditions can whip up fast on the lake, which has a fair amount of fetch. The winds pick up in the afternoon and I was actually stranded on one occasion on a lake just down the road, Caballo Lake. I had a marine radio, but apparently nobody monitors 16, that along with the fact that cell service was unavailable, I had to use a small VHF transceiver (Ham radio) and have another operator telephone my location to my wife from a repeater in Albuquerque.

I gave them EXACT coordinates and they still had trouble finding me, an aerial flare positively effected my recovery. I actually had installed a bilge pump in the canoe which kept me from swamping as I was taking on quite a bit of water prior to throwing in the towel and landing! Wave heights were maybe 1 to 2 feet, but the period was what was really the problem, which was very short.

- The Discovery Sport 15 has a polyethylene hull and began to "oil can", I trailered it with a Trailex SUT-220, which probably did not help, I ended up giving the boat to a friend.

- I suppose I could have added a sail, but that coupled with some of the other issues might not have been prudent.

I've watched quite a few videos on the "Stitch and Glue" method, and it looks relatively straight forward. I should not need to scarf (I actually purchased the tool) as I intend to use butt blocks for joint strength

So here is the experiment, given the conditions which I can encounter, as well as a desire to try sailing, not to mention, some fishing, I figured a custom design might get me to where I need to be. I already have much of the running gear, anchor, safety kit, trailer, outboard, etc. I upgraded the trailer to 250 lbs, and I suspect it can take more, but I don't wish to "push the envelope", so the boat cannot be too heavy.

The Discovery Sport 15 had a length of 15' 4", beam of 40", hull depth of 15" increasing to 23" at the bow.

My idea, build a plywood, 3 chine boat of 15' 6 LOA, beam of 48", 30" transom, hull depth of 23" (I have a long shaft Suzuki DF 2.5 with low hours), and a hull depth of 30" forward. Additionally, the aft portion would be covered 1' 6" forward to the cockpit with a bulkhead, a cockpit size of 6', and then covered the remaining 8' to the bow. Additionally, the possibility of coaming on the forward part of the cockpit.

Construction would be monocoque save for the frames, (5) including the transom. Basically, my Discovery Sport 15 on steroids. Additionally, Duckworks sells an 89 square foot sail for the Oz Goose Racer. I've run the numbers, and while with the weight of the boat, myself, outboard, and other gear, I won't be going anywhere fast, I will likely have fun!

I intend to use a leeboard on the starboard side vice a centerboard or similar. And I am only using one leeboard, as for a boat that size, I probably would not notice much of a difference.

I suppose this is a "challenge" for me, the mountain is there, I would like to climb it, maybe learn a few things, but most importantly, enjoy myself!

Garry

[Autonomous]

Re: Hull design for plywood boat...

gc9773, consider the following counsel that has proven itself many times. It is not at all original, it is time-tested.

Do a statement of requirements (SOR) to determine what boat style will best fit your needs. Be brutally honest. Do not look back and put bandages on an inappropriate design.
Buy plans from a well-regarded designer that are engineered for modern materials and techniques. While you build and sail a proven design you can learn boat design with better insight.

Duckworks Supply and Wooden Boat magazine have amazing catalogs of designs to peruse.
Do Not make the mistake of trying to pinch pennies on plans. Been there, done that. Learn from my mistake.

Boat Plans & Kits | WoodenBoat Magazine
Plans & Kits - Page 1 - Duckworks Boat Builders Supply

[Scary Borg Craft]

Re: Hull design for plywood boat...

I did not find Freeship or Delft easy to grasp. Hulls will do what you want, but you must know, like the other programmes, what you are putting in. This sounds close to what you want, if a bit more beam; when you cut away the hull at the waterline for another panel, you reduce stability, so a bit more beam is helpful. Simple boat like this can be done with pencil and paper, a scale cardboard model will give you a close enough idea of the panel shapes.

Ladybug Plans PDF - Duckworks Boat Builders Supply

There does not seem to be plans for Family Skiff anymore, but that was the best camping dinghy i have owned, lots of storage, lots of bouyancy, good seating that can be slept on, and respectable performance under sail, for 15ft.



You sat "in" the boat, not on it. Recommended.

[Peerie Maa]

Re: Hull design for plywood boat...

gc9773, consider the following counsel that has proven itself many times. It is not at all original, it is time-tested.

Do a statement of requirements (SOR) to determine what boat style will best fit your needs. Be brutally honest. Do not look back and put bandages on an inappropriate design.
Buy plans from a well-regarded designer that are engineered for modern materials and techniques. While you build and sail a proven design you can learn boat design with better insight.

Duckworks Supply and Wooden Boat magazine have amazing catalogs of designs to peruse.
Do Not make the mistake of trying to pinch pennies on plans. Been there, done that. Learn from my mistake.

Boat Plans & Kits | WoodenBoat Magazine
Plans & Kits - Page 1 - Duckworks Boat Builders Supply

This ^.
If you do want to design your own, do the research amongst designs that meet your needs and then create one with the same overall dimensions and form, including similar section areas and water plane shape/fullness.

[gc9773]

Re: Hull design for plywood boat...

This ^.
If you do want to design your own, do the research amongst designs that meet your needs and then create one with the same overall dimensions and form, including similar section areas and water plane shape/fullness.

This is the route I am going... I've spent more money on plans than I care to think about, plus, books, books, books... I have 3 gigabytes of info on boats, boat design, sail design, sail types, what have you, on a network server here at my home.

The CLOSEST design I could find which most likely meets my needs is the "Otter" (Boat Builder Central) or Dobler "Lissa" (very similar design), I purchased both. The "Otter" appears a very simple build. Interestingly enough, a fellow out of San Diego, Don Barthel, supplied me with plans for a design he put together which is EXTREMELY simple, yet works!

The first set of plans I purchased were for the Glen L "Minuet". After careful study and research, I quickly discovered this was going to be much more difficult than I imagined... It's too bad steel were not lighter, I have Hobart MIG welding equipment, plasma cutters, etc and am much more confident with this material!

[Autonomous]

Re: Hull design for plywood boat...

If you want to keep the same trailer something along the lines of Jim Michalak's Mayfly 14 or Woobo might fit your needs too.

Notes on propulsion.
I like the balanced lug; it is simple and effective with lots of tutorials online.
A 2 hp outboard is more than enough for these easily driven hulls. E.g., my 17' sail-n-oar loaded to 1,000 pounds uses less than 1/2 throttle with it's 2.5 hp outboard.

[gc9773]

Re: Hull design for plywood boat...

If you want to keep the same trailer something along the lines of Jim Michalak's Mayfly 14 or Woobo might fit your needs too.

Notes on propulsion.
I like the balanced lug; it is simple and effective with lots of tutorials online.
A 2 hp outboard is more than enough for these easily driven hulls. E.g., my 17' sail-n-oar loaded to 1,000 pounds uses less than 1/2 throttle with it's 2.5 hp outboard.

I agree, although not experienced with sailing, much of the research I have done suggests the balanced lug is the way to go, and that little Suzuki DF 2.5 should be more than enough for auxiliary, or even need be, primary.

I love the Trailex SUT-220 trailer! And yes, I had wished to keep it and find a boat which would work well with it. I was trying to avoid too much of a flat bottom boat as I don't enjoy the pounding. The Discover Sport 15, while a great deal of fun, was flat bottomed and pounded considerably in even mild wave heights...