sailing dinghy questions

Hello everyone,

A friend of mine and I have been discussing a small sailing dinghy project, and we have a few questions to pitch toward the knowledge base here

For starters, what would be the minimum boat size that could be a 'safe' 3-man boat in a pinch? Maybe 10 feet with a 4.5 or 5 foot beam? We've been looking at some of the Glen-L boat designs for ideas, but a big part of the project would be that it is our own design. Foolish? maybe...

Thanks,
Ryan

 

Safe is a relative term, depending on the venue and expected conditions.

You CAN fit three people in 10,', but I wouldn't. Since the plan is already over 8', you are going to be scarfing plywood to make large enough panels, and if you are scarfing, why not make a dinghy big enough to be comfortable and safe?

Your boat building experience level is a topic worth discussing as well. A great boat builder can do a lot more with a lot less effort than a beginner, so choosing the design and build method is really important and depends on experience.

I would not want to sail a dinghy with three people under 14' long. Otherwise tacking and gybing gets to be really crowded and dangerous.

Performance is the real question - and what is acceptable? You can make a wide boat to carry lots of load, but it will be dog slow.

Tell us more about where you are going to be using the boat, the conditions and what expectations you have - we will be able to help a lot more.

--
Bill

 

Thanks for the reply Bistros.

Our size is limited by material (3-4 4x8 sheets of ply max) and the ability to carry in the back of a pickup (albeit with overhang out the back). The vast majority of the time she'll be a single or two man boat, but it would be nice to be able to carry three at times.

Our sailing area is a small lake, and blue-water conditions are not on the agenda. We're not building a regatta boat, but it would be nice to have a boat that didn't need 20knots of wind just to move, either.

Regarding experience, both of us have moderate sailing experience and are familiar with wordworking in general, but we are rash newbies at boat building The current plan is standard stitch-and-glue ply hull, with hardware and other items creatively scrounged.

Basically our expectations/requirements are 1) to have a boat that is mobile in mild lake conditions, 2) can be carried and launched from a pickup bed by two, 3) can carry three, and most importantly, 4) can be built under a strict budget.

Thanks again,
Ryan

 

Considering you don't see why it's unreasonable to have a 8 to 10' boat and a three person crew, strongly suggests you don't have the necessary grasp of the principles, concepts and fundamentals of yacht design, sufficiently enough to consider self designing. I may be wrong and I'm not trying to offend. In that vain, where do you estimate the maximum beam will be on your little design? The target Cp? Preferred hull form? How about your method for calculating sail area?

Or you could get a set of Glen-L (or other) plans and have fun. Consider 14' as a staring point for a three man boat. Smaller craft just don't have the internal volume to recommend them well for this load. Have a look at the Glen-L 12 for a minimum 3 man boat. It will be quite crowded, but possible. Personally, I'd rather build a more modern design so you can incorporate taped seam construction which is easy for a lot of folks, especially builders with a little experience. Unfortunately, Glen-L doesn't have many taped seam designs (the vast majority of their designs are quite old) and no sail boats in the size range you need.

14' will be a much better "fit" for a 3 man crew, with plenty of room for Fidel the wonder dog and a cooler full of beer too.

 

PAR-

I know I may be wrong in thinking that a three-man boat is a reality given our limitations, but I'm basing my ideas on my Catalina Capri 14.2 that I've comfortably sailed with 4 on board. Unfortunately the Catalina is in upstate NY and in need of TLC (new sails + glass work) at the moment, and I'm in college in Arizona on a limited budget.

At this point design is purely TLAR (that looks about right). I do plan to make a small model of it to make patterns from, and I might make it radio control (another hobby of mine) to determine trim and balance in a rough fashion.

What is taped seam construction? Is it basically stitch and glue without stitching?

Thanks for the input as always,
Ryan

 

Stitch and glue is taped seam (so to speak), but taped seam isn't stitch and glue. A stitch and glue boat needs no chine logs or keelson since the glue (usu. epoxy) can be thickened and coved into the inside "corners" essentially replacing the longitudinal joining pieces mentioned.
Taping the seams adds some strength, but its principal use is to waterproof as plywood screwed to chines is structurally adaquate.
Stitch and glue is glassed inside and out but taped seam isn't as a rule. Usually only the outside is taped with taped seam since the chine logs and other longitudinals get in the way.
As with any methods, there are variations combining several methods, such as a seperate stem both screwed between the bows and taped inside and outside for strength.

 

Taped seams are as the name suggests and the seams are taped (over fillets on inside corners). Stitch and glue is the same thing as taped seam except it has the seams held with stitches of various sorts of things (wire, cable ties, etc.).

In both situations, the joint gets it's strength from the fillet on the inside and the tape on both sides.

What Alan refers to, is what I call a glue and screw build (plank and frame). This is where the boat still has most of it's traditional framing elements (frames, floors, chine logs, stringers, etc.), but has it's exterior seams taped. This once was a separate build method, but hasn't been used (wholesale) in about 30 years. It was dropped (1970's) in favor of the lighter weight and simplified methods of true monocoque forms, found in stitch and glue. The exception (again) is taped seam doesn't need to be stitched and uses a different method to hold the panels together (such as Bolger's tack and tape) while the goo cures. It really is a hair splitting thing. A taped seam build may use a jig to hold the panels, while stitch and glue will generally be "free form" molding, possibly over a temporary bulkhead or two.

I generally use the two terms interchangeably, preferring taped seam over stitch and glue because it's all encompassing and less specific then stitch and glue.

If a build has framing and stringers, etc. I'll typically call this plywood over frame, regardless of how the seams are treated.

 

Interesting to hear PAR's definition. I will defer to him since he is the more knowledgable one. I've always thought taped seam was only outside taping, but now I can see why the confusion, and I wonder if others are also confused (or, like me, discovering that I'm not using the same terms a pro would use).

 

These terms are fluid, if given enough time Alan. I'm old enough to remember the old glue and screw jobs, before and after seams got taped. In those days, it was polyester and all sorts of crazy things were being done with the "miracle goos in a can". Of course none of them worked and it took me a long time to accept epoxy as a result, when it showed up in the late 60's (for me anyway). I still know folks that use nails with the heads exposed an 1/8" so the polyester has something to grip or staple the mat down, thinking it's now mechanically and chemically bonded to the surface. Hey, we didn't know, so we tried anything and everything to improve peel strength.

These old glue and screw builds where as the name suggests, the plywood was glued and screwed to the frame work, but the structure is still basically a plank on frame thing. Eventually things started to change and the frame spacing was increased, with many being removed if sufficient internal structure existed. Stringers and battens were the longest hold outs from the old days, but finally they got round filed too. All this came about with the faith epoxy brought to the table and the test results of different "liquid joinery" approaches.

 

I've seen a few builds still using stringers and battens, or some sort of the concept- are these still used/necessary, i.e. to allow a thinner-than-normal plywood for a lighter hull, or is it still a throwback that stays in a few designs?

 

I suppose the word 'safe' has to be used in the context of "where".

Lakes and rivers, 3 people in a 12 ft boat - maybe, in open waters "most probably not".

In any event, the pain and possible disappointment of building your own design when a great little boat is only a few hundred dollars away in a proven plan, seems unnecessary.

I can recomend the book 'Devlins Boat Building' as a great insight into self design as well as the 'stitch and glue' or 'taped' method of boat building.
http://store.devlinboat.com/

For more thorough confusion, the thred at http://www.boatdesign.net/forums/boat-building/building-methods-29256.html

is great value too.

 

Go purchase a Grumman Aluminum dink in the sailing model. just over 8ft .

Will transport 3 folks with ease in really sloppy (2 -3ftwaves) conditions.

2 rowing locations for 2 rowers.Rows well, powers well and sails really well.

For cruising it can take the imbecile dingy crushes (10 dinks tie up close to "capture" a spot, instead of using a 20 ft painter and having 30 dinks share).

The aluminum does really well in crush conditions with ply wood or condom boats, and chews its away into GRP like Boston Whalers well too.

OK on a rocky or coral beach too.

FF

 

Have a look at the Mirror dinghy, slow but capable.

http://en.wikipedia.org/wiki/Mirror_(dinghy)

 

About like PAR says...12 ft would be the minimum. Using a Pram design you could cram 3 in if it was beamy and still be ok. No speed records but should be a relatively OK performance wise and still be fairly easy to build. You would want some decent rocker to get weight carrying capacity, enough freeboard to keep the water out, enough beam to give room and capacity. Something like the SKETCH below would be a starting point. I might rig this Catboat style with the mast far forward and use a Sprit Sail or a Leg 'O Mutton sail with a sprit boom or even a Gaff rig if you feel salty. That way you have maximum room in the interior to move around and get the best balance. For an easier build you could go with a flat bottom but that would tend to increase your drag a bit and pound on the water when not heeled over some. This sketch shows a level waterline in the 700 lb displacement range. I assume you would be using this on the lakes in AZ and not in the Atlantic, on nicer days rather than during a raging T-Storm etc. Decking and general 'making it more seaworthy' will add to the weight as well as the safety and will cut your carrying capacity. If you were to add a foot to the length you would increase capacity by over 100 lbs and probably only increase the boat weight by 25-30 lbs so you might want to consider going for the extra foot.




PS: Now Paul...no need to dissect the drawing to bits...I'm just using it to illustrate the capacity and usefulness of the pram style in getting the most boat in the shortest length.

 

May I recommend the Puddle Duck, it fits the requirements. Okay it looks like a concrete mixing tub with a sail, but hey it has serious load capacity and is only 8' long.