Sturdy 14 Sailing Dinghy

Since I appreciate any kind of feedback, I’d like to share my new design here as well.

Sturdy 14 Sailing Dinghy

A few years ago, I received a challenging request: design a 14-foot sailing dinghy with a hull that could be built from three sheets of plywood.
I took on the task and quickly arrived at a satisfactory result. However, I was undecided for a long time regarding the interior layout.
Using two additional plywood sheets, I finally resolved this issue as well.

That makes a total of 5 sheets of 6 mm, 244 x 122 cm marine-grade okoumé plywood.

LOA 430 cm
Beam 148 cm
Design displacement 250 kg
Draft 15 cm (99 cm with daggerboard down)
Freeboard 35 cm
Estimated weight 80 kg
Sail area 8.3 m²

The sail used is Michael Storer’s RSS 8.3 m² OZ Goose lug sail.

Check out the 3D model: Sturdy 14 - 3D Model - 3D model by flo-mo https://skfb.ly/pKVpq

 

Are there any built?

 

Hi flo-mo, that looks like it would be a very nice dinghy, possibly fast, roomy, aesthetically pleasing, possible to put a competitive rig on; it has potential back in 1970 when home made plywood boats were taking off. I don't think that happens much now due to plastics, resins, and fibres, and lack of keen home handymen, but maybe you could make one from foam sandwich and have a quick beach launch day sailer. I prefer a swinging centreboard myself, despite the penalties of the greater weight, and room lost. 14 foot is an ideal length I think, possible single handed launching, room for a family, or camping gear. You havn't shown all parts, stem, keel, hog, stringers, and the rest. Nice optimised sheet use. Make one and show us how the edges all line up. A scale model would look nice too.

 

Great work as usual. Lots of boat for the sheet.

 

Very nice. Looks like a lot of the most popular dinghies from the late fifties and early 60's. It would sail well with a pair of young teenagers. Pretty much no-one is going to use the bench seats, though, so you need an in-wale and out-wale that lets at least the forward person sit there all day. Kicking straps should be standard. A centerboard option would be nice.

Oh, and she really is sturdy in 6mm stuff. The entire boat can be made of 4mm, a bit of 2" glass cloth tape over the joints, and paint. I got nearly 30 years out of my 14'er that was made of 5/32" ply, 2" tape and red paint. It lived outside it's entire life.

The MerryMac | Small Boats https://smallboatsmonthly.com/article/the-merrymac/

 

I’ve received a lot of feedback on the various platforms where I’ve shared my design. Thanks to everyone who contributed.

I’m now going to try to respond to it all. This is going to take a while...

• No, I haven’t built the boat yet, and I probably won’t build it either. What I do plan to do is build a 1:10 scale model to check whether all the parts fit together.

• Yes, I plan to publish the cutting patterns for the panels and all the plywood components. I’ll put together a list of the required materials. There won’t be any building instructions. If anyone intends to build the boat, they’ll need the necessary experience. I’d then try to support them as best I can.

• Since the sail from Michael Storer’s OZ Goose is used, I recommend purchasing the instructions for that project. The OZ Goose is certainly much easier to build, but in principle, the construction method is quite similar in many areas.

• “Is it possible to build the boat lighter?” The weight of 80 kg is an estimate based in part on the volume of the individual components made of plywood and solid wood. This can be calculated exactly. However, the weight depends on the materials used.

• To save weight, you could use 4 mm plywood for the interior and lightweight woods such as western red cedar or paulownia for the wooden frames and stiffening components. One could even use 4 mm plywood for the hull, though this would require reinforcement measures, which ultimately means more effort without any significant weight savings. The boat would no longer live up to the name “Sturdy.” It’s more difficult to estimate how much weight the epoxy, paint, and fiberglass cloth will add. Then there’s also the hardware to consider. Since I don’t want to give anyone false hopes regarding the weight, I’ve remained conservative in my estimate.

• Here is a breakdown of the weight based on the volume of the components I’ve suggested, so everyone can form their own opinion.
• 6 mm plywood 80 liters 550 kg/m³ => 44 kg (29.3 kg for 4 mm plywood, not recommended)
• 20 liters of softwood 500 kg/m³ => 10 kg (6 kg for paulownia)
• 7 liters of hardwood 700 kg/m³ => 4.9 kg (3.5 kg for softwood)
• Metal parts (oarlock socket, gudgeon, fasteners) 0.5 kg
• Hatches 1 kg
• Epoxy for the fillets ?
• Fiberglass cloth ?
• Paint/varnish ?
• Total weight of known parts 60.4 kg (38.8 kg for the daring)
• Unknown remainder 10–20 kg
• Estimated total weight ~ 70–80 kg (minus 20 kg at your own risk)

• A pivoting centerboard has been suggested several times. This is certainly conceivable, but requires additional plywood.

• Car-toppable is not realistic without drastic weight reduction. A lighter construction is probably possible, but only at your own risk.

• The total volume of the buoyancy chambers is approximately 550 liters.

• The design displacement is 250 kg. At this displacement, the transom barely touches the water. With four people and light equipment, the displacement increases to approximately 450 kg. Although this does affect performance, the freeboard is still 29 cm.

• “That’s nothing out of the ordinary. It’s more typical of the ’70s.”Yes, I agree, and I don’t take these comments as negative.

• “Not suitable for hiking” The design is intended as a family boat that can also be used as a rowboat, rather than as a piece of sports equipment. Anyone who wants to sail really hard would have to make the appropriate modifications. Other designs are probably better suited for that. Since the hull is more of a displacement hull than a planing hull, the maximum engine power is limited to 2 hp.

It’s amazing to see which boats my design reminds different people of—though that’s certainly very good company. Here are a few examples:

Windmill
GIS
Jimmy Skiff 2
Flint
Argie 15
​

As for the hull shape, I don’t see the comparison. The internal layout may bear some resemblance to one design or another.

I see a much closer resemblance to Graham Byrne’s Spindrift and Core Sound series, and especially to Wolstenholm’s Gaffling 4.1.

(Repost from the WoodenBoat forum)

 

A few other thoughts from experience. The 6mm transom skin really isn't enough even if you frame it in all the way around. It needs to be 12mm and framed-in as well. The corners of little boats take a beating and the extra flange length at the panel ends will aid construction. You can also add a OB pad to one side. The topsides in way of the oarlocks aren't going to be rigid enough. I would run an inwale all the way from the bow to aft of the oarlocks, and put a brace under the oarlock to make that area feel solid. Removing the transom panel for the nesting should help a lot with extra bits for reinforcing, like an inner keelson piece applied after the hull has been tabbed. Asking the builder to make a few odds and ends out of sticks will help a lot in terms of the perceived size of a three sheeter.

As a personal preference, I find bow braces as shown annoying. On small boats, I want to be able to stand or sit at the bow, and therefore want a small foredeck with a hatch that you can drop a bucket through. I carry the anchor and rope in the bailing bucket below the hatch. Most 14's do have a foredeck. Getting rid of the transom would give you ply for a foredeck.

 

Thanks, Phil—those are valuable points that I’ll give some thought to. I appreciate that you’ve really taken the time to analyze my design.

Now, on to something else.
I’m just having too much fun with Sketchfab.
But there’s definitely an educational aspect to it as well.
Here I’m showing a comparison of the hulls of the following boats (waterline at 272 kg displacement):

CLC Jimmy Skiff - Sturdy 14 - Windmill - Storer GIS - Argie 15

Sturdy 14 - 3D Model Comparison - 3D model by flo-mo https://skfb.ly/pLpIP




This comparison is almost a little embarrassing. The similarity between the three boats is striking. During my design process for the Sturdy 14 hull, I hadn’t yet heard of the other two designs (Gaffling 4.1 and Jack Holt’s GP14). It wasn’t until I was laying out the interior that I drew inspiration from the Gaffling 4.1.

The hulls shown at a displacement of 272 kg.

Gaffling 4.1 - Sturdy 14 - Jack Holt GP14

Sturdy 14 - 3D Model Comparison 03 - 3D model by flo-mo https://skfb.ly/pLpTM

 

The forward portion of the bottom surface with the straight sections and changing deadrise is not developable. A developable surface bounded by the keel and chine curve would have curved stations. The straight ruling lines would not be parallel to the stations.

 

Yes, you need to start with an actual developable surface, and force cad into working with it by suppling the model mesh with edges that lie along ruling lines and panel edges only. This will get you a realist shell that you can run decent hydrostatics on. It may not make for the best renders, but it makes accurate unfoldings.

Development of intersection of two cones and two planes. https://www.boatdesign.net/threads/development-of-intersection-of-two-cones-and-two-planes.51910/#post-713716

See also my post two above the one linked above.

 

There seems to be a misunderstanding here.
I did my design work in Rhino, a very powerful CAD program, especially when it comes to 3D surfaces and their development. So don’t worry—the surfaces that define the boat can definitely be developed (though that doesn’t necessarily mean you can build them out of plywood).

Sketchfab, the other program I used, is not so much intended by me to create pretty pictures as it is to give the viewer the opportunity to inspect the object from all sides and examine it critically.

Nevertheless, I plan to build a 1:10 scale model, which is an integral part of my design process. If unexpected problems arise during the construction of the model, it means I’ll have to revise the design again.

In any case, I’ll report back as soon as I have new insights.