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Dinghy build questions: layup strength, foam vs plywood


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I have flirted with a build of a Chameleon dinghy for two years.  Last summer I re-shelved the project when a couple of used boats landed in my lap -- a 14' aluminum boat from the early 1960s that was in great shape but needed paint, and a 12' fiberglass sailboat with a heavy liner, rather like a scaled-down Wayfarer, suitable as a knockabout, needing sails, varnish, and minor fiberglass work.  Other than the arrival of competing projects, there were several interrelated reasons I had hesitated to build it:

  1. Local unavailability of truly suitable materials for spars, short of buying timber on the stump or paying boutique coastal prices plus truck freight. whcih
  2. Known problems building the daggerboard case as drawn based on other builders' experiences and analysis of the plans.
  3. It's too heavy, with most builders ending up with a boat weighing over 100 pounds.two layers

I want a nesting dinghy for an upcoming trip to Lake Superior because we want to visit the sea caves.  Otherwise we wouldn't need a dinghy at all. I'm thinking about the Chameleon again.  Now I'm thinking that I would be happier with a rowing-only build, which would solve 1 & 2 and help with 3.  I have my 12' knockabout and am less interested in a sailing rig as a result.

I'm looking for straightforward ways to lighten up the materials on Chameleon.

Here's what the stock design weighs, more or less, based on my calculations.

Hull including mating bulkheads, roughly 7 square yards or two sheets of 6mm Oakume.  Plywood 5.9#/yard, coating with epoxy on both sides adds 1.1#/yard, 4 oz glass on both sides plus epoxy at 1:1 with glass adds 1#/yard.  Add it up and you get 8#/yard or 56# for the hull.  I would allow 2# for seam fillets for a total of 58#.

The aft buoyancy tanks, bow locker, and plywood for the seats are 2 square yards.  Not everything is glassed but still probably another 16#.

Gunwales are about 5#.  Bulkhead beams and hatch framing cut from dimensional lumber are probably another 3#.  Dimensional lumber in the seats and seat brackets is probably another 6#.  Figure 3# for connecting hardware, oarlocks, cleats, hatch hardware, fasteners etc.  Brings us to 91#.  The stock design specifies two layers of 9 oz tape on the seams, 6" and 8" wide, plus 6oz glass on the exterior, which is about 8oz a yard (4# total heavier) than putting two layers of 4oz glass over everything.  The two skegs, if included, add another pound or two.  So pretty close to the 100# the designer states.  Most builders are new enough to boatbuilding that they use extra epoxy, and most builds are sailing builds that include the daggerboard case and some turning blocks and so on, bringing the total weight a little higher.

There are several obvious-to-me areas for significant weight savings:

  1. The design of the seats and brackets can be lightened up without changing materials by careful contouring of the dimensional wood.  That's easy, lots of choices. save 3#
  2. Vacuum bagging the hull, save 2# and get a stronger layup.
  3. Using thinner plywood.  4mm Oakume is available and is 7# a sheet lighter.  Using it throughout would save about 17# at the cost of some strength.  The strength could perhaps be made up by switching to one layer of 6 oz. S-glass for the hull and vacuum bagging, which would add back roughly 3#, still a net savings of 14#.
  4. Using foam (such as Divinycell or Core-cell A500) in place of plywood in areas that are noncritical and flat, such as the seats, buoyancy boxes, and bow deck.  This would save 12# over 6mm plywood or 8# over 4mm plywood.
  5. Redesigning the seats as a thicker cored composite so as to dispense with the dimensional lumber side rails entirely, using for example 3/4" end-grain balsa or 3/4" thick foam.  Maybe save another 3#, though the seats are removable so it's not clear how much this helps in practice.

All together that's 30#, which means a 70# boat instead of a 100# boat. 

The questions I have are these:

* How does the strength compare if switching from 6mm BS1088 Oakume with 6 oz E-glass on the exterior only (as designed) to 4mm BS1088 Oakume with 6 oz. S-glass vacuum bagged both inside and out?  If that layout is too weak, are there obvious ways to recover the necessary strength while still saving weight compared to the 6mm ply (for example by adding another layer to the layup or using biaxial 18 oz E-glass fabric instead)?

* Does using foam in place of plywood in the flat noncritical areas make sense?  Which foam products are worth considering?  Same 6mm thickness as the plywood design?  6 oz S-glass on both sides enough?

* Making a 5' long by 10" wide seat for one person, what is a sensible foam thickness and layup to use?  I'm guessing 3/4" foam and 6 oz E glass wrapped around it, but that's a guess

Advice welcome.

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I've seen some of Danny's in person and thought they were overbuilt. Too much dimension lumber.

Because I could do better, I designed and built a ply 11' nesting dinghy (yes it's for sale and has been for decades but I won't link to the site). The prototype was in daily use for 8 years while cruising/rowing to work, before I moved and passed it on to another cruiser so yes, it was durable.  It used heavier 1/4" marine fir the hull (Okume was not affordable locally) and was < 100 lbs.

It uses:

- single layer 4" wide x 9 oz tape for the seams. This is plenty for a rowing dinghy. Really, it is. I built a 25 mph 11' planing dinghy that used single 12 oz x 6" wide double bias for the seam. That is roughly similar in strength to the 2 x 9oz, 6" and 8" wide, but half the weight. If you're concerned about my narrower woven tape being too light at least use single layer of 6" double bias. But it won't be. Build a sample piece of 1/4" plwood with a angled fillet joint, nice epoxy putty on the inside, proper radius on the outside. Use a single layer of 4" x 9 oz. Try to break the sample. It will likely break in the plywood just past the glass, not in the joint.

- no glassing of the hull. Just coated with 2 coats epoxy and then paint. It doesn't need glass on it except for added long term durability. If you touch up the inevitable scrapes through the paint from dragging it over rocks then it will last many years.

- for buoyancy I glassed in 2 pieces of extruded polystyrene pink foam (red shading) in the aft corners and covered with glass. The removable aft seat sits on wood cleats above the foam blocks. When filled with rain water it still had enough buoyancy I could stand in it and bail it out.

- the aft seat was removable so you can put the bow section in place. It has an alternate position shown in blue. If you are rowing with 2 people, aft seat is in blue position. If rowing with 3 persons or 2 + groceries in the bow, put the seat above the red foam blocks. This solves the trim issue that Danny's super long seat is used for, but does so with much less weight penalty.

image.png.f40acbcd3db9c03352237894599ff452.png

It rows very well. .  And it is light. Notice there is very little boat in the water.

image.png.c5e7f09e2f798b52a0fb82d7d56b2fae.png

The tucked up buttocks keeps the transom (red arrow) out of the water even when loaded

image.png.af34542cf795c385a47064387e62c32b.png



I can't think in "Lbs/yd" because those are insane units but here are my thoughts to modify the Chameleon design

- no glassing
- lighter seam tape
- reduce the bow locker size.  Do you need that much buoyancy? The damn thing is made of wood + framing + hatch etc etc. The wee bow locker on our boat was enough for a small anchor and 100' of 1/4" double braid rode. What else are you carrying that you need something that big.
- the super long seat is going to be heavy because of the span. yes foam would be lighter but ugh. Put a support under it half way to split then span in 2. Then 3/4" foam + 2 layers of 9 oz will be stiff enough.
- carry a bean bag chair for the cockpit? Use it instead of the long seat.
- S glass is stronger than E-glass but not much stiffer. And it's very expensive. Use carbon where weight really counts and you need stiffness (like top and bottom of a seat). Yes, it's 2-3x more than S glass but you use less, and use less resin. And you probably could do it with 2 yards.

http://www.fiberglasssupply.com/Product_Catalog/Reinforcements/Carbon_and_Kevlar/carbon_and_kevlar.html

- I doubt very much you'll save much weight vacuum bagging plain weave onto plywood. Use peel ply, squeegee well and you'll get fiber ratios of maybe 5% heavier than vacuum bagging
- thin 6mm foam + glass is not going to be as durable as plywood. Be sure you're aware of that tradeoff.


 

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100lbs seems super heavy for that boat. It should be plenty strong enough with 6mm occume, and no glass other than tape on the seams. Foam or vacuum bagging seem overcomplicated, and introduce other issues (puncture resistance for one).

Check out Michael Storer's or Russell Brown's designs for ways to build strong, stiff, lightweight boats.

Use a light, strong wood like western red cedar for all solid wood.

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Yes, I really like Russell's PT11 too. Sort of pricey because they are only sold as kits. Works of art when he builds them.

My designs are more uh, utilitarian I'd say. But some people finish them very nicely. I do not because to my the boat's dinghy is a bit of workboat. It gets beached on rocky shores, stuck against concrete docks with rusty rebar sticking out and gets smacked when a local in his boat comes in a bit hot to the dock. 

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3 hours ago, andykane said:

100lbs seems super heavy for that boat.

I've got one. Bought it, not built it. It weighs 48 kg.

For comparison a Swanson Pug f/g nesting dinghy weighs 45kg and my 2.4m aluminium dinghy weighs 52kg. I use the aluminium one as my main tender, keep it in davits.

They're all bloody heavy, ideally I'd want something around the 20kg mark. And the only way I can see of getting one is to build it myself out of polyethylene foam and f/g epoxy.

FKT

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5 hours ago, 2airishuman said:

 

Advice welcome.

Firstly, how robust a dinghy do you require.

The strength of the thinner Glassed ply won’t be an issue, the  Panel stiffness may be.

Leaving  the bottom panels as 6mm and going to 4mm for the sides and seats will probably give you a dinghy that’s fit for purpose.
Weight saving will be minimal. 

 

 

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There has been research, both pro and amateur, into the properties of 'glass covered plywood. See here as an example. If you can find a results table, it may help you choose the combination of ply  and epoxy/glass that you want.

The late Phil Bolger often wrote that putting a sailing rig on a small boat compromised the boats qualities for rowing. Also, that it has a significant cost in dollars, time and effort. He would have approved of your decision to leave the rig off your dinghy and doing your sailing in a boat that's already sailboat. 

There is a school of thought, which sometimes comes up here on SA, that you should build your boat out of ply with no glass or epoxy. Paint it with porch and patio paint. Don't make a big deal of fine craftmanship. Accept the fact that the boat's working life may be short because your need for the boat may also be short. 

Zonker and others went down this rabbit hole a couple years ago. 

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3 hours ago, WetSnail said:

Jerome Fitzgerald, in one of his books, swore that the best dinghy is an inflatable kayak.  And just yesterday, I watched an introduction into what is available: https://www.youtube.com/watch?v=5U8u_rkNTSY  I think they are all lighter than what you think of building, and they pack down smaller. 

On a guess, Jerome is lithe and limber with good balance.

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10 minutes ago, SemiSalt said:

On a guess, Jerome is lithe and limber with good balance.

Don't know.  But narrow inflatable kayaks are pretty recent designs, so he most likely used one with a fat tube either side of the paddler, and those are quite beamy and stable.

I forgot to mention https://woodenwidget.com/  Their Fliptail folding dinghy and Stasha nesting dinghy are both quite light, being skin on frame boats.  So those might also be suitable alternatives if light weight is important to 2airishuman.  Of course, if the Chameleon is a favourite design, alternatives may be irrelevant.

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19 minutes ago, SemiSalt said:

There has been research, both pro and amateur, into the properties of 'glass covered plywood. See here as an example. If you can find a results table, it may help you choose the combination of ply  and epoxy/glass that you want.

The late Phil Bolger often wrote that putting a sailing rig on a small boat compromised the boats qualities for rowing. Also, that it has a significant cost in dollars, time and effort. He would have approved of your decision to leave the rig off your dinghy and doing your sailing in a boat that's already sailboat. 

There is a school of thought, which sometimes comes up here on SA, that you should build your boat out of ply with no glass or epoxy. Paint it with porch and patio paint. Don't make a big deal of fine craftmanship. Accept the fact that the boat's working life may be short because your need for the boat may also be short. 

Zonker and others went down this rabbit hole a couple years ago. 

Glassing seems like overkill to me, to. I bought plans to build a 9'6" Joel White Nutshell pram 30 years ago. It took a few years to get to them. The recommendation was Okume ply which was costly and hard to get where I was (living in Vermont at the time). So I went with marine-grade Fir plywood. 

The boat has spent over season since, in the water for 5 months, and every off-season, outside under a tarp. Now over 25 years old, only the bottom is showing some signs of ply loss. But that piece is 3/8" thick and 5 ply so it's irrelevant. Unlike most dinks, this one is dragged up granite shorelines often encrusted with barnacles. If it had a layer of glass added at build, that would be shot anyway in places and way past due for replacement. 

Here it is dragged up on a soft golden mat, of fresh barnacles. 

2041552277_EdenEve(1of1).thumb.jpg.dd4f22e359172cddbde4b42841f7cb17.jpg

 

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9 hours ago, Zonker said:

I've seen some of Danny's in person and thought they were overbuilt. Too much dimension lumber.

Because I could do better, I designed and built a ply 11' nesting dinghy (yes it's for sale and has been for decades but I won't link to the site).

I was hoping you'd post.  Thanks for the analysis.  I've seen the FB11 plans for sale and remember you mentioning your goals for the design in another thread but I wasn't aware of the differences.

9 hours ago, Zonker said:

- no glassing of the hull. Just coated with 2 coats epoxy and then paint. It doesn't need glass on it except for added long term durability. If you touch up the inevitable scrapes through the paint from dragging it over rocks then it will last many years.


- for buoyancy I glassed in 2 pieces of extruded polystyrene pink foam (red shading) in the aft corners and covered with glass. The removable aft seat sits on wood cleats above the foam blocks. When filled with rain water it still had enough buoyancy I could stand in it and bail it out.

- the aft seat was removable so you can put the bow section in place. It has an alternate position shown in blue. If you are rowing with 2 people, aft seat is in blue position. If rowing with 3 persons or 2 + groceries in the bow, put the seat above the red foam blocks. This solves the trim issue that Danny's super long seat is used for, but does so with much less weight penalty.

[...]

I can't think in "Lbs/yd" because those are insane units but here are my thoughts to modify the Chameleon design

- no glassing
- lighter seam tape
- reduce the bow locker size.  Do you need that much buoyancy? The damn thing is made of wood + framing + hatch etc etc. The wee bow locker on our boat was enough for a small anchor and 100' of 1/4" double braid rode. What else are you carrying that you need something that big.

..nod..  The bow locker could at, a minimum, be lightened up, by removing all the dimensional lumber, and using a magnetic hatch like the kayak guys use.

It appears to me that both the bow locker and the aft buoyancy tanks also serve as stiffeners, which function would be lost if they were replaced with foam, no?  Or is the hull stiff enough without?

9 hours ago, Zonker said:


- the super long seat is going to be heavy because of the span. yes foam would be lighter but ugh. Put a support under it half way to split then span in 2. Then 3/4" foam + 2 layers of 9 oz will be stiff enough.
- carry a bean bag chair for the cockpit? Use it instead of the long seat.
- S glass is stronger than E-glass but not much stiffer. And it's very expensive. Use carbon where weight really counts and you need stiffness (like top and bottom of a seat). Yes, it's 2-3x more than S glass but you use less, and use less resin. And you probably could do it with 2 yards.

http://www.fiberglasssupply.com/Product_Catalog/Reinforcements/Carbon_and_Kevlar/carbon_and_kevlar.html

- I doubt very much you'll save much weight vacuum bagging plain weave onto plywood. Use peel ply, squeegee well and you'll get fiber ratios of maybe 5% heavier than vacuum bagging
- thin 6mm foam + glass is not going to be as durable as plywood. Be sure you're aware of that tradeoff.

Thanks

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7 hours ago, Zonker said:

Yes, I really like Russell's PT11 too. Sort of pricey because they are only sold as kits. Works of art when he builds them.

Right now they're out of production, sadly, so I have to figure something else out.

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5 hours ago, MRS OCTOPUS said:

Firstly, how robust a dinghy do you require.

The strength of the thinner Glassed ply won’t be an issue, the  Panel stiffness may be.

Leaving  the bottom panels as 6mm and going to 4mm for the sides and seats will probably give you a dinghy that’s fit for purpose.
Weight saving will be minimal.

Well, I'm not going to beat it up on purpose, but Superior, Vermilion, and Lake of the Woods are some of my favorite places.  They are rocky and I visit unimproved portions of shoreline.

 

3 hours ago, WetSnail said:

Jerome Fitzgerald, in one of his books, swore that the best dinghy is an inflatable kayak.  And just yesterday, I watched an introduction into what is available: https://www.youtube.com/watch?v=5U8u_rkNTSY  I think they are all lighter than what you think of building, and they pack down smaller. 

 

47 minutes ago, SemiSalt said:

On a guess, Jerome is lithe and limber with good balance.

Admiral has lousy balance and is recovering from two knee replacements

 

32 minutes ago, WetSnail said:

Don't know.  But narrow inflatable kayaks are pretty recent designs, so he most likely used one with a fat tube either side of the paddler, and those are quite beamy and stable.

I forgot to mention https://woodenwidget.com/  Their Fliptail folding dinghy and Stasha nesting dinghy are both quite light, being skin on frame boats.  So those might also be suitable alternatives if light weight is important to 2airishuman.  Of course, if the Chameleon is a favourite design, alternatives may be irrelevant.

I'm not stuck on the Chameleon.  I've had trouble finding designs that I like better.  The FB11 may be worth considering but Bateau's website has so little detail I felt that I had to buy the plans to figure out what it was.  Zonker's posts upthread have helped and given me a reason to consider that direction.  I looked seriously at the CLC Passagemaker but it doesn't really nest properly.  I want the carrying ability of a 10'+ pram, we're not small people.

 

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@2airishuman

I documented (here) stages in building my Two-Paw 8 nesting pram last year.  About 6 months total work.  Would’ve built the 9 but it wouldn’t fit properly, nested, behind my mast.
 

Certainly weighs less than 100 lbs.  No glass on the bottom; I did, though, add extra layers of fiberglass tape on bow, stern and boat bottom chines/joints.  Stainless steel rub strip on keel for occasional grounding.  We carry it up beaches.  I’m just about to make a little assembly using 1x8 or something, with two wheels on it, that will simply slot into the daggerboard trunk to allow me to wheel the boat up a beach.

See TwoPaw specs here.  https://bandbyachtdesigns.com/new-store/plans-and-kits/dinghies-and-tenders/ (Click “Catspaw prams” —which are non-nesting) to get to the Two-Paw (nesting).  We’ve carried three people in it no prob (160 lbs, 120 lb, 110 lbs).

Fantastic support from the designer and company (Graham and Alan), and a large online community of folks who’ve built them.  B and B does a LOT of design and building work.

Just build it and use it and don’t fuss too much about the details.  It’s never be perfect :-)

97381CAD-ECED-4F3A-8975-4E5D5A8D9136.jpeg

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6 hours ago, Kris Cringle said:

I watched a couple deploy and launch a (I think) Chameleon. I remember it looking pretty easy for them to lift and launch off the foredeck. 

1417559445_Nestingdinghydeployed(1of1).thumb.jpg.6fec01f46f0916b67fd874d33d8b5851.jpg

It hauled an impressive load. 

2049347142_Nestingdinghydeployedloaded(1of1).thumb.jpg.61197c361d6cc73f416a6a6201aedcd8.jpg

Friend of mine has a Chameleon, in fact he's on his second. He decided the first one was too heavy/bulky so sold it and went to a deflatable. After a couple years he decided he hated the deflatable so built another Chameleon. Second time he used lighter material, didn't glass the hull, didn't build the sailing rig etc etc. I don't know what his weighs but it's a lot less than mine, which is way overbuilt, double-glassed etc. But mine did, with its previous owner/builder, survive a lot of use on a passage around the Pacific and abuse by their children.

I personally find the Chameleon a bit too tender for my liking and moreso for my GF who has a bad habit of not watching where she steps - one day she will be swimming. PITA to motor one-up unless you have a pretty decent tiller handle extension and that's with a 2HP lightweight Honda. I definitely prefer my tin dinghy. As I'm still repairing the Swanson Pug I can't comment WRT the Chameleon and anyway, you can't build one or buy one regardless.

Anyway it's nice to be faced with the next boat question. I'd probably build one of the B&B designs myself, the 9' one for preference. And maybe in 10mm polyethylene foam with stainless rub stringers on the bottom.

FKT

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2 minutes ago, Fah Kiew Tu said:

Friend of mine has a Chameleon, in fact he's on his second. He decided the first one was too heavy/bulky so sold it and went to a deflatable. After a couple years he decided he hated the deflatable so built another Chameleon. Second time he used lighter material, didn't glass the hull, didn't build the sailing rig etc etc. I don't know what his weighs but it's a lot less than mine, which is way overbuilt, double-glassed etc. But mine did, with its previous owner/builder, survive a lot of use on a passage around the Pacific and abuse by their children.

I personally find the Chameleon a bit too tender for my liking and moreso for my GF who has a bad habit of not watching where she steps - one day she will be swimming. PITA to motor one-up unless you have a pretty decent tiller handle extension and that's with a 2HP lightweight Honda. I definitely prefer my tin dinghy. As I'm still repairing the Swanson Pug I can't comment WRT the Chameleon and anyway, you can't build one or buy one regardless.

Anyway it's nice to be faced with the next boat question. I'd probably build one of the B&B designs myself, the 9' one for preference. And maybe in 10mm polyethylene foam with stainless rub stringers on the bottom.

FKT

Not steel? You could probably keep it under 400 lbs.

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7 hours ago, 2airishuman said:

I'm not stuck on the Chameleon.  I've had trouble finding designs that I like better.  The FB11 may be worth considering but Bateau's website has so little detail I felt that I had to buy the plans to figure out what it was.  Zonker's posts upthread have helped and given me a reason to consider that direction.  I looked seriously at the CLC Passagemaker but it doesn't really nest properly.  I want the carrying ability of a 10'+ pram, we're not small people.

Another one to take a look at is the Spindrift from B&B Yacht designs. 

And Zonker, I don't think anyone would object to you posting a link here to your design. You add heaps of value with your posts. If you don't think you should post a link, could you post some google keywords that will help others find it? My search failed.

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There's a pretty decent looking design in Dave Gerr's book 'The Nature of Boats' including complete lines etc needed to build it.

The clamps to hold the 2 halves together are overly elaborate but easily ditched and something a lot simpler substituted. I could build those clamps but not sure I could be bothered unless I was really bored.

I may build one of them one day just because.

FKT

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Lightest dinghy I have built was a Bolger Elegant Punt, in the original design form it just squeaked in around 20 kg.

In my opinion it’s 6” too narrow, but Phil designed it for two sheets of ply and it’s a work of genius.

Rows fine, carries a decent load, didn’t make the sailing rig.

modified it by widening it 6”, stability and load capacity much better, still rows fine. I ended up making three or four as they were regularly stolen from the shores of Sydney Harbour, but they only took a weekend to build so no big deal.

if you don’t like stitch and glue, which I don’t, they are easy and satisfying to build.

I eventually graduated to the Nymph, and widened it by 6” as well, it is an exceptionally good small dinghy, but significantly heavier. My current one is around 33kg with a glass covered bottom, could probably get it down around 30 kg if I tried.

S&G construction is surprisingly heavy, especially if you like to use double bias tape, but very strong.

I have owned a couple of Snug nesting glass dinghies, more trouble than they are worth. My current Nymph is a couple of inches short so it fits between the mast and inner forestay, a better solution.

Keep the dinghy light enough to launch with a halyard and forget davits.

 

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11 minutes ago, olaf hart said:

Lightest dinghy I have built was a Bolger Elegant Punt, in the original design form it just squeaked in around 20 kg.

In my opinion it’s 6” too narrow, but Phil designed it for two sheets of ply and it’s a work of genius.

Rows fine, carries a decent load, didn’t make the sailing rig.

modified it by widening it 6”, stability and load capacity much better, still rows fine. I ended up making three or four as they were regularly stolen from the shores of Sydney Harbour, but they only took a weekend to build so no big deal.

if you don’t like stitch and glue, which I don’t, they are easy and satisfying to build.

I eventually graduated to the Nymph, and widened it by 6” as well, it is an exceptionally good small dinghy, but significantly heavier. My current one is around 33kg with a glass covered bottom, could probably get it down around 30 kg if I tried.

S&G construction is surprisingly heavy, especially if you like to use double bias tape, but very strong.

I have owned a couple of Snug nesting glass dinghies, more trouble than they are worth. My current Nymph is a couple of inches short so it fits between the mast and inner forestay, a better solution.

Keep the dinghy light enough to launch with a halyard and forget davits.

 

IF anyone wants a Douglas Fir mast for an Elegant Punt, let me know.

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Yes, it's been sold there for a few decades. Jacques Mertens (the original owner of the site) approached me on the old usenet rec.boats group when I mentioned I had designed and built one. He didn't have one in the portfolio and I added to it. We always operated on a virtual handshake agreement and royalty cheques arrived every month. He has retired, sold the business but the new owner is happy to keep selling it, along with my other designs.

https://boatbuildercentral.com/product/nesting-dinghy-11-boat-plans-fb11/ 

It uses 4 x 5/16" bolts with wing nuts to assemble. Not as fancy as Dave Gerr's or Russell's specialized clamps. I used to assemble ours on the foredeck, balancing the halves sticking over the lifelines. Then heave it into the water. Assembling in the water is possible, but tricky if there is any wave chop. 

 

 

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1 hour ago, olaf hart said:

I have owned a couple of Snug nesting glass dinghies, more trouble than they are worth.

In what way? Mine is capable of being used as is, I've just been using up the excess epoxy & fairing compound on it as I build my hard dodger. Once I finish I'll sand it all back and repaint it.

Looks a fairly decent design and each piece is ~ 22kg - I weighed them - so easily deployable but I've no idea what useability is like yet. If I don't like it - shrug - I have plenty of space down near my back gate to litter with dinghies.

WRT davits I think this is very much a personal thing. I can carry a virtually indestructible dinghy, launch and recover it in minutes. The Chameleon is a *lot* fiddlier and takes longer. OTOH you can have a wind vane steering gear or whatever without davits so - shrug. Currently I'll take the speed & convenience of davits. I can fit a 2250mm dinghy on the cabin top or the tin one on the aft cabin and seats if I decided to go that way.

WRT bolts & wing-nuts to hold the halves together - please don't. OK it's cheap and it sort of works if you use some tool to hold the bolt head on one side and something to tighten the wing nut on the other. Or have fingers like vise grips. Otherwise it's a poor solution IMO, cheap and fast being the sole benefits. I made captive nuts for one side and big hand-tighten threaded screws for the other, basically all-thread embedded in a nice big grippable timber handle. No fiddly bits.

FKT

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The Snugs are probably the best nesters ever designed, particularly the dovetail joint.

The problem is assembling them on deck or in the water, after a while we just gave up and went back to smaller hard dinghies.

The original Snug, around nine feet, is built like a tank and quite heavy to move on deck or hoist.

We also had a newer, lighter 8’ one that was a lot easier, but the bottom flexed and it was quite fragile.

The best dinghy we have owned was a 9’ Minto that came with the Tartan 30 in Seattle, it fit nicely on the foredeck, was a delight to row, and comfortable enough for two ...

 

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1 hour ago, olaf hart said:

The Snugs are probably the best nesters ever designed, particularly the dovetail joint.

The problem is assembling them on deck or in the water, after a while we just gave up and went back to smaller hard dinghies.

The original Snug, around nine feet, is built like a tank and quite heavy to move on deck or hoist.

We also had a newer, lighter 8’ one that was a lot easier, but the bottom flexed and it was quite fragile.

I think mine is the 9' model. Have to measure it now you tell me there were 2 variants. It is pretty flexy but I think that's hard to avoid. I cut off the stupid raised ribs, they were damaged and the foam core was breaking down anyway. Current plan is to lay some unidirectional glass into the moulded longitudinal ribs, top with polyethylene foam then use some of the scrap glass to get a flat sole except for the centre rib. Shouldn't add much weight.

IMO the Chameleon is a PITA to assemble on deck too. If I find this one is annoying I'll keep an eye out for Plan C. Which is unlikely to be a deflatable, I'm too damn blase about running dinks up onto rocky beaches with oysters.

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Thank you all for the replies.

I believe that an 80# build is possible.  Here's what I'm thinking:

1) Rowing only version, saves 5# by lack of a mast step, PVC pipe, bow deck doubler, daggerboard case, and rudder gudgeons.

2) Reduce seam tape to one layer of 4" tape on inside seams; use 6 oz S-glass sheet on outside in place of any tape.  Saves at least 8# from the designer's layup which is one layer of 6" tape and one layer of 8" tape inside and out.  (Adapted from advice received from @Zonker)

3) Redesign the seats and seat brackets.  Replace 1x2 spruce wood rails with 1/4"x3.5" Douglas fir (aft) and 1/4" x 2.5" fir (front); reduce front seat width to 9.375" to allow it to nest inside rear seat for storage.  Rear seat add a plywood crossbrace in the center to control twist.  Closely fit seats to transoms and bulkheads to minimize the size of brackets.  Build brackets out of plywood in an H shape extending to the bottom of the hull to better transfer the load while reducing weight with the stern transom bracket also serving as a quarter knee to transfer the thrust from an outboard if fitted.  Total savings 4#

4) Replace aft buoyancy tanks with low-density foam blocks (e.g. the pink "Foamular" insulation available at any lumberyard) of the same size covered with fiberglass.  3# savings (again based on suggestions from @Zonker)

5) Change bow locker hatch to be flush using nylon hinges, a stamped stainless steel lift ring, and neodymium magnets encapsulated in the layup with a narrow plywood jam under the deck.  1# savings compared to the friction-fit dimensional frames as drawn.  Use a nylon bow cleat.

6) Eliminate quarter knees at mating bulkheads and reduce transom quarter knees to the minimum size necessary to accept a hoisting line.  I believe there is enough strength in the hull that these aren't necessary, because of the tops of the buoyancy compartments aft (even with just glass and foam) and the bow locker forward.  1# savings

I have some other changes in mind that are functional rather than weight-saving:

A. Use 3/8" wing bolts (https://www.mcmaster.com/92625A124/) in 18-8 stainless and adhesive-mount nuts (https://www.mcmaster.com/98007A412/) in 316 to fasten the two halves.  I believe this is the most functional arrangement that can be built with off-the-shelf hardware.

B. Use Douglas Fir rather than sitka spruce for the gunwales and beams for reasons of local availability.  Fir is stronger and denser in equal measure, so reduce dimensions accordingly to maintain strength and weight as designed.  Drop gunwales from 1" x 7/16 to 3/4" x 7/16 and the thin the beam pieces from 3/8" x 1.25" to 5/16 x 1.25"

C. Reduce the size of the stern transom doubler to 7x7". Extend the seat bracket sides (now made of plywood) upward to the gunwales to form a transom brace.  Adjust the stern gunwale dimensions.  Use an outwale of 1/4" x 3/4" so that the outwales are flush with the transom doubler.  Use an inwale dimension of 3/4" square.  Use 3/4" x 1.5" 6061 aluminum square tube, 1/8" thick walls, in a 10" piece between the seat braces to take the clamp load from the outboard.  All this adds maybe 8 ounces and will be much stronger for dealing with the clamp load and torsional forces on the stern.

D. Taper and shape the skegs to reduce weight and cross section forward (while still retaining area for directional control) and maintain cross section aft where dragging loads are present.  Inlay UV-resistant MDS-filled nylon skids in the aftmost 4" for easy damage-free dragging over sand, concrete, and asphalt.

E. Run a 9" wide kevlar strip under the keel.  Several builders have suggested reinforcement here for longevity.

I've looked at alternatives for the bow locker.  Yes, it's heavy, about 8.5# with the hatch and hardware, once the dimensional lumber framing is removed.  If removed, 1# of foam would be needed for flotation and the front seat would have to be extended increasing its weight by 3.5#.  So removal would only be a net 4# savings.  Could save 3# building it out of corecell and fiberglass but I don't think it's worth the cost and complexity.

Based on the weights of other builds and an analysis of area and weight of the different pieces, I think this puts me right at 80# total of which 5# is the removable seats.

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I am reminded that someone, maybe Gary Hoyt, added buoyancy and anti-tippiness to a dinghy by putting a string of foam flotation along the gunnels. Something like rope floats would do. They would also act as fenders when snuggling up to the mother ship.

This could make an inverted boat hard to right, OTOH, it would float better swamped.

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Can you link to some images that show the interior geometry? it seems like you are on the right track, but I would weigh in if I could get my head around it. I'm assuming you will use 6mm Okoume for the hull. That can vary from about 21 to 24 pounds per sheet, so 3 sheets can make a pretty big difference. Usually a unit of ply all weighs roughly the same, so no sense taking your scale when buying. I built a PT 11 using 4 mm for the upper hull (over half the surface area of the hull). It was much more challenging to build, substantially weaker, and removed only about 6 lbs.

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56 minutes ago, Russell Brown said:

Can you link to some images that show the interior geometry?

Here are a couple of photos.  I'm not sure of the sources.  The first one has a modified transom doubler, a modified hatch, and no aft seat.  There is also an extracurricular doubler for the towing eye, plans only have one on the inside:

image.thumb.png.5de53b4ab84f0e43672a02bf6b5eb9b5.png

 

This one is more faithful to the plans showing the hatch, seats, and seat supports more or less as drawn:

image.png.44ee94d2a2cfb84edf84572d208f945d.png 

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2 hours ago, SemiSalt said:

I am reminded that someone, maybe Gary Hoyt, added buoyancy and anti-tippiness to a dinghy by putting a string of foam flotation along the gunnels. Something like rope floats would do. They would also act as fenders when snuggling up to the mother ship.

This could make an inverted boat hard to right, OTOH, it would float better swamped.

Here's what I did on the boat I currently use as a tender:

image.thumb.png.6f266e84da24f2acc2f3b588df6848f7.png

They're easy to flip into the boat where they are more or less out of the way for trailering or fishing

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Pretty sure it's Richard Woods that has the floats along the outside of the gunnels on one of his dinghy designs. We built one of his Crayfish designs about 19 years ago from a sketch in Multihulls Magazine. I think it's 4mm lightly tortured occume, glassed on the outside, epoxy everywhere. weighs 48 lbs., still going strong. nothing elegant about it, rows okay, carrys a load pretty well. Thin ply works great if you can twist some shape into it. The penetration resistance isn't great, but it's really easy to repair. 

Pat

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8 hours ago, SemiSalt said:

I am reminded that someone, maybe Gary Hoyt, added buoyancy and anti-tippiness to a dinghy by putting a string of foam flotation along the gunnels. Something like rope floats would do. They would also act as fenders when snuggling up to the mother ship.

This could make an inverted boat hard to right, OTOH, it would float better swamped.

Pool noodles. I cut some in half, haven't gotten around to sewing the cover sleeves as yet.

FKT

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16 hours ago, 2airishuman said:

Thank you all for the replies.

I believe that an 80# build is possible.  Here's what I'm thinking:

1) Rowing only version, saves 5# by lack of a mast step, PVC pipe, bow deck doubler, daggerboard case, and rudder gudgeons.

2) Reduce seam tape to one layer of 4" tape on inside seams; use 6 oz S-glass sheet on outside in place of any tape.  Saves at least 8# from the designer's layup which is one layer of 6" tape and one layer of 8" tape inside and out.  (Adapted from advice received from @Zonker)

3) Redesign the seats and seat brackets.  Replace 1x2 spruce wood rails with 1/4"x3.5" Douglas fir (aft) and 1/4" x 2.5" fir (front); reduce front seat width to 9.375" to allow it to nest inside rear seat for storage.  Rear seat add a plywood crossbrace in the center to control twist.  Closely fit seats to transoms and bulkheads to minimize the size of brackets.  Build brackets out of plywood in an H shape extending to the bottom of the hull to better transfer the load while reducing weight with the stern transom bracket also serving as a quarter knee to transfer the thrust from an outboard if fitted.  Total savings 4#

4) Replace aft buoyancy tanks with low-density foam blocks (e.g. the pink "Foamular" insulation available at any lumberyard) of the same size covered with fiberglass.  3# savings (again based on suggestions from @Zonker)

5) Change bow locker hatch to be flush using nylon hinges, a stamped stainless steel lift ring, and neodymium magnets encapsulated in the layup with a narrow plywood jam under the deck.  1# savings compared to the friction-fit dimensional frames as drawn.  Use a nylon bow cleat.

6) Eliminate quarter knees at mating bulkheads and reduce transom quarter knees to the minimum size necessary to accept a hoisting line.  I believe there is enough strength in the hull that these aren't necessary, because of the tops of the buoyancy compartments aft (even with just glass and foam) and the bow locker forward.  1# savings

I have some other changes in mind that are functional rather than weight-saving:

A. Use 3/8" wing bolts (https://www.mcmaster.com/92625A124/) in 18-8 stainless and adhesive-mount nuts (https://www.mcmaster.com/98007A412/) in 316 to fasten the two halves.  I believe this is the most functional arrangement that can be built with off-the-shelf hardware.

B. Use Douglas Fir rather than sitka spruce for the gunwales and beams for reasons of local availability.  Fir is stronger and denser in equal measure, so reduce dimensions accordingly to maintain strength and weight as designed.  Drop gunwales from 1" x 7/16 to 3/4" x 7/16 and the thin the beam pieces from 3/8" x 1.25" to 5/16 x 1.25"

C. Reduce the size of the stern transom doubler to 7x7". Extend the seat bracket sides (now made of plywood) upward to the gunwales to form a transom brace.  Adjust the stern gunwale dimensions.  Use an outwale of 1/4" x 3/4" so that the outwales are flush with the transom doubler.  Use an inwale dimension of 3/4" square.  Use 3/4" x 1.5" 6061 aluminum square tube, 1/8" thick walls, in a 10" piece between the seat braces to take the clamp load from the outboard.  All this adds maybe 8 ounces and will be much stronger for dealing with the clamp load and torsional forces on the stern.

D. Taper and shape the skegs to reduce weight and cross section forward (while still retaining area for directional control) and maintain cross section aft where dragging loads are present.  Inlay UV-resistant MDS-filled nylon skids in the aftmost 4" for easy damage-free dragging over sand, concrete, and asphalt.

E. Run a 9" wide kevlar strip under the keel.  Several builders have suggested reinforcement here for longevity.

I've looked at alternatives for the bow locker.  Yes, it's heavy, about 8.5# with the hatch and hardware, once the dimensional lumber framing is removed.  If removed, 1# of foam would be needed for flotation and the front seat would have to be extended increasing its weight by 3.5#.  So removal would only be a net 4# savings.  Could save 3# building it out of corecell and fiberglass but I don't think it's worth the cost and complexity.

Based on the weights of other builds and an analysis of area and weight of the different pieces, I think this puts me right at 80# total of which 5# is the removable seats.

I mean, it’s cool - but you may be overthinking it.  Two-Paw 9, bit of extra fibreglass tape on bottom chines and bow/stern transom: done. 

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On 3/12/2021 at 11:11 PM, Jud - s/v Sputnik said:

I mean, it’s cool - but you may be overthinking it.  Two-Paw 9, bit of extra fibreglass tape on bottom chines and bow/stern transom: done. 

I rechecked your build thread and B&B's web site to see if I was forgetting something.  I'd originally ruled it out because I think it's too small for my situation.  I want either a 10' pram design or 11' with a pointed bow for reasons of capacity and stability.

I don't see the two-paw as being an especially lightweight design.  In your build thread you said that the spec was 80# for the 8' version.

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50 minutes ago, 2airishuman said:

I rechecked your build thread and B&B's web site to see if I was forgetting something.  I'd originally ruled it out because I think it's too small for my situation.  I want either a 10' pram design or 11' with a pointed bow for reasons of capacity and stability.

I don't see the two-paw as being an especially lightweight design.  In your build thread you said that the spec was 80# for the 8' version.

I was sort just being facetious - I’m actually impressed how thorough/methodical you’ve been about trying to find ways to reduce the weight of the Chameleon.

If I can find a way to get mine home today (and borrow a neighbour’s scale), I’ll weigh it - each half at a time.  For sure it’s not particularly extremely light, but I can manage each half just fine.  As far as length, indeed, the B and B Two-Paw 9 is the longest.  Graham also designed the Spindrift to be nesting - the Spindrifts being their pointy bow smaller dinghy line.  Up to 12’, I think.

For light - see Stasha (nesting m, too): https://www.woodenwidget.com/stashaspecs.htm

I’d like build one of these, after having a good experience with my kayak.  “Ballistic nylon” and the urethane coating is really tough.  (Within reason, of course. But you can literally hit it with a hammer and it can withstand the blow.)

83E4594C-5C65-4A70-BE8F-E3DA4B67A9C2.jpeg

7051B9A1-21B9-4F70-B18C-A12892AAFE55.jpeg

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