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Discussion Starter #1
Does anyone know of any good plans to build a solid but lightweight rowing/sailing dinghy? Ideally I'd like to build it out of something light like divinicel and fiberglass (sandwich). Something about 8ft should do the trick. The idea is to haul it up on deck when sailing so I'd like something light. Has anyone built one they could recommend? Has anyone tried building one using a foam/fiberglass sandwich technique? Thanks in advance!
 

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I think a stitch and glue marine plywood design in that size range would be lighter than a foam cored GRP dinghy. Check out the CLC line of designs.
 

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I thought a foam core would be lighter than ply, but thanks for the suggestion.
In larger sizes, yes, but the smallest boats are often lighter in stitch-and-glue than in GRP. A stitch-and-glue boat doesn't even need to have a full coat of fiberglass on it, where the skins on the foam-cored GRP boat have to have a minimum thickness to guarantee the core's integrity and provide sufficient stiffness to the design. Marine plywood, even 1/8" is pretty stiff torsionally, unlike foam, once it is bent and held in that position.

For instance, the Chesapeake Light Craft's Eastport Pram is 7' 9" x 48" and only weighs 62 lbs. One 8' GRP/Foam dinghy that I found on the net weighed in at 130 lbs... People often underestimate how much epoxy or vinylester resin and fiberglass cloth actually weigh.
 

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I'm planning the same thing but I want to stick to all composite so my plan is a fiberglass and carbon fiber dink with vinyalester resin. I'm shooting to keep the weight under 40 lbs. I happen to have a 7 foot pram mold but if I didn't I would build a quick and dirty pram mold using masonite with a little stitch and glue technique. There are plans out there if your not up to designing one yourself. I still plan to use my inflatable but this one will be designed with a removable seat so it can act as a cover for the rolled up inflatable. I never tow the dink so this one is just in case I need to kedge out an anchor or make a quick trip to shore and not bother blowing up the inflatable.
 

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Have a look at the designs from B&B, Graham has drawn some very sweet boats… I built a nesting Spindrift, really nice little boat that rows beautifully. If you built one from a material called Coosa, it could come in at a fairly light weight. I’ve never used that material, but have heard great things about it…

spindrift

Now, if you want to go ultra-light, have a look at Platt Monfort’s boats, they’re very cool… Whether they would stand up to the rigors of use as a yacht tender, of course, is another matter…

Geodesic AiroLITE Boats - ultra lightweight SOF canoes and boats; plans, projects and tutorials

 

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Please be aware there are BIG differences in rowing boats compared to trade offs like flat bottom skiffs that row like a brick.
 

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Like Denise said. The Nutshell dinghy from Woodenboat is supposed to row and sail well. They have a number of other designs that might do what you need - including a Whitehall, but that's another thing entirely. Chesapeake Light Craft is expanding beyond kayaks too, and might be worth a look. One caveat: I've heard that if you go too light in a boat designed to be capable of carrying a load (not a single scull, for example), the boat doesn't carry well between strokes. There's simply not enough inertia to maintain speed.
 

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Have a look at the designs from B&B, Graham has drawn some very sweet boats… I built a nesting Spindrift, really nice little boat that rows beautifully. If you built one from a material called Coosa, it could come in at a fairly light weight. I’ve never used that material, but have heard great things about it…

spindrift

Now, if you want to go ultra-light, have a look at Platt Monfort’s boats, they’re very cool… Whether they would stand up to the rigors of use as a yacht tender, of course, is another matter…

Geodesic AiroLITE Boats - ultra lightweight SOF canoes and boats; plans, projects and tutorials

I have a Spindrift 10N (N for nesting). I like it a lot. It's definitely light enough, especially once split into the two halves.

My only complaints are:
Low freeboard. Could another 3-4" there.

Low Boom for the sailing kit. The little boat has a huge sail for it's size, but the boom is a bit low for operating while sitting on the seat. Sitting on the bottom, you tend to get a wet bum (see freeboard issue). I planning on having the boom raised (shortening sail) a bit to make it more manageable. I don't race so I don't really care about top speed.

The spindrift does row and sail very well.
 

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As sailing dog said, the Chesapeake Light Craft Eastport Pram is a very light dinghy and these boats row like a dream. You can even add a sail kit if you choose.<O:p</O:p
<O:p</O:p
 

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I'm planning the same thing but I want to stick to all composite so my plan is a fiberglass and carbon fiber dink with vinyalester resin. I'm shooting to keep the weight under 40 lbs. I happen to have a 7 foot pram mold but if I didn't I would build a quick and dirty pram mold using masonite with a little stitch and glue technique. There are plans out there if your not up to designing one yourself. I still plan to use my inflatable but this one will be designed with a removable seat so it can act as a cover for the rolled up inflatable. I never tow the dink so this one is just in case I need to kedge out an anchor or make a quick trip to shore and not bother blowing up the inflatable.
The problem is that you've got demands for a light boat, but it has to be big enough to carry a load, durable enough to survive contact with docks, the beach, boats, etc. Build the boat too lightly and it won't survive the use it is intended for.

A glue-and-stitch plywood boat with kevlar reinforcement for the exterior to provide some abrasion/puncture resistance is a good compromise for a home-built tender. I don't think you can make one with carbon fiber and fiberglass that will weigh under 40 lbs. and be strong enough to be usable.
 

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SailingDog,
I built a dink out of the same mold 30 years ago with just glass matt and polyester resin. Also had a big Teak seat and rub rails. The weight as I recall was around 60 lbs. Since that time I have spent more than a few years working for a well known jet engine maker and have aquired materials and knowledge to greatly reduce the weight while increasing the flexural strength and stiffness. My test samples for this dink showed the hull weight at 18-20 lbs. using the carbon fabric I currenlty own. I added 20 lbs for the rub rail, fasteners, seats and flotation. This is not going to be a work horse dinghy but just an occasional use one for 2 people and a small outboard if I'm not using the inflatable. I will sacrifice a bit of ultimate strength to keep the weight down enough so I can hoist this up on deck without any assistance or mechanical advantage. 40 lbs is not a problem.
 

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My dinghy came in at 50 lbs without the benefit of carbon fabric and jet engine experience, so I think your goal is attainable.
However, if we reverse engineer this equation, does the fact that i have experience building dinghies mean that I am qualified to work on jet engines? ;)
 

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My dinghy came in at 50 lbs without the benefit of carbon fabric and jet engine experience, so I think your goal is attainable.
However, if we reverse engineer this equation, does the fact that i have experience building dinghies mean that I am qualified to work on jet engines? ;)
I just get to work on some of the material and design aspects. They won't let me touch the engine!
 

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Discussion Starter #17
Bljones, that D4 looks nice, but how did you build it with a finished weight of 50lbs? The finished weight in the plans is 75lbs.

SD I'll look into the ply option again. Tks. I still can't get my head around why it should be lighter than a foam sandwich. My boat's decks and hard dodger are divinicel sandwich to reduce weight so I just assumed the same would apply to the dinghy. Also, foam sheets seem to lend themselves to stitch and glue like plywood or even strip-planking, making the construction simple. Would glassing in some etxra foam ribs/stringers give it the stiffness and strength you feel is lacking in foam construction? I'd like to keep the weight down to no more than 50lbs, but it also has to be tough enough to be used as my main dinghy (after I happily torch the unruly and leaky inflatable one!)
Mirari, I'd love to make one in carbon fiber as well. Light and strong. A bit out of my skill set though....
 

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just wondering, once you factor in the cost of materials and the time involved, might it not be cheaper to buy one?
 

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Discussion Starter #19
QuickMick, I live in Brazil and we don't have the same range of nautical products here. I can't find a hard dinghy here, off the shelf, that is well made and light. If I were in the US I'd just go out and buy one! What I wouldn't give for a Westmarine here!
 
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