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  #41  
Old 06-30-2013
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Re: Motor vs Rowing inflatable dinghy...

I would alwsys go with a low hp motor
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  #42  
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Re: Motor vs Rowing inflatable dinghy...

Am thinking about building a hard rowing dinghy, maybe a nesting dinghy to replace my rubber ducky. I like the idea that the RIB can be deflated and stowed for long trips. It also rows quite nicely...BUT not like a well designed rowing hull like a Whitehall or Adirondack Guideboat or similar hull shape. Something like a Dyer dink shape is very seaworthy and would be great except for the weight. Does anyone have a hard dink that is seaworthy, slips through the water nicely, and is light enough to drag aboard without a major block and tackle operation?

I built a (plywood core) stitch and glue pram style dink a couple of years ago but it is neither very light nor is it very stable and seaworthy. It's ok to get from boat to shore on Lake Champlain in a protected spot but I would not trust it in a following sea on salt water or bring it cruising.

I'd like to lay up a very light foam core via stitch and glue and then cover with Kevlar, emulating the construction of some ridiculously light whitewater racing canoes I've had. The last 18' Sawyer weighed in at something like 45#. A boat as small as a dink, say 8', constructed with these ultra-light materials shouldn't weigh more than about 40#. I just need a design so as not to reinvent the wheel.
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Re: Motor vs Rowing inflatable dinghy...

Sounds like a good way to design a lightweight boat and save some money
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  #44  
Old 06-30-2013
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Re: Motor vs Rowing inflatable dinghy...

Every year some one gets in to trouble out here where the trades blow trying to row an inflateable upwind.
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  #45  
Old 07-01-2013
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Re: Motor vs Rowing inflatable dinghy...

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Originally Posted by smurphny View Post
I'd like to lay up a very light foam core via stitch and glue and then cover with Kevlar, emulating the construction of some ridiculously light whitewater racing canoes I've had. The last 18' Sawyer weighed in at something like 45#. A boat as small as a dink, say 8', constructed with these ultra-light materials shouldn't weigh more than about 40#. I just need a design so as not to reinvent the wheel.
These seem pretty interesting and similar to what you're talking about.

Dinghy plans for the spatially challenged

They're crazy light.
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  #46  
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Re: Motor vs Rowing inflatable dinghy...

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Originally Posted by shadowraiths View Post
These seem pretty interesting and similar to what you're talking about.

Dinghy plans for the spatially challenged

They're crazy light.
Thanks for the link. Those fabric boats are interesting but don't look durable enough. They're probably suitable for calm harbors. I am looking for a hull design to lay up in kevlar, a super tough, light fabric that is commonly used in whitewater boats. These river craft take a real beating. Polyester resin and standard mat/cloth are certainly plenty strong but the thickness required to attain adequate rigidity and strength results in a lot of weight. Kevlar can be laid up thinner because it is much stronger than traditional glass fiber. Marine Composites | DuPont? Kevlar®If the pram design were more seaworthy, it could probably be built light enough with these kinds of materials but I'm looking for a hull design that rows really well.
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Re: Motor vs Rowing inflatable dinghy...

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Originally Posted by smurphny View Post
Thanks for the link. Those fabric boats are interesting but don't look durable enough. They're probably suitable for calm harbors. I am looking for a hull design to lay up in kevlar, a super tough, light fabric that is commonly used in whitewater boats. These river craft take a real beating. Polyester resin and standard mat/cloth are certainly plenty strong but the thickness required to attain adequate rigidity and strength results in a lot of weight. Kevlar can be laid up thinner because it is much stronger than traditional glass fiber. Marine Composites | DuPont? Kevlar®If the pram design were more seaworthy, it could probably be built light enough with these kinds of materials but I'm looking for a hull design that rows really well.
Great points. And yes, while they're pretty and light, I agree. They do not seem to be something that would work well in anything other than very protected waters.
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Re: Motor vs Rowing inflatable dinghy...

Quote:
Originally Posted by smurphny View Post
Am thinking about building a hard rowing dinghy, maybe a nesting dinghy to replace my rubber ducky. I like the idea that the RIB can be deflated and stowed for long trips. It also rows quite nicely...BUT not like a well designed rowing hull like a Whitehall or Adirondack Guideboat or similar hull shape. Something like a Dyer dink shape is very seaworthy and would be great except for the weight. Does anyone have a hard dink that is seaworthy, slips through the water nicely, and is light enough to drag aboard without a major block and tackle operation?

I built a (plywood core) stitch and glue pram style dink a couple of years ago but it is neither very light nor is it very stable and seaworthy. It's ok to get from boat to shore on Lake Champlain in a protected spot but I would not trust it in a following sea on salt water or bring it cruising.

I'd like to lay up a very light foam core via stitch and glue and then cover with Kevlar, emulating the construction of some ridiculously light whitewater racing canoes I've had. The last 18' Sawyer weighed in at something like 45#. A boat as small as a dink, say 8', constructed with these ultra-light materials shouldn't weigh more than about 40#. I just need a design so as not to reinvent the wheel.
Smurphy, I went through the same thought process a while back. I wanted to build a decent nesting dinghy that rowed well, could carry 3 or 4 adults and that was stable and not too heavy. I thought about using divinycell sheets for stitch and glue construction. A former member here pointed out that I probably wouldn't save any weight since the divinycell sheets had to be saturated with resin and sheathed with cloth inside and out. It seems that quality thin 4mm or 6mm ply has a lot going for it in both weight, stiffness and strength. Long story short, I searched around for plans and found Danny Greene's Chameleon, a 10ft nesting dinghy that weighs 100lbs, rows and tows well and is very stable. I'm actually building it right now and the design is very nice. I wouldn't say it's the easiest dinghy to build (it has a bow locker, aft buoyancy tanks and other fiddly things to build), but it is well within the abilities of an amateur builder. I wanted to reduce the weight a little so I used slightly thinner ply (but quality Brazilian hardwood marine stuff) and slightly lighter cloth. I'm hoping it will weight 80 to 90 pounds when finished. This means each section will be a very manageable 40 to 45 pounds to raise on deck and lower into the water. My stupid inflatable must weigh this much...
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  #49  
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Re: Motor vs Rowing inflatable dinghy...

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Originally Posted by copacabana View Post
Smurphy, I went through the same thought process a while back. I wanted to build a decent nesting dinghy that rowed well, could carry 3 or 4 adults and that was stable and not too heavy. I thought about using divinycell sheets for stitch and glue construction. A former member here pointed out that I probably wouldn't save any weight since the divinycell sheets had to be saturated with resin and sheathed with cloth inside and out. It seems that quality thin 4mm or 6mm ply has a lot going for it in both weight, stiffness and strength. Long story short, I searched around for plans and found Danny Greene's Chameleon, a 10ft nesting dinghy that weighs 100lbs, rows and tows well and is very stable. I'm actually building it right now and the design is very nice. I wouldn't say it's the easiest dinghy to build (it has a bow locker, aft buoyancy tanks and other fiddly things to build), but it is well within the abilities of an amateur builder. I wanted to reduce the weight a little so I used slightly thinner ply (but quality Brazilian hardwood marine stuff) and slightly lighter cloth. I'm hoping it will weight 80 to 90 pounds when finished. This means each section will be a very manageable 40 to 45 pounds to raise on deck and lower into the water. My stupid inflatable must weigh this much...
The plywood seems to be the greatest percentage of weight in the usual stitch & glue process. What I'm thinking of doing is using 1/4" polyisocyanurate foam (if I can find it that thin) to establish a shape. With a couple of layers of Kevlar over exterior and interior, using some large, taped corner fillets, it should be possible to build an extremely light and strong boat. As in the Adirondack Guideboats, which were designed to carry for miles through the woods, caned seats would also reduce weight.

I may just try this using the pram I mentioned above as a plug, eliminating the need for a core except for the transom.
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Re: Motor vs Rowing inflatable dinghy...

Quote:
Originally Posted by smurphny View Post
Thanks for the link. Those fabric boats are interesting but don't look durable enough. They're probably suitable for calm harbors. I am looking for a hull design to lay up in kevlar, a super tough, light fabric that is commonly used in whitewater boats. These river craft take a real beating. Polyester resin and standard mat/cloth are certainly plenty strong but the thickness required to attain adequate rigidity and strength results in a lot of weight. Kevlar can be laid up thinner because it is much stronger than traditional glass fiber. Marine Composites | DuPont? Kevlar®If the pram design were more seaworthy, it could probably be built light enough with these kinds of materials but I'm looking for a hull design that rows really well.
I don't think you'll find a sweeter design than a Spindrift...

spindrift

I (over)built one about 10 years ago, so it came in a bit heavier than intended... If I were to do it again, I'd seriously consider using a lighter weight material called Coosa, instead of plywood...

Coosa Composites, LLC - Manufacture of high-density, fiberglass-reinforced polyurethane foam panels

After a trip south one winter, I quickly came to appreciate the downsides of a hard dink for a boat the size of mine... I wound up purchasing an Avon Lite RIB with a folding transom at that year's Miami Boat show, and have never looked back, it's the best all around compromise for me...

I still have the Spindrift, and use it on occasion when I'm just going out on the bay for an overnight, or a weekend, and will simply be towing it... For extended cruising and passagemaking on a boat as small as mine, however, I think hard dinks represent way too much drama bringing back aboard, and stowing...

Sure, it rows very nicely... but in anything other than a flat calm, it can quickly become a VERY wet boat... My girlfriend hated it, and as far as load-carrying capacity, it was minimal compared to an inflatable...

The amount of time spent re-launching and assembling the 2 pieces was always longer than expected, and could be a real PITA... As a result, I often wound up towing it, when prudence might have dictated shipping it back on deck would have been the more seamanlike option... Having said that, it does tow beautifully, and effortlessly...

It's really the stowage on deck that became the problem, for me... Despite it's compact size, it still represented a HUGE box on my foredeck underway, and obscured the visibility from the cockpit to a considerable extent... In a real blow offshore, I'd be very concerned about a boarding wave sweeping the foredeck, and the dink taking lifelines, stanchions, and who knows what else with it over the side...

Again, for one cruising in more protected waters, say the Chesapeake, or the mid-coast of Maine, it could make a a more suitable tender... but if you're going offshore and need to bring it back aboard, I think you need a mother ship of at least 40 feet or more to make these things work...

Others' mileage may vary, of course...

With just the bow section on deck, not too bad... Fit the stern section on top of it, whole different ballgame... Plus, it just really looked STUPID sitting up there, my inflatable stowed on deck is WAY less obtrusive... (grin)





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