Interesting dinghy...

[Godot]

Somewhere, don't ask me where as I've already forgotten, I ran across a link to a gentleman's discussion of a one sheet boat.  That is a small boat built out of just one sheet of plywood.  His concept which is well thought out is called the prism (http://personal.eunet.fi/pp/gsahv/oss/oss.htm). 



The boat is 10' x 2'8"
With 6" Freeboard the displacement is 445 lbs
With 8" freeboard the displacement is 300 lbs
with 10" freeboard the displacement is 180 lbs

He gives all his info and it is easy enough to resize the boat.  The bottom end of looking ok by the authors opinion would be a short and fat boat of 6'9" x 4' which would have a maximum displacement of 1300lbs!

The boat is simple to make (he shows construction on his web page) and very adjustable.  It seems to be that you could cut this thing in half and have a light weight nesting dinghy.

Off course, with a nester there are a couple issues.  First, if you cut the boat in the middle, you would cut it right through where you would put the seat.  Low Center of Gravity is important, so you couldn't make a full size bulkhead to keep the water out.  I'm thinking that a short bulkhead of a couple of inches all around might provide enough space for a gasket material to keep the water out.

Along similar lines the boat would definitely have to be assembled and disassembled on deck for the same reason.  Separate, this wouldn't be two boats that join together, it would be one boat cut in two.

But I'm thinking this might make a reasonable small boat dinghy.  I think I'll sleep on the idea.

[Lynx]

Does not look like it will tow or stow on deck to well.

[Godot]

Does not look like it will tow or stow on deck to well.

Regarding towing, I have no idea.  I'm not sure what makes a dinghy tow well (very little experience with it).  As to stowing on deck, that is why I was thinking about cutting it in half to make it a nesting dinghy.  It's made out of only one sheet of ply.  Even with  some extra material thrown in to make it a nester, it can't weigh all that much.  And this version would only take up about 5' x 2'8" (okay, plus a little) nested together.

I was mostly thinking of the somewhat shorter and wider version.  I may be tempted to buy a cheap luaun sheet and throw something together as a proof of concept.  Either it would work, or it wouldn't.   In either case, it shouldn't cost much.

[Captain Smollett]

In my opinion, some of the small sailing prams designed by guys like Phil Bolger would make pretty good hard diinks for a small-boat tender.  Check out Dynamite Payson's Instant Boat books (there are several) for examples.  For the cost of a couple of sheets of plywood and a gallon or so of resin, you'd get a sailing dinghy that you built yourself.

I built a Bolger Gypsy; if I can do it, anyone can. The Gypsy is a beautiful little dory, but not really suitable for a small-boat dink (14.5 ft LOA).  I think a pramis the right "shape" for storage, durability and stability under sail/rowing.

I agree, Adam: I definitely would want the wider version than is shown in that pic; I bet rowing ashore in chop would be a nightmare in that particular version.

[CharlieJ]

B and B Yacht designs- Graham Burns and wife Carla.

http://bandbyachtdesigns.com/

Two lines of dinghies Pram and regular bowed, in fixed and nesting models, from 6'6" to 12 feet.

Our Minipaw is from them and has 3200+ miles under her keel  being towed, including 3  1/2 days offshore. That's the dinghy you see in the video I posted here.

[Godot]

I've ordered the two-paw 8 plans from B&B (http://www.bandbyachtdesigns.com/cpaw.htm), but I've only just, so I won't expect to see the plans for a little while.  I know you love your dink.  I wonder a little at the choice of the mini-paw.  It looks like you tow it everywhere instead of storing it on deck.  Given that, I would think a slightly bigger dinghy would be more suitable.  Especially if it has a sail rig.  I figure the two-paw would probably be happier in the water with it's extra length and sail, and as equally happy on deck (should I chose to ever do that) given that it nests.  I also have, somewhere, the plans for a 7'9" strip built Selway Fisher Ariel (http://www.selway-fisher.com/Otherupto10.htm#ARIEL) as well as Merrell's 7' Apple Pie dinghy (http://www.boatdesign.com/applepie/index.htm). 

I just have to admit to a bit of fascination with the prism.  The simplicity and economy of materials appeals to me.  The light resulting weight appeals to me.  And, frankly, there is something (I'm not sure what) about the looks which greatly appeals to me.

Lots of choices.  Lots of plans.  Which will be my next project and my next dinghy?  Time will tell.  I like around 7-8 feet for a towed dinghy.  I've looked at plans for a 5 footer that could easily store on deck (but may not carry just me, never mind stores and a passenger).  Nesting dinghies seem like a good compromise; but I'm a naturally lazy person and wonder how much work it is to assemble, launch, deassemble, and stow.

Whatever happens next, first I need to get a new house with space for a workshop!

[edit to add pictures...]

Selway Fisher Ariel


Apple Pie as built by Dale Austin


B&B Two-Paw

[CharlieJ]

We picked the mini because it would fit on the fore deck of our last boat, the 21 footer.

Unfortunately it will NOT fit on the foredeck of Tehani, due to the shape and geometrics of the fore cabin. Nor will any of the nesters. So we tow. I don't particularly care for that, but until we do something different for a dink it'll have to get drug along ;D

When you tow a dink offshore, you do so with the understanding  that is is disposable. If things get iffy out there, the dink would get cut away. So you split the jetties firmly understanding that.

We'd love a sailing dink too, but for longer trips, I think we'll eventually wind up with an inflatable- a small one that can be stowed in a cockpit locker.

It's one of those areas where we just have to keep looking til we find the answer.

[barnaclephill]

Hi,
This is my first post here.
I built a Simplicity 9Nester from B&B's plans and only then did I realise that the stern of the dinghy was too wide for the foredeck of the 26 foot yacht. So I made another front part, but extended it 8" and then cut off 8" at the pointy end. So now I have a canoe-stern'd dink on the foredeck that fits....quite well sort of. Attached is a photo of it unpainted, just epoxied.
It's a breeze to row or motor, the sail (cloth) wasn't perfect, and being narrower was less stable. The remedy is for buoyancy bags one on each side, outside the stern. The main problem I find is that I only have about 3inches beside my feet when I go forward, and the hassle of lifting it to anchor and the lack of access to the inner forestay attachment point. Anyway, look at the photo and say what you think.  If you know how to loft and reduce the size, especially in narrowing it with keeping all the shape, then teach me how.

[barnaclephill]

Forgot to mention that the 8" cut of the pointy end was done to attach the pintles and/or small outboard engine - obviously. Here's a picture of it assembled.

With the issue of it being too wide on the fordeck, and after building about 3 tenders, my next idea is to make an Origami folding dinghy of about 6 or 8 feet. It's located at  www.woodenwidget.com  and the plans are available. What does the forum think of folding dinghies as a viable and realistic tender?
Phill

[krissteyn]

Anybody thought abaout using LEXAN instead of plywood ?
using the correct adhesive and joining technique would create a bullet proof boat that you could see with ???

comments ?

kris

[Captain Smollett]

Lexan, hmmm.  Makes me think of merging a nesting dink idea with the hard dodgers we saw in the other thread.   ;D

[AdriftAtSea]

Couple of problems with doing this with lexan.  Lexan is subject to UV degradation.  It is also denser than water IIRC.  Also, most adhesives have problems with bonding to Lexan with any significant strength or durability.  It is also considerably more expensive than plywood. 

[Captain Smollett]

Lexan is subject to UV degradation.

So is epoxy.  The fix is to paint it.

It is also denser than water IIRC.

So is steel.  I think I've heard of boats and ships being made of that material.   ;D

Also, most adhesives have problems with bonding to Lexan with any significant strength or durability.

Not true.  The principal problem with gluing polycarbonate is moisture absorption.  If you dry it thoroughly before gluing, and use an adhesive known to work with it (such as those made by the IPS Corp.), it glues just fine to a wide variety of materials.  They use polycarbonate glued in place in aircraft applications, which I doubt would be common if it did not glue up well.

[Fortis]

I think the winning argument was the admirably understated "is considerably more expensive then plywood"...yes.....by a factor of 7 or 8.

I have seen a lovely sailing dinghy made out of plexi, it is indeed very clear, though it creates some weird lens effects at the bow. It was heat welded plastic along the seams and is used as a promotional display craft (though it works just fine) by a company selling polishes and hull coatings.

If I spent an hour or so I might be able to track donw a pic...but it is in the mess of the old alvaged hard drive data (you know, the stuff that seems so important to save when it crashes...and three years later you have barely had to fish anything out of now that you have a new comp?)


Alex.

[AdriftAtSea]

So is epoxy.  The fix is to paint it.

Doesn't that kind of defeat Krissteyn's original point about having a dinghy you could see through??? Also, I'd imagine that most finishes will have some trouble sticking to polycarbonate. 

So is steel.  I think I've heard of boats and ships being made of that material.   ;D

Yes, but boats and ships are rarely of such low freeboard, and not commonly towed as a daily practice.  If you make a dinghy out of lexan, and it gets swamped... it is most likely going to sink and break the painter. Last I checked, there were NO dinghies made of steel. Your point seems to be made just to be argumentative, and is moot.

I'm just curious—when was the last time you saw a steel dinghy??

Not true.  The principle problem with gluing polycarbonate is moisture absorption.  If you dry it thoroughly before gluing, and use an adhesive known to work with it (such as those made by the IPS Corp.), it glues just fine to a wide variety of materials.  They use polycarbonate glued in place in aircraft applications, which I doubt would be common if it did not glue up well.

From the following website:

Lexan is another type of plastic. The generic term is polycarbonate. Polycarb for short.  It's main differences to acrylic are that it is nearly unbreakable, bulletproof when thick. It's main drawback is, it scratches more easily than acrylic. The properties that makes it unbreakable, namely its elasticity and flexibility, give it a softer surface. Lexan is the trademark for GE's polycarb product.  Polycarb is less clear than acrylic but clearer than glass.  Also a thermoplastic, polycarbonate may be formed in various ways, similar to acrylic.  One property of polycarb that causes problems when heating and gluing is that it is more porous than acrylic and tends to absorb moisture from the air.  The moisture will boil when heated causing the sheet to turn white or bubble as the vapors expand, destroying the material.  In gluing, the chemical that bonds will react with the moisture and may cause the seams to turn white in places.  Very ugly.  The only way around it is to dry the material in an oven before heating or gluing.  This can obviously be a problem if you don't have a large oven handy. 
We really dislike fabricating polycarb.  Usually it is limited to uses where looks are secondary to strength such as machine guards.

It strikes me that gluing up a lexan dinghy would require a bit more in the way of technical resources than does making a stitch and glue plywood dinghy. I would rather be making a dinghy from materials where assembly is not so sensitive to curing issues, especially if I was going to be using said dinghy on a near-daily basis. I seriously doubt that you have the facilities to be making a Lexan dinghy... most of us don't. However, most of us do have the facilities to make a stitch-and-glue plywood dinghy.

Also, as a general rule, the parts on an airplane that you mention do not spend a good portion of their working lives immersed in salt water, do they?  Also, much of the polycarbonate constructs you speak of are held and supported by a surrounding frame, as they would in the case of cockpit canopies and such.  A low-cost Lexan dinghy is unlikely to have any such supporting frame, other than a possible thwart and bench.

I've also used the IPS adhesives quite a bit in the course of my working with a plastics engineering company.  Even the ones they recommend for ABS have statements about limited strength and adhesion as a general rule with polycarbonate.  Unlike acrylic, the polycarbonate does not dissolve/melt and then become a single, structural piece.

Finally, as mentioned in the quote from the plastics fabrication site above, Lexan has the additional problems of being relatively easy to scratch and rather flexible as materials go. It would probably only be a short while before a Lexan dinghy looked really beatup, given the conditions most dinghies are used under.

Finally, I notice you say nothing about my final argument against Lexan as dinghy material—expense. 

[bayracer]

Finally, I notice you say nothing about my final argument against Lexan as dinghy material—expense

A boat has always been a hole in the water. Anything that you save in one area will be spent in another area with any boat. Don't worry, be happy. I subscribe to the idea that with a boat if its what you want and works for you, then its not expensive at all.............the first time around.

[s/v Faith]

Hi,
This is my first post here.
I built a Simplicity 9Nester from B&B's plans and only then did I realize that the stern of the dinghy was too wide for the foredeck of the 26 foot yacht. So I made another front part, but extended it 8" and then cut off 8" at the pointy end. So now I have a canoe-stern'd dink on the foredeck that fits....quite well sort of. Attached is a photo of it unpainted, just epoxied.
.....

barnaclephill,

  That is a nice dingy.  8) I really like the way you modified it to fit your foredeck.  I am planning to go with the dink I have, but if/when I lose that or get fed up with it I think I will try to do the same thing you did.

  I had looked at the messingabout web site, and admired the various designs there myself... alas the time left vs the projects left makes it unlikely I will get a 'round tuit'.







_____________________________

WRT Lexan... I really like the idea of the 'glass bottom boat'.  I think if you had a panel of lexan that you bolted into a cut out in the floor (much like a through-bolted window) that might be an acceptable compromise.  If you did not like it, you could just glass the plywood back in place.

[Cmdr Pete]

Hey barnaclephil. That's some nice work getting a dinghy to fit the foredeck of a small boat

[David_Old_Jersey]

barnaclephill

Stowing the Dink on the foredeck, Great idea!

I guess it goes on the deck when on passage, but if just pootling around can be left on the hook / mooring or just towed........

[skylark]

I just "scored" a portabote for $450.  Its the old style double ender without a transom, but thats OK as I intend to row it, not power it.  I have been looking for a good dinghy for a long time and finally found one I could afford.  The nesting dinghy plans are nice but I already have too many projects that I am not finishing in a timely manner and that keep me off the boat in the summer season.