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Hard dinks, nesting dinks, and why we like them


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What if someone had plans for a really cool dinghy like the Hydrolite above but they wanted a longer version;  what would be the drawbacks to adding say 1 1/2 - 2" between stations?  I get that the beam to length ratio won't be the same and therefore it will look different, but I'm curious.  How hard is it to 'stretch' a design?  Is this how the longer of the two Nutshells was born?   

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It depends on the build quality. We've sold lots of prototypes for 7- 9000 dollars with rigs and foils. I think a really carefully built PT 11 should be worth $10,000, but that seems a bit nuts. It's

I built a tender for when I was a full time liveaboard. I had a couple of neighbors in the anchorage build variations on my original with varying degrees of success. I ran the cabinet shop for the lar

somersault 26 Newick

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1 hour ago, Leeroy Jenkins said:

What if someone had plans for a really cool dinghy like the Hydrolite above but they wanted a longer version;  what would be the drawbacks to adding say 1 1/2 - 2" between stations?  I get that the beam to length ratio won't be the same and therefore it will look different, but I'm curious.  How hard is it to 'stretch' a design?  Is this how the longer of the two Nutshells was born?   

If you’re interested look up John Marples’ Gull dinghy. It was featured in an old WoodenBoat article “Bagging the Gull” which was an introduction to the Constant Camber build method. It is a frameless 11’ design.

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5 hours ago, mckenzie.keith said:

Has anyone ever built or seen in real life one of the Frank Pelin Aquarius Nomad dinghys, either the 10' or 12' ? I feel like the 10' could make a hard tender for a 40-ish foot sailboat. For someone who wants a planing dinghy but not an inflatable.

https://pelinplans.co.nz/boat-plans/dinghies

 

Never seen one 

I noticed that they have plans for a pram

prams, blunt bow craft ,   make great  rowing  yacht tenders 

when made  of plywood they are light , cheap and Long lasting 

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12 hours ago, Leeroy Jenkins said:

What if someone had plans for a really cool dinghy like the Hydrolite above but they wanted a longer version;  what would be the drawbacks to adding say 1 1/2 - 2" between stations?  I get that the beam to length ratio won't be the same and therefore it will look different, but I'm curious

Speaking extremely generally, probably no harm and possibly some improvement.  Most dinghy's would be improved by more length.  They're short and wide because keeping them compact is such a priority.  Adding length, if you can afford it, will probably do the design no harm.

Building different length boats with the same station moulds is an old tradition.  There can be some gotchas, especially around the stem profile if it isn't lengthened as well, but the longer boats are usually easier to plank.

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On 10/7/2021 at 8:51 AM, 2airishuman said:

I just told my wife, "no new boat projects this winter."  Trying to stash my cash for a 38' cruiser.

Um, Rasp, I don't know how this works with cut files.  I have a local source for Okoume but they charge so much that it ends up being cheaper to have it shipped from CLC.  Can I get some place (like CLC) to cut ply to your files and ship it here or do I have to find a local place that will do it and schlep them five sheets of ply?

Do you have a BOM for this or at least a layup schedule you recommend? Is it in fact five sheets of 6mm Okoume?  (I am guessing)

Is the transom in the wireframes cut for a short shaft?

Sorry to be so long in answering you 2. Shortly after you posted your inquiry, I had to drive over to the Mississippi coast for the day and visited a guy who had seen this thread and said that he had a new big CNC machine and could work with me on kitting the Split-V dink. He says he has a reasonably priced source of marine ply in New Orleans so I stopped in to meet the guy and his partner and see the almost new CNC machine he had bought for a pittance on Ebay. I'll keep you posted on what we come up with and hope to have a good winter project kit soon! 

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  • 1 month later...

Rowed out the one of our barrier islands for a low key hammock camp last weekend. Pre-paint on the dinghy. 

The design is Joe Dolber's pepita. Drawn for a cruising world competition I believe. I got the drawings from duckworks last year and redrew them in cad. Laser cut the parts this summer and just finished getting it all put together. Probably one more sanding session then into the cabinet to see what colors of left over 2 part paint I've got.

 

 

 

 

565109001_PXL_20211213_1353396462(1).jpg

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  • 4 months later...

I need some advice.

I recently purchased a j32. It has davits. I have never used davits. I have a PT11 skiff. I am blessed. Tacoma to Prince Rupert return is my goal this summer.

I expect to tow the PT 11 mostly this summer because that one of the reason for having a hard dingy. But should I choose to swing it on the davits would I use slings under it attach lifting eyes to the boat.

The PT 11 has a 3/4" hole in the breast hook in the bow and 2 in the inwhale at the stern. Is a 3 point lift stable enough? If the davits are 6' wide and troughs points are 11" apart will that cause huge tension? I simple have no experience with davits so I don't know what folly would be.

The 2 boats are in different States at this time so I am advance planning.

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40 minutes ago, rustylaru said:

I need some advice.

I recently purchased a j32. It has davits. I have never used davits. I have a PT11 skiff. I am blessed. Tacoma to Prince Rupert return is my goal this summer.

I expect to tow the PT 11 mostly this summer because that one of the reason for having a hard dingy. But should I choose to swing it on the davits would I use slings under it attach lifting eyes to the boat.

The PT 11 has a 3/4" hole in the breast hook in the bow and 2 in the inwhale at the stern. Is a 3 point lift stable enough? If the davits are 6' wide and troughs points are 11" apart will that cause huge tension? I simple have no experience with davits so I don't know what folly would be.

The 2 boats are in different States at this time so I am advance planning.

I use 3 point lifts in my tenders. Usually a single eye on centreline forward and a pair of Wichard type folding eyes at or close to the chine or gunwhales aft.

I have 3 dinghies I use as tenders depending on what I feel like.

3 point lifts are plenty stable enough IMO.

I make sure that the lift points coincide with the span between davits so the falls are vertical. I don't worry about weight balance though, usually leave the o/b on the tender because I'm far too lazy to take it off.

I also add hard points to the tender hulls if I think it necessary.

The 'new' big tender is 2.9m long, the davit spacing is 1.575m and the transom width is about the same, give or take. All the dinghies stick out some. If you never go alongside it's never a problem.

FKT

FKT

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54 minutes ago, rustylaru said:

I need some advice.

I recently purchased a j32. It has davits. I have never used davits. I have a PT11 skiff. I am blessed. Tacoma to Prince Rupert return is my goal this summer.

I expect to tow the PT 11 mostly this summer because that one of the reason for having a hard dingy. But should I choose to swing it on the davits would I use slings under it attach lifting eyes to the boat.

The PT 11 has a 3/4" hole in the breast hook in the bow and 2 in the inwhale at the stern. Is a 3 point lift stable enough? If the davits are 6' wide and troughs points are 11" apart will that cause huge tension? I simple have no experience with davits so I don't know what folly would be.

The 2 boats are in different States at this time so I am advance planning.

That's what I do with mine - but just to lift it out. 

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1 hour ago, rustylaru said:

If the davits are 6' wide and troughs points are 11" apart will that cause huge tension?

I assume you mean 11 feet apart?  So 2.5 feet overhang on each end?  Yes, that could be a problem.  You could suspend an 11 foot long pole from the davits, then hang the dinghy on the pole?

How about this?

Hanging the PT Spear on Davits
http://ptwatercraft.com/blog/?p=1845

wells-swallow-on-davits.thumb.jpg.d3cbd3813755374cab4f45dda2f955d8.jpg

IMG_4845.jpg.458c33275bf153d4694aab14a7c8bc9d.jpg

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4 hours ago, rustylaru said:

I need some advice.

I recently purchased a j32. It has davits. I have never used davits. I have a PT11 skiff. I am blessed. Tacoma to Prince Rupert return is my goal this summer.

I expect to tow the PT 11 mostly this summer because that one of the reason for having a hard dingy. But should I choose to swing it on the davits would I use slings under it attach lifting eyes to the boat.

The PT 11 has a 3/4" hole in the breast hook in the bow and 2 in the inwhale at the stern. Is a 3 point lift stable enough? If the davits are 6' wide and troughs points are 11" apart will that cause huge tension? I simple have no experience with davits so I don't know what folly would be.

The 2 boats are in different States at this time so I am advance planning.

Seems like a J32 is a bit small to carry an 11 foot dinghy on davits. Of course it depends on the conditions.

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1 minute ago, mckenzie.keith said:

Seems like a J32 is a bit small to carry an 11 foot dinghy on davits. Of course it depends on the conditions.

Yes, I suspect I will mostly lift the dingy up at night so it doesn't bonk against the hull at anchor.

The j32 came with them. My first reaction was to just remove them. But I'll try them for a summer.

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Just now, rustylaru said:

Yes, I suspect I will mostly lift the dingy up at night so it doesn't bonk against the hull at anchor.

The j32 came with them. My first reaction was to just remove them. But I'll try them for a summer.

Yes. It seems sensible to at least try them out if they are already there.

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Why a spreader? I've never seen that done for a dinghy.

The inward compression forces using 2 lifting points to the gunwhales or the transom or a seat frame for lifting a PT11 dinghy are minimal. Simply doesn't weigh enough to matter.

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8 hours ago, Zonker said:

Why a spreader? I've never seen that done for a dinghy.

The inward compression forces using 2 lifting points to the gunwhales or the transom or a seat frame for lifting a PT11 dinghy are minimal. Simply doesn't weigh enough to matter.

That depends on what's in it (full of water being the worst case) and the "angle of the dangle".  Let's see the math?

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Since it's a nesting dinghy, I'd worry more about the connection fittings. They are very sturdy, but everything has a limit.  

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When the lifting sling is not vertical, the load goes up considerably.  Let's assume it has only enough water in it to match its normal displacement with two people - say 500 lbs.  That's 250 lbs. on each davit.  Then assume the vertical distance between the davit and the dinghy attachment points is one foot.  Given the 2.5 feet overhang, that's a triangle like this:

triangle.png.cd2ebe89e1c6908bcaca4a854452f993.png

Given a=1 and b=2.5, c = 2.69258

https://www.calculator.net/right-triangle-calculator.html?av=1&alphav=&alphaunit=d&bv=2.5&betav=&betaunit=d&cv=&hv=&areav=&perimeterv=&x=39&y=22

So tension on 'c' is 250 lbs. (the load on 'a') X 2.7 = 675 lbs. at a single point on the bow, split between two points at the stern (though stern bridle geometry is slightly more complicated).  Add shock loads when the boat bounces and/or more water and/or shorter 'a' value and the tension on 'c' goes up rapidly.

If the dinghy were full of water, I would guess a weight of at least 2,000 lbs.?

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On second thought, I believe my math is very wrong since tension on 'c' goes down when 'a' is reduced... that can't be right?  Oops!

I'll dig deeper but maybe @Zonker knows how to compute this?

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18 minutes ago, Zonker said:

Make sure your lifting slings are more vertical than shallow horizontal angles. 

Naturally, that's the key.  But the 2.5 feet overhangs make that difficult.

I dug up a Grasshopper model I wrote two years ago for two, three or four point slings on a 4,000 lb. boat, adjusted the numbers to match this scenario, and get nearly the same value: 673 lbs. tension on 'c' when 'a' = 1 foot.  This model makes more sense when 'a' is reduced, showing 870 lbs. tension on 'c' when 'a' is 9" (0.75 feet) and 1,275 lbs. tension on 'c' when 'a' is 6" (0.5 feet)

If the flooded dinghy weighs 1,000 lbs., it shows 1,346 lbs. tension on 'c' when 'a' is 1 foot, 1,740 lbs. tension on 'c' when 'a' is 9" (0.75 feet) and 2,550 lbs. tension on 'c' when 'a' is 6" (0.5 feet).

I remember the model was much more complicated than I expected so won't dig any deeper.  Why should I be the only one who cares... ?

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19 minutes ago, rustylaru said:

Thank you everyone for advice.

I think i will have to use some kind of spreader bar as the davits are just not high enough off the water to allow for a relaxed angle.

Broken wind surfer masts are relatively cheap and super strong.

By the way, my old model shows that if 'a' is 2.5 feet, same as the 'b' overhang giving a 45° angle, the tension on 'c' would be 354 lbs. (each, at both ends) with a 500 lb. dinghy.

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3 hours ago, Russell Brown said:

Hang it from the three corners and fill it with a garden hose. I'm kidding, but I think it would take it. 

What do you think of the extra holes through the gunnels as pictured above?

I have some 1/2" G10 tube I could line the holes with.

You were so clear in the building manual how important the gunnel reinforcement was to the shape of a nesting dingy. I really don't want to compromise it.

 

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Just now, ProaSailor said:

Broken wind surfer masts are relatively cheap and super strong.

I've used up my supply of broken carbon masts. I need to find more but all my hood river friends switch to kite boarding which was very selfish of them.

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After labor day, people have taken to just abandoning worn out gear around the launch sites.  Presumably clearing out the vans before they fuck off to Baja.  

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5 hours ago, Russell Brown said:

Hang it from the three corners and fill it with a garden hose. I'm kidding, but I think it would take it. 

Well, that alleviates my concern about suspending my assembled PT11 from the garage ceiling using a Harken Hoister.  Thanks Russell. 

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3 hours ago, ProaSailor said:

Naturally, that's the key.  But the 2.5 feet overhangs make that difficult.

Why?

Are you assuming that the lifting points will be at bow & transom? What makes that assumption reasonable?

As for the load, commercial davits aren't rated to carry 500+kg each so they'll collapse if the dink gets close to full of water. The better answer is to make sure it doesn't.

FKT

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7 hours ago, rustylaru said:

What do you think of the extra holes through the gunnels as pictured above?

I have some 1/2" G10 tube I could line the holes with.

You were so clear in the building manual how important the gunnel reinforcement was to the shape of a nesting dingy. I really don't want to compromise it.

 

The G-10 tubes are the way to go, but challenging to install, especially after finishing. 3/8" or 1/4" ID would be better. Keeping the holes inboard near the hull wouldn't weaken the gunwales, unless they leak water into the gunwales, of course. There are methods...

Where are you, Rusty?

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1 hour ago, Russell Brown said:

The G-10 tubes are the way to go, but challenging to install, especially after finishing. 3/8" or 1/4" ID would be better. Keeping the holes inboard near the hull wouldn't weaken the gunwales, unless they leak water into the gunwales, of course. There are methods...

Where are you, Rusty?

I'm in Arizona with the PT11. Heading north in a few weeks to Tacoma to get the big boat ready for the summer.

Maybe easier to drill at 3/8" with a chamfer and fill with fumed silica or high density filler and then re drill it at 1/4". 

1/4" spectra would still be overkill I hope. IMG_3395.jpeg.7436d19f6b4c54ffff86778cdf87bc19.jpeg

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No way to fit it under the boom or on the foredeck? It does nest pretty compactly for an 11’ dinghy. I keep mine under my boom. 

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18 hours ago, rustylaru said:

What do you think of the extra holes through the gunnels as pictured above?

I have some 1/2" G10 tube I could line the holes with.

You were so clear in the building manual how important the gunnel reinforcement was to the shape of a nesting dingy. I really don't want to compromise it.

Why lift at the gunwales?  Aft, bond a gusset with a hole in it down lower, at the first chine maybe, and use that.  Or put the gusset between one of the planks and the buoyancy box. Forward, put an eye (or two, if you want four points) with a backing plate and/or doubler under the bow deck.

The gunwale is the weakest part of the boat when it comes to resisting forces that pull the gunwales together.  Lift from somewhere lower and you'll benefit from hull strength, and will not have as large an angle from vertical on the sling.

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3 hours ago, Elegua said:

No way to fit it under the boom or on the foredeck? It does nest pretty compactly for an 11’ dinghy. I keep mine under my boom. 

Davits on a 32 footer when Rusty has a great nesting dinghy does seem counterintuitive...not to mention somewhat unfriendly to waterline trim, especially on a boat of this length.

If it were me, the davits would be gone if the PT 11 was the support boat...seems like there’s gotta be 6/7 feet of space somewhere on deck/cabin house aft of mast.
 

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The other problem with davits is that you need to have a low point drain hole for when the dinghy is in the stowed position.  Very often it isn't actually level so just a centerline drain may not be enough.  Very thin plywood is not conducive to off the shelf type drains as they all have a lip that stands proud and leaves a puddle of varying size depending on the design/angle.

 

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57 minutes ago, fufkin said:

Davits on a 32 footer when Rusty has a great nesting dinghy does seem counterintuitive...not to mention somewhat unfriendly to waterline trim, especially on a boat of this length.

If it were me, the davits would be gone if the PT 11 was the support boat...seems like there’s gotta be 6/7 feet of space somewhere on deck/cabin house aft of mast.
 

The biggest issue under boom on modern boats is clearance with the rigid vang.  It looks a bit tight on the J32.  I have to squeeze mine between a mid-boom sheet and a vang.  

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In my marina there is a too-small boat with a too-big hard dinghy hung on davits off the stern.  Apparently not a problem because AFAIK it never leaves the dock.  But yesterday I noticed that the dinghy hangs bow-down.  IDK why it doesn't fill with water???  Bung hole in the front?  Somehow it gets through snow and ice season - I never thought to look.

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5 hours ago, Veeger said:

The other problem with davits is that you need to have a low point drain hole for when the dinghy is in the stowed position.  Very often it isn't actually level so just a centerline drain may not be enough.  Very thin plywood is not conducive to off the shelf type drains as they all have a lip that stands proud and leaves a puddle of varying size depending on the design/angle.

 

I put 2 drain holes in my nesting dinghy, one in each section.

Now for extra yoga brownie points, reach those bungs when the dinghy is in the davits...

FKT

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Yes for our dinghy in davits (ok stern arch) I could JUST reach over the top and unscrew the bung on the inside. Took a bit of a leaning over the water and cursing.

Usually I'd have to do it on day 2 of an offshore passage when I realized I had forgotten to do it before hoisting.

Again.

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1 hour ago, Zonker said:

Usually I'd have to do it on day 2 of an offshore passage when I realized I had forgotten to do it before hoisting.

That sounds like having to untie the mizzen cover on my yawl. Everytime. And everytime I swear i fit a long enough rope to lead it back inboard, this is obviously forgotten when I put it back on. Nothing more funny than climbing out 1.5 meters on a skinny boom in a chop.

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