Atom 6.5 Divinycell

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lsheaf
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Atom 6.5 Divinycell

Post by lsheaf »

Hey guys,

I started constructing the Atom 6.5 a few months ago and have worked on it intermittently since then. I have no previous experience building small dinghies so I made a lot of mistakes which I’ll share here as I upload.

The primary purpose of building the dinghy out of Divinycell was to eliminate the worry of wood rotting and to potentially save weight.

Materials: this is just what I ordered, not how much I actually used

2 sheets of 3/8” H80 Divinycell - Merrit Supply
5 gallon kit of West Systems epoxy
Colloidal silica thickening additive
20 yards of 9 oz fiberglass cloth
Roll of 3” wide fiberglass tape
Box of round tooth picks
Box of chip brushes
Stir sticks
lsheaf
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Re: Atom 6.5 Divinycell

Post by lsheaf »

I started by tracing out all of the templates onto the sheets of Divinycell. Then cut them out with a sharp razor blade.

Since the stitch and glue method doesn’t work very well with foam, I decided tooth picks would be suffice for holding the main panels together while I tabbed all of the joints.

Once the main panels were tabbed together, I began laying fiberglass cloth on the inside and topsides. I also used toothpicks to hold the cloth tightly in place while fitting and trimming the cloth.

I then applied a generous amount of epoxy to the panel, placed the fiberglass, and wet out the cloth.

The biggest mistake I made during this layup was not removing enough excess resin between the foam and cloth (I used a fiberglass roller). It left lots of bumpy areas which now require additional fairing.

Lesson learned:
I discovered afterwards that the cheap yellow plastic spreaders are much more effective at removing excess resin that may get “stuck” under the cloth.
Attachments
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Last edited by lsheaf on Sat May 21, 2022 7:54 am, edited 3 times in total.
CapnK
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Re: Atom 6.5 Divinycell

Post by CapnK »

O oh oh - awesome! :shock: Been wanting to do similar for years! *Very* interested in finding out how she comes out weight-wise... :mrgreen: Good on ya' for using good core! She will still be a lot cheaper than an inflatable, and more durable. Love it. :D
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Re: Atom 6.5 Divinycell

Post by pmnfernando »

cool project!

will it be just a ferry for you (assuming you´r on a mooring) or a cruising dinghy, ie, something you carry aboard(deck davits)?

ive been looking for a cruising dinghy, but at 29 ft and not wanting to store on deck im quite limited. True Kit in New Zealand makes a couple of different lines of inflatable ones. really nice and sturdy built in Valmex (german fabric) but the downside is the price......
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Re: Atom 6.5 Divinycell

Post by lsheaf »

@Capnk - thanks for the response, I’m definitely looking forward to the final build weight too.

I did have an 8ft West Marine inflatable but it only last about 6 months before the transom fell off with my outboard included. :shock:

@Pmnfernando - It will eventually be my full time dinghy that will fit on the forward deck. It gives significantly more working room on the foredeck, unlike the inflatable.
I would reconsider the inflatable idea. They are never the same once they start leaking air and unless you’re getting a 10-12ft fiberglass bottom inflatable, they aren’t much more stable than this dinghy.
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Re: Atom 6.5 Divinycell

Post by pmnfernando »

I do not have the deck space to store a solid dinghy and i wont clutter what little is left.
The dinghy i was refering to is a completely inflatable one (including floor), the good thing is, it not glued, its welded, it isnt made of hypalon or pvc.
There is a british couple who have been using one for more than one year (they are full time cruisers)an they are pretty happy with it so far. im still a fair bit of time away from purchasing it, so i will keep an eye on their reviews.
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Re: Atom 6.5 Divinycell

Post by CapnK »

lsheaf wrote: Mon May 23, 2022 9:12 pmI did have an 8ft West Marine inflatable but it only last about 6 months before the transom fell off with my outboard included. :shock:
WHA..? lol Sometimes the best stories come from the worst 'happenings'. :D

I had one of those. Fortunately that did not happen while I had it!
Kurt and Barque, the CrewDog.
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Katie Marie, Ariel #422
Melelani, Islander 36 (shoal)

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Re: Atom 6.5 Divinycell

Post by lsheaf »

CapnK wrote: Tue May 24, 2022 12:06 am
lsheaf wrote: Mon May 23, 2022 9:12 pmI did have an 8ft West Marine inflatable but it only last about 6 months before the transom fell off with my outboard included. :shock:
WHA..? lol Sometimes the best stories come from the worst 'happenings'. :D

I had one of those. Fortunately that did not happen while I had it!
Haha yes it was a tragic day… the engine still rests on the bottom.
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Re: Atom 6.5 Divinycell

Post by lsheaf »

Next I begin fitting and tabbing the forward seat sides and back.
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Re: Atom 6.5 Divinycell

Post by lsheaf »

Does anyone know why some of these photos are posting in a different orientation than how they display on my phone?
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Re: Atom 6.5 Divinycell

Post by CapnK »

lsheaf wrote: Mon May 30, 2022 6:38 pm Does anyone know why some of these photos are posting in a different orientation than how they display on my phone?
I'm not sure, but would guess that your phone is reading the background EXIF data of the image(s), and so knows automagically to rotate it when you view it, without telling you it is doing so...

Thus, when you post it here, it gets shown in original (ie; 'as taken')orientation. Does that make sense?
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Re: Atom 6.5 Divinycell

Post by lsheaf »

Interesting,
Thank you for the in depth answer haha. It makes more sense now, I wonder if the forum has a plug-in that could automatically correct the image after uploading.

Anyway,

The next step was glassing in the knees, forward seat top and aft seat sides.
For these smaller sections, I experimented with pre-fiberglassing the panels (as suggested by James).
It was a bit more time consuming than fiberglassing over the larger panels which were held in place with toothpicks (forward sides and back panels), however provided noticeably more stiffness to the superstructure.
These panels were held in place by tooth picks but required pre-drilling on both ends of the mating surface for installation.
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Re: Atom 6.5 Divinycell

Post by CapnK »

I did look into the picture rotation issue, and it has been around for some time, even thru different versions of the Forum software wherein it was supposedly fixed. :)

So far I have not found a definitive solution, but if I do I will implement it ASAP!
Kurt and Barque, the CrewDog.
Sundance, '71 A-30, #429
Katie Marie, Ariel #422
Melelani, Islander 36 (shoal)

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lsheaf
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Re: Atom 6.5 Divinycell

Post by lsheaf »

@CapnK - I also did some extensive research on the Image rotation for PHPBB forums and it seems to be a rather complex issue. There was a piece of code I found on the PHPBB forum that could solve the issue but it doesn’t appear to be supported as a legitimate extension and is probably outdated by now (posted in 2018).

The next step in constructing the Atom 6.5 was adding the top of the aft seats, rub rail, and longitudinal stringers. I added a few extra layers of fiberglass to the aft rub rail to help support a small outboard engine.

All stringers and rubrail pieces were cut to length from strips of 1/2” wide x 3/8” thick divinycell.
I rounded the edges with 120grit sandpaper and a random orbital sander.

The next step is to laminate and install a solid fiberglass skeg and 4 small blocks for the oar locks to mount to.
I already fabricated these pieces but haven’t taken any photos yet.

After, I should be ready for fairing and

Would it be best to smear a thin layer (as thin as possible to cover any surface deformities) of West System’s 407 filler with a wide 6-8” spreader over the entire hill sides? And then maybe sand with a longboard?

Maybe I can post some closer up photos of what I’m talking it.
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Re: Atom 6.5 Divinycell

Post by atomvoyager »

Looks nice. You mentioned to me earlier that you had some ripples of thick resin under the single layer of outside fiberglass. If they are small you can add 407 as you described and long board it but if they are high I would probably sand them out and add a single layer of 6oz cloth instead and take care not to get puddles of resin trapped under it. That would add some needed abrasion and impact resistance to the single layer on there now.

For a motor it's best to glass in two small 1/4" thick triangular G10 gussets placed vertically about 8" apart to support the motor.
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Re: Atom 6.5 Divinycell

Post by Lloyd »

She is looking really good. Did you ever put her on a scale and come up with a weight? Eventually I will have to come up with a very small dinghy for my Bristol 27.
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Re: Atom 6.5 Divinycell

Post by lsheaf »

@Atomvoyager
I will sand down the hull sides and add another single layer of glass as opposed to adding unnecessary weight with 407 fairing filler.

@Lloyd
Hey Lloyd,
Current build weight with skeg and solid fiberglass oar lock backings is 39.5lbs (not shown in the most recent photo).
I would say I added a lot of weight by using a single layer of 1708 Biax on the bottom of the hull but it has given the hull incredible strength and provides extra protection against abrasion/holing on a rocky beach.
I also used an unnecessary amount of epoxy and fiberglass in some areas due to my own inexperience. I’m sure someone experienced can easily reduce the overall weight by 5lbs or more with proper technique.
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Re: Atom 6.5 Divinycell

Post by atomvoyager »

The next person to build might compromise weight to impact/abrasion resistance and use 1208 on the bottom instead of 1708 but I think it is a good idea to have something down there thicker than on the sides. The plywood version I built ended up about 59.5 lbs after all hardware and gunwale guard were added. Yours should be about 10-12 lbs or 20% lighter and more buoyant. As long as the extra cost is in the budget I'll build using Divinycell rather than plywood next time for sure.
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Re: Atom 6.5 Divinycell

Post by lsheaf »

Here is an image of the oar lock mounting blocks fiberglassed into position.

I laminated (4) 2” x 4” blocks that consist of 14 layers of 1708 Biax fiberglass.
I then cut these square with a miter saw.

After preparing the surfaces, I smeared colloidal silica behind each block and pushed them in position. I filleted the edges using West System mixing stick.

Then I applied 1 layer of 6oz cloth over the top.
Maybe a better choice for laminating the blocks could have been a higher density filler but maybe it wouldn’t fillet as well?
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Re: Atom 6.5 Divinycell

Post by lsheaf »

Update:
We begin filling imperfections on the hull with 407.
I found its easiest to long board the hull with 3m wet or dry sand paper. I’m sure it will yield better results than using only an orbital sander.

In order to firmly secure the dinghy for sanding,
I used a ratcheting strap from Home Depot. I attached the ends to a rail next to the shop and tightened the strap. If doing it in your backyard maybe you can find two small trees side by side to strap it to.

The transom and bow are a bit hard to long board so I put the dinghy upside down in the bed of my truck and strapped it down.
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Re: Atom 6.5 Divinycell

Post by lsheaf »

Update photo:
Post long-boarding
Current weight: 41.5 lbs
Hopefully I can take another half pound off by sanding more excess epoxy inside the boat.
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Re: Atom 6.5 Divinycell

Post by lsheaf »

Update:
I primed the dingy with 4 coats of interlux epoxy primekote and sanded the primer smooth.

I followed the primer with 3 coats of Snow White Awlgrip.

I am now installing the PVC rub rail
I found it was best to start trimming the rubrail at the stern. This ensures the PVC won’t be trimmed too short by the time you get to the bow.
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Re: Atom 6.5 Divinycell

Post by lsheaf »

With the rub rail installed, I next install the oarlock hardware.
Since I was trying to make a weather window to the next island, I only added Kiwi Grip nonskid to the floor area and installed 1 deck plate in the center compartment. I used a Wichard bow eye fitting to attach my painter to.
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Re: Atom 6.5 Divinycell

Post by lsheaf »

So far I’ve used the Atom 6.5 throughout the entire British Virgin Islands.
Since it is so light and has a flat bottom, it towed very easily, even in short choppy seas.
I’ve mostly rowed in and out everywhere, sometimes with a second person loaded with groceries. It has done very well.
I found it difficult to row in with 25 knots of wind so I opted to buy a 3.5HP Nissan Marine outboard engine. I believe it weighs around 29 pounds. I’m pretty sure with a tiller extension I’ll be able to get the boat to plane.

One addition I may want to add is a drain plug. For me, Kiwi Grip tends to collect dirt quickly. It would be nice to be able to brush the Kiwi grip and flush the sole with water while motoring around with the plug out.
What do you guys think?

Another addition I want to make is some type of hoisting Bridle to lift the dinghy out of the water at night.
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Re: Atom 6.5 Divinycell

Post by atomvoyager »

Thanks for the report. If you sand the kiwigrip with 120 grit it will be easier to wipe clean. I don't think motoring with a drain plug out is going to work since the loaded waterline is too low and it's not likely you feel like motoring while cleaning. A sponge and bailer cup will work better than a drain plug. It will get decent speed but I don't expect it to truly plane with 3.5hp.

For the times you want to hoist it horizontally you already have the 3 point bridle - tie the ends of the two stern lines to a shortened loop in the painter. I always have stern lines rigged anyway because in port I keep the dinghy alongside with a fender and use the bow and one stern line tied to deck stanchion and cleat so it never bangs the transom as it would trailed behind. Otherwise, I hoist it vertically by the painter to stow on deck because it's faster and easier to rotate.
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Re: Atom 6.5 Divinycell

Post by lsheaf »

Okay I’ll try giving it a quick sand.

I ended up installing a drain plug anyway. I’m not able to go fast enough for water to drain.

The drain plug is still good when pulling it up on the beach and using a small bucket to rinse it out though.
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Re: Atom 6.5 Divinycell

Post by Lloyd »

Turned out to be a nice looking dinghy. Saw your other post where you are out and about cruising with it. Love it.
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Re: Atom 6.5 Divinycell

Post by Eidoloneliz23 »

Isheaf! Nice work, that’s a fab looking dinghy.
How did it tow?
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