# Captive 14 Plug/Mold Build



## Guest (Dec 10, 2018)

Nice! Here she comes! Looking forward to the build, good luck with your venture maybe we’ll meet at a show where we are both showcasing our babies!


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## trekker (Sep 19, 2015)

Good stuff. Where is the blog ?


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## Pole Position (Apr 3, 2016)

trekker said:


> Good stuff. Where is the blog ?


https://captive-skiffs.com/index.php/blog/


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## Sublime (Oct 9, 2015)

Nice. I hope to get around the elusive “straight board from the lumberyard” unicorn by utilizing ripped sheets of MDF as the edge of what my stations sit on. Even if you planed the 2x4s, chances are they are still going to keep fluctuating. I’ve seen some real bananas at the hardware store. They didn’t leave the mill like that. They arrived at the store in a nice neat bundle. But cut those straps and give them a few days and bam.


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## Indoman (Jul 25, 2013)

Cool! 

I believe I read somewhere that 6hp was max....13-15mph?
Will it actually plane at that speed?


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## PropGunOne (May 27, 2018)

The 6hp I believe is on the slippery dick design. Measurement-wise this skiff maxes at 15 per the rules. One of the big goals of this was sub-10 HP and decent speed. Hoping low twenties with an 8HP, after that we’ll see what happens.

As for the wood, the original plan was to use shorter, theoretically straighter lengths, but seeing the 14’ lengths we couldn’t pass it up. In retrospect another sheet of MDF, ripped and laminated, is probably a pretty good way to go.


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## Pole Position (Apr 3, 2016)

Sublime said:


> Nice. I hope to get around the elusive “straight board from the lumberyard” unicorn by utilizing ripped sheets of MDF as the edge of what my stations sit on. Even if you planed the 2x4s, chances are they are still going to keep fluctuating.


Metal studs would work as well, and are available in longer lengths than sheet mdf


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## PropGunOne (May 27, 2018)

If the table construction was phase one, and assembly, squaring and gluing of the frame was phase two, then that means...

*Phase Three - Warm Liquid Goo Phase*

Started trying to create a decent method of semi-accurately pouring expanding foam up the vertical side of a sheet of wood. First method involved a sheet of 1/4” ply held up against the sheer line with scrap wood used along the bottom of the spray rails to sort of guide the expansion. The goal isn’t a perfect pour, but one that extends past all stations by maybe an inch, giving enough to carve into and filling all voids. First method worked okay, but it was messy, difficult and slow. Nevertheless, we kept trying it through about eight different sections until we decided it sucked as much as we suspected. Results were okay, though:
























Method two was going to be the use of tape, spanning each section and leaving ourselves a hole to pour foam into, sealing the hole before expansion began. This we abandoned before even attempting, as the time to tape would’ve been ridiculous.

Method three was to take Saran Wrap in two lengths, each slightly longer than one station gap, and adhere the two pieces vertically with a piece of duct tape, like so:










This worked better and ran much more smoothly, allowing one person to do all the work, instead of the two needed to pour foam and hold plywood in place. Much cleaner, better expansion, less waste (there really is none yet) and a faster pace.

Unfortunately the real job came calling and we stopped work for the day. Hoping to see above freezing temps soon as the torpedo heater is struggling to hit 65F. Expansion has been good nonetheless, getting about 25x-30x the original volume, as anticipated. Waste at this point is minimal because all trimmed material is returned to the hull gaps to help fill voids and take up space. Also useful was a load of crown molding I’d ripped off a ceiling a few weeks ago....


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## el9surf (Dec 23, 2008)

Looking forward to seeing this come together. I don't understand why you poured the foam. How are you going to get it even to lay glass down? Will the foam expansion push on the spacing of the bulkheads?


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## yobata (Jul 14, 2015)

There are easier ways to do this, for example, build a foam core one-off (but usable) skiff and then make a mold out of it ("splash" it). You can then sell the one-off and recoup some cash.


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## DuckNut (Apr 3, 2009)

Your making a mess.

Buy something like this https://www.homedepot.com/p/Touch-n...Component-Spray-Foam-Kit-4006022200/204962748 and save time and money.

Cut small boards and glue them to the stations an inch inside the outer edge and then spray. You can use cardboard as well. You have too much space being filled and foam is expensive.

If you don't want to buy it see if there is a foam insulator dude in your area and hire him for 15 minutes.

That is a really cool design. I wish you well with the project.


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## PropGunOne (May 27, 2018)

Most of the space is being filled prior to pouring the foam, three two gallon kits should be sufficient to foam out what we’re measuring as a 46 ft^3 hull. As for deformation, the framework itself is cut to very tight tolerances, so much of its strength comes from that. All joints are glued and the scrap wood is cut to further reinforce bulkheads. You could stand on it right now and get no deformation. Granted, it’s probably over-engineered and using cardboard to span the remaining distances is probably fine, but we didn’t want to have to worry about it flexing when it gets shaped out. Always a better way to do things though, kind of learning as we go along.

We gave serious consideration to doing a one-off, but as the end goal was an absolute minimum of two hulls, with a goal of at least ten (just to get more data and better prove the concept) we decided to go straight to the plug. Couple other reasons too. If purely getting a hull on the water was the goal then a one-off would have almost been complete by this point I would think. 

We were discussing it the other day when someone asked about shipping costs from our CNC guy... some guys are having a hard time finding someone to cut stations on a router. The neat thing is that the stations are thin enough that we could feasibly puzzle-piece the longer segments, mainly the keel guide, and cut them short enough to fit into a box. That, plus some CNC divinycell cutting if you wanted to make things really easy, and you could sell this thing as a kit ready to assemble. Programming is a significant portion of the cost, so once you set that up the price of repeated cuts should drop significantly.


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## PropGunOne (May 27, 2018)

el9surf said:


> Looking forward to seeing this come together. I don't understand why you poured the foam. How are you going to get it even to lay glass down? Will the foam expansion push on the spacing of the bulkheads?


It’ll be shaped out with hand tools/power sanders to match the bow stations, then glassed with 3/4 oz CSM for strength, then faired and primed with duratec prior to polishing.


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## DuckNut (Apr 3, 2009)

Question:
Why would you build the plug, then build the mold, then produce a hull?
Wouldn't you want a hull to tweak and ensure the handling is what you are after before making the mold?
There is another builder who did not make a test hull first and they found that their production hulls would bow plow. then they redesigned it and started producing hulls again only to quit 18 months later due to the bad rap of not getting it right the first time.

My posts may sound like I am sideline quarterbacking you - that is not my intention. My intention is make you think about what you are doing and the ramifications of those actions. This will help you down the road with your business. I realize this is a new endeavor for you and I really hope you make a career of it but you have to make smart decisions so the career will be there for the taking.


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## PropGunOne (May 27, 2018)

We talked about going that route for awhile, but in the end decided that we wanted to produce at least three boats. We also wanted the plug/mold build experience as it is new to us on this scale. We figured on needing at least that many hulls to really get good test data. Additionally, a foam sandwich hull would behave somewhat differently (though not vastly) than a female mold hull, as the layups are different. This lets us play with those layups as well. On top of that, computers will tell you all kinds of neat things about a model.

The bad thing about having a real, full-time job is that you can’t mess around with boats all day, but the good thing is it means you don’t have to rush things to market to recoup investment costs. Right now this is about half personal hobby and half future boat for sale. If it performs the way we want it to then great, we’ve got a mold ready to go. If it doesn’t we have a few hulls we can mess with and modify and remold relatively fast, since we’ll already have the experience of molding it once. If the whole thing should, for some reason, be a complete bust then it’s still not that big a deal, just out some cash, which I figure is worth it for the experiences alone.


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## el9surf (Dec 23, 2008)

We need an update. Really wanted to see how this one came out.


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## PropGunOne (May 27, 2018)

Sorry, one coming soon. Xmas/New Years and eight days in Costa Rica put it on hold for a bit. I’ll be throwing some pics on instagram here shortly. Just sanding and filling at this point. We are running into an interesting issue with the hard chine... trying to determine whether the drawings indicate a long, straight edge or one with a slight curve to it. More to follow soon.


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## Pole Position (Apr 3, 2016)

PropGunOne said:


> We are running into an interesting issue with the hard chine... trying to determine whether the drawings indicate a long, straight edge or one with a slight curve to it. More to follow soon.


If I'm not mistaken, I think some of the Conchfish builders had the same issues / questions -- weren't sure if the hook was intentional or not; maybe one of the builders can chime in or CM finds the internet


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## Chris Morejohn (May 12, 2014)

In WiFi now for a few days. On this design the lower chine curves up slightly forward.
But at the transom area it tilts back up aft. This will allow the bow to trim up.
The sponsons are for at rest stability. The aft up tilt aids in poling too. Won’t get drag from a strait bottom like most skiffs.
The plug is really coming out great, and we have all benefited from Jon taking the leap of trying something different.
Well done Jon


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## PropGunOne (May 27, 2018)

Well the leap got interesting today. Had the plug perfect and ready for CSM two days ago. Went out to glass this morning and discovered... low spots, high spots, small cracks in the filler... all kinds of stuff.

What happened was about a 35-degree temp swing over the last 24 hours. Didn’t consider the thermal expansion abilities of 2-part foam. The amount of movement is minimal... almost imperceptible, but it’s enough to throw fairing all of of whack. Basically the areas between the bulkheads dropped down about .25mm. We could fill back in and re-sand, but then when temps rise again everything is off once more.

Trying to figure out the smartest move forward: build up a CSM “exoskeleton” on the plug to give us a hard, (hopefully) unflexing surface, then fair out from there and prime/polish, or cut the losses, call it an interesting experiment, and foam-sandwich our way through it.

The pic above is of that hard chine from before much sanding or shaping was done. Ignore the roughness. Tried to get an angle that shows the curve in its most extreme form. Really not as harsh as it looks. In the foreground you can see the upwards sweep. That sweep then straightens out until it hits a point about even with the transom, then it takes a very slight concave shape towards the back of the sponson. Think it’s an artifact from CAD conversion, and instinct tells me it should be a long, straight shot back, but when you sight along it it looks aerodynamically “correct,” if that makes sense. Almost like the shape itself should trim the chine downwards. Hard to explain. Like the anhedral shape on the back of an F-4.

Still debating what to do going forward.


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## Guest (Feb 9, 2019)

How long did you allow foam to cure before cutting and shaping? The stuff shrinks on it’s own w/out thermal changes! I would throw a layer of 10oz cloth and a layer of 1 1/2oz csm on it then fair it out. The cloth will resist sag better than the csm.


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## Guest (Feb 9, 2019)

Whatever you do, your gonna have to move fast from fairing to mold making if temps are giving you this much of a variance!


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## PropGunOne (May 27, 2018)

Boatbrains said:


> How long did you allow foam to cure before cutting and shaping? The stuff shrinks on it’s own w/out thermal changes! I would throw a layer of 10oz cloth and a layer of 1 1/2oz csm on it then fair it out. The cloth will resist sag better than the csm.


Over a month at this point. Certainly had a full cure to it. Seemed like every time we sanded we’d ind more high or low spots, but overall it was getting to be about perfect. That was through constant, slowly rising temps. Saw 80’s on Tuesday, back to 40 this morning. Cloth is a good idea, mat certainly has no real shape-holding ability.


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## firecat1981 (Nov 27, 2007)

This was one of the reasons DuckNut was alluding to building a functional prototype first then splashing off of it. You would get the exact same results plus one hull. 

I've played with foam shaping similar to what you are doing and learned the pitfalls of using the 2lbs foam. It can regularly expand and contract no matter the age, so it's not suitable for a skin backing, it needs to be braced well. Because you essentially have no real core, atleast one you can rely on, you need to build up a glass skin stiff enough to stand on its own. 

Thin cloth will flex under the weight of the mold layup later on. Your best bet I think to get a truly fair plug that won't buckle and ripple, is several layers of glass. Maybe a few layers of cloth topped with csm at a minimum.


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## CurtisWright (May 9, 2012)

Icarrumba... Maybe rent a portable HVAC system for your Garage? Keep the temp and humidity constant long enough to re-fair and make a mold?


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## el9surf (Dec 23, 2008)

That or wait for more consistent temps in a couple months


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## jonny (May 1, 2007)

Ah the joys of skiff building. You live and you learn. You can get plenty of issues even if you do a cold mold one off. When you pull those off the stations. You can get a lot of movement in the hull. Once the interior support is removed. There are pros and cons to both. I personally like the cold mold approach. Due to the ability to work out issues. Before committing to a mold. I wonder if a different fairing compound would help. Something like that bondo with glass in it. That might have a bit more structure to it. Maybe enough to hold the foam in place.


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## DuckNut (Apr 3, 2009)

@PropGunOne - any progress being made?


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## DuckNut (Apr 3, 2009)

Also, on your website you are selling plans. Are these Chris's plans or your plans?


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## DuckNut (Apr 3, 2009)

Abandoned?


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## KurtActual (Sep 25, 2017)

Saw that this was popped off the mold.

Really interested in an update.

https://hogfishdesign.wordpress.com/2020/04/28/captive-skiff-coming-alive/


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## PropGunOne (May 27, 2018)

Hey guys sorry... forgot I left this thing unattended for as long as I did. I have a habit of short/long term abandoning projects and then getting mad enough at them to attack them at a ridiculous pace.

The plans I own, but Chris did all the drawing. I just commissioned and went to him with the ideas. He wrote it up awhile back. The build is on the ‘gram... @PropGunOne. Also updating the blog. I’ve stayed away from here because honestly I’ve been too dang tired from working on it. Back at work (real work) temporarily so I’m catching up on my internet duties. Plan was to get it near finished, then start a thread with a FAQ section leading it off so no one has to search through 14 pages for answers. Give me a day or two and I’ll get one running. Minus a ton of fairing she’s not all that far away from being a functional skiff.


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## bryson (Jun 22, 2015)

Really cool lines on that skiff. Glad to see you back at it -- looking good!


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