I’ll be running a parallel blog on the website for all this, but I wanted to throw a down/dirty version on here as well:
Plug Construction began for the skiff on 12/5, beginning with the build of one big-assed table, 16x5.25. Level to as was not so important as being flat, as the CNC/CAD work we did beforehand pretty much ensures that the angles will be what they need to in relation to all the parts. Flat was far more difficult to achieve as finding a straight piece of lumber at Home Depot is impossible. In retrospect we should have had the longitudinal table beams (2x4x14) planed straight and to even widths, as well as the lateral joists. In reality we spent about three hours with a T-Square and a flashlight looking for any waves in the top as it was screwed to joists, then evening these out with a combination of wedges and screw pressure. No real pictures of this.
After that we threw all the CNC parts together (30 total), just to get an idea of how everything fit. Very surreal at this point to see six months of planning suddenly come together and start looking like a boat with less than five minutes of assembly. Had major issues with alignment of parts when we sighted down the keel. The bulkheads are symmetrical in their outer dimensions, but the registering grooves are not, meaning each piece essentially has a bow side and a stern side. We did this to help minimize the amount of MDF needed (only four sheets for the whole boat). We just forgot we did.
Next morning we began the process of closing in the central “coffin box” and excess spaces with 1/2” OSB. Part of this was done to minimize the foam usage - internal volume is 46ft^3, just the coffin box alone cuts 23ft^3 of space out. The other benefit was additional strengthening of all components, which by this point were glued to the table. Biggest issue here was the incredibly slow cure time of wood glue in the 50-degree temps. Eventually we switched over to standard gorilla glue which cured in about 1/4 the time. Even with a propane-powered torpedo heater running full-time (plus a CO detector) we were unable to achieve decent cure times on the wood glue - surfaces just stayed too cold.
As of this afternoon all major voids have been sealed off by OSB. The additional large cavities will be partly filled with scrap lumber laying around, cutting as much spare volume as possible, before expanding foam gets poured into the remaining space. Then begins the shaping/sanding process prior to everything getting a 3/4oz mat layer laminated over it.
I’ll throw some additional stuff into the blog when I get around to it, or you can follow along on instagram @PropGunOne. Hoping to get some foam poured tomorrow if we can get the climate control under... well... control.
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.
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.
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.
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....
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?
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.
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.
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.
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.
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.
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.
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.
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
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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