Building a Bolger Bobcat (Payson Tiny Cat) catboat from CAD on up

Hi Sonny. I am starting on a trimaran project, an 18 foot Scarab. I will be cutting panels from one side epoxy/fiberglass laminated polycore (honeycomb) sheets. Where would you suggest I learn how to redraw my offsets plan to a Fusion 360? plan. I have Fusion 360 and can’t see how I get there from my offsets plans. Thank you! Danny

2 Likes

Good question, @dmydlack, as the best way to get into offset translation is to start with the learning about the whole Sketch paradigm in Fusion360. Once you do that, the easiest thing to do is start by setting up a series of singular points that are measurement-constrained to a baseline (such as the bottom of the page and side) in the X,Y dimension that match your offsets. Then, take a bezier curve or spline and connect the dots, as it were. Once you do that, and close your entire ‘curve,’ you have a Sketch that you then can extrude/loft and make a solid. Once you have the solid, you then go to the CAM suite to make the toolpath. Sorry if that doesn’t make sense, but in short, the best way to start is to get real good at the Sketch portion! Cheers!

7 Likes

Thank you for such a rapid reply!

1 Like

Sonny, Thanks again. Was able to punch in my first frame in just minutes (plan offsets to Fusion 360 drawing.)

5 Likes

An 18’ plans-built trimaran is a great project to amortize the cost of a full-blown Maslow setup! I almost started building Ian Farrier trimarans a few years ago. I would start with something simple like a rudder, then an ama and after succeeding at those, bang out the other ama to really polish your work flow. Then you can tackle the central aka hull. This will then give you the confidence to start cutting out interior furniture components based on templates you make in situ .

I would absolutely love it if there was a stand-alone boat-building thread on this forum! I have a DXF file for a beautiful 8’ pram, can develop a file for a 12’ pram and am willing to develop one for a catboat or a Stornoway.

4 Likes

I can handle an 8 ft project so I may have to take a try at it after I get my other responsibilities out of the way.

Thank you

2 Likes

Take a look at my 8’ Eastport Pram project below…:sunglasses:

Midnight-Maker.com - Eastport Pram Build

There are plenty of other 8 foot dinghies that fit within a single sheet of plywood (e.g. bateau.com D5, etc.).

1 Like

Interesting to hear your thinking on this, MidnightMaker. I am building amas first in my cellar where they will just barely slip out the door when finished. After that, I’dd assemble the vaka in a backyard shed; by then the weather will be warm.
Rather than table-laminating one side fiberglass panels, I’m going to simply construct in bare polycore over the frames then laminate the outside surface in place. I’d like to minimize all the post tooling/cutting of cured laminate. Epoxy/fiberglass is so manageable and friendly as liquid and cloth, so unyielding as laminate, and so, so fundamentally evil as dust.
Cutting polycore panels should be much easier. I think. (there is the issue of melting - probably can control with tooling speed.)
My single biggest concern right now is measuring/cutting accuracy across each entire 8-foot panel. Since my Maslow is not yet in place, I’ve lofted out test panels in masonite and dry fit them over the forms (at 18’ feet, they are like wrangling wet spaghetti.)
Regarding accuracy, even small discrepancies result in non-matching chines.
Although, that’s not necessarily the end of the world; seams can be closed with bog and lightweight filler.
Google Photos
Another question is whether the eventual polycore pieces need to be cut as full-length (18’) panels (already seam-joined) or can be seam-joined in-place on the boat forms.
I have drawn plans for an 18’ long-frame with a ‘sliding’ repositionable Maslow. But that may not be necessary. I’ll know once I get my polycore and make some test cuts and joinery.
I’ve been asked why I don’t construct in Okoume. I have stitched and glued other boats and love, love Okoume. I believe, though, I can significantly reduce weight, raise strength and resiliency, remove threat of rot and do it all at the same price with polycore (based on my research of suppliers and prices.)

1 Like

Back in the 70s I lived on a small airport in Texas where a couple airline pilots we’re building a pair of 50 foot catamarans, one of epoxy & fiberglass, one dacron & polyester. The owner’s son sunk the dacron one in a storm off the coast of Mexico, lost track of the still floating glasser.

I got to ride down the highway to the Seabrook Marina on the fiberglass one as a wire pusher, plus visited a lot in the marina, but they didn’t take it out while I still lived there

Gosh, he’s on Twitter, mentions living on ocean going sailboat, but the last twit was in 2014. Gotta be in his 90s

2 Likes

I did a sailboat delivery of an old prototype cat from a popular monohull manufacturer that never went into production. It was from Florida to Texas. In the middle of the Gulf, we got hit by hurricane Irene. One of my least favorite things about deliveries is being on a time table that compromises your weather window. Anyway, we lost some boat cushions, but ducked into the ICW safely and rode out the worst of the storm by circling under a train trestle bridge. It acted as a lightning rod to protect the mast. By the time we got it to League City, the transom had delaminated pretty badly. Ugh…

I actually test-sailed a Precision 21 that I bought in Houston on Clear Lake (which is neither clear nor a lake). Sailed my Hobie cats off Texas City Dike a million times.

Love that area. Lots of good memories. Was there from 2000-2005.

4 Likes

That’s very cool! Thanks for posting this. I’m actually also going to the not inconsiderable effort of making tempered hardboard (masonite) templates of the 12’ dinghy I’m making. I’ll have to be careful to not get those templates mixed up with the 8 footer ones…

I think that unless you’re planning on a bright finish, it would be almost silly to build an 18’ tri with okoume. Your solution sounds spot-on to me. Traditional boat builders scarf planks in situ all the time. I think they plan their scarfs over a frame or mold so they have some clamping leverage.

Once you nail your spindle speed and feed rate, you should be able to cruise nicely. Do you plan on doing puzzle joints or just let the lam sandwich hold itself together over butt joints?

Another thought I just had, if accuracy is super important, and I think you’re definitely in that arena, is instead of tiling across an 8’ work space (where you might be off a 1/4" on the edges, just tile every 4’ and stay in Maslow’s sweet spot. It’s not that much more effort and could significantly increase accuracy for critical parts.

1 Like

This issue can be addressed with tooling as well. O-Flute bits have specially designed geometry to avoid melting plastics as much as possible. I would still recommend running some feed and speed tests to get it dialed in, but it shouldn’t be too hard to cut without melting. Of course, famous last words :wink:

The other tricky thing with polycore is that they are mostly hollow on the inside. I’ve worked with the stuff before in theatrical scenery and we had to run higher feed rates than I expected to avoid burning our bits or melting the core.

All this being said, I’ve really been admiring reading this thread. This has been a super cool read and now I want to try to tackle a boat myself. I’m still split between working from a Nick Shade kayak plan or a CLC Northeaster Dory. Knowing me, I’ll probably only get about halfway through working on both before I get distracted :stuck_out_tongue:

3 Likes

test the accuracy of your machine when you get it with cuts on cheap material.
With the most recent updates, I think we are far better than 1/4", I think we
are at about 1/16" to 1/32" now.

4 Likes

If we are truly that close, then you can totally cut out your own kit! If you’re using the stitch and glue method, you can literally pull the boat together to close most gaps. Heck, there are people building professionally cut out kits that have a harder time stitching their boat together than I did with the parts I cut out with a Japanese pull-saw. The key factor now is creating or buying an accurate file. @Sonny_Lacey has taken matters into his own hands and has created a very workable file from purchased paper plans, which should be an inspiration to us all.

2 Likes

Hey @Sonny_Lacey any progress? It’s starting to get a little warmer and the trees are budding here in the PNW. I’m feeling some pressure to make some serious progress on my pram since I’ll be starting teaching in a few weeks and we’re trying to get the house ready to sell this Spring.

Worst case scenario, I’m hoping to live vicariously through you for a few months…:sunglasses:

Evening, gents! …man, I wish I could say I was near my shop, but unfortunately work takes me to South Africa for the past couple of weeks. I hope to be back home and back at it by next weekend. Here, we are heading into fall…yes, I cannot wait to get back over the Equator to see spring in the Mid-Atlantic.

To date, however, up until I left, I got the centerboard trunk complete, sealed up and installed in the hull. The centerboard is all done, and lead weight is epoxied in. The inside and outside of the hull seams and frames are all epoxied in 3" tape. When I get back it’s time to seal the inside and then flip it to fiberglass the outside. I plan to do double-thickness glass on the bottom panel.

The rudder and spars are next for main parts construction, and then it’s getting near the end, really. I’m cutting out the (thick) rudder on the Maslow, but I am doing the spars on the router table, due to the fact that I am going to make them with the “birdsmouth” method. I plan to shimmy it out of the basement workhouse where the hull width (6’) will JUST barely scrape through the door… I want to work on it in the outside workshop (covered), but I am waiting for it to warm up a wee bit more so I won’t have to use the winter hardener in the epoxy and use the normal slow-cure mix.

4 Likes

Awesome! Thanks for the update. Sounds like you’ve made some serious progress. Don’t you hate it when work gets in the way of boat building?

It sounds like you’re still on track for a splash pretty soon. Would you be able to do a few seconds of video cutting out your blades? I think that would be a great visual representation of what you’re accomplishing. Did you use lead shot encapsulated in epoxy? I keep seeing people pouring lead and it makes me feel like I’m getting cancer.

The birdsmouth spars will be very cool. You could use your Maslow to cut the cradles that you’ll need to support the facets during glue-up.

I feel you about the door thing. I just built my shop specifically to build boats and I made the barn door 1" wider than the beam of the boat I’m building.

I’m seriously thinking about laying up my scarf joints this week so that even though its cold, they’ll have several days to cure before I can get back to them.

I’m also considering doubling up on the fiberglass on the bottom myself after holing my first boat on a small rock when beaching with crew up on the bow. I came in a little hot, but geesh…

Have you given any thought to a graphite or aluminum powder mix? I used graphite on my first boat and it turned out really well cosmetically. I can’t really say if it helped with abrasion resistance though. I may experiment with aluminum this time.

I’ll probably do some glass tape on some seams to beef it up. I want this boat to last quite a bit longer than the 4 years I got out of the first one.

I wish I could be there for the big flip! Post some pics when you get home. Take care!

1 Like

Hey @Sonny_Lacey,
What have you been up on the Bobcat build?

I am just lately back from a LONG series of overseas work trips, yet again. Luckily, I have been able to squeeze in Bobcat work every time I have a long layover at home, ha! I am pleased to say that the Bobcat is DONE! All that remains is to take it out to a park to dry-sail it and test the rigging before setting sail. I hope to do a launch up in the Middle River area of Maryland on the Chesapeake sometime within a week before I have to head out again.

Here are a few pics from the last couple of months. The gaff and boom jaws were Maslow-shaped, of course, but the spars themselves were laid up and drawn smooth by hand plane and saw.

Google Photos

Google Photos

Google Photos

Google Photos

Google Photos

Google Photos

Once I get the dry-rigging all tested, I’ll take some pictures of the “complete” setup and then another set of the launch. To be shared here!

Thanks,
Sonny

7 Likes

any chance you would share your pattern files?

1 Like