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Boat Build: Unicat 2.4

My old dinghy (a RIB) is at the end of its service life. So, I decided to build a new dinghy using the Maslow. This was actually one of my justifications for building a Maslow in the first place.

The panels for the boat are cut from 5mm plywood using a 1/8" bit. The Maslow is doing an excellent job of cutting them. I’m able to get within about 3" of the edges without any problems. Only the lower right corner has some accuracy issues. Overall I am very pleased with how it is cutting.

Pic for some of the first cuts and link to Unicat web site.

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Very interesting, look forward to seeing your progress.

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Me too! I can’t wait to see the results.

This will be a great project for me to learn from!

Yes, the Unicat is simple build. Ive been around boats all my life. Have several friends who have built all manner of watercraft, up to boats in the 50’ range, but I have never built a boat. So, one reason I chose the Unicat is that it is a simple build.

Update:

Dinghy panels are now assembled!

All parts were cut from 5mm plywood. For me this is intended to be a short-term dinghy and a learning experienced so I did not use marine grade plywood. It will be sheathed in fiberglass so should hold up a few years anyway.

The Maslow did a very nice job of cutting. I used a 1/8" down cut bit (1/4" shank) at about 13,000RPM, feed rate 700 mm/min, cut depth 2mm (makes quick work of 5mm plywood!). I was able to cut within about 3" of the edge and still cut quite accurately (except the far lower left and right corners where my Maslow often has some accuracy issues). The 1/8" bit makes a much cleaner cut in my experience than a 1/4" bit in such thin material. In the case of this plan I needed to make some slots the same size as the thickness of the plywood so could not cut these slots with a 1/4" bit anyway.

In order to cut this close to the edge, I could not use clamps in the area being cut because they would interfere with the sled. So, I counter sunk small screws along the perimeter of the work piece. This is needed for cutting such thin plywood as it does not lay as flat as thicker stock, and any unlevel areas will effect the Maslow’s depth of cut.

On my Maslow I built a “skirt” along the lower edge to support the bottom edge of the sled when cutting near the bottom edge. Without this support the sled will tilt when the edge of the sled goes over the edge of the work piece. This allows me to cut close to the bottom edge as well.

One problem with using the Maslow for this project is the fact it cannot cut to the edge of the material. In this case the “topside” panels use the full length of a sheet of plywood…right up to and including the factory edge. To work around that limitation, just in the case of those 2 panels, I had to shorten the drawing by a few inches, cut these incomplete panels, then cut the remainder separately. I drew the remainder up separately (only a few inches of the bow end of the topsides) and significantly longer than needed. This extra length was to allow me to make a “scarf” joint to add this small piece to the larger panels. Ideally a scarf joint would be included in the original design and cut by the CNC or at least cut using a jig. However, since it was such a small scarf joint (just a few inches across), I just roughed it out by hand using a big sanding wheel on an angle grinder. It came out better than I expected. I glued in place with epoxy then filled and faired the joint. All other pieces of the plan were cut completely by the Maslow.

The construction method is “stitch & glue”. Using this method you “stitch” the panels together by drilling small holes along their perimeter and connecting them via cable ties or wire. I used galvanized wire since I had plenty on hand, it can be adjusted if needed (unlike a cable tie), and in the end I’m not tossing a bunch of plastic into the environment. After stitching you then temporarily secure the panels into place with epoxy glue. This is a quick and easy construction method.

As of today I have stitched and glued the complete main hull and dry fit all the bulkhead and seat panels. The main hull panels went together quite well with almost no fairing needed. I did have to make some adjustments to the bulkhead panels, but these were just a matter of a few millimeters here and there (my jig saw blade is about 2mm thick so often just one saw kerf wide).

I think the accuracy of the Maslow made this process go much smoother and quicker versus hand cutting with a jig saw (common practice for amateur builders). When cutting by hand, the cuts are relatively rough and inaccurate. A common practice is to cut out side the plan lines and then fair the cut down to the line using a block plane/sanding. Doing this for every cut on every panel would have consumed a lot more time. Cutting with the Maslow almost eliminated this step. I just did some light sanding of cut edges to debur them. The only significant errors I encountered were either due to errors I made in drawing the plan and/or scaling errors between software tools that I missed correcting.

Pic attached of hull with bulkheads/seats dry fit.

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Looks great!

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Update:

I’m on the home stretch to completing the Unicat 2.4!

Currently filling/fairing the interior in preparation for painting. Will paint with a 2 part
epoxy paint textured over the entire interior, except the wooden trim pieces…these will be coated with epoxy and then varnished (epoxy does not have good UV resistance so the varnish is there to protect the epoxy).

After fairing the interior, I will flip the boat over and glass the entire exterior. Exterior will also be painted with 2 part epoxy paint, but without texture. Exterior wood will be treated same as interior wood.

After exterior is glassed, I will set up to paint the entire boat.

The bulk of the work on this design is all the interior joints. These are all fillet joints which are filled (filleted), faired, then bonded with fiberglass tape, then faired again…and there are almost 50 of them! There is one exterior fillet joint that runs the entire length of the hull.

What creates all these joints is the use of longitudinal and transverse bulkheads. The upside is that these bulkheads make the boat strong, stiff, and positively buoyant (they form compartments which trap air…so in theory, even if filled with water, the boat should still float).

I’m very pleased so far with the light weight (build spec is 35kg) and stiffness of the boat…even before glassing the exterior.

I did do some extra glass work which is not part of the original design. I glassed the interior of both bow and stern transoms, doubled up on glass tape along critical interior joints (like bow/stern transom joints to main hull), and added several layers of glass to areas on bow and stern transoms where I plan to attach lifting eyes (for raising the boat in davits). I will match these reinforcements at the lifting points on the exterior.

Picture attached of boat during interior fairing process. Filling and fairing is a significant amount of the labor and the Maslow is of no help there! (But it was great for cutting all the panels!).

Link to all pics of work progress and video of Maslow cutting panels.

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Very nice!! What wood are you using?

Sorry for the delayed reply.

5mm plywood for the panels. Did not use marine grade since this was my first build and I plan to sell the larger boat that this will be a tender to in a couple of years. However, it is entirely sheathed in fiberglass on the outside and coated with epoxy resin on the inside (with glass in reinforced areas) so it should last for years anyway.

Cedro Amargo (Bitter Cedar) for the solid wood pieces. We have a lot laid up curing for future furniture projects (commonly used for that here in Panama).

ITS A BOAT!!!

Fiberglassed the outer hull of the Unicat 2.4 yesterday, so it is now structurally finished. Could be dropped in the water and used, but I’ve still got a lot of fairing, painting, and outfitting planned.

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Done!

All done except for touching up some varnish work.

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Fantastic work! That turned out amazing! I’ve always been interested in building a boat of some sort, but also scared to sink hours of work in the pond because I missed some small detail. :sweat_smile:

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Thanks! It turned out better than I expected.

Unlikely to sink, but it was quite a bit of work. I didn’t track my time, but I guess ~100 hours.

Pretty sweet, IMO.

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Unicat is launched!

Hauled it over to Bocas del Toro (Panama), where my catamaran is docked, on my old Jeep XJ (another project) and launched it. Worked out great. Lots of reserve buoyancy. I tested this by letting it fill over half full with rain water and then standing my (fat COVID lock down ass) in it…no problem.



Link to all pics, and a Maslow cutting video, taken during build here:

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That is a beautiful build! It’s been fun to follow along.

Does the catamaran hull change the way it feels to row at all?

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Yes, it rows quite well. I think it is more directionally stable than would be a flat bottom or normal “V”.

The “hybrid” hull shape is a unique design feature. It tracks quite well and is easy to row. There are also a couple of keel skegs which help. You can give it a stroke, lift the oars, and it will just glide straight.

I think the shape also helps with stability. I can put my full lock-down overweight self (220lbs!) anywhere in the dinghy and it wont submerge the gunnel. It will respond significantly to the weight shift, but it wont flip or take on water.

It is surprisingly light (spec is about 35kg, but I’ve not actually weighed my build). Two people can very easily pick it up an move it around. The light weight also helps with rowing…it takes very little force to move it through the water.

The downsides are that it makes it slightly more complicated to build (very little really) and there are no really flat sections in the sole.

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