SCARAB 22 MODIFICATIONS
From the beginning of the construction, I revised the design and incorporated some modifications to the Scarab22. Some are the result of my experience in composite design in aerospace and others came up during the fabrication. Initially I wanted to follow the plans very accurately for a change. I had never built a boat exactly as designed before and wanted to try. Well, I could not! Next boat I will design it completely myself and it probably will be a folding catamaran.
During the Scarab22 built, I started the design of another trimaran, the OB650. I developed a building method that was easier and went through all the necessary stability calcs and some structural calcs also. After sailing the scarab this OB650 project stalled, altough today I still think it would be a good cruising folding trimaran design.
| MODIFICATION, in random order | REASON |
| Centerboard pivot position and case shape: The pin was lowered to increase the control lines leverage and reduce the slot length. Also, the pin was replaced by a hollow FIBERGLASS tube 1 inch in diameter. The complicated pin cover in the plans was totally eliminated. |
The slot length was longer than necessary. I was able to go to a 1:1 purchase instead of 2:1, reducing the clutter inside the trunk. |
| Cockpit coaming shortened. | The shape in the plans is quite useless. It is too low for back support and is a tripping hazard when you leave the cockpit. I was able to install a longer mainsheet traveller. The remaining coaming is still quite useless but it is pretty! |
| The whole rudder assembly is my design | The design in the plans is 1970 style... I wanted something stiff and light so I went full carbon. |
| Float transon shape changed | I increased the aft volume of the floats and created a shape that mimics the centerhull. It is also quicker to build and stronger. |
| Pop-top construction and lift geometry changed. | My fabrication method is way faster than in the plans. I basically build the cabin top in one piece and cut the top from it. To open it, I removed all the metal pieces and replaced them with simple fiberglass props. So far it works great and I have standing headroom in the cabin. It also looks real cool when it is opened! |
| Front and rear spar shape and composite design changed. | The front spar shape in the plans prevents the access to the fwd berth. It is too high. I curved it down. The rear spar shape is too thin in the center, creating a flexible section. I increased it to the full depth of the cockpit. The inertia is better and it is also easier to build. The fiber directions is not optimum in both spars. I redesigned both spars using FE analysis and added a lot of unidirectional carbon fiber. After 3 years of sailing they are rock solid. |
| I redesigned completely the aluminum folding struts. | Rays's design is full of welds and does not have plastic bushing. Also, I checked the bending stresses in the pivot pins and they were too high for my taste. I optimized the shape and the spacing of the struts and upgraded 4 pins from aluminum to titanium. Erik Precourt made the parts using my design and they work beautifuly! |
| I redesigned the forestay fitting. | I wanted a fitting better suited to a roller furler and also I wanted a pivot point for the bowsprit and a place to hook the trailer winch strap. |
| I redesigned the trampoline attachment concept completely. | The method described in the plans required a lot of bracket fabrication and was not strong in my opinion. The shape of the cross beams and of the float deck and hull sides lent itself naturally to what I did: sail track on the hull and floats and eyestraps on the beams. It is really nice! Check the pictures. |
| New bowsprit design | When I got the drawings, bowsprit was not designed yet. I did my own design, using the same aluminum tube than the boom. It is fixed on the forestay fitting. I am using my Olivier Links fittings to attach the lateral stays. After 2 years of sailing I shortened the tube by 12". The boat is more balanced now with the screecher. |
| Center hull assembly: I assembled foam panels with fiberglass only on the INSIDE surface. I glassed the OUTSIDE in one go, just like the Farrier's, but it is easier since the panels are flat (hard chine boat). | It is slow and requires too much fairing compound to tape sandwich panels together. It is easier to bend and twist foam panels with only one surface glassed. |
| Centerboard case reinforcement: I replaced foam with higher density material where the centerboard bears. I added frames to take lateral loads. I kept the top of the case closed to prevent opening under high loads and leaks. I install and remove the centerboard from under the hull. | The current design does not take load paths into consideration. |
| Jib track position: I moved them aft so that the sheet car ends up in the center of the track. After racing, it is evident that the tracks are too far outboard but I added barber haulers to correct this since the pop-top is in the way. | In the plans, they are too far forward and too far outboard. |
| Rotating mast: I am using a typical beech cat setup, with some mods. | Rotating masts rock! They make everything better, from performance, to hoisting sails, to taking reefs and to raising mast. |
| Anchor locker removal: I removed the locker completely and keep the anchor in a bucket inside the cabin. | This way I keep the foredeck clean for the bow pole and the weight of the mooring is better placed. Anyway I always drop the anchor over the cross-beams or the stren. |
| Mast post + support bulkheads: I replaced the aluminum tube with weird structure with a carbon fiber post with a single low profile bulkhead. | The design was complex with a wierd choice of material (fiberglass over aluminum). |
| 4 hold-down bolts: The cross-beam locking bolts are now just 4 bonded studs, that's it! I am using large wing nuts to hold the beams in place. The net lacing is used to lock the wing nuts in place (the wing nuts are used as small horn cleats). | The design had complicated barrel nuts to make and fit, with no locking features. |
| 4 compression pads in cross beams: I am using bolted fiberglass pieces instead of the weak metal assembly. | My design is cheaper with immense strength and stiffness. |
| Float bow shape: I rounded the deck to stem corner. | With the boat folded on the trailer or on the water, the forward deck tip is the widest point and is prone to damage and is a hazard to people waking around the boat. |
| Float access covers location: I relocated them on the inboard face of the floats. | I wanted to conceal them as much as possible. It is still not perfect, I find I can never leave them open and there is always 100% humidity in the floats. |
| Motor bracket: I designed my own. It was too high the first season, had to cut it down. | Nothing in the plans... |