Design the ultimate Frankenboat-1) for Speed in water; 2) for comfort; 3) how fast to get done

H

hobiedd97

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23
Virginia

Alien Trimaran – Not From Outer Space | Small Trimarans

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I bought this a few years ago, and I've had it in storage since. The vaka was built as an experiment/POC by a potential manufacturer, then it was completed (more or less) by the prior owner by adding the aluminum beams and a-cat amas. I don't think it had been sailed for a while when I got it, and I planned to upgrade some aspects. I have plans for what was then called the Sting 600, and was thinking of using those plans to build the folding mechanism into the existing hull. Additionally, I've got Prindle 19 hulls that I've considered using as amas. Essentially, further frankenboating a frankenboat!

I've got several other boats, so I'm not sure when I'll get to it, but the subject of this thread has long been an interest.

alien 2.jpg
 
revintage

revintage

Member
342
76
Eskilstuna, Sweden
This is the Frankenbeachtrimaran I am building, no comfort though. LxB 5.8x4.6m. The amas are Nacra 5.5 and the aka is Nacra 5.8. At first I opted for a Tornado aka but the hull I was given was to far away in Sweden and not economical to pick up. It would also have needed quite a bit of work to be paired to the amas.

With three Nacra hulls everything will be plug&play, as they have the same beam pockets at the same distance between them. Inner beams 100x3mm with waterstays, outer(last 90cm) beams 90x3mm. Mast is an aluminium Marstrom Tornado, mainsail Inter20(18sqm), jib Tornado Sport and spin Nacra F18. Daggerboards Inter20, rudders Nacra 5.5. The amas are 20cm shorter at the transom and 10cm shorter at the bow. Height difference between 15 and 20cm, but the volume difference is huge.
All components are things I have collected through the years, the only items missing are the outer beams but they are on their way from Germany.

The boat will be completed 2023, but the hulls and beams will be joined within a few weeks.

https://www.facebook.com/groups/1192604934176635

68173411117__4F863BE9-840B-4A72-B87C-DCB5AC7FC000.jpeg trinetcat58.png tempImageg3voF4.png
 
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MultiThom

MultiThom

Super Anarchist
1,921
502
Benicia, CA
revintage said:
This is the Frankenbeachtrimaran I am building, no comfort though. LxB 5.8x4.5m. The amas are Nacra 5.5 and the aka is Nacra 5.8. At first I opted for a Tornado aka but the hull I was given was to far away in Sweden and not economical to pick up. It would also have needed quite a bit of work to be paired to the amas.

With three Nacra hulls everything will be plug&play, as they have the same beam pockets at the same distance between them. Inner beams 100x3mm with waterstays, outer(last 90cm) beams 90x3mm. Mast is an aluminium Marstrom Tornado, mainsail Inter20(18sqm), jib Tornado Sport and spin Nacra F18. Daggerboards Inter20, rudders Nacra 5.5. The amas are 20cm shorter at the transom and 10cm shorter at the bow. Height difference between 15 and 20cm, but the volume difference is huge.
All components are things I have collected trough the years, the only items missing are the outer beams but they are on their way from Germany.

The boat will be completed 2023, but the hulls and beams will be joined in a few weeks.

https://www.facebook.com/groups/1192604934176635

View attachment 533432
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Should be a nearly turnkey type of frankeboat requiring little in the way of glasswork. Bet it will be quick. Boat footprint will be very close to what my SeaRail 19 is with similar powerplant. Post video, please during assembly and sea trials. Lots of folks would like an easy tri to put together without having to learn how to make hulls.
 
revintage

revintage

Member
342
76
Eskilstuna, Sweden
MultiThom, I have noted the Sea Rail 19 after we discussed W17 rigs in another thread and the similarities are obvious. With lower weight, a more effective sail plan(boom and long sheet track), fuller amas and slender center hull, I anyway hope it will be faster in high winds(but also more wet to sail). Might later build a cockpit above the center hull to keep the water out, but it depends on how well it sails.
Do you ever sail the Sea Rail single handed?
 
MultiThom

MultiThom

Super Anarchist
1,921
502
Benicia, CA
revintage said:
I have noted the Sea Rail 19 after we discussed W17 rigs in another thread and the similarities are obvious. With lower weight, a more effective sail plan(boom and long sheet track), fuller amas and slender center hull, I anyway hope it will be faster(but also more wet to sail). Might later build a cockpit above the center hull to keep the water out, but it depends on how well it sails.
Do you sail the Sea Rail single handed?
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Yes, I fitted an autohelm (single rudder boat) to give me a hand when I need to leave the tiller to do this or that while single handing. With self tacking jib and being boomless it is quite safe to sail alone. However, your project boat ought to be a bit faster if you can keep it on its feet. I don't think you have any choice in position of mast vs daggerboards, it'd be nice to be able to have the mast forward of boards some so you can have mast rake to help keep the bows up. Mast on the SeaRail is forward of the akas leaving a big gap to the leading edge of the vertical daggerboard--SeaRail sails with a lot of rake which keeps bows up most of the time. Took some getting used to since my F242 had daggerboard under the mast (trunk actually provided the support) and very little rake.
 
revintage

revintage

Member
342
76
Eskilstuna, Sweden
MultiThom said:
Should be a nearly turnkey type of frankenboat requiring little in the way of glasswork. Bet it will be quick. Boat footprint will be very close to what my SeaRail 19 is with similar powerplant. Post video, please during assembly and sea trials. Lots of folks would like an easy tri to put together without having to learn how to make hulls.
Click to expand...
I prefer to call it "frankentri":).
 
D

don54321

New member
34
23
My tri experience is limited to one boat, a factory, glass, Tremolino 23' with all the good stuff including factory half moon profile amas and factory Supercat 17/19 rig (28'9"). The early original boats were designed to uses a Hobie 16 donor for rig and floats. Dick Newick designed the main hull, and later bigger floats for the bigger, factory, Supercat Mast. Floats are low boyance and low drag, and are a good indicator of being overpowered. The main hull is the most basic, easiest to build hull imaginable. The bottom is flat, about 8" wide at the widest with near vertical sides (guess 15 degree flare). I can tell you that it is a very smooth ride. Beams are mounted high on the cabin tops, way above the deck and provides support for high backed bench seating (in my case hard seats) outboard of the hull flush with the tramps terminating at the bottom with the low freeboard hull. It is extraordinarily fast (for a family boat), in < 10 knts wind, usually exceeding wind speed nicely. Given the simple to build main hull, it proves to me that simple hull forms, when narrow, work great. The boat begs to be built in flat panels. If the boat folded in some manner, it would be perfect. The pictures are very old, from perhaps my first year of ownership, but they are the best pics I have showing the simple hull form.

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MultiThom

MultiThom

Super Anarchist
1,921
502
Benicia, CA
I thought it might be interesting to list some accumulated stats of existing boats since a Frankentri "designer" will have decisions to make about a few things.

Beam to Length ratio.
70% is the smallest B/L with F27 and F28 being this ratio...The biggest ones I've calculated are Diam 24 at 77.5 and F22R at 79. My SeaRail is 71%.

Mast Length to Length ratio
The older Farriers/Corsairs hover in the 130-140%; the more modern designs are in the 152-158%. My SeaRail is 157%.

Mast Length to beam ratio
The older Farriers/Corsairs are in the range 177-194% with the F27 being the 194% which is matched for the F22R. Other designers are in the 200%s with my SeaRail topping the list at 220%.

Weight is not easily ascertained from stats available...but if the Frankentri designer already has the donor catamaran, he should try to make the overall weight of the boat equal to the flotation in one of the hulls. Easy enough to measure, just fill one hull with water a gallon at a time until full. then multiply the number of gallons by 8.33. That would be a good design displacement in pounds. Then after weighing the two donor float hulls, you now would know how heavy the mast and vaka and beams are allowed to be. Good way to check for leaks, as well.
 
revintage

revintage

Member
342
76
Eskilstuna, Sweden
MultiThom said:
Easy enough to measure, just fill one hull with water
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Are you sure this is the way to go? The water pressure from inside the hull might ruin it. Sinking the hull in water would equal the inside/outside pressure, though.

But the idea to find out the ama volume is important, but there is not one answer to this. The importance of this is when we are talking of a tri with lifting center hull. If not lifting it is more a question of righting moment.

About the Searail 19 I wonder if its tiny amas, can take the weight of the boat+crew(1000lbs?), but I am sure you have the figures?
 
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