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

[revintage]

Hi Billy,
I have gotten lots of inspiration from seeing your beautiful build and I am now even more eager to get my boat on the water in April/May when our season starts.

I have no doubt in my measurements, doing the math and adjusting before making any finish job. Unlike you, I am building a Frankentri in beachcat style with everything bolted together to make it easy to correct before adding the last pieces. As I have a solid background in Tornado racing and cat sailing, I am into this to get maximum efficiency and speed, with top finish less important. Anyway it is great fun to make use of old parts like Nacra hulls, Marstrom Tornado rudders&rig, Nacra F18 Evolution daggerboards and heaps of sails that I have laying around.

My main problem at the moment is how to build the cockpit light enough, although I have reserved 15 kg for it, to keep total weight under the 250kg target I have set.

 

[MultiThom]

Sailed my first race in B3 tonight. We finished right with the leaders so it is pretty much why I built the boat. To be in the mix for first to finish at our club. Of course there is a lot of room for improvememt/refinement. Pretty happy overall. Go the Frankentri!

Just to satisfy my curiosity. If you can get the numbers, can you provide the SA and length and approx weight of a couple of the others who were near to you...just curious as to how the TCF serves as a predictor. Of course, if your fleet is rated, their (and your) respective rating will likely provide me with the same data since your raters likely use something similar.

 

[Billy Bob]

When I get time I will get you some numbers to play with. I am not sure what our rating system is we race under as I have never cared. Correcting out is for the alsorans and
pickle dish wanters. It seems to be a PHRF type rating but is adjusted after every race. I will ask the number crunchers for you.

Upwind we seem to be about as fast as the well sailed 30-33 ft monos and GBE 8.5. This is all very preliminary as it will take a few more races to learn how to sail the boat properly and streamline the rigging issues. Off the wind weather it's skill or the boat is fucking fast (which I think it is) we have blinding speed where the speed seems to be about twice the speed of all the others in our fleet. If they are going 8kts down wind we are doing 16. The biggest boats are monos about 40 to 50ft. The biggest multi is Pulse a TC designed 30+ft cat. Good mixed fleet of enthusiastic Kiwi boats.

Great to be out there enjoying the completion and to be in the hunt for the fastest boat at our club at 18ft, by far the smallest. It is what the boat was built for. A two person easily sailed fun boat with a bit of attitude.

 

[MultiThom]

When I get time I will get you some numbers to play with.

Great to be out there enjoying the completion and to be in the hunt for the fastest boat at our club at 18ft, by far the smallest. It is what the boat was built for. A two person easily sailed fun boat with a bit of attitude.

Don't go to any heroic lengths to get data...I have been curious my whole life but have lots of unscratched itches.

 

[revintage]

Slowly getting there, trying out the side walls for the cockpit. Floor and side walls made from polypropylene honeycomb. As they are not UV-proof, side walls will be clad with matte silvery vinyl film and floor with grey EVA foam.

 

[Billy Bob]

I have pulled Frankentri B3 out of the water for the winter. This exercise is so much easier than my 36 ft cat used to be. I can do about 95% by myself and will work on that last 5% this winter. Just about everything worked very well. We sailed the boat 6 times with each of those being big boat YC racing. B3 is by far the smallest boat in our fleet and except for the first two races where I went the wrong way in light air B3 has been 1st or 2nd to finish on the line. B3 is well balanced and very fast upwind with all 5 blades (2 rudders, 2 C foils and a dagger board) in the water and a ridiculously fun ride in any wind over 8kts off the wind. Just technical enough for an aging racing minded boomer.
Overall very happy with the design strait out of the box. Are there things I would have done differently along the way? yes. Very minor tweaks that would enhance comfort. A small sailing craft should be spot on with regards to the comfort/ergonomics.
MultiThom,
I still have not looked up the sail area but it is the same rig and sails (unmodified) that come on an NACRA F17. Boat length is 17' 6". Boat weight is about 175KG with all sailing gear, safety gear and 3.3hp mercury outboard fuled up. That obviously doesn't include crew on board.
Rating system here is a hybrid of PHRF except it is a valuation of numbers in decimals. Our fleet ranges from .633 to .843. B3 sits at .788. If there are 7 boats for example, if you win your rating goes up .015 second .010 and third .005 fourth stays the same. Fifth place your rating goes down .005, sixth .010 seventh .015. hope that explains the rating system. You are constantly being adjusted unless your in a bigger fleet where there are more boats in the middle of the fleet and so there is no adjustment.
Revintage,
I hope your project is going well and you are close to getting that boat in the water

 

[MultiThom]

Thanks for the information. I like that version of PHRF, it is the spirit of PHRF to adjust based on actual performance seen on the water and helps reduce the "arms race" where your rating adjusts as your sails degrade. Folks who object to that seem to criticize the skipper handicap element (ie, like a golf (or bowling) handicap system, better players get handicapped on their skill). Seems appropriate for amateurs, but that is just my opinion. Your boat looks like fun.

 

[Kurtz]

Re: the franken boat concept, can leftover building materials be included in this?

I'm pulling down an old chook house, ive got some parts.

 

[revintage]

I have pulled Frankentri B3 out of the water for the winter.

Great to hear that it worked "right out of the box". Did you keep the self tacking jib arrangement?

As I am not as shure as you about how my boat will work. I will just bolt the gear together as is, do some testing with a smaller rig(Nacra F18), adjust and then make the final touch. Stay tuned!
Building an adapter for the mast base of the smaller Nacra rig.

 

[Billy Bob]

Revintage, I did not keep the self tacking jib arrangemet. It did not fit the situation I had to make some of other things work well. Jib is very easy to pull in by hand so far. Maybe next time?
Sorry but that main cross beam attachment and mast base looks like trouble to me on your build. Unless the main tube is through bolted in multiple locations to the bottom tube in your fiberglass cradle. Even then a lot of twisting load on two round sufaces? Also the mast support bolt/ball has a lot of load on it. If it isn't in compression to something very solid. Not just though the top of the aluminum tube?
This is just a critique on what I see in the photos. I don't know your design, skill level or what you have actually done.

MultiThom, B3 is really fun. I am so stoked. A little more comfort would be nice but you can't have everything on a fast, small boat.

 

[revintage]

Hey Billy, did you really think the M16 cone stud was unsupported all the way down through the structure without spreading the load ? So no need to worry about twisting and compression. On the downside is added weight, but I will still keep the 250kg total.

Just found an old image showing the partly shadowed 25mm dia stud in the lower 3.2mm wall tube, off course there is one in the 3mm wall crossbeam too. The stud is clamped from the bottom up into the lower end of the M16 with a long bolt. In the foregrund is the bolt and aluminium piece that locks the tube to the beam pocket. And don’t forget the four pillars, clamped in front and rear, centering the beam and tubes in the pocket.

Had to cut two openings in the hull, forward and behind the beam pocket, to reach down to install the waterstay fittings. I was very pleased to find a solid bulkhead centered under the pocket.

About the self tacking jib I am little reluctant to add the custom bent Harken track I have for the Tornado jib, but will wait until the rig is up. I have three jibs from 3,7 to 5,4sqm and three mains from 14 to 18 sqm to choose from. Will be great fun to try out the best combination.

I also have both Nacra Infusion F18 and sturdier I20 daggerboards to try out, either in the center hull or the amas. The final thing to do, if Threepence is working like it should, is substituting the old Nacra rudders with my Marstrom Tornado pair.

 

[MultiThom]

MultiThom, B3 is really fun. I am so stoked. A little more comfort would be nice but you can't have everything on a fast, small boat.

stadium seats with adjustable backs add a lot of comfort with little weight.

 

[Billy Bob]

stadium seats with adjustable backs add a lot of comfort with little weight.
View attachment 588851

My motto is "if you can see it, it weighs something" and it's just slowing you down while racing. For day sailing the seats would be a good call. For now a few cocktails at the club after the races and stretching in the morning will have to surfice.
Hey Lars, thanks for posting the pictures. I hope that the cross beam attachment structure works well for you. I look forward to hearing how it all works when you get out there on your patch of water.

 

[MultiThom]

My motto is "if you can see it, it weighs something" and it's just slowing you down while racing. For day sailing the seats would be a good call. For now a few cocktails at the club after the races and stretching in the morning will have to surfice.

I understand. For the longer races you might want to consider padded mountain bike shorts.

 

[Billy Bob]

Cheers, I wasn't thinking I needed to wear my mountain biking shorts on the boat. Never needed extra padding for my ass (just a dry ass). A good pair of goggles though would add a layer of comfort off the wind.

 

[[email protected]]

I understand. For the longer races you might want to consider padded mountain bike shorts.
View attachment 588969

Why not just get padded shorts that're actually designed and constructed for sailing? I've got Mustos, but pretty sure most manufactures would make a variant.

 

[revintage]

Hey, the padding is already on the akas as their decks are covered with EVA. Should be enough for any bony ass.

 

[munt]

Actually, the key is to achieve some elevation so the legs can bend as well as having something to lean back against. The combination greatly reduces stress on the lower back as well as gently cradling the bony ass. To this end I employed folding beach chairs tied on with whatever cheap string was laying about. I also duct taped pool noodles on the bases for padding. Very light, cheap and comfy and when they inevitably go rotten you buy a couple more.

 

[Billy Bob]

munt you have room on that Weta for 2 beach chairs with string? I'm impressed. Agree with you on the back comfort and being able to bend the legs. As a boomer its a struggle. That's were the adult supplements come in handy after the sail. If your flying along where it's hard to see without goggles you won't feel a thing until the next day when the grin is gone.

 

[munt]

Sold the Weta a long time ago and have been using other peoples' boats for a while. I still get to sail a lot but often on vessels that make me grind my teeth. I was recently on a newish 50 foot mono sitting in front of the compass while the lady driver told us about her latest shopping trip whilst randomly driving through 90 degree turns. This in 20+ kts of breeze and 6 foot breaking chop.