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

[MultiThom]

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?

People have been filling their hulls with water to check for leaks since before Napoleon. Filling with water may not get an accurate answer, though, since some floats (like my SeaRail) have front sealed compartments that won't be 'fillable' from the accesses (has breatherhole to equalize pressure on hot/cold day, but no way for air to escape to fill). I don't know if beachcat hulls are built that way, though. Some smaller tris are right'able by filling one float with water as much as possible and standing on it--so I'm pretty sure filling the float will not hurt it. Given the tortuous shapes of floats, without the design drawings, you won't have an easy way to calculate the buoyancy and not many frankentri builders will be able to submerge a hull and measure how much water is displaced--hence the suggestion to fill with water a gallon at a time. On the chance that you have a bunch of buddies available, though, you could add one person at a time straddling the float until it is underwater. Would like to see the video if anyone does it!

The SeaRail is not designed to lift the center hull-and the amas are not tiny unless you are comparing with an F31 or bigger. The volume is about 850 pounds buoyancy (I had the design drawing)--or about the same as the weight of the boat without crew.

 

[revintage]

Hi Thom,
Think you missunderstood my concerns. A way to fill the hull to get equal pressure both in- and outside is to, as you suggest, fill water 1 gallon at a time when the hull is on water, instead of on land, and gradually sinking it. Should not be a problem to pump it out afterwards.

I have had a great help extrapolating the volume of my amas to somewhat over 600kg as I found the drawing below. It is a pity there aren´t more design drawings or manufacturer specifications around. I have then calculated the equalized boat weight to ca 600kg with a 160kg crew hiking full out to windward at designwind(ref. Bethwaite).

About needed ama volume it is important to include crew weight and its placement.

 

[revintage]

Hi,
Planning the rig on my Nacra hull Frankentri. I first intended to use the Marstrom Tornado alu mast tube I have, with the boom attached a little less than 400mm above mast foot, but realized I might need more headroom. How much do you need from deck to gooseneck for a comfortable ride? I have a 160x76mm alu profile that I can lengthen up to 10m.

 

[MultiThom]

NIce looking tri you have for a reference boat . With a boom, you'll want more room if only to keep from getting bonked. However, if you plan on driving from the nets, it doesn't matter so much. At this stage you don't know what mast rake you will need so that will likely also change the boom height.

 

[revintage]

I have not had any problems with boom height racing with the Tornado, but getting 70+ and a lot less athletic takes its toll.

Multithom, would you mind checking the distance(red arrow) on your "reference boat"? Guesstimating it to be 2-3ft.

 

[MultiThom]

No problem. Distance from sail tack to seat is 90 cm. No boom on mine. When sailing, I do still have to duck while sitting on the seat during tacks and gybes. Had to do that, as well, on the F242 (with boom). Boom did collide with crew occasionally. I would guess that'd be the design criteria, people can get out of the way by ducking.

Are you mounting the cat hulls vertical or are you introducing a 5-10 degree angle, if angled, how'd to get that?

 

[revintage]

Thanks for the measurement.
Thinking 70-80cm be good enough for me. I have a F18 main that will give enough headroom and I have an 18sqm Inter 20 main that I opt for, but that one will not leave more than 40cm with the T mast.
I have given canted amas a thought, but I don’t think it will be worth the effort at this stage. Might do it after having sailed the boat. The beam pockets allow for max 4 degrees, if making angled adapters for the 90mm beam ends in the 4” beam pockets. My idea is that you point higher without canting with daggerboards in the amas.

 

[Billy Bob]

I am about 2 weeks from getting my frankenboat in the water for a good hoon. It's been about a 9 month pregnancy to birth this boat. A lot of sanding and engineering! As a retired boomer it has been about the right amount work every day for me. I hope it will be rewarding when the sails are up and the wind is strong enough to light it up. I have taken pictures of every detail along the way. When I have some idle time after launching I will post pictures.

The boat began as a 16' center hull ( similar to a woods design) that was free with a trailer i bought. It was foam glass and carbon and had an old-school look. Not now. A new bow and stern were added and faired in. This matches the NACRA F 17 simi foiler I bought for Gemma Jones Olympic sailor and Josh Jr America's cup sailor. It has been quite a ride meeting all the people along the way on this build. The 3 hulls all look the same in the bows and sterns. Carbon tubes connect the hulls. The NACRA came with 90% of the gear I wanted. Mast, rigging and sails. All have been modified to work as not just a beach cat but to sail with proper yachts from the club in relatively near shore races. Name of new boat B3.
99 % of the work has been my own with no help so I think it qualifies as a Frankenboat as I am not a navel architect just enthusiast with lots of experience fucking around with boats. To my eye it looks right. When I post pictures you can give me criticism about what I should have done different to make it what you would have liked. For now I am getting excited about getting it in the water and getting it on a good long plane!

 

[revintage]

Hi Billy Bob,
Nice, have waited for your update and got it! Will be interesting with a few images though. I am a bit behind, having built the alu beams and have cut up the bow of the center 19ft Nacra 5.8 hull for attaching a forestay chainplate. Also adding a small open cockpit. No hurry here, as we are still in the middle of the winter.

 

[Billy Bob]

Here are a couple pictures 2 weeks ago before hardware installs and final paint to match NACRA F17 simi-foiler bought from an olypian. I am installing hardware now and grey nonskided areas. the whole project has cost less than a used weta without my labor (but that's love).I have the option of going with single dagger board or ama c foils for now.

 

[MultiThom]

Looking really good. Kind of a small main hull daggerboard slot so I assume you are going deep with it? I don't see slots in the amas for the c foils so I'm probably missing them. Are you going to install a traveler?

 

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Here are a couple pictures 2 weeks ago before hardware installs and final paint to match NACRA F17 simi-foiler bought from an olypian. I am installing hardware now and grey nonskided areas. the whole project has cost less than a used weta without my labor (but that's love).I have the option of going with single dagger board or ama c foils for now. View attachment 571358 View attachment 571359 View attachment 571360

Doesn't look to be much dihedral - will all three hulls touch the water at rest? I'd assume getting your weight to leeward would lift the windward hull clear in the light stuff.

 

[david r]

Wow. looks cool.
You must have gotten a screaming deal on that used nacra17 and the carbon beams to have paid less than a used weta.

 

[Billy Bob]

Center board is bigger front to back than the c foils by about 50 mm and about the same length. The c foils are there and go up and down nicely. It will be interesting to see what the difference is beating and reaching. There is a Harken traveler installed now from side to side on center hull. I'll take pictures in a few days when the non skid is on, most of the equipment bolted down, all the hulls bolted together and mast up one final time before it is launched.

Not much dihedral. The original center hull pretty much dictated where the tubes went through for strength in my opinion after cutting into the structure. I did raise the back as much I dared to get all three hull rocker lines to line up from a side profile. I didn't want to mess too much with the NACRA structure so just added a secure cradle structure for attaching the carbon tubes. There should be some dihedral but not heaps. It's pretty constantly windy here so not too fussed. I may change my mind after sailing this season. That's the great thing about having a small boat to fuck around with at home in the winter.

I got a very good deal on the NACRA and it has good provenance (Olympic sailed by the previous owner). Good equipment and 2 sets of great sails one set used only in the Olympics the other never been up. Used about 90% of the NACRA parts in the build. Good quality Harken gear.I

I did put a new Mercury 3.3 2 stroke as an auxiliary. Lightest and most powerful I could find here. The boat will sit on a mooring and with the tides here is a must for getting out of the harbor.

Looking forward to getting it to the water and putting sails up

 

[revintage]

Hi Billy Boy,
I am a lot behind you, but I have to work outside in -8 C and inside the workshop in +8 C. Anyway completed the main beam and main hull fittings today. To get enough dihedral I added 10cm at the center hull beam pocket. This makes 19cm dihedral when the height difference between the hulls is taken in account. The rear will sit even higher up, to point the amas a little nose down. After next weeks ski vacation, it is time to fit the rear beam, that I built before Christmas.

the

 

[MultiThom]

I believe you two might "win the prize" for the frankentri that is fastest to get done since you purchased all three hulls. Can either of you give a guess as to how many manhours to make your creations?

 

[revintage]

I believe you two might "win the prize" for the frankentri that is fastest to get done since you purchased all three hulls. Can either of you give a guess as to how many manhours to make your creations?

Hi Thom,

My and Billy's boats are exactly fullfilling the "Franken" concept, as Frankenboating means using and modifying parts from different used boats, to create one.

Hard to estimate manhours, as the build is spread over a long period. My feeling is sourcing components(even if I have had most of them in my backyard) and planning has been the most time consuming.

 

[MultiThom]

I thought it might be the case that the time spent is distributed over a long period due to the nature of creating a boat. To digress a little, I'm wondering if a kit boat (boat in a box) would be attractive versus frankentri creation. The owner of SeaRail is considering making the boat available as a boat in a box (at considerable discount from fully assembled) and he was wondering how much interest there would be--I answered -- "Duh, I dunno". I believe that it takes about a month to assemble a SeaRail (they do arrive in the USA as a boat in a box--container with parts goes by sea then by rail to the assembler in Illinois (hence, sea rail). Of course, none of the trailer or mast or assorted rivets and bolts are included in the container--those are stocked in Ill.

 

[hobiedd97]

I'd consider getting a SeaRail "boat in a box." Cost and availability of the necessary components to complete it would be things I'd be curious about. I've got things like masts, sails, etc. If there are some custom components required for the beam assembly, for example, and I'd have to fabricate those, I'd be somewhat less interested.

 

[Billy Bob]

I am about 10 hrs away from birth. I have pretty close to 1400hrs into the project. To build a boat of similar size I was quoted by a yacht architect to expect about 3000 to 4000 hrs to complete.
Revintage I feel for you building outside in -8. I had a pretty wet summer here that set me back a bit because I am building outside as well for the most part.
Your center hull looks a lot lighter than mine. I have made it my mission to be able to carry the safety gear (easily accesable) for our category 4/5 yacht club racing and to be a fairly comfortable old man with a bit of easy access storage for dry gear/snacks when out yacht racing all day.
Multithom the proof will be when the boat goes sailing as how successful we will be? A kitset Searail sounds great. Would have been right up my alley but I certainly had fun doing this project and as I have said before the people I have met putting it together has been totally worth the price of admission. Even if the boat is a total failure which I don't think it will be. I just hope it is fast enough to keep up with the other YC boats.