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

[revintage]

Your center hull looks a lot lighter than mine.

It is light at the moment, but a 10-15kg cockpit will be built above deck level, between the beams at 140cm width. The floor will be 20cm below deck level on both sides of the hull, and will be built once the rear beam fittings are in place. Have done a preliminary weight calculation and the tri will be below 250kg ready to sail.

 

[Billy Bob]

All thats left is to spray the bottom of the center hull with bottom paint.

 

[munt]

Mr. Bob, congratulations, that is really beautiful!

 

[revintage]

Wow, thats an impressing quality build. Great finish. The only thing that might be changed is moving the beams up above deck level, but time will tell. Looking forward to the premiere sailing video.

 

[cholsson]

All thats left is to spray the bottom of the center hull with bottom paint. View attachment 572906 View attachment 572907 View attachment 572908 View attachment 572909 View attachment 572910 View attachment 572911

Looks really great!!! Well done!

 

[revintage]

Just had to do a presentation of Billy Bob’s trimaran in my FB-group:
Frankencats & tris Sverige

 

[Billy Bob]

Cheers for the comments.
Now if it goes fast as well?
i weighed the center hull yesterday, it came in at 95kg with all the hardware on. While not supper light pretty light. Coupled with the F17, overall it should be very light.
The thing I love the most is I can do all of work myself. I have relied only on the wife for a little moral support and my mates that drop by to give me encouraging commemts. No one wants to help you sand. I feel I should have bought into a sand paper and tape company. One thing for sure is I will be one of "The Last Man Sanding". I am quoting myself.
At this point God willing and the creek don't rise Friday will be launch day. All it takes is one fuck up to slow everything way down.

 

[MultiThom]

Cheers for the comments.
Now if it goes fast as well?

I ran the numbers for upwind using the TCF formula and compared to my boat. I guessed about 24 sq m for sail area (Main plus jib), 330 kg with one up and 5.8 meters long (Using Revintage length) and it comes to 0.91. Compared to my SeaRail, you should be quicker which comes in at 0.85 using the same calculation and one up. To compare to a more "normal" boat the F242 comes in at 0.77 (3 up). Numbers aren't proof, but I can tell you that my SeaRail is slightly faster than my old F242; so they do somewhat reflect the real world. I used 81 kg for people weight. If you add another person it generally changes the rating by about 0.04 depending on how light your boat is.

 

[harryproa]

I ran the numbers for upwind using the TCF formula and compared to my boat.

What is the TCF formula please?

 

[MultiThom]

What is the TCF formula please?

Time Correction Factor
Length (meters) ^ 0.3 power TIMES Sail Area (Sq Meters) ^ 0.4 power DIVIDED BY Weight (kilograms) ^ 0.325 power.
Inverse of the Texel formula for ratings. Empirically derived. Just basic power/weight ratio with length added in there since we all know waterline length counts as well. The rating folks add-on lots of adjustments to accommodate whiners.

 

[harryproa]

Thanks.

 

[revintage]

Thanks MultiThom! Interesting, is TCF a specific formula for daggerboard multihulls? Do you have link with some in depth info?

 

[revintage]

i weighed the center hull yesterday, it came in at 95kg with all the hardware on.

So in the ballpark of 260kg for the boat ready to sail? TCF is then 0,82, which should be good if you always sail in windy conditions.

 

[revintage]

Much more important factors are RM and Design Wind. I have made a simple Excel spreadsheet to compare different boats. Will come back to that when I have arrived to the ski resort I am going to today.

 

[MultiThom]

Thanks MultiThom! Interesting, is TCF a specific formula for daggerboard multihulls? Do you have link with some in depth info?

History of texel rating calc

 

[MultiThom]

Other important factors are RM and Design Wind. I have made a simple Excel spreadsheet to compare different boats. Will come back to that when I have arrived to the ski resort I am going to today.

There are a lot of other important factors not amenable to calculation. Such as pointing ability and ability to handle chop. Just comparing my old F242 and my current SeaRail...SeaRail points higher-I attribute that to the raked mast but I dunno for sure-could also be the aspect ratio of the mainsail. SeaRail handles chop better-which is weird since lighter should be stopped easier, but I think the reverse bows might be the reason--but it might also be the chop period is not matching the boat length where I sail where it did for the F242. Sailing is more fun than calculating and every boat is a mystery in my experience.

 

[revintage]

These are the figures I get when comparing Billy Bob´s frankentri with mine, with crew hiking out to windward. As expected Billy´s is more seaworthy, which probably means a speed advantage in higher winds. About "Design wind" this is referred to Bethwaite. The SeaRail is not included, as the spreadsheet is for flying center hull trimarans. I can be mistaken, but my guesstimate is that SeaRail does not have enough volume in the floats.

 

[MultiThom]

These are the figures I get when comparing Billy Bob´s frankentri with mine, with crew hiking out to windward. As expected Billy´s is more seaworthy, which probably means a speed advantage in higher winds. About "Design wind" this is referred to Bethwaite. The SeaRail is not included, as the spreadsheet is for flying center hull trimarans. I can be mistaken, but my guesstimate is that SeaRail does not have enough volume in the floats.

View attachment 574348

Not mistaken, SeaRail is not designed to fly two hulls. Volume in floats (buoyancy) is just shy of total boat weight without crew.

 

[revintage]

Not mistaken, SeaRail is not designed to fly two hulls. Volume in floats (buoyancy) is just shy of total boat weight without crew.

Have done a few alternative calculations for SeaRail with 330kg flotation and arrived at an estimated Design wind of 9,7 m/s with 160kg crew.

 

[Billy Bob]

We launched the boat on Friday. This was just before the cyclone that we are experiencing right now hit I hope the boat is still on it's mooring? 160 KPH winds last night. Today the wind and seas have dropped quite a bit but are expected to pick back up tonight and come with a 180deg wind shift. Boat is in a very good harbor on my mooring that is for 36ft 20,000 lb boat. should hold with enough knots!