Formula 40 singlehanded trimaran build log

This is just a preliminary render and it's not settled yet but thought some people might be interested in how the process is coming along. Main hull now 39'4" to fit into slightly less stringent Cat1 requirements, 200kg extra displacement which has driven 1" wider beam on main hull and 1" greater draft, worth the sacrifice we think there is more displacement available of course with higher levels of immersion but the performance suffers somewhat if you use it. There will be nets forward of the front beam just not rendered in. Outboard up next to cockpit now on starboard side and float rudders.

 

So, it's not really an F40 anymore maybe as I'm getting older and a bit softer, I want just a smidge more comfort anyway the revised boat which is more like Phil Steggal's concept now and has a little write up on Kurt's blog. We now have standing headroom in the cabin and a bulge that allows bunk space or stowage internally, cockpit is a little more spacious due to the flare. Still looking at similar lightship weights as foam sandwich main hull a little lighter than the CM original. Demounts still to a 40' container but now will require a high cube type. Float construction method not settled yet it could be foam sandwich or CM, beams still WRC with carbon uni and glass for off axis loads but now a different shape due to changes in main hull height and a bit slimmer at the centre of the beam.

40 Foot Performance Shorthanded Trimaran for Owen http://multihullblog.com/2017/10/40-foot-performance-shorthanded-trimaran-for-owen/

 

Maybe softer is wiser? Keep it up and the family can come. Seriously, elbow room doesn't cost you racing if you don't bring too many elbows. Being able to bring more for a sail is priceless.

 

Now that is a cool project! More I look at my situation more it makes sense to build a demount-able tri in the backyard shed.
At 40ft size are we looking at around $200k or so?

 

Yes, it will be somewhere around that point. 100k for the platform or so depending on what choices you make and the rest on deckgear/electronics/rig/sails. I'm using a secondhand mast and sails to try and keep the overall cost down.

 

Seems like an exciting way to go-like the beam. Any particular reason to not go oversquare? Best of luck!

 

Hi Doug, the physical constraints of the 40' container are to a degree dictating the overall dimensions but I wouldn't call a boat with a 39' beam inadequate in that department

 

I was curious about what motivated the choice of beam-I think its great. Now all you need is a lifting foil on the daggerboard so you can fly the main hull in light air!
Sure going to be a fun boat....

 

The latest updates from Kurt seem really cool. I think about F40 based trimaran for minimalist cruising for years (see for example guys with Spirit tri). I'm not sure about daggerboard in the main hull, would be better (for space in the hull) to have boards in arms? It seems Kurt believes that his solution is better for single handed, but...

 

If you fit float boards you need two cases and they are quite heavy and require local strengthening of the float in their vicinity you also need the boards themselves and each has to be as large as the single daggerboard you would otherwise use. You also need additional control lines for raising and lowering the boards. The positive of float boards is you get more space in the main hull which isn't an insignificant consideration as the board and case is bulky and takes up a lot of room in the widest part of the hull. There are some hydrodynamic advantages to the float daggerboards too but it doesn't seem to be a race winner in itself for example the Multi50 Prince de Bretagne had float mounted daggerboards and wasn't faster than the Multi50's with a single centrally mounted daggerboard.

 

Thanks, makes sense.

 

Corley, can I ask what is your waterline beam now ?
Peter

 

It's about 1 metre now near enough at maximum Beam on the main hull and a 12/1 fineness ratio, previously it was 13.7/1 fineness ratio on the longer waterline (That's just a rough measure off the .pdf, I'll update that once I've printed the plan page if there is an error).

 

I received the mainsail back from the sailmaker. It looks like it should be ok to use now that every seam isn't threatening to fall apart. In hindsight it was somewhat remarkable that the battens were staying in their pockets given the amount of debonding that had occurred in the glued joins. It's pretty light for such a large sail I'd estimate about 50kg without battens. The battens are solid fibreglass so I'll look for a better solution for that.

 

Sounds correct - but one moment, not quite so: the leeward float is pressed down harder than main hull, therefore the float foil there is operating in deeper, less disturbed water ... and therefore can be more efficiently designed and have less area - which means higher aspect ratio plus the dagger foil can be asymmetric - which is a large advantage in terms of lift and drag and is more efficient than conventional symmetric board setup. Also the main hull conventional symmetric board setup requires it to be longer (because it has to go through the deeper main hull) and also larger in area to compensate - (because it is often aerated by main hull lifting out at speed). And if we're talking F40, the top boat in those times was Biscuits Cantreau ... which had deep, high aspect ratio asymmetric daggers in floats.