Foiling Trailer sailer

Short answer is yes but not thru the wind range and angles that americas cup or Flying Nikta can do ie mostly beam reaching and below .
Long answer since I do not have access to Gomboc i have done some linear calculations of lift ,righting moment at various speeds with certain assumptions
Primary lifting foil is 144 cm in span 29 cm chord in centre 60 cm with 42 cm tapers to 17 cm chord at the tip
effective area is 3800 cm2
section is a modified Fk131/33 flapped section Hydro balance actuated by a wand
between Reynolds’s 800,000 and 3 million This section has a max CoL greater than 1.5 plus 0.9 for a 33% flap
low drag bucket 0.008 to 1.25 with flap range +/- of 12.5 degrees
aspect ratio of 5.4 so degrades max CoL to 78% ie .97
CoD 0:008 to 0.005 lift to drag ratio 75 to 150 over this range of Reynolds’s numbers 5 to 20 knots
Sailing displacement 1100 kg with 115 kg of crew hiking or on trapezes
lifting foil acts 1.1 m off centreline nominal CoG
So using a CoL of 0.8
6knots. Lift 148 kg Rm in kgm 752
7. 204. 780
8. 267. 810
10. 333. 842
12. 601. 970
14. 819. 1075
16. 1071. 1196
unlike a conventional yacht righting moment increases substantially with speed with associated reduction in displacement and wave making . Moreover LD improves as velocity and Reynolds’s number rise . I am being conservative with my assumed CoL for a flapped foil so lift off will probably occur at 12 knots not 16 which is obviously way above hull speed but entirely inline with a melges 24 power reaching . I expect many years playing with foils both section and size . You will also note that I have not included the rudder T foil contribution of 15 to 20 % nor possible differential rudder AoA
Flying to windward may be possible particularly with a reefed main but sea state will likely intrude .No bets on Best Vmg
Productive day we drove 500 km round trip to pickup my carbon Forte 112x 69 mm 9.7 m long 19 kg mast from Spokane . All went well I borrowed my neighbours Martin 242 trailer . I am very pleased with the mast at $4890 US but will need to put a 13 mm harken track on it as well as spreaders sheave boxes gooseneck and headbox . Lots of fiddle carbon bits to make. But such a relief to have it at home. I was considering using the antal/ hall track and reached out to IanA who referred me on to Johnny at hall spars. Unfortunately the base of the section is 45 mm wide which will not fit on my oval mast.
Painting the hull is finished far from perfect but it will do and finished in my weather window .Antiskid will be rolled on later when all the fittings are positioned .
Back to foils and now spars much better than sanding



Though a little indolent toward the end of summer with 65 th birthday and all I have done a little work. That really means a lot of sanding and painting whilst the weather window is open .
I have removed the 2 top halves of the main foil out of the mould . Thank goodness for poly vinyl alcohol transforms mould release. Also discovered need for 25 gm fibreglass veil to stop air pockets in the weave surface showing .
3 full length and width 400 gm uni carbon then 7 more layers in step down length 100 mm wide 400 gm uni at 90 degrees 3 layers of 100 gm biaxial carbon 1 layer of 200 gm carbon cloth. 100 gm and 25 gm fibreglass cloth .
bottom halves to come then shearweb foam and making a Kevlar hinge in flexible epoxy to fit in the rebate in the lower mould see tape at 33 % chord from trailing edge . Plus spreaders . I did get titanium rod and tube from china for masthead axles and spreader compression tubes which will double as tangs for the dynema rigging not as nice as Julian’s but should do .




Thanks for the interest . I am fiddling away making spreaders, headbox for the mast prod and reradiusing the leading edge of the rudders . I was slightly interrupted fixing up a 7 ft wide trailer that I was swapping with a friend for his 8 ft wide easy loader trailer. Registration was a protracted process for my wife but that is now complete .
I have some lengths of 10 inch diameter stainless steel tube 1/10 wall that I am going to make into a cradle for the keel bulb and hug the ground with torsion rubber axles to minimize the ground clearance and depth of water needed to float the boat off.
lots of welding and fabrication to come
spreaders came out quite nicely with 4 layers of 400 gm uni lengthwise 1.5 layers of 100 g biaxial carbon 200gms of glass boat cloth all spirally wound with flagging tape then vacuumed . 400 gm each for upper spreaders 800 mm and 600 gm each for 1200 mm lower spreaders . After fairing these will be cut to fit on mast .then slid over 15 degree bent 12 mm titanium compression tube’s which will double as the D 1 and D2 upper termination.
Headbox is mostly done carbon inside and out over 4 mm ply with rod batten wrapped in carbon sock as the top flange . Protect tape lines the inside where the sheaves are and an Allen alloy doughnut eye awaits basalt filament winding in place .
I expect to vacuum 3 staggered layers of 400 gm uni on it tomorrow reflecting the lateral cantilever forces and the vertical compression from the bobstay. I rather like Julian’s bobstay prod end fitting arrangement and may copy him! Seems like such a good idea to get rid of a separate downhaul .
Rudders needed reshaping on the leading edge after vacuuming over male forms .As you can see I used Alloy angle with a radius to act as the female form which I waxed and coated with pval then poured a micro sphere/ballon epoxy mix in and stood the foil up to bisect the 90 degree angle.This separated of nicely so I can get on with refairing the leading edge with a good starting point. Then on to making adjustable angle of attack rudder boxes using sliding 25 mm thick UHMW upperplates.
I drove over to Kelowna last week to get the plastic sheet stainless steel tube and rod as well as the torsion axles.
I also acquire 250 kg of tire weights most of which I hope are lead which I will use to cast the keel after I have made some green sand for casting .
so many jobs so little time but only 36 days before I retire whose counting !







im really glad that there is still guys like you in this world who can do projects like ths, gives me hope to do the same one day.


New member
“Registration was a protracted process for my wife but that is now complete .”
l leave mine unregistered and hope I don’t get caught.
I would try that except insurance and crossing the us border makes it difficult.
I continue to fiddle on .I like Julian b pu blow moulded cores I don’t think my moulds would take the pressure so I strip planked with foam vacuumed into each side of the asymmetric foil then sanded flat . Now I have to rout out grooves for my plywood sheer webs ss T bars and ss pivot for the flap actuator to push on. Not nearly as neat but I will copy Steve Clark and put glass cloth inbetween to reinforace the trailing edge and add a 1/4 in glass rod inside the leading edge . I will have to rout a space for the flap rotate into . Hinged on bottom surface with probably a flexible strip of G Fle x epoxy in sunbrella cloth with light glass over . I am currently experimenting with samples . Kevlar in G Flex is way to stiff.
I have also been working up the boom making a sheave box for outhaul and reef line in Bakelite . Carbon ply tangs to carry the gooseneck and tapped alloy ply plates to take the constrictor clutches semi externally on the sides of the boom . Putting them inside would have been cleaner but really hard to service .



Bakelite/ tufnol phenol reinforced fabric !!! Old hospital flat sheets in 5 mm makes reasonable sheave box sides and glues quite well .
I have made the boom vang attachment. 6 layers of 400 gm uni 4 layers of 100 gm biax and a little sacrificial glass cloth vacuumed on . A little bit of yellow bog on the head box and prod .I am copying JB with the prod outhaul and will copy Jim Donovan re internal shroud attachments to titanium cross tube but I will glue my spreaders on .
Joanna is finishing up cabin top to deck junction inside. I am prepping mahogany grab rail all around the internal perimeter.