I was asked by a fellow Seabreeze'r to add some info on how I've modified my RS:Flight F4 Foil to end up with what you see in the first pic below; and yes that was also a JP 135. When I originally bought it the Starboard race foil was not available and I've been continually tinkering with it in order to keep it on pace with latest foils, which it seems to be, failing the big front wings most now have for light conditions. I'd also add that unless you have a fair bit of experience with this sort of stuff it's probably not worth entertaining these mods...cutting up a 2k+ carbon foil is not everyone's cup of tea

First step; Anyone who has raced a windfoil knows that fuselage length is your friend and front wing placement is important. Pryde/F4 jumped the gun on both these counts, while the overall wing profile design and shape is really good in standard form the fuselage is way too short and the front wing too far back. This has been discussed before in other threads and we can again later here if anyone is interested but for now, to the cutting.

I dealt with the rear fuselage first as it looked like the easiest thing to change. Initially I made a short 110mm extension and straight away it was better. I then went all in and added 300mm; skip to 1)


1) Out of some 10mm 316 S/S plate I water jet cut a profile with a front bayonet to go in the existing fuse and then the mirror on the rear end. It is drilled and tapped on the front end exactly as per the existing rear stabiliser bayonet.

I then 3D printed a large section of tube which matches the existing fuselage outer profile and slides over the S/S profile. I bevelled the edges with a grinder so I could keep some wall thickness in the corners where it is thin. 3D print material is PLA and solid fill as you need good compressive strength. See a few pics below.

1.1) S/S Profile and 3D printed tube.

1.2) 3D printed outer fitted to S/S, also note tapped holes as per standard rear stab

1.3) Rear where stabiliser will now fit.


2) Below you can see a few pics of how much has been added to the rear; existing position and new position.


2.1) Original rear stabiliser position.

3) Then I glued the 3D printed outer on with epoxy and fitted it to the fuselage. I used the bolts exactly as per how you'd fit the original fuselage. This lets you get the alignment perfect along the longitudinal axis as this is very important. I then gave it a bit of a sand to remove all the existing clear coat and filled over the bolts and the join etc, see below in 3.1)

3.1) New rear extension fitted.

4) Prepare the carbon: Over the fuselage I used 7 layers of 3K carbon sleeve; 4 off 25mm, 3 off 38mm. Then 5 layers each side and bottom of 80gsm Unidirectional carbon. The sleeve was progressively layered back from right at the mast to the tail, it is important to ensure you get a good amount right at the tail as that is a high stress point from the stab loading but you also want to keep it nice and streamlined.

The uni-di extended from just behind the join to just behind the front of the mast. This is important because we have just added a huge lever to the rear, the torsional moment around the mast is much larger. If you do not add this it's only a matter of time until whole rear end snaps off, probably right between the mast and the original end of the fuse. This is why you can't just bang a 300mm S/S extension in and happy days, it would just snap the fuse straight off.

Then it's just standard wet it out and vac bag. Vac bagging is important as it ensures very good cloth/resin ratios for maximum strength and minimal voids. Failing a vac bag you could probably spiral wrap it but the result won't be as good.

4.1) Carbon, peel ply, breather fabric, vac bag shown below.

4.2) Vac bagged

4.3) Vac bag removed, quick sand and microballoon fill any areas that need attention.

4.4) Bit more sanding and some high fill primer.

4.5) Lick of paint, done.

4.6) Compared to a starboard race foil, you can see the front wing position difference.

4.7) Bag no longer fits.

So I sailed it like this for quite a while and it was very successful. Much improved over the standard foil and particularly good in strong winds which made sense given the front wing position. I always new the front wing had to move but it was a much bigger job and irreversible if it didn't work out. I then finally sailed a starboard race foil on my board and rig combo and I knew straight away it had to be done. Queue phase 2:

5) Phase 2 is a little more out of reach of the 'home gamer' but you could still probably do it with a grinder, some skill and a bit of time. I'm lucky to have a lot of resources at my disposal so...CNC mill it is. Measured up the fuse and played around in CAD for a while till I was happy. Ended up moving the front wing forward 130mm, which is a lot given the relative amount of lift this wing provides. It's actually about 20mm further forward, relative to the mast, than the wing on a starboard race fuse. I have seen they have a new race fuse called the 'plus+' which I think may have moved their wing further forward too....but that's speculation on my part, it's not in the public domain yet really.

5.1) Pressed a few buttons, had a coffee, front wing adaptor machined.

5.2) Front of existing fuse sanded to match new 316 S/S plate

5.3) Mocked up

Now I didn't take any pics of this carbon process but basically I cut up strips of 200gms 3K carbon twill to completely fill up the void around the existing fuselage and the stainless steel plate and to form the basic shape of the nose; solid carbon no fill, vac bagged. I then sanded this all down to a rough nose shape. I then added 4 layers of 3K carbon sleeve over the whole lot and blended it back towards the mast, vac bagged. The front end is in standard form a lot stiffer than the rear and I could see the thickness with I cut the nose off so all good as far as I was concerned.

5.4) Carbon rough sanded and wing fit check.

5.5) Other side. note; went to a stub nose shape for simplicity and probably cleans up the flow under the wing...but I didn't CFD it so just eyeball calcs here.

5.6) High fill primer and paint as per the rear fuselage.

5.7) Finished product.

So how does it sail. Well basically like a starboard race hahah, although I think more powerful or front foot biased anyway as the front wing is further forward. It's much easier to sail in light conditions as the load between the feet is much more even. In light conditions with the original front wing position and long rear fuse you had to really work hard. It's more of a challenge downwind in breeze to keep it in the water but that's to be expected. Much more balanced trim when healed over upwind, no more nose drop. Super stable longitudinally now....although was already good with the 300mm rear extension. Overall top speed I think has probably dropped 1kt or so from the very original short fuse due to the added fuselage drag but the upwind/downwind VMG is night and day.

As I kind of alluded to at the beginning, this is a mod purely aimed at racing, although just the rear extension did make it a way way better every day foil. Anyone who's not crazy would just go and buy a starboard race or the new Pryde F4 race foil etc but as I said I've tinkered with this thing over time as I started racing.

Flame away

Fantastic insight into your development there, thanks for sharing

Impressive! Shows that there's lot of improvements that can still be made in foils.

Good job! You're right about the plus+ having the front wing further forward btw ;). Did you move your straps at all compared to the unmodified version?

Piece of cake!

Very clever boy !!!

CONGRATULATIONS !!!

Wow. You do excellent work sir! well done! Glad it works better than expected!

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WhiteofHeart said..
Good job! You're right about the plus+ having the front wing further forward btw ;). Did you move your straps at all compared to the unmodified version?

I wonder how much further forward?
Thanks!

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WhiteofHeart said..
Good job! You're right about the plus+ having the front wing further forward btw ;). Did you move your straps at all compared to the unmodified version?

When I modified the JP 135 I moved the strap inserts back about 40mm to move the front wing forward relative to body position; this was just when I had the extended rear fuse.

Once I moved the front wing forward I had to move everything forward again, so they are probably now about the second hole from the back on a standard JP 135 board...it's as far forward as I can go now. I also had to move my mast base forward about 50mm, mainly to survive downwind . The power is still a lot further forward than before, relatively, perfect for racing.

Good job. After the the first cut the rest was relatively easy? I suppose that with a longer fuselage you can run the stabiliser with less angle of attack for the same balance point ahead of the front wing. Or do you run the same angle of attacks, front and rear, and just stand further forward?

I'm wondering how do you trim the front and rear wings to ensure the fuselage is running parallel to the water at race speed. Not easy to look down there. Might be a small reduction in drag to be made? Maybe not?

running out of green thumbs for this topic !

Awesome work !! soooo impressed by the finished product !
I should be able to accomplish that with my angle grinder and a couple of duct tape rolls in a few .....errr never !

Thank you so much for sharing ! You could almost come up with a DIY kit to sell to NP owners !!!

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Ian K said..
Good job. After the the first cut the rest was relatively easy? I suppose that with a longer fuselage you can run the stabiliser with less angle of attack for the same balance point ahead of the front wing. Or do you run the same angle of attacks, front and rear, and just stand further forward?

I'm wondering how do you trim the front and rear wings to ensure the fuselage is running parallel to the water at race speed. Not easy to look down there. Might be a small reduction in drag to be made? Maybe not?

You're onto it Ian, no surprise As you eluded to because the longer fuselage has more longitudinal dihedral you can run less AoA on the rear stab, also since I shifted the balance point further forward I can get away with even less.

It's hard to measure relatively as I also trimmed up the front wing a bit for, as you mentioned again, more parallel running at normal foiling speeds. Certainly quite a bit it less AoA than before though. Re the fuselage running parallel it's hard to measure what it actually is when you're sailing as you say so once again I 'eye balled' it

CJW fantastic work and very impressive craftsmanship. Have you compared the new modified foil against the new Pryde F4 Race foil in its longest fuselage ?

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sl55 said..

WhiteofHeart said..
Good job! You're right about the plus+ having the front wing further forward btw ;). Did you move your straps at all compared to the unmodified version?

I wonder how much further forward?
Thanks!

Looks like quite a lot, 5cm? I haven't measured, bought the new Lokefoil for racing anyway.

has anyone in w.a done something like this mod as I have one of these foils now and have heard they are a bit of a handful unmodified
and struggle for lift with a heavier rider.

White of heart, why lokefoil for a course racing foil, as compared to npf4, starboard or phantom?

White of heart, why lokefoil for a course racing foil, as compared to npf4, starboard or phantom?

CJW- great thread and beautiful work! no question it's a lot of effort and easier to buy off the shelf but Ive found you get great satisfaction when you get to try things out and it's successful especially if it takes a few evolutions!

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ratz said..
has anyone in w.a done something like this mod as I have one of these foils now and have heard they are a bit of a handful unmodified
and struggle for lift with a heavier rider.

Ratz - lunney has made a few very high quality carbon fibre variants of the extended tail sections for the F4 here in WA and pretty sure he's posted something previously on this

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RichardG said..
CJW fantastic work and very impressive craftsmanship. Have you compared the new modified foil against the new Pryde F4 Race foil in its longest fuselage ?

No I haven't as I'm yet to see one of those in the wild. Probably quite hard to compare as their new version has the fuselage and front wing as one piece so you can only run their longest fuselage (1200) with the big 1000 wing. My only direct comparison, seeing as it's the off season is the SB race with 800 wing, which is a pretty direct comparison. Compared to before I think it's now faster upwind...seems to be the case anyway. It's always been fast off the wind and remains so, that could also be a function of my relatively light 70kg. It's a lot easier to sail now though, much less energy to get it into the groove upwind, which took effort before and a few techniques; by before I mean still with the 300mm rear extension, I ran that most of last season.

Attention do not forget that the load from the wing is very large. I made a homemade fuselage of aluminum profile and with the wing of the Horue xlw was all right. And when I put the wing XXLW from large loads the fuselage is caved in. I'm going to make CNC machined from a solid rod 30 mm here is the drawing. Carbon might break, too, so be careful.

raceyou.ru/attachment.php?attachmentid=49313&d=1559458349

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regal1 said..
White of heart, why lokefoil for a course racing foil, as compared to npf4, starboard or phantom?

The Loke is fast and has the best angles upwind. The Phantom might be a little faster allround, but I think in the PWA the best rider is winning, not necessarily the best equipment. Untill now every brand has been up there this year, so they're all good.

Lokefoil is small brand, which somehow means delivery time is shorter.... For starters NPF4 racing is not available anywhere and they have the longest delays in delivery by far. The Starboard is heavy and durabilitywise not much better then their boards after a year (from what I've seen from the first model), add to that that the old 115 fuselage is no longer as competative and the new Plus+ isn't commercially available.

That leaves the Phantom Iris R teamset, and the Lokefoil LKRace. Both use way higher quality carbon than all the other brands on the foil market called M40J. Their masts are significantly stiffer than anything else you can buy. the LKRace is full carbon, compared to an alu detachable fuse for the Phantom. I've seen reports of the Phantom fuse not being as stiff (on the F) due to it having to be connected to the mast, so the Loke it is for me. The loke wing is also a little smaller for the same amount of lift, which I see as a plus, same goes for the stab.

Add to that my homespot is Jordy's homespot too, meaning we can ride together with the same equipment, and that Lokefoil offered me the better deal and a very good experience in the past, the choice is easy.

(It wasn't as easy cause I've been shifting my favour between the Phantom and Loke for a long time, but the Starboard and NPF4 dissappeared from my list when the smaller (in my opinion better/more dedicated) brands came out with racing foils.)

I left the Z-Foil out because I have never felt much for Z-Fins, their quality varies too much for me personally (the fin you test isn't necessarily the same as the one you get when you order, that sort of thing. If you get a good one you're a winner, but there is a chance you wont..), and their foil seems a little underpowered / short compared to the competition. I haven't seen any other racefoils being comercially available yet.

WOH, i ppreciate the detail and thought behind it.

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sl55 said..

WhiteofHeart said..
Good job! You're right about the plus+ having the front wing further forward btw ;). Did you move your straps at all compared to the unmodified version?

I wonder how much further forward?
Thanks!

I took a better look today, its way more than 5cm. It looks like the mast is almost in the middle of the fuselage. Have to say however, that the one I saw today was black, not gray, so maybe a once again newer version?

Quite interesting RE the plus+, the front wing does look a long way forward on the shots I've seen from the PWA. Must be a handful downwind but might also have trimmed out the rear stab a touch to compensate; although this would effect pitch stability. I'm sure I heard Ben.P in one of the broadcasts say there was a 'plus' and a 'plus+', so maybe more than one version?

Interesting regardless but I can't really play around with that on mine being a solid carbon/mast join, as it is though it's 20mm further forward than a standard race fuse.

Hi, just wanted to say amazing job on the modifications. You are spot on with the geometry. Couldn't believe that anyone would try that. Front wing more forward makes the foil more powerful and more front foot heavy. Also you can reduce the angle difference between the front wing and rear stabilizer. This compensates a bit for the extra wetted surface from the longer fuselage. Longer still makes the foil more stable and able to handle more power. Shorter is more lively and maybe a bit faster in some conditions. I think + means 5cm more forward, at least that's what did for the 120cm fuselage registered for the PWA. If anyone has any questions or comments, feel free to reach out.
Br,
Chris

hi all
have just tried to fit my np f4 2018 carbon foil to what I believe is the standard deep tuttle box in my sb 162 formula board
to find that it stuck out by about 10 mm .
is it just a matter of sanding the head of the foil until it fits in
and do dedicated foil boards have a slightly bigger box in them.
any replys gratefully accepted. cheers ratz

I wouldn't mess around with it Rob, unlike a slapper it's not that critical and that bit is not in the water most of the time

If its anything like my SB formula, first time i used a foil in it without a flange to distribute the load it failed after about 3 seconds of flight and the head of the foil went in quite a long way at the front. Unless you have given up pies Rob this may happen to you.Managed to repair it and beef it up without replacing the box.
Only one way to find out mate, give it a go.

you boys fill me with so much confidence.

The recommendation for AA was, Try if it works ok, if not then reinforce it.

Simplez

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ratz said..
hi all
have just tried to fit my np f4 2018 carbon foil to what I believe is the standard deep tuttle box in my sb 162 formula board
to find that it stuck out by about 10 mm .
is it just a matter of sanding the head of the foil until it fits in
and do dedicated foil boards have a slightly bigger box in them.
any replys gratefully accepted. cheers ratz

Does your box go all the way to the deck (eg. Only the holes), or only to about half way (with pipes and screwholes a little deeper in the board)?

the first option s****, the latter might hold up for a while (I never reinforced my formula and I used it a lot with big sails / a lot of pumping upwind legs etc.)

wouldn't know why it doesnt fit, I guess you could see that best hahah, is it stuck against the walls or is it just sitting against the box cealing? I rode with a pryde ally foil in a foilbox which was too small for it (foil against the cealing, but not against the front and aft box walls), and it worked fine, just had to tune the rake a little.