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DarrylG said..
Don't get me wrong Decrepit, I think there is nothing better that making and sailing something you make your self. I just don't like the idea of delta style fins so people can sail in shallower water. If I am touching bottom in 30 cm of water I am touching cloth and get out of there quick. Stories of people grinding down 19cm fins in shallow water just has me concerned.

Bottoming out in shallow water with a sub-20cm weed fin I've found to be a graceful dismount (if one can describe over the handle bars graceful with me it's more of a violent roll out!!), not the full on shock of a catapault, unless your striking rocks then the dismount can be a tad more perilous!!
Keep in mind an upright fin in the shallows bottoming is way more catastrophic than a weedie sliding over objects even rocks....

Cheers Peter

Having smashed up more Deltas on the real estate than most, here is my two cents to muddy the water. Firstly, I find that its a bit like the circus high diver into the shallow pool - because you are landing with a large surface area ( in my case anyway :-) you do not penetrate the water very far at all and I have never hit bottom even when it was ankle deep on a limestone reef. But I have impact vest and helmet on always. The chances of landing awkwardly might be higher, but I cant quite figure out why that would be so - perhaps someone else can postulate on that one.However if you do manage to get flung at an awkward angle where you do present a smaller surface area and you do penetrate the water deeper, then yes absolutely things are going to be more unsavoury than in deeper water... So take care people :-)

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decrepit said..

Paul Kelf said..
>>>
Mike, Stainless steel work hardens, so bending & beating it makes it harder to work with.
You can anneal it by heating it up after working it for a while to bring it back, you can even quench it which won't affect it.
Working it hot is another way.

Ideally what you need is a flatbar the thickness of the fin, radius the leading edge & machine a step back from the LE to start the carbon.
Drill a heap of holes right through the stepped area (perforated) so the resin will go through & grip.

Have you tried any of the ceramic coating available, unfortunately some need to be baked on I think & also hard to get a smooth finish.

Thanks Paul, I've given up on the idea of shaping a skin. I'll see if anybody around here can machine a step into a bar.
But I'm sure the bar doesn't need to be fin thick, as I said 5mm should be enough, but I haven't done any measurements, it may need 7mm to get back to 5mm from leading edge.

Mike, if you don't have the St St the full thickness shaped back to the thickest part of the fin won't you still get the front ~1/3 (carbon portion) wearing just behind the St St?

the stainless is 3mm so there's not a lot of glass at the tip, too repair the worn section what you do is mix some very fine carbon dust with resin and airosil, let it stand for a few hrs then add the hardener again let it gel to the consistency of Marjorie and wipe it onto the fin, again let it set and then use a bit of detergent and wipe it over the resin until you have your foil back , let it harden and it will be very smooth
the fin below is strait from the box from a repair months earlier , the fin has had two seasons at primbee and one season at sanctuary point and has done 40 knts
you can get the powder shaker from Woolworths

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Paul Kelf said..


Mike, if you don't have the St St the full thickness shaped back to the thickest part of the fin won't you still get the front ~1/3 (carbon portion) wearing just behind the St St?

A very small amount Paul, by far the worst wear is over the first 5mm, that's the point of maximum pressure, where the water is being accelerated away from the fin. May be going back 10mm would be better, but that means a lot more stainless to shape, I'm not sure it's worth the effort. If I can get a bar machined, I'll try 5mm first and see how it goes.

Keef, tried your small 17cm 45deg today, as you said, it's a great little fin, unfortunately the forecast said wind would peak around 1800, and I changed down to my small board and your little fin around 1700, was getting some good runs, everything felt nice. Was looking forward to wind picking up so I could get a feel of it going fast, but at 1730 wind started to die so I'll have to wait for next time we get good wind.

Hey Paul, just to add to the 15cm Delta that you saw last time I have just added 2 new standard speed weed fins a 18cm and a 20cm (the 24cm is on its way)

Unusual the tips are cut 90deg to the blade, not parallel to the flow?
This wouldn't be because you've just reboxed an upright blade at 45 deg by any chance?

Weed heads, could you mix in some diamond powder with the resin for the leading edge? this should make it more abrasive resistant

http://www.ebay.com/itm/Lapidary-Diamond-Powder-14-000Grit-Mesh-0-1-microns-weight-25carats-5-grams-/321609678055
www.diamondtech.com/products/categories/diamond_powder_price_list.html

You are correct decrepit they were from a mold I made a couple of years ago.

They are only the starting point and will be modified over time, as you mentioned some will have extra area to the tips added to 90deg and some will get the surface area increased.

Keep you posted

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choco said..
Weed heads, could you mix in some diamond powder with the resin for the leading edge? this should make it more abrasive resistant

http://www.ebay.com/itm/Lapidary-Diamond-Powder-14-000Grit-Mesh-0-1-microns-weight-25carats-5-grams-/321609678055
www.diamondtech.com/products/categories/diamond_powder_price_list.html

I've been using carborundum powder, but it doesn't have as much effect as you'd think, no matter how concentrated you make the mix.
I think the resin gets worn out around the particles, which then fall out.
Other guys are thinking about moulding a ceramic leading edge in, hopefully something practical will eventuate from all this.

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dweller said..
You are correct decrepit they were from a mold I made a couple of years ago.

They are only the starting point and will be modified over time, as you mentioned some will have extra area to the tips added to 90deg and some will get the surface area increased.

Don't bother changing it in the short term... it is just another variation of an elliptical foil.

I worked a ceramic knife in. Stiffer and good for the tip. Wolfgang

All it will take is a couple of trips to Primbee and they will be parallel and then will need to rebuilt

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decrepit said...

choco said..
Weed heads, could you mix in some diamond powder with the resin for the leading edge? this should make it more abrasive resistant

http://www.ebay.com/itm/Lapidary-Diamond-Powder-14-000Grit-Mesh-0-1-microns-weight-25carats-5-grams-/321609678055
www.diamondtech.com/products/categories/diamond_powder_price_list.html

I've been using carborundum powder, but it doesn't have as much effect as you'd think, no matter how concentrated you make the mix.
I think the resin gets worn out around the particles, which then fall out.
Other guys are thinking about moulding a ceramic leading edge in, hopefully something practical will eventuate from all this.

In my profession we have found that particle size is very important - typically less than .4 micron filler size. So whatever surface wear improver you use make sure is is ground very very fine.

Got the 18 @55 delta up to 38.22 through the weed at Liptons yesterday



Surprisingly the tip which was slicing through the mud at the end of the runs was pretty much undamaged but from 1/4 to 3/4 down the leading edge it ended up like a serrated bread knife by the time I had finished slicing through the surface weed. Wish I had put that stainless ruler in between the 2 halves.

Just finished a 19cm delta to add to the 15cm. Just need to tidy the base up and fit the barrel nuts.

they look great Stuart are they more than 55rake , i'm looking for someone to sail lake wollumbulla on Tuesday , there's a huge bed of dense green weed that stops the water movement and is supa flat and fast , I cant think of anywhere else your going to use them this time of year,
the lake has had a huge dump of water and I dough it will effect the speed strip because the weed is so dense , if anyone is interested send me a PM , I sailed there a week ago and bagged a 34+ and Tuesday is looking better

Hopefully the winds up on thursday when i get back keef ! by the look of it tuesday is looking good at the burra have fun

Yep look great..nothing seems to stop a 55 and they don't seem to have any trouble getting over 40

Was thinking of adding even more rake for less drag

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yoyo said..
Yep look great..nothing seems to stop a 55 and they don't seem to have any trouble getting over 40

Was thinking of adding even more rake for less drag

stroppo certainly doesn't have a problem with the deltas at 55 deg for me it's 50, with the deltas I find i'm always looking for a bit more lift as I find they tend to ride a bit flat, also with less rake it's harder to make ground after sailing off the wind
yoyo your on the money by making the fin in 2 halves , we have a guy over here that make beautiful fins the same way and he's consistently getting 40 knts
what he does is vacuums one half at a time , so it's a wetter layup with the carbon fibers being compressed, as well as there is no air in the fin
my layup is similar except I lay the mold up with carbon wet it out by hand and then close the mold , then hook up the vac lines and a resin line and suck the pressure out of the mold for almost 1 bar, then open the resin line and suck 100grams of resin through the mold , its a bit of a resin waste but it ensures an even wet out and releases any trapped air

Keef would you not need to pull at least the entire volume of wet-lay resin through to eliminate all the air? I would have though quite a bit more actually as trapped air is harder to move when the resin is taking a natural path of least resistance. Surely you are not worried about strength with such a low aspect/low load fin so perhaps its just a cosmetic thing and you are probably tackling that with carful wet-lay in any case. Overcomplicating your process perhaps? Just curious - I'm about to start a run of fins(in lieu of xmas break) and was intending to use wet lay and pressure only even with the high aspect narrow chord fins.

I think if I was going to infuse a fin I would pull the resin from the base and draw it into a 10-15mm bleeder around the fin - the bleeder incorporating the outer ply of carbon/other and central glass ply/s. Same would apply if moulding in halves for a weed blade.

I'll try the wet/squeeze on a few and if needs must adapt for infusion - quick & dirty suits my needs better tho

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Man0verBoard said..
Keef would you not need to pull at least the entire volume of wet-lay resin through to eliminate all the air? I would have though quite a bit more actually as trapped air is harder to move when the resin is taking a natural path of least resistance. Surely you are not worried about strength with such a low aspect/low load fin so perhaps its just a cosmetic thing and you are probably tackling that with carful wet-lay in any case. Overcomplicating your process perhaps?

my first mold had two gaskets as you can see on the first page of this post. with 2 vac lines , one to pressurize the mold and the other for the fin , it has a perfect seal but only one gasket is necessary
what I find is if you load the mold up with to much carbon (dry layup) it will compress and you get some dry spots , also if you don't use a release agent with some waxes fisheye will come through on the finished product
so what I do is always use a release agent and lay down a thin layer of resin to make sure there's no fisheye , when it's tacky but still a bit wet I put 2 layers of 9oz satin weave, if its wet enough it will soak up any pooled resin and will be nice and even
next step I have pre cut 450gr carbon in the shape of a butter fly that opens out like yoyo's two halves , then with some 5mm seam tape I stick another 8 layers of 450gr uni and some Kevlar glass composite in the center but still leave it open
at this stage I forgot to mention (you will need 150grm of infusion resin and fine carbon dust that has been sitting over night and degassing)
now you have two 2 butterfly's , with the 9oz being tacky ,stick one side of the butterfly's mix some hardner into the presoaked resin and wet out the carbon , then fold the other side over and do the same ,( to do both sides of the mold it shouldn't take any more than 5min)
now shut the mold with cramps and hook up your vac and resin line( make sure the resin line has a cramp +100grams of resin)
bring the pressure down to just short of 1 bar , you will notice some frothy resin coming through the vac line , slowly open the resin line and suck the extra rein through until the resin coming through the vac line is clear , clamp both lines off and wait until its cured
I forgot to mention the infusion resin i'm using has a 30hr cure time , its not the best and im looking for another resin

"edit" yes I have a 2mm bleeder around the perimeter of the fin ,( this I forgot to mention ) the cavity is used to lay 4 layers of 9oz satin weave in the center of the fin , you then have a solid glass layer around the whole fin , the leading edge is much tougher and you can get a much finer trailing edge with the glass

Leading edge hardness
No experience with making fins but plenty of hobby experience making tough molds for model airplanes

We use a tough ceiba geigy tooling gel coat that has enhanced anti wear properties as a surface coat for molds. You can chisel along it to cut cured carbon without damaging the flange. Can't sand it!!! Used professionally as anti wearbeds for large belt sanders I believe. Wondering if a layer of this first into the mold would help anti wear properties??

It's so tough that it can't be sanded to key in the next layers in making the molds.

If it sounds useful I will dig up the numbers for you

Cheers Jeff

Sounds excellent Jeff, would be well worth a look at. I wonder if it's a ceramic thing?

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jirvin4505 said..
Leading edge hardness
No experience with making fins but plenty of hobby experience making tough molds for model airplanes

We use a tough ceiba geigy tooling gel coat that has enhanced anti wear properties as a surface coat for molds. You can chisel along it to cut cured carbon without damaging the flange. Can't sand it!!! Used professionally as anti wearbeds for large belt sanders I believe. Wondering if a layer of this first into the mold would help anti wear properties??

It's so tough that it can't be sanded to key in the next layers in making the molds.

If it sounds useful I will dig up the numbers for you

Cheers Jeff

yes please!

Gelcoat Resin
Araldite® SW 404 Resin with HY 2404 Hardener
Filled epoxy system, abrasion resistant


• Easy to apply with brush or spatula, or by pouring
• Easy to use
• Covers sharp edges
• Cures rapidly at room temperature
• Outstanding mechanical strength
• Very hard, abrasion-resistant surfaces
• Very strong edges

www.allnexconstruction.com/

OT.....
Where we used it Enjoy....
www.rcgroups.com/forums/showthread.php?t=1139397&page=5&pp=100#post13863928

cheers Jeff

I see the Shore D hardness for the araldite 404 is 85-90 . West epoxy is ~ 83 so it not that much harder.

After a few sails I can confirm that Deltas don't really work in chop! So I had to make some more fins these a 21.5 cm and 26.5 cm @ 42 deg.

I like the 21.5, looks very similar to my PB fin a 19.5 45deg