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Atomicsurf Weed fin Prototype

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Created by sailquik 1 month ago, 22 Jan 2020
sailquik
VIC, 4874 posts
22 Jan 2020 3:50PM
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I was pleased to test Martins weed fin prototype last week at Lake George.

It is 20cm deep and around 42 degrees at the base, 45 degrees in the middle of the leading edge.

It worked very well indeed in my Carbon Art 40 speed board with 5.2m 2020 KA Speed sail.

At LG I would normally used fins around 17cm to 20cm deep and between 35 and 40 degrees rake in the early season conditions I encountered. The weed is varying between 20cm and 5cm from the surface, with a just a few small patched where it is touching the surface. There are also a few small patches where there are 'weedbergs'. These comprise of that light green, slimy, long strand, very thin weed that seems to have grown in the past two seasons, and it accumulates on top of the normal weed where it touches the surface. Normally, I can go through these at speed without even feeling them, but there are some larger and denser ones here and there around the islands and off the end of the spit that slowed me a bit. Easily avoidable.

Where the weed is deeper below the surface, waves up to around 30cm can develop. Elsewhere, where the weed is close to the surface, the waves are quite small and easily 'rattled over' deep downwind.

What I was immediately impressed with was how safe this fin felt. I launched at the '5 mile' and wanted to go deep downwind to the islands immediately. Running over the waves in the middle of the lake gave me great confidence. A few times I hit cross chop at low 30's and the board bounced and 'fluttered'. That is where spin out is highly common, but in this case it just never happened. Very impressive! In fact, I didn't spin out for the whole session as far as I can recall, even going upwind.

In the areas where the weed was thick and close to the surface (especially Kev's Bay), i could feed a bit of drag only when I slowed in the gybe, but I only got caught once when I fluffed a gybe and stalled. That is no different from the other fins I use in these conditions. It was easy to get going again and any caught weed washed off almost immediately.

I actually did my best 2 seconds speed, just over 41 knots, in the thickest weed in Kev's bay on a lucky gust, and gybed out a number of times with no problems.

I also did a 41 peak and a string of 40's on the other side of the lake near the islands in 'rattle' water. The fin felt super safe.

While I didn't do any comparison test on this day with my other fins, I am confident that this fin is at least as fast given that the wind was not over 27-28 knots. For me, those were right up with speeds I would expect in those conditions.

Martin has some ideas on possible improvements from my feedback, so I am quite excited to see what can be done.

Pics:








On my Rake-o-meter, it is 45 degrees in the middle of the leading edge and a few degrees less right at the base:





Visual comparisons with the classic KA MacDougal/Lockwood assy 20cm and the Tribal Lockwood assy 18cm.









Session trackmap and link:



gpsteamchallenge.com.au/sailor_session/show?date=2020-01-16&team=16

sboardcrazy
NSW, 6875 posts
23 Jan 2020 9:45AM
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It sounds good. The fin looks better than the bottom of your CA board..

sailquik
VIC, 4874 posts
23 Jan 2020 9:49AM
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Select to expand quote
sboardcrazy said..
It sounds good. The fin looks better than the bottom of your CA board..


I'm living proof that looks don't count for much!

mr love
VIC, 1882 posts
1 Feb 2020 4:18PM
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Remodelled since Andrews feedback. Main change is a different tip outline that has more of an excellerating curve into the tip to help shed weed. The rake changed 0.5 deg to 42.5 at the base and 20mm from the tip it is 52 deg. I also changed the foil profile to a new section I designed for the slalom fins, managed to increase the lift for no drag penalty. The chord thicness varies from 9.5% to 10.5% so each size is individulal it is not just the long fin cut down.

Will do some more protos soon....20cm and 38cm shown.

And by scaling in z only I can change the rake angle without impacting the foil section and its relationship to the flow direction...don't you love CAD!....This is a 30 and 20cm with 49deg base rake angle...the Nuclear Weed!!




kato
VIC, 2649 posts
10 Feb 2020 9:43AM
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Had my first sail on my one on Saturday. Board 52 wide /81L, sail 5.7 Ka Speed , 22 Weedie . Flat water with small running chop.
First impressions, nice looking fin, well finished with a straight leading edge.
Fit into the box was perfect and flush.
The run up wind wasn't as bad as I thought and I could make the upwind turn point. The usual spin out at low speeds.

The run in was gentle through the chop, not wanting to pop the fin out.
The first run in was smooth with lots of grip but slippery, even through the bumpy mid section. Gave me heaps of confidence to push harder. 42 peak, 41+ 10 sec peak.
The next runs were all quicker resulting in a board Pb 42.3 peak.
Bloody great fast fin that Martin says he can make better.....I want that one too
I did find that I've been running all Martins fins 25 to 50mm further back on the board than any other of my fins. Love these fins

mr love
VIC, 1882 posts
Sunday , 23 Feb 2020 9:58AM
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After sailing at lake George this week I have a much better understanding of fins for heavy weed. I have now 2 designs I will prototype. The first is more for small slaom boards or speed boards with a tapered outline, the second for running larger boards in shallow water or for speed sailing in really shallow water at fin lenths down to 15cm




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"Atomicsurf Weed fin Prototype" started by sailquik