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MarcusK
8th January 2007, 06:16 AM
I have owned (and sailed) a Go 155 for about 16 months and within the last month or so I have been involved in the following situation in several ocations: 15/20 knots of wind with a weed fin (32 cm) which I have used since I got the board with no problems. Sailing in reasonable flat, chest deep waters, and with no aparent inconvenient, suddenly the back of the board spins out pointing the wind so I have to get out of the straps and start again. At the begining I was able to bring it back and keep sailing but it is getting worse and worse. Any thoughts, comments advise etc, on what on earth is happeneing???

Roger
8th January 2007, 09:42 AM
Hi Marcus K,
I'd venture to guess that one of 2 things is happening here.
First thing, a 32 cm weed fin is extremely small (span wise (depth) for sure, but perhaps not area wise) for your 85 cm wide GO 155.
So, perhaps you are finally getting your skills up to a level where you are truly "loading up" your 32 cm weed fin.
OR
Perhaps over the last 16 months you've run the 32 cm weed fin aground a few times, hit a few submerged "hard" things with your fin, and the profile of the fin has changed a bit and what was once a really good fin is now getting to be not so good.
My guess would be that you sail in really shallow waters (or you would have selected a somewhat larger 40-53 cm weed fin to go with the 85 cm wide GO 155.
So, how to "fix" this?
Try a larger fin (the stock 41 cm shallow water fin or better still use the 52 cm vertical race fin if you have the water depth to use that large a
fin.
If you have heavy weeds, then a slightly larger weed fin (what type of weed fin are you currently using (brand/model) may be the only solution.
Also, your current weed fin may have some "nicks and scratches" that are imparing it's ability to shed weeds and your "spin out" problems are related to having some weed on your fin.
If, as I suspect, your skills and speed have improved to the point that you are now able to really load up your little 32 cm weed fin, perhaps the only solution is a larger better weed fin, or trying to use the 42 or 52 cm vertical fins.
Hope this helps,

MarcusK
8th January 2007, 12:17 PM
Hi Roger
Thank you for your suggestions
I think what is happening is a combination of what you described. I think (and particularly hope) that my skills have improved a bit and I may be asking for a bit too much to the big GO (I borrowed a GPS and clocked 25+ kts max). I am not aware of having hit hard things with the fin but certainly of dragging it on the sand (good guess! we do sail on very shallow waters). The fin is common amongst our group although most of the other guys have Hyper-Sonics and mine is the only GO. The fin is a Select antiweed Eliminitator (32). I can see the the fin has worn out a bit (approx. 3mm, between the tip and 5about to 7 cm form the tip) and the front edge has gone square. Would that be enough to cause such problem? I was told to sand it (with sand paper) to give some "sharpness" to the edge. Would that do things worse?
Nevertheless I will try to use a 52cm straight fin I have. Altough I may plow the seabed with that one...
thanks mate
Marcus

Roger
8th January 2007, 11:24 PM
Hi Marcus,
Wow, great GPS speed results for the big GO 155!
Be careful with the 52 cm fin. If you "hook" the bottom at speed
with the vertical 52 cm fin you will get catapaulted pretty much for sure.
Might damage the fin or the fin box in the board also. So be very careful or sail somewhere in a deeper water channel (just to try the larger fin).
I looked at the Select anit weed 32.
A pretty nice fin, but it sits well behind the fin box and sticks out behind the board quite a ways and this could also be a factor here.
If you look at the weed fins (True Ames Shallow Water, Tangent Dynamics Reaper, Gorge Fin Co.Some weed) that are set well forward of the fin box, you can see that the designers have worked to keep the center of resistance of these "set forward" fins as close to where the center for resistance would be with the OEM stock vertical fins.
Sounds like the minor "wear" on your fin could be part of the problem, if you are having to reshape the leading edge and tip.
Hope this helps,

MarcusK
9th January 2007, 12:08 PM
Thanks Roger
just one more...
On True Ames' web site they mention a 6.5 sail as the biggest sail recommended for a 32cm weed fin. Would the fact that sometimes I use a 7.5 contribute to the problem?

Roger
9th January 2007, 01:09 PM
Hi Marcus,
Yes, an increase in sail size, normally moves the CE of the sail back away from the mast foot, and at the same time closer to the fin.
When you rake the rig back one of the things that happens is that the CE (Center of Effort) on the sail moves back and is supposed to balance over the CLR (Center of Lateral Resistance) of the fin.
This is one reason why sailors normally move the mast foot forward a bit as their sail size increases.
The idea here is to strike a balance between the resistance of the fin and the power in the sail.
When you get everything prefectly balanced, sailing is soooo easy. Everything seems to work. No spinout, no "upwind or downwind tendancies", higher speeds with improved control become easy to achieve (up to a point of course).
So, it's very likely the larger 7.5 rig, the definitely too wide for a 32 cm fin GO 155, and your skills are all contributing factors.
Harness line balance/positioning, footstrap positioning, boom height, type of harness, stance, all are contributing factors in the overall "balance" of your board and rig.
It's always necessary to try changing things (one at a time) to see if you can improve the overall balance.
So, basically, your "spin out" problems are most likely the result of something not balancing. Could be the fin/board combination, could be the fin/rig combination, or simply a technique issue like getting your skill level up to where you are simply pushing too hard for the size of the fin.
Hope this helps,

MarcusK
10th January 2007, 05:24 AM
Thank you Roger
I will try a few combinations and let you know what happened...
thanks again

MarcusK
18th January 2007, 07:25 AM
Hi Roger
I had the chance of trying a few combinations
I stuck to the weed fin and put the mast base as far forward as I could on the 7.5 rig. Massive improvement! I also changed the height of the boom as I started using a "sitting" (kite) harness rather than a waist (wave) one. I do not know whether that would have had any effect. I did not have the chance of measuring speed but it felt pretty good. I am also trying to work on my stance and even though I still can't get consistency I can feel the increase on speed and stability of the board when I get it right and I can push harder. Wind was a bit light but it was great for fine tunning a few things to get more balance. I got a couple of gusts that I was able to handle pretty well but ass soon as I got some chop I "lost the fin" and had to stop and start again. Nevertheless, I think that some good speed can be reached with this fin/GO155. I am jumping to a smaller board (slalom) but I am still keen on finding the limit of this board in light winds, just for the hell of it and because it is the board I have (can you provide me with some performance stats of the board?). I am happy now because at least I know what is happening.
Thanks for your advise
Marcus

Roger
18th January 2007, 09:05 PM
Hi Marcus,
Great progress!
Glad to hear you are beginning to feel the balance, and even better to feel when things aren't in balance so you know you need to do some additional tuning and "tweaking".
Not sure how far (inches) you moved the mast foot, but in my experience all the way forward would probably not be the fastest or best position.
Can you now try moving it back a little at a time and see if there isn't a position that gives you the same control, but better speed due to a little shorter waterline length when fully planing?
It may be that due to the small fin size, you need the all the way forward position to get the fin and rig to balance, but then again, maybe not. Give it a try.
I used that same strategy last year in Bonaire where the max. fin size is about 33-34 cm due to the very shallow water, and it really did solve some serious spin out problems, but made the board feel very "sticky".
Yes, changing the type of harness you use can change the boom height and harness line length substantially. Do you have adjustable length harness lines? Try some and if possible, try some "on the fly" adjustable lines like the Sailworks "Quick Tune" lines http://www.sailworks.com/06/moreinfo_1.cfm?Product_ID=82
so you can adjust the lines as you are sailing to see what differences having shorter or longer lines can do for your control and speed.
Getting the line length to feel "perfect" can help a great deal to "adjust" your stance, give you some indication when your boom height is high or low, things like that, that really do affect the overall balance of the rig to the board.
It seems you are still fighting with the chop a bit.
How big is this chop? Knee high....; waist high...; bigger?
Chop mostly affects the fore and aft (pitch) attitude of your board, so it may be that either your weed fin is also being adversely affected by rapid changes in the pitch trim of your board (causing your spin out) or you may be trying to compensate somehow when you see the chop, and your compensations are making a bad situation worse.
What I have learned about short wide boards (like your GO) is that we often try to control things (like pitch attitude) by moving our weight, changing our stance, changing pressure on the feet, and when we develop our skills a bit further we discover that all of our "compensations" are actually causing more problems than they solve.
Give this a try.
When you are sailing along at your fastest, just try to let the board "balance out". Don't try to steer it around the chop, but rather kinda let it pick its way through the chop.
You just keep a steady "power pressure" on the mast foot, steady foot pressure on the fin. Often you will discover that the board just seems to glide through or over the chop that you were compensating for.
Try to keep the pitch and roll attitudes of the board consistent and I think you may find the board settles down and the fin will stay "stuck" quite a bit better.
Hope this helps,

MarcusK
19th January 2007, 06:24 AM
Hi Roger
I moved the mast base about 2.5in so I will try to bring it back a little bit at a time (how much would you recommend? 0.5in at a time?) Chop can vary between knee and waist high according to winds and tide and you are right, I have been trying to "sneak" between waves but every time I have gone over a decent wave the board kinda takes off and when it lands it is a big splash and it slows down a lot (something you would expect wouldn't you?)
Yes, my harness lines are adjustable, and after a few changes in length they are feeling very comfortable although I think I have to work a bit more on the position.
Could you please explain a bit more the concepts of ???pitch and roll attitudes?? of the board?
Thanks again

Roger
19th January 2007, 10:33 AM
Hi Marcus,
Yes, use 3/8- 1/2" increments, and then when you really like the way your board handles, try even smaller increments, but try to only change the mast foot position. That's the key to finding the "balances"..... only change one thing at a time so you begin to understand what each type of change can do for you.
OK, you have a bit larger chop to deal with than I was thinking.
So, you are actually kinda making little "chop hops" when your board takes off the top of a swell or wave.
This may be a huge part of your problems with the fin letting go.
When we "chop hop" and get the board up off the water and the fin mostly out of the water we need to instantly change stance a little or try to tuck the back foot under our butt. You cannot keep "pressuring" the fin when most of it is out of the water or the fin will go back into the water pointing alot higher upwind than your board is going.
If you "land the fin" it needs to be pointing a little downwind of your course so it can reenter the water without any sideways pressure.
Even if you aren't getting the fin clear out of the water when you go over the larger chop, if the board comes off the water, the amount of fin span (length) in the water will be reduced as well. If you continue to push on the fin, the board will move away from you and the fin will settle back to its full depth pointing much higher than the course your board is sailing.
This "overloads" the fin and leads to spin out (the fin lets loose) virtually all the time.
The roll attitude of your board essentially controls direction due to the way that the water flows along the bottom.
If you have the lee rail lower, the board will tend to turn off the wind (like setting up for a jibe).
If you have the upwind rail lower, the board will tend to head upwind.
There is another dynamic here that it sounds like you may be ready for.
That's the concept of sailing upwind on the lift from your fin.
If you tip your board very slightly lee rail down, and push across the top of the fin with your back foot, the fin will become super efficient and will tend to take you upwind very fast and at a better angle than you can achieve with the upwind rail down.
If you aren't fully planing, then you simply have to use upwind rail down roll trim to get upwind.
If you are fully planing, try lifting slightly with your front foot in the front footstrap and pushing horizontally across the top of the fin with your back foot.
This will roll your board slightly lee rail down and increase the fin lift (horizontal lift here) to the max. and allow you to simply rip upwind, "on the fin".
Pitch attitude is the fore and aft angle at which your board travels through/over the water.
Pitch attitude can be changed to make the board faster and more lively in marginally to normally powered up conditions and also changed to push the nose down more to help your board "stick to the water" in really overpowered conditions.
The things that have the most significant "effect" on pitch trim are the mast base positions (fore and aft along the centerline of the board in the mast slot or track); footstrap positions (fore and aft), and boom height harness line length can also have a somewhat mininal effect.
What's the "best" pitch trim angle...and how would we measure it?
Depends alot on the design of the board, the discipline we are sailing,
the amount of power we have to work with and to some degree the fin we are using.
My version of a "perfect" fore/aft trim is when the board is very fast and lively and virtually on the verge of tailwalking.
If I have enough wind, I will move the mast foot all the way back in the track, and hope the board actually does tailwalk or becomes hard to control. This means I have too much fin, or I've moved the wetted surfase/waterline length too far back for me to control the board.
Using this as a starting point I move the mast foot forward until I'm just slightly uncomfortable and the board feels lively and almost wants to tailwalk. This usually proves to be the fastest setup for me personally.
Formula racers (I did that a few times) like the mast foot much further forward (at or near the front of the mast slot) to give the best upwind performance and to hold the nose of the board down somewhat going off the wind.
So, it's a very personal "what you like and what works for you" kinda thing.
I do know that most boards can be slowed down and will stick to the water better with the mast foot a little further forward, but you need to be careful that you don't get the mast foot forward to a point that the hull of your board gets into a bound and rebound cycle. Then it becomes very hard to control as it seems like you are constantly "slamming' into the chop. Move the mast foot back slightly and you can normally find a "sweet spot" where you have the best mix of control and speed.
But, it's always good to try slightly different mast foot positions, until you really learn your board and what small differences in MFP will do for you.
Same idea applies to all of your rigging and tuning. Keep trying something slightly different, and see what happens. When it all feels perfect, mark it so you can get as near perfect as possible the next time your sail.
Hope this helps,

MarcusK
28th February 2007, 06:40 AM
Hi Roger
I have been "playing around" with your tips to find "balance" and working on my stance (this with the help of a local "big gun" ) and look at these numbers on the GPS
max 2 sec: 26.5kt
Average x 10 sec: 24.9kt
Not bad for a big GO 155 with a 32 weed fin, huh? THANKS HEAPS FOR ALL YOUR SUGGESTIONS!!! :)