Hi Alan
Just an off topic message.
I can’t send you private messages, you have to clean up you rcsailing-mailbox.
BTW Finn box looking good!
/Anders
:ouch: Now I know why my in-box was so quite …clean-up done, Thanks !
Yes Alan, it is physically possible if the Rules allow to let move/rotate the fin blade. If the bulb CG is behind the fin pivot the fin will rotate producing two effects, reducing the lee way and probably inducing a couple for the nose down and increase the heeling effects. The contrary by shifting the bulb CG ahead of the pivot. Soft rubber will keep the bulb aligned when the boat is upright
Ciao
ClaudioD
Hi All
Here is a link to Lesters page
http://www.onemetre.net/Design/Fillets/Fillets.htm
Down towards the bottom read Larry Robinsons comment. Now I’m not sure if the rubber locator that Claudio is thinking about would allow the same vibrations as the less stiff fin that Larry tried but it’s food for thought. The rubber may actually act as a damper to the vibrations.
Don
Hi Don,
I had been thinking (more like worry) about your “wiggle room” point as you call it for final fin alignment and decided to find a way to check alignment before bonding the box into position.
After cutting the keel slot in the hull I then placed hull in the cradle on the building board and aligned the “hull centre line” to the “building board centre line” and then looked shadow #10 alignment to the building board …wow it was out by 3 mm !!
After making adjustment to the keel slot in the hull, for extra assurance I then cut 10 mm high section of the fin box and the glued into position on the building board centre line and will now use this to lock the fin to the building board to bond the box into the hull.
Then asked myself how could I be out by 3 mm when scribing the hull centre line using laser light, well the answer to that puzzle was that I had not leveled the table before scribing the line and was not until I cut the slot in the hull did I see the problem.
Don, thanks for raising the point on “wiggle room” otherwise I would not have thought about this until it was too late otherwise…owe you few beers for that one !!
Cheers Alan :zbeer:
To close of the subject the keel fin assembly for the profiled fin box, was not as easy as I thought it would be and took quite bit of time to get everything right.
The purpose of the exercise is to have a “single keel” fin where I can adjust its length for different wind conditions e.g shorter keel = less drag for lighter wind conditions and longer fin for heavier winds for maximum righting moment…well that’s the theory I like to test
First thing was to drill hole through the fin spine to take 4 mm SS bolt, the maximum chord of the fin is 7 mm so had 1.5 mm each side of the bolt. After drilling I found the bolt threat was catching on the sides of the 60 mm length hole drilled in the fins spine …hmm after lot of peanut scratching finally decided needed to have 6 mm carbon tube bonded into the fin spine so the 4 mm bolt would slide and not catch on removal, the carbon tube has 6 mm O.D which left 0.5 mm each side of tube before goes through the wall of the fin…lot time was spend making sure the fin was 100% square to the drill bit before drilling.
Then drilled lateral hole in the fin to accommodate a SS nut and bonded the tube and nut into the fin, after bonding needed to tap the epoxy out of the nut so the bolt would freely threat. Now can thread the SS bolt into the fin to the same depth of fin spacer that determines the length of the fin.
Then cut off 30 mm section of fin so when inserted into the fin box the two facing edges are flush.
The fin and spacer has as minimum tolerance when inserted inside the fin box but when tighten up the fin head bolt to lock in place, there was a movement present. The problem was I have angled cockpit floor to allow water run-out of the cockpit. Here the bolt head nut was not sitting square on the deck hence needed to make angled deck plate that removed any movement when the fin is locked into place.
Now everything works nicely.
To bond in the CF tube inside the fin I had to dissolve the foam core (acetone) I was side tracked and left the acetone in the fin too long and it dissolved the entire foam core, so now the fin is hollow, tested deflection and there was no measurable change whew !! lucky. This mistake gave another possible benefit, I can now add small amounts of lead into the bottom of the hollow fin to get exact race weight, possible could even shave the bulb little smaller (less wetted area/drag) and add shavings into the bottom of the hollow fin :rolleyes:
Now only task left is to find correct position of the bulb on the fin in water tank for correct static LWL.
Cheers Alan
This is how I do the fin and bulb - using a jig.
http://www.wcmya.ca/pop_topic_items/iom_fin_jig.pdf
John