Dear all,
thanks for all comments!
On the one hand hand I am glad that I have not missed something obvious, on the other hand I am a bit disappointed that nobody has a really convincing idea (which is no critizism at all!!!). so I have to continue testing …
Here are some further infos:
CB is located approximately in the middle of the fin (buoyancy of fin & rudder included). Center of gravity of the bulb is (depending on the keel) some millimeters in front or after this point (in front for light winds, more in the back for heavier winds)
CLR is located at the trailing edge of the fin when taking fin and rudder into account
CE of the sail plan - no idea, I still have to figure it out, but the boat is well balanced
Fin area is about 150cm², rudder about 38-42cm², lateral area of the hull is also about 150cm²
Sheeting angles are looking good. Sails start luffing more or less simultaneously. In no case the main sail starts luffing first.
Rudder angle - Claudio, you are right on a straight course. When turning, the rudder angle may be much more, because the flow is coming no longer from the front but more or less from the side. Therefore angles up to 45 deg. or even more will work without stalling. Of course you have to put the helm not tto fast to this angle … (I am sailing big boats since 40 years by myself)
Btw. stalling cannot be the reason because the boat starts to turn quickly. Stalling is a topic downwind, when the thumbs are too nervous and the boat will not gybe …
To much sail area/profile depth - I have aready thought about that. I think I will this check next. But I do not (yet) understand why other boats are carrying the same sails area without (or at least less) problems.
Hopefully it will stop freezing next week, but it will take a long time to melt the ice this year. Ice thickness around here is up to half a meter.
Just finished reading thread and from your descriptions of the various scenarios I’m inclined to agree with Jim (Astute Composites). As others will testify from my previous posts, the sum of my RC sailing experience adds up to just very slightly above zero. What I do have is many years of big boat sailing both for pleasure and professionally (it was really tough being paid to do something I loved !!!) both fully crewed & single handed. The only time I can recall experiencing what you’ve described was in high wind + big seas with a relatively novice crew who were in a ‘racing round the cans’ mindset, and kept all sheets cranked in tight through the tack which then lead to being in ‘irons’. Once the headsail trimmer was made aware of his oversight tacks became much quicker - so instead of losing places at the windward mark or when tacking to the mark overall fleet position could be maintained.
Bearing that little lot in mind, and of course once your sailing waters are a little less solid, try the boat with the jib sheet eased slightly for the bigger winds. Obviously, there’s always that compromise between heeling moment & drive from the jib so I’d imagine the adjustment will be tiny. Hope that helps & do keep us posted of your experimentation.
Hi,
just an intermediate result:It was not too much wind last sunday (between 0 and “nose-diving” with an A-rig), and I tested the same hull (No.3) the first time with a swing rigg. It was a completely different boat. She went well, so I sailed the whole day with my new “Swinging 3”. Must be really a problem of rig/sails with my old one …
Hi,
today I had the chance to sail again in heavier winds. I even had to change to the B-rigg at noon.
I got an hint from the multi-hulls, that too much rake can influence the tacking beheviour negatively. Seems that those guys were right …
I moved the foot of the mast back 5mm and left the poistion at deck level. Jib had to be moved forward, too (about 10mm). As a result rake is now approx. zero.
Tacking was much easier
the other sailing properties have not been changed noticeably.
rudder seems to be critical,too. It stalls easily. I have to be carefull when steering into a tack. Less rudder is more effective (just vice versa than before)
when it was impossible to tack, it was obvious, the the boat carried too much sail area. Going down to B helped a lot.
Nevertheless, the same hull performs much better with a swing-rigg.
Hi, Alan,
lead was enlarged. Mast position at deck level is the same but foot went aft, so the COE of the sail plan has moved forward while rake is reduced … No idea what happens with more rake
Swing rigg: no idea why the boat behaves completely different… Concering sailing properties swing rigg should be a little bit worse upwind, because luff of the jib goes more to windward usually. It has advantages downwind because effective sail area is larger.
Came across a very interesting article about [u]David Creed[/u] where says:
"I deliberately use this induced twist in most of my designs to "wash out” the lift from the bottom of the fin by placing the ballast CG near the fin LE.”
I have David Creed Fin on my IOM with option of using long thin bulb (370 mm) where the bulb C.G is well aft of the fin axis that gives 2 degree deflection.
From Aussie II days with wing keels they also used a trim tab at the tail edge of the keel so that when trimmed to leeward increased lift to carry boat more to windward and when trimmed to windward counteracted heeling moment but the leading edge of the keel always had the same angle of attack.
With a deflection in the leading edge of the fin is twisting and I’m wondering if this can be used in a positive way, if so which is better ?
Bulb C.G central to the fin axis (level bulb when heeling)
Bulb C.G aft of fin axis (increased lift to windward)
Bulb C.G forward of fin axis (resisting heeling moment)
Further, to use option 2 & 3 you need to build boat underweight so you can ballast hull to sail on LWL that may well affect fin/mast position with different CLR for each set-up ?
I have a question about the LCB in the attached pic from Claudio.
In there you say. (post #3)
"Note : on top of the deck shall be provisionally fixed representatives
weights corresponding to the Rig , Electronics, Fin and Rudder at the right position they will have definitively. "
Does this mean that the finished boat will/should balance on the same spot as the empty hull that is shown ?
I am most interested in RG65’s to apply this to.
Step one shows balancing the complete Hull. Is this true or should the balance point come from the underwater part or the 3D center of balance of one or the other?
To be clear is LCB Longitudinal center of Balance (2D) or longitudinal center of Buoyancy (3D) ?
Probably the same thing in the end. This is all such a vicious circle.
I work on the computer CLR is easy to find so is CE. I just never took those back to the LCB.
Need to figure out how to find that on a hull.
Finding LCB on existing hull is quite simple, I strip all gear out of the hull (servos etc) and place hull in water and use depress the hull on the centre line with finger to search to find point until the hull sinks equally into the water.
There maybe other ways, but this is easy & fairly precise.
And if you push the hull laterally while still in the water you will find the CLR.
The trial centering will start with the CE falling on the leading edge of the Fin.
Cheers
ClaudioD