Centreboard angle

[seanslife]

Gday Investigators and Happy new year!
I've finally been able to get Whispering Wind up on the club's hoist to free up the centreboard. When I finally got it moving (after many years moored by the previous owner there was quite a sizeable colony of molluscs and shell fish growing there, not to mention the rust) I noticed the knot in the pennant line prevents the board from dropping any further than the angle in the attached picture, maybe 45-50 degrees. Rust and anti foul line show it hasn't been beyond this angle for a very long time.

Is this the right angle (couldn't help the pun) with so much rake? Or should it be closer to vertical? Does it matter?

Cheers
Sean in Canberra

[atles]

Hi Sean!! it neatly down !
but yes it should be 90 degree does it matter not much at the point you have it.
it would drive me up the wall not having it working fully.but that just my personal choice.

[seanslife]

Atles
According to the drawings at John Crawford Marine (It appears the angle is slightly more acute, say about 80 degrees? Regardless, you'reright I 's much more than the 45 degrees previous owner had it set to. See drawing: http://www.johncrawfordmarine.com.au/tr ... 3-drawings

[Steve]

Hi Sean,

Raking the centerboad back helps control the helm.( it reduces weatherhelm) . I often lift it right back and/or up when sailing to windward if I have good boat speed and always up when down wind. I have marks on the lift rope to tell me where it's at.

[Dr. Peter]

Changing the rudder for something decent reduces weather helm.

Reefing the main reduces weather helm.

I reckon the best angle is 0.

This weekend, we were out in 25 knots, 1m swell, two reefs in the main, and a big deep and wide ex-Hartley 18 rudder (it's steel plate) in place of the standard rudder, which is crap, and we pointed better than a Timpenny 770, and showed no visible slip to that other boat, although he beat the hell out of us for speed. Irrespective, that was a thumping good sail and our centre-plate remained firmly jammed in the casing.

I know my view is controversial, but really, do we need this problematic centre-plate on our boat?

Obviously, the previous owner of your boat did not care about it too much. Perhaps, because it wasn't worth getting worried about.

[Steve]

You may be right about the the centerboard Dr Pete but comparing performance to what you think another boat on the water is doing is irrelevant.
Above 15knts of true wind, I find it hard to get my boat to sail better than 65 deg to the wind. Where my boat is pointing and where I actually are going are two different things. The angle to apparent wind which makes the performance to windward appear good is deceiving. I often throw tacks of 140 to 130 deg to sail upwind in 15 to 20knts true wind. I gather this info from gps data, print it out and measure the tack angles. I overlay it on google earth for a real visual display and the results are usually pretty disappointing performance wise. A boat that sails to windward well will tack at 80 to 90 deg and a real upwind performer will do better.

In the meantime I will continue using the centerboard like I have been until I can prove it makes no difference. I usually lift it to reduce drag and like I mentioned before, to reduce a bit of weather helm. The advantage of leaving a centerboard up may be that the boat is faster and spends less time on a tack, hence less time slipping away to leeward, and that is the approach I take on it.
Next sail out I will collect the data with the board up and do a comparison.

[Dr. Peter]

Next sail out I will collect the data with the board up and do a comparison.

Now that would be good data but Steve, make sure you think carefully about the design of the experiment. You need to make it so the only factor being altered is the centerboard position if you can. Try and keep everything else unchanged. Also do more than one test so we can get an average. That is a very good idea. I may end up having to change my mind.

BTW it was the skipper in the other boat who made the observation that we were pointing high and did not appear to be slipping much.

As I said we had two reefs in (In 15 knots I would have the first reef in, at about 20 the second goes in). This was in combination with the standard-sized headsail although the barber-haulers were set so the sheets pulled along the foot of the headsail and allowed the top to vent. The boat felt good on the tiller - it wasn't an arm wrestle and we rarely let out the main to de-power in the gusts. I think having a rudder which goes slightly under the boat is better for balance.

Anyway - looking forward to that data.

By comparison the other boat in my story was over-powered a lot of the time and that might have been a factor. I think technique may have played a role too. At higher wind speeds waves become a factor, especially for small craft like ours and you have to bear away for speed. What the other skipper did not do, but I did, was get hard on the wind after the wave had passed under the boat and before the next wave came along. However, he was overpowered

[Yara50]

A small angle of the centreboard is needed to keep tension on the liftng cable. Otherwise the board can move every time the boat pitches. (Assuming of course, that it is swinging freely).
Even though it is not an aerofoil shape, the centreboard is a lot more efficient than the shallow keel, and I find it does make a big difference to the pointing ability.

A barbour hauler is a good idea. (Adjustment rope to change jib sheeting angle.) If you have one can you please post a pic of the design. I am thinking of just having a clip on the fixed end of the standard sheet, and moving it to the chain plate when I want a more open angle.