Michael Moore wrote:

Richard Brooksby wrote:

Perhaps the CLR is shifting a long way forward on heeling. Maybe because the keels are assymetrical foils that “fly” upwind, and the windward keel lifts when heeling. I can imagine that would move the CLR a great deal if the keel foils are effective. But this is speculation and I have no proof.

All monohulls do this. When a boat heels the underwater shape changes and the result is they turn to weather. You can test it, as I have done, as follows.

On a F2 or F3 day set up to go to windward, then let go the tiller. My Coromandel will carry on without luffing up. Slowly move over to the lea side and the boat will luff up a little. Move to weather and she will bare away! All well set up boats will do this tegardless of their rig!

Er...
.. that depends on the hull shape. However, during the last forty years, most boats have been made with broader and broader sterns, known as unbalanced hulls, and these certainly will develop weather helm when heeled. If they are not fitted with large, efficient and well-balanced rudders, one will have a struggle to keep them on course. Remember, it is not enough to fix the balance by moving the CE of the sail forward. When rolling in a seaway, downwind (with or without sails up), an un-balanced hull will be prone to broaching, again unless there is a big rudder or two to hold the course.

I may sound like a rudder nutcase, constantly nagging about this. Maybe I am. Remember though that this was how the Chinese seamen and boatmen controlled their ships. Their rudders were (and are) made oversize, in our eyes, to act as centreboards number two. The bonus was quick tacking and better handling downwind  -  most probably with the fore cb. raised.

My last boat, the 6.5m Frøken Sørensen had a typical unbalanced hull, with an axe-type bow and a very wide stern. She got away with it because her designers had fitted her with a huge, deep, well-balanced and perfectly streamlined swing-up rudder. Her rudder never let us down.

Arne

Yes indeed. I'm a bit startled by how much though. It probably makes both the “push the boat” and “balance a silhouette” methods a bit useless. I'll have to keep experimenting and using empirical methods. Darn :)

According to my measurements, Tammy Norie's CLR is almost exactly 60% of the LOA from the bow. In the original sail's normal position, the COE (measured using the gravity method) is 50%. That gives a lead of 0.63m.

PJR says "Our normal rule is to give a single-masted Chinese rig a lead of 9 per cent of the length of the waterline". That's 9% of 4.9m, or 0.44m.

That gives a lead well in excess of that recommended by PJR, and yet the weather helm is quite bad.

Any thoughts?

Perhaps the CLR is shifting a long way forward on heeling. Maybe because the keels are assymetrical foils that “fly” upwind, and the windward keel lifts when heeling. I can imagine that would move the CLR a great deal if the keel foils are effective. But this is speculation and I have no proof.

I've just spent some time determining Tammy Norie's CLR by repeatedly pushing and pulling her sideways from the dock with a boathook in fairly windless slack water.

I can announce… https://flic.kr/p/Yu5PPf

I also tried the experiment with the Hebridean in the water (its pendulum is far back) and with the outboard lifted from the well. The Hebridean may have shifted the CLR back by a few centimetres (¾%) but that could be within the margin of error. Lifting the outboard made no detectable difference.

I think the middle of this stanchion is right.

If any other Coromandel owner knows better or can repeat the experiment please post your results.

Once again the answer is yes and no, Arne.

Yes, I am spending a little energy but I'm not trying to invent anything new, simply trying to simplify its construction to the bare minimum while keeping its critical and useful features. Apart from being rather expensive, the commercial units cannot be easily repaired without expensive spare parts, and certainly not while at sea. A cheap DIY unit tailored to the size of boat means a full set of spare parts can be carried and assembled into a spare unit if needed. There is no reason a DIY unit would not have comparable performance to the commercial gears. My friend Roy preferred the standard Belcher pendulum gear on his Folkdancer with horizontal hinged OTG Mk2 over his later Windpilot Pacific on a Rival 32.

Re. your PS, Arne, it's much easier to stabilize a wing with tail feathers on a nice moment arm than without, and similarly a nice rudder at the aft end of the waterline is the sensible way to control a boat. The Splinter doesn't need an auxiliary rudder as the existing is more than adequate. However there are other designs that do need something.

Cheers, Slieve