Thread: The Goat Lug...another use

Originally Posted by Compass Project

I have drawn Mik's beautiful lug into a new version of the Chamberlain Beachcomber-Alpha Dory that I intend to start next year. Here is the sketch at this point and it will be fine tuned a bit more...

Your idea is similar to my idea to use lug yawl rig for Radoslaw Werszko's 4.2m skiff:



http://www.dinghy.pl/42m_skiff.htm

Howdy Robert,

The 4.2 skiff has its centreboard and case a loooooong way forward. It would have to be moved to the right position once you worked out where the lug rig was going to go.

Just looking at the drawing its centreboard looks way too shallow and maybe too wide. My standard size for boats from GIS to PDR size is to try to get almost 3ft deep and 10 inches wide into the water - which means the centreboard needs to be longer than this.

The boat will perform so much better.

There is a lot of internet wisdom that the centreboard needs to be a certain size relative to the sail area. This advice is wrong and based on yacht design (where it works a bit better, but still is a poor guess).

IT is as silly as the internet wisdom that you can
shrink or stretch a hull by a certain percentage (don't! Speak to the designer to make sure it won't cause any problems) or that
having a spar distort sail shape on one tack makes a big difference (some difference, but not much at all - with a properly set up sprit rig I can't notice it all)

The reason a fixed percentage of sail area for the centreboard is wrong is that small boats are slower, so need a bigger board to develop enough side force.

You could reduce the size a little for a small boat for a child that did not have a lot of sail ... but not too much.

A further possible reason the board is so small is that many think that the area of the centreboard is the most important thing. All competition sailors know it is the depth. So if the board is shorter, you need a lot more area.

But the rest of the boat ... I quite like it Robert and those things are easy to fix.

Best wishes
Michael.

Michael,

Hmmm
I think you are quite right (about efficiency) but 4.2 m skiff was designed as a rowing skiff with auxiliary sail for light wind... She is not a racing boat - she is a boat for slow rowing on tiny lakes and reaching in light air ...

My idea of yawl rig for 4.2 m skiff was for traditional character similar to English beach boats and yawls - not for efficiency. And for drop down centre of effort for stronger winds for beach cruising. Deep (hi aspect ratio) centreboard is not good for this purpose.

And: Proa PJOA (classic shunting proa with crab claw rig) has not centreboard and she is able to go close to wind similar to most contemporary sea boats (40 degree)

Aloha!!!

The proa will go upwind nicely because she has so much lateral area. She is deep and long in the water. Sensational amount of area!

With the dinghy ... make the board longer ... doesn't take any time or much extra material. But see how much difference it makes. You can always cut it smaller if it doesn't make a difference between deeper. And if you raise it to the design depth it still will not interfere with the sail.

MIK

Originally Posted by Boatmik

The proa will go upwind nicely because she has so much lateral area. She is deep and long in the water. Sensational amount of area!

Yes!!! That is truth! And shape of her hull is asimetric in lateral surface for more efficiency.

With the dinghy ... make the board longer ... doesn't take any time or much extra material. But see how much difference it makes. You can always cut it smaller if it doesn't make a difference between deeper and raised to the design depth.

You are right! Thanks a lot!

Aloha!!!