I decided to do a tank test to check for leaks and do a push CLR test
This brought up an interesting result the CLR was further back than expected at 195mm from bow
I pondered on this for a while and have decided that the method of calculation which I did in AutoCAD to form a region and then got the x; y; coordinates of the centroid as described in this statement might be inaccurate with only a half size rudder?
The information I had said - “Imagine a cut out of a side view of your boat including only the under water part. Balance it on a pin. That’s the centre of lateral resistance CLR.
Include the centre board and a half sized rudder.”
For those of you who may have AutoCAD but do not know how to use it the procedure is as follows
Assuming your profile is in AutoCAD, a 2-D drawing, using a polyline, trace around the entire underwater profile area.
With the REGION command, declare the polyline a REGION (Type REGION on the command line, and select the tracing polyline as the region).
Set the Origin of the drawing at some convenient point on the drawing, such as the front end of the waterline (TOOLS-NEW UCS-ORIGIN).
Then on the command line, use the MASSPROP command to determine the mass properties of the region (MASSPROP, select the region you just created) and a window will pop up with the mass properties of the region. Included in those properties will be the centroid coordinates of the centre of area (or mass) from the origin. Using those coordinates, you can put a point or a set of cross hairs at the centroid location.
Well to try and pre-empt your answers, (because I did not want you to get splinters in your fingers) I have recalculated the area including the whole rudder (in Brown) and included the results
(I switched off the layer with the picture to make it easier to view)
The only thing I can think to explain the difference between the push test and the re-calculated area is that the results of the push test are not accurate enough and that maybe on a much calmer day the averaged figures obtained from the push test would come closer to arithmetical result but for such a small hull I would have expected it to be closer than 12.96mm??
Just had another thought ~ should the waterline length measurement include the rudder past the hull?
Thanks Rick
Made a suit of sails for her today from some off cuts from a hot air balloon and stuck her deck down having first filled her fwd. 50% with foam off cuts.
Now have to get the servo to sail geometry right, stick on the gunwales and then give her a trial ~ lots of fun
Rgds
AndyT
A quick question about her sails… i’ve noticed that on many (most?) sloop-rigged footies there is a stick (a spar?) along the bottom of the jib. I don’t see those on full scale boats, nor on your boat here. Is there a performance loss at our wee small scale with a floppy jib?
I’ve avoided the issue with my intended first footy (gotta love a catboat!) but after we settle in (just moved to the Huntsville, AL area) and I get my first boat built, I’m sure I’ll be looking at a second boat, and while I’m sure McRigs are most excellent for newbies, they’re just not very sexy!
Hi Rick
The rigging of the jib is dependant on what you are trying to achieve
Jib’s rigged are more common in true life as they pivot from the attachment point this naturally means that you are reliant on the a separate sheet setting for the jib. This i have achieved by a separate sheeting arrangement that can me slid along the main sheet to adjust tension.
Models incorporating a jib boom, typically have a pivot point about 1/3rd back from the leading edge and have the ability to tension the jib in lots of different ways ~ sliding the pivot point of the bow sprit also allows the skipper some alteration of the CoE in relationship to the CLR and hence the performance of the model.
Real sailing boats have different means to achieve this trim like moving the dagger board etc
Any news on sea trials? I love this little boat :).
Is this sort of sailplan (yawl?) dependent on a particular hull layout, or could you take most any hull (say, a bobabout, or a razor) and sucessfully give it a sailplan of this nature?
Hi Rick
Its a Gaff rig ~ its not specific to the West Country Trader
If you like this type of setup you may wish to get a book from the library called “The Gaff Rig Handbook” by John Leather ISBN 0-7136-6174-7
I based West Country Trader on a Falmouth quay punt called "Pride of Port circa 1880 and built by Thomas of Falmouth
My model is yet to be completed with a blue gunwales and scuppers to be added to the hull.
The hull is vac formed and obtainable from Mike Mayhew at Waverley Models.
In her supplied form, she is slightly too long for the Footy measuring box, so I cut off and the stern and made a new one from plasticard.
The attached pdf shows the drawing from the Gaff Rig Handbook and the subsequent COE / CLR calculations that needed to be transferred from the drawing
I guess this type of setup could be used on any hull and makes for a very nice character craft
As soon as I have done some more work on her I will post some more photos.
The wee mizzenmast (is that the right term?) adds alot of character, I think, even beyond the already sexy gaff-rig :). Character craft appeal to me much more than pure racing footies, but maybe that’s because there aren’t any footy sailors nearby. I’m hoping to get down to the local pond this weekend to watch the local model-yacht club sail their victorias, though.
I’d be interested in seeing how you run the sheets for all 3 sails… is a single servo controlling them all?
