I’m building Chesapeake Bay Log Sailing Canoe http://www.logcanoes.com/ . The hull is about 40 inches with a LOA of about 54 inches. The scale sail area is about 1400 square inches, but I’ll use less probably around 1000.
I need to determine the optimum location for the keel.
For those who don’t know the Chesapeake Bay Log Sailing Canoe has an a typical rig with two masts and three sails of unconventional dimensions. (see the attached image).
The full sized canoe has a center board. In the model the centerboard will be
replaced by a keel.
I’ve glassed the hull and I am in the final stages of fairing the hull. I’m close to the point of mounting the keel trunk.
I’m having trouble coming up with a good location for the keel that will provide good balance (or as good as can be expected). I’d rather have a first good guess than several refits of the keel.
Does anyone have any suggestion on how I might determine the center of effort for the rig, which will give me an approximate location for the keel.
My idea is to try to calculate a weighted center of effort using the center of
area of each sail weighted by the sail area.
I dont have a definite answer so hopefully somebody else can put something here from experience and wisedom. But I did find a pretty neat website that gives formulas to compute the keel placement for “life size” yachts.
I looked at the site. It is helpful for keep design, but what I’m looking for is something to help me calculate the center of effort. Once calculated, I can place the keel below the center of effort.
Cut out a paper plan of the sailplan…balance it on a pin,That will be it geometrical centre…
Take a guess at the ammount of “lead” the sailplan will require(about 4% wl for a sloop) and place the sailplan on the hull accordingly.
Some ammount of trial and error is required even by experts.
What a cool site, what abour Noddy 1940 with walking stick masts long before the British 12 meter “Lionheart”. Love the crew stacking, whats with the stern dickie seat?
What a interesting project.
I will have a look in my achives for a acticle on finding the CoE of mutliple mast yachts. Once that is found then you need to work out the CoLR. Cut out the underwater profile of the boat on stiff paper or cardboard include the keel in the shape and then balance the shape on a knife that is at right angles to the waterline, where it balances is the vertical line of the CoLR. The CoLR needs to be in front of the CoE.
The position is a % of waterline length, is the big question, how much it as it varys from 3 to 10 % depends on the type of hull and a whole lot of other hydrodynamics and some poeple would say witchcraft.
I think they are one of those boats you never really own - you just act as custodian for the next generation. In that respect they are a bit like the Mullet Boats and the M Class up here in Auckland (for your non-Kiwis; no - not the Marbleheads - an 18 foot clinker dinghy, see here http://www.mclassyachts.org.nz/. They look nothing like the Chesapeake Bay Log Sailing Canoes - but they have a similar tradition.)
David
As for keel placement - comments thus far have focused on centre of effort and lead. Good stuff - but don’t forget the other centres - floatation and bouyancy - which like effort, are dynamic with heel. On a Chesapeake canoe they will not move much (very long and narrow). Placing you CoG (of which the keel bulb will be a determinant factor) at or near the same vertical point (without heel) as the CoB, may help the boat to behave - then determine the rig postion from there.
Subject to the more learned comments of my colleagues on this site, the position of the CLR need not alter with scale - nor should the position of the rig. The area of the “keel” and the ballast ratio will need to be altered for scale effects - and of course these boats rely on the crew for ballast anyway. They sail with a centerboard or leeboard, which can be moved to various positions - but the most common position when sailing upwind will give you a good idea of where the CLR is best positioned. Gross up the keel in area, but keep its centre about the same.
As as with any prototype model - if possible you should provide for both a choice of mast positions and mast rake so that you can get it right by trial and error. Even at 1,000 sq in of sail, this is going to be one exciting model!
Its time for floatation testing and to roughly deterime the ballast needed. I’m just going to float the hull and put 1# lead weights at my intended keel position to find the amount of ballast needed to float the canoe near the scale water line…
My plan is to have a 4 inches (10cm) wide keel. If I were to make the keel the width of the scale centerboard the keel would be 8 inches (20cm) wide. For keel depth I’m looking at 14 inches (35cm).
You will require a larger area of keel than the scale-equivalent. So if halving the chord, you’ll need double the draft, and then some more. Sounds like you’ve got it about right. You could maybe add even a little more draft to the keel fin and it wouldn’t hurt. Good luck - and we’ll look forward to the pics.
The full size Cheasapeake Bay Log Sailing Canoe has a centerboard.
So what ever I finally choose for the keel will provide 10 to maye 15 times the lateral resistance over what a scale centerboard would provide. Besides, the boat wouldn’t stay dry side up without a drop keel.
I floated the hull today and it looks like my bulb will need to be 5 to 6 pounds (2.2kg to 2.7kg) to float near her waterline. I’m leaning toward 5 pounds because I figure that I’ll have atleast another pound of deck, electronics, and sail rig.
I solved the keel placement problem but making a 9" keel trunk that allows me almost 6" fore/aft keel positionin.
After I thought about it a bit, I decided that this project would be a prototype and I should use it to learn something about the rig’s sailing characteristics. If she sails fairly well I’ll build another that is a a bit more refined.
I attended the USVMYG Traditional Watercraft Regatta this past weekend.
My log canoe sailed very well. I have a little work to do on the rig.
For sailing the foot each sail needs to be raised at least two inches. because they drah when heeled.
The jib needs to be reduced so the keel can be move aft, the canoe was a little deep in the bow.
The balast needs to be trimmed by about one pound, she was riding below her typical waterline.
To place a centerboard on a full-size dinghy without math or too much head-scratching, guesstimate the CE of the sail plan, tie a string to the gunwale, tape your keel in place and tow it sideways…
Orr as a Scoutmaster’s wee3kend project for the troop, we ‘built’ a sailboat, which consisted fof lashing a Folbot lateen rig (45 sqquare feet) into my 17’ Old Town monster canoe. Then picking 2 Scouts, giving them each a paddle and telling one hewas the rudder and the other that he was the daggerboard. I told 'em how it worked, then we went sailing :). How’d it work, you ask? grin The boat was a rocketship…
Thanks for the suggestion. However, as you can see from my previous post ( http://www.rcsailing.net/forum1/showpost.php?p=21502&postcount=14) the boat sailed well with my solution of a oversized (lengthwise) keel fin truck that allowed me to adjust the keel fin placement.
