Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(15jan03) In this issue we'll look at ways to change sail rig balance. In the 1feb03 issue we will take a look at a new type of Bolger cabin.
THE BOOK IS OUT!
BOATBUILDING FOR BEGINNERS (AND BEYOND)is out now, written by me and edited by Garth Battista of Breakaway Books. You might find it at your bookstore. If not check it out at the....
ON LINE CATALOG OF MY PLANS...
... can now be found at Duckworks Magazine. You order with a shopping cart set up and pay with credit cards or by Paypal. Then Duckworks sends me an email about the order and then I send the plans right from me to you.
Lincoln Ross completed this Roar2 up in Massachusetts.
Sail Rig Trim 2
Last issue we looked at the basic balance of a sailing rig and looked at things that can change it. It is quite a compromise, isn't it? If you set your rig up to sail with just the right helm on one point of sail, everything conspires to change the helm on the other points. In this issue we'll look at trimming your sail rig to get the best compromise.
What I usually look for first is a good handful of weather helm in a good sailing breeze, enough wind to heel the boat maybe 15 degrees when on a close reach. A "good handful" would not be enough to tire you over the space of a few hours, but if you released the tiller the tiller would swing to the lee side of the boat quickly and the boat round up into the wind within a few seconds. When tacking through a good wave, the boat would swing quickly with maybe 30 degrees rudder deflection, that done in one quick and smooth motion. A sharpie, even a larger one like Birdwatcher, can run out of momentum quickly when tacking so the tack must be quick, perhaps less than five seconds to swing through 100 degrees although the larger the boat the more time it will take (and the larger boat will have more momentum to get though).
Having that I would hope for at least a neutral helm when sailing to windward in light winds. I think about every boat I've had, including all the Bolger boats, had slight lee helm in very light winds and I lived with it. Tacking in lighter winds might be a lot slower. If there is a lot of motorboat wake around you often won't be able to complete a tack in very light winds and will have to paddle your way to the new direction, then get the sails drawing again on the new tack.
Then I would look for enough rudder control on downwind.
WHAT TO DO ABOUT IT...
If your boat has too much weather helm you would think that the sail forces are too far aft of the hull forces. If you have a pivoting leeboard or centerboard, you can sweep the board aft on its pivot. That should move the board area aft and bring it into alignment with the sail force. There is a powerful arguement that boats should be designed this way from the start - with the sail area too far aft with the idea that the pivoting board will be swung up to adjust. Trouble is that we have in our minds an idea of what a boat is supposed to look like - the sails way up front. On a leeboard boat that is hard to get along with since the leeboard will have to go up front too and with it the widest beam of the hull. It would work pretty well with a scow hull but with a pointy bow we all seem to want our sails up front and our big beam behind!
ADJUST SAIL POSITION...
This rig trim game is usually one of inches. I think about the most effective way to trim out a rig is by adjusting the rake of the mast. If you look in Howard Chapelle's great books about boating 50 or 60 years ago, you will see that the old timers sometimes used adjustable mast steps. They could move them fore and aft just a few inches. But a few inches of motion on the step moves the sail above by a lot, usually maybe four times the step adjustment. For example, if I were to move the mast step on Birdwatcher forward two inches, the mast is raked aft and with it goes the sail. The tip of the mast would move aft about ten inches. The triangular sail of Birdwatcher is tied right to the mast. Its center of area would move aft about 4".
For a lugsail the effect is even more pronounced because the sail is tied right to the top of the mast. So, let's say with IMB that we have a 16' mast with 2' between step and partner, then moving the step forward .5" moves the tip of the mast aft 3.5". With it would go the entire sail area since the entire sail hangs from the masthead.
Of course, you would get the same effect by moving the mast partner aft instead of moving the step forward.
Rob Rhode Szudy had the best arrangement for this type of adjustment that I have seen. It was on his Piccup Pram. The mast heel on Piccup Pram is 2-1/4" in diameter. He whittled one side of his mast heel down like this:
So it would move foreward and aft in the step. Then he whittled out a shim to fit. If the shim is installed towards the front of the step the mast is raked forward. If the shim is shifted to the back part of the step as in the photo then the mast rakes aft. I think the old timers sometimes did something similar by fitting wedges at the mast partner.
My own Piccup has something similar by accident. When I enlarged the sail area by increasing he hoist by 2' I had to lengthen the mast. How to do that? I cast about the shed and found an old oar. I cut the blade off and found the loom was the same diameter as the Piccup mast tip. So I scarfed the oar loom to the original mast tip to lengthen the mast 2'. But he loom was not straight! The oar was a "found" oar, probably pitched because it was so crooked as to be useless. So my mast was not straight. It is curved a few inches! Usually I mount the curved mast with the sweep aft. That sets the sail aft a bit and I get a bit more weather helm. So if you make a mast that is not straight, don't dispair. What you have there is a special "adjustable helm" mast.
IF YOU HAVE A LUG RIG...
...you have another option of moving the hoist point fore and aft on the yard. Having used these for almost 20 years now I can tell you that they function best with the yard crossing the mast at about 40% like this:
So what is "about 40%". That is within a couple inches on a normal sized boat - not much variation allowed. If you move it forward on the yard you will get more twist to the sail which can hurt you a lot when close hauled. If you move it aft on the yard the sail may be overbalanced and not flop over to the new tack at the right time. Also remember that there must be some looseness up there to allow the yard to swing freely but not so much that the yard pumps back and forth in rough water. Usually everything conspires to pull the sail aft of the desired hoist point, so if you tie it at 40% the sail might set at something like 35% which is probably OK.
Here is a little trick I like to use on my own lug sails. Have two hoist points on the hard, one at 40% and another at maybe 35%. In strong winds you hoist at the 40% point and in light winds you hoist at the 35% point.
So in strong winds you would expect the most weather helm and the most sail twist due to the increase force on the sail. So you hoist the yard aft which sets the sail forward which reduces weather helm and sail twist.
In lighter winds you would expect the least weather helm, maybe even neutral or lee helm. So you hoist the sail with the halyard forward a bit on the yard, which sets the sail aft and that increases weather helm. Excessive sail twist is usually not a factor in light winds so you can get away with it.
Experiment a bit here.
Next time we'll look at Bolger's "Navigator" type cabins.
PHILSBOAT, SAILBOAT, 15' X 5.5', 550 POUNDS EMPTY
Philsboat is essentially an IMB with the nose extended to a pointy bow. The width and multichine configuration are the same as IMB's. The cabin is 3" deeper because Phil is at least 3" taller than most of us. In a boat with a Birdwatcher cabin like this one added depth to the cabin makes it safer in that the righting forces in a knockdown are greater. That would be true of any boat if the center of gravity did not move with the cabin roof but with the normal cruiser adding depth to the cabin also means raising the crew deck up so the folks can see over the raised cabin. And that means the CG is elevated too, and then all bets are off concerning self righting. But with a boat like Philsboat eveyone rides down low inside looking out through the windows.
Here is a photo of Bob Williams' IMB:
In addition to the pointy bow and added headroom I added what I hope is a serious motor mount. Probably 3hp will drive it as fast as it will ever go and that at part throttle. But the motor well gets to looking pretty large even for such a small motor. For one thing it must be deep to put a short shaft motor on a deep stern like this so I ran it straight down to the boat's bottom. Working on the motor down it its well will be about impossible and you might need to keep an eye on your knuckles when you pull the starting rope. And the well must be surprisingly wide to allow the motor to swivel in steering although the usual case here will be to keep the motor locked straight ahead and steer with the tiller. The wide well pushed the rudder off center and you need a crooked tiller or rudder linkage to make it all work. I opted for a simple but crooked tiller.
I also added low seats like those I saw added to the two IMB's that came to the Lake Conroe Messabout. Pretty much the same as what I have in Scram Pram where the seats do double duty as water ballast tanks. Philsboat seats could easily be converted into water ballast tanks also but the IMB capsize tests imply the ballast isn't needed.
The sail rig uses a balanced lug, 113 square feet and the same as that of a Bolger Windsprint which should be available from Harold Payson.
Philsboat uses taped seam construction. Five sheets of 1/4" plywood, five sheets of 3/8" and three sheets of 1/2" plywood.
Actually the size and material list for Philsboat are about the same as that of Scram Pram. So which boat would be better? Take Philsboat if you are a pointy bow guy. It should be better in really rough water. On the other hand Scram is wider and roomier. It has a flat step through bow that will splash and spit in rough water but makes beaching a very nice experience.
Prototype plans for Philsboat are $30.
Some of you may know that in addition to the one buck catalog which now contains 20 "done" boats, I offer another catalog of 20 unbuilt prototypes. The buck catalog has on its last page a list and brief description of the boats currently in the Catalog of Prototypes. That catalog also contains some articles that I wrote for Messing About In Boats and Boatbuilder magazines. The Catalog of Prototypes costs $3. The both together amount to 50 pages for $4, an offer you may have seen in Woodenboat ads. Payment must be in US funds. The banks here won't accept anything else. (I've got a little stash of foreign currency that I can admire but not spend.) I'm way too small for credit cards.
Here are the prototypes abuilding that I know of:
The Australian Dorado builder is done and is testing.
The Australian Twang builder is done and is testing.
The Oracle builder in St. Louis is waiting for his paint to cure.
Here is a Skat 12' catboat started in Alabama.
AN INDEX OF PAST ISSUES
BACK ISSUES LISTED BY DATE
Mother of All Boat Links
The Boatbuilding Community
Kilburn's Power Skiff
Bruce Builds Roar
Rich builds AF2
JB Builds AF4
JB Builds Sportdory
Hullforms Download (archived copy)
Plyboats Demo Download (archived copy)
Brokeboats (archived copy)
Brian builds Roar2 (archived copy)
Herb builds AF3 (archived copy)
Herb builds RB42 (archived copy)
Barry Builds Toto
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