Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(1February 2014) This issue will be about hiking on sailboats. The 15 February issue will take a longer look at dory stability.
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...
...which 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.
Brian Graham sails into the sunset with his new Mayfly14.
Hiking and Sail Forces
EFFECTS OF HIKING....
In the last issues I looked at the effect of ballast on the boat's stability but limited things to having the CG on centerline. But the effect of a crew's being off the center of the boat, "hiking", can be significant even for mid sized boats like Jukebox and Jewelbox. Let's look at a couple of examples based on the new boat Frolic2 shown down in the featured boat section.
Take a look at Figure 1 which shows why hiking works so well. If the boat's overall CG is offset from centerline, that offset is added, to a certain degree, directly to the righting arm calculated by the stability program. I say "to a degree" because the added effect is actually the offset multipiled by the cosine of the heel angle. That would mean it is quite effective at small heel angles, drecreasing as heeling increases to the point where hiking has no benefit at 90 degrees of heel. (Unlike traditional ballast which is most effective at 90 degrees of heel.)
So here is how you can do the numbers. First you need to figure the CG. But now we also need to figure the lateral CG where in previous examples we figured only the vertical CG.
Here is a first cut at the CG for Frolic2: Item Weight (W) Height(X) (Y) WX WY Hull 400 12" 0" 4800 0 Mast 20 90" 0 1800 0 Yard 8 190" 0 1500 0 Sail 5 120" 0 600 0 Boom 6 65" 0 390 0 Crew 200 20" 24" 4000 4800 Total 640 20.5" 7.5" 13100 4800
So the chart shows the Frolic2 with a 200 pound crew sitting on a side bench has a total weight of 640 pounds, it's total vertical CG is 20.5" above the inside bottom (which I used as a reference point), and 7.5" off centerline to the side the crewman is sitting on.
With this information, and knowing the lines of the boat, we can fire up Hullform6S and crank out a few stability calculations to get an overall picture of the boats stability. But there's a problem for now: Hullform6S won't figure CG's that are not on centerline. So we run the stability calculations on centerline and adjust them afterward by hand (or write a simple spreadsheet if you must).
In detail here is how I do it. Hullform gives the righting moment (in foot pounds) and I divide those numbers by the weight (in pounds) to get the righting arm (in feet). Then I take the CG offset (in feet it equals .625'), multiply by the cosine of the heel angle, and add that to the Hullform righting arm to get the new righting arm (in feet). That gets multiplied by the weight (in pounds) to get the "hiking" righting moment.
Here's the example for Frolic2 with the single off center crewman: Heel (H) H6S Righting Arm .625' X Cos H Total Arm Total M 10 .64' .615' 1.26' 800 20 .82' .59' 1.41' 900 30 .77' .54' 1.31' 840 40 .61' .48' 1.09' 700 50 .44' .40' .84' 540 60 .25' .31'. .56'. 360 70 .09' .21' .30' 190
Here is what is looks like:
Well, you can see that the effect of the skipper hiking (or in this case just sitting on the upwind side of the boat), about doubles the righting moment of the boat. I'm a bit surprised that the boat still shows a positive righting moment up to 70 degrees of heel. But the Hullform analysis indicated that the rail is going under at 60 degrees. If it really works out that way it ain't so bad. It certainly ought to give the crew a good indication that it's time to back off the sheet! Actually, if the oarports are left uncovered there will be some flooding even before then.
On the chart I've also shown the effect of a second 200 pounder on the upwind seat. Quite an effect. Righting moments are way up again, although the program showed the boat would now flood over the rail at 50 degrees of heel. I want to show this because the crew you sail with will certainly have an effect on the impression a boat leaves you. Sometimes I've admired how some folks seem totally unfazed by stiff winds only to find they are always sailing with heavy crews. (My old Jinni capsized on me twice while solo, but never with two crew even though there were some wild sailing days.) One similar problem is the case where a swimmer tries to reenter a light boat. If solo, the boat might easily capsize as he loads his weight on the rail to pull himself into the boat. He may not think too much about that if he never sails solo and the extra crew weight in always in there to stabilize things as he climbs back in over the rail.
Another thing to consider is the case of the solo skipper who is seated upwind with the boat clipping along at maximum righting moment. He has to lean to the center or lee side to clear a line or something. The force on the sail is not affected by his actions, but the boats righting abililty is cut in half, or less. The boat capsizes! He needs to depower the sail by slacking the sheets before leaning over to the lee side. I suspect this may one of the most common reasons folks capsize small boats.
CONVERTING RIGHTING MOMENTS TO SAIL FORCES....
This is easy as pie! Look at Figure 3:
Once you've figured the righting moment, all you need to do to balance the boat is to divide the righting moment by the distance between the center of area of the centerboard (or daggerboard of leeboard or keel, whatever you are using to prevent leeway) and the center of area of the sail. On Frolic2 the two area centers are about 12' apart. So if the maximum righting moment is 900 foot pounds, the maximum sail force (and centerboard force, on a normal boat the sail force and centerboard forces are equal and opposite) is 900/12=75 pounds.
What does that mean? We'll return to this subject in a while and relate the righting moment curve and the resulting sail forces to the wind's speed over the sail and the water's speed over the board. Given the righting moment curve and a certain sail we can figure the wind needed to capsize the boat. Or given a wind speed figure the maximum sail we can carry.
SHANTEUSE, SHANTYBOAT, 16' X 6', 700 POUNDS EMPTY
Shanteuse is a slight enlargment of the mini shanty Harmonica. Shanteuse is 1' wider than Harmonica and has a 3' extension on the stern to allow a small back porch and a motor mount that is totally out of the living area.
Above is a Shanteuse built in Florida by Vince SantaMaria a couple of years back but he stretched his to 24' so I couldn't really call that one a Shanteuse. But here is one by Douglas Snelson in Tennessee that looks to be right to the plans so I will call this one the prototype. He sent a bunch of photos:
I've also made Shanteuse a little heftier. I'm thinking this one will weigh about 700 pounds empty where Harmonica comes in at around 400 pounds. I'm not sure if the extra beef is needed because Harmonica seemed totally adequate to me as far as strenght and stiffness go. But the extra size of Shanteuse is probably going to take it out of the compact car tow class. The plywood bill for Shanteuse looks like six sheets of 1/2" plywood and eight sheets of 1/4" plywood. I would not use fancy materials on a boat like this and am reminded of Phil Bolger's warning to never spend a lot of money building a design that was intended to look cheap. I see pine exterior plywood at my local lumberyard selling for $11 or a 3/8" sheet and this entire boat could be built of it. So the plywood bill would be less than $200 and I'm thinking the entire bill less than $500. The pine plywood looks quite good to me, its main drawback being that it doesn't lay very flat.
These boats can be very comfortable to camp in. The interior volume and shape are not unlike the typical pickup camper or the volume in a full sized van. It's not huge, it's cozy. The top has an open slot 28" wide from front to back on centerline. You can close it over with a simple tarp, leave it open in good weather, or rig up a full headroom tarp that covers the entire boat. I've shown lots of windows but the window treatment can be anything you like. You do need to see out. I would be tempted to cover the openings with screen and use clear vynal covers in the rain or cold. For hard windows I think the best material might be the Lucite storm window replacements sold at the lumberyard. Easily worked, strong, and not expensive.
As for operation, these are smooth water boats. So it is best to stay on small waters that never get too rough. On bigger waters you need to watch the weather very carefully. For power I would stick to 5 or 10 hp but I'm very much a chicken about these things. To plane a boat like this, remember the good old rule of a horse for each 50 pounds. So if you are running at 1000 pounds total you will need at least 20hp to do the job and then at full throttle. So I think you would want at least 30 hp to plane at 2/3 throttle. And this boat could easily be loaded to over 1000 pounds.
Plans for Shanteuse are $35.
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.
I think David Hahn's Out West Picara is the winner of the Picara race. Shown here on its first sail except there was no wind. Hopefully more later. (Not sure if a polytarp sail is suitable for a boat this heavy.
Here is a Musicbox2 out West.
This is Ted Arkey's Jukebox2 down in Sydney. Shown with the "ketchooner" rig, featuring his own polytarp sails, that is shown on the plans. Should have a sailing report soon.
And the Vole in New York is Garth Battista's of www.breakawaybooks.com, printer of my book and Max's old outboard book and many other fine sports books. Beautiful job! Garth is using a small lug rig for sail, not the sharpie sprit sail shown on the plans, so I will continue to carry the design as a prototype boat. But he has used it extensively on his Bahamas trip towed behind his Cormorant. Sort of like having a compact car towed behind an RV.
And a Deansbox seen in Texas:
Another prototype Twister is well along:
And the first D'arcy Bryn is taped and bottom painted. You can follow the builder's progress at http://moffitt1.wordpress.com/ ....
AN INDEX OF PAST ISSUES
THE WAY BACK ISSUES RETURN!
MANY THANKS TO CANADIAN READER GAETAN JETTE WHO NOT ONLY SAVED THEM FROM THE 1997 BEGINNING BUT ALSO PUT TOGETHER AN EXCELLENT INDEX PAGE TO SORT THEM OUT....
THE WAY BACK ISSUES
15feb13, Drawing Boats 3, IMB
1mar13, Figuring Displacement, Paddleplank
15mar13, Drawing Boats 4, Frolic2
1apr13, Drawing Boats 5, RiverRunner
15apr13, Drawing Boats 6, Picara
1may13, Two Letters About Keels, Blobster
15may13, Drawing Boats 7, Roar2
1jun13, Drawing Boats 8, Polepunt
15jun13, Rend Lake 2013, Toto
1jul13, Drawing Boats 9, AF4 Grande
15jul13, Taped Seams, Mikesboat
1aug13, Plywood Butt Joints, Paulsboat
15aug13, Sink Weights, Cormorant
1sep13, Lugsail Rigging, Hapscut
15sep13, Sharpie Spritsail Rigging, Philsboat
1oct13, Modifying Boats 1, Larsboat
15oct13, Modifying Boats 2, Jonsboat
1nov13, Modifying Boats 3, Piccup Pram
15nov13, Sail Area Math, Caprice
1dec13, Stretched Stability, Ladybug
15dec13, Trailering, Sportdory
1jan14, Cartopping, OliveOyl
15jan14, Width/Stability, HC Skiff
Mother of All Boat Links
The Boatbuilding Community
Kilburn's Power Skiff
Bruce Builds Roar
Rich builds AF2
JB Builds AF4
JB Builds Sportdory
Puddle Duck Website
Brian builds Roar2
Herb builds AF3
Herb builds RB42
Barry Builds Toto
Table of Contents