Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(15MAR98) This issue will discuss putting water ballast on a real boat, some details of the tank, and the effect on stability. Next issue I hope to have some photos and test results of my new AF4. If not I will carry the stability discussion a bit farther showing how to size the sail rig using the stability curve.
KILBURN STURDEE DORY UPDATE...
You may recall my writeup on Kilburn Adam's Sturdee Dory that was tinkered with to make for minimal and efficient (cheap) cruising. Kilburn and son have whipped up a page at http://home.stlnet.com/~altojazz/kilburn.html which includes lots of big photos of his boat. Take a peak by clicking on KILBURN.
AF4'S FIRST FLIGHT
WATER BALLAST DETAILS...
SO you've decided to try water ballast. How to do the ballast box? How to flood and drain it? The only boat I've designed with water ballast (so far) was Scram Pram. There were two Scam prototypes built and the first one had the water ballast and second didn't. Here is a letter from the first builder......
.........My sage and good friend, Tim Webber, keeps sending me articles on water ballasting from his homesite. I built a waterballasted boat called Ghostling(design is listed as Scram Pram on Jim Michalak's page).
Of the articles I read I have no real substance of disagreement. However, my experiences with Scram Pram may add these different observations.
First, it is highly impractical to be shifting water ballast from one side to the other unless the boat is: 1) large and 2)on long tacks. Even given these requirements it is still a risky business to make an emergency maneuver with this profile. Before I leave this subject, I would like to point out that of the articles I read I did not find a mention of stress loading on the rigging caused by loading one side and making the other bouyant. Having collapsed two mast supports on previous crafts, this is a phenomenon that I've had some time to contemplate.
Next I want to approach the recurrent subject of water ballast taking up too much space in the craft. If one is going to water ballast they should choose a boat with not only the right shape, mainly wide and fairly flat bottom, but also a design that could integrate the tanks into the structure. For example, Scram Pram easily takes on 300 lbs of water ballast and it actually improves the interior of the boat by adding a strong internal keel, comfortable seats/beds, and providing foot rests. In this case the tanks were in the design from its' inception and of course, Scram Pram is 100% waterballasted. Also, she moves exceedingly well in light air whether ballasted or not.
On Scram Pram I devised a 3 tank system(the third tank being Jim Michalak's idea to be used as a trim tank). Scram had two saddle tanks forming the beds, seats, foot rests and internal keels.
The two saddle taks accounted for about 250 lbs. of the water and each one had 3 apertures in it. 1) first there was the obvious hole in the bottom at the deepest point of 1/2 inch and it filled it like a water fountain. 2) Next was a port hole directly over it with a see-through cover just large enough to put you hand through to put in a stopper if you cared to. This was not necessarry since the tanks were capable of holding their fluids by sheer force of vacuum. 3) The third apeture was at the front of the tank and had a PVC pipe of 3/4 in. rising a foot or more with a screw-on cap with petroleum jelly kept on it as well as the screw-down port cover to prevent air leakage; remember, a tight seal is necessary if we are going to create a vacuum.
This arangement fills and empties quickly giving one the option of using no ballast at all on those light days when you have a number of passengers that you can shift from side to side catamaran-style and the see-through port allows you to check the status of your tanks to see if they are loosing their water and if your vacuum is working properly.
One thing I did not test with Scram Pram that should work is the addition of a bicycle valve at the top of the PVC cap. This simple addition would allow one while under way to "blow" the tanks submarine style when the wind dropped, you picked up more gear, or for those suicide jockies, just to blow the leeward tank to gain more upright sail area at the cost of some stability on the boat.
The air used to empty the tank could come from a compressed can, an electric pump or a manual foot pump. The last two options are certainly inexpensive enough.........
I've never seen the installation mentioned above, but the Scram tanks look like this:
My idea at the time was to fill the tank by removing the deck plate, reaching into the tank and pulling the drain plug. Then stand by as it fills to replace the plug just as the tank is full. If the top of the tank is above the normal waterline, the tank may not fill all the way and you have to top it off with a bucket and replace the deck plate. If the tank top is below the waterline and you forget to replace the plug, your boat could sink. Anyway, I think he system would work with very cheap stuff and no external plugs to deal with. (I'm not sure how Bolger did it on Martha Jane?)
What the Texas Scram builder did was the above but he added a standing pipe with something like an airtight valve on the top, as I understand it. So he can fill the tank by opening the bottom port and let the water rush in while the air rushes out of the open tube. When full (assuming the tank top is below the waterline) the tube is sealed and the water somewhat trapped in the tank. It's very much worth a try and is a noble experiment in that it is cheap, and that if it works is an improvement, and if it doesn't work it can be returned to the original design very easily.
I don't know how much testing the Texas Scram got, but one thing I would watch out for with the tube system: On a long, long tack with lots of heel, the up side tank may not hold its water by vacuum alone. It may dribble out slowly. Solution would be to just use the plug. But for a fin keel water ballast system designed merely to right the boat in a knockdown, wouldn't this system be perfect?
EFFECTS ON A REAL DESIGN....
Last issue we used the Hullform6S program to look at stability of a simple rectangular "boat". Let's look at a real design. The example here will be Jukebox2, featured later in this issue. And we'll put in some spice by comparing the results with Jewelbox, a very similar boat that used the unballasted Birdwatcher cabin system.
Here are some rough cuts at the weights and CG's:
Jukbox2: Item .Weight(W) .Height above bottom (X) .WX Hull 700 21 14700 Bottom
4 400 Mast 50 100 5000 Yard 12 210 2520 Sail 5 150 750 Boom 16 70 1120 Crew 200 36 7200 Ballast 300 3 600 Totals 1380 23.4" 32300
Jewelbox: Hull 700 21 14700 Bottom 100 4 400 Mast 50 100 5000 Yard 12 210 2520 Sail 5 150 750 Boom 16 70 1120 Crew 200 18 3600 Total 1080 25.9" 28090
Running the above weights and CG's through Hullforms and I get the following righting moment curves:
Both boats have the same basic length, cross section in the cabin, and bottom shape. They have identical sail rigs. In the weights you will see the item "bottom". Both boats have a thick 1" bottom and this separate item is supposed to account for the extra weight there. As for the crew situation, it changes all the time, of course, but the crew on Jukebox is above the overall CG and adding more crew makes it less stable. For Jewelbox the opposite is true. Adding more crew to Jewelbox makes her more stable since the crew sits below the overall CG. Also, in the analysis of Jukebox, only the watertight volumes of the hull were used in the Hullforms file. If you look at the gif of Jukebox below, Craig O'Donnell has presented one that shows the watertight volumes. For the Jewelbox, all the volume is watertight except for the small bow well.
I had hoped this boat would be self right up to 90 degrees but it looks like it goes to 80 degrees in this ballast situation. (What does that mean? Chapelle considered righting from 45 degrees of heel was fine for a sharpie while today's bluewater sailors like to self right quickly from 140 degrees of roll.) I think another 100 or 200 pounds of ballast is needed to get it to 90 degrees. Although this discussion is about water ballast, any ballast material of the same weight mounted inside the hull at the same location will have the same effect. (The Jukebox2 plans show the ballast as steel bars bolted across the bottoms of the bulkheads.)
I didn't have a chance to show a "no ballast" situation for Jukebox but the numbers show that removing the 300 pounds of ballast reduces the weight by 300 pounds and raises the CG almost 6". Maximum righting moment goes from 1170 ft -lbs with 300 pounds of ballast to 820 ft-lbs with no ballast (both at 20 degrees heel). Worse yet, the unballasted boat will capsize at 50 degrees of heel. So here the ballast seems well worth it.
I might add that the 300 pounds of ballast, if done with water, would be about 5 cubic feet. This boat is 5' wide on the bottom so the ballast tank might take the form of a full 5' width box, 6" high and 2' long.
...JEWELBOX... I think the fact that the Jewelbox righting moments are generally less than Jukebox's in the usual sailing range is mostly because she is about 30% lighter. If she were loaded with two more people and brought up to a weight about equal to Jukebox's I'd think she might be even stiffer than Jukebox. But the most valid comparison might be with the unballasted Jukebox which weighs the same as the Jewelbox. The advantage of the Jewelbox is that it won't flood and maintains a small righting moment past 80 degrees of heel.
JUKEBOX2, BEACHBOAT, 19' X 6', 1200 POUNDS EMPTY
Someday I may get to put my full catalog on the net. For now I'll put one design in each issue.
Last issue I showed some photos of Jewelbox. This issue features Jukebox2. These boats are both "inspired" by the Bolger AS19, having the same size and boxy shape. They all have the same mainsail, too, although the AS19 has a mizzen and mounts the main as a gaff sail instead of as a balanced lug. The actual progression of the designs started with the original Jukebox. It was really, really functional! It's gone forever now, never sold one set of plans. Then cam Jewelbox, a Birdwatcherized version of that original Jukebox. Then Phil Bolger warned me that the original Jukebox was too ugly for anyone to take. I redrew it as Jukebox2. The size and rig and cross section are the same as the original, but I sleeked it up a bit.
Thanks to Craig O'Donnell for the colorized gif's.
.....The original Jukebox design had a wider bow than this Jukebox2. In fact the first hull was identical in shape to Jewelbox's. Eventually I was chided into drawing a version of the first boat that was a little sleeker in styling and Jukebox2 was born.
I kept the basic layout of the first boat because I think it's really hard to beat for a beaching cruiser. The bow transom on Jukebox2 is just wide enough to step through. Then one finds a small draining well for wet and muddy things followed by a front porch deck. The cabin is a full 7 feet long, 4 feet deep, and 5 feet wide with storage access to the volumes under the fore and aft decks. The aft deck is a 6 foot long flat and will sleep two. That deck had a hatch which provides leg space and access to the under deck storage (in good weather). This type of deck is also far easier to build that any other. Finally, there is a draining stern well for the motor and more wet junk.
The sail rig is basically the same as Jewelbox's but here I've specified 300 pounds of inside ballast, minimum, that Jewelbox doesn't need. In spite of the invention of the Birdwatcher cabin, I don't think this older style of boat is obsolete. Many folks prefer the open sunny deck and the privacy of the separate cabin. This type hull might weigh 30% or 40% more than a equal Birdwatcher type but I don't know if that really matters too much. You can't tow something this size behind a small car anyway. The men who rate cars for towing aren't concerned with either vehicle longevity or the steepness of launch ramps.
Simple nail and glue "instant" construction is used in spite of her size. Plans are four blueprints with basic keyed instructions for $20 until a prototype is tested.
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. (If you order a catalog from an internet page you might state that in your letter so I can get an idea of how effective this medium is.) Payment must be in US funds. The banks here won't accept anything else. (I've got a little stash of foreign currancy that I can admire but not spend.) I'm way too small for credit cards.
Anyway..... Anytime a design from the Catalog of Prototypes starts getting built I pull it and replace it with another prototype. So that boat goes into limbo until the builder finishes and sends a test report and a photo. There are three boats in that catagory right now.
Scram Pram, a 16' multichine Birdwatcher type, has been completed and had its first sail near Savannah. I'm hoping for a good photo one of these days. The builder said it's hard to get good photos of your own boat and he's quite right about that. The surest way is to get a good beach shot of it.
And Skat, a 12' cat boat daysailer, is being built near Phoenix. Latest word from the West Coast Spy is that the boat has been glassed on the outside and ready to flip and finish.
The Kansas Boat Psychologist keeps plugging away at his Harmonica (ex Fusebox). The hull has been flipped, the bottom installed and glassed. Bottom stiffener/skids going on now. I'm leaving Fusebox in the Prototypes Catalog for now because it has appeared on at least three web pages.
I got this letter from the North Country about an AF3 (see the 2dec97 issue):
I was surprised how quickly I received my plans for the AF3, just slightly over a week from when I ordered them. This has to be some kind of record. I wanted to let you know that I have started building and have the frames completed. I am waiting for it to warm up so that I can start final assembly in my unheated garage. Here in Edmonton Alberta even with el Nino it is cold with -16C for a predicted low over the weekend. No real need to hurry as no sailing 'til mid May.
I am a now periodontist but I used to paint houses as a business while in school. I still like to paint. I can give you an answer about the oil primer for latex paints. The theory (party line) is that the water-based primers raise the grain of the wood and an oil-based primer will not. I question this dogma as a good friend of mine who was a drywaller and is now an industrial arts teacher in Lac la Biche notes, "never use oil based primer as it dries too hard and does not sand quickly". He is saying this in reference to new drywall, which is paper and will lift the grain as much or more than wood. I have tried this on drywall and he is right. Latex primer sands quicker, does not wear out your paper and gives a smoother finish. I will try the water-based primer on AF3 and let you know how it works. By the way if you came to my office I would talk to you about boats not flossing.
As for adhesives I have taken to building my boats with BullDog PL Premium construction adhesive by Lepage. It is a low VOC polyurethane that can be used on frozen wood and will cure at +5C. The bond is good over a broad temperature range up to +204 C. It will gap fill to 3/8 on an inch (saves needing to bevel frames) and can be sanded and painted. The shear strength is in the range of 350 to 400 LBS/square inch after 24 hours and in seven days is 850 LBS/ sq. in. You must wear gloves as moisture is the catalyst for the adhesive and it sticks like crazy on your hands (it will not come off for days and you have to wait for your skin cells to slough). I have test fractured scarf joints and wood broke not the glue line. For comparison the powdered formaldehyde glues have a shear strength of 300 lbs/sq.in. I built a Ken Swan Little Gem 4 years ago with this adhesive and all the joints are holding up with no leaks.
As for a sail I will be using the main sail from my 19.5' Reuel Parker cat ketch sharpie. It is 103 square feet. I will have to only move the mast towards the stern by a couple of inches to get the CE to align. If it gets really windy I will be able to switch sails to the mizzen which is 69 sq. ft. Both sales can be reefed and it has been windy enough here that on my 19.5' boat it was a lot to handle sailing with only the reefed mizzen.
I will let you know when I am done the AF3 and will send you a scan.
Here on the AF4 home front, she got launched on March 4! Two days later I made some timed runs with the Sears 7-1/2 hp motor that was loaned to me. This is a simple single cylinder air cooled job that weighs 32 pounds. To report just the facts for now let's say this: Empty weight, no motor, is 300 pounds and the trailer weighs 200. Full testing weight was probably 550 pounds. Speed over a mile (four runs in different directions) was 12 mph or 10.2 knots. She planes very quickly and easily with the Sears motor. I'm really happy with the results. By the next issue I should have some photos and perhaps more test results, weather and schedule allowing. I'd like to make a 10 or 20 mile run at part throttle to get a handle on fuel consumption. I now have an old (it has "wings" molded into the cowling ) 10 horse Johnson. It pushed the AF4 mightily when we had it running but it likes to run only a minute or two at a time. Also would like to test with my old Clinton motor which I think puts out 2 hp.
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