Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(15September 2015) This issue will try another look at box boat stablilty. The 1 October issue will look at center of gravity calculations.
TIME FOR THE INDIANA MESSABOUT!
July 4th is behind us and mid-September is closing fast. We just wanted to send a short reminder that the 24th occurrence of the Lake Monroe Midwest Messabout will be September 18, 19, & 20 -- mark your calendars.
Go to https://sites.google.com/site/lakemonroemidwestmessabout/home for additional information and feel free to drop us a line if you have any questions. If you're planning to attend, and want us to add your name/boat/homeport to the website's "Who's Coming" list just send us an email.
Hope to see all of you in just a few weeks. We have the ice cream maker standing by!! Pass the word to all your boating friends. Regards, John & Susan McDaniel
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.
Ken Giles' new Picara and Dennis Bradley's Bolger Long Micro in Duluth.
118 E Randall,
Lebanon, IL 62254
Send $1 for info on 20 boats.
Boxboat Stability 2
...A few issues back we looked at the Jukebox3 prototype and the scare it gave me as four men quickly went to one side during launching. A look at the stability curves showed, no, you can't do that. That would have been enough to knock the boat over even with no wind in the sails.
Then I reran the "Navigator Cabins" essay which again looked at the stability curve of the original Jukebox and then the Jukebox3 which is essentially a Jukebox with a short stand up cabin section. That showed the great benefit of the little pilot house when the boat was knocked all the way over to 90 degrees and beyond.SECOND THOUGHTS...
It usually takes a long time from initial design until a prototype is built and tested. Then it might take a few more years to get the feedback a designer needs to improve things, if required.I think in the boxboat case, after Jukebox3 was designed and before it was built, I found of several cases of cabin boxboats (not mine, none of mine had been built yet) where knocked down hulls did not return to upright even though they were properly ballasted. Anyway, I guess the usual was to design the ballast to the minimum needed to right the boat from a knockdown assuming the designed construction and a sharp crew.
No one wants to lug around a lot of ballast so maybe in some cases the boats were not fully ballasted, or maybe not ballasted at all. But the two cases I knew of were both properly ballasted with 500 pounds of water as shown on the plans.
One boat would not return upright until the crew, which sits above the usual overall center of gravity and thus is a destabilizing factor, abandoned ship. They slipped into the water, the ship immediately returned upright without them and they climbed back aboard and went on their wet way. Now, we have talked at times about reboarding a boat and it is something you must plan for. It ain't all that easy, especially with a cruiser sized boat. So this crew was prepared.
The second case was similar exept the boat did not return upright on its own. It took a small nudge from the swimming skipper to get it started and then up she went. So the ballast on this one was even more marginal than that of the first, although one might argue that this case was actually safer than the first in that you could perhaps prepare for reboarding while the boat was still on its side. In the case of the boat that returns upright as soon as the crew abandons ship, there is a real possibility that it will sail off without you much faster than anyone can swim.
So don't skimp on the ballast and watch the topside weight.
Another thing I was finding out from letters is that some boats were very tender to sail, even though they would return to upright from a knockdown. They were tender to the point that no one wanted to sail them and in one case so tender without proper crew weight and position that it would not stay upright rigged dockside. The boats I am thinking of were sort of second generation Birdwatcher types, again not mine but I suppose they might have been. I still have what is the second Bolger Birdwatcher built and can assure you it behaved very very well. Similarly I think my own Birdwatcher designs have all worked well as far as stability goes. But mine and the original were all simple crew sitting down inside designs with light rigs. Later boats had heavier rigs and maybe also, something that I had lots of requests for but never bit on, exterior raised seating for some crewmembers. So the cg gets raised up and the boat becomes tender. Oddly, the ultimate knocked over stabilty might still be quite good because as we have seen raising the cabin top adds lots of knocked over stability. So the great ability of a Birdwatcher cabin to provide a self righting boat without ballast is still there but with the raised cg you might need a lot of ballast to make it sail upright as desired.
A navigator type cabin is clearly in the middle. It has the raised cabin that gives great buoyancy in a knockdown to return the boat upright, but with its crew sitting in a raised position it needs ballast to keep it on its feet in regular sailing. Don't forget that in a true Birdwatcher cabin the crew weight becomes your ballast, the bigger the crew the more solid she becomes. But with a raised seating deck a boat can become less stable with more crew. The skipper needs to be aware of that.
Now, one of the things that worries me about Navigator cabins is that no one wants to sit down on that raised aft deck. The crew is supposed to sit down on the aft deck, as usual, and look through the pilot house windows to see forward. Thus their weight is down low. But with my short Jukebox3 venture, it was clear no one on the aft deck wants to sit. They all stand if possible and look over the pilot house instead of through it. The cg calculations go into the trash then and the stability calculations are based on that cg. I am pretty sure in a standing crew situation the boat will get knocked over easily and self right quickly once the crew is swimming.
We talked about this in the past. The effect of standing in a smaller boat is very destablilizing. I know of two AF3 capsizes and a Frolic2 capsize. Those boats aren't ballasted but as I recall in all three cases at least some of the crew was standing at the time.
So, ladies and gentlemen, keep your seats.
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.
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.
Update, 2007. Chris Feller completed his Philsboat, probably the first prototype completed, and brought it to the 2007 Rend Lake Messabout. Very well made and to plans except he used the 91 sq ft lugsail he had on hand for his AF3, with some mast rake changes he calculated with his "sail area math". Sailed correctly rigtht off the drawing board, so to speak. We had a chance to use it for a few really nice days. In a good sailing breeze, say 10 to 15 knots with occasional whitecaps, our gps bobbed between 5.5 and 6mph for two hours of reaching as we crossed back and forth on the big lake. When I used the Philsboat I thought it was probably just as easy to enter from a beach as the blunt bowed Scram. The front deck is about 2' high so you can sit on it and swing you legs around onto the deck and then into the cabin.
Chris is a big boy but there was plenty of room inside for the two of us and more. Rumor has it that at the campsite the night before Chris slept in the Philsboat on the trailer with an airconditioner in the front hatch plugged into the campsite power. So the boat is plenty big in the way most people would use it.
The stern layout has the motor in a small well to one side and the rudder offset to the other side to give the motor room to swing. There is no linkage to the tiller, the tiller is simply "unstraight" so that is falls on centerline at the skipper's hand. Seems to work well and is quite simple. Chris uses a 2hp Honda which has a fairly large cowling for its size and must be rotated 180 degrees to grab reverse. He said the motor well size is a bit too small for that. Karl James had the same problem with his Jewelbox a long time ago and simply cut away the side of the hull in top of the motor well region - after all it is just there for looks. Chris said he tried the boat under power and found it went 6 mph max, just like under sail. No surprize to me. My Birdwatcher also maxes out at 6mph under 3hp and under 5.5 hp. This sort of hull will only go so fast. Add more power and you just dig a deeper hole and make a bigger wake - you won't go faster. But sometimes more power is nice on a windy day.
(As an update, Chris has brought his Philsboat to several more Rend Lake meets. In 2008 the meet was very windy and Philsboat got a full windows wet knockdown with Chris and Tom Hamernik on board. She self righted with no issues and they kept right on sailing, but Chris confessed he has 100 pounds of lead shot under the seats. Also he is using a 3hp vintage Johnson which he says is quieter and smoother than the Honda.)
You might recall from the Prototypes section recently that there was another Philsboat being built in California. That one last I heard was about to be launched. Has more changes from blueprint than Chris's boat but still is pretty true to form. Seems to be known as Bumble and made by Rex Meach.
And in New Zealand Rob Kellock has been sailing his with a junk rig. He has been knocked down a couple of times and self righted as planned:
Plans for Philsboat are $45.
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.
We have a Picara finished by Ken Giles, past Mayfly16 master, and into its trials. The hull was built by Vincent Lavender in Massachusetts. There have been other Picaras finished in the past but I never got a sailing report for them...
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 to the point the builder can sit and relax in it and imagine boating. You can follow the builder's progress at http://moffitt1.wordpress.com/ ....
The first Jukebox3 is on the (cold) water. The mast is a bit too short - always make your mast too long. A bit more testing will be nice...
A brave soul has started a Robbsboat. He has a builder's blog at http://tomsrobbsboat.blogspot.com. (OOPS! He found a mistake in the side bevels of bulkhead5, says 20 degrees but should be 10 degrees.) Double layer bottom on and glassed, hull returned to upright. He is decking it now...
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
1oct14, Guessing Weight, Larsboat
15oct14, SailOK2014, Jonsboat
1nov14, Chine Runners, Piccup Pram
15nov14, Lugsail Rigging, Caprice
1dec14, Sail Area Math, Ladybug
15dec14, Poly Laminates, Sportdory
1jan15, Sharpie Spritsail, OliveOyl
15jan15, Knockdown Recovery, Dockbox
1feb15, Mike Monies, Laguna
15feb15, Cartopping, IMB
1mar15, WeeVee Lessons, Vole
15mar15, Bulkhead Bevels, Frolic2
1apr15, Capsize Lessons, Riverrunner
15apr15, Hollow Spars, Slam Dink
1may15, Boat Costs, Blobster
15may15, Small Boat Rudders, Roar2
1jun15, Emergency Flotation, RB42
15jun15, Thailand Mixer Cruise, Mixer
1jul15, Rend Lake 2015, Musicbox3
15jul15, Box Boat Stability, Mikesboat
1aug15, Taped Joints, Cormorant
15aug15, Plywood Butt Joints, Paulsboat
1sep15, Navigator Cabins, Vireo
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