Jim Michalak's Boat Designs
1024 Merrill St, Lebanon, IL 62254
A page of boat designs and essays.
(1 May 2017) This issue will discuss scarfing lumber. The 15 May issue will rig a lugsail.
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.
MESSABOUT NOTICE:THE REND LAKE MESSABOUT WILL TAKE PLACE ON JUNE 9 and 10 AT THE RINGNECK LOOP OF THE NORTH SANDUSKY CAMP GROUND AT REND LAKE IN SOUTHERN ILLINOIS. USUALLY THE SANDUSKY CAMP GROUNDS MIGHT BE FULL FOR THAT WEEKEND. BUT SOME OF OUR BOATERS HAVE RESERVED SOME OF THE SITES THERE SO YOU (AND I) MIGHT PASS THAT WAY FIRST SINCE SEVERAL TENTERS CAN SHARE A CAMPSITE. IF NOT, THEN I WOULD TRY THE WAYNE FITZGERRELL STATE CAMPGROUND WHICH IS ON THE MAIN CAUSEWAY LEADING TO SANDUSKY. THEIR WEBSITE SAYS IT IS STRICTLY FIRST COME FIRST SERVE, NO RESERVATIONS ALLOWED. IT IS A VERY QUICK DRIVE FROM THERE TO SANDUSKY. HOPE TO SEE YOU THERE!
Rick Cunningham's Vamp at age 9.
1024 Merrill St,
Lebanon, IL 62254
Send $1 for info on 20 boats.
There will be times when you can't buy lumber as long as you will need. This will be especially true for masts, but it can also be true for elements like wales and chine logs. At my lumber yard many boards max out at 16' long, although some such as 2 x 10's can still be got in 20' lengths (if you can lift them). The standard solution to the length problem with lumber is to scarf it together.
Here is what a proper scarf joint looks like:
The reason scarf joints have always been used to joint lumber pieces lengthwise is that a butt joint, where one end of a board is glued directly to the next board with cuts at 90 degrees, never works even with modern glues. The joint is all end grain to end grain with no chance of getting a good glue line as you would with a scarf joint, or even with a butt block joint where the glue is loaded in shear instead of tension. By using a scarf with a 6:1 slant, the glued area is over six times the area of a straight butt joint.
I've shown how to piece plywood sheets together with butt plates instead of scarf joints, to make sheets longer than the standard 8' lengths. That usually won't work well with lumber elements. For example, if butt blocks were to joint the boards that make up your mast, the butt blocks would have to be on the outside of the mast to be effective. It could be done but would look clunky is nothing else. As for length, if you were joining 3/4" lumber with a 3/4" thick butt block, the block would need to be 12" long to get the 8:1 scarf ratio that might be considered to be the minimum.
SAWING THE SCARFS...
Actually scarf joints are easy except for cutting the scarf angle. There are fixtures made for circular saws that cut a scarf automatically like this:
Pro builders use these to cut scarfs on plywood, but the plywood has to be thin. The usual circular saw protrudes about 3" maximum below the guide, so if you are scarfing at an 8:1 ratio, the thickest wood you can cut this way is 3/8". Still, for a pro scarfing plywood it is very useful. But useless for scarfing 3/4" lumber.
Let's say you need to join 3/4" x 1-1/2" lumber to make wales or chine logs for your boat. An 8:1 scarf in 3/4" thick lumber will be 6" long, like this:
It's easy to draw the cut on the end of your sticks. You can try cutting it with a really good handsaw. It pays to practice. I've been able to cut the stick with a really good saber saw or circular saw but the guide has to be set exactly at 90 degrees and you can't waver in your cut. If you get a bad cut, you can try again on the same end. In fact if pays here to start with extra lengths of lumber so you can try several cuts on each board until you get the knack. You can also try working the cut to shape with a plane or rasp. If you have a power plane, you might try whacking the scarf to shape with only that. When you think you have two good ends cut, clamp one against a firm surface such as a length of 2x4, like this:
Slide the mating piece into position and check the fit. Remember that as you glue these up they must be straight. I think they should fit within about 1/32" to make a good glue joint with thickened epoxy. Like this:
ROUTING THE SCARFS...
When I built a Birdwatcher a while back I needed to join a lot of lumber since the boat was 24' long and the mast longer. I built a simple fixture for my router for cutting the scarfs. It looks like this:
The base plate of the router needs to be removed (three screws) and replaced with a one wide enough to span the fixture opening in all positions. The fixture needed to be wide enough to scarf the 3" wide boards I was using for the mast.
Here is how I make a scarf cut with this fixture. The board is clamped into the fixture such that the router will cut no more than about 1/4" deep. The router is turned on and worked around the fixture until it has cut all the available material. Like this:
Then the board is unclamped and slid forward into the fixture such that once more the router will slice off another 1/4" of material, only this time there will be a lot more wood to cut. And so forth until the the entire scarf is cut. Or is it? I've found it best to avoid a total feather edge at the end of the scarf cut - leaving about 1/32" uncut seems ot work best, like this:
That's all there is to it. One of the nice things about this fixture is that it is pretty compact. So instead of moving those long boards to the fixture, it is usually a lot easier to move the fixture to the boards, a nice feature when you start working with really long boards.
GLUING THE SCARF...
Now it is time to glue the boards together. Best to glue them up on a piece of 2x4 such that they will be straight as you glue them. Cover the 2x4 with waxed paper so that the backup board doesn't become a permanent part of your boat! Clamp the first board on like this:
Trial fit the second board. Butter it well with epoxy thickened to about mayonaise consistancy. Push it into place but not so hard that all the glue squeezes out. Now clamp the second piece to the backup 2x4. If you are going to have problems with gluing the joint I think it will be with glue squeezing out too much and also with lifting of the first board at the feather end of its scarf. You can help that out by carefully drilling a pilot hole for a screw right through the scarf and carefully installing a temporary screw with a backing washer like this:
That temporary screw will help a lot for overall alignment while the glue sets. It's a fact that glue is very slippery until it sets up and tapered clamped joints like this can slowly slide apart without really good clamping.
DON'T PLAY WITH THE SCARFED LUMBER UNTIL THE GLUE HAS CURED REALLY HARD! It may take a few days, depending on your glue and your climate conditions. Almost no glues set well below about 70 degrees. When I did the Birdwatcher mast scarfs it was in the middle of a wicked winter. I cut the scarfs with the router fixture, glued and clamped them up, covered them with a blanket blasted a salamander kerosene heater under the blanket. It got well over 100 degrees under there and they cured very quickly. Those scarfs are still holding!
Once your glue is completely cured the joint should be as strong as the basic wood and you can go on building as if there were no joint there. But it doesn't hurt to be prudent. I try to locate the scarfs in wales and chine logs where the curvature will be the least. I try to locate the scarfs in masts towards the top, where the bending loads are the least. And on elements that have several boards with scarfs, such as wales with multiple laminations and boxed masts, I stagger the scarfs such that they are not all one atop the other.
BLOBSTER, SAILBOAT, 16' X 6.5', 750 POUNDS EMPTY
Blobster has a lot of features I like in a boat. Lots of volume for its size, sort of like Micro or Scram Pram. The multichine shape is almost exactly like Scram's but this one does not have a Birdwatcher cabin. It has the more traditional cabin with a raised watertight deck behind. Also it has one feature I would love to have in my personal boats - a step-through bow so that when you beach you can go forward through the cabin and out the front without going into the water or climbing over the bow. The cabin also has a slot top roof.
This shape of boat with multichines has proven good in rough water and with fair speed in spite of its blobular proportions. Blobster has about 600 pounds of water ballast in its belly and should be OK to 90 degrees heel although such depends mostly on weight distribution of the crew, something the designer has little control over. On the other hand, if the crew jumps overboard the boat will be almost assured of righting without their help. Then the problem becomes reboarding. Be prepared!
Sail rig is a large but simple 139 square foot balanced lug on an 18' mast. Mast is stepped off center to allow you to walk upright down the slot top and out the front. Should be rigged in an instant with no one going on deck ever. All very low tech built with common materials but effective.
The prototype Blobster was built by Miles Bore in Australia. He had built several boats prior, including a Micro, and did a great job of it using very nice materials.
Outside and on its trailer for the first time, the likeness to Micro is clear. But you can see it was meant to be much easier to trailer and launch.
Then he used it for a while as a low power motor cruiser while he finished the sail rig. You can see how easy the boat was meant to use from the beach with its step through bow transom.
Then for the rig and off for a sail, shown here with ballast tanks full. Miles reports it sails with no vices so far. No, he hasn't capsized it yet.
Miles got this photo of the inside. The living platform you see is 7' long and 6' wide max and about 42" at its deepest from platform to slot top. With the slot top cabin and step through transom it is a pretty airy home. Maybe not the little cruiser that Micro is but clearly much easier to use in general and a good choice for a daysail when you have but a couple of hours at the lake.
Great job, Miles!
Blobster uses taped seam construction. Five sheets of 1/4" plywood, eleven sheets of 3/8" plywood and one sheet of 1/2" plywood.
Plans for Blobster 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:
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.) This boat has been sailed and is being tested. He has found the sail area a bit much for his area and is putting in serious reef points.
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
15may16, Prismatic Coefficient, Roar2
1jun16, Figuring Displacement, Mayfly14
15jun16, Rend Lake 2016, Mixer
1jul16, Ballast Calculations 1, Dorado
15jul16, Ballast Calculations 2, Robbsboat
1aug16, Ballast Calculations 3, AF4
15aug16, Taped Seams, Cormorant
1sep16, Butt Joints, Vireo
15sep16, Old Outboards, Philsboat
1oct16, D'Arcy Ballast, Larsboat
15oct16, D'Arcy Ballast 2, Jonsboat
1nov16, D'Arcy Ballast 3, Piccup Pram
1dec16, Sail Area Math, Ladybug
15dec16, D'Arcy Thoughts, Sportdory
1jan17, AF3 Capsize, Normsboat
15jan17, The Weather, Robote
1feb17, Aspect Ratio, Jewelbox Jr
15feb17, Aspect Ratio 2, IMB
1mar17, Normsboat Capsize, AF4Breve
15mar17, Underwater Board Shape, Harmonica
1apr17, Capsize Lesson, RiverRunner
15apr17, Measuring Leeway, Mayfly16
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