Monday, January 30, 2017

A Good Start On An Off Center Board

I made the decision some time ago not to use conventional leeboards.  There are several reasons:  The windward board provides no function.  Also, since Autarkia will heel very little, an off center board  able to bear the load on either tack will be effective enough for us.  A single side mounted off center board is used by Jim Michalak in many of his designs.

I intend to mount the board flat against the hull with a single pivot bolt, bearing the flat surface of the board tight against the hull with a piece of sheet plastic sandwiched in between.

Today I started making up the board.  I cut 16 pieces of 2by4 8 feet long.  This is the good structural fir I had left over from the boat build.  Here I just laid them out on the bench and clamped them together to see how they fit and to do some marking.




I drew an arc here.  The area to the right of the arc will remain flat on both sides, since this is the area that will be in contact with the hull side.  It has to bear tight against the hull without any play, and be able to take torsional loads as well as side loads from port and starboard.  Below the arc is where the board will be shaped to a symmetrical foil.   Much of the material to shape the foil is removed on the table saw.  I stop ripping at the arc and use a handsaw to remove the piece.



Of course I need to know what to rip away, so I made up a template to give a rough idea.




I did not angle the saw blade to follow the exact contour.  The reason is I would only be able to do one side since the blade only angles in one direction.  To do both sides I would have to cut from eith end, and that was impossible since I am only removing material partway up the board.  No matter, since once it's all together there will be a lot of grinder and belt sander work anyway to do the final shaping.



Those transitions will get a nice radius and b blended in smooth.



Here they are going together with PL Premium and 3 inch  epoxy coated deck screws.



All together and curing.



So once cured in a couple of days I'll fair it up.  I may use some steel as a leading edge and for weight to sink it, and then it will all get glassed over with a couple of layers of 10 oz cloth set in epoxy.  I may also put in a sleeve for the pivot bolt.

Saturday, January 21, 2017

Update

The cold weather has left us, the ice has melted or drifted away and things are back to normal in Mission Harbour.



Work has continued on Autarkia during the bad weather - during which our little Cubic Mini woodstove has been greatly appreciated.  The water system has been almost completed with only the footpump and 12VDC pump to be installed for the sink spigot.  I have completed the forward hatch made up from aluminum angle and 3/8 inch thick smoked plexiglass.  There are two panels - one vertical and one horizontal that are held in with over-center catches (stainless steel, reasonable quality and found  surprisingly at Home Depot).

I will be ordering the 6 inch foam for the mattress in a few days.  It's big - 73" by 85".  Though part of the bed will extend under the side deck, and no one can actually sleep that far outboard - a leg or a knee or a foot can be nicely accommodated.  With throw pillows and stuff bags it makes for a large lounging platform as well.

With the forward hatch as a means of emergency escape in place, our bed installed, and shore water and power, we will be able to go down and spend the odd night aboard while we finish her out.


In the meantime at home, we (fellow junker Jeff and I) have been working with a fabric store that is becoming a distributor for awning fabrics such as Odyssey, Top Gun, Top Notch and Weathermax.  As a result of our research on the Junk Rig Association website, other blogs, and advice from other junk sailors, we will probably be going with Top Notch fabric to make our sails.  Of course, once that starts there will be much more detail posted here.

More interior detail to come soon as I get her cleaned up, organized and the aforementioned jobs completed.

Wednesday, January 4, 2017

Mast Design With Counter Weight

It has been a while since I've made a post with any real meat in it in terms of design ideas but because of the weather these days I have been able to put some time in.

I just got back from checking on the boat by the way, and she's frozen in!  So here are a few pics to start of with of the harbour and river:








So I have been working on my mast and tabernacle design.  I have decided to make a hybrid mast with the lower 20 feet constructed of 6 inch Schedule 40 aluminum pipe.  This pipe is made from 6061-T6 alloy, and the O.D is 6.625 inches (168.275 mm) and has a wall thickness of 0.28 inches (7.112 mm).  A 20 foot length weighs 131.28 lbs.

The upper section will be made with fir, laminated up from the pile of leftover 2 by 4's I have left over from the build.  This section will insert into the top of the pipe by around 18 inches, and will be bonded in with epoxy.  I'll taper it down to 4.5 inches at the top, and epoxy fiberglass it.  This section will weigh around 50 lbs at 12 feet long including the inserted end.

The whole mast will weigh around 185 lbs with fittings and will be 30 to 32 feet long depending on my final sail design.  The pivot in the tabernacle will be about 5 feet up from the bottom, leaving 25 to 27 feet above the partner (tabernacle pivot).

The bottom of the mast will have attached a lead counterweight weighing in the vicinity of 300 lbs, that I will cast from a pile of tire weights I have already.

I worked out the counter balance as follows:  The weight of the aluminum mast above the pivot point will be 98 lbs.  The center of balance of the pipe will be 7.5 feet up from the pivot so its moment times the arm will exert 738 ft/lbs with the mast horizontal.  The wood section's center of balance will be 19.5 feet up from the pivot, and with the wood section weighing about 50lbs, will exert 975 ft/lbs.

Add the two - 738 ft/lbs plus 975 ft/lbs and we get a total of 1713 ft/lbs to counter balance.

If we take the weight of the mast below the pivot point (32.82 lbs) and put it's center of balance at 2.5 feet down the mast when horizontal, we get 82.05 ft/lbs. That still leaves us with 1713 - 82 = 1631 ft/lbs to counterweight.  But if I can get a lead counterweight at the bottom of the mast that weighs around 300 lbs, then I can generate 300lbs times 5 feet or 1500ft/lbs.  That leaves around 131 ft/lbs to overcome manually to raise the mast.  Pushing down on the weighted end will only require about 26 lbs of pressure to raise the mast!



I can make a simple mold from plywood to cast the counterweight.  All I need is a honking big propane burner and a galvanized bucket to melt the lead tire weights in and a means of safely handling the whole works.

As for the tabernacle itself, I'm thinking to get it welded up from plate steel.  3/8" should do and if I paint it with epoxy it should stand up well.  I'll put a base plate that sits on, and is bolted to the deck.  It will also be bolted through the cabin bulkhead to additional steel structure inside the cabin, that carries the load all the way down to the floor.


I can likely carry a steel channel down to the bottom stringers and bolt it all the way down the bulkhead.  That bolt you see in the floor by the way is attached to the copper grounding plate on the bottom - so we have good lightning protection.

Fore and aft stresses have me a bit concerned if I allow the roof structure only to bear them, so I may carry another brace from the top diagonally down to the bulkhead aft.  Still thinking on that...

Anyway, here's a few more pics of the inside.  It's starting to clutter a bit but I'll do a good cleanup once the weather breaks.