Saturday, November 10, 2012

AF3 Cockpit Tent

Fitted tent for camping
We used a polytarp for a recent trip to the Core Sound of North Carolina's outer banks and it served its purpose well.  

Polytarp cockpit tent for AF3 Cream Cheese
It kept the rain out during a 35-45 mph storm one night and sheltered us from the wind when it was in the 50's Fahrenheit.  But the tent takes a lot of time to setup, is noisy, ugly and bulky.  Running the lines under the hull is awkward.

Having achieved some sewing success with my third reef project, I decided to embark on another sewing project; a custom fitted camping tent.

I spent a few spare evenings reading through my copy of "The Complete Canvasworker's Guide" by Jim Grant.  Then I made a few line drawings of various designs including various configurations of hoops and frames.  I finally settled on a simple A-frame design slung over the sprit boom and bimini similar to what we had used in North Carolina:

Cockpit tent design - side view
Cockpit tent design - top view
Use gravity  
This project required many 10' to 12' flat felled seams.  At first I tried put the sewing machine and fabric on the floor but I quickly found out that my Janome Magnolia 7300 sewing machine doesn't have the power to pull all of that fabric.  I solved this problem by following the advice of of Emiliano Marino's "The Sailmaker's Apprentice" and constructing a gravity feed system.

Sewing long seams using a gravity feed system
Sailrite's 3/8" basting tape
I made the first seams using pins.  The results were crude and tended to have puckers.  Later in the project I ordered a roll of 3/8" Seamstick basting tape.  What a difference it made.  My seams were more uniform and took far less time.

Walking foot
Also halfway through the project, I ordered a walking foot attachment for my sewing machine.  It also makes for more uniform seams.

No boom needed
I sewed 1" polyester webbing along the centerline and terminated each end with 2" webbing and a 2" bronze ring.

Ridge reinforcement
This allows me to stretch the tent taught between the bow and stern and eliminates the need to use the sprit boom as a ridge pole.  I clip the mainsheet to the stern ring and pull it taught.

I used stainless rings and webbing to attach the cover to the boat.  I found sailrite's how-to videos to be very helpful in figuring out the mechanics of assembly.
Corner Attachments
Ready for assembly
Attachments and Setup
I sewed in sleeves for fiberglass tent hoops but after experimenting with the fully assembled tent, I decided that the hoops added almost nothing and complicated the setup.  The sides of the tent clip to lashing hooks fastened underneath the gun'nle.

Side attachments
The bow uses a single pole with a line tied to the forward mooring cleat.

Bow detail
The stern is open to the air, .  The corners are tied to the stern mooring cleats.

Stern detail

Next steps
I am very pleased with the results.  The tent only takes about 6 minutes to setup.  I will probably sew in a few windows and I may fabricate a panel to cover the stern.

Sunday, September 30, 2012

Leeboard repair - the "rope trick"

Dry fitting for the "rope trick"
I damaged the leeboard on Cream Cheese last year by driving away from the launch ramp with the board dragging in the gravel.  I discovered my error after about 50 yards, but by that time I had chewed off about 3/4" inch off of the bottom corner of the leading edge.  Later on Grahame Byrnes, designer of the Core Sound series, told me about "the rope trick".  The idea is to glue an epoxy saturated synthetic rope (usually nylon) to the leading edge of the board, thus providing a well shaped but very durable surface.  Here's an example from the Core Sound 20, Dawn Patrol:

Rope on the rudder of the Core Sound 20, Dawn Patrol.
It protects the leading edge of underwater boards

I decided to try the rope trick myself.  First I cut away the damaged wood and fitted the rope.

Fitting the rope
Then I soaked the rope in epoxy and draped fiberglass cloth over it and let it partially cure (8 hours over a cool night).  I made a mistake at this point in the process.  I should have used thickened epoxy to fill the spaces between the rope and the board but I didn't.  As a result, there are air pockets.  Hopefully this won't be a major issue since the boat is dry sailed and all surfaces are thoroughly coated with epoxy.

Fiberglassing rope in place

Then I filled using epoxy thickened with fused silica and microballoons and let it cure.

Filling and smoothing

I made a first pass at sanding and smoothing and filled some more with thickened epoxy.

Final sanding before painting

Saturday, September 22, 2012

Mainsheet for AF3 - third try is a charm

New nylon webbing reef nettles.

I've always resisted getting "yacht" grade hardware for my little plywood boat, but I've learned that sometimes the expensive stuff makes your boat far more seaworthy than the cheap stuff.

For twelve years, I sailed Cream Cheese with the simple mainsheet arrangement shown on the plans.

Then in March, I modified the rig to bring the sheet forward.

We sailed last weekend in gusty conditions (5 to 15 mph) and I was still unsatisfied with the mainsheet.  It suffered from a number of problems:
1. The line was too thin - 1/4" line is not comfortable to hold when it is really windy
2. Mainsheet was tied to a combination block/jam cleat forward.  This holds the mainsheet too firmly.  It was too difficult to release during gusts.
3. The mainsheet gets in the way when you are coming about.
4. Running the mainsheet through a block on the base of tiller creates an awkward weather helm.

So I looked at the mizzen for the Core Sound 20, which has about the same sail area and the same position in the stern.

Core Sound 20 mizzen sheet

It has three important features:
1. 3/8" line.  Easier to handle in strong winds, lays better in the cockpit.
2. Standup blocks on either side of the tiller - no extra forces on the tiller.
3. Cam cleats - super easy to set or release.  Much safer in gusts.

So I went to and bought some expensive hardware and 50' of low stretch line.
I tried out the new mainsheet arrangement today with more gusty winds.  Wow- what a difference.  Even Julie, who is doesn't usually like sailing in gusts, was very comfortable at the helm.

New main sheet - I'll fix that twist later.

Saturday, September 15, 2012

How to Install a Sailrite Jiffy Grommet

New jiffy grommet, old sail

Before installing the jiffy grommets on my clew and tack reef patches I looked for online tutorials or technical notes but didn't find much, so I'm posting my experience here.

When I got my jiffy grommet kit, there were no instructions other than what is printed on sairite's website "... Special tools are not required - simply use a hammer to mushroom the ends of the soft aluminum rivets in place ..."  After some experimentation, here's the process I decided to use.

I had to push the six rivets through seven layers of 4oz dacron.  I experimented on a test patch with a 1/8" drill, but I found that a 1/8" hole punch was far superior.

1/8" hole punch
After punching the holes, I assembled the grommet.

That jagged circle you see in the luff tape is where an old spur grommet used to be before the reef patch was sewn in place.

Rivets ready to be hammered down
Once I hammered down the rivet, used a soldering iron with a flattened soldering tip to cut the hole through seven layers of fabric.  This was quick and easy and had the added benefit of welding all seven layers together for added strength.

Cutting out the fabric - flattened soldering iron tip on right

Jiffy grommet, sail, tools

Third Reef Pictures

Here's a look at the third reef under sail.  I haven't been out in wind strong enough to know whether there will be significant lee helm.

Pretty Day at Marsh Creek Lake
Sharpie spritsail and clouds 

Sunday, September 9, 2012

Sewing a third reef

I decided to make a third reef for Cream Cheese in May.  It has been 12 years since I sewed the sail, and I wasn't looking forward to re-learning all of the special sail sewing techniques. 

Pretty stitches on the new clew reef patch
As it turned out, it was a fun project.  The first step was to pull out my copy of "Sailmaker's Apprentice," by Emiliano Marino, and re-read a few relevant chapters.  Then I ordered the cloth and jiffy grommets from Sailrite.

Next, I spread the sail out on the floor to plan the location and size the various panels that would be sewn together to make the reef patches.

Reef plan
 I did this by taking off the dimensions from the existing patches.

Reef patch dimensions
At this point I was ready to cut the panels.  My reading indicated that scissors aren't the best for cutting dacron sail material because the cut is more likely to fray under heavy use.  A hot knife is the preferred method, but I wasn't going to fork out $400 for an industrial hot knife.  I settled for attaching a rope cutting blade to my soldering iron (with a little modification).  The edges were a little rough, but it was good enough.

Cutting out dacron panels
I had to redo all of the cringle patches because I got the weave orientation wrong (see "Sailmaker's Apprentice").  Each reef cringle patch is 4" square.  There are two patches for each reef patch and the fabric weave should match the weave of the sail at the point of attachment.

I used basting tape to assemble the clew, tack and cringle patches and then put them aside.

Now I was ready to start sewing, but before I could do that, I needed to freshen up on my sewing skills and make sure the needle, thread and machine were going to be able to go through seven layers of dacron.  This probably took more time than any other part of of the project.  My sewing machine is a Janome 7330, which is a "home decor" machine.  It comes with a two kinds of zig-zag stitches, has a pretty good motor and a fairly strong feeder.  I discovered that this machine with a #90 needle will do a zigzag seam on five layers of 4oz dacron, but not on seven layers.  It works fine with a #110 needle but but I was worried that the holes in the fabric were a little too large.  After talking it over with a few people, I decided to go with the #110 needle and larger holes.  I've been happy with the results.

Janome 7330, basted reef patches, practice patch.
Now I was ready to sew!  This part of the operation went relatively quickly.  First, I cut loose the luff tape (seam along the luff of the sail) and pinned the pre-assembled reef patch to the sail.  Then I rolled up the excess material and started sewing.

First seams going together.
Once the tack and clew patches were sewn on, I pinned and sewed each reef patch.

Reef cringle patch
Now that all patches were on the sail, the last step was to install grommets.  The reef grommets were the easiest.  Simply, cut the hole with a 3/8" hole punch and install the #2 grommet with the two part die set.

Reef cringle patch and tools
Installing the sailrite jiffy grommets on the clew and tack were a bit trickier.  A jiffy grommet is comprised of two washers that are attached to the sail using six aluminum rivets.  The kit came with no instructions and there is very little on the web about the best way to do it, but I'm pleased with the results.  

Third reef  - project complete
Now the third reef is finished - I can hardly wait to try it out in heavy weather.

Sunday, July 8, 2012

Rowing, Rowing, Rowing

My niece just got back from Hurricane Island Outward Bound School.  The school recently introduced a modern 30' Sharpie Schooner pulling boat that is completely different from the one that I used when I attended in the late 70's.

2007 Hurricane Island Outward Bound Sharpie Schooner
The new boat looks like a lot of fun.  Notice those very deep reefs in the main sail and foresail.  Fast, shallow, seaworthy.

Old Spritsail Pinky
The old boats were carvel planked wooden spritsail cat ketches, "Pinky" style.  They were slow, heavy and didn't point well.  One thing both boats have in common is lots of oars and one thing that both our trips featured was lots of rowing (separated by 35 years).  When she got back last week, my niece arranged a fourth of july sailing afternoon with friends and siblings aboard my father's Drascombe.  Before long the whole crew was rowing.

The Drascombe rowing into a headwind
Julie and I have been talking about rowing lately because we are training for an upcoming Watertribe event which could involve many hours of rowing, depending on the wind conditions. To help with our training, we bought a used Concept 2 rowing machine.

Rowing machine with sail
(sail laid out in preparation for sewing the third reef)
We like the full body workout that the rowing machine gives us and even if we don't do the race it was a good purchase.  This morning we went out for a short row to see how our training has helped.  

Julie powered
It went OK, but the oars were a little hard to control.  Both of the oar leathers had slipped and the oars were bumping against the top of the oar ports.  To make things easier, I've added "buttons" to the oar leathers using a turk's head knot.  

Turks head knot for oar buttons
Before today, I didn't know how to tie this knot so I tried following the instructions in my copy of "The Young Sea Officer's Sheet Anchor", (pub 1819), but in the end I figured it out by watching this video on YouTube.  I am amazed at how tight this knot can get.  The leathers were slipping the length of the oar loom, but now they stay put.  

Sunday, May 27, 2012

A third reef for Cream Cheese? Wind Forces, Sail Math

I made the 96 sq ft mainsail for my AF3  from a Sailrite kit.  I gave them the dimensions and draft and asked them to put in two reefs even though only one is specified on the plans.  The second reef reduces the sail to about 49 sq ft.   Even with two reefs she is overpowered at anything above 25 mph.

Double reefed, 15 - 25 mph

No reefs, drifting along
An AF3 weighs 250 to 350 lb and has a 4' beam which is a bit narrower than other boats her size so her sail area has more of an impact on stability.  I am considering sewing a third row of reef points to get the sail down to 31 sq ft so that I can sail upwind more comfortably when the wind kicks up.

I don't want to spend a whole weekend sewing just to find out the boat won't point so I've done some searching on the web, some asking around (the watertribe forum was very helpful) and some calculating.

Will a third reef result in too little sail?
Adding a third reef will reduce sail from 96 sq ft to 31.5 sq ft.  Is that enough sail to make headway in 30 mph winds?  The force exerted by a sail is proportional to the square of the wind velocity.  Jim Michalak has given a simple formula:

 Max sail pressure (lbs/sq ft) = .0034 * V(kts)2 * C

where V is in Knots and C is a constant representing sail efficiency from 1 to 2.  My mainsail has good draft and a nice shape, so I'm calling it a C=1.5.  Since I like to measure speeds in miles per hour, I applied an additional conversion and came up with the following table for my mainsail:

Force on sail (lbs) for different sail areas (sqf)
and wind conditions (mph).
Unreefed going upwind, AF3 likes a 10 to12 mph breeze the best.  This turns out to be about 42 to 62 lbs force exerted by the sail.  She sails upwind fine with two reefs in 20 mph = 87 lbs.  She is overpowered at 25 mph = 136 lbs.  A third reef at 31.5 sqft should generate 126 lbs at 30 mph.  Still managable and certainly not too little force.  So a third reef to 31.5 sq ft seems to be plenty enough to make headway.

Another possible issue is related to force of the wind on the hull.  As you reef down the sail, the force of the wind on the hull has a greater effect on the total force.

Wind force on exposed hull (frontal area) as wind increases. 
I admit that this computation is pretty loose: it assumes the hull acts like a very poor sail (C = .5) and the area exposed to the wind is about 3' x 8' (because the boat is presenting about 50% of itself to the wind).  The table predicts that at 30 mph, the wind exerts 32 lbs force on the hull.  At that same wind velocity, the triple reefed sail will exert 126 lbs force, so the math is still looking OK.

Will there be too much lee helm?
I am also concerned about lee helm, an unsafe situation in high winds. Without any reefs, the centroid of the sail is even with the trailing edge of the leeboard.  With two reefs in, the centroid is 13" farther forward (see picture below).  I would have expected to experience lee helm with the second reef in, but instead I get significant weather helm, especially during gusts above 25 mph.  I have no idea why this happens, but I can think of a couple of possibilities:
  1. If you heel her over to port she wants to round up to starboard - just like steering a surf board.  Perhaps the turning forces due to the hull are a lot more powerful than the turning forces due to the sail center of effort..  
  2. As you heel the boat, the center of effort moves to lee because the mast is angled over the water and the center of resistance (leeboard) moves to windward.  Perhaps the geometry of this situation lessens the imbalances in force (there is still a tendancy toward lee helm, but the force vectors are smaller).
  3. An imbalanced rudder can make the problem more pronounced if the center of resistance of the rudder blade is too far behind the rudder pivot (thanks to SOS for that suggestion)
A third reef will move the centroid forward 19" (as opposed to 13" with two reefs).  So my tentative conclusion is - I'm hoping I'll get lucky and it won't cause lee helm.

Jim Michalak's articles on sail math: