Sail Mod -- Clueless?

[rgranger]

I need your help guys.

I have an old spinnaker I bought used for a boat that I have since sold. It is about 3 feet too tall for my current boat. So I'm thinking a nice weekend project might be to break out the sewing machine. .... However this is not something I've ever done before. I have "The sailmaker's apprentice" and have actually read it ...but it did not go into this sort of sail mod.

Can anyone tell me why lopping off the top 3 feet and putting a blunt head "board" is a bad idea? I'm thinking of using leather for the headboard. See pic.

 

[kenn]

You should probably be lopping that 3' from the bottom. More work, but this would produce a better sail.

 

[rgranger]

Better?

You should probably be lopping that 3' from the bottom. More work, but this would produce a better sail.

Thanks. When you say better... do you mean.

"Better" in the sense that the foot would be more appropriate for my size boat or "better" in the sense of sail shape?

I think you are right. It would be a LOT more work to cut from the bottom.
I also fear messing up the pocket if I cut from the bottom. But I have not really given much thought to the foot size and how that would effect my ability to handle the sail.

 

[RichH]

Agree with Ken.
Cut the bottom.

Cutting the top off and altering the head will require major 'broadseaming' of the panels and unless you know how to do this 'lofting' you will probably wind up with a VERY mis-shapen sail. Broadseaming is the technique wherein the flat individual panels are curved and tapered on their edges to affect a 'rounded' shape to a sail. A spinnaker needs 'roundness' (to affect a quasi-spherical shape) at the head panels as the sail also 'lifts' the bow of the boat as well as producing forward 'thrust', without that 'roundness' the sail can wind up being very 'unstable'. The bottom panels are more flat and have less 'broadseaming' and thus easier to make alterations.

If you have no expertise in 'broadseaming' (involves a lot of spherical trigonometry and spherical geometry plotting), I would give this project of head alteration a 99.9+% chance of failure.

Rx: Cut the bottom as that would require no change to the broadseaming. When altered, this modified sail will be tend to unstable because the point of maximum draft will be 3 ft. too low .... and the sail will be 'powered-up' and will be a bit hard to control the 'luff' stability. ;-)

 

[kenn]

When you say better... do you mean.

"Better" in the sense that the foot would be more appropriate for my size boat or "better" in the sense of sail shape?

Both. If cut from the top, I bet the modified spinnaker wouldn't set right.

You're cutting more material from the bottom, but I expect it still would be easier to hem and reinforce the bottom edge, and create two new clews, than to remake a new head and re-hem the top edges.

I haven't done this myself, I'm just trying to think it through.

[edit] RichH has the best explanation.

 

[Bill Roosa]

Head vs foot

If you lop off the head you change all the stress angles. The line from the head to either clew is no longer a nice uniform curve. So when you straighten it out by flying it you will get an ugly bulb looking weirdness just below the head. Also the fabric will be getting stressed in a way that is "out of weave" Kinda like having cross grain loading on a piece of wood.
A footectomy is covered in the sail makers apprentice BTW

 

[rgranger]

A footectomy is covered in the sail makers apprentice BTW

I missed it.

I'll look again.

Thanks.

 

[rgranger]

Rx: Cut the bottom as that would require no change to the broadseaming. ;-)

Thanks Rich

 

[RichH]

Thanks Rich

The easiest way to remake the clew attachment will be with D-rings and webbing (3 strips of webbing). You can use the scrap fabric you cut away for the new reinforcing corner patches ..... use 3M automobile headliner spray adhesive on the 'patches' and 'lightly glue' all the patches to the sail before you sew them - will avoid 'wrinkles'. http://www.sailrite.com/D-Ring-With-Bar-3-2 Also consider to 'edge' the foot of the sail with new spinnaker luff tape - sailrite stuff.

If you are using a 'home' sewing machine, SOAK the thread (should be "V-42" or equivalent for that size spinnaker) with a dry Teflon teflon spray lube, ditto where you sew on the sail.
No need for zig-zag stitching on a 'home/dressmakers' sewing machine on a spinnaker - straight stitching will be easier for a spinn repair if you dont have a 'good' sewing machine. You'll need to set the sewing machines 'presser foot' to near maximum to prevent the fabric under the 'foot' from 'jumping' when sewing - adjusting foot pressure on 'home' sewing machines is sometimes difficult unless you change the foot pressure spring - spraying the fabric with teflon spray where you sew will tend to lessen the 'jumping' of the fabric under the presser foot. You'll need to carefully adjust stitch tension ... practice on the scrap material especially when you sew through many layers of the patches - and make SURE that the 'knots' are pulled tight to the fabric. All this will avoid 'birdsnests' in your sewing with a 'home' machine.
Before you start sewing with a home/dressmakers sewing machine, get out the machine's manual and readjust / check the 'timing' of the machine (closeness of the needle to the machine's 'gib hook' on the bobbin holder) ... as well as lubricate the machine (internals/gears, etc.) with the recommended oil, etc. Be sure you match the needle size for the thread you are using ... consult your machine's manual; this will insure that the eye of the needle wont cut the thread.

hope this helps. ;-)

 

[rgranger]

The easiest way to remake the clew attachment will be with D-rings and webbing (3 strips of webbing). You can use the scrap fabric you cut away for the new reinforcing corner patches ..... use 3M automobile headliner spray adhesive on the 'patches' and 'lightly glue' all the patches to the sail before you sew them - will avoid 'wrinkles'. http://www.sailrite.com/D-Ring-With-Bar-3-2 Also consider to 'edge' the foot of the sail with new spinnaker luff tape - sailrite stuff.

If you are using a 'home' sewing machine, SOAK the thread (should be "V-42" or equivalent for that size spinnaker) with a dry Teflon teflon spray lube, ditto where you sew on the sail.
No need for zig-zag stitching on a 'home/dressmakers' sewing machine on a spinnaker - straight stitching will be easier for a spinn repair if you dont have a 'good' sewing machine. You'll need to set the sewing machines 'presser foot' to near maximum to prevent the fabric under the 'foot' from 'jumping' when sewing - adjusting foot pressure on 'home' sewing machines is sometimes difficult unless you change the foot pressure spring - spraying the fabric with teflon spray where you sew will tend to lessen the 'jumping' of the fabric under the presser foot. You'll need to carefully adjust stitch tension ... practice on the scrap material especially when you sew through many layers of the patches - and make SURE that the 'knots' are pulled tight to the fabric. All this will avoid 'birdsnests' in your sewing with a 'home' machine.
Before you start sewing with a home/dressmakers sewing machine, get out the machine's manual and readjust / check the 'timing' of the machine (closeness of the needle to the machine's 'gib hook' on the bobbin holder) ... as well as lubricate the machine (internals/gears, etc.) with the recommended oil, etc. Be sure you match the needle size for the thread you are using ... consult your machine's manual; this will insure that the eye of the needle wont cut the thread.

hope this helps. ;-)

Whew

I have my mother's machine from when she was married in 1963. It is a beastly cast iron machine. I hope it is up to the job. My experience is that stuff that has lasted this long has lasted for a reason so I'm hopeful.

 

[Seattle Scott]

Cut it out of the middle

When I took my oversize chute to the sail loft, they took out a couple of the horizontal pannels in the middle of the sail, didn't touch the head or clews. I noticed no difference in how the sail flew, other than the foot didn't end up in the water when the wind died.

 

[rgranger]

Sailrite is great

Hey All (And especially Rich and Kenn)

Thanks for all of the expertise.

I sent sailrite an e-mail describing what I wanted to do and the recommendations you all mentioned.

In a few hours I got a list of what I would need, including quantities AND PART NUMBERS

Thread, webbing, D-rings, basting tape and needles


All the stuff with shipping came to $37 (and $12 of that was shipping) and I took care of it all on line.

Now that is service.

So I wanted to put a plug in for these guys. If you need service e-mail Matt at customer service.

 

[gettinthere]

I thought this was going to be a discussion about sailingdog!!!

 

[wonkodsane]

Hey All (And especially Rich and Kenn)
Now that is service.

So I wanted to put a plug in for these guys. If you need service e-mail Matt at customer service.

Sail-Rite is absolutely the most email-responsive sailboat supply company that I have ever dealt with (Except for Phil and SBO!). Kudos to them.

 

[kenn]

We bought a SailRite kit for a mainsail cover last year. Great kit, with everything included, and detailed instructions. We had no problems making it.