Range of adjustment on Loose Footed Main

[alahol2]

Just got a loose footed main and am about to modify the stackpack. Need to add a bolt rope in the bottom of the stackpack and cut a slot for the new clew slide. Anybody got any feel for the amount of adjustment I need to cater for on the clew of the main? ie outhaul hard on (flat main) to outhaul loosed off (bellied main). The sail has a 3 metre foot.

 

[Wing Mark]

I think having the middle of the foot about 15% (of its 3 metre length) away from the boom would be as full as you want, based on a few dinghies.

 

[Poignard]

Just got a loose footed main and am about to modify the stackpack. Need to add a bolt rope in the bottom of the stackpack and cut a slot for the new clew slide. Anybody got any feel for the amount of adjustment I need to cater for on the clew of the main? ie outhaul hard on (flat main) to outhaul loosed off (bellied main). The sail has a 3 metre foot.

I have a loose-footed mainsail with a foot about 12 feet long. I have never felt the need to slack it off more that about a foot.

 

[wilkinsonsails]

Should be less than 15”

 

[dunedin]

Are you sure of these numbers - a slight easing of the outhaul will give a lot of extra depth?

I would expect you would never need more than about 10% depth = 30cm

Using an approximation by Pythagoras theorem
- Half length of foot = 150 cm. = hypotenuse
- Sail depth = 30cm. = opposite
Square of hypotenuse = square of opposite - square of adjacent
Square of adjacent = square of hypotenuse - square of opposite
21,600 = 150x150 - 30x30
Adjacent = c.147 cm
Length along foot circa 294cm

Allowing for curvature rather than straight lines perhaps 290cm

Clew movement for 30cm depth around 10cm ?

Does that make sense, or have I missed something?

 

[alahol2]

Clew movement for 30cm depth around 10cm ?

Does that make sense, or have I missed something?

That agrees with a similar calculation I did for the 15% depth which came out at about 14 - 15 cm.
I'm thinking I'll give it 8 or 9 inches (20 - 22 cm).

Thanks all for the suggestions.

 

[Wing Mark]

I worked it out that the clew has to move by about 4 or 5% of the foot length.
I suggest drawing a little diagram, because I can't explain it very well.
Make the loosened foot an arc of a circle and draw some triangles etc.
But allow some for errors in the length of the foot, where the tack attaches, the stackpack not fitting as you think it should etc etc.
I've just been through this sorting out an outhaul with a 4:1 tackle inside the boom.

 

[Gwylan]

Well I'd go with Wilkinsonsails. The clue is in the title and based on experience

 

[fredrussell]

Well I'd go with Wilkinsonsails. The clue is in the title and based on experience

Pah! This is an internet forum - we’re all experts!

 

[alahol2]

After calculations, drawings and bending bits of string I think my suggested 9" (22cm) pretty much encompasses everyone's suggestions. I can always make the slot bigger, making it smaller would be a bit more difficult.

 

[wilkinsonsails]

Allow for slider,shackle etc,sail cover should really finish at least 4 to 5” beyond the sail clew to fully protect the sail cloth .

 

[alahol2]

Allow for slider,shackle etc,sail cover should really finish at least 4 to 5” beyond the sail clew to fully protect the sail cloth .

Yes, that's why I need to cut the slot in the bottom of the stackpack, so there is some stackpack beyond the sail with its own bit of bolt rope.
Thanks for your input.

 

[thinwater]

Math class must have been rudimentary, no one has a tape (you can measured this in the time it took to type the question), or they don't use a loose-footed main (you only ease it a few inches).

Only Dunndin got it right, at no more than 100mm. Generally about 1/2 that.

 

[Daydream believer]

I would not put the stack pack cover in the sail groove.
Purchase 2 strips of aluminium track as used by caravan owners for their awnings on the side of the caravan. Pop rivet one each side of the boom. Then fit one half of the cover in each side. That way you are independant of the sail. Plus , in the future, if you go back to a bolt rope sail you do not have to faff trying to get it into the same channel. When you remove the sail you can leave the cover on until the sail has been fully removed ( or vice versa)

 

[Daydream believer]

On my 38M2 sail I would ease by up to 150mm & often do whilst sailing. I cannot ease more as this sail is full bolt rope. My cruising one has a 1/3 bolt rope, which I prefer & i can ease another 25mm.
But it is really all a product of sail cut & design.

 

[Tranona]

I would not put the stack pack cover in the sail groove.
Purchase 2 strips of aluminium track as used by caravan owners for their awnings on the side of the caravan. Pop rivet one each side of the boom. Then fit one half of the cover in each side. That way you are independant of the sail. Plus , in the future, if you go back to a bolt rope sail you do not have to faff trying to get it into the same channel. When you remove the sail you can leave the cover on until the sail has been fully removed ( or vice versa)

Batter still use sail slugs as Kemps did on the last one they made for me for a loose footed main - and will do on the next one. I had the tracks you described on an old wooden boom. Worked well with a slug attachment for the foot. Much better than the slide in the groove type, but not necessary with a loose footed sail.

 

[alahol2]

I would not put the stack pack cover in the sail groove.
Purchase 2 strips of aluminium track as used by caravan owners for their awnings on the side of the caravan. Pop rivet one each side of the boom. Then fit one half of the cover in each side. That way you are independant of the sail. Plus , in the future, if you go back to a bolt rope sail you do not have to faff trying to get it into the same channel. When you remove the sail you can leave the cover on until the sail has been fully removed ( or vice versa)

I can see arguments in favour of that but the arguments against are compelling:
Much more work and expense involved in adapting the stackpack.
Much more work and expense in adapting the boom. Not even sure it would fit because I've also got a Barton reef track. blocks and clutches on the side.
I actually like to remove sail and stackpack as one long sausage that can roll up into the boot to take home.

Slugs on the stackpack are a thought.
I'll give my original plan a season and see how it goes. I may re-think next year (or when the stackpack needs replacing.

 

[fredrussell]

I just sewed a bolt rope in my stackpack. Easy. Why one would want to start drilling holes in their boom to mount a stackpack is beyond me.

 

[dunedin]

I would not put the stack pack cover in the sail groove.
Purchase 2 strips of aluminium track as used by caravan owners for their awnings on the side of the caravan. Pop rivet one each side of the boom. Then fit one half of the cover in each side. That way you are independant of the sail. Plus , in the future, if you go back to a bolt rope sail you do not have to faff trying to get it into the same channel. When you remove the sail you can leave the cover on until the sail has been fully removed ( or vice versa)

Disagree entirely. Works well with bolt rope in boom (and for sails that still have foot rope, thin slidy material on sailcover works well).
Drilling lots of holes in side of boom, then adding more metal on outside of boom seems madness to me - risk of extra head damage if anybody gets hit by boom as well as extra corrosion opportunities and marginally weakened boom.

 

[Laser310]

i guess it's obvious.., but you need to measure the slot from where the clew would be with the outhaul tight.., which probably won't be the end of the boom.

one thing you might try, is to just hoist the main without a slug and use a clew strap instead. You can sail it this way and see how much adjustment you need.

plenty of boats, even really big boats.., only use a clew strap... no slide at the clew at all.

you don't really need a fancy velcro clewstrap - several passes of dyneema will work fine.