On Wed, 03 Nov 2004 12:26:05 +0000, Ian Malcolm wrote:

Morgan Ohlson wrote:
On 24 Oct 2004 14:06:56 GMT, William R. Watt wrote:


Stephen Baker ) writes:

Morgan says:


Center or transom sheeting is what I'm just conserning my brain with.

If you have a loose-footed main, then I would seriously recommend end-boom
(transom) sheeting, or the bending moments in the boom will be extremely high.

you can run the sheet from the boom end to a block in the middle of the
boom. that keeps it up out of the way and drops it pretty well into a
block mounted, say, on the rear of the centreboard trunk. with a 70 sq ft
main sail you'll need the leverage (mechanical advantage) of a multi part
mainsheet fed through blocks. if you are going to be cruising small lakes
and rivers with shifty winds you won't be able to cleat the mainsheet.
you'll have to hold it in your hand all the time. you probably won't cleat
the mainsheet on an 18 ft dingy anyway. too light and responsive. a rachet
block is quite common and would take some strain off the arm holding the
mainsheet. something to consider later if you find the strain on the arm
too uncomfortable.

the centreboard has to be top braced against lateral (sideway) stresses,
sometimes done with a seat, sometimes with a simple thwart, on which a
traveller and compass can be mounted. I seem to recall the back end of dingy
centreboard trunks being braced by a metal mainsheet traveller alone. the
traveller mostly just helps keep the sail flat when close hauled but also
helps as a preventer. it's not essential for dingy cruising. you can see
these things on photos and diagrams of sailing dingys like the Wayfarer.
I don't know if there are any formulae covering these things, except of
course for the mechanical advantage of the main sheet blocks. It's mostly
trial and error and tales told by old dingy racers.



It's quite common with slightly bent travelers (low at ends)... more seldom
straight. (correct?). What is the main benefit?

To get a transom sheeting an extended boom may be necessary. Does that have
any complications in other ways?


I have seen no end of trouble with boom end sheeting on dinghies. The
usual problems include the common pin and swivelling strap boom end
fitting failing in heavy weather, the multi part mainsheet wrapping
round itself when gybing so you cant let the sail out without hauling
it right in to clear the jam, and the mainsheet catching on the rudder
stock or the corner of the transom when gybing causing all sorts of
grief :-(. For a crusing dinghy, it will also make it unsafe to keep an
outboard on the transom.

I strongly reccomend reconsidering the boom end sheeting. If you go to
centre sheeting, you will also need the foot of the sail attached to the
boom which is no problem with a bolt rope on it.

Have eyelets fitted in the foot of the sail just above the boom 2" aft
of vertically in line with the reefing clew eyes on the leech so the
sail doesnt get worn through by being trapped against the boom by the
reefing lines. Each reefing line should be tied off using a bowline
round the boom through the eyelet, leaving just enough slack to not
affect the set of the sail when you arent reefed and led up through the
appropriate reef eye in the leech and down to the end of the boom and
then to whatever system you use for cleating the reefing lines. Although
the eyelets just above the boom wouldnt be needed if your reefing lines
were secured to the side or bottom of the boom like on a yacht, that
would put a massive twisting load on the gooseneck, which dinghy
goosenecks are NOT designed to withstand.

Dont bother with single line reefing, a spring gate hook at the
gooseneck on the same pin as is used for the Tack eye is much better
than the extra friction and complexity of having shuttle blocks inside
the boom. I have thin bungee threaded from the luff to the leech and
back again through all the cringles for each reef with small plastic
hooks on one side of the sail so I dont have to bother with tying
reefing points, they just hook together under the boom round the hanging
'bag' of sail. The bungee should be just slack with the sail streched
tight along that line of cringles before you hook it round the boom.
Also if you forget one when shaking out a reef, there is enough stretch
in the bungee to save the sail from being ripped.

The only difficulty I have with the system is that the luff has a
boltrope that slides into the mast groove so I have a lot of loose sail
+ the boom to control when lowering it. For a cruising dinghy 15' I'd
strongly reccomend having slides up the luff retained by a pin or a gate
at the bottom of the groove and a topping lift or better yet lazyjacks
so the sail can be dropped quickly under full control without bashing
the helm on the head with the boom or loosing the crew under the heap of
sail.

An unstayed rig with a jib is going to be a lot more trouble than having
shrouds as the mast will need to be a heavier section and there will be
a lot of stress on the partners and step. You will also have a LOT more
trouble getting satisfactory jib luff tension. Avoid highfield levers
for the jib halyard tensioner, IMHO they are the invention of the devil.
I have a tensioner setup that uses a 2:1 tackle that sweats the halyard
sideways before the cleat. Looking at the angles I reckon its worth a
4:1 or 5:1 advantage pulling on the halyard. You may not be able to use
this setup, but if I had to use a different setup I'd rather have a
muscle box that can be released in a controlled fashion (even though
they are very inefficient) thatn a highfield lever which will do its
bset to take your fingers off if you are tired or careless when you let
it off. Figure on carrying a minimum of two jibs if you are not having
roller reefing as you will want to keep the rig balanced with one reef
in to avoid excessive weather helm. N.B. most small jib roller gears are
only designed for furling ie. 100% out or 0% out and will break if used
for reefing eg. 50% out in strong winds. The roller reefing gears are
quite a bit more expensive, so I decided NOT to get one.

On the subject of travellers and sheeting etc. The total sail area of my
Albacore is ~125 sq feet (11.65 sq m) and she's 15' LOA and LWL which
would be pretty close to the LWL of an 18 footer that doesn't have a
vertical stem so the loads are closely comparable to your proposed
design. The beam is 5'6" which would be less than you'd want for an 18'
cruising dinghy and my traveller horse is unsupported 1.5" aluminium
alloy tube running right across the full beam. Three parts of the four
part center mainsheet lead to the traveller car, the fourth part runs to
a swivel block with a cleat (which does get used quite a bit, mostly to
rest my hand) on the back of the centerboard capping about 6" behind
the traveller. The mainsheet leads through two single blocks on the
boom, one over the traveller, the other over the swivel block. This
spreads the load on the boom. When gybing I grab two parts of the
mainsheet and control the boom as it comes over (keep your elbow bent
:-) ). The traveller control line is a 3:1 continuous loop with turning
blocks and cleats on the centreboard cap so I get a streight pull on it
when I want to use it when sitting out. The original system was 2:1
cleating under the gunwales which was pretty useless in a blow. The
traveler horse bends up about 3" in the middle if close hauled in a
force 5 with two people hiking. Its been doing that for the past 40
years without any problems. I reckon you'd be fine with a modern X
section track bolted to an alloy tube to stiffen it for a span of about
6 feet. No bulkhead required. Remember a 6' long track at mid boom is
equivalent to one 12' long :-) at the transom. With centre boom
sheeting and a traveller you dont need quite as powerfull a kicking
strap (boom vang). If you stick to boom end sheeting you will need
about 16:1 to get the leech flat enough off the wind in a blow. This
will mean you will need either a massive boom section or to internally
sleave it for the forward third of its length to stop it buckling. You
will also have problems with the amount of mast bend it induces pulling
all the shape out of the luff of the sail. I find 4:1 works well for me
with centre sheeting and a full width traveller.

Finally I hope you are fitting a pivoting centreboard not a daggerboard
as the ability to fine tune the CLR to match the CE when reefed and
reduce the weather helm if using main only is worth all the added
complexity alone and if you touch bottom with it at speed you will be
glad it can kick up rather than snapping off or ripping the trunk out of
the hull with you miles from where you launched.

Lot's of language trouble here.

You say that the main sheeting get twisted around it self??? ...is rear
sheeting different towards center sheeting in that aspect?

Have eyelets fitted in the foot of the sail just above the boom 2" aft of vertically in line with the reefing clew eyes on the leech so the sail doesnt get worn through by being trapped against the boom by the
reefing lines.

Do you intend that the sail should be reefed towards itself instead of the
boom?
Towards a kind of ´support reef line¡ ???
Does anyone have a link on this?

So you would recommend stays (2 or 3?), perhaps with harken quick fasteners?
Are there other good ones?
How much lighter do you think a stayed mast will be? (for a 14m2 main+jib)

You say bolt rope for the sail, but travelers up the mast (not bolt rope?)?

There will be 2 thin pivoting lead ballasted steel centerboards in around
20deg angle from the lateral plane. (draft only ~0,8m for lakes).
...foil advice???? (and fat foil for rudder)

Words Q
Roller?
spring gate hook?
Cringles?
partners and step?

Great answers. Thank you for your advice. ...I will dwell on this a while.
)

Thanks!


Morgan O.

Morgan Ohlson wrote:

On Wed, 03 Nov 2004 12:26:05 +0000, Ian Malcolm wrote:
snip
I have seen no end of trouble with boom end sheeting on dinghies. The
usual problems include the common pin and swivelling strap boom end
fitting failing in heavy weather, the multi part mainsheet wrapping
round itself when gybing so you cant let the sail out without hauling
it right in to clear the jam, and the mainsheet catching on the rudder
stock or the corner of the transom when gybing causing all sorts of
grief :-(. For a crusing dinghy, it will also make it unsafe to keep an
outboard on the transom.

I strongly reccomend reconsidering the boom end sheeting. If you go to
centre sheeting, you will also need the foot of the sail attached to the
boom which is no problem with a bolt rope on it.

Have eyelets fitted in the foot of the sail just above the boom 2" aft
of vertically in line with the reefing clew eyes on the leech so the
sail doesnt get worn through by being trapped against the boom by the
reefing lines. Each reefing line should be tied off using a bowline
round the boom through the eyelet, leaving just enough slack to not
affect the set of the sail when you arent reefed and led up through the
appropriate reef eye in the leech and down to the end of the boom and
then to whatever system you use for cleating the reefing lines. Although
the eyelets just above the boom wouldnt be needed if your reefing lines
were secured to the side or bottom of the boom like on a yacht, that
would put a massive twisting load on the gooseneck, which dinghy
goosenecks are NOT designed to withstand.

Dont bother with single line reefing, a spring gate hook at the
gooseneck on the same pin as is used for the Tack eye is much better
than the extra friction and complexity of having shuttle blocks inside
the boom. I have thin bungee threaded from the luff to the leech and
back again through all the cringles for each reef with small plastic
hooks on one side of the sail so I dont have to bother with tying
reefing points, they just hook together under the boom round the hanging
'bag' of sail. The bungee should be just slack with the sail streched
tight along that line of cringles before you hook it round the boom.
Also if you forget one when shaking out a reef, there is enough stretch
in the bungee to save the sail from being ripped.

The only difficulty I have with the system is that the luff has a
boltrope that slides into the mast groove so I have a lot of loose sail
+ the boom to control when lowering it. For a cruising dinghy 15' I'd
strongly reccomend having slides up the luff retained by a pin or a gate
at the bottom of the groove and a topping lift or better yet lazyjacks
so the sail can be dropped quickly under full control without bashing
the helm on the head with the boom or loosing the crew under the heap of
sail.

An unstayed rig with a jib is going to be a lot more trouble than having
shrouds as the mast will need to be a heavier section and there will be
a lot of stress on the partners and step. You will also have a LOT more
trouble getting satisfactory jib luff tension. Avoid highfield levers
for the jib halyard tensioner, IMHO they are the invention of the devil.
I have a tensioner setup that uses a 2:1 tackle that sweats the halyard
sideways before the cleat. Looking at the angles I reckon its worth a
4:1 or 5:1 advantage pulling on the halyard. You may not be able to use
this setup, but if I had to use a different setup I'd rather have a
muscle box that can be released in a controlled fashion (even though
they are very inefficient) thatn a highfield lever which will do its
bset to take your fingers off if you are tired or careless when you let
it off. Figure on carrying a minimum of two jibs if you are not having
roller reefing as you will want to keep the rig balanced with one reef
in to avoid excessive weather helm. N.B. most small jib roller gears are
only designed for furling ie. 100% out or 0% out and will break if used
for reefing eg. 50% out in strong winds. The roller reefing gears are
quite a bit more expensive, so I decided NOT to get one.

On the subject of travellers and sheeting etc. The total sail area of my
Albacore is ~125 sq feet (11.65 sq m) and she's 15' LOA and LWL which
would be pretty close to the LWL of an 18 footer that doesn't have a
vertical stem so the loads are closely comparable to your proposed
design. The beam is 5'6" which would be less than you'd want for an 18'
cruising dinghy and my traveller horse is unsupported 1.5" aluminium
alloy tube running right across the full beam. Three parts of the four
part center mainsheet lead to the traveller car, the fourth part runs to
a swivel block with a cleat (which does get used quite a bit, mostly to
rest my hand) on the back of the centerboard capping about 6" behind
the traveller. The mainsheet leads through two single blocks on the
boom, one over the traveller, the other over the swivel block. This
spreads the load on the boom. When gybing I grab two parts of the
mainsheet and control the boom as it comes over (keep your elbow bent
:-) ). The traveller control line is a 3:1 continuous loop with turning
blocks and cleats on the centreboard cap so I get a streight pull on it
when I want to use it when sitting out. The original system was 2:1
cleating under the gunwales which was pretty useless in a blow. The
traveler horse bends up about 3" in the middle if close hauled in a
force 5 with two people hiking. Its been doing that for the past 40
years without any problems. I reckon you'd be fine with a modern X
section track bolted to an alloy tube to stiffen it for a span of about
6 feet. No bulkhead required. Remember a 6' long track at mid boom is
equivalent to one 12' long :-) at the transom. With centre boom
sheeting and a traveller you dont need quite as powerfull a kicking
strap (boom vang). If you stick to boom end sheeting you will need
about 16:1 to get the leech flat enough off the wind in a blow. This
will mean you will need either a massive boom section or to internally
sleave it for the forward third of its length to stop it buckling. You
will also have problems with the amount of mast bend it induces pulling
all the shape out of the luff of the sail. I find 4:1 works well for me
with centre sheeting and a full width traveller.

Finally I hope you are fitting a pivoting centreboard not a daggerboard
as the ability to fine tune the CLR to match the CE when reefed and
reduce the weather helm if using main only is worth all the added
complexity alone and if you touch bottom with it at speed you will be
glad it can kick up rather than snapping off or ripping the trunk out of
the hull with you miles from where you launched.


Lot's of language trouble here.

You say that the main sheeting get twisted around it self??? ...is rear
sheeting different towards center sheeting in that aspect?
Any setup where there are more than two parts of a tackle running
parallel, really close to each other that goes slack during a gybe can
cause trouble, but the longer the tackle is and the smaller the gap
between the parts the more likely it is to twist. Also some sorts of
apparently braided rope actually has a three strand twisted core and
this makes it twist up if a load is applied then rapidly released. You
*can* get the same problems with center sheeting, but as the tackle is
typically half the length and it does not have to run to one
multi-sheave block but can be spaced out along the boom using a couple
of single blocks to keep the parts away from each other, its not a
common problem. If, by mistake, you fit the boom end with a swivel
block, you are guarenteed a problem. Its bad enough with the bottom
block on the transom free to swivel. Its also a lot worse if you use
'hairy' thicker rope that is easy to grip. 8mm smooth rope is about as
heavy as can be used on our club wayfarer without twisting up as
described, whereas on my Albacore I have a 12mm hairy rope for the
mainsheet which never seems to get fouled up (unless I tread on the end
:-)) and is much more comfortable to hold for hours at a time.


Have eyelets fitted in the foot of the sail just above the boom 2" aft of vertically in line with the reefing clew eyes on the leech so the sail doesnt get worn through by being trapped against the boom by the

reefing lines.

Do you intend that the sail should be reefed towards itself instead of the
boom?
No, the reefing line is tied closely round the boom through the eyelet
and then lead up through the reefing eye on the leech and out to the
boom end. By having the eyelet, the sail is not trapped and crunched up
where you are tying the reefing eye at the leech to the boom but is
free to hang in a fold wich will be gatered up later by your reefing
points or by sail ties or shockcord (bungee) through your reefing cringles.
Towards a kind of ´support reef line¡ ???
Does anyone have a link on this?


So you would recommend stays (2 or 3?), perhaps with harken quick fasteners?
Are there other good ones?
Three 4mm wire stays, Forestay and two shrouds. You probably want a
fractional rig (the stays go typically 3/4 or 5/8 the way up the mast,
not to the top). I have two twist lock shackles on my shrouds under the
deck (the swaged eye in the end goes through a small hole in the deck)
joining them to the vernier plate shroud adjusters. My forestay is
connected using a drop-nose pin. To make it lock positively, I have a
short length of rubber tube over the pin just under its head to act as a
spring to keep the nose of the pin pressed against the fitting it goes
through so the nose cannot pivot back into line to take the pin out
unless I press the whole pin in a bit.

How much lighter do you think a stayed mast will be? (for a 14m2 main+jib)
I dont know, but I can easily lift my 22'6" Albacore mast one handed.
Mine isnt very light, it has survived 40 years of use and abuse without
any serious damage.


You say bolt rope for the sail, but travelers up the mast (not bolt rope?)?
You can have a bolt rope up the mast, but dealing with a sail that comes
away from the mast when you drop it in a hurry is more difficult the
bigger the sail is. Nearly all yachts with slab reefing use slides for
this reason. N.B. a system that lets the slides escape when you lower
the sail or one where you have to remove several slides from the track
to reef is a disaster and is worse than a boltrope.


There will be 2 thin pivoting lead ballasted steel centerboards in around
20deg angle from the lateral plane. (draft only ~0,8m for lakes).
...foil advice???? (and fat foil for rudder)
Do you mean the planes of the centreboards are tilted outwards at the
bottom? Have you considered that the draft will increase as the boat
heels up to 20 deg.? This means that if you touch a shoal and the boat
heels a little more as the wind blows you sideways, the centreboard will
dig in.
I suspect that lead ballast will not be required. Why not specify
slightly thicker centreboards and grind the edges to a somewhat better
foil section before you have them galvanized. Dont forget you will need
a pair of decent winches for lifting them and provide a rope to hold
them down in bad weather as otherwise if you capsize they may crash back
into their case and break out through the top of the case.


Words Q
Roller?

Roller was in the context of roller furling gear or roller reefing gear
for the jib. An arrangement with a swivel above the head and a drum
with a rope on it below the tack so the jib can be wrapped around
itsself like a roll up window blind. On its own the word means a
cylinder that turns or something wraps around. Gear in this context
does NOT refer to a toothed wheel as it can also mean a mechanism or
mechanical device.
spring gate hook?
A hook with a wire spring that goes accross the opening so that anything
hooked onto it cannot shake off on its own.
Cringles?
the little eyelets along the line of the reef that reefing points are
traditionally tied through for tieing up the part of the sail you are
not using.
partners and step?

'Partners', where the mast goes through the deck, on a dinghy, often
known as the mast gate. Mast step, the fitting on the deck (for deck
stepped masts) or keelson (top surface of the keel) (for keel stepped
masts) that the heel (bottom) of the mast fits into.
Also note 'Hounds' (where the shrouds and forestay attach to the mast)

Great answers. Thank you for your advice. ...I will dwell on this a while.
)

Thanks!


Morgan O.


--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- &
[dot]=.
*Warning* SPAM TRAP set in header, Use email address in sig. if you must.
'Stingo' Albacore #1554 - 15' Uffa Fox designed, All varnished hot
moulded wooden racing dinghy circa. 1961

Ian Malcolm ) writes:

.... You
*can* get the same problems with center sheeting, but as the tackle is
typically half the length and it does not have to run to one
multi-sheave block but can be spaced out along the boom using a couple
of single blocks to keep the parts away from each other, its not a
common problem.

I think one advantage of centre sheeting is the blocks being one above the
other making the sheet less likely to hang in great loops and get tangled up.

Three 4mm wire stays, Forestay and two shrouds. You probably want a
fractional rig (the stays go typically 3/4 or 5/8 the way up the mast,
not to the top).

My understanding is a "fractional" rig is one where the jib only goes part
way up the mast, eg Albacore. When the jib goes to the top of the mast
it's called a "mast head" rig.

It might also be useful to point out that the forestay is only there to
keep the mast from falling down when the jib is not up. When the jib is in
up it's the jib haliard which takes the strain, and it's important that
the jib haliard be tight enough to stay straight or the jib won't work
well going up wind.

The big difference in stress between a stayed mast and and unstayed mast
is the stays direct the stress straight down the mast into the bottom of
the boat, called "mast compression". As the stays force the mast downward
they pull the gunwales upward, so the gunwales have to be strong. On an
unstayed mast the stress is off to the side. There is only 6 ft of 2"
solid spruce mast above the partners on the small 32 sq ft sail on my
Dogskiff but I can watch it bend off to the side as the wind pick ups.
Fore-and-aft it actually takes up a curved shape due ot the greater
pressure in the middle countered by the fixed position in the partners,
same as on a Laser.

On a small boat like a dingy the heeling force of the mast and sail puts
quite a torque or "twist" on the hull. If you look at the partners on the
thin plywood Dogskiff on my website you can see how I've used X-shaped
struts to redirect some of the sideways heeling force down to the chines.
This has worked quite well. On the Albacore the deck and floatation tank
underneath help stiffen the hull and spread the stress from the mast. I'd
think about accomodating these stresses in designing a home built dingy.

Do you mean the planes of the centreboards are tilted outwards at the
bottom?

Twin centreboards or keels are usually called bilge boards or bilge keels.

...Have you considered that the draft will increase as the boat
heels up to 20 deg.? This means that if you touch a shoal and the boat
heels a little more as the wind blows you sideways, the centreboard will
dig in.

Bilge keels are actually an advantage in shoal water. As soon as you feel
the lee one ground you tack away to lift it and keep it from digging in.

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