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.

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- &
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'Stingo' Albacore #1554 - 15' Uffa Fox designed, All varnished hot
moulded wooden racing dinghy circa. 1961