Building Shesha, a Hunter Valley GIS, Australia

[IanHowick]

Well, I was about to cut out the ply for my centreboard case this morning, but I think I'll leave it till you have figured out what is going on with the balance with the stiffer yard.

Regarding fiddling with the ties along the yard:

Exactly ... If the sail is given something like the curve it has at the top on the wooden spar then it will be interesting to see if the handling goes back to the original.
MIK

But I'll also fiddle with the ties on the yard. Leaving the end ones tight and slackening the middle ones will induce more shape, which may be just enough.

Are you both thinking in the same direction? If I read Mik correctly, he's talking about letting the sail edge curve go back closer to what it was on the wooden yard by keeping the middle ties tight and the end ones slacker, so that the upper part of the sail has less shape, and is more like it was before the change of yards.

Perhaps Mik can clarify.

Ian

[woodeneye]

No I'm probably off at a tangent by the look of it.

I might try slackening off the ends with the middle ones tight and vice versa as well to see what happens!

Regarding the daggerboard, I left the trailing edge untapered like bitingmidges GRUFF. Would tapering the board affect the COE significantly do you think?

[Boatmik]

Regarding fiddling with the ties along the yard:

Are you both thinking in the same direction? If I read Mik correctly, he's talking about letting the sail edge curve go back closer to what it was on the wooden yard by keeping the middle ties tight and the end ones slacker, so that the upper part of the sail has less shape, and is more like it was before the change of yards.

Perhaps Mik can clarify.

Ian

Ian is correct.

cable ties tight in the middle of the yard, but progressing to slack at the ends.

If you wanted to play it safe, Ian, you could move the centreboard forward by an inch and a half or maybe we could rejig the angle of the board - that would have a bigger effect for a smaller change.

Or you could get on with some other bits until we find out the reason for this.

The Goat is pretty close to a dead neutral helm as designed. Any small discrepancies can be picked up by fiddling with the sail position a bit.

But the stiffer spars have this really strange effect.

The loose tie trick might pin down whether it is something about sail depth, but I am really expecting the extra depth to give more weather helm. Unless it is adding way more depth at the front.

The other way would be to lie the boat on its side with everything at about the same tension as sailing in medium wind and have a look at the depth of the sail at different heights and just where that depth is ... and then swap to the other yard.

A lot more sail depth up forward might have this effect ... maybe.

Be interesting to have some numbers at the throat level and halfway up the yard and can do this if the sailing weather is not too good.

(that's one way to make the wind come in so you can try the loose lashings on the water!)

MIK

[IanHowick]

If you wanted to play it safe, Ian, you could move the centreboard forward by an inch and a half or maybe we could rejig the angle of the board - that would have a bigger effect for a smaller change.

Or you could get on with some other bits until we find out the reason for this.

The Goat is pretty close to a dead neutral helm as designed. Any small discrepancies can be picked up by fiddling with the sail position a bit.

But the stiffer spars have this really strange effect.

Thanks, Mik, yes, I'll leave off cutting out the centreboard case till you two get to the bottom of why the stiffer spars are affecting the balance.

Bruce - it might he worth talking to your sailmaker regarding what's going on, see if he has an opinion on how much spar bend he allowed when he cut the sail, how changing this would affect the draft and COE position.

Good that you are finding these things out in time for me!

Ian

[woodeneye]

Ian is correct.

cable ties tight in the middle of the yard, but progressing to slack at the ends.

If you wanted to play it safe, Ian, you could move the centreboard forward by an inch and a half or maybe we could rejig the angle of the board - that would have a bigger effect for a smaller change.

Or you could get on with some other bits until we find out the reason for this.

MIK

I’ll have a fiddle with the sail attachment to the yard this Sunday. I likely won’t get any sailing in due to other commitments though, but with a bit of luck, who knows…

However, the throat attachment at the front of the yard cannot be slack at all, so any slack will have to be toward the peak. Secretly I think I know what’s going to happen but I won’t pre-empt anything in the interest of good science!

I agree with MIK about the daggerboard casing. Extending it forward a bit would be fine and won’t hurt anything. Allowing for a little bit of adjustment of the board will help with tuning. From my experience of other boats with daggerboards this gives some “on the fly” adjustment while sailing without resorting to messing with the rig.

[Boatmik]

Howdy Ian,

I am not sure the sailmaker will have a lot to add. I think they will be as mystified as we are.

Give it a bit of time to see if we can sort it out. If not, I think there are a number of ways we can hedge our bets allowing some possibilities for raking or moving the centreboard or making by changing the case or making the board a bit narrower.

I don't see it being anything big in the scheme of things, but if stiff spars have this effect then it is nice if we can balance it out.

Want to make this big funny rig Cherub of yours sail really well.





Images from the magnificent UK Cherub website I've mentioned before.

MIK

[woodeneye]

Kim and I are back from Sydney having enjoyed the show we went to see, The Jersey Boys which told the story of Frankie Valli and the Four Seasons. The show is just awesome and I can recommend it to anyone, even if they are not Frankie Valli fans as the music is just brilliant. I wasn't aware of their story which traced their rocky rise to fame, and which was interupted by stints in gaol!

Anyway Valli aside, sailing wasn't on the agenda today as there is no wind at all, so it was some more driveway development for testing maybe next weekend.

I've installed the vang, reconfigured the downhaul, moved the sail attchment on the front of the boom back a bit, moved the yard attachment back to the 40% position, and added a 2:1 purchase on the clew adjustment.

Just to explain a bit for those who haven't been following this thread, I have been having issues with lee helm when close hauled. Hopefully these mods will sort that problem, and introduce some desirable slight weather helm.

This pictures show the vang installed, and the downhaul moved to to the front of the boom. Here the downhaul is pulled on so that the luff of the sail is 200mm in front of the mast. This is 200mm further back than the standard position of 400mm in front of the mast, and demonstrates one end of the available adjustment. This position moves the rig back for close hauled sailing and to induce (hopefully) some slight weather helm.
Attachment 152301Attachment 152306DSCF0423.jpg

This next picture shows the downhaul released and some vang tension applied. You will see that the boom has now moved forward to place more of the sail to weather of the mast. The object here is to help balance the rig for downwind sailing and reduce rolling from side to side. It also balances the helm. Of course, in between these extremes is the ideal adjustment for the point of sailing (ie. close reaching or broad reaching) and the wind strength on the day. I have already played with this in actual sailing, but without the assistance of the vang which now makes the adjustments easier, and provides more control of both the luff and the leach.
Attachment 152302DSCF0432.jpgAttachment 152309

The pics above show how the rig is easily adjusted while sailing. Ideally, with this set-up, the downhaul should be attached in front of the mast. With the downhaul currently fixed to the original fixture on the deck just to the left of the mast, it is binding slightly when the boom is gybed to starboard tack. If this arrangement works well in sailing, I'll move it to the front of the mast. The vang attachment is on the deck behind the mast, and this proved to be the correct place for it as there is no binding of the vang at all.
Attachment 152310

Notice I have applied traditional systems and have not used a cascading system for either the vang or the downhaul. The reason is because the cascading systems could not cope with the large amounts of movement and are better suited where the adjustment ranges are small. As you can see I just bolted the two single pulleys for the vang together to make a double.

Once the system is proved, then I will bring the controls back to cleats on the front edge of the seat. I don't want to drill holes unnecessarily at this stage.

These next two pics show the effect of the movement of the rig on the mainsheet. I had already moved the sheeting aft last weekend and found that this worked better for me. The rear sheeting does not interfere with the tiller as much, but the main thing I wanted to achieve with this arrangement was to prevent the boom being pushed forward when sheeting in hard. This arrangement works well to solve that issue. I can't say it will suit everyone, but I like it. The traveller is also adjustable via a clam cleat located beside BH4.
Attachment 152311Attachment 152312

Finally, here is the simple 2:1 adjustment for the foot of the sail. The line runs around a sheave set into the end of the boom.
Attachment 152313

[Boatmik]

[ame=http://www.youtube.com/watch?v=iE83jU1dkmQ]YouTube - Goat Island Skiff - Maitland NSW Australia[/ame]

[woodeneye]

Just back from a day's sailing at Grahamstown Dam. This time I was accompanied by my two daughters, the first time we have sailed 3-up in Hakuna Matata. Forecast winds of 10-13 knots in the morning did not materialise, and we had at most 5 knots. This afternoon we were chased off the water by a nasty looking thunderstorm, which saw all boats skedaddle for the shore before it hit and we were lashed with heavy rain. By the time it cleared, everyone was off the water and all boats packed up.

For a lot of the time we were just ghosting along, on flat, shiny water. Even so, I was quite impressed with the Goat's ability to foot quite nicely in such light stuff with a decent load aboard. Both girls spent most of the time propped up against BH2 while I either sat on the floor behind the seat or on it. Clearing the transom from the water makes a huge difference in those conditions. As soon as the breeze picks up a bit and there are ripples on the water, moving back a bit to lift the bow just clear of the water seems to work best, and produces that familiar chuckle which is nicely amplified by the front compartment.

Realistically the wind was too light to be able to make any judgments as to the helm. However the vang and downhaul seems to work just fine in concert with each other, so this week I will move the downhaul attachment to the deck in front of the mast to prevent it binding when the front of the boom moves around the mast.

[Boatmik]

Howdy,

Seems to me the logical place is underneath the boom beside the mast.

What are you thinking?

I mean that in a nice way. It is not like

WHAT ARE YOU THINKING??!!!!!!!??????

Best wishes!!!

MIK

[woodeneye]

Hi MIK

Haha, I know what you mean, and sometimes I wonder what I'm thinking too!

OK, I'll try to explain. Consider the picture below and imagine if you will what happens when the boom goes from one side to the other. (In the pic you can't actually see the interference with the mast, as it's on the other side)

DSCF0432.jpg

When the boom swings out on the port side, the downhaul attachment at the boom end swings around to the starboard side. A straight line between the attachment at the front of the boom and the attachment at the deck on the port side of the mast bisects the mast; ie. the downhaul has to bend around the mast. If the attachment at the deck is in front of the mast, it will be free to pivot unobstructed by the mast. This is the case with the vang (kicker) which is attached at the deck behind the mast and swings back and forth unobstructed by the mast.

Yesterday, when close hauled, we were able to tack back and forth without problems. This is because the front of the boom travels in a relatively small arc. Remember too that when close hauled, the downhaul is on hard to pull the boom back. However, when running the downhaul is freed off and allows the boom to slide forward. When we gybed from port to starboard, the front of the boom moves in a much wider arc and would not swing all the way across because the downhaul was binding against the mast. We needed to free the downhaul a bit in order that the boom could swing right across. Remember the conditions were quite light.

I hope I've done a reasonable job explaining this.

Can you believe it? Yesterday we had no wind and today there was a lovely breeze, but I had other obligations. Aaarrrggghhh

[Boatmik]

Hi MIK

Can you believe it? Yesterday we had no wind and today there was a lovely breeze, but I had other obligations. Aaarrrggghhh

It's a sailor's lot. It is also a cyclist's lot with the wind usually coming from ahead on most trips, with a nice downwind peddle on the day after.]

I must be misunderstanding what you mean. It seems to me that moving the attachment point away from beside the mast will mean that you get more interference from the mast with the downhaul and vang) on one tack or gybe) than the other.]

I am wondering about whether taking the "dowhaul" so far forward is creating wrapping problems that don't need to be there.]

But lets see what happens.]

MIK

[woodeneye]

I must be misunderstanding what you mean. It seems to me that moving the attachment point away from beside the mast will mean that you get more interference from the mast with the downhaul and vang) on one tack or gybe) than the other.

MIK

No! I haven't moved the downhaul yet. It's still beside the mast. The binding against the mast will be cured by moving it in front of the mast

[MiddleAgesMan]

I could be wrong but it seems MIK is suggesting the wrapping-binding problem is exacerbated by the extreme forward mounting of the downhaul.

It seems the changed geometry of moving that attachment point back closer to the mast might solve the problem easier than moving the deck mounting point.

We could be wrong but I would try it before drilling more holes in the deck.

[woodeneye]

OK, I got the cat by the tail. For now though I need the downhaul attachment to be quite far forward so I can pull the boom back sufficiently to counteract the weather helm and also balance the vang.

However, moving the downhaul attachment on the boom closer to the mast will still cause binding against the mast when it is released for reaching and running.

Lots to play with yet and nothing is final though. It's just a starting point.