Rake it.

One of the ‘rigging bag’ posts.

In the first series of posts about Inanda’s rig i wrote about the problem of trying to get decently tight forestays when the boat doesn’t have anything to counter that forward pull…namely backstays.  Inanda relies on her aft 2 pairs of shrouds, uppers and lowers to give both lateral and fore-and aft support.  The problem lies in the fact that neither of them are far enough behind the rig to really help keep the forestay’s in tension. One solution i have been talking about is the running backstays idea, gaffers when they have running backstays often have 2 pairs that pull respectively from the inner and outer forestays. In gaff rig the running stay to the topmast and jibstay is often called a preventer, for simplicity i will just refer to them as runners.

When i was trying to describe the mechanics of this in the first series i struggled a bit to describe a way to visualise how a gaff rig is set up and what part is doing what job.  What i might have said is to think about the rig as having a pair of 3-dimensional pyramids of rigging with one apex at the inner forestay attachment point (the hounds) and a second attachment point higher up at the jibstay (outer forestay) and upper shrouds attachment point. Seen from the side each pyramid will have a long front leg and a much shorter aft leg….the distance that the stay is attached behind the mast.  The shorter that distance the less it can aid in pulling aft against the forestay.  Seen from directly aft and all you would see is the side element of the pyramid which should be at enough ‘angle’ to give the mast side support.  Looking at that angle in the upper pair of shrouds and it might seem a little narrow….in fact it is and gaffers often have a set of spreaders just like tall and skinny bermudan rigs have.

Today i want to look at a different method of giving the forestays more support but by raking the mast aft a bit and moving the aft shrouds back a bit.  A good example is our local working barge ‘Lynher’ shown here.  That’s quite a sexy rake for a big gaff rigged barge and to me it and it’s aft led shrouds make a lot of sense.   So why does this work and why do i like it ?

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What this comes down to is simple trigonometry again but not Pythagoras this time, rather sines and cosines and because it’s a Sunday and i’m being kind i won’t try and explain how to do this with maths.  Instead lets do it with a little imagination. Looking at the rig above just imagine what happens when load is applied to the forestay…lets say when we apply some tension to it.  The masthead will try to move forward and will be prevented from doing so by the aft shrouds with the mast acting as a strut/lever in between the 2.  As the mast is pulled forward it will become apparently longer in the vertical plane because it is pivoting at deck level.  As it ‘tries’ to get longer in that plane the shrouds would have to lengthen significantly to allow it to do so. Unless the shrouds are extremely stretchy (they won’t be) or there is massive slack in the deadeye lacings then that can’t happen and the forestay is kept tight.  The effect is most pronounced when there is strong aft rake in the mast and when the shrouds are well behind the mast at deck level.   My little Wharram catamaran was set-up like this :

SBW_1530

Very pronounced aft rake, shrouds well behind the mast and a really tight forestay which i achieved by hauling hard on the masthead forward with a serious multi-part tackle : i made a 6:1 tackle acting on a 2:1 whip….and then lacing the forestay down hard before releasing the tackle.  The whole boat creaked and squeaked while i took up the load and it only worked because i had a dolphin-striker/spreader and wire stays under the mast beam.

Where this is leading to is whether i should or could use this method on Inanda.  At the moment it’s difficult to get the forestays decently tight which means i have saggy jibs and a subsequent loss of upwind performance.  The option i have discussed already is running backstays which i still might use but i might also use the rake technique to increase standing tension in the forestays.    To every change there are of course side effects….in this case raking the masthead aft would lower Inanda’s boom even further at the cockpit end and to really make the technique work i would need to move a chainplate aft to get one shroud pair further aft.  The greater problem is the boom being already too low with the full mainsail hoisted…what i am already thinking about is generally sailing with the first reef tied in and the gooseneck band moved up the mast a few inches to regain the clearance under the boom.   The second consequence of course is increased weather helm which is a technique i had to use with my Frances when i increased her forward sail area from small skinny jibs to a healthy 130% genoa.

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This is an extreme example of the idea on a Daniel Bombigher design, for me that’s too much rake but the principle is the same.

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Borrowed photograph. (pride of baltimore)

Pride of Baltimore-018

Ultimate solution.   While Inanda’s mast and rig is basically healthy i won’t mess around too much but if i had to completely re-mast and re-rig i would do so with a high-aspect Dutch style gaff rig with a much taller mast, much shorter gaff and boom and bring the whole rig inboard a bit but with longer luffs all round :

wingsail_fig_1_2

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