Pete Hill on mast rake

A discussion about mast rake has been running on Frederik’s HFJR34 thread  -  mainly my fault. To stop contaminating that thread even more, today I jump to this thread from last year.

To get some answers, I sent this e-mail to Pete Hill, a week ago:

"Dear Pete and Linda.
I have followed your blog from your long voyages in Kokachin, and am duly impressed!  As for me, my adventures are limited to day-sails around Stavanger (17 outings this summer), and that suits me fine.

Now Ingeborg rests in her berth through winter, and I visit her for checking her lines, the humidity in her cabin (I use a bag of road salt as an air de-humidifier), brew a cup of coffee, and sometimes run the outboard engine.

(..photo of Ingeborg in her berth...)

I have a technical question.
The background for it is a friendly discussion about mast rake versus no mast rake, on the JRA forum (“HFJY34”). Since you (Pete) have crossed oceans, both with plumb masts and with forward-raking masts, I wonder if you could tell us what you have found about that, and whether it is an issue at all or not.

Real, deep-water experience beats armchair expertise...

Cheers,
Arne"

Yesterday (8.12) I received this e-mail from Pete, and later a permission to share it with you. Here you are:

"Hi Arne,

Thanks for your email and kind comments.

Kokachin, and Missee Lee are the only boat that I have had with forward raking masts.  The reason why the designer chose fwd raking masts on Kokachin was to get the C of E far enough forward. The foremast could not be moved any further forward because of the lack of bury and the mainmast because of the centreboard. So that dictated the forward rake. On Missee Lee it was also to get the C of E forward so as not to interfere with the double bunk, and the sail balance was at maximum.

The only advantage ( apart from moving the C of E) is that the sails will naturally stay put when running in very light winds, rather than wanting to swing onboard. In my experience this is more theory than practice as it only applies in flat water, a seemingly rare occurrence. And it does look Chinese!

The problems with fwd raking masts are that it is much more difficult to climb, as you swing out from the mast and need a restraining rope to keep this under control. Also, the mast head fittings of lights, wind indicators etc. are more difficult to mount. I can't really say that there were any disadvantages sailing with fwd raking masts, but building the step and deck partners was 'challenging'.

If you need to get the C of E forward I think more balance is the way to go.

I hope that this helps your discussion.

By the way, Linda and I are now in Tasmania having succumbed to the temptation of buying back China Moon. Working away on her to get her in trim for more voyaging.

Best wishes,

Pete"

I hope you find Pete’s words interesting.

Cheers,
Arne

Len: "I did not include any attributes as to who wrote it..."

I'm pretty sure the author of that was David T as he gave almost the identical reply to me, to the same question, some years ago.

I think a more generalised answer, is to keep the halyard angle within reasonable bounds. Wiser heads than mine can advise what the maximum angle ought to be, but the smaller the better.

This is in relation specifically to the question under discussion (ease or otherwise of raising the last couple of panels).

Lots of other things need to be considered too, of course.

Paul wrote: What does make a sail get steadily harder to pull up, is not having enough drift between the masthead and the halyard block on the yard.

That can be the case, but does not get to an understanding of the reason for the difficulty.

The drift, per se, is not the reason, though it can sometimes provide a solution.

A short rope (or a tackle with a short drift)  needs no more force to raise an object than a long rope (or a tackle with a lengthy drift). It's all to do with the direction of that lifting force.

The reason for the last couple of panels of a junk sail being harder to hoist (apart from the obvious fact that more and more of the bundle is being hoisted) is because as the sail approaches its fully hoisted position, the direction of the force on the halyard becomes increasingly less effective.

The force can be resolved into two components, one component in the direction we want, and the other component wasted effort.

Arne nailed it by coining the term "halyard angle".

If the halyard angle becomes too great, then the component of force which is wasted (indeed probably adding to friction also) becomes too great - and the effective component which is doing the job of hoisting the sail becomes correspondingly less.

This comes more noticeably into play as the sail is near the top of its hoist, as the angle of the halyard is getting near its greatest. This very exaggerated diagram attempts to show this.

The problem is not caused by the amount of halyard drift per se.

However, Paul is correct in a way, because if we are using a conventional halyard system and if the attachment point on the yard is near the middle, as is normal, then the problem could be solved by increasing the halyard drift (meaning a taller mast) - because this has the effect of reducing the halyard angle. (At least, that can be done at the design stage - it can be a little difficult later to increase halyard drift!) 

 "PJR clearly spells out what is the minimum drift (and it is the minimum drift) that is required". I don't think this is explained in PJR. and I would be grateful if Paul would give the chapter and page number because I can't find that in my copy. On p32 of my copy, halyard drift is briefly referred to in relation to masthead wringing, and on page 37, 38 there is a reference to the direction of the halyard pull in relation to friction, and the counter effect of a horizontal tack parrel. PJR does stress the need for "sufficient" halyard drift, but does not go as far as providing a force diagram showing resolution of the halyard force into its two components, and misses this particular point. 

I can't find anywhere in PJR (Hasler/McLeod) which actually recommends how to arrive at a figure for "sufficient" or "minimum" halyard drift (I stand to be corrected) and this is why I think Arne's notion of "halyard angle" is a useful way of understanding the true cause of the problem, and what to aim for in the design of a sail. If the halyard angle is to be kept within reasonable bounds, then it is a simple matter of geometry to find the right amount of halyard drift required. I think Arne has suggested that he aims for somewhere around  a maximum of 12 degrees of halyard angle (or was it 15 degrees? Arne?). There is a bit more to it, too, of course - there always is! (See below)

While on the subject, I should add that the above example was deliberately exaggerated to demonstrate the point - and it is also a deliberate example of bad design. The relationship between the mast balance on the yard, and the yard angle chosen, is all wrong and that is what has given rise to the problem of halyard angle being too great, in this particular case. It might be overcome by greater forces being applied to hauling parrels to get the yard to sit right - or by increasing halyard drift which in this inharmonious case would mean a pretty tall mast. This relationship between yard angle and mast balance also is not covered in PJR, but fortunately an excellent description including a very good diagram illustrating how to achieve harmony between these two parameters, was posted here some time ago by Paul Thompson - a very valuable contribution I believe. I can't go back and find it now, but perhaps Paul will post that diagram again some time, because it explains it all very well. (Paul has also mentioned this need for harmony between mast balance and yard angle, in the previous post in this thread. And "keeping the halyard block close to the mast" is another way of stating that the halyard angle should be small).

PJR (Practical Junk Rig by Hasler and McLeod) is required reading - but more has been added to the knowledge base since it was published, both empirical knowledge and theory, and thanks to the excellent contributions by people like Paul and Arne, we can have a better understanding of how things work.

The above is based on first-hand experience with a sail which initially had too great a halyard angle - and the solution which was (fortunately in my case) the ability to increase halyard drift to get it right. That - and a little bit of understanding of elementary geometry.

(All other things being equal, a low yard-angle sail needs a taller mast than a high yard-angle sail, in order to get a sufficiently small halyard angle. Or needs a greater amount of mast balance. Or both. Again, simple geometry, and in effect, has already been covered by Paul, sometimes in other words.

I never dared to say so before, but I will say it now - I always thought Annie's mast was a little too low for that original sail. I can say for sure that with the Amiina sail at least, which has quite a low yard angle, the mast head needs to be at least as high as the highest point of the yard when the sail is fully hoisted. (Experimentation led to that "rule of thumb" for low yard-angle sails). I note that the new sail, which Paul has designed, has a higher yard angle and I presume it is fitted to the original mast. It is easy to spot straight away that the result is: the new sail has a much lower halyard angle than before. And I'll bet that the result will be a little less force needed to haul the sail into shape - and that the last couple of panels will be a bit easier to hoist than before. OK, I have stuck my neck out now.)

Not much difference in halyard drift here, but better harmony between yard angle and mast balance, in this case, has resulted in a huge reduction in halyard angle.

Geometry. And we are talking here about the geometry of sails which have soft batten parrels and a yard approximately the same length as the battens. There are other planforms (eg possibly the short-yard fanned Reddish type, definitely the unusual sail which was featured as Boat of the Month in September 2023 - which might require a different geometric analysis. Weaverbird with it's "hard parrels" may be another example which is possibly outside the scope of the above analysis of halyard arrangements vis a vis mast balance, yard angle, halyard angle and halyard drift. There's always more to dig into).

All I can say is that I haven't subjectively noticed that my sails on forward raking masts are more difficult to raise than those on vertical masts.  

I think you are right about that Annie, and I was wrong in suggesting that forward rake increases the halyard angle. I realised after writing that lengthy tome - at least, I think now, anyway, - that the halyard angle should indeed be in relation to the mast, not to the vertical, and therefore raking the mast does not affect it. Hence the "apology to Arne" I put at the end - but I forgot to correct that other bit.

In summary I think your impression is correct and that (within reason, anyway) the difficulty of raising sail shouldn't be affected by mast rake.

It is affected by halyard angle though - and with a low yard-angle sail you need a little bit more mast length than some people think at first glance, in order to get that halyard pulling in close to the right direction, when that last bit of sail is being hoisted. My experience is vastly less than yours, no doubt about that - but that is one mistake I have experienced at first hand, and was able to correct. I am not sure if you have found the same thing.

(I like the high balance of the Amiina sail, but it's a downside of that type of sail, compared with the high yard-angle Johanna or HM types, that more mast length per sq ft of sail is needed, if the conventional halyard system is employed. Of interest too is the low AR fanned sail type that Paul is developing now - that too gets away with a shorter mast than the Amiina sail would need).

You new sail looks lovely by the way, it's great to see. No doubt about Paul's workmanship. (Now, how about a write-up for BOTM?)

Arne wrote: One may wonder how the Hong Kong seamen handled their mainsails. I guess there was some brute force involved...

I would have thought the issue here is not just friction. The sheer weight of those sails would make it hard labour to raise sail.

I read somewhere, in regard to Dr. Moran’s Cocachin: “The 'bundle' of combined sail, yards, and bamboo battens weighed over one ton. Four men on a capstan would need 20 minutes to raise and trim sail…”  

And Cocachin’s main is only a toy in comparison with the main of a large working vessel, whose mainsails would be of the order of 200 sq m (2,000 sq ft).

Of Keying it was written: "Her sails consist of stout matting, ribbed at intervals of three feet by strong bamboos, and are hoisted to the mast by a single rope of immense size, formed of plaited rattan. The mainsail is of gigantic dimensions, weighing nearly 9 tons, and engaging the entire crew two hours to hoist it..."

I used to have a flax canvas tarpaulin and it was impossible to lift, without a fork lift, so I can imagine that.

Returning to today's world of modern, light-weight materials

Arne: "I think I will keep an eye on this new-found CG offset angle on future designs ..."

My gut feeling is that by considering "cg offset angle" Arne is "overthinking".

"Halyard angle" is also a term coined by Arne, and that seems to me to be the more important and useful concept.

If the friction force of the parrels on the mast is proportional to the weight of the bundle (let us assume that it is) then raking the mast forward will certainly increase the friction. For example a 10 degree forward rake will increase the so-called cg offset angle by 10 degrees (because gravity acts vertically). Say, from 20 degrees to 30 degrees. The force of the parrels on the mast thus goes from Wsin20 to Wsin30 (that is to say, it increases from W x 0.34 to W x 0.5) which is quite a lot, almost a 50% increase

Thus, in that scenario, in theory, the resulting friction is also going to increase by almost 50%.

But, an increase of 50% of what? In regard to the effort of hoisting, lifting the actual weight of the bundle, probably not a lot - until the last couple of metres, and that's when "halyard angle" comes into play.

(Incidentally, the force required to drag a weight up a 80 degree frictionless slope is about 1.5% less than the force required to do a vertical lift, so that is a slightly mitigating fact).

Halyard angle is what I would be more concerned about. Arne has already explained a lot of this. When raising the sail, it is during the raising of the last panel or two that halyard angle starts to play a part. The angle of the halyard in relation to the mast starts from about zero at the start, to its full amount as you get near the top of the hoist. If the halyard angle is too great, as one reaches the last panel or two, much of the effort of lifting the dead weight of the bundle is starting to become wasted by pulling the yard towards the mast. Thus, the amount of force required to continue raising the sail begins to increase rapidly. (And, yes, that is when friction of the yard parrel on the mast would be the greatest also).

On my first attempt at rigging a junk conversion, the halyard angle was too great. It was almost impossible to raise the last panel. Luckily I was able to reduce the halyard angle by increasing the mast height. Another way of reducing friction would have been to reduce forward rake in the mast (except in my case the mast was already vertical). (Slinging the sail further forward, as Arne can do with his rigs, is also not an option with the type of rig that I have).

The greatest halyard angle I have seen would have been Steven D's Serenity (see Sept 2023 Boat of the Month). which I thought would have been almost a hopeless case, impossible to hoist or to set properly.

However this rig seems to work perfectly. Steven got around the problem of offset by having a completely different sort of halyard arrangement. And, by the way, that mast looks to be raked aft - which would reduce the offset angle somewhat. Also the "D-formers" on this rig, made from plastic, are, evidently, very low-friction "solid short parrels". It's an innovative exception.

Friction when raising sail?  I would forget about "cg offset" - or, should I say, I think it is more useful to consider halyard angle, to design the over-all rig itself  to have a moderate halyard angle. This goes beyond simply the shape of the sail, but comprises also harmony between mast-balance, yard-angle, mast height etc. 

Friction when dropping sail? One of the joys of the junk rig is ease of dropping sail. On my boat the sail flops down and stows itself the instant the halyard is released, but that is possibly partly due to the nature of its running parrels.  With today's light-weight materials, would a lot of mast rake create enough friction to be an issue? With standing parrels, perhaps it might. If so, perhaps parrel beads would help? I can notice even the friction in the halyard tackle, although that alone is not enough to cause a problem.

An apology.  I used to think that halyard angle should be calculated by reference to the direction of gravity (vertical) but thinking about it afresh, I think Arne was correct in his original concept, to calculate halyard angle by reference to the direction in which the yard is being hauled (eg the mast centreline).

Both halyard angle and CG Offset are concepts arising from the inherent offset nature of the lug sail. I think they are related but not quite the same thing. This interesting post of Arne’s has forced a re-think.

Halyard angle must be kept within moderate bounds, or the problem of raising the last part of the sail is real. Difficulties arise from wasted effort (not hauling in the direction of the mast centreline) as well as friction.

Parrel friction exists, but how much of a problem is it? It will be more if the halyard angle is great – and even more still if the mast is raked forward (which increases Arne’s “CG offset angle”). But I am not sure if it is such a great problem just on its own.

I still think it is much more important to keep halyard angle within moderate bounds. I suspect that by doing so, CG offset angle will be found to be automatically within reasonable limits.

Or, is it the other way round?

I remain a little confused myself. I hope this is not what Arne means by "... kind of blown up..."   Certainly "overblown" I suppose (sorry).

Another thing - my mast has to be vertical - but I do love the look of a junk rig boat with a forward raked mast - it's become an acquired taste. (Sorry for that too, Arne)]