Aftmast rigs???

[markstrimaran]

20 minute trailer sailer

It's has been 17 months, since I did any sailing, had surgery last year, so I never stepped the mast. I am surprised the aft mast is not equipped on a few trailer sailors, as I can launch, after 20 minutes of rigging. It took me 30 minutes to derig, in the dark. Single handed. It would be easy to do it in 10 minutes, with two.

The wind was 20 mph, the helm is super easy to balance out with the swing keel, moved forward, from last season.
Tacking through the irons, is smooth and steady.

 

[brian eiland]

Prout Rig Praise
Affect of mast location on a Catamaran - Cruisers & Sailing Forums http://www.cruisersforum.com/forums/f48/affect-of-mast-location-on-a-catamaran-21229.html#post226491

There is another rather long subject thread on that forum that talks about an owners efforts to newly build an unfinished Prout catamaran

hi all
As some may know I have acquired a Prout Snowgoose Elite 37 hull and deck,standing for 20 years next to the factory, in more or less pristine condition,apart from 20 years of dirt on the gelcoat.
Modernizing a Prout Elite 37ft

http://www.cruisersforum.com/forums/f48/modernizing-a-prout-elite-37ft-103739.html
http://www.cruisersforum.com/forums/f48/modernizing-a-prout-elite-37ft-103739.html

He has made some interesting changes to the vessel, and some conservative changes to the rig he is installing. Lets hope he gives us an update when he gets it out sailing.

Brian had asked, "Just to brief me, Atoll, what decision did you make in terms of re-rigging your vessel.?"

I am sticking with the conventional prout 40ft aft stepped mast,but with a few slight differences,that perhaps you might comment on

firstly the mast will be rigged fractionally,using a bobstay/pole 2-3ft out from the crossbeam then with a code zero to the mast head,this will be removable in stronger winds.

the roller furling genoa will be rigged from the cross beam to the mast aproximatly 3 ft below the masthead ,giving the same size genoa as the earlier prout elites with the shorter 37ft masts.

the inner forestay stays basically the same,but terminates slightly further forward in front of the cabin windows on the bridge deck.

(this is to alleviate the leaking window problem in many prouts of this design where the stay terminates at the top of the coach roof between the two forward windows,and causes the windows to leak as the structure flexes.

the mast itself will have single spreaders ,rigging terminating to the designed chain plates on the coach roof.

for stiffness the inner forestay and forestay shrouds will terminate to chainplates on the outboard of the hull(this is instead of the standard design where the chainplates are on the side of the aft cabin top.

the backstays remain the same to the mast head,as does the mainsail to the mast head.

this rig should allow me to carry a very large light weight sail,and a slightly smaller genoa for stronger winds that are both easily managable,it will also lower the center of effort in stronger winds reducing the risk of capsize.

sorry i haven't worked up any drawn plans yet to show but here is a photo of the larger rig,fyi

 

[brian eiland]

Attaching shrouds and stays to the mast column.

I've spoken of this before,...here in a page of discussions
Aftmast rigs??? https://www.boatdesign.net/threads/aftmast-rigs.623/page-66

And here in my rigging force analysis... Aftmast rigs??? https://www.boatdesign.net/threads/aftmast-rigs.623/page-23#post414479

AND it will NOT consist of two individual jumper stays (wire cables), but rather will be fashioned of a continuous loop of ‘cable’ that would wrap around the back-side of the mast at its lower ‘termination’, and might even do so at its upper ‘termination’.

The actual jumper stay ‘cable’ itself will be constructed from one of the new-age synthetic rigging materials such as Dyneema, Spectra, PBO, LCP, Aramid, C-6 carbon tow, etc. Ideally this stay material will have NO pre-stretch requirements thus no pre-loading. It should be very strong upon immediate application of force, and in a minimal diameter that it can be looped around the mast section in a continuous manner, at least on one end, maybe both. As a continuous loop, ‘both sides’ will always be carrying ½ the total load, rather than one side under load, while the other might be slack. There will also be a minimum of ‘fittings’ required to attach them to the mast (less weight, less failure pts). I imagine a simple ‘block’ of material attached to the mast around which the loop of this jumper stay can not slide any further along the mast….and one end needs to be adjustable

Just this past weekend I had the occasion to view a beautiful schooner that had been designed by Alden for General George Patton. It was dockside here in Lunenburg NS, and was now named 'When & If'.

Another thing I found interesting on this vessel was the method utilized to attach the shrouds and intermediates to the mast column. Instead of poking holes in the mast tube, they warped the rigging around the mast column and kept that rigging from sliding down the tube by attaching 'cheek blocks' to the mast.

It harkens back to older days when a lot of square-riggers had their multiple rope/wire shrouds wrapped around their mast columns at their upper locations.

I've made the same suggestion for attaching rigging to modern mast, particularly carbon tubes where I hate to see holes poked in and those odd-ball kinked swaged fittings used.

For a few photos of the whole vessel go to their website, and here on the forum I posted a few....
General Patton's Sailboat https://www.boatdesign.net/threads/general-pattons-sailboat.59021/

 

[sharpii2]

This is the ancient loop-and-hound system, which dates back to the time of the pharaohs. I've used it myself on the sailing raft I built when I was 17. I used nails driven into the mast at approx 45 deg. angles as my hounds. It worked fine except the clothes line I used was not up to the loads. I replaced them with poly line and those troubles were over.

This system can work quite well, but there is one major issue to keep in mind.

This is that the downward component of the load is going to be much greater than the sideways one. For this reason, your loop is going to try to wedge itself under the hound. Simply gluing it to the mast might not do, because the top of the glue joint might suffer a tremendous tension load, as well as shear load. The more acute the stay angle is, the more true this statement is.

This is even more true if very thin but strong line is used.

In this case, thicker line might be better, as it will distribute the load on the top of the hound. Thinner, lower stretch line could then be connected to the loop, for most of the length of the stay.

I would go with an angle of 14 deg. or more. Even then, with a sideways load of 100 lbs on the mast, at the top of the hound, the tension on the line stay would be about 412 lbs, with 312 lbs of that being directly downward, parallel with the mast.

The more acute the angle, the more carefully the hound has to be designed.

 

[brian eiland]

I just had to go look up the term 'hounds'. I can see where they surely were called this in the old days, but these days I refer to those blocks of material as the cheeks, or cheek blocks.

1) http://www.ybw.com/forums/showthread.php?397970-Why-are-the-Hounds-on-a-mast-called-the-HOUNDS
2) https://www.boatdesign.net/threads/hounds.4583/
At both of these sites I see a reference to 'hound cheeks'

Perhaps a cheek block something like this...

Newer soft rigging attachments
Mast Connections http://www.colligomarine.com/mastconnections-gallery/

 

[brian eiland]

I just really like the idea of wrapping the rigging AROUND the mast tube rather than drilling into the tube and using those swaged fittings etc.
Plus perhaps on some of our vessels we could keep the mast 'tube' watertight,...floatation?

 

[brian eiland]

Mast (leaning) Aft

I've got a big SURPRISE coming soon,...a new rig idea with the mast tilted back almost as much as mine is titled forward. Got the idea while viewing the 'tall ships' that were visiting Lunenburg NS about a week ago.

 

[brian eiland]

Been quite some time since I visited this old subject thread,...so long that I had trouble finding it.

I just happen to be reading an interesting article that appears to reinforce the use of headsails,...AGAIN in this modern world,....just when many of the naysayers on this subject thread claim that fractional rigs with small headsails were the only way to go.

Not a Genoa. Not a Spinnaker. It’s a Tweener!
https://offshoreracingrule.org/63-2019-news/161-not-a-genoa-not-a-spinnaker-it-s-a-tweener

“A tweener can turn a white-knuckle reach into a fun sail,” says Al Declerq of Doyle Sails Detroit. “And it can sail surprisingly fast at deeper angles than expected. In 10 years, every boat will have one.”

During the 2019 CYC Race to Mackinac, Arctos sets a tweener headsail (gray) in light conditions, to leeward of a 75-percent girth spinnaker. Photo by Photoboat.com.

......."Just in case you thought this was a brand new idea, note that multihull sailors have long carried a similar roller-furled sail called a “spreacher”—short for spinnaker reacher. Whatever you call it, it looks as if the sail is now aboard monohulls to stay, and you can put one to work for you as long as you’re racing with an ORR or ORR-Ez rating."

 

[pbmaise]

Philip here with update on his big trimaran. Well I sold her. She is now hauling up to 60 tourists per trip in Langkawi.

This thread predated my purchase in 2009 and continues forward after her sale a few months ago.

The key mistakes I made with my experiments were:

1. Attempting to gain too much sail area by using a very tall aft-mast.

2. Allowing Tasker to talk me into sail cloth far too heavy.

3. Not using a roller furler.

My later conversion to a modest gaff rig taught me that there really was no reason for a cruising sailor like myself to be flying so much canvas. Further, I DIY'ed my own roller furler for the headsail and learned that since I didn't want to fly any canvas in a squall or very high winds that a hank on foresail really isn't anything to be ashamed of.

 

[pbmaise]

I want to relate a very pleasant experience I had with what I call a screecher.

I inherited the sail when I purchased the vessel and never had a big tall center mast to fly it. Being the experimental sort, I hauled it up the mast sideways.

I apologize I have the gaff rigged main in the same shot. Notice the screecher "head" is out of view to the left in the photo. I had to secure it on the rear cleat on leeward ama. Before everyone starts yelling at me, let me first admit that yes this sail obviously was not designed to fly this way. This said, I was able to sail my vessel up to 8.5 knots on this sail alone. Wind was beam on and about a constant 15 knots. Yes, that is right, the mainsail was down and this sail, that I could pickup out of my storage locker single handed, powered a 65ft trimaran at 8.5 knots.

This was working so well I was thinking of making a larger one with a bigger foot so I didn't miss so much wind escaping below it.

The point I am slowly coming to is all about the cut of the sail used in an aft mast rig. I had Tasker make my foresail very much like a jib with a tall luft back end. What proved workable in my little experiment was a sail that came to a point down on deck level. Again what I so anxiously wanted was even more sail area up front.

And that brings me to the whole point of my post. Gollywobbler. There I said it. I just so much like using this odd word.

Follow the lines of my main sail and see the gaff pole. Now imagine that gaff pole is replaced by a wire leading up to a mast behind the boom. Also while we are at it. Ditch the boom. I've never liked booms!

I believe I am correct when I say, that after the addition of the second taller mast, my mainsail seen above would be a gollywobbler. The enter rig would be called a schooner.

But let's not stop modifications just yet. If I shrank the foremast and moved it forward, I could gain the sail area I enjoyed getting by using a separate foresail. If I was to approximate on my vessel, the foremast would be about 20 ft tall and located 10 ft behind the front chainplate. The aft-mast would only need to be about 45-50ft.

The whole point of these modifications is to maximizes the size of the gollywobbler. I believe this sail alone would be adequate for cruising. More speed could also be obtained by adding an inner stay sail connected to a boom, a very small foresail, and a stern sail.

 

[tgtony52]

Also while we are at it. Ditch the boom. I've never liked booms!

My thoughts precisely. Glad to see something on his thread again after quite some time.

Since my last post I’ve replaced my Honda outboard, located in the cockpit, with a Torqeedo electric drive and designed out my mainsail boom. I’m not sure what you call it, but the length of boom that I cut off the original 5m long boom when I moved the mast 2m aft is now pivoting off the aft deck, a bit like a flag pole, to which the clew of the main attaches. I haven’t had a chance to try either the boomless main nor the electric motor as all my time is taken up in restoring a 25’ 1950s timber cruiser.

 

[CT249]

I want to relate a very pleasant experience I had with what I call a screecher.

I inherited the sail when I purchased the vessel and never had a big tall center mast to fly it. Being the experimental sort, I hauled it up the mast sideways. View attachment 149432

I apologize I have the gaff rigged main in the same shot. Notice the screecher "head" is out of view to the left in the photo. I had to secure it on the rear cleat on leeward ama. Before everyone starts yelling at me, let me first admit that yes this sail obviously was not designed to fly this way. This said, I was able to sail my vessel up to 8.5 knots on this sail alone. Wind was beam on and about a constant 15 knots. Yes, that is right, the mainsail was down and this sail, that I could pickup out of my storage locker single handed, powered a 65ft trimaran at 8.5 knots.

This was working so well I was thinking of making a larger one with a bigger foot so I didn't miss so much wind escaping below it.

The point I am slowly coming to is all about the cut of the sail used in an aft mast rig. I had Tasker make my foresail very much like a jib with a tall luft back end. What proved workable in my little experiment was a sail that came to a point down on deck level. Again what I so anxiously wanted was even more sail area up front.

And that brings me to the whole point of my post. Gollywobbler. There I said it. I just so much like using this odd word.

Follow the lines of my main sail and see the gaff pole. Now imagine that gaff pole is replaced by a wire leading up to a mast behind the boom. Also while we are at it. Ditch the boom. I've never liked booms!

I believe I am correct when I say, that after the addition of the second taller mast, my mainsail seen above would be a gollywobbler. The enter rig would be called a schooner.

But let's not stop modifications just yet. If I shrank the foremast and moved it forward, I could gain the sail area I enjoyed getting by using a separate foresail. If I was to approximate on my vessel, the foremast would be about 20 ft tall and located 10 ft behind the front chainplate. The aft-mast would only need to be about 45-50ft.

The whole point of these modifications is to maximizes the size of the gollywobbler. I believe this sail alone would be adequate for cruising. More speed could also be obtained by adding an inner stay sail connected to a boom, a very small foresail, and a stern sail.

But hang on - 8.5 knots is slow for a 65 foot tri in 15 knots of breeze, therefore the fact that it was achieved with a small sail proves nothing.

It's a bit like the fact that my 36 footer can be driven by the 3.3hp dinghy outboard; it doesn't show that the dinghy outboard is efficient, adequate or safe, it just proves that it can move the boat slowly in good conditions.

 

[CT249]

Been quite some time since I visited this old subject thread,...so long that I had trouble finding it.

I just happen to be reading an interesting article that appears to reinforce the use of headsails,...AGAIN in this modern world,....just when many of the naysayers on this subject thread claim that fractional rigs with small headsails were the only way to go.

Not a Genoa. Not a Spinnaker. It’s a Tweener!
https://offshoreracingrule.org/63-2019-news/161-not-a-genoa-not-a-spinnaker-it-s-a-tweener

“A tweener can turn a white-knuckle reach into a fun sail,” says Al Declerq of Doyle Sails Detroit. “And it can sail surprisingly fast at deeper angles than expected. In 10 years, every boat will have one.”

During the 2019 CYC Race to Mackinac, Arctos sets a tweener headsail (gray) in light conditions, to leeward of a 75-percent girth spinnaker. Photo by Photoboat.com.

......."Just in case you thought this was a brand new idea, note that multihull sailors have long carried a similar roller-furled sail called a “spreacher”—short for spinnaker reacher. Whatever you call it, it looks as if the sail is now aboard monohulls to stay, and you can put one to work for you as long as you’re racing with an ORR or ORR-Ez rating."

Huh? That's a very strange claim. The Tweener you are advocating is SMALLER than a spinnaker, therefore it does NOT show that bigger headsails are the way to go. If bigger headsails were better then the assymetric, with its larger mid girth, would beat the Tweener.

The Tweener is bigger than a genoa, smaller than a spinnaker, so it proves absolutely nothing about headsail size per se. What it proves is that bigger sails are faster in light winds and that specialist sails are faster in specialist conditions. Those are not exactly new ideas!

 

[brian eiland]

Recently had a gentlemen add some questions about the rigging forces I had calculated for my aftmast rig way back in an earlier posting. I began to answer him on that other subject thread, but upon further thought I should add that discussion here as well.

Catsketcher's posting
I don't follow your rig analysis. It doesn't look the same as what I am used to in books like Skene's. It doesn't seem to deal with torque.

I've forgotten exactly how the various books presented it, but I went back to good old vector analysis. ie...

Use of Scaled Vector Diagrams to Determine a Resultant
Vector Addition https://www.physicsclassroom.com/class/vectors/u3l1b

Net Force Problems Revisited https://www.physicsclassroom.com/class/vectors/u3l3d

My worry about the force on the rig comes from the substantially differing angles of the forestay and backstay. Both stays have to exert the same force fore and aft, or the masthead would move. The forestay has an angle of 33 degrees to the masthead. So the forestay exerts 53% of its force into a horizontal vector or X component.
The backstays have an angle of (if I get the angles right ) about 8 degrees to the top of the mast (The torque has to be exerted at the top of the mast otherwise it will move so even thought the stays attach to the mast lower down the effective staying base is about 8 degrees). At 8 degrees the backstays have an effective X component of 0.14. So you need to increase the load by 7 times to get a set X vector
........deleted remainder
Catskecther

Brian replied: Okay I think we are starting off from a different perspective already. You seem to be viewing the image from a different perspective than myself. Who says true vertical can only be viewed with respect to perpendicular to water level? I am choosing to view my 'vertical component' as directly in line with mast tube itself,....and then my 'horizontal component' as perpendicular to that chosen vertical, tilt the whole picture over a little bit.

Now look at my masthead a little closer,..

My forestay and my backstay are both very close to one another in their angles of force. They might be made to be 33 degrees each, or as I have chosen here the forestay is 33 degrees and the backstay is 25 degrees.
If I choose an arbitrary force amount for my forestay (length of the vector) I need to match that force equally in the opposite direction,...shown in that diagram. As you said the masthead must not move fore or aft, so we need directly opposing forces of an equal amount.

Now you see the force components that each of those vectors transmit in the perpendicular direction (the perpendicular direction in this analysis is that direction in-line with the mast,...mast compression force). Yes we have added a little extra compression force to the mast tube itself, but not that much extra. The base our mast sets on (part of the boat's structure) will also have to account for a horizontal force component in addition to just pure downward loading.

As I originally posted,..
MASTHEAD
Lets start at the very top masthead. There is the primary forestay, a backstay, and two shrouds…all rather traditional. I’ve chosen to represent the force in the forestay with a 5cm long vector. Lets say this vector represents 1000 force units, thus each 1cm on the force diagram will represent 200 force units.

At the masthead the forestay force is broken down into two perpendicular forces, the compression load down the mast and the forward pulling force. The fwd force needs to be directly and equally offset by the aft pull of the backstay. The backstay is at a more shallow angle so it must pull a bit harder to exert its rearward force. If we draw the length of the forestay force, then we can measure the lengths of the other vector components and arrive at their values

Forestay Force............................................1000 kg
Backstay Force...........................................1260 kg
Forestay compression Load in Mast.................820 kg
Backstay Compression Load in Mast..............1150 kg
Total Compression Load in Mast....................1970 kg
(at very upper portion & disregarding shroud loads)

.....nothing very unusual....very conventional. The mast is experiencing compression loads from both the forestay and the backstay force components acting in the vertical direction. And it’s doubtful that those compression loads imparted to the mast by the backstay and forestay are much greater than in the case of a purely vertical standing sloop rig mast.

My masthead backstay then passes over an aft jumper strut that redirects its force down to the base structure supporting the mast.

[IMPORTANT NOTE] This backstay that originates at the masthead DOES NOT reattach to the base of the mast itself, but rather to a structure of the vessel, …and preferably to the structure that accepts the compression loads of the base of the mast to the vessel.]
So we have that one masthead backstay that delivers a force of 1260 kg to the vessel.

Can we agree thus far?

(to be continued)

 

[sharpii2]

Recently had a gentlemen add some questions about the rigging forces I had calculated for my aftmast rig way back in an earlier posting. I began to answer him on that other subject thread, but upon further thought I should add that discussion here as well.


I've forgotten exactly how the various books presented it, but I went back to good old vector analysis. ie...

Use of Scaled Vector Diagrams to Determine a Resultant
Vector Addition https://www.physicsclassroom.com/class/vectors/u3l1b

Net Force Problems Revisited https://www.physicsclassroom.com/class/vectors/u3l3d

Brian replied: Okay I think we are starting off from the wrong perspective already. You seem to be viewing the image from a different perspective than myself. Who says true vertical can only be viewed with respect to perpendicular to water level? I am choosing to view my 'vertical component' as direct in-line component with mast tube itself,....and then my 'horizontal component' as perpendicular to that vertical. Now look at my masthead a little closer,..

My forestay and my backstay are both very close to one another in their angles of force. They might be made to be 33 degrees each, or as I have chosen here the forestay is 33 degrees and the backstay is 25 degrees.
If I choose an arbitrary force amount for my forestay (length of the vector) I need to match that force equally in the opposite direction,...shown in that diagram. As you said the masthead must not move fore or aft, so we need directly opposing forces of an equal amount.

Now you see the force components that each of those vectors transmit in the perpendicular direction (the perpendicular direction in this analysis is that direction in-line with the mast,...mast compression force). Yes we have added a little extra compression force to the mast tube itself, but not that much extra. The base our mast sets on (part of the boat's structure) will also have to account for a horizontal force component in addition to just pure downward loading.




Can we agree thus far?

(to be continued)

No. We can not. In an earlier post, I agreed with you. I regret that now.

From looking at your incomplete diagram, I see as single or perhaps a pair of back stays, which attach to the mast at the base of an aft facing spreader. I also see that the mast tilts forward to such a degree that there is only a 10 deg. angle between it and the back stay. The twin forestays, one of which attaches far above the back stay, are at much more generous angles.

Before I go any further, we must remind ourselves that the purpose of the mast is to keep the fore stays tight. This is to insure that the jib and stay sail set properly.

To accomplish this, we need a lot of tension on these fore stays. This tension must be there even before the sails put any load on them.

As tempting as it is to draw an imaginary line dead vertical down from where the back stay meets the mast, such does not accurately indicate the true situation. To get a better grip on the true situation, it is better to measure the distance between where these stays attach to the boat and and where the base of the mast is.

The stays which attach closest to the base of the mast are under more tension than those which attach further from it. Dividing the smaller distance into the larger one will give a rough estimate of the of how much more tension the back stays have to endure than the forward ones.

I believe that if you tried this approach you would be shocked.

Granted, the mast is not vertical. So the downward thrust vectors due to the fore stays alone will be somewhat less. But the load savings would be pennies on the dollar compared to the downward and aft vectors imposed on the mast step. The back stays have to bear both of them.