Aftmast rigs???

Discussion in 'Sailboats' started by jdardozzi, May 28, 2002.

  1. brian eiland
    Joined: Jun 2002
    Posts: 4,924
    Likes: 173, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Yes, on a catamaran you require very little 'lead' distance of the CE (sail center of effort) over the CLR (hulls lateral resistance center).

    But on the monohull the lead distance can be considerable depending upon the heeling angle,...the more heel, the more lead required to keep things in balance.

    I had practical experience with ketch rigs when I originally drew up this mast-aft idea, and that mizzen sail was my saving grace that could help balance out small discrepancies in helm balance.

    A few years ago I really contemplated getting an old Lightning vessel and changing its mast to an aft position like mine,....then take it out and sail it against a stock vessel to show a lot of naysayers that the double headsail rig of mine could point very well against the stock boats. ....real life.

    Problem is my age, and lack of a nice little shop is working against me.

    ....and I've gone over to the 'dark side' of powerboats looking at a liveaboard like this Pilgrim 40 nostalgic vessel....ha...ha
    http://www.trawlerforum.com/forums/s3/redesigning-pilgrim-40-trawler-canal-boat-11212.html
     
    Last edited: Nov 10, 2013
  2. pbmaise
    Joined: Jul 2010
    Posts: 115
    Likes: 5, Points: 18, Legacy Rep: 80
    Location: Cebu the Philippines

    pbmaise Senior Member

    Aft-mast rig survives super typhoon Yolanda - Drawings

    Aloha All,
    I weathered Yolanda (Haiyan) well. It was a near miss. The eye made landfall about 30 miles or so to the North of me. Trees in front and behind the boat were uprooted, however, my new dynamic-compounded rigging worked perfectly.

    I did nothing to prepare the rig for the winds. Everything was left hand tight.
    I have prepared a presentation explaining how I got here and how I came up with the new rigging.

    Sorry the presentation is a bit long.

    Note: I don't want to tempt mother nature to make another strike. So let it be known I don't expect the rig to stand after 145 knots.

    Philip Maise
     

    Attached Files:

    Last edited: Nov 18, 2013
  3. brian eiland
    Joined: Jun 2002
    Posts: 4,924
    Likes: 173, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    How about that latest typhoon?
     
  4. bluebox3000
    Joined: Sep 2013
    Posts: 33
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Freehold, NJ

    bluebox3000 Junior Member

    I have read through this whole tread and you guys have me almost converted.... These are actually amazing ideas. I did a little calculation on my draft (cant call it a design yet) for sail area. It looks like I will need to increase the mast height to maintain the same sail area. My drafts are for a cruising catamaran, 40 ft long 22 ft wide with tip of mast 50 ft above waterline.

    So with a different sail configuration with two jibs and no main sail, I'm wondering about performance change with 20% less sail area? Bpmaise point out that cruisers typically do not use full sails anyway.

    The second thought I have is on mast load. With no boom or sail attached to the mast creating transverse force along the length of the mast (force only hitting the mast where the shrouds, forestay and backstay connect to the mast) can the mast itself be made of smaller diameter extrusion and lighter construction?
     
  5. sharpii2
    Joined: May 2004
    Posts: 1,903
    Likes: 105, Points: 63, Legacy Rep: 611
    Location: Michigan, USA

    sharpii2 Senior Member

    Probably not.

    Here's why:

    With a boom and the sail attached to the mast, much of the stress the rig has to withstand is bending. The mast cannot be allowed to bend to the breaking point.

    That is a lot different than saying it cannot be allowed to bend at all.

    In fact, with free standing rigs, there is noticeable bend in the mast.

    With a jib only rig, the mast still has bending moments at the top of the mast, as the fore stay(s) tries to pull it sideways.

    But what you really have is an awful lot of compression loads, as the leading edge (luff) of the jib(s) try to sag off down wind.

    First, you enough tension to keep the thing from collapsing. Tension equals compression. Then you need even more to make the luff(s) stand tolerably straight.

    The big problem with compression loads is that the column subjected to them must stay straight. Once there's any bend in it at all, the compression loads become bending loads.

    Since it is nearly impossible to keep a tall mast perfectly straight, especially when standing on a rolling and pitching deck, the mast has to be made somewhat stronger than mere compression loads would seem to specify.

    Keeping the mast as straight as possible has to be a major goal, with a rig like this.

    This can be done with numerous spreaders and shrouds. The lighter and thinner you make the mast in section, the more of these you will need, to keep it tolerably straight.

    These not only add windage (that the smaller sectioned mast was probably intended to reduce), but add complexity and more fail points.

    Any one of these failing can bring the rig down with a quickness.

    For this reason, the mast, its spreaders, and it shrouds, are likely to be designed with high safety factors.

    It not only needs to be strong enough, but, to be safe, it has to be way stronger.

    Fortunately, this is easily achievable without ridiculous weight.
     
  6. pbmaise
    Joined: Jul 2010
    Posts: 115
    Likes: 5, Points: 18, Legacy Rep: 80
    Location: Cebu the Philippines

    pbmaise Senior Member

    Dynamic hand-tight compounded rigging

    Hold on here. What does sail load have to do with designing mast sections?

    I don't think sailing has anything to do with design case.

    Are you still flying sails after winds hit 75 mph? Probably not. However, don't you expect your rig under bare pole to survive a local storm? How are you going to get home thousands of miles with no mast? Remember if you are rescued far out at sea, they can't tow your boat back. So, they sink it.

    So what storm are you expecting.

    In my case I specifically did all calculations and rigging to stand up to 145 knots. That is a wind speed of 166 mph. It is based upon a real storm that hit my area. See typhoon Paka. http://en.wikipedia.org/wiki/Typhoon_Paka

    Yolanda (Haiyan) with winds that clocked in at an average strength of 195 mph exceeded my worst design case. The eye didn't directly hit me. So I can't say it stood up to that storms full strength.

    There are always two sides to a coin. When I did my calcs and came up with requirements to buy 7/8" and 1" galvanized forged and rated shackles to tie into 7 chainplates I felt like I knew something. However, when I got to the stores and finally found these big heavy shackles I felt foolish putting them on. Surely I thought everyone will laugh at me when they see the size of these shackles. Am I just wasting my money?

    One super typhoon near miss is enough to tell me that I did right.

    Therefore, absolutely no. Do not reduce mast section and strength just because you are flying less sail. Consider maximum winds.


    Notes:

    1. This new mast I put on in the Philippines and the new rigging I designed is using a far different approach than the one I attempted in Thailand. I listened when I was in Thailand to all those that said it was critical to have a tight forestay. What I didn't know then was this only applies if you are using driving sails. If you are using lifting sails it is actually important to have a loose halyard. The loose halyard enables the sail to adopt a curve that adds lift and speed. It was a break through for me to realize that a low tension lifting sail is better. Therefore, low tensioned rigging was possible.

    2. The second break through for me on this rig was how to position a line mid-air and tie it down to two different chain plates to obtain a better angle of support.

    3. The third break through was figuring out how to run just one line up and down the mast to 4 different chainplates. This enable me to have balanced dynamic rigging that responds to the wind. Really, it really does shift slightly based upon wind load.

    4. The strain insulator was the fourth break through. Seriously, look at that brand new thimble cutting into my brand new Dyneema line like it was a sharp knife.

    I have updated my presentations.

    Philip Maise

    This week I loaded 8,000 lbs of typhoon relief onto a neighboring boat.
     

    Attached Files:

  7. brian eiland
    Joined: Jun 2002
    Posts: 4,924
    Likes: 173, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    You got that correct in my opinion. I think what pbmaise has not done is differentiate the static loading verses the dynamic loading. We can do the straight forward static load calculations/diagrams. It's those dynamic ones that are more difficult to pin down, and that change so dramatically under sail in a seaway,...and can be significantly higher.

    The mainsail loading on a mast does help positively with distributing loading on the rig,...and it does help with reducing drag of a bare mast.

    There is a lot of good discussion here, but it gets quite involved.
    http://www.boatdesign.net/forums/sailboats/sail-loading-rig-rig-loading-vessel-2293.html
     
  8. pbmaise
    Joined: Jul 2010
    Posts: 115
    Likes: 5, Points: 18, Legacy Rep: 80
    Location: Cebu the Philippines

    pbmaise Senior Member

  9. bluebox3000
    Joined: Sep 2013
    Posts: 33
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Freehold, NJ

    bluebox3000 Junior Member

    I would argue that there is a lot less force being applied to the mast as only one of three connection points is tied to the mast itself vs a traditional mainsail where most of the force is applied to the mast.

    The mast itself is also a lot stronger than the wires holding it and as we know no chain is stronger than the weakest link. With the force pulling mainly at the top of the mast the pressure is applied down the mast and stays. Would we then not expect we need stronger stays than with a traditional mast/boom configuration where there is a more even distribution of the load to the base of the mast?

    And therefore a lighter mast would be warranted as there is less overall load being applied to the mast?
     
  10. sharpii2
    Joined: May 2004
    Posts: 1,903
    Likes: 105, Points: 63, Legacy Rep: 611
    Location: Michigan, USA

    sharpii2 Senior Member

    A good way to understand the difference between between the stay loads on a mainsail as opposed to those on a jib (what we're really talking about here) is to take an 8 ft long line, attach it to something, and hold the other end, so the line is straight an horizontal. Next, have someone hang a book on the middle of it. You should notice two things:

    1.) the line is no longer straight and
    2.) the tension on the line is quite high, as you try to keep it as straight as possible.

    In this case, the line is the fore stay or jib luff, and you are the mast.

    If the mast were in the mid length of the deck, both the back stay and the fore stay would have equal tension, as both would have the same angles, in relation to the mast.

    With a mast aft rig, the mast must be quite far back from the center length of the deck, to allow room for adequate sail area.

    Now you have a much sharper angle for the back stay than you have for the fore stay. Since the back stay must keep the mast head from moving forward, it must equal forward vector of the fore stay. It must do this with far less leverage. If the mast is stepped two thirds of the deck length aft, the back stay is going to have at least twice as much load on it as the fore stay. Much of this load, most of it, becomes compression. So stepping the mast two thirds aft produces close to 50% more mast compression than stepping it on the center length.

    The shrouds, since they, more or less, just keep the mast from tilting side to side, have the same amount of tension as they would with a more conventional rig.

    Now. Suppose we decide to make a Bermuda main only rig, with the mast stepped on the deck. The shrouds will take pretty much the same loads as before. The back stay will keep the mast from tilting foreword. This load would, more or less, be equal to the propulsive force of the sail. The fore stay would keep the mast from tilting aft, but only when the sail is luffing. The luff of the sail would be held straight by the mast itself, so there would be no tension needed on any of the stays or shrouds to do this. So the tension the fore stay would experience would have little or nothing to do with that of the back stay. For this reason, the angle of the fore stay can be quite sharp, as is seen on a cat boat.

    The main the compression loads on the mast, in this case, are caused by the shrouds, which must keep the mast from tilting side to side. This load would be in proportion to the righting moment of the hull. It will be considerably greater than this, as the angles of these shrouds will be quite sharp, as the mast is considerably taller than the boat is wide.

    With this main only rig, we can get away with not even running either the fore stay or the shrouds to the top of the mast. If the mast is made a bit stiffer, the fore stay and the shrouds can attach as little as half way up the mast. The mast can then be made much finer in section, as, with a triangular, Bermuda sail, only about 25 to maybe 40% of the actual Sail Area is above the stay attachment points, so the loads above them will be relatively modest.

    With the lower attachment points, the shrouds can have a much greater angle to the mast. This reduces the mast compression even more, even though the load on the attachment points will be greater, due to the Sail Area above them. This will probably still be less than if we ran the shrouds to the top of the mast.

    A reasonable way to imitate this situation is to get a length of conduit of maybe an inch or less in diameter and 8 ft long. Set one end on a ledge against a wall, secure it so it can't pull away from that ledge, and tie a line to the other end. The line can be just as long as the one you used before. hold the other end of the line, so the pipe is horizontal, then have someone put the same book on the pipe's center length. Now try to hold this as horizontal as possible. You will almost certainly find it will take a lot less tension to hold it as nearly horizontal as you did holding just the line itself with the book hung over its center length.

    With a jib only, mast aft rig, the shrouds must run to the top of the mast, They must do so to keep the top of the mast from bending sideways. If the mast bends sideways, it will no longer be in column and the massive compression forces, caused by the back stay will easily bend it to the breaking point.

    Spreaders are used to create bigger angles between the mast and the shrouds by dividing the mast into shorter masts stacked on top of one another. Each angle is measured from the end of the spreader to the attachment point on the mast. The shroud is either attached to the end of the spreader directly, with another part attached to the same end, leading to the chain plate, or it runs past the end of the spreader then to the chain plate. Either way, the effect is the same. The loads on all these smaller masts, stacked on one another, must be totaled up, but they area lot less, in total, than the compression load of a single shroud attached to the top of the mast and leading directly to the chain plate. You cannot have a single shroud and a single spreader without a lower shroud beneath that spreader, or the portion of the mast at the spreaders will be free to move sideways, causing the mast to go out of column.

    With a mast aft, jib only rig, spreaders can be set up for the back stay, with the same effect. The more spreaders you have, the smaller the mast section has to be. There has to be enough material in the section to resist the compression loads to prevent the mast from shortening too much or even being crushed under the load. You can have any number of back stays but only one, two, or three fore stays, one for each jib, with no spreaders. It is this fact that limits how fine the section of the mast can be. The center length of mast can bend backward if the fore and aft dimension of the section section is too short.
     
  11. pbmaise
    Joined: Jul 2010
    Posts: 115
    Likes: 5, Points: 18, Legacy Rep: 80
    Location: Cebu the Philippines

    pbmaise Senior Member

    Aloha Sharpil2

    I believe you are speaking mainly of monohulls when you say that the forestay and backstay lengths and angles are roughly the same for a mid-ship mast.

    I just want to point out that on big multihulls there is no similar backstay. Instead there are what I like to term aft leading side stays.

    These stays do not go all the way to the back of the boat since they would interfere with the boom and mainsail.

    On a cat, the rear aka (connection arm between the two ama) is usually well in front of the back edge of the ama. True, I have seen running backstays mounted on a cat's aka, however, see later note in this post.

    This is one area that trimarans have an advantage of a cat. The trimaran's wa'a (center) hull is the longest section of the boat and it is possible to add new chainplates way in the back.

    When rigged for a Bermuda rig, my aft-leading side stays were 17 feet behind a 79 foot mast. With the new aft-rig the two new chainplates are 16 feet behind a 62 foot mast.

    In other words I lost zero aft support by putting the mast way in the back.

    What I lost was heeling load support since instead of having plates separated by 40 feet, my new chainplates were separated by just 12 feet.

    It was the new rigging I created that helped solve that issue by integrating ama chainplates with wa'a chainplates.

    I must disagree with anyone who states that running rigging, and namely running backstays can be depended upon to help support the mast. The reason is running backstays are not always set before load is placed on the mast after tacking. Too often I see the running backstay as an afterthought. As in, oh yes we should set this thing too.

    I do agree with your position that a jib sail that must be kept under high tension will effect the amount of backstay support needed. That is one reason I switched to a lifting sail under low tension.

    Your statement that read
    For this reason, the angle of the fore stay can be quite sharp, as is seen on a cat boat.

    Sparked me to remember that there is a consequence to this. The short sharp angle of the catamaran usually is so sharp that the designers don't dare run the forestay to the top of the mast. Instead they terminate the forestay at the 7/8th fractional point. It is largely only on a big monohull that I still see a forestay still going to the top of the mast.

    Philip Maise
     
  12. upchurchmr
    Joined: Feb 2011
    Posts: 2,961
    Likes: 117, Points: 63, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    Arguing from verbal descriptions, assumptions, and similarities has become a waste of time.

    If you want to prove your point show some calculations and how you got them.

    There have been multiple statements which are just silly, partly because the statements are so imprecise as to not make sense or do not describe any actual facts.

    You can't prove anything without facts.

    "Catamaran.... designers don't dare run the forestay to the top of the mast" - if this is so, then what is the actual consequence? Mast compression?
    You might want to ask Iriquois catamaran owners why their designer "dared" to use a masthead rig. http://iroquois-owners.org.uk/wp-content/uploads/2011/04/Cheetah-304.jpg
     
  13. sharpii2
    Joined: May 2004
    Posts: 1,903
    Likes: 105, Points: 63, Legacy Rep: 611
    Location: Michigan, USA

    sharpii2 Senior Member

    The masthead rig, with the fore stay attached to the top of the mast, seems to have been a popular rig, during the earlier years of multihull development.

    a good likely reason for this is it kept the the Center of Area low, for a Bermudan rig, and designers, back then, were quite concerned about capsizes.

    Sail plans tended to be somewhat small, about as big as those on monos that were roughly the same length. Arguably, a multi would be about 2/3rds the displacement of a light displacement mono. In practice, the weight of the connecting structure and the wing deck took away some of the savings of not having ballast. Since most of the multis built back then were used for cruising, they tended to get loaded down with cruising gear, which subtracted even more of the former weight advantage.

    The masthead rig tends to work its best with Sail Area/ Displacement ratios in the mid teens. This way, the fore stay and back stay angles could be kept more reasonable and the mast doesn't have to be so tall.

    So, if the goal was to have a rig of small to moderate SA, the masthead rig works quite well. Especially on a multi, where you can replace the single back stay with a pair of back shrouds and make the boom a bit longer, as was sometimes done.

    A fractional rig was used for higher performance boats, because the jib was smaller and it required less tension to keep its luff tight, and, as a consequence, it usually sailed upwind better than its masthead rig cousin

    Also, the boat could be made lighter for the same amount of sail set.

    Even cruising multihull designers were a bit egotistical speed. And for many people, speed is the main reason for choosing a multi. Add to that the fact that the racing community seems to be a bit evangelical about their rigs and gear, and, IMHO, you get boats that end up being quite unsuitable for novice and casual sailors.

    As for Hot BuOYs, the rig seems a bit small for the size of the boat. It appears that the intention is to use her as a motor sailor. In that case, the smaller rig is somewhat justified.

    The back stay angles seem to be a bit sharp, as there are no aft spreaders. In order to keep the luff reasonably tight, it would see that there would need an inordinate amount of mast compression. But how tight is "adequate"?

    There are three possible criteria to judge that by. Starting from the most extreme, they are:

    1.) Tight enough for optimum windward performance,
    2.) Tight enough for adequate windward performance, and
    3.)Not tight at all, because windward performance is not even a consideration.

    In the case of Hot BuOYs, the third criteria may be the relevant one.

    The fact that the bare mast withstood a severe Typhoon has little relevance to the adequacy of the rig.

    With just the bare mast standing, the major wind stresses are the wind drag on the mast itself and the the rigging.

    As for the mast. If it is 62 ft tall and say 1 ft wide, it has a total frontal area of 82 sf. The center of this frontal area is roughly half the length of the mast above the deck, or 31 ft. So the total moment per one pound per sf of drag is 41 * 62 or 1922 ft/lbs. Now a wind of 16.1kts produces about 1 pound of pressure per sf.

    This increases by the square of the velocity. If the Typhoon had wind speeds of 195 kts, the pressure or drag would be (195/16.1)^2 or 147 lbs per sf.

    147 lbs/sf * 1922 lbs/sf or 282,534 ft/lbs. Sounds impressive. Let's double that to take into account the shrouds and stays.

    This gives us an incredible 565,068 ft/lbs.

    But this is at deck level. The shrouds and stays are attached at the top of the mast, or nearly there. Say they are attached 3 ft from the top.

    In that case, the new moment is 565,068/56 or 9,577 ft/lbs.

    This is divided by the two forward shrouds, which are taking the whole load.

    These shrouds are at a considerable angle from horizontal, so they are taking considerably more load than my last number indicates.

    Say their angle from the mast is 30 deg. The tangent of 30 deg. is around 0.577. We divide 9577 by 0.577 and we get 16,598. this should be close to the total tension on the forward shrouds. 9577 lbs of that is holding the rig up to the wind. the rest, 7,021 lbs, is compression.

    Because the boat most certainly had its bow to the winds, I think those loads, or something close to them, are realistic.

    Under sail, the loads on the back shrouds are likely to be much higher.

    First, because they are at sharper angles to the mast.
    Second, because they must hold the luff of the jib at least somewhat straight for anything but downwind sailing.

    Just how straight this has to be is a point of great interest to me.

    I know, for it to be competitive with other rigs, it has to be quite tight.

    But for adequate upwind performance? Just enough to make some headway against gale winds?

    What's the strongest wind you ever sailed Hot buOYS against, without the engine? And how well did she do?
     
  14. pbmaise
    Joined: Jul 2010
    Posts: 115
    Likes: 5, Points: 18, Legacy Rep: 80
    Location: Cebu the Philippines

    pbmaise Senior Member

    Aloha Sharpil
    Your figures are very much in line with what I calculated. For 145 knots I found tension on forward leading stays (shrouds) would be 13,500 lbs.

    I was concerned that this load would not be evenly split between the two chainplates on the ama. My Dyneema line on each stay is rated at 16,528 lbs. In my book that is cutting it close, so I attached the halyard to the chainplate in the bow to act like a conventional forestay. It pulls at a better angle so adds a lot of strength.

    I don't usually have the forestay installed here at the dock since it is horizontal enough to attract birds. And birds ....

    I want to first answer your question with a clarification.

    You wrote:
    The back stay angles seem to be a bit sharp, as there are no aft spreaders. In order to keep the luff reasonably tight, it would see that there would need an inordinate amount of mast compression. But how tight is "adequate"?

    There are three possible criteria to judge that by. Starting from the most extreme, they are:

    1.) Tight enough for optimum windward performance,
    2.) Tight enough for adequate windward performance, and
    3.) Not tight at all, because windward performance is not even a consideration.


    All of the statements above apply to a driving sail where being tight is a requirement for windward performance. Again, there is no forestay for my rig. I attach the tack of the sail where the forestay used to be, and lift the sail with the halyard. My sail doesn't hang onto a forestay wire. Within the sail I have a 14mm Dyneema line that serves like a forestay when the sail is raised. My sail has zero camber and a spar in the foot.


    During my sea trials, I experimented with tension on the halyard. I found at one point we were not making adequate windward progress, so I tightened the halyard. This hurt performance. So I let the halyard out more and found performance improved.

    I have perhaps a very strange way of defining a rig that performs the best.

    1. In light winds, the sailboat can still make windward progress.
    2. The sailboat can tack in light winds without turning on the engine.

    As a cruising sailor these performance goals mean the following:

    A. During a passage, there is no need to take down the sails when the winds slack. On one boat I was on we were always dropping and raising huge sails because the wind died every night, then in the middle of the night we attempt some sailing, fail, and drop sails again. These were sails so big we had to use coffee grinders to raise them. That wasn't fun.

    B. It saves fuel. As long as some progress is being made, it is so much nicer to just leave the engine off.

    C. Having a smaller and windward performing rig keeps the boat with the group. Many big multihulls when in a regatta end up sailing circles around the other crusiers and arrive at the next port a day or two ahead. They then spend their days on the SSB speaking with the fleet about entrance, where to anchor etc.

    D. At first I wasn't happy at all with the spars made for me that go in the foot of the sails. (There is a big and smaller sail) They are very heavy. However, their weight has proved to be a good thing. They keep enough even tension on the sail to help prevent flogging during a tack.

    So in this regard, the lowest winds I have been in that allowed me to still make windward progress were only 5-6 knots. As winds increased, my ability to point increased. The highest winds I saw so far flying sail are only 10-14 knots. That was during the ill fated South China Sea crossing when I over compressed the 82 foot tall wooden mast made in Thailand.

    This new mast at 62 feet hasn't flown any sail yet. I just finished installing it in the Cebu Yacht Club a month ago, and then Yolanda hit giving me lots of other stuff to do. I am currently working on painting projects before I get ready to do new sea trials on the new mast.

    I also want to perfect a way to drop, wrap, and stow the sail completely without touching the deck.

    Philip Maise
     

  15. sharpii2
    Joined: May 2004
    Posts: 1,903
    Likes: 105, Points: 63, Legacy Rep: 611
    Location: Michigan, USA

    sharpii2 Senior Member

    Hi pmaise.

    Thank you for your detailed answer.

    The interest I have in this type of rig is for a motorsailing craft, most likely a monohull, with a small engine and a small rig.

    The rig is small, because there is a small engine to push the boat through calms and help power her through light winds. The engine can be small, because the sail rig can help keep her off the rocks in windy conditions.

    Faster speeds are traded away for easier handling, more course choices, and better range under power.

    But this can be criticized as a dangerous combination.

    In strong winds, the small engine will most likely be inadequate, on its own, to keep the boat off the rocks.

    The sail rig must be able to help in this situation, if this logic is to work.

    Most rig types should be adequate, once the boat is settled on a tack.

    The problem is coming about.

    With the mast forward, there is a considerable danger that the boat could get caught in stays and refuse to change tacks.

    This was a common problem with a small cabin sailboat I once had.

    On its first sail, the engine locked up and the boat got caught in stays, hung there for a moment, then reverted to its old tack. It ran smack into the break wall, and I had an unwelcome lesson on gel coat repair, after my first sail on a brand new boat.

    I later learned to back the jib, when changing tacks, and let it push the bow over to the other tack. When the jib was down, the main got the same treatment. The boat changed tacks smartly from then on.

    I would never want to do this in stormy conditions on a bigger boat.

    The mast, on a mast aft boat, acts like a riding sail that is never furled.

    It tends to help point the bow into the wind, by itself, leaving more forward momentum left to get the boat over that crucial last few degrees to get the sail to set on the new tack. With a small engine this could be a winning combination.

    The only alternative I can think of would be a schooner rig, with the fore mast considerably shorter than the main. This should deliver pretty much the same effect.

    But why go with another mast when you can get away with just one?

    Only to save money on expensive standing rigging and expensive fittings that go with it.

    If the tensions don't have to be jacked up to the moon to get adequate windward performance, then a jib only, or jib as mainsail rig might be back in the picture. It could be conceivably less cluttered and lighter than a multi masted alternative.

    Attached is a sketch a showed earlier, pages and pages ago of a mast aft cutter rig.

    Non of the three sails has reef points.

    Each is either fully set or fully furled.

    The inner jib is furled first in a rising wind.

    If the wind gets stronger, the main, which is really a mizzen, in actual proportion to the others, is furled, along with the outer jib.

    The center jib is then re raised.

    Down wind, the main is furled and the two jibs are forward enough to provide sufficient lee helm to keep the bow from rounding up, on a down wind tack.

    A spinnaker of some sort can be set to make up for the area lost from furling the main.

    At least that's the idea.

    Your boat is an interesting experiment on the jib only concept.

    It will be interesting to see how well it performs with the new shorter mast.

    I think another pair of shrouds is needed.

    They should extend from the mast head to the ends of the crossbeam the mast sits on.

    These would greatly improve the side to side support of the mast considerably, and may even relieve some of the tension on the back stays, when the boat is sailing on a reach.
     

    Attached Files:

Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.