Aftmast rigs???

Good question.

The heeling angle would increase because the heeling moment would increase.

And this would happen because the mast will be on the starboard side (it would be on the port side, if I were left handed).

When the boat heels, the down wind side (leeward side) gets pushed down by the heeling arm of the sail. When that happens, the windward side rises up a bit.

If the mast happens to be on that side, it rises up a bit too. When this happens, the Center of Area (CA) of the sail rises up as well. This, in turn, increases the length of the Heeling Arm (HA). So, if the sail is producing as much heeling force on this tack as it was on the port tack, the Heeling Moment will be greater.

If the Heeling Moment is greater, the boat will heel over further.

I hope this helps.

 

Thanks sharpi, iIdidn't realise the mast was off center. Now it makes sense.

 

Too bad Eric is around to defend himself. He's gone out sailing (cruising) around the world with his wife

 

Brian, two points;

1- Eric did not give those he called “insane” a chance to defend themselves.

2- If Eric is going to use such language against others then it is hypocritical to complain when similar language is used in reply

3- I put this information before Eric on this very forum. He admitted that some of what he said in his article was wrong or said he had just got the info second hand. He still left the article on his site, containing derogatory comments that he admitted here to be untrue

4- Are you claiming that I made factual errors? In which case, what ones? When it comes to the remarks on rating rules, for example, I checked old books and confirmed without doubt that some of Eric’s claims were simply not true.

Why should derogatory and incorrect claims be allowed to remain unchallenged and uncorrected on a site about the subject?

 

@CT249,
To tell the truth I am tired of arguing with you about this stuff.

The simple truth is there are likely numerous new (and radical) ideas that might not have come to the sailing world had everyone 'conformed' to the rating rules of racing,...or 'convention thinking'.

Do you think these ideas would arise in the conventional rating rule world?

1) Saphira
Atlantic 70F https://www.chriswhitedesigns.com/atlantic-70f



2) https://www.boatdesign.net/threads/understanding-wing-technology.34697/page-22#post-874007

3) Eagle 53
Eagle Class 53 Catamaran Foiler https://www.boatdesign.net/threads/eagle-class-53-catamaran-foiler.60758/#post-873270

Etc, etc

PS: Yes Eric and I and a number of other fellows thought the 'conventional sailing world' was mired in a bunch of horse manure at times.

The convention world stifled progress, not intentionally, but rather as a result of their efforts to handicap racing.

 

For one, you're setting up a strawman there, Brian. I never said anything that claimed or implied that those craft could be created within most rating rules - but that is completely ignoring the point that there are many OTHER areas of sailing that do NOT have such restrictive rules. Many such areas, like Skiff sailing, Moths, Canoes, shorthanded yachts, sportsboats, etc etc etc are well funded and have very high profiles. To somehow assume that some ban on things like roachy wingmasts in SOME classes has lead to sailors from ALL classes to be "blind" to them is incorrect, illogical and insulting.

The underlying assumption that what is banned in some "mainstream" classes is thereby made invisible or dramatically restricted is utterly untrue, as many examples can prove. So even if it had been true that rating rules banned roachy wingmast rigs, for example, that did NOT mean that the sailing world would have been "blind" to them. Perhaps the East Coast USA sailing world may have largely ignored them, but that is far from the entire world.

When I was a kid, for example, my first boat had no backstay, a roachy fully battened main, and a rotating mast. It was one of the most popular classes in the country. We had wingmasts on kid's boats, mum-and-dad boats, and roaches on most boats. There were six classes of wingmast/fully battened roachy main boats within about a mile of my home. To say that the people who grew up in this and similar environments were "blind" to things like roachy mains and wingmasts is just ridiculous and untrue. Okay, maybe some people grew up where IOR, Flying Scots, Stars and Snipes ruled, but those people should learn that their experience is not that of the entire world.

As already noted, most of the world's most popular classes (including the most popular class of all, the two most popular dinghy designs, the most popular dayboat keelboat, the most popular cat, etc) have "unconventional" rigs. It is silly to claim that the many people who come from such environments are "inbred" with the belief that we need wires and triangular mains.

Yesterday, my boat was in a line with two other yachts. All three of the yachts were owned (or in one case perhaps just sailed) by people with years of experience with wingmasted roachy rigs on both monos and cats - and all three of them have conventional rigs. No one was "blind" or "insanely conservative"; in fact we may have more time with wingmasts than you or Eric do. We chose different rigs for different uses because we have lots of experience with each type and we know their benefits and issues.

I don't really see why telling the truth, and implicitly defending people from abuse such as claiming they are "insanely conservative" and "blind", is seen as anything to be concerned about. The truth is surely a good thing.

I don't really understand why Eric is allowed to sling **** at people for being "insanely conservative" and "blind", but it's said to be offensive when he gets called on it. He's not a protected species or a special case. If he is going to write stuff that is not true and to insult people, then he cannot get offended when the truth is stated.

 

Actually its simple nonsense founded on blinkered eyes and lack of awareness.

 

Brian, I just came across this article from almost 40 years ago about wind assistance for commercial shipping, and I thought you might be interested in it..
A FRESH WIND FOR SAIL POWER https://www.nytimes.com/1981/12/06/magazine/a-fresh-wind-for-sail-power.html

They mention Jesse Briggs and SAILA - I had a subscription to the SAILA newsletters in the mid 80's, but sadly something happened, and they were no more.
Later on they also mention Lloyd Bergeson and the Windship Development Corporation - I will attach a copy of a paper that he presented at a conference in 1985 on wind assist developments for commercial shipping.

 

Isn't it interesting that the article talks about the discovery that the sail assist provided as much as 40% fuel savings, when a century before, the engine was the "assist" technology.


What's old is new again.

-Will (Dragonfly)

 

Very interesting submission,...long article that I will have to return to and read more thoroughly.

Perhaps it would be best posted on this other subject thread??

New Age Trawler/Motorsailer; Kite assisted PowerYacht

New Age Trawler/Motorsailer; Kite assisted PowerYacht https://www.boatdesign.net/threads/new-age-trawler-motorsailer-kite-assisted-poweryacht.20319/

 

I know this is three years out of date, and is not my intention to be critical. A few years ago I read all 70 pages of this thread. IMHO there was a maths error with the aft mast rig of Running Tide yacht. From memory Brian calculated back-stay tension as 1.34 tonne for every 1 tonne of fore-stay tension. My maths gives me 4.44 tonnes per tonne of fore-stay tension. I have a suspicion that this has been all sorted out now, and am not saying anything that nobody is unaware of. My solution, partial solution would be to use long stern overhangs and locate the back-stay there. This would give much lower back-stay tension and much lower mast compression. The downside of course is more weight building a stern overhang, more windage, a boat appearance not in fashion therefore lower resale value, slightly wetted surface area meaning more drag, a longer LOA meaning higher marina fees, extra cost in building the overhangs, and also the elimination of useful transom steps.
Anyway, I have attempted a simple force diagram. I also did a simple comparison with stern overhang and show how much lower the rig forces would be, and by using a stern overhang backstay tension goes down to 2.1 tonnes per tonne of forestay tension. This also means lower mast compression. This may be a little high compared with conventional rigs, but far better than the 4.44 ratio as per now.
I am also aware that I as a reader did not bother to do the force diagram and thus I missed the mistake
I am aware that this is all old news and Brian is no longer here,

 

And now with a stern overhang. A rough estimate gives 2.2 tonnes back-stay tension for every 1 tonne fore-stay tension, better than before, maybe still a bit high. Going two masts, with two jibs. might be even better again in terms of geometry. Note I personally like stern overhangs, even though most modern multi-hull designers detest them

 

possible layout with foresail only rig using two masts

 

Hi peterAustralia,
First off thank you for reading thru this entire thread.

Next, I'm not dead yet, just turned 80

I'm going to have to look thru your suggestions.

I've have not totally given up on this idea of a 'single-masted ketch', with all roller furling sails. That 'short-handed' handling aspect alone warrants another review.

Yesterday I was looking back at the model I had built over in Thailand and thinking about some modifications that might make sense. I have a few other projects (non-boating) in the works right now, but I'm going to give it some more thought. I sure would like to talk to some experienced world CRUISING sailors that have gotten a little discouraged with man-handling a conventional sloop or even ketch rig.

 

The design could be greatly improved, in my opinion, by making the mast vertical and having the mizzen sail's luff on the mast instead of on a line. This would reduce the tensions on the back stays by quite a bit and therefore the compression of the mast. The mizzen would be bigger of course, but nothing like the huge main on a more conventional catamaran sloop design. As it is, the design would probably be able to be made to work, but relatively large catenaries would have to be cut in each of the three wire-luff sails in order to keep them from bagging due to low luff tensions. A long time ago, a guy in the pdracer fleet made an aft rigged boat. It had only an unstayed mast, stepped just forward of the aft transom. Its mast was a 3.0 inch pvc pipe. It did sail, even upwind decently. But it never had to face gale or storm conditions.

I have thought of the idea of a two-masted sloop. The aft mast would be vertical. The foremast would step right at the stem of the boat then slope back until its head connected with the shorter aft mast.

I could see an idea like this working here, but with the foremast stepped in place of the inner forestay. This of course would added some wieght higher up where it is most unwanted, but it would further reduce the stresses on the rig. In wild, blowing conditions, the outer jib would be furled, and the mizzen may be too. This would leave inner foresail, which would be attached to the mast instead of a wire. Arguably, it would be less efficient. But it would be sturdy and put minimal loads on the rig.