Heavy sailboats : Can they point ?

Even a blind pig finds an acorn every once in a while?

 

Whoops, Paul B you pointed out another error in my typing - thanks.

I meant to say IRM in that last sentence, not IRC.

Interesting point whether IRC is a development rule; on the one hand it tries to keep old boats competitive, on the other it allows lots of development to happen; I'm due for a sail on a kite-powered water-ballasted Open 66 soon, and it rates OK under IRC.

 

You can power up, but the boat must heel more to accept the force and then delivers less of its force in the desired direction.

So you are saying that it is the heeling angle that causes the problem, if any. A heavy boat with, say, a canting heel will not have any such disadvantage, right ?

 

"So you are saying that it is the heeling angle that causes the problem, if any. A heavy boat with, say, a canting heel will not have any such disadvantage, right ?"

My thought is that it is the blunt shape that leads to the drag, which increases as a function close to cubed, while the misdirection of heeled forces is described by a lower order function, so, the added drag is the central problem that gets worse at a faster rate than increasing rig area can compensate.

If you are talking about a masssive boat with a fine form and a canting keel, you are not going to have the drag of the boats of yore.
Dan

 

Thank you. There must be a formula or measure or something to define precisely what we mean by a "blunt" shape causing excessive drag. I suppose it will depend upon the angles of the hull lines . Any thoughts on that?

 

Not so fast, Dan...
If blunt-nosed shapes were so draggy, then bulbs and keels wouldn't be that shape.

Steve "trolling..."

 

I prefer to think of the IRC as a handicap system rather than a measurement rule. Once someone has the opportunity to say, "The calcs say x, but I'll add/subtract y because I THINK..." then you don't have a measurement rule.

Sailing the Grundig? Going out on Boxing Day? What is "Rates OK"? Is it competitive in bouy races in a "high end" IRC Fleet? What's the story on SL's new Canting Decker?

Replace "IRC" with "PHRF" in your statement above and you have an equally correct thought. However, I doubt many would agree that PHRF is a Development Rule. A few people have talked to me about using IRC for our proposed sportboat class, but as I've looked into it I don't see the advantage.

Back to the original topic. Too many of the "heavy displacement faithful" rely on published opinions of people who really have no idea. Just because someone has circumnavigated and writes eloquently about their "man against nature" battles does not mean they know anything about sailing or boat design. Usually they best sailors have the fewest interesting stories because they aren't getting themselves into so many predicaments by lack of knowledge and poor abilities.

Anyone who knows how to sail and has sailed both modern and classic designs knows which will get uphill better in the nasty stuff. If my life depended on getting off a lee shore in a gale I'd take a modern, fin/bulb keel, fractional rigger against something like the Baba 30 mentioned earlier. Hopefully everyone realizes that the heavy boat actually has a higher CG, less RM, less responsive steerage, and will be tacking though a lot greater angle while making far more leeway, perhaps as much leeway as headway.

It's funny to hear the same people who think the Baba-type would be better in a gale are also the people who complain about trying to get their heavyweight, non-responsive full keeler into a slip with a 5 knot crosswind.

 

Paul

That sounds like a pretty narrow view of things. There is a broad spectrum of issues that need considering here, and too much overall generalization.

There are a lot of modern "heavy boats" that would sail off in more comfort with excellent steerage and minimal leeway .

Less RM ? Greater GM yes but GZ ?
integrate the stability curves and look at the ratios and you will find the heavy boat is far more "Stable" remember stability is far more than initial stability.

For example consider that in a cruising situation you have say 5 people aboard your normally 7 ton 45 foot racing boat, with a tonne of drinking water half a ton of fuel half a ton of food stores and another ton of miscellaneous gear plus a dinghy on deck and a cruising anchor at the rollers. If you do the calcs you will find that your stability will be abysmal compared with the heavy boat.

Your draft will be deeper so you have to tack sooner but in tacking your keel will stall more easily , the extra weight aboard your light boat has immersed it and made it a cow, suddenly you are not so confident.

If you so much as touch a rock on your way past the reef your light racing boat with its bulb will be lost. The heavy boat being heavily built will need to run onto the rocks before she is lost. If she touches at the bottom of a swell after tacking too late her skipper just gets a rush of adrenaline.

If my life was on the line in this situation I wouldn't go near your idea of a modern hull.

 

Mike doesn't it all depend on other factors, as you say?

For example, a 20 tonne badly-designed ferro cruiser may only have a very low ballast ratio plus enormous freeboard and high-windage rig, may it not? Add the same weight to it, and the already low ballast ratio suddenly looks even worse. Sure, that won't happen to a well-designed heavy boat. I'm not familiar with the Baba 30, it may well bark severely.

But if we're looking at well-designed boats, surely we can have lightweight cruisers or cruiser/racers that will be designed with a high RM and it will be designed to handle further loads. I wonder how much weight the 50s that did the RTW non-stop carry? The only person I know personally who circumnavigated non-stop (with no problems) did so in in a medium-displacement Davidson 37, which has a fairly dinghy-shaped hull. No probs with carrying lots of gear on that boat.

There's a French couple sailing around the Pacific long-term on the 1979 IOR 2 tonner Accanito, a lightweight fractional rigger still with runners etc. They reckon it's a great cruising boat and have no problems getting upwind fast. Like others (including heavy-boat sailors) they just prefer to sail more (cutting down on that 500 kg of fuel) and economise on water (cutting down there) and of course they are a couple (reducing water and food). Surely that is a valid way to go?

I had liveaboard gear on my 28'er for 2 years (I was low on water and fuel, though) and really could not feel any loss of handling qualities. That's not to say other lightweights may be affected; it's just that perhaps you can't categorise all lightweights, or all heavyweights?


I agree that waaaay too many lightweight boats are underbuilt, and the deep high-aspect keels must be an engineering nightmare. I've sailed on one that hit bottom at a few knots and the damage was severe. Another 56 I used to sail on lost her bulb when she ran aground. I do agree there's no way I'd feel really happy cruising with that sort of foil underneath me.

On the other hand, a mate's heavy-ish Top Hat 25 suffered major structural damage around the keel in deep water, another mate sank a Top Hat after hitting rocks, and the Swanson 42 sank inthe '98 Hobart. Even classic timber S&S leadmines like the original Ragamuffin and Stormy Petrel suffered structural damage early in their lives so not all heavy boats are immune.

In terms of ultimate safety, though, isn't it easier to design full flotation into a light displacement boat, which needs less volume in the flotation?

I've never run hard aground in my 2200 kg 28'er with a steel fin keel of medium length - but I always think I'd be happier with 1500 kg of hull bouncing on top of the keel, than 3000 kg of hull bouncing up and down. This is a boat with two skins of ply on the cabin side etc, totalling 16mm for a 28'er which isn't too light. I like being able to just careen the boat easily, knowing I have a tough keel with a long root and low C of G, well secured to a lightish hull.

 

Strange, I don't recall mentioning anything about a racing boat. I guess you haven't been paying attention for the past 25+ years regarding the light cruisers that have been built to my description.

I'm going to take my own advice to 249 and not argue with the faithful, especially with someone who derives their living in part from cultivating the scare tactics that keep uneducated sailors buying into the "heavy" myths.

 

I don't know, Paul, isn't Mike perfectly entitled to his view? I only had a got at him (and others) when they seemed to imply that only their view is right.....

It's such a personal issue, isn't it? It depends on the motion you like, the tweakability you like, the comforts you like down below, the way you prefer to enter an anchorage, how much daysailing you do and what type, the schedules you keep to, the sort of cruising you do......

re "I prefer to think of the IRC as a handicap system rather than a measurement rule. Once someone has the opportunity to say, "The calcs say x, but I'll add/subtract y because I THINK..." then you don't have a measurement rule."

I'm not sure that's the way the rule works.....I think (having spoken about it to a few designers) that it may be that "well, that's an IOR hull style with a DLR of X on a beam of Y and a draft of Z and a stern overhang of Q (etc etc) so that gives it a hull factor of 8.5, and when we plug that (and other factors) into the formula it gives a rating of 1.234".

The "subjectivity" comes into the fact that, for example, they haven'rt defined a bulb keel - David Lyons hassled Mike Unwin about this and Mike said "nope, we are not going to tell you what a "low c of g keel" and a "bulb keel" is, because as soon as we do that you'll design right to the edge of a low c of G keel to get the rating advantage".

But it may well be a handicap system as you say.


Re "Sailing the Grundig?"; yep, should be.

"Going out on Boxing Day?"

Nope, my Hobart days are over I think. Not enough small boats going and I don't like big ones.

"What is "Rates OK"? Is it competitive in bouy races in a "high end" IRC Fleet?"

I've forgotten the rating; close to 1.6 nowadays; but on long distances races she can get into the chocolates. On buoy races, she can't. There's not really any way a single-figure system can rate such a boat for long races and for short courses, where she hits corners and has trouble if someone parks a high-pointing boat under her lee off the line.

Andy Dovell and Scott Jutson both do Open boats that are excellent all-rounders for Open boats, AFAIK, yet both say the Open style is intrinsically wrong for maximum round-the-buoys performance.


"What's the story on SL's new Canting Decker?" Dunno, I haven't spoken to Sean or Andy in yonks. I'll hassle Sean about it.

 

Paul
This is supposed to be a forum for discussion. If issues are raised that you feel are opposed to your beliefs then discuss them rationaly.

I am not the faithfull just the an experienced engineer and experienced sailor.

I have analysed design failures and inspected the wreckage of enough disasters to have some conservative proff. views. Not predjudices just cold hard fact driven analysis. That people can have a conservative view should not annoy you.

One of the duties of proff engineers is to protect the public we tend to be a bit conservative. If I design a boat I want to know that it will be safe and will look after the people aboard in all that implies.

The scare tactics I think were yours. I was simply pointing out a contradictory line of thinking to your example with issues you have not considered. This is what forums are for. Did you even think about what I posted? if you did then how about discussing them.

Have you ever done a stability calculation and seen just how much that cruising gear changes the numbers on a light boat? I think you would be surprised.

 

The former, probably - the latter, not neccessarily. Remember that RM is composed of two things - lever and displacement. If the GZ is only 75% of the light boat, but the displacement is double, then the RM is 50% higher.

Steve

 

Hey Steve,

If the blunt shape is breaking the surface it is going to be slow.

All those blunt entry bulbs you refer to have very fine exits so they won't induce turbulence.

Do you dispute blunt shapes induce more votices?

Dan

 

You must have missed the smiley and the "trolling" reference, dan. Not intended to be serious, just poking you with a stick, hopefully gently.

Steve