design for light airs

Question:

Do some of the older designs offer advantages for cruising boats in light airs?

Specifically, I'm thinking short waterlines and wineglass keel shapes. Both of these design attributes reduce surface area, which is the main drag in light airs.

Also, these older designs have much more narrow hulls, something to which I have always been attracted. Yes, you give up lots of room inside, but narrow beam sure seems to cure a lot of other ailments. Light air sailing being one of them.

These older designs typically do not have fin keels and spade rudders, but they attempt to get to the same place, sort of, by having a cut away forefoot and deeply raked attached rudder. Down wind handling suffers, but I never seem to sail down wind anyhow. Clearly, a full keel doesn't help in light airs.

Light weight is sold as the ticket to light air performance, but I don't buy it for cruising. Light boats have their SA/D go south pretty easily with cruising stores, and the stability curves don't seem to survive too well either.

Obviously, plenty of sail area is critical, whether light or heavy hull.

I'm just a recreational sailor thinking of purchasing his second boat (not counting daysailers) and I'm not yet convinced I need a new design for my purposes. Thinking of eventually cruising inside passage to Alaska, and I see lots to recommend an older design in a metal hull. In a word, rocks.

Am I off base? Comments? TIA.

-John.

 

John

I also enjoy charging around Puget Sound and Northwards in 2 Knots of Wind, and I've thought about it a lot. Looked around a lot for a new 30 sq, but couldn't get any builders to respond. So my current boat Amati was designed by Bob Perry, and my design brief was 'an amalgamation of a 30 square meter and an IMS Mk I that will be really fast in light airs'. Back when IMS was wholesome. There's a bit of Open 50 in her too... Although not made of steel, a 30 sq. can absolutely smoke in light airs, and meets the rest of your criteria. If you get a chance to look, there's one named Bijou II around Port Townsend, although she's not for sale, as far as I know. She's one of the most beautiful boats I've ever seen. If small quarters are OK, how about a Dragon? Except for steel, meets your criteria. Modify the rig a bit, and fit out the interior cleverly and I think you'd have a great NW cruiser. After all, one of the Dragon's design briefs was to be an overnighter.

Swede 55 might be an option too, although I'm not sure about the underbody, and she's fibreglass, I think.

I've hit some things too. One BIG rock, a few submerged deadheads. Insure your boat well- even steel needs repair. We hit the rock up by Silva Bay, in a wood boat. No leaks, but a nice repair at Jespersen's. There was a steel motorboat up at the yard near Jespersen's that had AMAZING rock damage. Ran into an Island at night at high speed. Wish I had a pic.

Paul

 

Thanks Paul. About the Swede 55. I should have added that we are in the market for 30 to 40 feet of boat. The smaller the better.

Our last boat was a Wauquiez 33. Still thinking of buying another one but that darn Practical Sailor article has ruined the price of them.

 

Some of the old international classes (say Q,R, & S) can do quite well in light air due to their displacement and shapes ability to carry way through light chop. I saw a Q once ghost past an IOR fleet like they were anchored in little more than a knot or two of wind. As for SA/D, some of those old vessels were MUCH higher than modern ULDB's

On the down side, they have little form stability and high pitch inertia which makes them poor sea boats.

What you are complaining about is what I refer to as the "sandbagger or canoe problem". To go fast in light air you need sail...lots of it. A heavy boat (think plank on edge cutter) needs more displacement and therefore more wetted surface and drag than a light boat. A light boat needs either high form stability (think skimming dish), or large moving weights (think 10M canoe) to carry sail. High form stability requires beam, which means wetted surface or the "cat" route. Large moving weight means bodies, and/or a system to move the weight. These are not new problems as a look at high-speed sailing over the last 150 years will attest. The Open 60s & 70s are just the latest attempts to marry these to disprate concepts....very shallow with wide beam sailed at a moderate angle of heel to reduce wetted surface and a canting keel for moving the weight around. Unless you want to work, you are not going to get that in a "recreational" sailboat.

I'm not sure steel is needed (but if was going to have a world cruiser built, that would be my choice), but a moderately burdensome hull is required for extended voyaging. As for light air...remember that sailing/voyaging is about the journey, not the destination. What little light air sailing you will do is insignificant compared to having a well rounded vessel.

 

I have first hand experience that some charts up north have rocks where none are noted and no rocks where some are noted.

When I lived in Alaska us sailors were eternally grateful to the tourist industry because their commercial boats were continually finding new rocks for us, at their great expense.

And even if the rocks are not new, sometimes the anchor don't hold so well, and the rocks like to get close and personal to say Hi first thing in the morning. I've seen that happen many times. Not in MY boat, mind you. I personally don't sleep too well on a sailboat precisely because of this problem.

Surely you meant to say, "What little light air sailing you will do is insignificant compared to having a large and reliable diesel." That seems to be the preferred local fix.

 

What prompted me to start this thread is that I have in my eye an older steel boat, with a very short waterline, very narrow, etc., etc.

Allen Buchanan design.

Can't quite figure out what to make of it.

But even in the abstract, the older designs with respect to CRUISING in light airs pose an interesting issue. The key is the resignation that the boat ain't gonna be light. At that point, the issue becomes, I think, how best to reduce surface area, an issue that perhaps older designs paid more attention to, while modern designs seem more focused on squeezing out speed when it's blowing the perfect 15 knots.

All comments welcome. I might be all wet here, but somebody needs to say so and explain why. Thx.

 

Hiracer, the only reason i would chose steel for a hull it that it is easier to fix in a 3rd world location than composites. Composites are far stronger, lighter and damage tolerant than steel. Even composite concrete (Fibersteel) is overall a better choice. The problem is that high tech is not easy to repair in the field WHEN you go up on the rocks.

Whole different issue than your anchor watch problems.

 

"…only reason i would chose steel…easier to fix in a 3rd world location than composites…."

And what about the costs?

" Composites are far stronger …"

Abrasion resistance? Plastic range?

"…damage tolerant than steel…."

???

 

For a moderate sized crusing vessel, the difference in initial material cost of the hull between most materials is trivial, it is labor and outfit that drive costs. This is why many homebuilts fail at the "sheerline" stage...getting the hull fabed is the easy/cheap part.

It is the availability of repair skills, equipment, and material that drive my comment about steel. A sledge hammer, buzzbox and a handfull of 6111 rod can fix most steel structural problems to 95% of original strength. It requires no environmental controls or specialized material or equipment.

For a workboat lying alongside a stone quaywall, I would agree; for adequately handled moderate displacement crusing boat the argument is moot. It doesn't matter if the hull is 3/4 solid E-glass or 1/4" steel. I know what will happen to both if you put them up on a sand beach, or on a coral reef, or nail a pinnacle a 6 knots.

Why design for plastic, when you can design for elastic. This is the old stiffness/strength tradeoff. The real issue here is energy before shell rupture and residual hull strength. Which leads to the next question....

Maybe the question here is what is "damage". You sink boats by putting holes in them or causing the hull gurder to fail. The amount of energy required to hole or deform a steel hull panel is less than the amount of energy required to hole or deform a similar designed composite one. See the Gibbs & Cox manual for the design of fiberglass reinforced plastics. That is the real issue. To compare a 4mm CF skinned racing hull to a 6mm steel trawler hull may be a match in strength, but not a match in design requirements.

Which brings us back around to the initial topic of hull material selection. I want to design a "world crusier". The design requirements of the hull make no difference wether it is steel or composite. I can design a hull in either material to meet those requirements. The design requirements of the vessel may lead to the selection of one over the other. And when two similar designed vessels go up on a motu in a typhoon, the composite one may be stripped and abandoned because the damage is too expensive to repair there, while the more damaged steel vessel can be beat back to shape and welded tight.

 

Jehardiman, I am a little confused here. I don't know what you mean by a "similar designed composite one". Do you mean the same weight on a hull?

Nobody wants a composite boat with the same weight of a steel one. If you want a light metal boat you should chose aluminium, and then for the same weight as a composite hull, aluminium is more resistant to rupture.

A steel hull or aluminium hull can be bent or deformed more easily than a composite hull, but in what regards holing, I don't think that is true.

This graph compares the strength of different materials in N/mm2.

 

OK. Thread police. Bzzzz. This NOT a thread about hull materials. Nor is it a thread about a world cruiser.

I am looking to purchase an older boat, not design a new one. So, most of this discussion about materials is completely irrelevent to my situation.

This is a thread about older designs and how well they sail in light airs compared to modern designs. I have suspicions that they sail better in light airs than might be generally appreciated, but I haven't actually sailed them so I don't really know.

My thesis is that modern designs sail better in perfect conditions (15 knots) but a GOOD older design will possibly keep up in light airs--if you start with the premise of a medium to heavy displacement (which I am, because I never see any light, older cruising boats for sale in my area).

 

"…A steel hull or aluminium hull can be bent or deformed more easily than a composite hull, but in what regards holing, I don't think that is true…"

I agree.

"… the difference in initial material cost of the hull between most materials is trivial, it is labour and outfit that drive costs…"

That's exactly what I mean, steel isn't just much cheaper as a raw material, it's also much faster to build, (a lot lower labour costs), very tolerant and forgiving to work with, you can work even outside in a low or high temperatures, humid or dry atmosphere it makes no difference. Even not so perfect workmanship isn't a problem. Instead of zillions of layers of sticky stuff and small pieces, you work with a big plates. If one of the time saving chine hull methods is chosen, two people can build sizeable steel hull in a few weeks. Steel is also comparatively very cheap and fast in outfitting phase. Deck fittings can be easily made from stainless and welded to the deck. Motor foundations, fins, tanks and similar are also much faster, stronger and easier to install.

Compere that with a composite building which needs perfect labaratorium conditions and immaculate work procedures and discipline.

"…For a workboat lying alongside a stone quaywall, I would agree; for adequately handled moderate displacement crusing boat the argument is moot…"

Well, if that cruising boat ever ventures to the 3rd world or even in remote regions of the industrial developed countries, she better be able to mess with a working boats and their facilities, chances are that they might be the only type around.

"…The amount of energy required to hole or deform a steel hull panel is less than the amount of energy required to hole or deform a similar designed composite one…"

There is an enormous difference between forces needed to deform steel (which is relatively low), or to actually puncture it. I have some experience with that. I was once rammed in the lock by 4 big charter motor boats lashed together, with a skippers who didn't really new what they were doing. I had at the time unusual small sailing boat with a steel hull from riveted galvanised plate just 1.5 mm thick and plywood deck and cabin. I was moored against the wall of the lock. Powerboats were slowly turned from opposite side of the lock and went straight in to the side of my boat. Bow of one of them just sort of came in to the mine boat for about 20 centimetres and then stooped. My plywood deck around the area of impact was lifted up and broken, but hull just flexed and was hardly damaged at all, slightly deformed, (2 or 3 hammer blows took care of that) and scratched paint. I repaired damaged part of the deck for about 100 Euro and after the week was back sailing. I doubt that any other similar boat built from other non-metal materials would stay afloat.

On other occasion, I saw when hevy tug rammed small, open, steel rowing boat against the channel wall. Boat was realy deformed but didn't leak and all what was needed was heavy hammer and a bit of paint to make it look as new.

Composites can't tolerate deformation. When thin, outer skin is damaged and water finds it's way into the foam there is real trouble.

But back to the thread topic, Hiracer, I apologise for hijacking your thread. I think that you are right, many older designs with long overhangs and lot of sail area are really good light wind performers. In your part of the world look for CCA class boats.

 

Actually the boat I'm reviewing was made in your part of the world, Medemblick in 1964, with a rebuild somewhere in 1991. 4mm steel hull below waterline, 3mm above. Lot's of useless overhang on the stern. She was a yawl at one point. 36' overall with only 24' waterline. 9.5' of beam.

She won't be fast overall, but if she can sail in light airs, that might be good enough for me.

 

Okay, fair enough

The answer is no, If you put that in a generic way. New boats are lighter and carry a lot more sail than old ones (they have a lot more form stability)....but old ones are a lot more comfortable in a sea way and for the same size a heavier boat will be normally more seaworthy.

If the boat you are talking about has a narrow hull, then probably it will have a relatively good upwind performance, but will have a worse downwind performance. In any case (if it is a steel boat) it will be slow in light winds, compared with a modern typical boat.

You can approximately see how the performance of that boat will be in light winds, comparing the SA/D (Sail Area/Displacement) of that boat with the SA/D of a modern one of the same size and that will give you an idea (the bigger the number, the faster the boat).

Of course your boat is narrow, but it is also heavier and that means that the immersed area is bigger, and that is what counts mostly in light airs (the bigger the area, the slower the boat, for the same carried sail).

The typical light weight modern sailboat will only need about 10 knots of apparent wind to sail well. Many will start to think about pulling in the first reef at the 15knots you have referred.

 

Yes, that's my problem. We don' t have the displacement for this boat. And it's on the hard, so test sail is not an option.

But the price . . . well, it's priced to reflect the problems in the sale.

I think I've resolved this issue coming at it from another angle. Even assuming this boat has decent sailing upwind in light airs, if you cut off that stern hanging in the air, it would sail even better by virtue of having less weight. So a short waterline, in the abstract, may help light airs sailing upwind, but the overhangs do not. Yes, I get some storage space with the overhang, but not enough to get excited about. All in all, those overhangs are starting bug me more and more. They just don't do all that much other than drive up moorage fees.