The Offshore Voyaging Reference Site

Cyclical Loading: Why Offshore Sailing Is So Hard On A Boat

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It’s often said that offshore sailing is much harder on the boat than lake or inshore sailing. Surely, we can quantify that statement and determine whether or not it’s true.

Spoiler alert: It’s true. Oh man, is it ever true.


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Jacques Landry

Good analysis Matt.
Being an engineer I have to agree with your approach and conclusion, but I know some out there will comment about a few points you did not mention!
To start with, the “abuse” experienced by the club racer might induce higher stresses than that from some ocean crossing conditions (ok, with reefed down sail and common sense), as the boat will be sailed over-canvassed and to the limit most of the time. You will also have several heavy sailors running on the deck at all time and that is quite dramatic for most balsa/honeycomb/other laminates as well as for the whole rigging. This combination must have an effect as the boat will be driven close to breaking all the time. But I have to agree that this would not be apparent in a simple “hours of usage” summation. Some will say that an ocean going vessel will carry more “cargo”, but 8-10 250lbs sailors on a light 30 footer would be about equivalent!
The Great Lakes will also present a few other challenges. The wave period being way shorter combined with too much sail will be tough on the rig. The engine not being used often might not be a plus, as we know that diesel engines like to run, or at least get to their operating temperature before being shut down. And finally, winter! I am sure you have looked at the effect of freezing temperatures on all parts of a sailing vessel, with different thermal expansion coefficients for different parts of the vessel while most will lay them down fully rigged over winter. And all that water that expand when freezing in all crevasses, holes, and engine “voids”.

The final conclusion with all of this taken into account will be just the same, but might not be as black and white!

I personally would still rather buy an ocean going vessel that has been well kept (John, call me when yours’ for sale !) than a club racer that has been abused by “racers” who don’t really care about how long this thing is going to hold up together!

Dick Stevenson

Matt, Lovely essay and such fun for me to read your analysis where you bring your engineering skills and knowledge to a subject that all of us are aware of on largely an experiential and subjective manner. Although it makes no difference to your theme, I find open ocean waves/swell periods in the 10-15 second area rather than 2-3 seconds but perhaps we are referring to different things. I also agree with much of what Jacques writes. Competitive pursuits often lead inevitably to abuse as Jacques well describes which seems different from the inevitability of the extra-ordinary challenges a boat faces on ocean passages. Having just finished a 2 1/2 day crossing of the North Sea, I am also reminded of how hard work I generally find open water passages are for people as well, even relatively benign passages as ours was.
Dick Stevenson, s/v Alchemy

Ben Rusi

Hi Dick, regarding your North Sea passage……. from where to where did you do it and generally speaking how was it?
My future plan, from Galedonia Canal to Norway.
Txs, Ben (Freedom 32 “Christel” of Lunenburg, NS)

Travis C.

Nice write-up Matt. A good reminder of courses I’ve had during my instruction. For those who love books that send you to sleep, Lloyd’s “Seakeeping” gives great information on determining the effect that various sea states have on vessels. Rather technical, but comprehensive. I think it’s available as a Google book as well…

The issue is certainly a long-view one; I just spent two days on the Chesapeake that undoubtedly loaded the boat in question great than five weeks of Pacific Ocean sailing with several squalls did. But in the long run, a skipper’s choices add up. Additional cyclic stresses that a boat experiences: wind loading (obvious, but there & a factor in sail life), thermal (depending on your location & seasons), and rudder systems.

Jacques Landry

I just thought of another “cycle loading” aspect : In a weekend club race, there might be more tacks and gybes (with the inevitable mistakes) than during a 2-3 weeks ocean crossing !

But don’t read me wrong : this is a very nice analysis and I agree with it, it just you are still young so us old salts need to put our 2 cents in 😉

Matt Marsh

Jacques, you are certainly correct that it’s not a “black and white” comparison, and that a club racer is subject to some loads that an ocean cruiser might not see (e.g. lots of winch gorillas running around on deck at every tack).
The point about running a racer over-canvassed and near the limit, with rough tacks and the occasional crash gybe, is an important one worthy of further emphasis.
If we are racing, pushing a boat right to its limit and sometimes doing something stupid, we expect that our actions will produce loads near or in excess of what the boat was designed to handle, and that we may break things as a result.
If we are on a long cruise, trying to make sure that we go easy on the boat and don’t overload anything, we do not expect that we will be loading any critical hardware to its limits. But, because of the fatigue that results from loading and unloading each component a million or more times, some of that critical hardware could be only half as strong as we think it is.
It is this insidious nature of material fatigue that makes it a risk. If a part wasn’t designed with fatigue in mind, repeated use- even at loads well below its intended strength- can gradually weaken it. On an inshore boat, other factors (corrosion, overloading, damage, wear, etc.) are likely to take effect before fatigue becomes an issue, but in continuous offshore duty, it’s possible (even likely) for a part to become fatigued before it’s old enough to show obvious signs of deterioration.

Marc Dacey

Matt, my experiences with a 40 year old lake racer and my “never seen salt water” pilothouse cutter would support your theses. The racer, despite being sailed hard and overcanvassed (by myself for the last 14 years..I’m the fourth owner) had its original standing rigging for 39 years (1/4 inch 7 x 19 with Merriman terminals/turnbuckles).

I’ve removed it and bought new standing rigging as a 40th-birthday present “just because”. While it still looks fine, it’s cheap insurance. The fact that I’ve had to retab bulkheads and furniture make it clear that the boat has and will continue to flex, especially as I like to make it go fast. The rigging is hardly exempt.

The steel cutter, by contrast, has 11 5/16ths with Staylok terminals on a similarly sized mast as the old racer: The whole rig is “overdone” by comparision and has, like the 39-year-old stuff, no visible wear. But it too is original to 1988 when the boat was splashed and so before we leave for the ocean, I will “roll back the odometer” with all-new standing (and running) rigging, due to concerns exactly as you’ve expressed. Many of the items I am replacing or upgrading are getting a better and larger set of fasteners based on the same logic. A related habit for the ocean-voyager is to examine the deck each morning for evidence of popped pins or bits of line or metal where they shouldn’t be. They say rust never sleeps, and they are right. Less obvious is the invisble (at first) damage of what you are callling “cycle loading”.

A very good reminder to both lake and ocean sailors alike.

RDE (Richard Elder)

Anybody want an half interest in an (Adventure) Swan 48? All you need to do is charter a helio to fly me out to her. I’ll bring some line for temporary forestay and backstay, a spare hank on jib and a tool box and sail her back.
http://www.wavetrain.net/news-a-views/463-come-and-get-it-free-swan-48-available

re our current discussion: Amazing testimony to the strength of a carbon mast. Still standing after months at sea with no forestay or backstay.

John Harries

Now, if I was not still on a cane…

RDE (Richard Elder)

Hey John,
Do you need a cane to sit in the helio as a spotter?
Richard

Marc Dacey

Don’t get me started. I would very much enjoy a salvaged Swan between, say, 48 and 53 feet.