Saving Weight

[Cheechako]

If you really want to accelerate faster up to hull speed get rid of weight in the rig and sails. More sail area = more Horsepower.
Unless you plan on surfing, your speed is limited by your waterline length. You just need enough HP to get there, regardless of your weight overall.

[hellosailor]

Thinwater, did I miss it? Or did you not state your rationale for saving weight?


Are you looking to cruise faster, or outright race flat out?


The cruiser compromises on costs, the racing zealot burns dollars.


If you want "fast" you get rid of every stainless or brass fastening and rigging and block on the boat. That's what titanium is for. You also get rid of any dinnerware, and replace it work titanium sporks. Got a 3-burner stove? Replace it with two burners and no stove, big weight change. Got a head? Get rid of the door, replace all doors with curtains. Replace any tower bars with light plastic hooks.


Look at anything made from wood and consider replacing it with honeycomb composites. Or at least, taking a sander and seriously thinning it down until the engineers get uneasy.


Prop shaft? No, really? A shaft weighs more than a composite or titanium tube. Betcha the companionway steps could also be replaced with lightweight aluminum, if your titanium budget is spent. As well as the companionway hatchboards. Got settee cushions? Sure there is no lighter alternative for them too?


Anything in the galley that you wouldn't be willing to carry on an assault on Everest? replace it too, look at the lightweight mountaineering gear.


A friend of mine had the builder re-spec this floorboards to save weight. The new ones literally rebound under your feet, flexing with every step. But, they're strong enough to work.


There's even the bottom paint to consider. Remember how heavy a gallon of antifouling weighs? Keep it down to a single coat, maybe save fifty pounds right there.


And of course the lead-acid batteries must be replaced by lithium, that's good for at least half the battery weight gone in one shot.


A lot of structural parts on a lot of things can literally be turned into "swiss cheese", if you know your engineering (or hire an engineer) and make the lightening grooves, cuts, or holes where they won't compromise the strength.


It all depends on what you goal is, and badly you want to reach it.

[thinwater]

Originally Posted by mikereed100

Have you noticed a difference in speed? I've considered doing the same but I wonder how much of a performance benefit I would actually see.

I have done most of the things mentioned on this thread; water-maker, glassed-in backing plates, getting rid of unused stuff, books and DVDs are on the hard drive etc. To be honest I don't see much of a difference. When we fill our fuel and water tanks the boat gains 2200 lbs and I always expect the boat to slow down but we seem to carry on as normal. We are surely a bit more sluggish but I don't notice it. I continue to try the lighten the boat but I am no longer obsessive about it. I particularly don't scrimp on tools or anything that will keep the boat running. I hope to eventually get rid of the band saw, drill press and chop saw, but will always carry scrap wood, fiberglass and epoxy. Hopefully the carbon fiber toilet paper will help to compensate.

The short answer would be to refer you to this long blog post:
Sail Delmarva: Extended Transoms: The Process

A few tenths when above hull speed, very little in light air. Mostly it helps up wind, with L/D is everything, and motoring when the transoms are lower.

For me, the big help was loading and unloading. Nothing like twin swim platforms on a cat.

[thinwater]

Originally Posted by hellosailor

Thinwater, did I miss it? Or did you not state your rationale for saving weight?


Are you looking to cruise faster, or outright race flat out?


The cruiser compromises on costs, the racing zealot burns dollars.


If you want "fast" you get rid of every stainless or brass fastening and rigging and block on the boat. That's what titanium is for. You also get rid of any dinnerware, and replace it work titanium sporks. Got a 3-burner stove? Replace it with two burners and no stove, big weight change. Got a head? Get rid of the door, replace all doors with curtains. Replace any tower bars with light plastic hooks.


Look at anything made from wood and consider replacing it with honeycomb composites. Or at least, taking a sander and seriously thinning it down until the engineers get uneasy.


Prop shaft? No, really? A shaft weighs more than a composite or titanium tube. Betcha the companionway steps could also be replaced with lightweight aluminum, if your titanium budget is spent. As well as the companionway hatchboards. Got settee cushions? Sure there is no lighter alternative for them too?


Anything in the galley that you wouldn't be willing to carry on an assault on Everest? replace it too, look at the lightweight mountaineering gear.


A friend of mine had the builder re-spec this floorboards to save weight. The new ones literally rebound under your feet, flexing with every step. But, they're strong enough to work.


There's even the bottom paint to consider. Remember how heavy a gallon of antifouling weighs? Keep it down to a single coat, maybe save fifty pounds right there.


And of course the lead-acid batteries must be replaced by lithium, that's good for at least half the battery weight gone in one shot.


A lot of structural parts on a lot of things can literally be turned into "swiss cheese", if you know your engineering (or hire an engineer) and make the lightening grooves, cuts, or holes where they won't compromise the strength.


It all depends on what you goal is, and badly you want to reach it.

I very purposefully did not specify. It's been a good discussion. I've had a 27' / 1200 pound Kevlar cat and I've had a cruising cat. Mostly now I am interested in cruising, but I like an efficient boat.

Many respondents think this is all about speed. It is not. Weight in the ends or up the mast make the motion worse. VMG to windward means you sail instead of motor. Less weight might mean you can carry more food. And no boat is at its best over weigh. Why did I stretch my boat? Primarily to improve boarding for my disabled wife. So there are many reasons to do things.

I did mention that ideas should pass the $/pound litmus test. That means you can set you own value, but it must be examined rationally. I was thinking about G70 chain vs BBB and not carrying more than you use, rather than spectra shackles (though I have a few of those for non-weight reasons). Floor boards are valid; a dockmate replaced the floor in his Prout and it was 1" thick solid wood, more suitable for a chopping block than something mobile. There is a middle ground.

[hellosailor]

"Weight in the ends" or on the mast, that's called balance, not just weight. And the combination of balance and weight and where everything centers, can make the boat counter-intuitively more unbalanced or less sea-kindly than not. Like the old warships hoisting cannonballs aloft, to reduce the rolling motion of a ship. So, I just focused on "weight". How you balance it, well, once you get some proper hydrofoils installed, that will all change anyway.(G)

[UNCIVILIZED]

Originally Posted by poiu

How much difference does it make on a mono? I know it makes a massive difference on a light cat to go from under to overloaded, but on my 42 ton mono, probably not much?

I've thought about this and by spending a good chunk of money I could shave up to 3 tons off the boat. Maybe 1 ton for free or cheaply, going up in cost to unviable loony levels.

If I can do 6kt reaching in an 8kt wind now, what will happen if I am 2 or 4 tons lighter as an example?

How much depends on; how in tune with your boat you are, how hard you push it & or compete, how much weight you add/remove & where on the vessel it comes from/goes.

I mean there are 60'-80'ers who'll leave a crewman or two on the dock for the day if the wind's light. And such as been the case for decades. Long prior to the suber light boat, racing craze.

Or, put simply, if you're backpacking in the mountains, does 1kg added to, or removed from you pack make a difference?
To me it does! Yet it's all of 1% of what I weigh, Before I don the pack.
And the numbers ration work out similarly for 100kg on a 10,000kg boat. So IMO, it the weight matters.

Heck, just ask yourself how you'd feel after carrying that extra 500kg - 1000kg (or more) ashore. As the boat has to carry it everywhere it goes.
Or if you can swing it, go or a ride on a boat with water ballast, & feel the acceleration when they dump a ton or more ballast overboard.


To answer the question as to whether or not there are boats which are faster when they're heavier. The answer is a categorical, YES. Albeit, it's not common, & finding such designs is a rarity. But they do exist. And for several years, drove the racing rule makers loco, in the later '70's - early '80's.
I'm sure that Bob Perry, & some other prolithic designers could come up with a few. As I was just a wee lad back then.

[GILow]

We've come down from nearly 18 tons to 15 tons through a process of removing everything as uncivilised suggested and only putting back what we needed. That saw a good half ton in spares that were no longer functional or applicable to components in the boat. I also made nearly AU$1k at the scrap metal merchant. But one of the sleeper items of really impressive weight was the laminex liners on everything. They easily came to 100kg or more.

Also took a moment to move big items like the battery bank to improve trim.

The boat sails a hell of a lot better now.


Sent from my iPad using Cruisers Sailing Forum

[mikereed100]

Originally Posted by thinwater

The short answer would be to refer you to this long blog post:
Sail Delmarva: Extended Transoms: The Process

A few tenths when above hull speed, very little in light air. Mostly it helps up wind, with L/D is everything, and motoring when the transoms are lower.

For me, the big help was loading and unloading. Nothing like twin swim platforms on a cat.

Interesting, I would have thought the opposite, but the slow-witted are often surprised.

Back on subject, I think a lot of people underestimate how much clothes and linen weigh. A lot of weight can be saved by cutting back on spare sheets, blankets and clothes. This may be easier for a retired couple with a home base on shore who are on a tropical cruise, not so much for liveaboards who are still working and are sailing higher latitudes. My wife's philosophy is 'you can never have enough pillows' which drives me nuts due to the weight. On the other hand, I feel lucky to have a partner who is willing to put up with all the sacrifices to share my dream so if it's pillows she wants, it's pillows she gets. the same goes for the ceramic bowls our daughter made. The shelves are bowing under their weight, but I know better than to even mention it.

[barnakiel]

Originally Posted by poiu

After having filled up all the tanks recently and observing the waterline, I reckon on about an inch per ton. If slow speed performance is roughly proportional to wetted area then maybe each inch is only a couple of percent of my wetted area as a wild guess, so 2 tons weight reduction = 4% wetted area decrease. So a speed of 6kt becomes 6.24kt after a diet. Is that how it works?

I believe this is the general rule. % less wetted area = % more speed. I cannot say if the relationship is exactly linear for big changes, but even in the worst case scenario, for small changes, its approximation may be linear (due to properties of tangent lines).

In the racing aspect, less weight also counts as better acceleration, this is a plus when you consider one boat may go on the plane while the other may be just a bit too heavy! But the downside is that less weight also implies less momentum ;-( I think this is why racers like to have plenty of the weight in the bulb and as little as possible in the rig. Same weight, different distribution, big speed and handling differences.

When you think of the wetted area, consider benefits from having yours very very clean. As soon as the flow turns from laminar to turbulent, drag grows very fast, so you want to have laminar flow as far as possible, so you want to have that wetter area very very VERY clean and smooth. IMHO, in the cruising aspect, this may be better / easier gain that the one gotten with shedding weight.

And do get a folding prop - this is around an extra 0.5 of a knot in light to moderate winds.

b.

[hellosailor]

Well, let's say you have a 9AM start and a 3PM "first finishes". Six hours at maybe ten knots, and the first two boats usually cross within 10-15 seconds of each other. So that's a ten second lead being critical--after a ten six hour race, which is 360 minutes? 21600 seconds? long. Ten seconds out of 21,600 is a tiny fraction of a percent. If you can make your boat even 1/10th of one percent faster, you'd still come in third place.


When folks start to lose by those margins, they get out the sandpaper and start thinning out the remaining paneling.(G)

[UNCIVILIZED]

Regarding onboard weight. It probably wont work with the wife, but give everyone a locker, shelf, & or duffle bag for their personal gear. Which they can fill with whatever they like. Even the kids. And, knock on wood, it does a pretty good job of limiting excess gear.
Plus, the same principle(s) can be applied to storage space X, reserved for; linens, clothes, or whatever.

Also, a LOT of (heavy) interior stowage, which normally is made of; lumber, fiberglass, etc., can be replaced with; canvas, mesh, netting, & or isenglas. And you can make some Trick hanging bags/stowage, by attaching bolt rope to the edge(s) of said storage, so that it can be "tucked" into out of the way spots, & you know that it'll stay there.

One of the other perks of this kind of soft stowage, is that much of it breaths, thus cutting down on dampness & or mold.
That, & you can see if what you're looking for is in the "locker" without opening/digging through it.

To deal with the changing climates, & the subsequent changing clothes & bedding needs; some would say that when you're heading off to somewhere chilly, then you stop in the local thrift shop & pick up what you need for said expedition.
Then, when you're going the opposite direction, you sell or donate same.

For the Drag vs. WL/Wetted Surface thing. Yeah, more surface area is slow, at low speeds, but once you put any real way on (3kts +/-), the extra WL more than pays for itself.
And when it's light, especially if you're going downwind, shift as much weight as you can, forward (within reason).
Because the bow being slightly more immersed produces a LOT less drag & extra immersed surface area, than does a heavy, dragging, rear end.

And if you're going to break out the sandpaper. The first place to go to work is on your foils (after you've templated them), then the first 6'-10' of the bow.
As, generally speaking, it's tough to keep the flow attached much past the 2-3m mark. Or at least to keep it attached consistently.
- That, & the fanatics out there will tell you that #1200 Wet/Dry is the minimum level to which you need to polish things So yeah, about as course as an angora sweater.


PS: Here's a reference article which covers a lot on this topic http://l-36.com/ep_advice.php