How to cut weight in a multihall

[madprops]

I’m looking for ways to cut weight in a multihall. Most of the boats I’m looking at are trimarans with a lot of wood in the interior. I was wondering if anyone has ever tried pulling out the cabinets, tables, ect and making them out of carbon fibre to save weight? I would also like to hear other modifications you could do to save weight. I already know to pack super light, and not cram all the holds full of stuff, I’m more interested in mods like carbon fibre stanchions and other low weight things that can be done, but I’m happy to hear all your ideas.

I’m interested in cruising trimarans like the Searunner or cross, and from what I hear an easy way to make them fast is to make them light.

[Chotu]

Mostly it will come down to your tankage and your gear. If you go ahead and take note of the way the Cabinetry is built, the way different non-structural bulkheads are built, and check out the weight per square foot of the current material vs. weight per square foot of carbon foam sandwich, you will find that changing materials doesn't save you much weight at all.

You are talking about saving hundreds of pounds. Just a couple hundred or something. Like having one other crew member on board.

Wood can be built very close to carbon in weight. It just can't be overbuilt.

You actually have to do the math on this one.

If the Cabinetry was built in a weight conscious way, not perfect like we have today with carbon, but at least eight weight conscious way, you will find it there is very little weight savings changing that to carbon.

Not to mention, there are thousands of hours in building those cabinets out of carbon with a foam sandwich.

[Hesti]

Low battery weight. Smallest possible engine. Ground tackle. Tanks and especially the stuff in the tanks.

[thinwater]

Ground tackle

• rope vs chain
• G70 chain
• Light (but smart) anchors

Power system

• LEDs (makes power system lighter)
• Batteries, even LiFePO4. Lead is heavy.

And above all, simplicity. None is always lighter.


Re. cabinetry, fabric is lighter still.

[madprops]

Originally Posted by Chotu

Mostly it will come down to your tankage and your gear. If you go ahead and take note of the way the Cabinetry is built, the way different non-structural bulkheads are built, and check out the weight per square foot of the current material vs. weight per square foot of carbon foam sandwich, you will find that changing materials doesn't save you much weight at all.

You are talking about saving hundreds of pounds. Just a couple hundred or something. Like having one other crew member on board.

Wood can be built very close to carbon in weight. It just can't be overbuilt.

You actually have to do the math on this one.

If the Cabinetry was built in a weight conscious way, not perfect like we have today with carbon, but at least eight weight conscious way, you will find it there is very little weight savings changing that to carbon.

Not to mention, there are thousands of hours in building those cabinets out of carbon with a foam sandwich.

I'm not sure where you get the "thousands" of hours from so I can't speak to that. From the home built searunners and Cross Trimarans I have looked at you could save around 200 lbs with just cabinat doors, drawers and tables remade, and removing some storage that is not needed.

I have a close friend that works with carbon fibre and has all the tools/bags that I would need (I also may have saved his life )

My end goal is to try and save around 500 to 700 lbs in mods on a 37' to 44' tri. water tanks can be run dry and fuel can be burnned, and not that I have a lot of gear but if I did, it could be left on the dock.

[madprops]

Originally Posted by thinwater

Ground tackle

• rope vs chain
• G70 chain
• Light (but smart) anchors

Power system

• LEDs (makes power system lighter)
• Batteries, even LiFePO4. Lead is heavy.

And above all, simplicity. None is always lighter.


Re. cabinetry, fabric is lighter still.

I didn't think of fabric! that is a wonderful idea! Also much faster.

As for the batteries, I would plan to go with the lightest, but will have to save money for that. The good thing with lithium is that I can also add to it without getting all new batteries, just have to make sure I set it up so I can add on easy. That way I can start very small and just get the bare minimum AH that I need. There is also weight to be saved in solar panels.

[44'cruisingcat]

Carry a watermaker instead of water.

[mikedefieslife]

Batteries
Water
People
Diesel

These are heaviest items on any boat in terms of kg/m3.

So before you even bother with cabinetry you'd do well to buy LiFePO4 batteries saving of around 80kg on a typical 4 battery Trojan bank. Then a water maker. If your tankage is 200l, you can carry just 100l and save 80kg by having a 20kg watermaker.

Next it's people. "Solo sail is best sail"

You also need to be prepared to carry hand tools only and to limit your spares. This might restrict your cruising (these are Cruisersforums after all).

Better instead to just buy a Neel and be done

[Dave_S]

Synthetic rigging.
Tender


Today I cut out some large holes 165mm to fit inspection hatches. The material that came out was 2 x 400gsm glass on both sides covering honeycomb. If you have the same material you would have to replace large amounts to lose much weight of significance.

[Chotu]

Originally Posted by madprops

I'm not sure where you get the "thousands" of hours from so I can't speak to that. From the home built searunners and Cross Trimarans I have looked at you could save around 200 lbs with just cabinat doors, drawers and tables remade, and removing some storage that is not needed.

I have a close friend that works with carbon fibre and has all the tools/bags that I would need (I also may have saved his life )

My end goal is to try and save around 500 to 700 lbs in mods on a 37' to 44' tri. water tanks can be run dry and fuel can be burnned, and not that I have a lot of gear but if I did, it could be left on the dock.

Of course the time it takes depends on the number, intricacy of the cabinetry and the size of your boat. Don't underestimate the hours. Go for the low hanging fruit first. Tankage, gear/equipment as mentioned by the others.

My point is, do the math. It doesn't save all that much weight assuming the cabinets weren't built with 3/4" ply or something outrageous like that.

How much does your current cabinet material weigh per square foot or square meter?

How much does your proposed cabinet material weight per square foot or meter?

How many square meters total are you replacing?

(Weight old material )x(area to be replaced)-(weight new material)x(area to be replaced) =????

[mikedefieslife]

Originally Posted by Dave_S

Synthetic rigging.

This adds a lot of windage though by having to go up a couple of sizes in diameter plus probably adding UV/chafe sleeves. Unlike with monohulls, and to a lesser extent catamarans, the weight aloft isn't going to affect a trimaran as badly.

[madprops]

Originally Posted by mikedefieslife

This adds a lot of windage though by having to go up a couple of sizes in diameter plus probably adding UV/chafe sleeves. Unlike with monohulls, and to a lesser extent catamarans, the weight aloft isn't going to affect a trimaran as badly.

I have never heard this before? Also wouldn't it still affect the total weight?


So far there have been some really cool ideas. Keep in mind i'm looking for mods to save weight. I know about the low hanging fruit (liquid, junk, people)

I have a very light but still great aluminum anchor that I could use with all rope and drop the main anchor/chain off on a friends boat or at the dock.

any other mods I could make to a boat to cut back on weight with out making cruising suck to bad.

[thinwater]

If solo, us a kayak for a tender. Light, no motor, and more fun. Heck, I carry one on my F-24. The Walker Bay Airis is only 14 pounds.


Synthetic lifelines. They don't last as long on monos, because people lean on them. Cas they do fine. Watch for burs in stanchions.



I've written article on evaluating weight in $/pound, depending on location. The easiest savings are often NOT carrying an item.

[Hesti]

Engine. An old 2 stroke outboard will likely be far lighter than a diesel inboard at the same hp. If you reduce hp on the outboard versus the inboard, you may save even more. There were times when 15 hp in a boat was a lot.


Of course, less engine hp will reduce your ability to go to windward against strong wind and waves, an outboard is more prone to be stopped by high waves than an inboard and a very light ground tackle almost certainly has less holding power than one with conventional chain ...

[thinwater]

Originally Posted by Hesti

... very light ground tackle almost certainly has less holding power than one with conventional chain....

In fact, when weight matters, this isn't even close to true. Chain has advantages (chafe, yawing in light winds), but ultimate holding capacity is not one of them.


I've dragged with chain but never with rope. Yup, there were other factors, but the chain rig was MANY times heavier.



I'm currently doing a bunch of stuff with Practical Sailor relating to anchoring with all-rope, and yes, my last boat was all chain, so I know both well. Heck, I published a book on the subject. Thousands of hours of testing.


You just need to be smarter with rope.