Carbon Fiber Spars

Moderator: GreenLake

Carbon Fiber Spars

Postby talbot » Wed Jun 11, 2014 3:16 pm

There was a brief discussion last winter about retrofitting a DS for cruising with carbon fiber spars, the main advantage of which is reduced weight aloft. I would like the engineers on the forum to, um, weigh in on how much of an advantage this would really be. A standard Dwyer DM284 aluminum extrusion weighs .908 lb/ft, or 20.43 lbs for a 22.5 foot spar section. A Forte R2490 carbon fiber spar weighs .587 lb/ft, or 13.21 lbs for 22.5 feet. (I am ignoring the weight of fittings and any taper in the spar.) So what would we gain by losing that 7.12 lbs (along with class legality)? What is the effect on righting ability? I sort of understand the concept of 7 lbs at the end of a 22 ft lever, but I have trouble imagining the effect of paring .321 lbs from each one of the 22 feet of the lever arm.
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Re: Carbon Fiber Spars

Postby GreenLake » Wed Jun 11, 2014 5:15 pm

The last bit is the easy part. If you loose 7lbs distributed, classical mechanics tells you it is the same as loosing that much at half the distance, or half that much at the full distance. The additional heeling moment is always the product of weight and lever arm. Now, the actual lever arm is the projection on the horizontal plane. If the boat is perfectly upright, you won't notice a thing. If it is capsized, the lever arm is half the mast length - measured from center of buoyancy, not from the deck.

At 30 degrees of heel, when you are sitting on the rail (not hiking, just sitting) your lever arm is about 2' more or less. I the effective lever arm is half the mast, then it's around 10' and because of the angle, the projection is 1/2 of that. So at that angle you would have to carry a camelbag with no less than 18 lbs of water to balance the heavier mast.

Then there are the dynamic effects. Heavier mast can store more rotational energy, so the boat rolls a bit more. I'm not going to try to capture that in numbers.
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Re: Carbon Fiber Spars

Postby talbot » Wed Jun 11, 2014 7:04 pm

OK, let me make sure I've got this. I assumed a total distance from step to peak of 24', with weight distributed equally over the full length (ignoring the advantage of the hull's weight down low and the disadvantage of the sail and fittings aloft). It looked like the projected lever arm at 30 degrees of heel is based on cot(60). Is that right?

In practical terms, my table below [which I see will NOT format properly as text] suggests that to bring Blue Moon upright after a capsize with its present mast, I would certainly need at least one crew member besides myself. However, it's at least possible my 145 lbs could be leveraged at the end of the CB to right the boat with a carbon fiber mast. That would seem to be the crucial issue if I ever have the opportunity to upgrade. Do my estimates pencil out? Does anyone reading this have some actual experience to contribute? (I mean with sailing, not with trig.)

Code: Select all
                                  Aluminum         CarbonFiber
wt. per foot                       0.908               0.587
length from mast step             24                  24
weight of spar w/o fitting        21.79               14.09
lever arm (capsized)              12                  12
heel mmnt (capsized              261.50              169.06
lever arm (30 degrees)             6                   6
heel mmnt (30 degrees)           130.75               84.53
advantage (capsized)              92.45   
advantage (30 degrees)            46.22


[fixed it for you. ~GL]
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Re: Carbon Fiber Spars

Postby GreenLake » Wed Jun 11, 2014 7:56 pm

I think it's sin, not cot, but that's the trig part.

you need to divide the moment by the lever arm. For fully heeled, you can assume the full length of the CB, so about 3', so you get 87 lbs (261/3) of total moment to overcome, or 30lbs for the weight difference. Not a full crew member, in other words.

A carbon mast would be easier to rig, even a keel-stepped version, and might have other advantages that would make it worthwhile.

There was a discussion in the DSA started by someone based around the difficulty of sourcing replacements for the best racing masts, with the idea that nowadays sourcing carbon spars might actually be easier. If that's the case and if the cost comes down to (roughly) the price of a set of racing sails (or better, decidedly below that) then the advantage of the class rules limiting an "arms race" begin to diminish. Esp. if such a spar would "improve" the boat for people that cruise most of the time and race only occasionally.

What data do you have about availability for such spars where you are? How comparable are the mechanical properties of these extrusions? (Other than weight)
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Re: Carbon Fiber Spars

Postby rnlivingston » Wed Jun 11, 2014 9:26 pm

Being an Ice Boater I'm very familiar with carbon fiber spars. Most ice boats built today use carbon fiber masts. While they work so much better than aluminum, the cost is very high...at least in my opinion. A 16 foot mast for a DN Ice Boat with cost $2200.00 while wing type mast is around $2600.00. Now demand for any ice boat equipment is quite low so production costs are high. We are seeing more and more production soft water sailboats using carbon fiber spars...especially catamarans. Costs are still high, but their lightweight make rigging a lot easier and their bend characteristics make them excellent racing spars. Is it a good choice for the Daysailer? We had this same dilemma when the DN class wanted to move to carbon fiber masts. The group finally decided to try them as an experimental option to see if they really had that much advantage over aluminum. It turned out they did, but so many racers were using them, the class had to accept them. At this time, the Daysailer is no longer a true one design boat. I see this every time I race. One of my Daysailers is tricked out for racing with a newly stiffened hull, tapered mast, racing boom, racing foils and North racing sails. I can point higher up wind and I'm faster on all points of sail. My point is I think carbon spars will just move us that much further from a true one design class.
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Re: Carbon Fiber Spars

Postby talbot » Thu Jun 12, 2014 1:47 am

I think a mast project would need a quote from Forte. I did not see a price per foot for spar sections. A plain 2.5" carbon fiber tube 23' long costs about $1400. That's with no taper, no slot. So a couple of grand for the naked spar would be likely. Plus shipping. Plus fittings. (And surely you are going to get a boom to go with that mast. Can I SuperSize that for you?)

Most of the CF spar manufacturers I found on the web seem focused on big-budget custom yachts. (i.e., call for a consultation on your next trans-pacific voyage.) They are not particularly interested in old farts who simply don't want to capsize their dinghies while gunkholing around some unexotic estuary. But see the latest issue of Small Boat Advisor for an account of how much adventure is latent in gunkholing. Spoiler alert: don't get swept out to sea.
Last edited by talbot on Thu Jun 12, 2014 2:07 am, edited 1 time in total.
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Re: Carbon Fiber Spars

Postby GreenLake » Thu Jun 12, 2014 1:52 am

Doesn't look like this in the ballpark for universal retrofit.
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Re: Carbon Fiber Spars

Postby K.C. Walker » Thu Jun 12, 2014 10:10 pm

So, you may be referring to this topic that I brought up last summer after breaking my mast. Forte is in my neighborhood, so I thought I would give them a call just to check out the possibility. I had pretty much the same idea as you about it just being easier to step. I talked to the owner, who is a nice guy. I met them at the wooden boat show at the Mystic Seaport a couple of years ago. Anyway, when I called I started the conversation with, "this is probably not practical but I thought it would just ask". He said he would be happy to turbocharge a DaySailer, he thought it would be a fun project. Of course, they're real busy with military contracts as well as sailing products so delivery would've been, like a month. As I recall, he said that they would use a 2 inch diameter and a taper for a DaySailer. The tapered 22" poll with reinforcements for the spreaders included was not that bad. I think it was even as reasonable as $1200 (more than I paid for the boat). However, you add the sail track and the masthead fitting and it was starting to look like it would probably be $1600 +. And, what about those carbon fiber spreaders and spreader brackets…

The guy from Forte said with the improved bend characteristics that I might want to consider a larger sail plan and that this would be a good thing to consider before they designed the mast. He said that the control was so much better and that's the bendy top would de-power the rig so well that the boat could easily carry more sail. Well, that sounds great! However, it starts looking like a fair amount of money to put into a DaySailer, one that has become far from classic legal. It is good to know that they are willing to design and build a mast for that reasonable a dollar, as a one-off.
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Re: Carbon Fiber Spars

Postby talbot » Fri Jun 13, 2014 12:29 am

I recall your comments about the larger sail plan. From my standpoint, the object is to make it easier to hold the boat to <15 degrees of heel and to make it easier to recover the boat in a capsize. (I would still use a hinged mast; rigging the boat is no problem.) My recent experience with various sail and wind combinations says that if you can't keep the boat below 15 degrees, it doesn't matter how much canvas you carry. You won't beat into the wind above (or even to) 5.46 knots, the theoretical hull speed. If you spend two or three grand on a carbon fiber mast and then increase the sail plan, you will see no advantage at all over a conventional rig unless you (1) eat fast food daily for a year; (2) put your crew in a hiking trapeze; or (3) add another crew member. You might be faster downwind and in light air, but you could get the same effect for less money by adding a UPS. Which is to say I am still intrigued by the idea, and I hold you responsible for bringing it up in the first place. If I ever end up buying a spar from Forte, you should ask them for a commission.
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Re: Carbon Fiber Spars

Postby K.C. Walker » Fri Jun 13, 2014 9:43 am

It's definitely an intriguing idea. At the time I was considering it, I had to replace my mast. I was looking at $600 + for the mast section from Dwyer. For a mere $600 + more, I could've had a carbon fiber mast. When a $300 used mast became available with all the hardware included, that ended the debate (no waiting and immediate sailing). I have little doubt that it would be nicer once it's all set up, with the present sail plan. That is, better control over what we already have. Also, with less weight and drag aloft the motion of the boat is more controlled. How much? Well… I would love to try it out and see.

I totally agree that the UPS more elegantly solves the light wind sail area situation.

It is rather amazing how little weight it takes to make a difference out on that long lever arm. Would it be enough difference to keep the boat from turning turtle? It would not add any flotation, I would think. It still is intriguing but until I have the need for a mast, I probably won't revisit that temptation.

One of the things that I found intriguing while talking to the guy at Forte was his thoughts on improved bend characteristics and being able to de-power the rig automatically. To get more improved bend characteristics out of my present aluminum mast, I've gone to a higher rig tension, the floating hinge plate (rear pin only), and the powerful boom vang. I'd be curious to know how much improvement in that area one would get with the carbon fiber. Especially, I would be interested to know if there's much difference once you start reefing. My suspicion is that there would not be much advantage at that point. That is, other than having the poll above the sail have less drag and be less weight. I would have to guess that most of the performance advantages are going to be at the edge of the performance envelope.

Once you've decided that your boat is not a race boat, and therefore the need to stay within class specifications is not a factor, these DaySailers are an excellent platform for playing with ideas. One certainly could not build as nice a hull for anywhere near what you can pick up a DaySailer for.
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Re: Carbon Fiber Spars

Postby talbot » Sat Jun 14, 2014 1:53 am

I guess the taper factor depends on where you taper. I looked at the racing measurements, and the official specs are that the taper is in the top 6 feet of the mast. So the taper might come into play on the first reef; probably not on the second. I agree that the DS hull makes a great "blank" upon which to build a really nice adventure boat or mini-cruiser. Most of the things that make the boat more seaworthy for adventures also make it more safe and convenient for family sailing. So you can say you are outfitting for an adventure, even if all you really have in mind is a dinner cruise. As we all know, the stories about sailing are at least as important as the voyage itself.;
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