How important is relative boat weight?

Interesting thought here. When the 18HT was used in the Tybee5 a huge complaint about the boat was that it didn't have the momentum to have much punching power. It just sat and bobbed back and forth.... in that cast it was a boat that was too light. The 20' light boats don't seem to have that problem, I suspect it's b/c of the longer waterlines.

You are right of course (take de Morrison's equation on forces on cylindricals for instance, the same is the case there for the

drag-part

of the equation). What I was thinking is that on these wessels, the wetted surface is relatively small compared to the sail area/area causing wind drag. Hence, the wind drag should be the biggest drag factor..?

Racing catamarans may spend most of their time at sustained speed. But any good cat racer knows that its Blasting off the startline and smooth tacks and bouy roundings are where most of the ground is made in a steady breeze. Accelertion to top speed is essential for this.

I know what you do for a living, you've told everyone it seems. I just believe you are grossly over complicating the argument. Im suggesting that you should go back to the basics to get a better understanding of whats going on.

I try not to spend too much time decelerating when racing so i dont need a heavy boat.

Sue

Are you explaining junior grade secondairy education physics to me and then misapplying it ?

You really have no idea of what I do in my professional life do you ?

of which the drag forces are an very important part as the accelleration is only the result of the net difference between drag forces and drive forces. When both are equal and opposite to eachother the boat stops accellerating and had achieves max sustained speed (=topspeed).

Newtons second law of motion is therefor not a factor with respect to sustained straight line speed (=topspeed) which is what racing catamarans spend by far most of their time doing.

Of course, in reverse, a heavier boat decellerates (slows down) less then a lighter boat in the lulls and when encountering waves. A light boat may win at the start-line but will loose in the lulls by the same token.

You cherry pick concepts and then simply ignore the reverse effects to argue your case. A failing grade skill level even for a junior secondairy level pupil/student.

Wouter

It is not so much a factor of being lightweight but more of being insufficiently damped.

It is the same with a car that has worn down dampers in its shock absorbers; it is very difficult to keep that car on the road in corners or uneven roads as well for exactly the same reason.

A long hull will introduce disproportionately more damping then the increase in mass-a-top and sailarea. All these dependencies are highly no-linear and that is why so many people become confused when the only look at the specs of boats and not model the behaviour mathematically.

Wouter

In the context of beach catamaran's (and high performance dinghies) which is what I beleive this thread is all about, Uffa Fox's comments still hold true, a lighter boat is always better than a heavier one.

Of course that does not mean that you can't design a lighter boat that is slower than a heavier boat, and you will be able to find examples where this does not hold true, but that is only because the lighter boat was not properly optimised.

Gareth

>>>Hence, the wind drag should be the biggest drag factor..?

I can't comment on the relative proportions of all the drag components, but consider that if you take a high performance rig and stick it on an ice boat it is capable of going 4 or 5 times faster than on a beach catamaran. To me, that's convincing evidence that the hull drag is still the highest contributor to overall drag.

sm

You can have a light boat, even one built without exotics. But it won't be as strong or as stiff as one thats built with high modulus materials.

I mention this here because I have been banned from the F16 Forum and there was an active discussion happening there until the moderators decided that it wasn't in the class' best interests.

no prizes for guessing what this boat is <img src=

alt=

/>

Another pic of a lightweight boat...

Macca,

You have not been banned ! (yet !)

It is only that your posts concerning F16 class rules and F16 boat weight are being locked down or deleted as you refuse to adhere to official F16 class procedures regarding rule changes and common respect for factual discussions. Many times over you have been both invited to submit official proposals for processing and warned of the next steps in the disciplinary path when continuing to grandstand.

Stop playing the victom !

Wouter

Macca makes a good point, when I said a light boat is better than a heavy one, I meant in terms of performance only, if you can't finish the race then you have gone too light <img src=

alt=

/>

I should have said a lighter boat is always quicker than a heavier one all other things being equal, but not necassarily better.

Gareth

That kind of cracking does not just happen on lightweight boats. That same kind of vertical hull crack, aft of the front beam, happened to us on a Hobie 18. I, as crew, was out on the trapeze, and it was maybe a couple of minutes after the start of the race when all of a sudden the hull just started to split open right in front of my forward foot. Very unusual location for a crack like that.

We managed to get the boat to the beach on the same starboard tack, keeping the starboard hull as far out of the water as possible. (Still got full of water, though.)

Mary,

Did you ever find out what caused the failure?

Such a crack will happen on any catamaran irrespectibally whether it is a 180 kg F18, 75 kg A-cat or a 18 ton Groupama 3 when an internal element like a bulkhead or subdeck comes undone or cracks due to production errors and no longer supports the hull skin.

As a result such damage has happened to pretty much any design out there in the world today and will continue to happen in the future. Boat builders are still not applying aeronautical or space-age quality control systems; as such these incidental mishaps are recurring.

More importantly is whether the company building/selling the boat takes responsibility and handles the warrantee in a proper way. That has always happened thus far.

Wouter

Mary's right - I have seen a very similar-looking issue on other

heavy

boats. Showed up on my old Mystere 4.3, which could never be confused with a high-tech lightweight boat. Not nearly a fatal issue, either - it was a straightforward repair and was completely invisible when complete. I sailed the boat for another two or three seasons without recurrence.

In the right hands, boat repair is not a death knell for racing boats - I think too many boats are

totaled out

after collisions and failures. Effective repair doesn't necessarily mean significant weight added.

I've read this thread and it's esoteric theory, anecdotal evidence, suppositions, etc. Simply proof to me that too much time is spent on worrying about reasons for a poor showing. There was a glimmer of light when people started ranking time on the boat above other issues, but then the wheels came off again. Full-circle, we're back to F16 sniping? *yawn*

Thanks for the numbers, that brings some light in the discussion. I don't worry about cat/sloop. Also the quality of Portsmouth numbers may be debated, but for our discussion it is fine.
In light winds, where we all agree that lighter is faster, 125lb heavier is just a 2.2% penalty. So 12.5lb weight increase is 0.2% penalty. That is just nothing, at least for me.
Maybe you talk with your upper skill sailor friends about this 125lb = 2.2% slower relation. Could get another anecdote.
What is the beam and mast height of a CFR20?

Cheers,

Klaus

Sue,

It must be very calm with no waves, that you can maintain a constant boat speed (and ones again, I agree, that in light wind the lighter boat is faster). I have attached a speed vs time gps track. Medium off-shore winds, waves 0.5m, Dart 18, data points are spaced every 15s. You can see the tacks as deep low speed points. But between these points there is not really a constant speed. Well, maybe I am a bad sailor... <img src=

alt=

/> then again I spend better my time in sailing the reducing the weight.

No, I don't, I think about about acceleration and de-acceleration, about light and strong wind, about steady movement and dynamic movement, so please don't blame me.

Cheers,

Klaus

The CFR currently has a beam of 8.5' and the same mast/main sail as the M20.

I have yet to see a F18 with such a failure. but to build a boat down to a very light weight and not use exotics will increase the chances of such a failure. Hence the Photos I posted of a F16 with catastrophic hull failure.

Macca, you did not say what brand of boat that was, and where, when, and how it happened.

I could give the details but then I would be accused of picking on a particular class...

They know who they are and they also know my position on their boat weights and current class rules.

macs - I respect you a great deal. I'm nearly a fan. But you're cherry picking the facts to support a position that has no bearing on the topic of this particular thread, unless your point is merely a cautionary statement that pursuit of lighter-weight platforms can be taken too far. I've seen structural failures (as have you) in

tough

boats like the Hobie 20, the Mystere 4.3 and the Nacra 6.0 - boats that some would contend are not good race platforms because they're

overbuilt,

even though each of them enjoyed excellent class racing in their day. I remember, not long ago, there were rancorous posts from people that seemed dead set on forcing the F18 Class to begin a phase-in of reduced weight boats because manufacturers

can.

I think that was just as much of a dead end as debating what they

can't.

On topic and paraphrasing a couple of great sailors - Bethwaite and Melges; Remove the excuses. Prepare your boat and kit as best you're able so that you'll have that confidence when you're on the race course. People carry this advice out to varying degrees. I know having a boat that is a specific weight is part of that preparation for people that I race often. I'm fortunate that it isn't something that worries me anymore with my current boat - at first I obsessed over it, but racing in the US F18 fleet has shown me there are other areas that require more of my attention.

my point is that the F16 class get on their high horse (lets call it a shetland pony) about the fact that the min weight they have set is perfectly easy to achieve and can be done so without increasing cost or reducing longevity.

Now at the last F16 intergalactics or whatever the event was called there was one boat that met the min weight set by the class. The average boat weight was more than 5kg over the min weight!

There are a good percentage of

professionally

built F16 platforms that are not withstanding normal use. Now I am certain that its possible to build a F16 to min weight by not using exotics but do do so takes an innordinate amount of time therefore increasing costs far above what is commercially acceptable.

To speak of realtive boat weights in terms of performance you must also factor in platform longevity. spending a lot of money on a light platform is one thing, having it last more than a season is another part of the equation.

You're sawing a familiar tune, but it's no toe-tapper. Point made, and time will tell - maybe sooner, maybe later. <img src=

alt=

/>

Quote

Exactly.

When structural materials seem to be failing, new methods of strengthing them should be sought out. Here's an idea that might help an issue apparent in this thread. <img src=

alt=

/>

UCLA research

LOL

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I Am A:
(please select)

sailor
Cat sailor
F18 sailor
F16 sailor
OD sailor
Pro sailor
dead boat sailor
retired
cyber sailor (and in the top 100 of tacticat rankings)

Everyone has read your

opinion

of weights and class rules. Your agenda to contiue harping on it does reflect badly on both yourself and your sponsors. Catamaran sailing is in decline and rather than expending effort in trying to use youre skills and position to grow something you feel the need to berate others and tear down what at least a few people feel is a good concept.

If you must bash boats on-line then you had better upgrade your conection speed becuase there is not any line of boats that I know of that have been built problem free no matter how heavy or light.

I have owned 2 H16s which had to have hulls replaced and this is a boat in production for almost 40 years and considered the benchmark for a

tank

beach cat. (I have owned 7 varying as much as 15 lbs in weight bty) Most of the first H20s had their rear beams pull out, a bunch of the first Caps in Europe all had to have hull defects repaired. I have fixed my fair share of other hull defects and failires on Hobie, NACRAs and all of the Trac 16's I have ever seen had their deck plates rip off sooner or later. One of the new Infusion owners I know spent 3 weekends putting his boat togther due to missing and incorrect parts, only to have his hull split in half on his very first sail. Your new V40 ride seems to be a little sensitive as well.

My point is, everyone involved in sailing can add stories to this list. Boats are built by people and there will be issues from time to time. NO class is free of problems no matter the weight. I do not agree with censorship, but a lot of people spend a lot of time effort and money all across the catamarn community to try and keep it alive. Rick and Mary have spent a lot to provide this forum as a place to promote and share ideas. Ideas are one thing and no one has to agree with them, thats the beauty of it. Deliberate and repeated cut downs of something though maybe provides a legitimate case for being banned.

Ok, lets change tack here.

If I put two Blade F16 on a beach, identical hull shape and setup. Both boats had the same overall weight and complied with the F16 rules.

One boat was a std Blade as delivered by Vector works, glass hulls, alloy beams, boom, spi pole and mast.

The other was build using carbon hulls, beams, boom, spi pole and mast.

Which boat are you going to choose? (anyone who says the std boat can leave the room right now)

So you are banning me from the room? <img src=

alt=

/>