So there is a speed advantage by having more beam.
But what is the difference in acceleration?
If you gain maybe 4 meters every tack than that will add up during the race.
Is there a way to calculate these variables as well?

I think that is so dependent on crew skill that it would be very hard to measure.

Sailing by yourself, on handicap or small fleet, the difference would not be noticeable. In a reasonable size OD / Class fleet, it is a game of inches when you are trying to sail under or over another after a start or on an upwind. Those inches can turn into many boat lengths if you get spat out.

As Tony_F18 pointed out, there is also a difference in acceleration when graced by a gust. It is more important on lighter boats where gusts will result in more healing motion before accelerating (Boat appears more 'flighty'. Wider beam means the boat will transfer the energy from each gust sooner and more efficiently into forward motion.

Even if you gain an extra 1 foot every gust, it will make a big difference when you are around other boats or coming in contact with other boats further down the course / race.

To all,

My own performance models predict a speed increase significantly more then SCHRS suggest, but it is still not a huge amount. Added to this is the comment by designer/builder John Pierce who widened the Stealth to become the Stealth F16 (among other changes) and said that the new layout made a very significant difference. Note however that the new F16 mainsail was part of these changes and will have caused the bulk of the performance increase.

For a 2-up boat my models predict a upwind speed increase in the order of 1 to 1.5% ; over an upwind-downwind race course this translates into about 25 seconds per 45 min. race.

The 1-up setup the increase is about 0.3% less => 20 seconds.

That is what my models say.

Of course these increases ONLY apply when the crew is maxed out on righting moment, meaning fully trapping and is depowering the rig. There won't be much of a performance difference at all in all other sub maxed out conditions.

However I also agree with Rolf here; 20-25 secs in a 45 min (fully trapped upwind) race is pretty small for 85% of all cat sailors and I'm not sure that it warrants the expenses to modify an existing Taipan to full F16 width. I think investments in a selftacker and new full F16 mainsail will result in much more gains and make the tramp alot more roomy.

We must also not forget that making the platform wider has a serious effect on the overall platform stiffness unless you make the new beams stiffer. This will most certainly require rebuilding the beamlandings. Again, I'm not sure whether it is worth the effort.

At some point it is just more financially attractive to buy a set of F16 hull and beams and then transfer your Taipan gear to that boat.

It is also my personal opinion that any perfermance difference in the order of 1% istoo small to be really noticeable on the race course unless you are racing in a really skilled fleet. 85% of us throw away multiples of 20 seconds by imperfect sailing and trim already and improving on that is nearly costless.

Wouter

The resulting feel is a boat that is more calm (sideways) in the gusts.

This is indeed a point that was taken into consideration when drafting the F16 class rules.

This enertia difference is actually quite noticeably.

For a 1-up boat the difference is in the order of 10%-15%

For a 2-up boat the difference is in the order of 20%-25%

That is with respect to increased enertia (=momentary righting moment due to accelleration of the crew upward).

Basically, for the same accelleration (speed) of the crew and luiff hull being lifted up away the watersurface the boat with F16 width will have, roughly speaking, 15-25 % more momentary drive, meaning the boats accelleration forward will be momentary 15-25% more. That is till the point where you sheet out and balance the boat at which point the difference in drive will only become in the order of 2-4% again.

How these differences are translated in to increased speed or covered distance is a different topic. 2%-4% increase in sustained drive for example will only result in about 1-1.75% increased sustained speed for example. Short momentary increased accellerations can quickly be downgraded to only a few meters of gained covered ground because these differences only last for a few seconds at the max (in a race of 2700 seconds !).

Of course a side effect of the wider boat is that this momentary increase in drive will push the bows down more during a gust and make a dive upwind more likely. I have personally never felt this to be an issue on the F16's but there are reports by some owners who have pitched the F16 upwind. On the other hand I wouldn't want to make the F16's wider then they are now, I do believe we are right on a max limit as we are. Some more lengthwise stability (T-foil rudders) on the downwind leg and the F16's will be fully maxed out with respect of what is potentially possible for a boat this size. And in my opinion that is quite alot especially compared to how it does in relation to larger boats.

Wouter

Improving on skills are not costless. It takes time and effort => work. Real work if you really want to improve. Much easier to spend money, or not, so we can put the blame for lack of performance where it belongs.
It is not just the odd 20 secs here and there, but the whole range of skills to master and finding the groove at all times. Need to spend lots of quality time on the boat to get all this right, and then there is the mental game in addition.
I guesstimate the number of 85% could be even higher.

Wonder if the original poster expected the current discussion

I think a 1% improvement in speed is very significant. Especially if it is enough to just inch ahead of the competition and gain clean air while feeding the competition bad air. If you can get to this position tactics become so much easier; and personally I find I make far less mistakes (goes back to the mental part of the game) and try less risky tactics when I know I have speed.

Too much beam can make you go slower in marginal conditions. It takes more breeze to get a hull flying and get the reduced drag happening. I would suggest it is one of the reasons A-Cats are so very fast in marginal weather.

To go back to Ausstricker’s original question.

Advantages
- Increased righting momentum
- Increased boat speed
- More efficient acceleration
- Improved behaviour in boat handling.

Disadvantages
- Boat wider then legal tow width means you will need to either de-beam, trailer on the tilt or tow illegally.
- Boat moves away from the Taipan 4.9 class rules which boasts a fleet that is so much bigger than the F16 fleet in AUS. This removes you from potential competition in one of the hottest fleets in AUS and also devalues the 4.9 platform.
- All performance gains would not be noticeable unless you are racing a significant OD / Class fleet. In AUS, the F16 fleet is not large enough yet to warrant the investment to modify the 4.9.

Wouter,

I'd like to understand exactly what you are saying here.

Do you mean that once you have maxxed all the de-powering options (such and downhaul, traveller and mast rotation), you will have this 1% gain?

To put it another way; if you two boats that were exactly the same, and trimmed in the same way, with exactly the same crew weight, in exactly the same place (so DH in the same place, mast rotation etc) that the wider boat would exibit this 1% gain when both crew are fully trapped?




The SCHRS calc of RMOM (Righting moment) comes out thus:

2 up boat

2.5m = 460.75
2.34m = 440.19

460.75 / 440.19 = 1.047 just under 5%

1 up boat

2.5m = 293.5
2.34m = 279.18

293.5 / 279.18 = 1.051 just over 5%

SCHRS defines RMOM as

1/2 the beam x (weight of boat + crew weight) + number of trapezing crew x COG of average person (0.93cm) x average weight of person worldwide (75kg)

RMOM = 0.5 x BEAM x(boat weight+ combined crew weight) + Num-trpx 0.93x75




I dont feel that 5% extra RM will provide 1% more speed around the course, overall, in a spectrum of conditions.

I assume your 1% gain Wouter is in a single, ideal windspeed condition?



I'd really like to understand this (without too much science, it is Sunday and I am tired as if people really feel that the SCHRS model needs re-visiting on this, the management group will.

We settled on 2.5 mtr overall width for the F16's as that is "tow legal" everywhere in the world. Ergo, there is no need to disassemble or tilt the F16's.

Wouter

My rule of thumb with respect to MAX righting moment is :

boat weight x boat width x 0.5 + number of crew (on traps) x (boatwidth + 1 mtr).

So for a 150 kg crew we find : max rigting moment is equal to :

107*2.5*0.5 + 150*(2.5+1) = 133.75 + 525.00 = rounded 659 kgm

In my earlier posts I used a lighter crew of 140 kg which is the average crew weight for competitive F16 crews.


I feel the formula that you use/presented is in error and I think what the error is.

You write :

1/2 the beam x (weight of boat + crew weight) + number of trapezing crew x COG of average person (0.93cm) x average weight of person worldwide (75kg)


Basically you have excluded "1/2 * beam * crew weight" from the total. Rearranging the items will show this (while replacing the factor 0.93 by 1 mtr for ease of calculations).

1/2*beam*boatweight + 1/2*beam*crewweight + number crew*1 mtr*WeightOfPerson =


rearranging further, assuming number of crew = 2 and 2*1 = 2 again

1/2*beam*boatweight + 1/2*beam*crewweight + 2 * mtr*WeightOfPerson

Note how the first term is valid but the second and third terms are insufficient when combined as the feet of the crew are located at the luff hull which is TWICE as far removed from the fullcrum point then 1/2*boatwidth. I hope this is clear enough.


Anyway back to the topic at hand.

2.30 mtr wide boat 2-up sailing with 150 kg crew ; max righting = 618 = 100.0%
2.50 mtr wide boat 2-up sailing with 150 kg crew ; max righting = 659 = 106.6 %

The difference being 6.6% in favour of the wider boat

Now typically a displacement hull travelling through the water at the surface can be crudely approximated by a drag curve that is 2.5 power of speed.. I say crudely as wave-making drag can place peaks or depressions on different locations depending on hull designs specifics.

This means a speed increase of 102.6 % = 2.6 % due to the later beam is all other things are equal and the max righting moment is the only limiting factor in achieving higher speeds (this implies identical trim, heading and windstrength etc)

Righting moment is not nearly as important on the downwind legs and we assume that it is NOT the speed limiting factor on these courses (diving is !) Also from measurements I have found that going downwind takes less time to cover the same distance then going up wind the ration is about 40-60% or 45%-55%. The first seems to be a very good upper limit. Meaning that only for max 60% of the time the extra leverage is effective (note 0.6*2.6% = 1.5%). This means that the wider boat completes a single upwind/downwind course in 55 secs less then the more narrow boat in a hour of racing (=40 secs in 45 min race). Of course in my other post I covered a range of percentages and that lead to an average conversative performance increase of 25 secs in 45 min race.

In this post I also simplified a few higher order dependencies (to keep things simple) and part of the differences will be the result of that, an example is the change in saildrive due to high boatspeed (higher apparent wind and smaller angle of incidence). However, I think the general method will however be clear.

Wouter

Having gone to all the trouble of widening my Stealth from the original R to the new F16 width, I would quite catergorically say don't bother. For all the time I spent changing everything on the boat to accomadate the extra width such as tramps, rudder connections, etc I would have been far better off spending time on the water where I would have got more gain than the 1 - 2% predicted and saved quite a lot of money.

Equally the boat behaves quite differntly with the wider beams, I personally think over all the wind strengths below fully trapped out, the boat is actually faster upwind in its narrower guise, other Stealth owners have commented the same, but at higher wind strengths the boat is much easier to handle, certainly out on the trapeze it feel much less flighty and "chilled out", its surprising how those extra few centimetres slow the heeling speed down.

So if you have one of the older style narrower boats, don't bother, just save your pennies and enjoy your sailing, it makes very little difference.

Appologies, had my F18 cap on then.

Thanks everybody i will leave it at the standard taipan width as advantages of widening it dont seem to be that great and then i can still race in two classes
Cheers Ausstricker

Sounds like the right decision to me.

Please get back to use when you rig it for F16 sailing with spi and selftacker (if you are sailing two-up). Would be very interesting to hear what your experiences are after some time on the boat racing with full width F16s.

perhaps in a couple of years time the scene may change enough to change your decision.

I think that to be the wisest decision as well.

Besides you got more then enough on your plate with the spinnaker, new mainsail and selftacker. The last is almost a must when spi sailing. You'll need the space on the trampoline and the jib sheets coming so far back really interferes with the spi halyard (retrieval line) and the spi sheets.

Best of luck and enjoyment !

Wouter

After converting the stingray to a self tacking jib when we added the spinnaker I would say don't bother. The performance hit upwind is considerable so we actually returned back to our full size jib. At the moment the Taipan has been grandfathered with it's big jib so I would take advantage of this while it lasts. Gybing with the kite and the regular jib does require some extra planning but you get used to it.

The spaghetti on the trampoline is another matter and i know the jib blocks are further back on the tramp than the stingray but the taipan 5.7 i sailed it wasn't a problem. You can take the barberhaulers off which does save some tangling.