Jump to content

Is it possible to come up with a S.A./Disp. definition of a sport boat?


Recommended Posts

it's not just a case of SA/D, size comes into it as well, a 100ft boat wouldn't really be a Sports boat.

They seem to be light displacement boats, but they generally have a lifting keel and no or little accommodation... Isn't that just the description of a dinghy?

 So is sports boat just a marketing description for a big dinghy?

 After all dinghies like the K1 have a lifting ballasted keel, and 100 year old dinghies often had a lifting steel plate. Are they Sports boats?

Going the other way a 20 foot fixed keel open boat like the Yeoman is that a sports boat? It's open, no cabin, takes 2 crew and can plane occasionally. But it's an older design about 50 years old, built like a brick outhouse we've been known to race them in 40MPH winds with full sail (OK no spinnakers up).

  • Like 1
Link to post
Share on other sites

From the ORC Sportboat Class Rules:

Length overall LOA (m) 6.00 – 9.15
Displacement in measurement trim DSPM (kg) < 2000
Displacement / Length Ratio DSPM / LSM0 3 < 6.00

This is a pretty good guideline as to what most consider to be sport boats.

  • Like 2
Link to post
Share on other sites

Down here “sports boats” are boats with bugger all displacement  , massive rigs , huge sprits , no cabin , racks and traps and some of the faster boats with small wings and no traps like the viper or vx1 

the likes of melges 24s , fareast 24/28 or seascape 27 etc with more displacement  are considered “ sport trailer yachts” 

Link to post
Share on other sites
On 6/21/2021 at 11:57 PM, The Q said:

it's not just a case of SA/D, size comes into it as well, a 100ft boat wouldn't really be a Sports boat.

They seem to be light displacement boats, but they generally have a lifting keel and no or little accommodation... Isn't that just the description of a dinghy?

 So is sports boat just a marketing description for a big dinghy?

 After all dinghies like the K1 have a lifting ballasted keel, and 100 year old dinghies often had a lifting steel plate. Are they Sports boats?

Going the other way a 20 foot fixed keel open boat like the Yeoman is that a sports boat? It's open, no cabin, takes 2 crew and can plane occasionally. But it's an older design about 50 years old, built like a brick outhouse we've been known to race them in 40MPH winds with full sail (OK no spinnakers up).

Then there are Sonder Boats…..

92CC8EF5-847C-4B01-8D43-39DF8BC2FE25.png

24EF44E3-203F-41F5-840C-B21D35477259.jpeg

Link to post
Share on other sites
  • 2 weeks later...

This is a really fascinating conversation, because it goes far further than a simple rating rule and what is or is not a Sports Boat.   Here in Australia, Melges 24 even a Mumm 30 which I have owned and done exceptionally well in are deemed "slugs".    In fact every boat on that list with the possible exception of the T870-850 (which I presently am involve with) would not even rate as a Sports Boat.   Interestingly, the T870 we recently sailed and recently won the Australian Sports-boat Nationals in (in Brisbane) , it's called 6-Pac (due to the lack of them) I will find a photo, I assume those numbers are pounds, our rating certificate has us weighing 770kgs and that's everything sails, boom, mast keel bulb, motor, etc etc, (1694lbs), and we had 6 crew, probably another 500kgs, some big boys, I'm 92kgs and I'm not the biggest, (1100lbs) so 2800lbs or 1270kgs.   So we are 500lbs lighter than your rating page.   And sure, a T870 is absolutely considered a Sports-Boat here.   If it was 500lbs heavier, hmmm.

We won on AMS, the whole event was AMS, the boat that won every race on Scratch "Lamborghini" (sailed by David Lambourne) has only a 90kgs (200lbs) bulb, probably similar all up weight, and this brings into question the AMS.  

And to call a Mumm 30 an ultra-light in Australia, they would think you are all on crack!     It's deemed very pedestrian!   

Fabulous boat, (Mumm 30) I hasten to add, we had a hell of a lot of fun, for over 2 years, winning more than our fair share of Super 30 races against T870, Hick 30's and the alike. We won Magnetic Island, but running square and doing 12 knts, maybe 13, is a far cry from being in a Vivace and sitting on 25 knts for the best part or 20 mins.    (A disclaimer, I designed Vivace in 2003 and it's still the Sports-boat to beat, down here, it's clones where at the Nat's sailed by some very good sailor who had spent a lot of money, think it was called Skeeter.  There is also French Kiss, Conquistador, plus others (about 20 of them) )    I presently starting the process of building a 8.5m (28ft) Sports-boat, which is max length under Aust rules.  (Vivace is 26.5ft).

I have been sailing Mumm 30's and Sports-boats now for probably 6 year, prior to that I was sailing multi-hulls, a boat called Trilogy (it’s a tri)

Whereas the OMR [Off shore Multi-hull Rule] is open sourced, in that anyone can go in and play, and when they are ready, they pay their $100 and out spits a rating doc, the AMS/SMS is a "black-box" and I really resent "black-boxes".

And it really does not matter if it's sports boats or Multi-hulls or Contenders or 49ers, people invest money when they have confidence.

So if these things are open sourced and "peer reviewed" by those playing the game, then people play, knowing the risks and knowing the game.

One could only hope for a global rating system where it's open sourced, where a Sports-boat is a Sports-boat.   I have a friend in Adelaide who watches the French very closely, he has a D24 and drives it all over Australia, meet him sailing Trilogy.   So we where both very heartened when the FFV came up with a formula, so we will watch that with interest.

But people need to be able play to their hearts content, tweaking the size of their jib or the weight of their bulb, in today’s society you question professionals as a matter of course, Naval Architects are no exception, nor is people offering black-boxes, but that too a lofty goal for me at present.   You do what all professionals do when confronted with an obstacle, you go around it and move on.    I would not have the patience!

p.jpeg?fv_content=true&size_mode=5

  • Like 1
Link to post
Share on other sites

https://www.dropbox.com/sh/xbyhmg82wfjww2p/AAD0KZJMcrqMyUoz9uocUuTVa?dl=0

Is the link to the photo's of the Nats, I'm 2nd from the back, Bright blue anorak with a Rooster life jacket over the top, glasses and very short beard.   My old 18teen mate GT [Graham Turner, ex Hooker, Finnair, Haminex] is steering.

We are A51, with bow number 20.

Skeeter (a 79er) is sail number 105.    Phil "Cub" Barnett who was ex Xerox & Chesty Bond was sailing it, way to many jugs of rum and coke to remember much.

Re the 89er (the 8.5m new idea), I tend not to crystalise designs until I am pretty sure of the direction I am thinking of going, because I find myself being committed to a path that I may latter regret.    You tend to buy into your own ideas.

But the Sports-boat rules are pretty well defined in this country LOA = 8.5m Max, Max Beam is 3.5m (max towing width is 2.5m) and you have to be able to ramp launch off a trailer behind a std car.   Most people have 2.4 - 3.5 liter diesels SUV's to tow.   Some have bolt on wings, (79er's has bolt on's) but after traveling through Europe and seeing RC 44 on tilt trailers and watching it happen, that is so simple. Max mast length is 12.5m so air draft is a little over 13m.   I doubt I will go that high, don't think it's warranted.   I get a bit thingy WRT sail plans, the minor things we have done with 49ers and the 29erC reinforces my belief in importance of sail plan.   To many people just go big without thinking drag and control.     The Cat 6, it has to self right.  They capsize you (90°) at the dock and for a 12m mast they tie a 85kg weight at the hounds (sails tied into the cockpit, not up the mast) and it has to self right.  I let the NA's look after all that stuff.     Mast is likely to be 110-120 Fore-aft, 60-70 Sideways, obviously Carbon, approx 28kgs all up inc synthetic rigging ("Lamborghini" carried all SK78 rigging, no wire and not slow) so probably look at PB20 for all standing rigging.   Bulb 140kgs, plus if needed another 30kgs in the fin, not a long fin, only need 1/2m² of surface area to handle side load.  May include DSS, but just a simple one, straight, just behind the fin but more for the Magnetic Island races, and the PHS racing that we did about a month ago in Port Stephens a FarEast 28R, that was fun also.  But they are not Sports-boats!   Crew of 5, all up weight close to a tonne (inc crew).   Construction, really liking Basalt Fiber, had some massive successes with it!  No fizzing of Carbon with Alloy or Stainless and no having to guard against it, plus it seems bloody tough, and 6 Pac and Lamborghini are both 21 years old (and that in itself is a statement of the status here)    Plus I'm a bit green so avoiding Carbon except where is a better choice for a range of reason (inc environmental) like in the mast,  so PET core in the hull, env Pu core in the foils.    Plus I need to play AMS games.

When I get to some stronger concepts and start sketching out a design, happy to send you some renders.   But you had better keep pestering me.   Plan to building it over the next 6 - 9 months, still got quite a bit on, but obviously not traveling so a bit of excess time.    We are taking 6 Pac to Ariel and Maggy in Aug-Sept!

                    jB

Link to post
Share on other sites
On 7/4/2021 at 4:22 PM, JulianB said:

This is a really fascinating conversation, because it goes far further than a simple rating rule and what is or is not a Sports Boat.   Here in Australia, Melges 24 even a Mumm 30 which I have owned and done exceptionally well in are deemed "slugs".    In fact every boat on that list with the possible exception of the T870-850 (which I presently am involve with) would not even rate as a Sports Boat.   Interestingly, the T870 we recently sailed and recently won the Australian Sports-boat Nationals in (in Brisbane) , it's called 6-Pac (due to the lack of them) I will find a photo, I assume those numbers are pounds, our rating certificate has us weighing 770kgs and that's everything sails, boom, mast keel bulb, motor, etc etc, (1694lbs), and we had 6 crew, probably another 500kgs, some big boys, I'm 92kgs and I'm not the biggest, (1100lbs) so 2800lbs or 1270kgs.   So we are 500lbs lighter than your rating page.   And sure, a T870 is absolutely considered a Sports-Boat here.   If it was 500lbs heavier, hmmm.

 

We won on AMS, the whole event was AMS, the boat that won every race on Scratch "Lamborghini" (sailed by David Lambourne) has only a 90kgs (200lbs) bulb, probably similar all up weight, and this brings into question the AMS.  

 

And to call a Mumm 30 an ultra-light in Australia, they would think you are all on crack!     It's deemed very pedestrian!   

 

Fabulous boat, (Mumm 30) I hasten to add, we had a hell of a lot of fun, for over 2 years, winning more than our fair share of Super 30 races against T870, Hick 30's and the alike. We won Magnetic Island, but running square and doing 12 knts, maybe 13, is a far cry from being in a Vivace and sitting on 25 knts for the best part or 20 mins.    (A disclaimer, I designed Vivace in 2003 and it's still the Sports-boat to beat, down here, it's clones where at the Nat's sailed by some very good sailor who had spent a lot of money, think it was called Skeeter.  There is also French Kiss, Conquistador, plus others (about 20 of them) )    I presently starting the process of building a 8.5m (28ft) Sports-boat, which is max length under Aust rules.  (Vivace is 26.5ft).

 

I have been sailing Mumm 30's and Sports-boats now for probably 6 year, prior to that I was sailing multi-hulls, a boat called Trilogy (it’s a tri)

 

Whereas the OMR [Off shore Multi-hull Rule] is open sourced, in that anyone can go in and play, and when they are ready, they pay their $100 and out spits a rating doc, the AMS/SMS is a "black-box" and I really resent "black-boxes".

 

And it really does not matter if it's sports boats or Multi-hulls or Contenders or 49ers, people invest money when they have confidence.

 

So if these things are open sourced and "peer reviewed" by those playing the game, then people play, knowing the risks and knowing the game.

 

One could only hope for a global rating system where it's open sourced, where a Sports-boat is a Sports-boat.   I have a friend in Adelaide who watches the French very closely, he has a D24 and drives it all over Australia, meet him sailing Trilogy.   So we where both very heartened when the FFV came up with a formula, so we will watch that with interest.

 

But people need to be able play to their hearts content, tweaking the size of their jib or the weight of their bulb, in today’s society you question professionals as a matter of course, Naval Architects are no exception, nor is people offering black-boxes, but that too a lofty goal for me at present.   You do what all professionals do when confronted with an obstacle, you go around it and move on.    I would not have the patience!

 

Julian:

Something fishy with your 1694 lb displacement.  German review of the T870 production design shows 1.5 metric ton =1500 killos.  (3300lbs)

Boating NZ review of T30 lists displacement at 1900 killos. (4180 lbs)

Even the very light low freeboard Viper 830GR lists at 2000 lbs which i believe is also a Thomo design.

How is your rating cert established ? 

 

 

Link to post
Share on other sites

 

5 hours ago, barefoot children said:

Julian:

Something fishy with your 1694 lb displacement.  German review of the T870 production design shows 1.5 metric ton =1500 killos.  (3300lbs)

Boating NZ review of T30 lists displacement at 1900 killos. (4180 lbs)

Even the very light low freeboard Viper 830GR lists at 2000 lbs which i believe is also a Thomo design.

How is your rating cert established ? 

If you go to https://www.raceyachts.org/images/rulebooks/AMS_SMS Year Book Edition 13_2017-18.pdf

You will see the rule and how it's measured.     My belief is on a given day, they book a crane, and a set of scales and hang/lift them.

I have seen it done at RANSA (Rushcutters Bay, Sydney) but we inherited the rating doc, of 6 Pac, the boats 21 years old.

 You can find 6 Pac in the system, but I don't have the Rating doc, but I will try and get it for you and copy it.   

Officially the boat is owned by my mate GT, and I am very confident of the number 770kgs as measured above, and 770kgs x 2.2 = 1694lbs.

Probably can't get that till the weekend.

The answer could be it's a Thompson 8, and maybe not a T870-850, I simply don't know.

image.png

Link to post
Share on other sites
  • 2 weeks later...
On 7/3/2021 at 1:38 PM, barefoot children said:

Here's a spreadsheet I'd come across a while ago for boats mostly in 27-30' range, sorry only have image of it now

IMG_0549.thumb.jpeg.10514e1c73a05a66f7cdb532f1d963b0.jpeg

My 40er cruiser is an ultralight!  :lol:
 

Let’s see, if I toss all the junk off, add a bigger main & jibs, assyms, sprit….. <_<  We’re at ~ 96 & 25 right now, so is <90 > 30 upwind & > 80 sport boat territory?  
 

Does dynamic length count?  Gets the LWL up to 39’+….. (design LWL = 36’ now). 
 

edit- Yes!  72!  B)  fun with numbers!  Like $$$$….

another edit… with our drifter, at design LWL (36’)  we are >30 upwind, and without junk, we’re 92…..

Getting rid of another 300 lbs (down to 9300 lbs) ~ 89.  Yay!

we’re wood/foam & aluminum rig….

 


 

Link to post
Share on other sites
  • 2 weeks later...
On 7/8/2021 at 3:28 AM, JulianB said:

 

If you go to https://www.raceyachts.org/images/rulebooks/AMS_SMS Year Book Edition 13_2017-18.pdf

You will see the rule and how it's measured.     My belief is on a given day, they book a crane, and a set of scales and hang/lift them.

I have seen it done at RANSA (Rushcutters Bay, Sydney) but we inherited the rating doc, of 6 Pac, the boats 21 years old.

 You can find 6 Pac in the system, but I don't have the Rating doc, but I will try and get it for you and copy it.   

Officially the boat is owned by my mate GT, and I am very confident of the number 770kgs as measured above, and 770kgs x 2.2 = 1694lbs.

Probably can't get that till the weekend.

The answer could be it's a Thompson 8, and maybe not a T870-850, I simply don't know.

image.png

JB, 6-pac is a thompson 8. well it was when it was called game on. 

Link to post
Share on other sites

I think there where 4 or 5 hulls pulled off a male plug to the original specificication.

So these boats where 1050kgs all up, inc crew, 210kg bulb, single layer of 450gm Carbon outer skin, 94mm OD mast, 11.5m tall (air draft).

Martin Billoch, who was the NA (Argentina) did an extrodinary job with my scribbles and Pierre Gal (the client) was truly brave.   He accepted everything we threw at him and did it, and that boat is still sailing and very competative today.

I'm guessing 2008 an Australian company did a deal with Pierre and initially me, to take Vivarce, fair it and make moulds.    Initially I helped, as did Martin, and the boat had a canting keel (with highinsight, not a good idea)  but I am not a NA and Australian insures needed a Australian NA.   The final straw for me was when the Aust. NA speced 1200gms of laminate on the hull, and the all up weight blossomed to about 1600kgs.    I left, took out TM's on 69er, 79er, 89er and 99er, and I quite litterally have no idea how many where built.   I am told there are about 20 in total.   I have searched for those moulds as I think it would be a great project, but I believe that they (the moulds) have been destroyed.

Besides Vivarce, Martin and I did the SKUD, along with some Libera's, the re-work of the 29er, so I have used him extensively over the years, last physically met him in the Sth of France on Clasics, and he now has Jacbo Zerbo as a partner.  Jacbo was part of teh Parda team in NZ, so sure young, but exceptionally skilled in foils and all things that fly!   Quite literally yesterday the 3 of us signed a multi year, mult boat contract with a builder so really looking forward to pursuing that.    I will be a busy boy.

But I am now in the final stages of doing a "89er", and as you can totally understand, Martin and I are as thick as thevies WRT the 89er, I also intend to "lean heavily on him" (and Jacbo) WRT the new "Bat Boat" (fully wired 49er) and all that is going to happen within the next 12 months.   89er, frames go up in 3 weeks.  Male plug.

Covid has been amazingly good to me, no travel, not sure my wife is all that impressed, but planning on the next 5 years of 89er sailing with 4-5 really good mates (male and female) who want to do all the sports boat and Super 30 races across this country.  Then imited (maybe 4 trips a year) overseas commitments (with the wife).

I'm in a really good space.

Today I spent 3 hrs looking at 3Di sails on the new CST masts (49er), and they are really good, the Maka kites looks great also, I know where I will be going for sails, but they wont be black, told Squarky (from Norths) that, they laughted, not sure they realise that I am very very serious!    FX sails Tuesday next week with any luck.

                           jB

 

 

  • Like 3
Link to post
Share on other sites

So this is me, quite a few years back.

Gallery of multihulls with sails by Sailtech Sailmakers

I'm sitting down, on the ahma, hanging onto the spin sheet, there are another 2 guys in the cockpit, one is grinding (the spinsheet winch), the other is on the mainsail winch.

The guy standing (Keith Glover) is steering, we have just landed, doing low to mid 30's, Port Phillip Bay, Melbourne.   

So I know what mono-hulls with training floats are all about, think we won 9 OMR's out of 12 attempts, 2 x 2nd's and a 3rd in this boat, Trilogy!

If John had put Vivace on the market 2 months earlier, maybe, but now, we own 6-Pac which is still stuck in Brisbane (I live in Sydney).

And the 89er becons, got the foam, got the bulb, having the ISO cert done now, so we don't make a error, and only yesterday we "gang of 5" started planning next years sojourns to all places that look like fun to sail, if we are ever allowed out of Sydney again.

                      jB

  • Like 2
Link to post
Share on other sites
  • 3 months later...
On 6/23/2021 at 12:04 PM, port tack said:

Its possible, but 49 won't agree with it, another 49% will agree and then 2% will want to see your girlfriends tits.

Only 2%???????????  This place has gone to complete shit

Link to post
Share on other sites

This could be a reprise of the Skiff not a Skiff debates of several years ago.

For my money, a sport boat is a keel boat that planes.  This means it has a displacement/length ratio of 100 or less and is more or less in the same bracket as most of the non trapeze planing dinghies.  I’m sure some will make a big deal of the asymmetrical spinnaker and full battened main, but I think this is hair style and fashion sense.

SHC

Link to post
Share on other sites
1 hour ago, Steve Clark said:

This could be a reprise of the Skiff not a Skiff debates of several years ago.

For my money, a sport boat is a keel boat that planes.  This means it has a displacement/length ratio of 100 or less and is more or less in the same bracket as most of the non trapeze planing dinghies.  I’m sure some will make a big deal of the asymmetrical spinnaker and full battened main, but I think this is hair style and fashion sense.

SHC

Yeh, but, Farr40 planes of Bichino on its way to Hobart at 22knts, and Ichi Bann did 27knts and was well and truly planning on its way to its historic Syd-Hobart win, (both times with Harry steering).

No one considers them Sportsboats.

Probably need you to explain the 100 length to disp ratio?

Really like the simplicity but!

      jB

Link to post
Share on other sites

How about this?

  • No downstairs other than storage hatches on the deck.
  • Insert minimum SA/D here.
  • Insert maximum D/LWL here.

So Melges32, Mumm30, Esse850, Viper830, Melges24, etc, all not sport boats.  If you can get downstairs out of the weather let it be called a sport yachts.

Let the tomato throwing commence.

Link to post
Share on other sites

Accommodation is a good part of the definition, I would also suggest that crew weight/total displacement is another good definition. In other words, a boat which relies predominantly for stability using crew weight as opposed to keel ballast weight.

Indicative fag packet:

Melges 24: ~ 32%, 6 Pac: ~ 38%, 89’er: ~ 39%, Mum 30: ~ 19%, Farr 40: ~ 9%. So anything (say) > 25%?

Above numbers use 500 kg crew weight except for the Melges (375 kg class max) and the Farr 40 (1000 kg for extra crew, safety gear and consumables).

FWIW, based on (guessed) effective water length, not static LWL, the respective Displ/L ratios are: 87, 68, 41, 97 and 95 respectively.  So anything (say) < 90?

And finally, to complete the comparative, the SA/Displ ratios of the above are: ~  25, ~ 33, ~ 43, ~ 29, and ~ 32 respectively. So anything (clearly) > 25?

For those enthusiastic enough, it wouldn’t be hard to set up a data base of everything which could be regarded as a sports boat and use these kinds of ratios, plus lack of accommodation, and I am sure that there would be a fairly clear dividing line between sports boats and fast yachts.

Over to someone else.

Link to post
Share on other sites

D/L is my favorite non dimensional number.

LWL tells you how long a wave you will make. Which defines hull speed.

D/L tells you how high a wave you will make, and by extension how much energy it takes to get over it.

Our old rule of thumb was that anything with. D/L of higher than 150 wasn’t going to plane.  It might go quite fast surfing down waves and so forth and exceed its hull speed, but that wouldn’t be planing.  Just sucking up horsepower.

Conventional British Sailing Dinghies of the Uffa Fox variety are all in the 130 region. They plane, but you have to work at it and it has to be blowing pretty hard.  Boats like 505 and I14 are grouped around 100. They plane reliably.  Then there the odd balls like ICs which have a D/L around 25. These are “humpless” hulls by eliminating the hump.

SHC

  • Like 1
Link to post
Share on other sites
47 minutes ago, Steve Clark said:

D/L is my favorite non dimensional number.

LWL tells you how long a wave you will make. Which defines hull speed.

D/L tells you how high a wave you will make, and by extension how much energy it takes to get over it.

Our old rule of thumb was that anything with. D/L of higher than 150 wasn’t going to plane.  It might go quite fast surfing down waves and so forth and exceed its hull speed, but that wouldn’t be planing.  Just sucking up horsepower.

Conventional British Sailing Dinghies of the Uffa Fox variety are all in the 130 region. They plane, but you have to work at it and it has to be blowing pretty hard.  Boats like 505 and I14 are grouped around 100. They plane reliably.  Then there the odd balls like ICs which have a D/L around 25. These are “humpless” hulls by eliminating the hump.

SHC

So what are the units imperial I'm guessing, lbs & ft??

Link to post
Share on other sites
5 hours ago, Steve Clark said:

D/L is my favorite non dimensional number.

LWL tells you how long a wave you will make. Which defines hull speed.

D/L tells you how high a wave you will make, and by extension how much energy it takes to get over it.

Our old rule of thumb was that anything with. D/L of higher than 150 wasn’t going to plane.  It might go quite fast surfing down waves and so forth and exceed its hull speed, but that wouldn’t be planing.  Just sucking up horsepower.

Conventional British Sailing Dinghies of the Uffa Fox variety are all in the 130 region. They plane, but you have to work at it and it has to be blowing pretty hard.  Boats like 505 and I14 are grouped around 100. They plane reliably.  Then there the odd balls like ICs which have a D/L around 25. These are “humpless” hulls by eliminating the hump.

SHC

Steve, glad you brought up the IC. Is this also related to the anomaly of the IC in terms of its Beam:Length Ratio?

All boats described prior to you and the IC would be grouped around the traditional 1:3 ratio. Not the IC however, which is borderline a single (wide) hulled catamaran.

I know elsewhere there is lots of conjecture and discussion about whether catamarans or multihulls ever plane. And some more recent designs have been squaring off the rear sections to aid water release. But none of them fit the chine descriptions that @JulianBreferences.....

I like this whole discussion forum  because it reminds you of what are the fundamentals of sailboat performance.

Having said that I think it is too simplistic to base it around only one, two or three ratios. Again to refer to mutilhulls: their success relies upon their slenderness ratios, WSA, their massive RM and thereby their capacity to exploit low drag rig opportunities. And so on...... 

Your comments about Humpless hulls are also very en-pointe considering JB's input here.

Your thoughts?

Link to post
Share on other sites

So I am starting to warm to Steve's concept!

It cuts to the chase, I thought it may need a max length, but as you go longer you get expodentially heavier, so it's self limiting.

So Lbs/ft works at about 100, and kgs/m works at about 150, it's quite compact, neat and if Steve with all his fiddeling comes up with 100, who am I to chalange that.

It's a littl ebit like the 5o5 and I14 string a month or so ago, they have become the trigger boats.

And 6Pac being 111 sort of makes sense, it's pretty displacment, and it will get up and go, so if you have a 120-125 boat then you just need to alter your sailing style.

Less than maybe 75, you fully tacking downwind with assymetrics, as you crawl up the scale, you get more into symetrical and running the rumbline.

Works for me!

Link to post
Share on other sites
10 hours ago, JulianB said:

So what are the units imperial I'm guessing, lbs & ft??

The traditional formula for Displ/L ratio is imperial: Tons/ (0.01*LWL)^3. With LWL in ft.

Steve Clark was being a bit hard on the I14 and 505 dinghies. My fag packet Displ/L ratios:

I14: ~ 85, 505: ~ 70, ICanoe: ~ 33, 49’er: ~ 75. All with 80 kg per crew member.

FWIW Trilogy comes in at 76 with 500kg crew weight. BTW, Sidecar comes in at ~ 34 singlehanded.

I stand by the Displ/L ratios given upthread.

 

Link to post
Share on other sites

Just to add a couple more boats to help define/confuse the issue further, the J 24, which some might regard as the first “modern” sports boat comes in at Displ/L: ~ 173, with a crew weight/total displ ratio of 22%. Guesstimated effective LWL of 6.6 m and 400 kg crew, which is the class max limit.

I make Uffa Fox’s Flying Fifteen to be Displ/L ~ 72, with a crew weight/total Displ of ~ 31%. Guesstimated effective LWL of 5.8 m and two crew @ 80 kg each. So one could argue that the FF probably was the first sports boat by my suggested definitions upthread.

FWIW the international Star comes in at ~ 106 and ~ 48% respectively.

Link to post
Share on other sites
49 minutes ago, Steve Clark said:

WildThingByKevinBell.png

The 110 precedes the Flying 15 by 10 years. 

At 24’ long and weighing 900 lbs absolutely light for its length, and only has to carry 2.

The humans are the biggest sap on performance of these things.

SHC

Good one:

Displ/L:  ~ 40, Crew weight/Total Displacement: ~ 28%.

A totally flat bottomed canoe….. I can relate to that!

7F383FD7-D437-4F35-96B2-418F2C2472F3.jpeg

A5FD90F8-A84A-4FAF-B200-1133EA91BD91.jpeg

Link to post
Share on other sites

Once you get down to including the flying fifteen in sports boat territory, then you are almost including my own design boat, which definitely wasn't meant to be a sports boat..

LWL 16ft.

Max beam waterline 3ft

SA, 130sqft

All up weight, 1100lbs less if I can lose another 60lbs..

And there is a slow plan to remove more above waterline weight from the hull. I know a lot more about hull construction now than 20years ago when she was first built.

What she was designed to do was to sail well in our, quite often, light air conditions.

Link to post
Share on other sites

Assuming that 16 ft is the effective sailing length, and the 1100 lbs includes crew weight, you would have a Displ/L of ~ 40, which is deep into sports boat territory. Refer to numbers above. Your  have a slightly superior SA/Displ ratio to a FF, ~ 21.61 vs ~ 21.16, so you should be slightly faster? But it could be that you have too much WSA compared to a FF, so perhaps not. Hard to improve Displ/L without increasing WSA.

But you both fail my suggested SA/Displ limit for sports boats > 25. As does the 110 canoe at ~ 21.66.

How much crew weight is in your total displacement BTW?

Link to post
Share on other sites
39 minutes ago, Sidecar said:

Assuming that 16 ft is the effective sailing length, and the 1100 lbs includes crew weight, you would have a Displ/L of ~ 40, which is deep into sports boat territory. Refer to numbers above. Your  have a slightly superior SA/Displ ratio to a FF, ~ 21.61 vs ~ 21.16, so you should be slightly faster? But it could be that you have too much WSA compared to a FF, so perhaps not. Hard to improve Displ/L without increasing WSA.

But you both fail my suggested SA/Displ limit for sports boats > 25. As does the 110 canoe at ~ 21.66.

How much crew weight is in your total displacement BTW?

Apologies Q … Sorry to get you excited, I made a spreadsheet slip copying formulas…. Your Disp/L is ~ 119. SA/Displ is OK. The FF is ~ 73 because of the extra effective length. How much overhang do you have, especially aft?

Link to post
Share on other sites

 The boats ballast ratio 54% including me, 35% without me.. 

If I've got my sums right when I designed her, there's no overhangs fore or aft, except for a Jib Club..

I designed her that way because;

We are taxed on block square area. and LOA is of course mooring costs..

Long overhangs in light winds, don't often get used.

We sail in narrow / shallow confined waters, a non overhang boat can sail right up the the river banks so using more of the rivers, effectively making a wider river, so longer tacks under wind power..  

 

I wasn't expecting her to be in Sports boat territory,. She  wasn't designed that way, with a bad back I can't sit out.. Had I wanted her in that territory, she would have been a couple of feet wider, and the hull itself less deep giving more form stability, less hull depth means a slightly deeper keel as well.

If you brought a genuine sports boat here, she wouldn't perform to rating, as she'd rarely plane.. Same happens with Dinghies here, a light displacement dinghy will out perform on handicap the latest,  all carbon, go faster, planeing dinghy because the go faster dinghy would very rarely get to plane.

 

Link to post
Share on other sites
5 hours ago, The Q said:

 The boats ballast ratio 54% including me, 35% without me.. 

If I've got my sums right when I designed her, there's no overhangs fore or aft, except for a Jib Club..

I designed her that way because;

We are taxed on block square area. and LOA is of course mooring costs..

Long overhangs in light winds, don't often get used.

In other words, your Crew weight/ Total Displ ratio is 19%.

So you will be relieved that your boat “fails” on all three suggested sports boat ratios..

With regard to long overhangs, the whole point of them is to reduce WSA for (extremely) light winds, whilst still having better performance once boat speed builds up. Granted, you won’t get much overhang on a 16 ft keelboat.

Making your boat 60 lbs lighter should also give you a little more overhang and less WSA, as will shifting crew weight forward. Go for it, you will be faster all round.

Link to post
Share on other sites

Which reminds me…… There are a lot of scows which (easily) meet the suggested criteria.

Eg A-Class Scows. Trailerable, and classic examples of short static LWL but long effective LWL..

Dipl/L: ~ 37, SA/Displ: ~ 40, Crew weight/Total Displ: ~ 37%. Using a guesstimated effective LWL of ~10metres and 500 kg crew weight, but they are unlimited as to the number and weight of crew.

1777F7C1-D1A3-49DB-BA4E-A7A7FBCFFB04.jpeg

957BAF52-E112-4BAA-8753-37D844430039.png

Link to post
Share on other sites
On 12/10/2021 at 7:41 PM, Sidecar said:

In other words, your Crew weight/ Total Displ ratio is 19%.

So you will be relieved that your boat “fails” on all three suggested sports boat ratios..

With regard to long overhangs, the whole point of them is to reduce WSA for (extremely) light winds, whilst still having better performance once boat speed builds up. Granted, you won’t get much overhang on a 16 ft keelboat.

Making your boat 60 lbs lighter should also give you a little more overhang and less WSA, as will shifting crew weight forward. Go for it, you will be faster all round.

Thanks, Though a shorter water line length, gives you a lower max hull speed, there is always a break point..

When I started the redesign / rebuild of the boat I was 251lbs, I'm down to 185lbs still a bit to go...

 

How about the Windermere 17ft  first designed 1904...  It was one of my reference boats, when originally designing my boat, until I decided that Max WLL and Short LOA  was necessary on our waters. Note one section of river we rarely, but  do race on, is only about 80ft wide..... Some people race 45ft yachts on it.. To much like hard work for me...

"Windermere 17" Specifications:

LOA: 25'6" / 7.8m  ,

LWL: 17'0" / 5.2m,

 Beam: 5'10" / 1.8m,

Draft: 4'0" / 1.2m,

 Hull Weight (min): 770 lbs / 343kg 

All up weight 1807lbs /  820KG.

See the source image

 

Link to post
Share on other sites

Lovely boat…and wood construction too.

Windemere 17: Displ/L ~ 66, SA/Displ: ~ 58, Crew weight/total displacement: ~ 49%. Guesstimated effective length 7.0 metres.

By all the suggested criteria, definitely a sports boat, but by looks, you wouldn’t think it.

CF204295-F039-4702-B347-8C58F3C7316B.jpeg

Link to post
Share on other sites

And here is another scow, never mind the foils:

Quant 23: Displ/L: ~ 63, SA/Displ: ~ 58, Crew weight/total displacement: ~ 33%.

If it hasn’t been mentioned before, to qualify as a sports boat, there should be no trapeze, sliding seat or any other type of hiking device? Which would disqualify this one and also the 110 canoe?

2CCFC072-1A8F-4406-8B60-14829428BBD2.jpeg

Link to post
Share on other sites
56 minutes ago, Sidecar said:

Lovely boat…and wood construction too.

Windemere 17: Displ/L ~ 66, SA/Displ: ~ 58, Crew weight/total displacement: ~ 49%. Guesstimated effective length 7.0 metres.

By all the suggested criteria, definitely a sports boat, but by looks, you wouldn’t think it.

 

This would bring me to the majority of Broads Keelboats and by definition, a broads keelboat doesn't have a cabin, it is the difference between them and a Yacht.

So going old school which is the majority of broads racing sailing boats.. The Yare and Bure One design a boat on which I based my final design on..

LOA : 6.71m (22ft 0in)
LOD : 6.1m (20ft 0in)
LWL : 5.49m (18ft 0in)
Beam : 1.91m (6ft 3in)
Draft : 0.84m (2ft 9in)
Displacement,   600Kg 1322LBS
Sail area  279.00 ft2 / 25.92 m2See the source image

 
Link to post
Share on other sites
On 12/9/2021 at 9:06 PM, Sidecar said:

Good one:

Displ/L:  ~ 40, Crew weight/Total Displacement: ~ 28%.

A totally flat bottomed canoe….. I can relate to that!

7F383FD7-D437-4F35-96B2-418F2C2472F3.jpegTh

It’s not flat. It has a 152” radius. The topsides and decks have about half as much camber. This and a 45 mm radius at the chine and gunwales make a boat that could be very ugly quite elegant.  I am probably building one in a bit.

SHC

 

 

 

  • Like 1
Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...