For comparison, a picture of the same sails on my Bentley.  I think this highlights the major problem with the 10R class.  Those sails are the maximum allowed for the Bentley's 1344mm waterline whereas the Pieces of Eight can have a significantly larger area.  In winds under about 7kts I don't fancy the Bentley's chances but over 10kts there is only likely to be one winner.  10R's are lovely boats to sail and very fast but you sort of need a different one for every wind strength if you want to race seriously.  Also probably best not to get me started on how hard it is to measure the damn things accurately.

With respect John, I’m not sureI agree with your take on the 10 Rater class. Those that do, or have raced them seriously have not found the need to have a specific boat style for a specific venue. The two examples posted above are possibly as far apart on the design window as you could expect that are still racing. Both can be matched and beaten in their ‘favoured’ conditions by well designed boats. it is actually an attractive aspect that 10raters have over other classes that there is so much freedom in design but sadly a lack of what is good about the class not being promoted and poor calendars help to keep it well hidden from designers trying their hand or new skippers wanting to sail the fastest monohull rc yachts.

It may be worth taking a look through past designs that have done well consistently. These are well thought designs that do well in all conditions. As for measurement, not so difficult, just a waterline and the largest rig that needs to be lower than 10. Some would say no harder than any other class, if you can find a measurer…

Edited January 17, 20224 yr by Brad Gibson

Of course a well sailed boat can beat a badly sailed boat but hydrodynamics still applies.  If you accept the well known maximum hull speed formula (for displacement mode) then the Bentley should be just over 5% faster at it's ultimate hull speed (when upright of course).  If we assume equal displacements, one would expect the drag curves for the two boats to cross over at some point towards their maximum speed. The POE would be expected to have a lower drag at low speed, because of it's smaller wetted area but it's wave making drag will rise faster due to the shorter waterline.  The overhangs on 10Rs are intended to increase the waterline length when heeled so it gets a bit more complicated but having a longer waterline to start with is generally beneficial.

My comment about measurement accuracy is to do with the waterline length.  The overhangs of a 10R (particularly at the stern) make a very small angle to the water surface so that if you are 1mm out in height you will be about 5mm out in length.  Now add in the meniscus problem and I estimate you could easily be 10-15mm out.  Incidentally I haven't found a definitive statement on how to handle the meniscus effect in the rules.  I just know the Messrs Bantock and Stollery both say that you should try to eliminate the meniscus effect when measuring the waterline.  I believe there is a more accurate way for boats that have been designed using a CAD modelling system and that is to produce a graph of waterline length v displacement from the model.  One then only needs to weigh the boat to determine its waterline (and verify that the hull is built to the model.)    I found it very difficult to get repeatable results when checking my Bentley so in the end I took a range of measurements at different displacements and then curve fitted a graph to the results so I can determine the waterline length from the weight.  My worst point was indeed about 15mm off a fair curve between the other points.

All very true what you say John in basic yacht design. Where 10s built to wide ends of the design window will vary is most often in both displacement and sail area. Static waterline length being long may be one thing, but a short waterline boat with overhangs, more sail area at a lighter displacement will usually sail right past on a run, increasing with wind strength. How they compare upwind is another matter, dictated heavily through righting moment as much as any static or heeled waterline. Does the heavy boat have a long deep fin for a high righting moment %? or …Does it have a shorter fin with a heavy bulb for a righting moment similar in % to the lighter displacement boat that has a lighter bulb set on a deep fin?

As I’m sure you are aware there are many options and parameters that can make designing a 10R a true test in design, like any open rule class. That those regularly doing well over time seem to have flowed into a narrow band of the design rule using the mix of variables mentioned above, shows the efforts designers have put in. Yes you can have a design pitched way out one end for a certain condition, but these types rarely are consistently near the top of results at competitions. No different really than what happens in any class with range of design.

I’ve seen no end of measurers offering the ‘right’ way to finding a waterline on an Rc yacht. Some tanks out there with no end of gadgets, screws, tin foil linked to batteries etc etc. To me most simple and repeatable is marking a brightly coloured strip of sign vinyl under a hull, with marked lines numbered at 5mm increments. Place the boat in a tank, then take a 9” x 6” mirror and slide it into the water to show the undersurface of the waterline and the accurately sight where that undersurface bisects the marked hull point. Record your measurements. I.e. transom halfway between 4 and 5… Do the same at both ends. Have a 10 minute break then do it again a couple of more times. When happy with consistency, mark those points on the hull. If you want a safety factor add 2-3mm each end for peace of mind.

Both of my own boats used for the last 2 worlds were measured with this method. Both were absolutely spot on when being measured in the elaborate tanks, with the measurer both times suggesting I could have been up to 4mm shorter on the waterline….the exact amount I add in for safety. 
so long as you can find a tank, it’s not that difficult, but no doubt I’ve been doing it wrong 😉.

 

Apologies Richard for not complimenting you on your build, great work in continuing to show home building is alive and well through all classes.

 

Wow !!! this is suddenly so interesting.

You are both correct, of course, concerning  the design extremes and relative virtues; or not. I did consider Bentley, but that was the polar opposite of what I needed for something to suit the very light conditions that I usually sail in. Also the boat was built to a tight (very small) budget.

My brief foray into the 10R class has stirred my interest in a boat that allows true performance with a fairly simple rule and, very important, not a lot of weight to cart around.  The overhangs introduce huge scope for hull tuning  since they are not tied to the simple WL formula as they must be designed to heel to an optimum WL; or sail flat in light winds well below hull speed. Aiming for the best of both worlds.    These boats must be the most exciting class out there.

Why on earth the class has not got a greater following is sad. I have built a few Mini40's and the same comment applies. Although to be fair you have to invest in at least two hulls there.  Neither class has a useful web site or forum with any discussion (apart from the MYA here) The Mini40 only exists on Facebook and the British Model Multihull website has been out of use for ages. Nowhere to gather info or discuss two classes that should be generating more discussion than most, due to their many diverse performance characteristics.

I would love to get my hands on a current design, but my Pof8 provides some fun sailing at least.  I think I would go lighter ballast on longer fin, thereby reducing the displacement and all the consequent form drag. Appreciate that this may limit some venues.

Measurement: As pointed out, should not really be a problem. Totally agree about WL being the most critical item WL. Tried various tricks short of getting into the water myself. I used bright tape with increments marked and then photographed, sort of nearly consistent. Even thought about the foil and battery mentioned. No tank though. 

Adding surfactant to the measurement tank would decrease the meniscus, but hey ! getting a bit chemical here.  What about a floating gauge, sharpened to a point and pre set to the boats declared WL. Go/No Go.   Could be used at the water side, if calm, and the draft subsequently measured.

Thanks for your appreciative comment, Brad.

Richard, P of 8 is a Roger Stollery design, does this mean it was designed for Swing Rigs?

If this is the case what modifications were required to fit a conventional rig? When you get round to a maximum size rig will it be swing or conventional and reason for choice?

Hi Eric, nice to hear from you.

Roger uses an offset mast fitting on his swing rigs and this allows conventional sails to be used. The 10R class seems to favour conventional rigs, based on all the advice I have received from those experienced in the class. I will be going that way and consequently do not even have a swing rig mast tube. The Pieces of  Eight has the mast in the correct position as a result. I checked out a few designs and found the mast / fin relationship pretty much standard as is the main / jib ratio. Actually a simple class to put together; well, just as straightforward as a One Metre anyway. Standard mast /  finbox mouldings are available which further removes any guesswork.

 

Brad,

I assume you've seen this:

https://www.sailsetc2.com/downloads/waterline end checking device 10R.pdf

It shows that Mr Bantock thinks the waterline is measured where the waterplane intersects the hull, not where the meniscus touches the hull.  When Roger Stollery checked my Bentley for me he also used a device that used the same principle.  If you measure by sighting the meniscus you will get a value some 5-25mm longer than if you use the Bantock / Stollery method (depending on the hull shape) so it is significant.  Unfortunately the rules don't help because they use the term ''waterline ending" without defining what this means.  One of the difficulties with the Bantock  / Stollery method is that you can't set the 'gauge' by sight, you have to 'feel' when the boat touches it - hence my original comment about it being difficult and error prone.

One of the reasons swing rigs aren't as universal on 10Rs as they are on Marbleheads is because the 10R rules require the B rig sails to fit within the profile of the A rig sails.  As swing rigs need to use a tall narrow jib, this severely compromises you if you want to use a conventional B rig, as ideally you would want to use a much bigger jib for the B rig (as Marbleheads do).  Some 10Rs use a B swing rig but I'm not convinced this is a great idea.  In my view this rule is unnecessarily restrictive  and is one of many I would change if I ruled the world.  The current rules require you to re-measure the boat and get a new certificate if you want to change the profile of the sails but keep the area the same, surely it is only necessary to measure the new sails and confirm that they do not exceed the area quoted on the original certificate?

On a lighter note............

 

As someone who raced in & placed 2nd, to my good friend John Cleave, in the first ever r/c 10r National at Poole in , I think 1976, I can offer the suggestion that more people are not racing the class is that although they are fabulous exciting boats to sail lots of us can no longer keep up with their speed!!  if you race them on big open waters where they should be raced.

 

 

John, 

The method I use with a mirror sighting through the undersurface of the water to where it bisects the hull, ignoring the meniscus. I am fully aware if taking a visual waterline marking from above the surface of how much the meniscus would add, hence the mirror method sighting below. It is accurate as any complicated system, as has been shown repeatedly when my designs have been checked with other elaborate ‘tank methods’. No need to overcomplicate things.

On swing rigs the jib area issue in getting lower rig suitable sizes can be solved with an off set pivot rig as Roger has shown and Richard mentioned on the measured rig. It can be done, but not a direction I would favour…

1 hour ago, Derek Priestley said:

On a lighter note............

 

As someone who raced in & placed 2nd, to my good friend John Cleave, in the first ever r/c 10r National at Poole in , I think 1976, I can offer the suggestion that more people are not racing the class is that although they are fabulous exciting boats to sail lots of us can no longer keep up with their speed!!  if you race them on big open waters where they should be raced.

 

 

A good point Derek, very similar in the effort it takes to chase after a Vane boat under spinnaker down the full length of Fleetwood or Gosport lake. Numbers were reduced in those disciplines a few years back but what we see now with good promotion and energy, is the Vane classes coming back to life with younger generations. People have the boats and want to use them again. People coming back enthused, who would have thought…

The 10R sits as the fastest and most modern in design of the International classes. The attractiveness of the rule to anyone thinking they are a designer is obvious for a real test. Yet the class is again floundering. If newer skippers have not been attracted to it like they have in other countries like France, Italy and Australia, then that falls on calendar and it’s promotion. If current owners are not coming out to race there is a problem. A poor calendar is hard to promote or sell someone on. Sort the calendar, then tell the world. Tell them regularly, make anyone not there feel like they are missing out. It goes the same for any class as the re growth in the Ms, IOMs and 6M classes have shown. Like in other countries we could then have our MYA be positive in supporting all of its classes as an avenue into the sport, through buying used boats instead of pushing the one avenue of entry.

There is a 10R ranking this weekend. How many know about it? Who would want travel for 1 day at this time of year?

Sorry Richard for the hijack and happy if this gets moved elsewhere.

Brad

Dumb question from a non technical person....

If a boat of a similar design has a waterline length of say 5mm more or 5 mm less so a tolerance of +/-5mm what is the sail area difference?

Darin

 

Edited January 19, 20224 yr by Darin Ballington
Spelling

Hi Darin, the amount of the leech of say a mainsail would be so small not to make any difference, if boats were the same weight. Now if the waterline is changed through a weight change, then that difference multiplies. I.e lighter boat with a bit of extra sail vs a heavier boat with less sail. The larger the change, the larger the multiplication difference.

As mentioned I’m happy to factor in a safety value from my actual waterline, making my boats 4-5mm longer for measurement than they actually are in the tank. The loss of that slither of sail is far less important than getting the whole project right I think. Remember it is only the largest measured sail for light airs that will have that slither off it that the lower ones need to fit inside of on the grid.

Brad

I would like to add / reply to the recent comments here. In order:

John; just looked at Graham Bantock's gauge that you referenced. My idea was also a floating gauge. A length of wood floated alongside the WL with a right angle fixed at one end and sliding the other. Sharpened "jaws: set to declared WL and used as a simple Go / No go gauge.

Derek; Pieces of 8 hurtled across our lake and several spectators asked what was powering it. I had difficulty keeping up with my iPhone to video and steer at the same time. Very impressive, particularly as Have been investigating speed sailing for a long time now.

Brad; No hijack at all and keep it coming. This boat was deliberately built as an extreme end of the rule for a reason and has resulted in me becoming interested in the class.

Darin; From previous I have distilled the following results out of data from Pieces of Eight and Bentley designs; summed up below.

WL 1150 & 1344 respectively Sail area 1.08695 sqM & 0.93005 sqM this is a difference in allowed max area of 0.1569 sqM.  This may not sound much in sqM but is 1569sqCm and this equates to > 39 X 39 cm of sail area allowable difference in area for the two designs. Amazing or what !   I think your specific 5mm is easily extrapolated from the rule.

Add to all this is the actual shape variation available to designers and many, many characteristics to play with. 

I don't think I have a measurer nearby so I will incorporate a tolerance on sail area and WL to ensure that I know the boat will be legal but not necessarily fully optimised to the rule.

 

Thanks Brad/Richard,

From what you are saying there is (obviously) a difference but I am seeing that the difference in measurement technique assuming a degree of competence from the measurer is not going to make as significant a difference as the build quality and skipper ability. And is not something that we should get too hung up on.

From a performance point of view I would suspect that a decent rig and keeping my boat dry would have a bigger impact than losing the last mm of WL.

Cheers

 

Unfortunately this picture doesn't show the meniscus as well as I'd hoped.  It does show how bad my paint job is though!   The blue line marks where the meniscus ends (if you look closely you can see the reflection of the bushes behind ends at this point because the water surface is no longer horizontal).  What I was trying to show is just how far apart the waterline mark and the meniscus are - it's around 25mm!

 

Brad,

I don't understand your comment about 'ignoring the meniscus'. If you look under the boat with a mirror, all you can see is the edge of the meniscus.  The sketch below reflects my understanding of the physics of surface tension.  I agree you can see where the meniscus attaches to the hull and where it stops distorting the water surface, but neither of these is where the hull intersects the waterplane.  In other words, you can see Point A and Point B but you can't see Point C

 

Hi John, 
I'm afraid things are probably a little lost in translation. I appreciate your picture and drawing as accurate. My point that i'm trying to get across is that in looking at the underside of the water surface, you can quite accurately see where it bisects the hull at point C on your above drawing. I ignore what is happening at point A & B (the meniscus). The mirror is held at an angle and you are sighting the under surface of the waterline to get a bisection, not holding the mirror up under the hull to see where the meniscus ends. 

Brad

Brad,

Ah I think I understand what you are saying at last.  I've just emptied the tank otherwise I'd have a try.

Richard,

sorry for the thread hijack, I promise to stop now, except.... how have you put the WL marks on your boat if you haven't made the A rig yet?  Setting up a 10R is a bit iterative as you have to sort of guess a waterline, make an oversize rig, weight it, re-do the WL, trim down the rig and so on. In practice one iteration is usually enough but you do need to know the weight of the heaviest rig (almost always the A) before you can finally set the marks.  I shall be interested to hear how it goes against other 10Rs.  I suspect it might go well until you have to change down to the B rig i.e. give up your sail area advantage but suffer with a shorter WL.  The Bentley's party piece is to be able to carry more sail area than most in a given wind strength, of course the wind has to be strong enough for everyone else to need to reduce sail area below the Bentley's maximum.  It's on these days that I remember why I like sailing it so much.  Makes up for all the drifting match days when I get embarrassed by well sailed IOMs!

Just getting around to the A rig now. I did the initial flotation with a dummy weight; adding a little to that last rig pictured. As you say, this is going to be iterative.

Not going for outright maxing out on the rule at the moment though. Pof8 has longer overhangs than Bentley, having LOA of 1930. Just like the J's of old and should heal to a greater wL as a result. I use the word "should" because I have not got any generated waterplane lines and have to wait for a nice sailing wind and see how it looks.

Have hit one problem with sail measurement though. Expected no problems here and made the measurement grid and took all the relevant measurements.  Appears straightforward until I tried entering the data on the IRSA spreadsheet. After having to make a few assumptions from a spreadsheet that is not particularly intuitive, I began.  Mainsail worked ok but when I entered the data for the jib I keep getting an error message. "Foot length does not match number of heights".  I did get that with the Mainsail also, initially, but found the error. I have spent hours trying to resolve the jib error and have got nowhere.  I know this must be a simple mistake and Have been back through the database figures and studied the cross width diagram; all to no avail.

Is there any guide for this ?

Have I Hijacked my own thread ?

Should I stick to the One Metre ?

Brain hurts.

 

There is an error that I found in the on-line forms in this area (which I have reported).  The spreadsheet counts the number of heights you enter and checks that this matches the length of the foot.  So, for example, if your foot length was 425mm there should be 9 entries - h0 to h8 at 0, 50,100 .... 350, 400.  Unfortunately there is a bug in the spreadsheet that if one of the entered values is zero, then it ignores this value and counts one less height than you have entered.  I don't know if this is your problem but try adding / removing entries until the error goes away and see whether it wants too many or too few entries.  Or if you post your data I can check it for you.

You may also notice that the graphs it draws of the sail profile look odd at the head.  This is because it assumes that the head width is zero (why I don't know) so if your sail has a reasonable head width (my mainsail is 90mm) then the graph is not very helpful.

I to have been entering my own data into the on-line forms and have many comments on the layout of the forms, the fact that huge parts of the final certificate are just guidance (and may be totally irrelevant to your particular sails), and the lack of any instructions / explanation on how to fill them in (even to the extent of which fields you have to enter and which are automatically generated).  The fact that all the formulae are hidden doesn't help you understand what they do and hence resolve issues like this.  If you want to see the formulae then is is pretty simple to unlock a sheet - you just take a copy of the spreadsheet and each sheet will then unlock without a password.  Unlocking the whole workbook is a bit more complex but Google is your friend.

 

Thanks for that, John.

I have now substituted value 1 for h0 mainsail and 1 for h9 jib, instead of value 0;  and errors disappeared. Hooray for that. 

Spent some time trying to make sense of the mast and spar form and sort of got a figure with no errors. However my total SA is way out. Have checked the old fashioned geometry way to confirm this.

So difficult to follow the form. I know a spreadsheet is going to make life easier for a class with variable sail areas like the 10R;  but it is so difficult to understand what is expected. As I said, I have made a few assumptions just to get started.  I know that anyone who has successfully done it once will laugh at my problems and I am a bit cautious about expressing any strong opinions.

Samples: why does sail 2 total have a title "Sail 1" as does sail I ?   What is spar 1 "E" measurement. and quite a few more.

I am using Excel for Mac 2008, which is the same age as my MacBook. Works ok for everything else I do.  I have been looking at the formulae in each cell but that is all. I feel the fault lies in the data I am entering, but cannot find out what yet. 

How did they measure the sails before Microsoft appeared ?

In relation to measurement Forms Try reading this document from the 10R section of the IRSA website.  When using the spreadsheet form the only areas which need completion by the measurer are those highlighted in blue.  It is important to pay attention to placing the sail/mast spar on the measurement grid correctly.

Thanks Solent, I did that before I started.

Thanks to John sending me a copy of his calculation forms I have realised that the forms I downloaded from the MYA IRSA page were not the same as his. Hence my earlier comments about the Sail 2 page having the same title of "Sail 1" and showing the picture of the Main. I just assumed that this was a generic sail shape.

I have just re visited the same source and downloaded the spreadsheet again and it is completely different. Now I have the same as John. Sort of irritating that the form I downloaded back in December was so different and I have spent two days finding out. Anyway; will try again in the morning. Taking note of the "fudge" that appears to get rid of the error messages because the spreadsheet cannot count from 0.

Appreciate all the help here.

Richard

Update to my last:  Thanks to John I have discovered that the spreadsheet I have been using, downloaded in December, was out of date. It was version 5 and the current version is 6B. Frustrating or what !

Unfortunately I am still getting a huge error in my sail measurements compared to old fashioned geometry calculations. Will persevere, of course. Have now spent more time on sail measurement than it took to build the 10R hull. Maddeningly I am aware that it must be something I am doing something wrong  However it is interesting that I can reduce the Sail area without incurring error messages by leaving out a few measurement values.

Richard,

I am unclear where you downloaded the version 5 form from but obviously not the IRSA website as the Version 6 form replaced the version 5 on their website in January 2020.  

Note: with the formation of ITCA all 10R documents have now moved to the ITCA website ( tenrater.org ) from the IRSA website.  

I am not sure what you data entry problem is but a common error is to double enter the last (top of the sail) measurement.

The uppermost cross width is always entered into the box marked cn

The aftermost height is always entered into the box marked hn