m_kiel

Moth decksweeper and lowered mast stumps

Recommended Posts

Hello fellow moth sailors,

while waiting for warmer weather I am considering some winter tuning projects for my Mach2.2. In context of the trend to low mast stumps and recently also decksweeper style sails the following questions have come up:

  1.  Do the decksweeper style sails use a significantly shorter mast or how do they get around the maximum sail dimension as measured from the throat point in the rules?
  2.  Do you think the small advantage of an endplate effect really outweighs the drawbacks regarding aspect ratio of the sail and  heavily disturbed flow on a significant part of the sail area?
  3.  In addition to cutting down the mast stump on my boat with KA sail and Mach2 mast there seems to be some space to cut down the mast, too - even with full cunningham there is some distance between the sail and the boom. Is that reasonable or not a very good idea?

I am looking forward to hear some opinions!

Share this post


Link to post
Share on other sites

Probably out of my depth here. Endplating only occurs when the sail is sealed to the deck, or some sort of other sealed transverse feature which serves to deter the creation of tip vorticies and seal the sail into the airflow across the deck. If you aren't sealing to the deck the "endplate" appendage is only very marginally moving the CoP down the sail. One example of actual endplating is the combined set of Mach 2 upgrades that extends the foot down and butts it against a semi-rigid foredeck extension. However, even this isn't endplating if it isn't in contact. Adding a feature that gives some elasticity to the seal is necessary to give an endplate tuning range.

As a comparison point for what's fashionable right now, take a look at the results from Wangi and bear in mind that Luca Damik's Scalpel is now ~7 years old and has, as far as I can tell from this distance, not been upgraded anywhere, barring fresh foils and sails. 

DRC

  • Like 1

Share this post


Link to post
Share on other sites

My2c

DISCLAIMER: I have to agree with Dave. Do not think that any progress you will change performance much.  Low rigs are a bit overrated, at least with current boats geometry and with the impossibility to properly seal the foot.

CUTTING MAST STUMP: if you are already on a low mach2 mast stump you can cut a little bit but not much; going to stump heights like those of the Maguire (close to 20 cm from kicker attachment to end of stump) increases loads exponentially. I'm not really sure a mach2 can handle those loads without significant reinforcements to the kingpost area. 25 cm, which is close to the standard mach 2 low stump, looks more reasonable.

CUTTING MASTS: with a m2 mast with a KA sail you have room to cut a couple of cm of mast if you really want to. beware that you will have of course to run a little less rake from that moment onwards.

DECKSWEEPER LEECH LENGHT. Ka decksweepers go precisely to 5,185 lenght from throat point (I assisted to measurement in Garda). All other sails measured before july 17 were 8-10 cm inside max lenght. Latest Lennons (goodison sail at the Garda worlds) and I suspect new 2018 norths go to max lenght as well. Ka decksweepers of course had to cut a good chunk of the mast, to go down to foredeck; all others decksweepers will have to do the same.

DECKSWEEPER EFFICIENCY: I have no proper technical Info. What I have been told by more informed people is exactly what Dave says. I suspect that decksweepers will properly start to make a difference only if they are put on a boat designed for them and if they are able to combine endplating with good sail shape and with good enough ease of handling. There is a lot of developement on them right now, we'll see in Bermuda if someone really finds a proper breakthrough. Until that happens, performance differences with standard rigs will be very small IMHO.

 

 

  • Like 1

Share this post


Link to post
Share on other sites

Time for a few home truths.

Unless you are battling to win the worlds with a name like Outteridge, Slingsby, Goodison or Burling. the modifications you are considering will make zero difference to your performance and your finishing position. Ask yourself whether you can regularly hit the same speeds as the top guys before the mods. If not, don't waste your money and note that Goodie won without a decksweeper

As for the "decksweeper", the name is misleading. Amac claims that in straight line speed testing by world class sailors, the KA "decksweeper" has proven to be faster, even without the special deck moulding and without the deck moulding, it clearly cannot be due to sealing the bottom of the sail. The question is whether it is due to the feature at the bottom or whether it is to do with the resultant change in overall profile, height etc.

7 hours ago, m_kiel said:

 Do you think the small advantage of an endplate effect really outweighs the drawbacks regarding aspect ratio of the sail and  heavily disturbed flow on a significant part of the sail area?

As said, here is no end plate effect but your comment about there being a drawback to sail area in heavily disturbed flow might be where you re going wrong. For most of the time, the Moth has more sail area than it needs and you are blading out the top of the sail to reduce power. What i think might be happening is that the new low down sail area is actually reducing turbulence in that area and as such, this is where the gain is coming from. Drag reduction seems to me to be one of the big areas that people are really working on and this could well be part of that strategy.

  • Like 1

Share this post


Link to post
Share on other sites

1. The KA decksweeper rigs used at Malcesine and Wangi have the mast shortenned by about 250mm, 100 off the top and 150 off the bottom from memory. In Malcesine they had weird boxes fitted to the deck which sealed the foot. These did not fit in for the return trip, so they were not used in Wangi. There are only 4 of these sails/rig built so far. They are not yet commerially available. 

2. Last year we changed the way the luff limit is measured. Previously it was  band on the mast at 5.185m now we measure the sail with a 5.185 max. So previously stretched, now in relaxed state, so new sails are being made longer by about 150mm. Same area limits, but now slightly higher aspect ration. The KA sails with the boom between a double skin measure to this luff length. The newest Norths and Lennons are also built to the new longer limit.

3. AMAC says the endplate effect of the deck box was significant, but he did not bother making new boxes and the boats went pretty well at Wangi anyway.

4. The 4 boats with these rigs had previously had the stumps lowered. (AMAC's and Harry's are teh same boats at both venues, but Peter's and Scott's at Malcesine were different boats to Nathan's and Scott's at Wangi.) Not sure to what extent. Lots of M2 have had these modifications. You can apparently cut up to about 40m off the bottom of the stump and just bend down the comp struts, sounds dodgy to me. many cut off more and then cut and shorten the comp struts and rebond them. These look like the later version of the fork/wing bars sold as upgrades. A few others, like Scott,  have lowered the stup to the foredeck level and moved the comp struts to the hull. A smaller number have strengthenned the main tubes and deleted the comp bars.

5. A few people are making big efforts to close the gap between boom and sail. Not just the double skin but also some soft panels with shockcord fitting neatly to the boom. 

6. Lowering the rig seems to be more advantage to small people. Bigger people appear to suffer more in lighter air.

7. Lowering the rig shortens the leach of the sail, considering we still need space to get under the boom quickly. Some aerodymacists consier leach length more important than luff length.  The deck sweeper component of these sails only extends back less than half the foot length, again the aerodynamic theory suggests the end plate is more beneficial at the back of the sail/wing.

  • Like 1

Share this post


Link to post
Share on other sites

GBR posted while I was writing. I totally agree with everything he has said. If you are not already doing 18 upwind and 29 downwind as well as nailing every tack and gybe plus all the shifts, just do not bother. Go sail your moth, keep learning and most of all have fun.

Share this post


Link to post
Share on other sites

Just curious... What % of Mothists are hitting 18/29 and nailing tacks, gybes and shifts?

Share this post


Link to post
Share on other sites

Hi guys,

thanks a lot for the swift and extensive replies. Just to clarify as it is not clear from my original post: The winter here is long and when I can not go sailing I do enjoy the tinkering a lot, too. Thus when thinking about changing parts of the boat the main motivation for me is simply that I enjoy the process of trying to understand something in theory and then implementing it on the boat. The possibility of increased performance is more of a side note - I am fully aware that if I had any of the top guys boats and they were in a Bladerider I would probably not stand a chance around a race course.

Now concerning the topic of a lowered rig in our German moth group Chris Rashley has been quoted to claim an increase of 0.5 knots over a standard rig. That would be more than one boat length every 100m, which I, based on my limited experiences when lining up with others that have the low rig, was finding hard to believe. I am happy that your general opinion seems to be that it is most likely not nearly as significant, especially as I am on the upper end of weight and height compared to the ideal moth sailor:

1 hour ago, Phil S said:

6. Lowering the rig seems to be more advantage to small people. Bigger people appear to suffer more in lighter air.

Currently I still use the high mast stump with a straight boom and have not had too many difficulties to get stuck underneath. Lowering the rig would also mean I have to kink the boom, which inevitably will add some weight, which is also true for modifying the compression bars and thus not helping low wind performance.

3 hours ago, 17mika said:

CUTTING MAST STUMP: if you are already on a low mach2 mast stump you can cut a little bit but not much; going to stump heights like those of the Maguire (close to 20 cm from kicker attachment to end of stump) increases loads exponentially. I'm not really sure a mach2 can handle those loads without significant reinforcement.

This is also a very valid point that had me concerned and will, together with the other points you mentioned, have me stay with my current setup: I do enjoy how resilient the Mach2 has been so far and I really don't want to change that.

Thanks also to Dave Clark and Team_GBR for clarifying some things concerning the endplate effect.

On the Lennon Sails website they have some short text about the A3.5m developed by Dylan, which is described by 'countering the direction of travel on [the other sails]' from which I read that the current trend is definitely not the holy grail yet.

 

 

 

Share this post


Link to post
Share on other sites
4 hours ago, Phil S said:

5. A few people are making big efforts to close the gap between boom and sail. Not just the double skin but also some soft panels with shockcord fitting neatly to the boom. 

 

YeeHaa, a move back to shelf foots and boltropes in the boom, circular development continues! :lol:

Share this post


Link to post
Share on other sites

No bolt ropes Jethrow, if the sail attaches along a spar the spar area gets added on.

Share this post


Link to post
Share on other sites
4 hours ago, bill4 said:

Just curious... What % of Mothists are hitting 18/29 and nailing tacks, gybes and shifts?

The 2018 Bangin' the corners cup video featuring some fairly well known Mothies might give you some idea (i.e. very, very few).

 

Share this post


Link to post
Share on other sites
16 hours ago, Dave Clark said:

As a comparison point for what's fashionable right now, take a look at the results from Wangi and bear in mind that Luca Damik's Scalpel is now ~7 years old and has, as far as I can tell from this distance, not been upgraded anywhere, barring fresh foils and sails. 

DRC

Luka’s boat has had significant upgrades. Significant lowering of rig and shortening of mast included.

Share this post


Link to post
Share on other sites
3 hours ago, teknologika said:

Luka’s boat has had significant upgrades. Significant lowering of rig and shortening of mast included.

Turns out I am out of my depth.
 

Share this post


Link to post
Share on other sites
15 hours ago, m_kiel said:

Hi guys,

On the Lennon Sails website they have some short text about the A3.5m developed by Dylan, which is described by 'countering the direction of travel on [the other sails]' from which I read that the current trend is definitely not the holy grail yet.

 

 

 

I think Dylan's sail was made to the old rules though, so this is also one of the reason the luff is shorter. Anyway I think he reads SA, so he may elaborate on that if he wants. We'll see what rig he and others will bring at the worlds.

Mic

Share this post


Link to post
Share on other sites

Just saw this and thought I would offer some stats. During the Australian Nationals I ran a lowered rig (by about 100mm) from when the boat was built in 2010, however mast is standard CST length which is actually 30mm longer than original Mach 2 length. The foil verticals are pretty old school (mach 2.3 centerboard and Lister rudder). Both are last generation. The horizontals were, Swift rudder I designed for Garda worlds and the new Swift Small centerboard + Macita for the sub 15kn days. The sail is last generation Lennon A3M, so overall the boat is a mix of 2/3 years old stuff with new horizontal hydrofoils.

Share this post


Link to post
Share on other sites

Mike explains my A3.5M pretty well on his website. After trying Goodies sail from Japan the A4m and my prototype design at the same time I decided to go down a different route to Goodie. 

I basically wanted quite an even depth over the sail with the head twisting off early. Working off the sails that I had we tweaked the luff round and seam shape to fit the CST 22 mast for the shape that I wanted. We also increased the luff pocket because I felt this may help reduce the amount of stall going on there when running a high amount of camber in the sail without having to push the draft further forward. 

I also wanted to lower the mast, but keep the leach length quite long. Which makes the sail hard to manoeuvre with due to the reduced gap between the boom and boat. Being lighter and smaller I figured I could cope with less distance here to try to drop the rigs CoE and try to claw back some of the gain from heavier sailors.  

There are some other tweaks but they are only small. 

In essence I think the A3.5m has a high available top speed than the other designs because you can run it flatter with a straighter leach but its harder to use. I think its a chunk harder to get it to 90% of its max speed than the A4 or probably A5 but in theory should be quicker top end upwind. Which seems to be the case, because I don't struggle upwind for my size. 

 

My boat new boat will be at the dinghy show sporting a few new developements, but you will have to wait until then to see what. Unfortunately I can not make the worlds once again, gutted to be missing out. 

Share this post


Link to post
Share on other sites

Lennon decksweeper version with boom, which I guess properly sweeps the deck on a thinnair moth

FB_IMG_1518878225572.jpg

Share this post


Link to post
Share on other sites
On 10/01/2018 at 10:26 PM, Phil S said:

Some aerodymacists consier leach length more important than luff length.  The deck sweeper component of these sails only extends back less than half the foot length, again the aerodynamic theory suggests the end plate is more beneficial at the back of the sail/wing.

Phil S

Thanks for these interesting comments, I am not a Moth sailor yet,  but I am very interested with the Moth developments. 

So regarding the end plate effect;  Intuitively, I though it was most effective where there is the biggest pressure difference between windward and leeward sides of the sail:  so in the front part near leading edge.

But it seems my intuition is wrong,

Have you any extra comments to help me understand

Thank  in advance

Erwan

Share this post


Link to post
Share on other sites

Word is a lot of decksweepers with booms are going at the words, from different manufacurers (ka, lennon, north).It will be interesting to see if boats end-up lowering the foredeck (thinnair style) or putting structures on the deck to go up (ka style at the 17 worlds). 

I suspect the thinnair starts to be pretty interesting to lowride in waves with its low foredeck.

 

 

  

Share this post


Link to post
Share on other sites
On 20/02/2018 at 8:43 PM, 17mika said:

Word is a lot of decksweepers with booms are going at the words, from different manufacurers (ka, lennon, north).It will be interesting to see if boats end-up lowering the foredeck (thinnair style) or putting structures on the deck to go up (ka style at the 17 worlds). 

I suspect the thinnair starts to be pretty interesting to lowride in waves with its low foredeck.

 

 

  

i heard Pete Burling ripped his funky fairing off at worlds, it looks like it would get in the way to me hahaha

Share this post


Link to post
Share on other sites

The deck sweeper Lennon does get within a 20mm of the deck on the Rocket SSD, we still need a small fairing to improve the efficiency but its way ahead of the Exocet in this area already. 

Only tested my A3.5m Decksweeper out a little but early testing shows some significant gains upwind and not much in it downwind. I can't quite sit at 19 upwind, but 18 on a good angle seemed pretty good. Overall it was higher and faster than the current standard design. Both boats were Rocket SSDs in 12-14 knots

Share this post


Link to post
Share on other sites

Cool to know dylan.

I Hope ho finally hit the water next weekend, to see how the ssd feels.

Later in the season I'll happily go for the low rig if it goes well, as you say.

 

 

Share this post


Link to post
Share on other sites
12 hours ago, skiffman said:

The deck sweeper Lennon does get within a 20mm of the deck on the Rocket SSD, we still need a small fairing to improve the efficiency but its way ahead of the Exocet in this area already. 

Only tested my A3.5m Decksweeper out a little but early testing shows some significant gains upwind and not much in it downwind. I can't quite sit at 19 upwind, but 18 on a good angle seemed pretty good. Overall it was higher and faster than the current standard design. Both boats were Rocket SSDs in 12-14 knots

Dylan, do you think that the ssd is going to catch on for more top sailors?

it looks sick for sure, what are the aero/stiffness weight differences like?

Share this post


Link to post
Share on other sites
3 hours ago, inebriated said:

Dylan, do you think that the ssd is going to catch on for more top sailors?

It had better. That thing is the tits!

Share this post


Link to post
Share on other sites

Sorry if the question looks stupid as I am not a Moothie:

I saw on Moth's measurement rules that the mast lenght is 6.25 meters.

On forum I see sail luffs are around 5.185 meters and masts a little longer I guess ?

So I don't know where is the difference 6.25 - 5.185 = 1.0625 meter

Or is 6.25 meters a maximum mast leght and

today's 5.185 meters mast is a result of an optimization for the foiler mode?

I would love to know actual mast lenght for last decksweeper sails.

Thanks in advance

 

Erwan

Share this post


Link to post
Share on other sites

They are all max lengths, the current rules have removed the black band requirement.

The trend has been to get the rig as low as possible to maximise the righting moment, and shorter masts help with that. I would guess the mast length is probably the one suitbale to get the maximum amount of downhaul to get the sail flat.

Share this post


Link to post
Share on other sites
6 hours ago, Erwankerauzen said:

Sorry if the question looks stupid as I am not a Moothie:

I saw on Moth's measurement rules that the mast lenght is 6.25 meters.

On forum I see sail luffs are around 5.185 meters and masts a little longer I guess ?

So I don't know where is the difference 6.25 - 5.185 = 1.0625 meter

Or is 6.25 meters a maximum mast leght and

today's 5.185 meters mast is a result of an optimization for the foiler mode?

I would love to know actual mast lenght for last decksweeper sails.

Thanks in advance

 

Erwan

allows for a keel stepped/unstayed rig

Share this post


Link to post
Share on other sites

Current rules allow for a sail with 5,18 luff when on the floor (I am simplifying a bit)  and probably 525/530cm luff when downhaul is pulled to max. Most sail are designed to max luff lenght (moreless)

"normal" moth masts are all between 532 and 538 cm, to use the above sails 

New decksweeper masts are  around 510, so that luff on the decksweeper goes below the mast and on the mast step, to sweep the deck. 

For example below is Goodie with a decksweeper with downhaul on. I guess mast is 510 or 515 and kingpost + end fittings probably other 10 cm, so total 520. luff, stretched by the downhaul is maybe 525-530 and starts to create some wrinkles at the bottom of the sail, cause the sail hits the foredeck.

Michele

 

Share this post


Link to post
Share on other sites

 

54 minutes ago, inebriated said:

do you guys think that the s/z boom will take off?

As I am not a Mothie, I hesitate to post, but I if my remarks can trigger some comments:

1-Windward, for me it is a no brainer, whether the foot sail is straight+ canted downward or stepped the narrower the gap, the less the induced drag, especially in the lights winds when you are  looking for hp in your sail.

 

2-Downwind, with more twist in the apparent wind,  if your leech is stepped, the stepped part is loosing some AoA according to the apparent wind, so the bottom corner of the leech could find an advantage to be pulled toward the middle of the boat with a rubber or similar.

In other words, the shorter the chord going down the leech, the more the leech need to be pulled toward the middle of the boat.

In conclusion as long as the bottom part of the sail is put at full use downwind, the new boom/sail arrangements should outperform the older ones both upwind and downwind.

Or at least upwind in any cases.

That is a rookie bet, so be indulgent Mates.

Cheers

Share this post


Link to post
Share on other sites
On 31/03/2018 at 12:36 AM, Erwankerauzen said:

 

As I am not a Mothie, I hesitate to post, but I if my remarks can trigger some comments:

1-Windward, for me it is a no brainer, whether the foot sail is straight+ canted downward or stepped the narrower the gap, the less the induced drag, especially in the lights winds when you are  looking for hp in your sail.

 

2-Downwind, with more twist in the apparent wind,  if your leech is stepped, the stepped part is loosing some AoA according to the apparent wind, so the bottom corner of the leech could find an advantage to be pulled toward the middle of the boat with a rubber or similar.

In other words, the shorter the chord going down the leech, the more the leech need to be pulled toward the middle of the boat.

In conclusion as long as the bottom part of the sail is put at full use downwind, the new boom/sail arrangements should outperform the older ones both upwind and downwind.

Or at least upwind in any cases.

That is a rookie bet, so be indulgent Mates.

Cheers

It is actually dependent on a lot of things. The deck sweeper moves the COE down, and looses power but has lower drag. So if you are sailing below the design condition I.e. looking for power the deck sweeper will be slower, esp downwind.

Once you are over the design condition and tying to depower the deck sweeper will be quicker, esp upwind.

A lot of variables determine the design condition. Crew weight, foil length, wing geometry etc. nothing comes for free and it is all trade-offs.

This is why the top guys in Bermuda are using normal rigs downrange and sweepers uprange.  

 

Share this post


Link to post
Share on other sites

Thank you Tecknologica for taking time to answer my candid post.

Regarding the loss of power, it should be interesting to guess if it is a consequence of a lower rig or a less powerfull sail ?

Decksweeping sails for A-Cat, not only have a lower induced drag, but everything else equal they are likely to deliver more hp, as the bottom is more efficient.

And if you have an elliptical lift distribution (with an elliptical area distribution like today's A-Cat sails) your sail CoE is at 42% height when trimmed for max power.

Of course, the above statements work well for decksweeping sails with 0 gap.

Decreasing gap is better, but as some gap still remains, improvements are probably less obvious and could be offset by other effects.

This development class is amazing and I feel confident it will remain so for a long time.

Thanks again for posting Tecknologica and fair winds.

Erwan

Share this post


Link to post
Share on other sites

Erwan main issie is not only rig height but that currently we decksweep through the boom (49er style), so bottom of the rig is by definition flat.

You definitely lose power like this. Acat style decksweeper would be more powerful but would need a different mainsheet system, which may be not usable on a moth

Share this post


Link to post
Share on other sites
On 02/04/2018 at 7:27 PM, Erwankerauzen said:

Thank you Tecknologica for taking time to answer my candid post.

Regarding the loss of power, it should be interesting to guess if it is a consequence of a lower rig or a less powerfull sail ?

Decksweeping sails for A-Cat, not only have a lower induced drag, but everything else equal they are likely to deliver more hp, as the bottom is more efficient.

And if you have an elliptical lift distribution (with an elliptical area distribution like today's A-Cat sails) your sail CoE is at 42% height when trimmed for max power.

Of course, the above statements work well for decksweeping sails with 0 gap.

Decreasing gap is better, but as some gap still remains, improvements are probably less obvious and could be offset by other effects.

This development class is amazing and I feel confident it will remain so for a long time.

Thanks again for posting Tecknologica and fair winds.

Erwan

The moth situation is a result of our class rules and a 5185 luff length limit.

If we only measured area, then we would have gains everywhere with a fully endplated sail, like the A class as we would just have a longer, higher aspect rig. 

Share this post


Link to post
Share on other sites

Thanks Teknologica,

In other words an actual breakthrough cannot happen in the Moth Class due to the rule box.

So I feel confident a smart guy will create a new rig/platform which will use the standard Moth foils

and will outperform the Moth at cheaper price, but of course, nothing will be compliant with the Moth rule box.  It will be another serie.

Happy week end

Erwan

Share this post


Link to post
Share on other sites

Poor logic Erwan.

A lot of reasonably clever people have been trying for many years to make faster moths or cheaper moths and other foiling boats which are not moths but are either cheaper or faster, and very few have been able to succeed with any of these objectives. There have been quite a few unsucessful moth designs and quite a few non moth designs which did not attract customers or which could not be built at marketable prices. So far it appears that only the Waszp and UFO have attracted enough buyers to gone into serious production. Both are aiming at the price market rather than the speed market.

Building a moth style boat which out performs a quality moth at a cheaper price is a fantacy which no one has come close to realising.

If you want to go faster for less money you need to learn how to kite sail a foil board. Maybe this proves simpler is better, and maybe thats why some of the bigger foilers are so disapointing in both cost and performance terms. If you want to sail something cheap but more conventional which still out performs almost most all other boats buy a well used moth.

wrt to question which started this thread, the moth trend with rigs for several years has been to lower the CoE to reduce capsize moment. This has resulted in shorter leach lengths and hence lower aspect ratios. Higher aspect rigs can be built within the rules with longer leaches and longer masts, the 5.185m luff just needs to be higher up the mast. But the serious mothies have decided that the increased capsize moment is a negative to performance except in very light low riding conditions, when championship racing does not happen. 

There are presently again several experienced moth people developing new designs, some of which may make it into production if they perform well enough to attract buyers, and the builders can make them at a marketable price. Winning a championship increases the market price of course but that is getting very hard. Some interesting ideas are beig floated. We will see how they go over the next year or so.

Share this post


Link to post
Share on other sites
Just now, Phil S said:

Poor logic Erwan.

A lot of reasonably clever people have been trying for many years to make faster moths or cheaper moths and other foiling boats which are not moths but are either cheaper or faster, and very few have been able to succeed with any of these objectives. There have been quite a few unsucessful moth designs and quite a few non moth designs which did not attract customers or which could not be built at marketable prices. So far it appears that only the Waszp and UFO have attracted enough buyers to gone into serious production. Both are aiming at the price market rather than the speed market.

Building a moth style boat which out performs a quality moth at a cheaper price is a fantacy which no one has come close to realising.

If you want to go faster for less money you need to learn how to kite sail a foil board. Maybe this proves simpler is better, and maybe thats why some of the bigger foilers are so disapointing in both cost and performance terms. If you want to sail something cheap but more conventional which still out performs almost most all other boats buy a well used moth.

wrt to question which started this thread, the moth trend with rigs for several years has been to lower the CoE to reduce capsize moment. This has resulted in shorter leach lengths and hence lower aspect ratios. Higher aspect rigs can be built within the rules with longer leaches and longer masts, the 5.185m luff just needs to be higher up the mast. But the serious mothies have decided that the increased capsize moment is a negative to performance except in very light low riding conditions, when championship racing does not happen. 

There are presently again several experienced moth people developing new designs, some of which may make it into production if they perform well enough to attract buyers, and the builders can make them at a marketable price. Winning a championship increases the market price of course but that is getting very hard. Some interesting ideas are beig floated. We will see how they go over the next year or so.

yeah, i agree

i feel like with the tech that we have at the moment, there really isn't that many concepts that will prove to be successful for a class that haven't already been used and are up and going.

any non foiler classes are really sorted, from one design to box rule

then with foiling, cats have the a class for dev and UFO for one D, with the possible nacra 17 for serious sailors wanting to ail with a crew

then there is the moth and ufo for mono dev and OD classes

i really think that the people trying to make some funky foiling class are really playing themselves, they may sell a few to some pockets of sailors in isolated areas who do not race outside of their bubble but that's it.

the one potential market gap i could see is a mono foiler, a bit like the nacra 17 but monohull. good luck getting that thing stable though, i don't see it happening in my lifetime.

Share this post


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

yeah, i agree

i feel like with the tech that we have at the moment, there really isn't that many concepts that will prove to be successful for a class that haven't already been used and are up and going.

any non foiler classes are really sorted, from one design to box rule

then with foiling, cats have the a class for dev and UFO for one D, with the possible nacra 17 for serious sailors wanting to ail with a crew

then there is the moth and ufo for mono dev and OD classes

i really think that the people trying to make some funky foiling class are really playing themselves, they may sell a few to some pockets of sailors in isolated areas who do not race outside of their bubble but that's it.

the one potential market gap i could see is a mono foiler, a bit like the nacra 17 but monohull. good luck getting that thing stable though, i don't see it happening in my lifetime.

Quant 23 in Europe 

Share this post


Link to post
Share on other sites
11 hours ago, inebriated said:

...the one potential market gap i could see is a mono foiler, a bit like the nacra 17 but monohull. good luck getting that thing stable though, i don't see it happening in my lifetime.

There's an old thread on the boat design list with lots of examples of multiperson monofoilers: https://www.boatdesign.net/threads/new-high-performance-monofoilers.25366/

Share this post


Link to post
Share on other sites

Thanks Phil, Doug, Connor & Inebriated for taking time to post.

I was travelling last week, and I am not confortable writing from a smartphone, that is why I waited to be back home to post.

"Poor reasonning"  Is almost a compliment as it was more or less intuitive, and based on former A-Cat induced drag calculations.

As most of you are engineers, I will try to post a few calculations to illustrate the intuition:

Of course it is purely theorical and the ability to tack or gybe in 1 second as can be seen on Youtube, is not considered .

 

                                            Classic Moth Rig                         Theorical DeckSweeper Rig

Sail Area                             8.25 m^2                                       8.25 m^2

Luff lenght                          5.185 m                                        5.70 m

Gap(% luff lenght)             10%                                                0%

Oswald Coef                       1.19                                                2

Geometric AR                     3.26                                                3.94

Effective AR                        3.88                                                7.87

For 10m/s Apparent wind velocity and a 350 Newtons actual sail lift, we should have

Cl(3d)                                  0.70                                                 0.70

Cl(2d) equivalent               1.06                                                 0.79

Cxi (Induced drag coef)    0.092%                                           0.0253%

Induced Drag                      46.3 Newtons                                12.73 Newtons

Detla= 33.5 Newtons

Main assumption : both rigs have the same height for their center of effort.

The 33.5 Newtons Induced Drag difference is interesting to consider relative to the total driving force created by these rigs.

With Apparent wind angle around 20° relative to the boat:  

The driving force is around   F= 350 Newtons * Sin (20°) = 119 Newtons.

Of course it is a bit meaningless as it is not possible to have both: a full decksweeping sail and the possibility to tack or gybe under the footsail.

If the crew moves his weight aft, in order to go behind the leech for tack or gybe, I dont believe it is possible according to the relative weight of the crew  vs total boat displacement.

But, because the performance "carrot" if even larger than for A-Cat, I feel confident a smart Aussie or Kiwi will bring a breakthrough  sooner or later.

Best regards

Erwan

 

 

 

  • Like 1

Share this post


Link to post
Share on other sites

The decksweeper rig is not 5.7m on the luff. The new rule says it can be no longer than 5.185m on the floor, which might stretch to 5.4 under extreme luff tension, but not likely to be more. 

Share this post


Link to post
Share on other sites

hey guys, 

my half-baked experience when I put one of these on the boat a couple of years ago now - i think the drag reduction from the boom / vang ropes etc. was an upside at least. The boat was quieter to sail. I felt like the lowered rig (250mm as you say) suffered when searching for power, but was an advantage in breeze. I really think there is merit to this idea though, and I really hope someone sorts it out before too long! Clearly the hull design needs to integrate.

What if you embedded a spring loaded seal in the bottom edge of the sail would drop down and account for changes in rake etc. If you look up smoke seals for fire doors in buildings, could be similar.

Phil, is there a rule governing the angle of the foot relative to the luff, like there is for the head?

Nick

Share this post


Link to post
Share on other sites

Nick,

I have tried two short rigs, both on masts 250 shorter. One  a few years back was a small area storm rig with conventional foot. An MSL10 with 250 cut off the bottom. It was fast upwind in over 20kts but needed more than 25 to go fast downwind. I gave the sail to a light weight senior mothie friend. The second has a pocket around the boom and vang, measures full size and like you I am amazed how quiet it is. But again I seem to lack pace downwind although I have not tried it in over 20kts yet. I am thinking it might suit the Perth WC if the Doctor attends.

The foot is limited by needing to fit inside a 5.185m radius from the top of the luff.

Any sail like extra which moves when the sail is trimmed has to be part of the sail, it can not be a separate item under the one sail rule. Some UK boats are fitting a fixed carbon shell across the deck to seal the foot. I agree a purpose designed hull can do it better, I think the Lennon ThinAir was going that way, but its been a long wait. There are some interesting new designs coming along this year, Moth aesthetics could be about to change.

Share this post


Link to post
Share on other sites

PhilS,

The 5.70 m luff is an assumption regarding a new rig trade-off regardless of the rule box.

But your remark prompts me to crunch the figures again with a 5.185 max luff lenght, in order to compare apples with apples.

So with a full decksweeping foot sail with a 5.185 luff lenght and a 8.25 m^2  we have: 

Oswald coefficient =2  

So we should have the following results:

Aspect Ratio           =         6.52

2D Lift Coefficient  =         0.91  (for a 0.70 3D lift coef as above-mentionned)

Induced drag coef  =         0.0404%

Induced drag           =         20.33 Newtons  (apparent wind @ 10 m/s)

So even in this case, the decrease for induced drag remains significant relative to the classic rig:

20 Newtons  vs 46  Newtons.

Wish you a nice week

Cheers

Erwan

Share this post


Link to post
Share on other sites

Ewan,

Fits with what we have observed about drag. But rig height seems inportant in lighter winds when its stronger and more useful up higher, especially downwind.

Inebriated,

James has done what looks right to seal the deck sweeper, but the full carbon wings look heavy to me. Radial track vang/kicker solves a lot of vang load/angle issues but the track would get in the way of my feet and toestraps when hiking.

  • Like 1

Share this post


Link to post
Share on other sites
On 30/04/2018 at 3:01 AM, inebriated said:

what is your thoughts on this one?

This makes a lot of sense to me, for what that's worth! Phil, maybe the large semi-circle fairing + vang track could just become the front wing bar - detachable, thick enough to not need compression struts and fairly light - and the rest of the wing structure could be traditional tubes, so that its easy enough to pack into a box and transport

Share this post


Link to post
Share on other sites
Just now, flutter said:

This makes a lot of sense to me, for what that's worth! Phil, maybe the large semi-circle fairing + vang track could just become the front wing bar - detachable, thick enough to not need compression struts and fairly light - and the rest of the wing structure could be traditional tubes, so that its easy enough to pack into a box and transport

alright

you still using the same moth from your blog?

Share this post


Link to post
Share on other sites

yeah, this was my last effort. forgot to write a blog post about it. this was from early 2016. It's very rough but it was a cheap / quick test of the idea, but it was promising i think. Would probably work better with the fairing from the other boat you posted. My boat was always intended to have some kind of fairing between the rig and the hull, but I never really figured out what to build there.

IMG_6782_ss.jpg

IMG_6784_ss.jpg

Share this post


Link to post
Share on other sites

well Nick that looks like where everybody is going now, 2 years after you.

But I really would like to see if the track idea works in practical terms. let's see how james actually can sail the thing.

Regarding the weight of the solid boats, honestly after sailing few times my rocket ssd I have to say I do not notice a big difference.it is probavly slightly heavier, but definitely not much. and it is by far the nicest moth I have ever said; the stiffnes, responsiveness and ergonomics of the platform are simply in another league compared to soft wing things :) veeery happy to have gone solid :)

Share this post


Link to post
Share on other sites

Nick's sail probably wouldn't be legal now. The head angle looks to be too big, which is a new rule that has been added since 2016.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now