# Moth on Foils: 35.9 knots(41.29 mph)

Discussion in 'Sailboats' started by Doug Lord, Apr 11, 2006.

1. Joined: May 2009
Posts: 16,679
Likes: 346, Points: 93, Legacy Rep: 1362
Location: Cocoa, Florida

================
So,wind,you have two identical Mach ii's one with Bora and one with,say Simon Payne. Lets assume there is a 15kg(33lb) difference. We know the SA is identical.
Lets assume that each boat weighs 66lb and that ,just for the heck of it, the mainfoil supports a nominal 80% of the all up weight. Guessing that Bora is 180 + 66=246lb then 80% =196.8. If Payne is 33lb lighter,then (180-33)+66=213lb. then 80% = 170.4lb.
If both mainfoils are identical at, say 1.1 sq', then Boras mainfoil loading= 178.9lb/sq.ft. and Payne 154.9.
196.8/"X"=154.9 and solving for "X" it can be seen that for Bora to have the exact same foil loading his mainfoil are would have to = 1.27 sq. ft.. which is .17 sq.ft. or 24 sq. inches more area or 12 sq. in. added each side. For a 4.75" chord foil that would be 2.5" added to each tip. Adding that area in light air would also increase the span, probably reducing drag. This is just an example-it might turn out after research that adding a small amount to the rudder foil as well would be beneficial.
---
You don't think that it would help for Bora to have at least the same foil loading as Payne? It might even be determined with more research, that if the span was increased a bit further it would be better still.
I can assure you that this is a long, long way from being a dead horse!

2. Joined: Dec 2004
Posts: 1,709
Likes: 82, Points: 48, Legacy Rep: 467
Location: Sydney Australia

### CT 249Senior Member

Some guys in the class feel that aiming it too much at foiling conditions will mean that gear will become ever more specialised for sailing in foiling conditions, to the point where Moths will no longer be able to sail at 'normal' sailing clubs on many days.

There are many people out there, like the head of the world's biggest windsurfer company, who feel that windsurfing was torched when it something similar and started to concentrate only on planing conditions.

So, depending on your view, going to a place that is not conducive to foiling could make very, very good sense.

3. Joined: May 2009
Posts: 16,679
Likes: 346, Points: 93, Legacy Rep: 1362
Location: Cocoa, Florida

Moth on Foils! Simon Payne wins Dubai Worlds

Dubai Worlds:
1st Payne,UK, World Champion Moth Sailor
2nd AMAC, Aus
3rd Funk USA
4th Psarofaghis
5th Bergen USA
6th Gulari USA( former World Champion)

http://www.dosc.ae/moths-entry-list/results/puma-moth-worlds-2010.html
===============================
Tidbits from after race conversation:
--AMAC is designing a much easier to sail foiler to get more juniors(and others) interested in foiling.
--Simon Payne on sailing in light air:" Part of saling is dealing with what Mother Nature throws at you."
--AMAC had most modified boat at worlds...
--AMAC said: " as soon as you're on foils weight is an advantage."
--Funk- Moth in Olympics great idea
--Gulari-Moth perfect for Olympics, but Olympics would hurt Moth.
--Payne-Olympics is nautical verson of Antiques road show-thinks Olympics would hurt Moth.
--AMAC-"I don't see the Moth as an Olympic Class" Thinks a purpose designed foiler will be in the Olympics(An Olympic one design)-not a Moth.

4. Joined: Oct 2006
Posts: 673
Likes: 21, Points: 0, Legacy Rep: 328
Location: England

### PI DesignSenior Member

Chris,
It's not long since Jeff posted a reminder of what he expects from forum etiquette. IMHO, you are bordering on crossing it. Please refrain from the constant sniping and post a bit more construtively!
Is the Mach 2 a faster boat, or just sailed by faster sailors?
Quingdao would have interesting for foiling Moths!

1 person likes this.
5. Joined: May 2009
Posts: 16,679
Likes: 346, Points: 93, Legacy Rep: 1362
Location: Cocoa, Florida

====================================
1) FALSE- I've always said that weight is critical within a class like the Moth.
But some Mothies(notably Phil Stevenson) and others said that a boat heavier than a Moth could not foil well. So I devised(borrowed) the formula W/SA ,where W=weight in pounds and SA= sail area in sq.ft. to illustrate where a similar foiler would have to be to have a chance of taking off when a Moth with Veal onboard(the standard) would. That is 2.56 and is reflected in the RS600FF and the 26' Mirabaud. The performance of the RS600FF is almost identical to a Moth even though it weighs 2.5 times as much. And the picture with the kid onboard was Mark Robinson.
---
2) FALSE-as I said above, weight is critical within a class like the Moth where
SA is fixed. If SA was adjusted for greater weight and foils adjusted for foil loading heavy people would be able to compete on a closer basis than is possible now. I have NEVER,EVER stated that Moths were for everyone of every size--quite the opposite. Within a class like the Moth weight is critical, but more weight on a different foiler is ok as long as it is matched by more SA and more RM.
--
3) FALSE-A Moth,under existing rules-could NEVER,ever be a Peoples Foiler! I never,ever would have suggested that!
--
4) FALSE- this is a scurrilous falsehood of the highest level. It was Mr. Gulari on SA that said "weight doesn't matter anymore"-not me. I would have NEVER made such a comment about the Moth class. As to "throwing dirt" on Mr. Gulari-that is another scurrilous falsehood: what I said to Mr. Gulari is right here for anyone to see. I asked him some questions and pointed out to him his comments on SA about weight. At NO TIME on this forum did I "throw dirt" on Mr. Gulari in any way whatsoever. I have repeatedly honored Mr. Gulari's accomplishments as anyone can see in the referenced instances in post 1018 of this thread.

Mark Robinson+ Kid-Hong Kong:

#### Attached Files:

• ###### robosan.jpg
File size:
49.3 KB
Views:
9,945
6. Joined: May 2009
Posts: 16,679
Likes: 346, Points: 93, Legacy Rep: 1362
Location: Cocoa, Florida

Weight and misinformation: 2008

Weight, from SA in 2008:

Note: some details need to be updated since the foiling 18 is now Mirabaud etc. but the post is still correct after all this time.Updated details can be found in the "Foiler Design" thread a few pages back from the current page.

The running theme of this thread has been my attempt to point out that the comparison of foilers of different weights WITHOUT considering POWER is ridiculous. Numerous experienced foilers(who should know better) tenaciously cling to "facts" that don't add up and hearsay about the role of weight in foiling. Few times if ever has anyone tried to explain why a boat like the RS600FF can be so similar to a Moth in performance yet weigh so much more. Weight is CRITICAL when comparing the performance of two identical foilers but WEIGHT AND POWER must be considered together when comparing different boats.

======================
Moth-
SA: 88.8sq.ft
Sailing Weight(includes crew): 220lb.
main foil area: 1.19 sq. ft.
Foil Loading(Lbs per sq. ft. at 80% max boat weight with crew):147.89
SA per sq.ft. of main foil area(a SA/ws ratio shortened to cover planform area of main foil only): 74.62
=======================
For ease of comparison foil areas for the next two boats were arrived at by using the same FOIL LOADING as a Moth.
Only upwind SA is considered. Moth crew=154lb.RS crew=160lb.; 18 crew =3X160lb.
=======================
RS600FF
SA: 131 sq. ft.
Sailing Weight(includes crew): 327lb.
main foil area: 1.76 sq.ft.
W/SA: 2.49 lb. per sq.ft.
SA per sq. ft. main foil area: 74.43
======================
Foiling 18
SA: 354 sq.ft.
Sailing Weight(includes crew): 854lb
mainfoil area: 4.61 sq.ft.
W/SA: 2.41
SA per sq.ft. main foil area: 76.78
+++++++++++++++++++++++++++++++++++++++
+++++++++++++++++++++++++++++++++++++++
Note the different weights of the boats . Then note the Sa/per sq.ft. main foil area-this is a comparison of Sail area to wetted surface when the boat is flying using just the planform area of the main foil for comparison-THEY ARE NEARLY THE SAME FOR ALL THREE BOATS. Note the W/SA is almost identical for all three boats. This means that all three boats will foil at about the same time adjusted for differences in rig efficiency(Moth probably the best) and for hull L/B ratio as a measure of early takeoff potential(Moth by far the best). As I just said there are other factors and details that will marginally affect performance but this clearly shows how close all three boats are in their ability to fly despite the fact that the RS is 2.5 times heavier than a Moth andthe 18 is 5.6 times as heavy as a Moth.
What counts is power to weight ratio as a first look. A more detailed look showing a comparison of SA/ws ratios for all three boats reinforces the accuracy of the power to weight ratio.

--------------------

7. Joined: May 2009
Posts: 16,679
Likes: 346, Points: 93, Legacy Rep: 1362
Location: Cocoa, Florida

=======
I am no fan of Mr. Gulari, but I have repeatedly honored his accomplishments both here and on SA. My sins against
Mr. Gulari were to ask him a few questions, to point out that his assertion that the standard Moth configuration was a canard was incorrect, and to point out that a dual strut foiler CAN sail with veel heel.

8. Joined: May 2009
Posts: 16,679
Likes: 346, Points: 93, Legacy Rep: 1362
Location: Cocoa, Florida

Moth on Foils! Dubai Worlds-Skipper Weights Analysis

From SA:
Sailor weights and some analysis have been published on the event site http://www.dosc.ae/moth-news/ - credit and copyright to Stefanie Schurer

I cannot post images here but the extract scatter diagram for Mach 2 sailors is revealing. Bora is clearly an outlier weight size amongst the top riders as the only rider in the top 25 who is heavier than about 77kg, his weight being around 85kg. In fact Bora is one of the heaviest riders at the whole event. In this regatta most of the top riders come in around 74kg-77kg with Payne being an outlier at 69kg.

See second article from top; click on plots....Not real usefull as presented unless you go back to the results pages and correlate the boat numbers with names.

Last edited: Mar 20, 2010
9. Joined: May 2009
Posts: 16,679
Likes: 346, Points: 93, Legacy Rep: 1362
Location: Cocoa, Florida

10. Joined: May 2009
Posts: 16,679
Likes: 346, Points: 93, Legacy Rep: 1362
Location: Cocoa, Florida

==============================================
A while back I asked Rick Willoughby to look at the figures in this post to see if my supposition regarding adding tips to a "standard" foil would help a heavy guy in light conditions. His conclusions show that the heavy guy would benefit from the tips (and resulting span increase) both when on foils and at takeoff. The structural integrity of the wider foil was not considered and it was assumed there would be negligible difference in wave making between the two foils.

Note: I have Ricks permission to post this and his worksheets but I can't seem to post them. If anybody would like to see them e-mail me and I'll send you a copy.

11. Joined: May 2009
Posts: 16,679
Likes: 346, Points: 93, Legacy Rep: 1362
Location: Cocoa, Florida

From SA-Julian Bethwaite talks about a new Moth from Bethwaite Design:

"It's just continuing on from dad's and my 49er/speed boat stuff. We will stay with Canard configuration, there are no throwbacks to old displacement moths, and we'll probably go to a wing mast and do some work on the wing bars. Production is a long way off, there are a few other projects I have to bed down first, but then again, I built the hull in under a day, and I'm starting on a deck now. This is why we do this stuff: To learn!"

12. ### Chris OstlindPrevious Member

Yes, Julian builds stuff. He learns from what he puts on the water. I have not seen him post endless lists of numbers and pictures while arguing, over long periods of time, about the potential of a craft without pursuing it, physically, for testing.

If there's something to be learned in this post, I wonder if it is truly going to sink-in?

13. Joined: Apr 2010
Posts: 52
Likes: 0, Points: 6, Legacy Rep: 10

### DocScienceWishful builder

naca numbers wanted

The post by Doug Lord, post #1026, was exactly what I was looking for, in information about the foils.

I hope this link is the link to the above post number #1026
http://www.boatdesign.net/forums/sailboats/moth-foils-30-31-knots-34-86-mph-11209-69.html#post351419

Is it possible for someone to give me the approximate NACA foil numbers that these crafts use on their hydrofoils ??
If that is not available, percentage thickness information on the hydrofoils would help.

I will also need the length or width of the foils linked with their corresponding boats, preferably both the lengths and widths.
Please excuse my several edits as the final copy is sometimes a bit different then the editor view.

Thankyou.

Last edited: Apr 7, 2010
14. ### bistrosPrevious Member

Dr. Science:

I have a book by a Dr. Science - it is a revelation and explains science in a way my teachers would never agree with. I wonder if you are any relation to the Dr. Science I know and appreciate.

I'd be cautiously objective about the calculations and conclusions reached in this thread. Much of the "science" done here is analysis of hearsay information gathered off the Internet. By forensically "analyzing" the developments of other people, some of the formulas and calculations here have been proposed as ways to predict the behavior of new foilers.

Many of these "conclusions" depend on being able to trust (!) what you read on the Internet - and guessing about many details, rather than bothering to clearly define the issue, measure, collect data first hand and have your work peer reviewed.

I'd certainly welcome some quality research in this area.

--
Bill

15. Joined: May 2009
Posts: 16,679
Likes: 346, Points: 93, Legacy Rep: 1362
Location: Cocoa, Florida

-------------------------------
Doc Science, go to Foiler Design ( http://www.boatdesign.net/forums/sailboats/foiler-design-2447-60.html )
posts 895,896,897 for updated information on the 26' monofoiler "Mirabaud",
the Rave multifoiler and the Moth-info from the designers. The two monofoilers use the 63412 asymetrical section and the Rave uses a proprietary 15% T/c ratio(15% of chord thick) symetrical section designed by Dr. Sam Bradfield. The Moth and Rave use a 7/1 aspect ratio and I'm not sure of the exact aspect ratio on Mirabaud. You can calculate the chord & span knowing the aspect ratio and area.* Mirabaud will be very close to 7/1.
--*Moth chord 4.75"(.396'), span 2.76' Note: Moths vary in section and a bit in span-this is based on a foil I have. The current refined shapes are faster....
--*Mirabaud(approx.) chord 8.76", span 5.16' (mainfoil)
--*Rave chord 5"(.417'), span 3.54'
Note: the best information on small foiler design including the Moth is in a new book by Ray Vellinga "Hydrofoils: Design,Build, Fly" ISBN number 9780982236116
available from Amazon.

---
Also: http://www.boatdesign.net/forums/sailboats/unlimited-c-class-sailboat-racing-rule-uccsrr-31154.html for a comparison of a C Class Catamaran and a proposed C Class monofoiler.
---
And: http://www.boatdesign.net/forums/sa...lass-sailboat-racing-rule-uccsrr-31154-2.html Comparision of the C Class foiler Rocker with the 26' monofoiler Mirabaud-enlightening!
---
All information supplied by the designers of the respective boats!
---
See Steve Killings report on the C Class Cats including Rocker below:

#### Attached Files:

• ###### SteveKilling F.pdf
File size:
4.5 MB
Views:
556
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.