After returning from the UK and licking my wounds, I decided if you can’t beatem (Graham, anyway) then joinem. So I designed my first lightweight and based it on my Cobra series.
Cobra4 has a Depron hull (thanks to Darrell for that piece of foam) and balsa foils. The leading edge of the fin is a carbon tube to add some stiffness.
Displacement all up except for rig is 330 grams. Nothing fancy or expensive about the electronics…mini servos and 4 AAA lithiums. The bulb is 220 grams, so I think she proves that lightweight hulls and good ballast ratios are possible for the kitchen-table builder. Of course, the longevity of the Depron hull remains to be seen…its stiffness is good, but it is easily dented.
Her maiden voyage was last evening. Flukey wind, so testing was far from definitive. It’s clear she handles well, but speed is TBD.
Now I’ve got to get going on some rig mods to complete the package.
Please do not take this as sarcasm, but …
How many grams of wire are there in that thing?
Are the diagonal struts in the way of the keel needed? If so, are they ever going to be in compression? Would a couble of cabon filaments do?
Light weight is a way of thinking.
Heh heh…now he wants me to shorten the wiring…sheesh.
I could, of course, Angus…but I have to consider the tradeoffs between weight savings and my soldering skills!
The bracing of the keel is probably overkill…I considered not doing it, but this is my first depron hull and I don’t fully trust the material yet. I thought it would reduce stress at the point where the fin enters the bottom panel of the hull. If you engineers can assure me that it won’t help that, I’ll leave it out and save 2 or 3 grams. I considered drilling holes in all that to reduce weight, but the boat is within my design parameters as it is…and the balsa isn’t necessarily heavier than carbon.
It was fun to see that a boat with comparable specs to MS can be built simply…but it remains to be seen if comparable specs equals comparable performance!
Looking good Bill !!
If you raise the bar any further I will be forced back into the shed for my next trick…
A big question remains: was the superiority of Moonshadow due to light weight, or hull form? Obviously, part of it is due to light weight, but did hull form also contribute?
There are many questions regarding hull form, especially at low Reynolds number. I have noticed that many hulls have their stems entirely above the water line, which enables a low entry angle in still water. Bill’s new diagonal hulls have considerable stem under water. It looks like Moonshadow may have less. Most hulls have significant transom under water when heeled, so Angus’ design may not be so different in that regard except directly downwind. There is still the puzzle of why measured hull drag is so much higher than expected. Has anyone done comparative drag testing of these diagonal hulls? I plan on doing some more of that kind of stuff with my new diagonal hull (a poor man’s Cobra 3 look-alike with round bottom). I suspect that Brett has also done some more testing.
I believe the jury is still out on MS. Graham is a very good sailor.
But there is no doubt that MS’s lines are very nice and well balanced,there is no doubt that she is fairly well made and that her detail design and construction of appendages(bulb/fin/rudder) have been done thoughtfully to the best of my abilities at the time.
Her rigs match the hull well it would seem.A pretty nice combination of design and construction matched with Grahams skill equals a winning boat.
Not Rocket science as this is the normal method of acquiring a competitive edge.
BUT…we need to see this boat come into contact with the best of the UK boats,we have not seen this yet.
MS needs to compete against the boats from Rogers stable and also against the likes of Richard Alford and the other Southwater sailors ,Rogers group and the Southwater group are the best in the UK and have not traveled to the Euro GP’s for whatever reason.
I believe we may know more soon…as a Showdown may be imminent.
I agree, Brett. Roger was unable to attend again this year, a disapointment for both of us, and it was just too expensive for me to stay for both the GP and the Nats. My designs have been successful here in the USA, largely due to Scott’s abilities, and seem to be stuck in second in the UK, maybe largely due to my lesser skills. I’d love to see Scott with a Cobra against Graham and Roger.
All the best…especially to Footy designers/builders. We’ve gone far beyond what most people thought these little boats could do, but you keep us working toward even better performance.
If the rest of you haven’t designed and built your own boat, give it a try. There’s no better feeling than seeing your own design work well. I’ll be happy to share what little I’ve learned with anyone who is seriously interested.
Walt, I don’t know if there’s anything to it, but my last couple of boats have been designed with both stem and stern somewhat submerged. I’ve built them, however, so that they statically balance with stem at the waterline and stern submerged. When a bit of wind comes, the bow presses down, and the boat is sailing on its designed waterline…more or less.
Whether that’s a factor or not, I’m not sure, but the boats handle well.
I agree about the showdown. On a kind or ‘family tree’ of who did what and with which and to whom, I think that MS may be superior - but on the other hand she may not!
For any bold souls, the Richardson drawing board has Footy designs to suit all tastes - from Chihuahua to Pawmark.
Geez Angus…go to bed. I’m not there to get drunk and solve all the problems of Footydom like a couple weeks ago. BTW…what were those solutions we came up with??? :zbeer:
This is a question from one who is just starting to design. I have been using Hullform 9s, and have just started experimenting with Prolines 7 Demo. My specific question is this: Is there any “freeware” program available anywhere which would take the hull parameters from Hullform and produce an initial estimate of hull resistance over a range of Footy speeds and heel angles?
Although Footys probably form an insignificant part of the yacht design market, nevertheless they are a size in which some testing could be done without breaking the bank. It seems like an ideal project for a graduate student thesis at some ‘Marine Design Institute’. It would have the added advantage that it would not step upon the toes of the professional designers of such yachts as America’s Cup contenders, and yet might well provide a basis for computer evaluation of larger size boats.
In an earlier post the point was made that Footys seem to have a higher resistance than would be expected—that surely is a valid reason for this type of study.
Download the pro version of hullform,you cannot save designs with this version but you can do what you want like this.
1 design your hull in the free version of hullform
2 once you have something worth looking at open the file in the pro version.
run all the hull drag estimates you want in the pro version and all other cool features.
3 identify any changes you might want to make in the design
4 go back to the free version and make your changes.
5…go back to 2,repeat as many times as needed
6 bask in the pleasure of your new footy design
Thats my cheap work around to using pro tools at no cost.
Mostly ethanol and sugar in water!
After I had written my post, I was looking further into the Prolines program and found that it did indeed contain a process for assessing the hull resistance at various speeds. However, I also discovered that it was not letting me save anything, and the help file was missing, so I’m trying to get back these capabilities.
Many thanks for your advice—I will try!
Did you mean that I can download the Pro version of Hullform 9s without paying for it? That I can use it, but just cannot ‘save’ anything I do with it? Can I ‘print’?
I came to modern computers late in life (I am 75) and find myself usually baffled by the jargon, and sometimes end up staring at the screen without the slightest idea of how to do some simple task like ‘open the file in the Pro version’. But I will “try it on the dog” and see what happens.
Install both the free version of hullform and the demo pro version on your system.
Use the free version for creating and saving designs.
Use the pro demo for looking at hull drag,centres moving on heel etc etc.
If you want to make changes to the design do it in the free version.
print whatever you need from the free version.
Hope this helps.
I know it’s a bit late to repond but a appreciate the thanks for the Depron. I hope it added something to your building toolbox.
I have done as you suggested and it works as you describe. I do have a question about keel foils and bulbs. As they form such a large part of Footy design, how can they be included in the design and its drag calculations? Could one design a whole boat whose hull was shaped like a keel and bulb, and then import it in some way such that it could be added to an existing hull to give a complete Footy design?
Or does one have to obtain all keel information from tank and pond sailing tests?
I may be asking here a more complicated question than I think it is.
We are way off topic now…but anyway.
I treat the fin and bulb etc separately.There is often more art than science in my designs:)
(though I don’t disregard numbers and do calculate many things)
I actually havn’t found any of the drag schemes in hullform that accurate when it comes to footy hulls.I have some data from actual tow tests which relate in a roundabout way to the hullform numbers.I think this has been discussed in more detail on this site somewhere.
If I was you I would concentrate on the hull design first…then appendages.