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Bob Perry's take on Wolfenzee's dream boat

187K views 1K replies 48 participants last post by  Rhapsody-NS27 
#1 · (Edited)
In the "Modern Hull forms and Motion Comfort" thread,

Post # 142, Wolfenzee said to Bob Perry " BOB: take a close look at the lines of my boat and tell me could a fin keel have been designed in relatively easily http://atkinboatplans.com/Sail/images/CaptainCicero-3.gif
[/I]"

And in Post #152 and #153 Bob Perry Responded:
(#152)"Damn it Wolfer!
You made me think.
I hate it when that happens.

Sure I could do your boat with a fin keel and a nice skeg hung rudder or better yet a spade rudder.

It would look just like your boat....above the water. Under the water you would not recognize it. I would have to shave away all that deadrise and reduce displ while carving away some volume forward and reducing some hollows aft.

But in the end you and me would love it. It would be a WOLF in sheep's clothing like NIGHT RUNNER."


(#153) "Wolfy:
Next Wednesday post your hull lines again and a photo or two of your boat.
When I start thinking about a new boat I need to see it and I think it would be fun for all of us to see what your boat would look like with a more modern hull combined with that traditional Atkin look.

I have to do this to get it off my mind. I'm built like that.

Or, Jeff could do it. I know he could.
Or, Jeff and I could do it together.
He'd do the hard work and I'd do the pointing and gesturing.

Either way let's see if we can produce a boat that will get your juices flowing."


And I am bowled over by that.

As a SailNet Moderator, I can only thank Bob Perry for that generous offer to come up with a design that explores Wolf's question. That is a true gift to this forum. Normal folk rarely get to see a custom design process and so this should prove interesting.

And I am truly honored that you would be willing to do this with me. I truly appreciate Bob's willingness to give that a try.

This is a thread for that process. I am excited to see where this ends up....

Jeff
 
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#5 · (Edited)
I must admit that I have been noodling the idea of an 'improved version' of Wolf's boat ever since I saw his post #142, but especially after seeing Bob Perry's replies. As the third wheel with someone like Wolf who has a strong affinity for his boat, and someone as highly respected as Bob Perry, I do not venture to see myself as steering this bus.

But as I have been thinking about this, it seems like there are three possible approaches which come to mind. I have given each of these approaches their own name; 1. 'caricature boat' (not to be mistaken for a Character Boat, a term which I personnally have never liked), 2. 'A squinter', and 3. 'A sleeper in Wolf's clothing'.

To define these terms as I am using them, I see the 'caricature boat' as having the obvious character setting features of a traditional design visible and in some cases exaggerated so that if you know the precedent design, you will recognize it, and yet it is not a literal interpretation. I would suggest that the best examples of this type would be something like the Alerion Express and Bob's own Valiants.

I would think that the hull and cabin for a 'caricature boat' would probably look like like Wolf's boat at least to the waterline, but the rig and underbody would be modernized. My sense is that would produce a boat that sailed well, might not be a fast as the 'squinter' or have quite as many of the traditional virtues of Wolf's current boat or the 'sleeper in Wolf's clothing'. It would be a nice boat.

The 'squinters' are boats that if you see them at a long distance, and squint enough to bring them into focus, they might appear top be traditional design. But as soon as you can see one clearly, they are clearly not traditional designs from any angle. In my mind, a successful example of that are the Schooner Woodwinds which sail out of Annapolis. They are perfectly suited to the job in life and not bad looking boats. They sail way better than first glance might suggest, but there is nothing really accurately traditional about these boats. I would think this would be the fastest of the three and perhaps the easiest to handle. I am not sure that this is what Wolf had in mind.....But I'll let Wolf and Bob negotiate that one.

The 'sleeper in Wolf's clothing' would take the basic design of Wolf's boat and subtly tweak the hull and rig. I figure under this approach, the basic canoe body would remain essentially the same, but we would add a fin keel and skeg hung rudder. The change might be as subtle as the profile of L. Francis's Ticonderoga or Bounty....Or perhaps more extreme in the mode of Brewer Bites...Or perhaps we go for broke and design a real fin and skeg hung or spade rudder (perhaps as extreme as a Galaxy 32).

This would probably be the closest in behaivor to Wolf's current boat. It would probably have a very similar motion, albeit a little nicer due to better dampening and more stability. It would ahve pretty much the same carrying capacity, although the overall displacement would be reduced. It would be faster especially in light air, and going upwind. It would probably be a better boat all around.

Whatever it turns out, from reading Wolf's concerns about grounding the keel will need a long chord in order to be able to distribute the shock loads of a hard grounding. Looking at the profile of Wolf's boat, the keel has a lot of drag (meant in the traditional sense of the word..meaning that the keel at the stern is much lower than the forefoot rather than meaning resistance). Since that is the case, going to a fin keel would probably move the center of lateral resistance forward and that would impact the design of the rig.

Wolf, I do not recall seeing a sail plan for your boat. If you have one can you post it....

Anyway, those are my thoughts, (for now)
Jeff
 
#6 ·
I kind of think the process will end up with something along the lines of Night Runner or Jakatan. Looks old at first glance afloat but that impression doesn't stand up to close scrutiny. :)
 
#8 ·
Looking forward to this too.. but wondering.

Is the intent to modify Wolf's exisiting hull with new appendage(s) to update performance?

Is it to redesign from the waterplane down to enhance performance while retaining the current positives (in Wolf's view)

Or is it a fresh start that may preserve the look and feel of the current boat with today's technological improvements brought into play?
 
#10 · (Edited)
To get this rolling I redrafted Wolf's boat on CADD so we had something slightly larger to work from. They are not fully faired since they are basically a tracing of the Atkin's lines drawings, but they should serve as a reasonable point of departure.



I can get them to Bob as a .dwg if he would like.

Jeff
 
#11 · (Edited)
So while we are waiting for Bob Perry to get back into town and he has a few minutes to look at this, and while I had a an hour to kill before yoga last night, I thought I would take a first stab at the 'A sleeper in Wolf's clothing' version. This would be the version where Wolf walked into a yacht design office and said, "I lost my boat in a hurricane and the insurance company is paying me to build a brand new boat from scratch. I really loved my old boat but would love to improve it a little...emphaisis on a little, without losing a thing I liked about my old boat." In other words, this is the "Mommy Jeans" version. It is also the version which requires the least time and skill to draw.

I figured we could employ comparatively modern wood building techniques, say epoxy saturated, glued, western red cedar, bead edge strip planking, with a couple diagonal WRC veneers and a perhaps a kevlar sheathing over a mahogany outer veneer for toughness. That should bring hull weight down a little, and improve strength and impact resistance a lot.

I don't have a lot of time this morning but here is how this stacks up....
Things which would not change perceptably:
-Carrying capacity
-Visual appearance above the waterline
-Draft
-Ability to run aground without damage (long keel root and foot)
-Tracking
-Same engine position and approximately the same center of buoyancy

Things which change a very small amount:
-Motion comfort (the boat should roll through a smaller angle at a slower speed therefore be more comfortable than this already seakindly boat)
-A little less displacement over all (maybe 500 lbs to a 1,000 lbs)

Things which should change noticably:
-More stability (center of the lead ballast is roughly 10-12 inches lower)
-Should be able to carry a considerably more sail area (good for light air) and have to reef later(good for heavier air)
-Less drag due to less wetted surface, smaller tip vortex, and less displacement (better fuel economy and better upwind and downwind speed through the water.)
-More efficient foils (better light air and upwind ability, lighter helm loads, less leeway)
-Better control backing and the ability to make tighter turns.

That is my first stab at this. I am sure Bob will be able to critique and improve this version a lot.

Jeff
Proposed new lines drawings:


Original design for comparison:
 
#13 ·
The canoe body did not change appreciably, but the construction weight went down, and displacement went down accordingly, so the surplus carrying capacity should remain virtually the same.

Jeff
 
#14 ·
Jeff.. can you edit the above and add the original plans from the previous page for a direct comparison?
 
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#15 ·
I would say that it can carry effectively a bigger load on the same waterline. To use Bob's words the foot print would be the same but the boat is lighter so you can turn that difference in weight to carrying capacity.

Not saying that is needed or that it would not be preferable to have a lighter and faster boat carrying the same load, but if weight carrying capacity is what matters (for much absurd as it is) then I think you can carry a bigger load on your version, assuming it is correctly stowed.

Regards

Paulo
 
#16 · (Edited)
Ron,
Good suggestion, I added the original version to the post. Below are the two sets of lines drawings superimposed over each other. The purple lines are the original lines.



Paulo,
Although I have not run any calculations, the assumption is that both the weight of the boat and the volume of the keel deadwood are assumed to have been reduced by the same amount so the boat should sit on her original waterline. That means she should have pretty much the same carrying capacity. She may perform better loaded since she should have less drag, and should also get a new sail plan with more sail area.

Jeff
 
#17 · (Edited)
Jeff:
Yes, a .dwg file would work best for me thaanks.

The idea here, as I see it, is to imagine Wolfer has just won the lottery and he wants a new boat. But he loves the way his old boat looks. It does not have what I would call modern performance. It's an antique design. A lovely antique but still an antique. So my idea is to see how we would preserve the romantic, traditional look of Wolfy's boat and at the same time update the hull form and appendages.

The idea is not to make everyone happy. The idea is to make the Wolf, Jeff and me happy. The outcome will not be everyones idea of the "ideal boat" but if we do this right it just might be Wolfer's idea of the "idea boat". But we can all have fun watching the process.

Jeff:
Good to see you off to the races here.
On your proposed profile change I think you should try to slide the fin aft almost one whole station. I'd lose the long chord tip on the rudder too and add more span while retaining the partial skeg you show now.

Given that the Wolf most probably will not build this boat the prime target to this excersize is fun and stimulating conversations about boats.

I need a couple days. I have just returned from the PSC yard in NC and I have a raging head cold. I need some time with my dogs.
 
#18 · (Edited)
Someone mentioned carrying capacity, the boat is rated at 10 tons net weight (carved in hull next to hull id #). As far as motion the boat is exceptionally sea kindly, quite pleasant in nasty seas. Atkin called for carvel plank the builder used strip plank with top nails screwed on to w/frames double frames that were beefy even for carvel plank which are bolted together and fiberglass on outside, it could have been built alot lighter.
A friend of mine who is all about modern rigs started to tell me how I could change mine...then pointed out the rig I have points well, is well balanced and powerful (I'd keep the rig, down to the cambered wood mast).
Below the waterline I would keep a transom hung rudder w/skeg to protect rudder and prop shaft (Atkin liked to have prop shafts almost horizontal). The skeg that far aft would help tracking. the modification I was thinking of was rudder separate from keel, but would not run the keel as far forward as suggested in the alternate drawings.
The rig was modified from the original design but has also since been made a cutter. Head stay is detachable to either have a 2/3 fractional or be detached at the bottom and shipped to allow a large jib to be flown off the masthead on the topmast stay or run parallel to as cutter, flying a jib off the masthead really only excels when you need to fly a large sail, it works best a cutter. Someone wanted to see the present sail plan (the second version shows where the stays are but is not the real cut of sails)
more drawings and pics including building can be found at SailNet Community - wolfenzee's Album: S/V Rover


 
#21 ·
It's not a matter of poor stability, boats of that time were designed to perform at a heel, doesn't take much to get my boat to 25or30degrees but takes alot to get to go beyond. Alot of modern day hulls are designed to sail flat or close to it.
The only reason I can figure that the alternate had a bulb on it was to be able to maintain the 5' draft anything else would require a deeper keel.
 
#23 ·
Remember Bob's criteria: If Wolfenzee won the lottery.<G>

Now, let's rethink that boat with a proper tungsten keel, none of this cheap lead crap. I have to ask, Bob, have you ever had a customer ask about a denser keel material for a better keel? Other than the spent-uranium-racers club?

Even at 20 degrees, having a keel with a foil shape that gains ground upwind ought to be an advantage. And it should have less drag than a bulb, at all times.

(Yes, I really am saving up old light bulb filaments. :)
 
#25 · (Edited)
Even at 20 degrees, having a keel with a foil shape that gains ground upwind ought to be an advantage. And it should have less drag than a bulb, at all times.

...
Not always. I have read a recent study aimed to evaluated the performance of several types of keels upwind and it turned out that an Iron bulbed keel had a better performance than a lead fin keel with the same draft, both keels providing the same righting moment. The study used lead for the fin and cast iron for the the bulbed keels but if they had used steel for the foil and lead for the bulb I think it is safe to assume that the difference in performance would be even more substantial since the bulbed keel would have a lot less drag.

regards

Paulo
 
#24 ·
All boats are designed to sail flat. That's why we design them at a zero angle of heel. But they do heel and there is little we can do about it. But almost any boat, except in very, very light air will sail best if heel angle is kept to a minimum. The keel is more efficient that way and the sails are more efficient that way. But try as we might, the boat will heel.

People often ask me, 'What heel angle is my boat desigfned to sail at?" I always say zero degrees.

Bulbs per se are not fast. A clean tip to your fin is fast. But if a bulb can signifigantly lower the VCG then the bulb may contribute to boat speed in that it will help keep the boat more upright.
 
#58 ·
Reminds me of bashing north thru the NE trades from Tonga. Tie a reef in and the speed goes up substantially.
With all the changes, it would be far easier, cheaper and quicker to simply build a new modern hull from scratch, than to change and existing one with so many changes needed. I can put a bare hull together in a couple of days. The extremely short waterline and excessive overhangs ( dead weigh in the ends) can only be changed with a new hull.
Bill Garden had a very traditional looking boat with a very modern underbody. People would challenge it, assuming it had a full length keel, then be surprized when they got their asses kicked
 
#26 ·
PCP:
Iron weighs around 450 lbs. cu. ft while lead weights around 700 lbs cu. ft. So to have two keels of similar geometries and one of iron and one of lead is very hard to imagine.
I don;t buy the results of that study at all. I have nothing against iron keels my own boat for 15 years had an iron keel.
 
#27 ·
Bob, maybe I did not make myself understood, the keels have not similar geometries. The objective was testing different keel shapes (all with the same RM and draft) regarding upwind performance. The bulbed ones were cast Iron, the fin one was made of lead and what I said was part of the conclusions.



The study is a serious one, it is a from the Department of Shipping and Marine Technology and Marine Hydrodynamics from the CHALMERS UNIVERSITY Of TECHNOLOGY (Sweden 2011), it is a Master of Science Thesis made on the sequence of a previous investigation and supervised by Prof Lars Larson, an authority in Hydrodynamics and with the participation of NA Stefan Qviberg, the long time designer of Arcona yachts, that was the one that come with the idea for the work.

The study:

http://publications.lib.chalmers.se/records/fulltext/148387.pdf

Regards

Paulo
 
#28 ·
Paulo:
Many thanks. Thst is a very interesting study and one that I would take very seriously.

But I would ask this:
What if they made a bulbed fin with lead and compared it to a bulbed fin with iron.
This seems a very conspicuous error in their study.

Seriously new,,,,,,If iron keels were more efficente we would see them okin more high performance boats. But the realitiy is we don't.

Reality has a way of sorting this out very quickly. I see it as all about lbs. per cu. ft.

If you want to join the ranks of "I see what I want to sse" then that is your choice. What I see is that every high performance boat built today uses a lead keel and at least a lead bulb.

Iron keels were all about saving money. It's a simple as that.
 
#29 ·
But I would ask this:
What if they made a bulbed fin with lead and compared it to a bulbed fin with iron.
The way I understood it from Paulo's description (haven't read the study yet) is that the different metals were used so that two keels could be made in different designs but have the same righting moment.. So that the designs themselves could be compared. If you compare fin vs bulb both in lead, the bulb would be better simply because it is has lower cg and greater RM- but by using iron for the bulb you could end up with the same RM as the lead fin, and compare just the shapes.
Dave
 
#31 ·
The premise was that you could build a more efficien( better performance) keel with iron than you could with lead.

To retain the same VCG of the keel the iron keel would have to have a much bigger bulb and a lot more frontal area I also think the fin portion of the keel would have to be bigger so even more wetted surface and frontal area is added.

It does not make any sense and I don't give a rip who did the study.

Think of it this way. If an iron keel could provide "better performance? why does every serious racuing boat in the world use lead for ballast. If spent uranium not not illegal for racing keels they would use that like they did back in the earkly '70'. It's denser than lead.

Open you eyes, not another book, the answer is easy to see in any boatyard. The more dense material gives the designer more freedom of design. Bulbs are slow. They cut into the clear span on the fin and reduce apparent aspect ratio. They add wetted surface and frontal area. Bulbs work because the allow for a very low VCG. This is far easier to achive with the more dense material.
 
#47 ·
The premise was that you could build a more efficien( better performance) keel with iron than you could with lead.

To retain the same VCG of the keel the iron keel would have to have a much bigger bulb and a lot more frontal area I also think the fin portion of the keel would have to be bigger so even more wetted surface and frontal area is added.

It does not make any sense and I don't give a rip who did the study.

Think of it this way. If an iron keel could provide "better performance? why does every serious racuing boat in the world use lead for ballast. If spent uranium not not illegal for racing keels they would use that like they did back in the earkly '70'. It's denser than lead.

Open you eyes, not another book, the answer is easy to see in any boatyard. The more dense material gives the designer more freedom of design. Bulbs are slow. They cut into the clear span on the fin and reduce apparent aspect ratio. They add wetted surface and frontal area. Bulbs work because the allow for a very low VCG. This is far easier to achive with the more dense material.
Bob,
For the third time I say that I agree with you, as certainly the authors of the study. It is evident that a keel with a bulb made of lead is more efficient than an all iron keel, assuming the same shape. That was never the point.

you say that :

"The premise was that you could build a more efficien( better performance) keel with iron than you could with lead."

but you are mistaken, they did never assumed that or wanted to verify that possibility. In fact the lead fin keel was only there for comparative purposes. They were studding basically different types of bulbed keels.

The fact that they had found that in some circumstances a torpedo iron keel could be more efficient than a fin lead keel was accidental and that is only valid to a fin lead keel versus an iron torpedo keel.

It is evident that if both keels had the same design, one in lead and other in Iron, whatever the design the lead keel would be more efficient (for the same RM) since it would have a lesser volume and a smaller drag.

what the study was aimed at was:

"The aim of this project is to evaluate four different keels and determine which one has best performance upwind. "

and about the keels and regarding the use of lead on the fin keel:

"The four keels should have the same righting moment in order to be comparable. This means that the static moment of the yacht which counteracts side forces from the sails should be the same. In the
redesign of the T-keel, this righting moment has to be kept constant. For an easy comparison between the keel designs the draft will be kept constant as well, and the fin size and shape will be identical between the bulb keels. ...

Keel 1 (Fin keel) was used only as a comparison for the other keels. It does have the same righting moment and maximum draft, but in order to fulfil this it had to be designed to be made of lead instead of cast iron as the other keels. This implies it will have a comparably smaller wetted surface, and consequently the drag forces will be smaller. The effects of these aspects were expected to occur in the results."

http://publications.lib.chalmers.se/records/fulltext/148387.pdf

Regards

Paulo
 
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