30-1 underbody

[Deborah Klaus]

Hi! Does anyone have a drawing of the underbody of the E 30-1. I looked through the brochures posted in Specs and Documents, but couldn't find my boat--just a color photo of the hull. I need to see how the rudder and keel are attached to the hull. Thanks for any information....

 

[Seth]

Full keel

IIRC, this an an Alberg or Alberg-like hull-meaning full length keel with the rudder hung on the back end of the keel. This was before my time at Ericson, but my guess is that the boat was constructed in 2 halves which are bonded together. The lead for the keel is then lowered into the "bottom" of the boat and glassed over on top to keep it on place. This is the same method used for the 27, 29, 32-2, 35-5, and it is too early to recall what others..Although they don't have "full" keels in the same sense-the keels do not run the whole length of the boat..

Martin may have more to add on this question.
Cheers,
S

 

[NateHanson]

I thought I remembered the late 60's E30 having a swept-back fin keel.

I can only find this one picture though, and it doesn't really show the keel that well, but it definitely looks like a fin.

 

[Seth]

Busted

Thank you Nate-I stand 100% corrected!! My apologies to all! I would still guess the build method is similar to that used in the 27, 29, 32-2, etc.

I will stay out of the pre-70's Model discussions from now on-I obviously have little to add. Martin will know more about this I would bet.

Yes-that is a fin-a long fin, but a fin without doubt.



S

 

[NateHanson]

No problem. I just happened to get lucky with the fact that somebody just asked a question about the only thing I happen to know about any Ericson - what the E30-1 keel looks like! (I was just looking at one for sale in this area)

I always like hearing from you folks that know so much about this builder.

Do you know when Ericson stopped building their boats as port and starboard hull-layups? Was that done to acheive tumblehome in the topsides?

 

[Seth]

This one I may know more about

The change came from 2 key areas-as I see them: As yacht design progressed and finer, deeper keels became the norm, it was not possible to have proper keels with the old type of construction-the newer keels were molded in lead and bolted onto the hull. With the 2 halve method the keels were too fat.

The other reason was part of the structural evolution-modern boats needed these kinds of keels, and the idea of the TAFG-a structural grid intended to tie in the rigging, deck and keel loads to reduce point loading (remember too, that newer boats have much higher loads due to the inboard chainplates, traller rigs, etc) and make for a more rigid hull-which results in a faster hull-

The TAFG was Ericson's method of achieving a strong, yet reasonably light hull.

Tumblehome.....sucks! But seriously, the tumblehome you see in the E-37 as a big example-had nothing to do with good shapes, or construction-it was aberration of the IOR formula-a trick to make the boat "look" (to the measurement process) fatter than it was-this formula took measurements at certain defined points, and determined the speed potential based on length, WL length, beam, WL beam, displacement, ballast, sail area, etc. These "points" formed a "connect the dots" hull shape-from which the formula determined the potential speed. The trick for designers was to make the boat sail faster than it "should" based on these measurement points-this is one reason you see many older IOR boats have a pinched-in shape at the waterline under the stern-by making the WL beam narrow at this location-the rule sees this for what it should be-less form stability, sailing length, etc, and indicates a "slower" boat-but aft and above this-where there was no actual measurement, the designers tried to smooth out the shape and negate the slowing aspects of this-with varying degrees of success.

The rule changed over time, and the big tumblehome look was prevalent during the late 70's. IOR boats in the 80's had much less. Some folks like this look, but it does nothing to enhance sailing qualities-quite the opposite! But for boats designed to compete under this formula, it was a necessary evil. This is why some models have this and some don't-it depended on what that design was intended to do-

Hope this helps!
S

 

[Deborah Klaus]

underbody E 30-1

That looks like my boat....does this boat have the swept up stern? I think it is a very pretty....

 

[Geoff Johnson]

Seth, who came up with the idea for the triangular-shaped lead keel. From what I have read, that is not a partcularly aerodynamic shape (and it fails to place the weight low)?

 

[Seth]

Good one!!

This is great-we used to talk about this at the factory! Basically-while I just can't remember what it was-there WAS a theory, becuase BK did a series of custom IOR boats-Madcap and Cadre-Madcap was a 40 footer and Cadre-(I think) was the prototype of the Ericson 34-both were VERY similar to the flush deck 34 of the 70's (3/4 tonner)-just that one was bigger. Both boats (and they were 100% race boats) had these keels-as did the 34, and then all the newer fin keel boats BK did for Ericson. Maybe Martin can explain the thinking behind it-I just don't remember-but he was the only one to draw 'em like that... I think they were OK-not the most common thinking at the time, but those boats were pretty good in their day. Different, but seemeed to work OK..

BTW-I have a nice explanation on the E-38 rudders from Alan Andrews i will be posting shortly..
Cheers,

 

[Geoff Johnson]

I found this explanation in a 1985 article:

"These results support the data presented by Pierre De Saix in SAIL several years ago ("Yacht Keels, an Experimental Study," May 1974). Tank tests showed that highest efficiency and lowest drag were achieved when low-aspect-ratio keels were highly swept back and high-aspect ratio keels were left unswept. A designer may still choose a sweep angle because he believes it will shed kelp or to achieve a particular location for the center of gravity, however."

http://www.vacantisw.com/keel design.htm

It explains why J-Boat keels, which are high aspect, are not swept back. However, I would not consider the keel on my boat to be low aspect. Maybe Bruce King was more concerned about kelp!

 

[Seth]

Keels

True enough-but in the days when these keels were designed )late 70's-early 80's) the modern racing keel was not the deep high aspect type you see on today's boats but the swept forward and straight back type seen on J 24's, J 30's, J 35's and most of the racer and racer/cruiser types of the day. The biggest difference in the King keels was the forwward sweep of the trailing edge. And you are also right that it does not maximize weight at the bottom.

The deep HA keels of today's boats (J, Farr, RP, etc.) began emerging in the 90's-for the most part, and in between we saw a brief period of elliptical shaped keels-with swept leading edges and rounded trailing edges-the thinking was less end plate effect (where it is not wanted-it IS wanted in other applications-such as rudder/hull joints)-ala Supermarine Spitfire airplane wings. Of course, the P-51 Mustang had squared off tips and was also highly maneuverable-so that argument was never settled definitively-both were functional-in keels the ellipse faded away, and eventually these new, deep, HA keels with bulbs became the norm.

At a time when the "norm" were the J-24 type keels, BK had some custom racers with his type of keel-who knows if they would have done better with a more typical keel-the boats were quite good upwind and downwind-weakest reaching-but this is more from hull shape, I think.

Can't think of anything else for now,
S

 

[Geoff Johnson]

Whatever works. I certainly have no complaints about the performance of the delta wing on the botton of my boat (other than showing some initial tenderness).

 

[Seth]

Exactly

Right-whatever works. And it does.

 

[Martin King]

Hindsight can be painful

OK enough with all the suppositions and theories about the keels. I'm going
to Maine in 2 weeks to see the Frog Princess launching and I will get
the answers straight from the horses mouth! Until then, all you Ericson
freaks move along, now. There's nothing more to see here.

Martin
Card carrying Ericson freak member.

 

[Seth]

Outstanding

Best thing yet on this thread-thanks Martin! I'm sure many of the E-gang will look forward to your report-I look forward to hearing about the Frog Princess!

Cheers,
S

 

[clayton]

So Martin...us Ericson freaks are dying for the skinny on the keel theory, "from the horse's mouth"! I moved along like you said, but I came back.

Clayton
'89 E32 with delta keel

 

[Martin King]

Back in Black

Well Seth has already given an excellent overview on keels. I would
only ad that the sweepbacks on the leading edges both on the older
IOR boats and the more modern delta keels were intended to shed
kelp. Are there any other specific questions?

Attached is a pic of the Frog Princess-she's been "in the build" for the
last 24 years! Finally got finished and launched. Don't let the traditional
exterior fool you- she's got a modern underbody and a bulb keel.

Martin
Ericson Freakazoid and owner of
hull #22 E31C

Frog Princess: Designed, Built, and owned by Bruce King

 

[Mike.Gritten]

Wow! Martin, she's beautiful.....I have no other words.

 

[Seth]

frog Princess

Martin-
Very nice..A "homebuilt" E/31C? Cool-I would love to know some details of how the underbody differs from the production boat, construction methods being changed (I imagine they were), etc.

Any construction photos or drawings or even commentary you could share?
I'm sure we are all interested.

Thanks,
S

 

[Martin King]

Well,
She isn't a homebuilt 31C. There are vast differences. For one thing
she's only 21' overall. The 31 has a house. The FP has a raised deck
similar to the 36C. The FP is a wood boat, built with cold molded
epoxy construction. The 31 is a fiberglass production boat. The term
"homebuilt" may be misleading. Although she was built mostly in a garage,
she is a custom boat and built to much higher standards than say
your average production boat. Almost every piece of hardware from
the bronze genoa cars to the prop strut was a custom casting. The
fit and finish on this boat is amazing-normally only seen on megayachts.
In fact I would say that the refinement of her design and execution
has more in common with his megayacht designs than any production
stuff. For those interested in this design I believe WoodenBoat magazine
published the drawings with commentary from my dad in issue #27.

Martin