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Full or fin keel?

191K views 846 replies 107 participants last post by  mstern 
#1 ·
Can somebody pro/con a full vs. fin keel for a newbie (will learn to sail on said boat) and taking it thru the Caribbean? All I can seem to come up with so far is fin keel is better to the wind, and a full keel will protect your rudder.
 
#836 ·
paulo with all due respect the problem is you are not. many here work with computers daily either doing cad/cam,economic predictions,hard science or medical science. we are aware of various types of multivarient analysis, basic and complex statistics,vecter analysis, engineering design and the various purposes computing can be put to. however, we are less informed as to why we get on some boats and they sail well, we are comfortable, everything is in the right place and we feel confident in all weathers and get on other boats and at some organic level it's just not right. Jeff and Bob have been teaching us why some things work and some don't. all boats are compromises. I been learning why I made the choices I have. I know what I want in a blue water vessel but I don't know why on a detailed level. it is self evident anyone in the competitive environment of yacht design will make use of what tools they can to produce the design their client desires. they have been the guides to understanding our desires and how they try to meet them . you have not. please allow the discussion to move on.
 
#837 ·
outbound, you hit it. did that with a block wall I had to build for aclient once. I could see generally how to design it, BUT, I had a feeling it was not quite right. Talked to some one, he cranked a few numbers, said do it this way, even tho the design specs said do it that way! Glad I did it this way, as a 5 something quake hit a yr or so later. While I will not say the wall would not have held as the spec said, the way it was built, it did hold up with more wt behind than initially though!

Like all things, there is more than one way to skin a cat! or dog, or catfish or __________!

If someone can get a full keel to plane at 2x the hull speed of a boat, I'll buy one, if not, I'll take the fin thank you very much!

marty
 
#840 ·
It is not being moved to "Off-Topic". Two posts were moved to a thread that only the moderators can see. We were asked to disclose when we moved things out of sight. That is why the bread crumbs were left.
 
#842 ·
Still going,eh?

Seems to me that one of the design problems with modern beamy hulls equipped with high aspect ratio and deep fins, and the resulting high bending stresses at the foil to hullbottom join, could be alleviated by using two foils, in a "V" configuration, with the bottom ends joined at the ballast bulb below and the top end affixed to the hull near the chines or bilges. The foils then are in almost pure tension and compression, aside from the lift force, with almost no bending stress.

Has anyone tried this?

K E Froeschner
Martin, Froeschner & Associates
Morgan 45 "Orion"
 
#843 · (Edited)
Kefer:
Not a bad idea. In a heeled position one leg of the fin woud be near vertical and that's good. The problem with any configuration of "tandem" keel isthat you have two trailing edges and more drag. There are a number of way to join high aspect ratio fins to hulls. On the SLIVER project we spread the loads out with a series of steel floors that all fasten to the outboard longitudinals that form the front of the setee faces. Keel bolts are well outboard in a T flange and extend all the way up through the floors. I'll see if I can find a photo.

The problem we had with the SLIVER was that the strip planked cedar hull was not capable of taking the keel bolt compressive loads without crushing. So we have to take the loads off the skin entirely. The wood strip planking was removed in a big pan shape around the keel and replaced with solid laminate.

Ok, found one:
 

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#844 · (Edited)
Bob:

Thanks for the reply and photo of Sliver's floors. Looked up "the Sliver Project" on the web ... OUTSTANDING.

Nice to read of your love of Wm. Garden. I checked his books out of the libary as a kid and pored over them for so long that they eventually fell apart -- maybe it was just books with his designs in them. And your love of 30 Square's as well. There was one moored in Mariner Lagoon for years that I drooled at. It was eventually hauled to Svendsen's in Alameda and rebuilt by Peter Schwab. He raced in the Singlehanded Transpac to Japan, but I can not recall the result. (Probably won.)

Sorry for the thread drift -- but, just had to thank you.

"Bob, You done good."

kef
 
#845 ·
Kef:
I still have the Garden design catalog he gave me whan I was 15 years old and depsite being referred to and read countless times I am happy to say it is not falling apart. I know where it is right now. I always know where it is. Wish I had had the brains to have had him sign it.

The SLIVER Project boat was moved last week to the yard in Seattle where it will be finished. Here are some pics
 

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#846 ·
One of the things which is happening on the more extreme versions of the small root keels is that they are building 'cassette' style keel connections in which the end of the keel inserts into a tightly fitting box inside the hull. This allows a much bigger contact area to resist bending and torsion. Of course the box needs to be heavily constructed and needs a sophisticated transverse and longitudinal framing system to be able to distribute loads outward into the hull.

FWIW I like Garden's work aesthetically and from a historic point of view.

Jeff
 
#847 ·
One of the things which is happening on the more extreme versions of the small root keels is that they are building 'cassette' style keel connections in which the end of the keel inserts into a tightly fitting box inside the hull. This allows a much bigger contact area to resist bending and torsion. Of course the box needs to be heavily constructed and needs a sophisticated transverse and longitudinal framing system to be able to distribute loads outward into the hull.

FWIW I like Garden's work aesthetically and from a historic point of view.

Jeff
That sounds like what Seaward does with its retractable keels; the high aspect keel slides up and down a box that looks (at least on their website's videos) to be rather robustly incorporated into the hull. Makes sense as a way to spread the load of a grounding even if the foil is nonmoving.
 
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