shortening the draft on a long fin keel...
KVL
My husband is planning to shorten the draft on our fin keel Carter33'
1972. It draws like 6' now and he plans to take off a foot. Once doing
this, he wants to add a bulb or wings to the sides of the fin to add
the weight back onto it.
If anyone knows of any good sources on the web of others being
successful with this kind of project, please email the links to
k...@usecashtobuyit.com
Thanks
Karolina
Wayne.B
>If anyone knows of any good sources on the web of others being
>successful with this kind of project, please email the links to
Lots of people have tried home made wings on their keel but I have
not heard of a single success story however, and most have been
removed.
You will probably end up destroying both the value and sailing
performance of the boat.
Why not sell it and get something designed as a shallow draft boat?
Steve Lusardi
I can appreciate the requirement. However, you had better do it right or you
will lose all the value in your boat. Please consider a Sheel keel. They are
the answer to your requirement. Properly constructed, with the correct
ballast load schedule and you will have a winner with a 4 foot draft. They
really work exceedingly well. Before doing this contract a qualified naval
architect. It will save untold grief in the end.
Steve
"KVL" <k...@usecashtobuyit.com> wrote in message
news:1166450596....@t46g2000cwa.googlegroups.com...
KVL
almost nothing) she was land sinking and had water & mold in her for at
least 3 years- after being abandoned. We had to redesign the entire
interior, so it's very customized - not much original structure is left
in the interior. The hull and the deck were in superior condition, but
the cabin top was soaked under the fiberglass to the balsa wood core.
We had to completely make a new cabin top core from the inside of the
cabin. My husband is a mechanical engineer- and quite handy with
rebuilding and designing almost anything. So I have no doubts, he would
do a superior job with the shorteneing of the keel . We plan to keep
this boat for many years and many of the places we like to sail too and
anchor (at our convenience-not waiting for high tides) are tight at mid
to lower tides - where we live.
It would still be great to get some more ideas of tohers who have
attempted this kind of project and were actually successful. They're
out there somewhere. Some people have knack of accomplishing things
they get told "can't be done right.
I will look into all the suggestions.
Much Thanks!
Karolina
Matt O'Toole
> The Carter33' is a very beautiful boat, but when we aquired her (for
> almost nothing) she was land sinking and had water & mold in her for at
> least 3 years- after being abandoned. We had to redesign the entire
> interior, so it's very customized - not much original structure is left
> in the interior. The hull and the deck were in superior condition, but
> the cabin top was soaked under the fiberglass to the balsa wood core. We
> had to completely make a new cabin top core from the inside of the
> cabin. My husband is a mechanical engineer- and quite handy with
> rebuilding and designing almost anything. So I have no doubts, he would
> do a superior job with the shorteneing of the keel . We plan to keep
> this boat for many years and many of the places we like to sail too and
> anchor (at our convenience-not waiting for high tides) are tight at mid
> to lower tides - where we live.
> It would still be great to get some more ideas of tohers who have
> attempted this kind of project and were actually successful. They're out
> there somewhere. Some people have knack of accomplishing things they get
> told "can't be done right.
> I will look into all the suggestions.
You have a big advantage with respect to cost if your husband can do the
actual work. So use the savings to hire a good naval architect or
marine engineer to do the design work. Even an otherwise competent
engineer could screw this up without the proper training and experience.
Your husband would probably enjoy working with one of these guys anyway.
That experience alone may be worth the cost.
Naval architect and marine engineer Eric Sponberg has a similar project
featured on his website: http://www.sponbergyachtdesign.com/Magic.htm It
might be best to work with someone nearby, and/or someone familiar with
your boat.
Matt O.
Bill Kearney
plumbing systems. Anyone with decent mechanical skills can tackle this.
But something that will affect how the boat actually SAILS when it's
navigating out of the shallows is not just a simple mechanical task. As
others have suggested, it's worth seeking out an actual naval architect
and/or someone that's actually DONE THIS to THAT MODEL boat.
It'll do you no good to have all that work go to waste only to discover how
poorly it sails once it's back in the water.
Roger Long
> But something that will affect how the boat actually SAILS when it's
> navigating out of the shallows is not just a simple mechanical task.
> As others have suggested, it's worth seeking out an actual naval
> architect and/or someone that's actually DONE THIS to THAT MODEL boat.
As a naval architect, I would say just go ahead and do it. When you look at
the incredible variety of keel sizes and shapes, you'll realize that it is
actually hard to come up with something that flat out won't work. If you
were racing and obsessing about gaining or losing an eighth of a knot in
identical conditions, it would be one thing. The chance that you won't like
the way the boat sails if you do a modification like this half way
intelligently is finite, but small.
The Sponberg solution linked in the other post is elegant. If the OP's
husband did all the other stuff and can avoid poisoning or burning himself
with the lead, he should be able to do this successfully with not much more
guidance than that and some volume calculations he should be able to manage
with a quick look at a geometry or naval architect text book.
If he just cut the keel off and carried more gear and stores or put the
weight in the bilge, the boat would not be as powerful or fast to windward
but quite possibly not by an amount that he would notice without careful
comparison. There have been many boats offered in two versions with keel
configurations that vary by this amount. I wouldn't recommend this as the
course to take but just to point out that this is hardly as critical an
issue as some responders are maintainng.
Still, it's a big, messy, and dangerous job. I'd focus on that instead of
the results.
--
Roger Long
KVL
and as it is now, this model boat isn't that terrific with the way it
sails. Of course we were used a Philip Rhodes - full keel, (that we
still own, but are selling) but we like the interior space of the
Carter for pleasure trips - weekends on the bay and such. This why we'd
like to have shorter draft on it - to access some of the places we
liked going with our Rhodes - which the draft is 4'9".
My husband likes a challenging project... he's a go getter!
Karolina
Roger Long wrote:
> As a naval architect, I would say just go ahead and do it. When you look at
> the incredible variety of keel sizes and shapes, you'll realize that it is
> actually hard to come up with something that flat out won't work. If you
> were racing and obsessing about gaining or losing an eighth of a knot in
> identical conditions, it would be one thing. The chance that you won't like
> the way the boat sails if you do a modification like this half way
> intelligently is finite, but small. ETC>>>>>>>
> --
> Roger Long
Wayne.B
wrote:
>Still, it's a big, messy, and dangerous job. I'd focus on that instead of
>the results.
That's very true and an important point. I know people who have tried
similar mods and been very disappointed.
The whole wing keel concept was really applicable only to the old
style 12 meter Americas Cup boats because of a design quirk in the
rating rule. As others have pointed out, the best bet for a cruising
boat is something called a scheel keel, or possibly a bulb.
http://www.cs.brown.edu/people/jfh/personal_other/boats/FAQ/node16.html
Jeff
> On Tue, 19 Dec 2006 14:21:17 GMT, "Roger Long" <rlon...@maine.rr.com>
> wrote:
>
>> Still, it's a big, messy, and dangerous job. I'd focus on that instead of
>> the results.
>
> That's very true and an important point. I know people who have tried
> similar mods and been very disappointed.
>
> The whole wing keel concept was really applicable only to the old
> style 12 meter Americas Cup boats because of a design quirk in the
> rating rule.
This is nonsense. It may be true that the particular design used in
the 12's wouldn't be appropriate for a cruiser, but the basic concept
is valid and quite useful. Simply put, the water that flows under the
tip of the keel reduces the effectiveness of the bottom foot or so of
the keel. The wing keel prevents this flow and keeps the last foot of
the keel effective. This permits reducing the draft by roughly a foot
in many cases. In addition, the ballasted wings are essentially a
bulb. It should be noted that the primary purpose is to reduce draft;
the deep keel will normally be more effective overall.
The quirk in the 12 meter rule was a draft limit of about 8.8 feet
(16% of WL plus .5 meter) so the wing allowed Lexcen to get better
upwind performance out of that draft. The story gets a bit more
complicated, but that's the most important part.
> As others have pointed out, the best bet for a cruising
> boat is something called a scheel keel, or possibly a bulb.
The Scheel Keel is certainly a neat design - it has the same design
goals as listed above for the wing keel, but it has less drag (or is
it more lift?).
>
> http://www.cs.brown.edu/people/jfh/personal_other/boats/FAQ/node16.html
This is a pretty simplistic view of the topic.
Evan Gatehouse2
>
> This is nonsense. It may be true that the particular design used in the
> 12's wouldn't be appropriate for a cruiser, but the basic concept is
> valid and quite useful. Simply put, the water that flows under the tip
> of the keel reduces the effectiveness of the bottom foot or so of the
> keel. The wing keel prevents this flow and keeps the last foot of the
> keel effective. This permits reducing the draft by roughly a foot in
> many cases. In addition, the ballasted wings are essentially a bulb.
> It should be noted that the primary purpose is to reduce draft; the deep
> keel will normally be more effective overall.
After the America's Cup where the winged keel appeared, a lot of shoal
draft winged keels appeared on cruising yachts.
Winged keels are actually very HARD to get right. The added weight
down low helps, but the extra wetted surface and drag are
considerable. You have to get the angle of the wings right and
without doing studies in a tank, that's hard to do.
My copy of Principals of Yacht Design has an interesting study of
shoal keels. Delft University researchers used a VPP to compare keel
shapes. Results of sailing an Olympic trial course in the computer.
Times are in decimal hours:
Deep Fin keel 3.96
Shallow keel + centerboard 4.06
plain shoal draft keel 4.13
Scheel keel 4.10
Winglet keel 4.04
(short wings, aft swept leading edge)
Winged keel 4.01
(wide wings, reverse taper)
Deep Elliptical keel 3.96
So a good winged keel can be nearly as fast as a deep fin keel. But a
bad one (as many were) can be quite slow upwind due to extra drag.
If your husband is a ME then adding a simple bolt on lead bulb is the
best bet to keep performance reasonable. I'd try to keep the bending
moment on keel root the same as the original keel. I'd also use a
body of revolution using a 64 series NACA foil to define the bulb
shape. He can use Profili to get foil sections in DXF format, export
into Autocad or any 3D modeler, and revolve to get a bulb shape with
the correct volume. Then plot out full size cross sections and make
templates to form the bulb. Make a bulb plug in foam or wood. Get
somebody else to cast it for you or DIY. Glenn Ashmore's RUTU site
has a good description of keel casting.
I don't like Sponberg's "beavertail" keel. I think there's a lot of
drag in the tail that isn't justified as an endplate astern of the foil.
Evan Gatehouse
(also a naval architect and ME)
Roger Long
>
> Winged keels are actually very HARD to get right.
This is a good point. I would agree about wings being difficult. A bulb
that doesn't do any lifting on it's own would be pretty hard to screw up
hydrodynamically unless you were obsessing about the last 1% of performance
for racing. Think about the drag of a lead wing that gets bent back on
itself after touching bottom:)
> I don't like Sponberg's "beavertail" keel. I think there's a lot of
> drag in the tail that isn't justified as an endplate astern of the
> foil.
I could agree with that for racing but this is a cruising application. They
probably wouldn't notice much difference if they cut the bulb off flat on
back unless they had an identical boat to sail next to.
The most critical drag issue if they are going to sail anywhere that there
is kelp or lobster pots is having stuff slide off the keel easily. This is
always a problem with bulbs and the Scheel keel is expecially good in this
regard. I look at the Sponberg idea as a way to get the required volume in
the bulb without having to put if forward where it makes pot warps and weed
more likely to stick.
I'd try to emulate a Scheel keel (may be still patented) if you can get the
required area in but the Sponberg looks like it would shed most floating
stuff as well as any bulb.
>
> Evan Gatehouse
> (also a naval architect and ME)
--
Roger Long
Carl
complicated. It's unlikely minor differences in keel shape will be
noticeable cruising - I bet a new sail or two would have a much bigger
impact. The Carter 33 was a very fast boat in it's time.
I am not a naval architect and you do the following at your own risk.
I'm also assuming you don't care about resale value - since you got the
boat for almost nothing. What I would do is a low cost test. Cut 9"
off the keel for a 4' 8" draft (wear a respirator) and chock the cut
off piece in the bottom of the bilge. The whole boat only displaces
8000lb so the last 9" of this fin keel isn't going to be very heavy-
you could cut it into smaller pieces so you don't hurt your back or so
it fits better in the very shallow bilge space in this boat. Then see
how the boat sails - she will be more tender -- so start off with a
reef in the main and a small jib. Get a good feel for any stability
changes. If it's too tender, you'll need to find a way to put more lead
at the bottom of the keel - but you may feel it's fine for your
purposes. Forget this whole plan if you ever think will do real
offshore work and tell any future buyer what you did!
Another plan - and safer - is to call Bob Perry. He worked with Dick
Carter when your boat was designed (as did a lot of other now famous
designers). He should know the boat and might have some creative
thoughts. Or he'll tell you it's a big mistake. Either way it won't
cost you much and you'll learn a lot of things about your boat besides
the keel.
Here's a link:
http://www.perryboat.com/page/consult
And enjoy the Carter 33. It's a great boat.
Carl
tsm...@gmail.com
...
> The whole wing keel concept was really applicable only to the old
> style 12 meter Americas Cup boats because of a design quirk in the
The Oz II keel had a lot of things going on including inverse taper,
and very thick winglets cum bulbs and, as a whole, it could only have
worked well on Oz II. When we saw it I think most of us though, "wow,
that keel is on upside down!" It is the upside down or inverse taper
part of that keel that was most notable and is least transferable to
non-meter designs. There is a theory that the inverse taper on the Oz
II keel smoothed out the spanwise lift for the entire boat including
its deep, narrow canoe body. If true, this would only work on oddly
shaped boats like late generation 12 meters and so, I think it's
reasonable to say that upside down keels are only applicable to 12
meters because of the rating rule.
Winglets and bulbs are a whole other kettle of fish, and they can work
well on many designs.
Anyway, for the OP, let me second the opinion that
http://www.marsmetal.com/newpages/torpedobulbs.html is worth a look.
-- Tom.
Rich Hampel
bolt on keel. So, Mars Metal may have either a direct replacment keel
or can simply supply winglets/bulb etc. that can be added to a cut off
stub on the current keel. You might be able to sell what's cut off
from the original keel back to them as 'scrap'. If this boat in fact
does have the bolt-on keel then definitely Mars Metals will probably be
the best source of well engineered alteration.
BTW Carters with their signature 'tumblehome' sides are BEAUTIFUL.
In article <jo8do2lfdo0vsu3kf...@4ax.com>, Charlie Morgan
<*@*.com> wrote:
> On 18 Dec 2006 06:03:16 -0800, "KVL" <k...@usecashtobuyit.com> wrote:
>
> Before you ruin the boat:
>
> Mars Metal
>
> marsmetal.com
>
> CWM