Scantlings, Or Where is the Weight?
rtu...@my-dejanews.com
This program has some rough spots, but is pretty nice for
freeware. And what else does a lonely software consultant do
on the road? (Well, there is *that*, but I meant, what else
that doesn't cost money?)
Anyway, I designed a hull for a 37 foot, double-chine, steel
sailboat with cruising keel. Naively -- let me repeat, VERY
naively -- I made the following scantling assumptions for the
hull plate:
keel panel: 1/4 inch (.25)
bottom and waterline panels: 3/16 inch (.1875)
topside panel: 3/20 inch (.15)
deck panels: 1/8 inch (.125)
I assumed that the internal metal framing would weigh 15%
of the skin. Using a spreadsheet to calculate total weight,
skin and framing are 6,000 pounds of metal. I estimated
another 3,000 lb. to finish out the rest of the boat, and
gave the vessel 8,000 lb. of ballast to balance the slender
hull (10.5 foot beam, 9 foot WB). The total *dry*
displacement is 17,000 lb.
Now, I hear all the horror stories that small steel boats
are heavy and poorly ballasted. But the stats for this
(naive) design are close to those for some well-regarded
fiberglass designs, and are much less than some of the
fiberglass heavyweights.
So .. where did I go wrong? Are my scantlings ridiculously
thin? Am I underestimating how much framing is needed? What
am I missing? A 6,000 lb. hull does not seem that bad for
a 37 foot cruising sailboat.
Russell
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Matt Pedersen
rtu...@my-dejanews.com wrote in message
<79fbqh$5q1$1...@nnrp1.dejanews.com>...
>
>Anyway, I designed a hull for a 37 foot, double-chine, steel
> Using a spreadsheet to calculate total weight,
>skin and framing are 6,000 pounds of metal. I estimated
>another 3,000 lb. to finish out the rest of the boat, and
>gave the vessel 8,000 lb. of ballast to balance the slender
>hull (10.5 foot beam, 9 foot WB). The total *dry*
>
>Are my scantlings ridiculously
>thin? Am I underestimating how much framing is needed? What
>am I missing? A 6,000 lb. hull does not seem that bad for
>a 37 foot cruising sailboat.
I think your assumptions about framing and hull scantlings are
probably pretty darn close to the mark (especially as a first
approximation). Where I think you underestimated is in the
fitting out. Here's some numbers I have for a similar sized
design (not steel though):
Interior 1600 lbs
Machinery (engine, shaft, wiring, tanks) 1500 lbs
Deck gear (anchors, winches) 900 lbs
Spars and sails (incl. running rigging, spin pole) 700 lbs
Payload (people, 75 gal water, 30 fuel, 15 gal holding - half tanks) food
2500 lbs
This payload is for coastal cruising and doesn't include about another 1000
pounds
of things most people carry for long distance cruising. As well, there are
a few
other things I should point out about the above numbers. Some of the
interior
used foam core panels, so it will be a little lighter than an all plywood
version.
Also, for a steel boat the insulation needs to be included, which may add a
couple hundred pounds more.
So 6000 hull + everything else =13,200
Ballast would be about 8800 for a total displacement of 22,000.
Some designers include the keel plating as part of the ballast
calculations and reduce the percentage accordingly, although
for a narrow boat like yours it might be good to keep the ratio
higher (which would, of course, improve your limit of positive
stability).
Have fun designing.
Matt
Hary
but the hull plate goes to 3/16
plate.
His plans are excellent and very simple construction procedures
rtu...@my-dejanews.com wrote in message
<79fbqh$5q1$1...@nnrp1.dejanews.com>...
>Last night, I was playing around with Carlson's Hulls program.
>This program has some rough spots, but is pretty nice for
>freeware. And what else does a lonely software consultant do
>on the road? (Well, there is *that*, but I meant, what else
>that doesn't cost money?)
>
>Anyway, I designed a hull for a 37 foot, double-chine, steel
>sailboat with cruising keel. Naively -- let me repeat, VERY
>naively -- I made the following scantling assumptions for the
>hull plate:
>
> keel panel: 1/4 inch (.25)
> bottom and waterline panels: 3/16 inch (.1875)
> topside panel: 3/20 inch (.15)
> deck panels: 1/8 inch (.125)
>
>I assumed that the internal metal framing would weigh 15%
>of the skin. Using a spreadsheet to calculate total weight,
>skin and framing are 6,000 pounds of metal. I estimated
>another 3,000 lb. to finish out the rest of the boat, and
>gave the vessel 8,000 lb. of ballast to balance the slender
>hull (10.5 foot beam, 9 foot WB). The total *dry*
>displacement is 17,000 lb.
>
>Now, I hear all the horror stories that small steel boats
>are heavy and poorly ballasted. But the stats for this
>(naive) design are close to those for some well-regarded
>fiberglass designs, and are much less than some of the
>fiberglass heavyweights.
>
>So .. where did I go wrong? Are my scantlings ridiculously
>thin? Am I underestimating how much framing is needed? What
>am I missing? A 6,000 lb. hull does not seem that bad for
>a 37 foot cruising sailboat.
>
rtu...@my-dejanews.com
dialogue makes me realize is that when I see "displacement"
bandied about from boat builders, I really don't know what it
means. Does it include (a) sails and running rigging, which
are sometimes after market items, (b) empty, half-full, or full
tanks, and (c) any allowance for payload?
In article <79ggjk$c22$1...@brokaw.wa.com>,
"Matt Pedersen" <pede...@halcyon.com> wrote:
> I think your assumptions about framing and hull scantlings are
> probably pretty darn close to the mark (especially as a first
> approximation). Where I think you underestimated is in the
> fitting out. Here's some numbers I have for a similar sized
> design (not steel though):
>
> Interior 1600 lbs
> Machinery (engine, shaft, wiring, tanks) 1500 lbs
> Deck gear (anchors, winches) 900 lbs
> Spars and sails (incl. running rigging, spin pole) 700 lbs
All this (less ground tackle) is what I estimated as 3,000 lbs.
Your numbers suggest I am short some.
> Payload ..
Though I did not post it in the original, I estimated 4,300 lbs.
payload, including full tanks, crew, victuals, and assorted junk.
> Ballast would be about 8800 for a total displacement of 22,000.
Yep. I estimated a fully loaded displacement at just over 21K
lbs. The 17K lb. was empty and dry.
Thanks!
Leo Voorneveld- NL
rtu...@my-dejanews.wrote
>One think this dialogue makes me realize is that when I see "displacement"
>bandied about from boat builders, I really don't know what it
>means. Does it include (a) sails and running rigging, which
>are sometimes after market items, (b) empty, half-full, or full
>tanks, and (c) any allowance for payload?
Hi,
this is hard to tell, I have some information from a certification bureau
who did measurements for
racing class/magazines etc.
From the 5 boats in the 6.5 meter range all are more heavier then the
designer/yard told.
This was for empty boat and no sails etc.
I will give three examples,which I could find quickly.
Units are m3.
given:
0.850 is actually 0.920 =ff 65
0.950 is 1.140 =dehler 22
0.975 is 1,100 =etap 22 i
All respected yards and designers.
I collect this kind of information in a database and allways the French
designs tended to be heavy, think they use half loaded weights.
In the sailing forum of compuserve ( not only accesable for members, but
public) you can find in the
design section a lotus dbase with 1000 (USA) yachts, free download.
Regards Leo Voorneveld
For Mini transat info surf to www.xs4all.nl/~blvrd
edgar cove
writes
>I thank Matt Pedersen for his comments below. One think this
>dialogue makes me realize is that when I see "displacement"
>bandied about from boat builders, I really don't know what it
>means. Does it include (a) sails and running rigging, which
>are sometimes after market items, (b) empty, half-full, or full
>tanks, and (c) any allowance for payload?
Displacement is not a constant figure since it depends on what you have
on board. Displacement is the weight of water displaced equal to the
weight of the boat and all gear and crew aboard at the given time and
therefore varies. Displacement at the end of a voyage is less than at
the beginning since you have burned fuel and eaten and, er, 'disposed
of' food, for example.
--
edgar (remove nospam from return address for e-mail reply)
Stephen G. Lusardi
deck, watertight bulkheads, cockpit, hatches, portlights complete weighs 7
tons. I have to carry 12 tons of lead ballast. You are also correct in
assuming everyone knows steel has to be heavy. It is often lighter than wood
and fiberglass. The important key is the design must be specific for steel
in order to advantage of all it's benefits.
Steve Lusardi
rtu...@my-dejanews.com
edgar <ed...@nospam.coves.demon.co.uk> wrote:
> Displacement is not a constant figure since it depends on what you have
> on board. Displacement is the weight of water displaced equal to the
Well, yes, we all know that.
But the specs for a boat typically give a single figure. It would be
nice if they gave several figures, e.g., DWL displacement, actual
displacement dry and empty, expected payload, etc. But they typically
just give one figure. The question was: what does that figure mean?
I suspect that what it means varies quite a bit, or rather, that its
meaning is vague.
John Abercrombie
>You are also correct in
>assuming everyone knows steel has to be heavy. It is often lighter than wood
>and fiberglass. The important key is the design must be specific for steel
>in order to advantage of all it's benefits.
One other commonly held belief about steel construction for sailing
yachts is that its advantages only become evident in larger size
boats. For a 58 foot boat it may be ideal; try the design exercise for
a 25 or 30 footer and you will see that you cannot get a boat which
will sail well (adequate ballast ratio) with plating which is thick
enough to a) weld without incredible distortion b) resist corrosion
long enough to last for a few years.
John
rtu...@my-dejanews.com
john...@netcom.ca (John Abercrombie) wrote:
> One other commonly held belief about steel construction for sailing
> yachts is that its advantages only become evident in larger size
> boats. For a 58 foot boat it may be ideal; try the design exercise for
> a 25 or 30 footer and you will see that you cannot get a boat which
> will sail well (adequate ballast ratio) with plating which is thick
> enough to a) weld without incredible distortion b) resist corrosion
> long enough to last for a few years.
Yep, I believe this. I had the definite sense that the size I
chose for my exercise (37 feet and approx. 8 tons) started to
push into the lower range. I have no doubt that reasonable
steel boats can be build and designed smaller than this, but
that you are also pushed into certain design directions where
you may not want to go.
Matt Pedersen
rtu...@my-dejanews.com wrote in message
<79kp6n$c17$1...@nnrp1.dejanews.com>...
>In article <8pnYGDAN...@coves.demon.co.uk>,
> edgar <ed...@nospam.coves.demon.co.uk> wrote:
>
>But the specs for a boat typically give a single figure. It would be
>nice if they gave several figures, e.g., DWL displacement, actual
>displacement dry and empty, expected payload, etc. But they typically
>just give one figure. The question was: what does that figure mean?
My feeling is it depends on the boat and who it's being marketed toward.
If you're trying to sell a race boat, you might take the designer's figures
for a totally light boat, no extra equipment and probably just working sails
and running rigging. That will give you a higher SA/Disp and Disp/L
ratios, which would indicate a higher speed.
For a cruising boat, I think they start out with the designer's figure
for a half-load condition - half tanks, all sails and running rigging,
and a nominal weight for food and crew. However, I think it's
generally acknowledged that most boats (including race boats)
end up being anywhere from 10 - 15% overweight coming out
of the factory (and Leo's figures seem to verify that). So
eventually, for race boats you end up with a brochure weight
that's a little light, and for a cruising boat it ends up with the
brochure weight showing the actual weight with no stores
or tankage.
There doesn't seem to be any industry standard here, and
I can't ever recall seeing any manufacturer saying that the
boat can carry X pounds of gear. I think most manufacturers
end up painting the bootstripe a little higher than is shown on
the drawings. I agree, it would be nice to know what
assumptions were made in the design of the boat, and I think
a really honest builder or designer will give you that information
if you asked.
Matt
Paul Kamen
Matt Pedersen <pede...@halcyon.com> writes:
>...There doesn't seem to be any industry standard here...
What Matt said.
Excpet that if a boat has (or once had) a MORC certificate, then it's been
hung from a scale in a known loading condition and the weight entered on a
certificiate that's readily obtainable.
For example, I know that my boat weighs 3,126 lb. in MORC measurement
trim (compared to "3,000" on the brochure).
IMS gets at the same number by measuring the lines and freeboards (and
water density). Even if only one boat of a class had an IMS certificate,
it would still be far more valuable than the number on the brochure. And I
suspect a significant number of boats currently in use for cruising have
at least one sistership with a certificate.
It would be an interesting exercise to go through a stack of MORC and IMS
certificates, comparing actual weight in this known loading condition with
brochure displacement.
--
fish...@netcom.com
http://www.well.com/~pk/fishmeal.html
-"Call me Fishmeal"-
macnaughton.com
designed displacement is whatever the designer figured you have in the boat
total. If you built the boat heavier or added more gear it will displace
more. If you leave off stuff the designer assumed it will displace less. It
is called "displacement" because the amount of water "displaced" by a
floating body weighs the same as the floating body.
Tom MacNaughton
Naval Architect
http://www.macnaughtongroup.com
rtu...@my-dejanews.com wrote in message
<79mpf9$tqv$1...@nnrp1.dejanews.com>...
rtu...@my-dejanews.com
fish...@netcom.com (Paul Kamen) wrote:
> It would be an interesting exercise to go through a stack of MORC and IMS
> certificates, comparing actual weight in this known loading condition with
> brochure displacement.
It would be interesting just to look up these numbers for specific
boats as they caught one's eye. How does one go about getting
MORC and IMS certificate measurements? Is any of this information
on the Internet? (It doesn't have to be on the Web, if it is
ftp-able.)
Paul Kamen
>...How does one go about getting MORC and IMS certificate
>measurements?
Years ago when I was a MORC measurer I had a printout of the master file
summarizing all ratings, including the weight of each boat with a
certificate. MORC is generally pretty open about access to that sort of
info, and it might be worth trying to dig up the current master file
online. IMS, as I understand it, will let you see any individual boat
certificate for a fee. But there might be a list of IMS "club ratings"
somewhere which would serve this purpose if it includes certificate
details.
(I'm adding r.b.racing to the cross-post. Cruisers are interested in the
measured weight or calculated displacement info from MORC/IMS certificates
so they can figure out how nominal "displacement" is being defined by
various builders in the sales literature.)
Joe Ozelis
> rtu...@my-dejanews.com writes:
>
> >...How does one go about getting MORC and IMS certificate
> >measurements?
> online. IMS, as I understand it, will let you see any individual boat
> certificate for a fee. But there might be a list of IMS "club ratings"
> somewhere which would serve this purpose if it includes certificate
> details.
You can get the "IMS Master File" from US Sailing for something like 25 or
40 bucks - it lists selected parameters (such as DPSL) of all of the IMS
ceritificate holders in the US. Go to www.ussailing.org
Joe
rtu...@my-dejanews.com
Joe Ozelis <joz...@enteract.com> wrote:
> You can get the "IMS Master File" from US Sailing for something like 25 or
> 40 bucks - it lists selected parameters (such as DPSL) of all of the IMS
> ceritificate holders in the US. Go to www.ussailing.org
Usually I am pretty good at finding such things given the Website's
URL. But even after going to their IMS page and their publications
page, and even after getting a publication fax index, I find neither
a reference to an "IMS Master File" nor any likely contact for
finding out about this.
Can you give a better pointer? (Undoubtedly, it's right in front of
my face, and I am just missing it.)
Joe Ozelis
>
> Usually I am pretty good at finding such things given the Website's
> URL. But even after going to their IMS page and their publications
> page, and even after getting a publication fax index, I find neither
> a reference to an "IMS Master File" nor any likely contact for
> finding out about this.
>
> Can you give a better pointer? (Undoubtedly, it's right in front of
> my face, and I am just missing it.)
I didn't actually remember where on the Web site it was ("Publications"
does seem like a natural spot), but it turns out that US Sailing lists is
under "merchandise" - go figure. Anyway, I found it at
www.ussailing.org/merch/main.html
Click on the "Offshore/IOR/IMS/MORC..." link. The data book is now
50 bucks for non-members, 30 bucks for members.
Joe
Leo Voorneveld- NL
>does seem like a natural spot), but it turns out that US Sailing lists is
>under "merchandise" - go figure. Anyway, I found it at
>
>www.ussailing.org/merch/main.html
>
>Click on the "Offshore/IOR/IMS/MORC..." link. The data book is now
>50 bucks for non-members, 30 bucks for members.
Thank you Joe,
I have bin on that page but missed it, what kind of figures are given in
this databook ?
50 bucks is not a bad price but shipping addded make it worth to inform of
the data in the book.
TIA Leo Voorneveld
Mini Transat design/info www.xs4all.nl/~blvrd