Draft specs all over the map

doogymon · 2013-01-17 00:09:00

Hi

How much water do I need under the keel, to float a 1979 C&C 27 MK III?

Cheers & thanks

Doog

clanning · 2013-01-17 23:07:15

Is this a trick question?
Chuck Lanning
NSC, Ottawa

Last edited by (2013-01-17 23:07:32)

doogymon · 2013-01-18 00:31:14

LOL Chuck

I guess I have failed miserably with my wording.

I'm seeing ads for C&C 27s (Mk1 to 4) with keel depths

from four feet zero inches(4'0") to five feet zero inches(5' 0").

4' 3 and 4 '6 and 4 '10 being the most common.

So to reword the question: What vertical length (depth) did the keel

on a 1979, C&C 27 Mk 3 come in? The boat I'm looking at does not

state the keel length. I chose to say it like the Navy guys, how

much do I need under the keel to to float "safely".

Cheers

Doog

davidww1 · 2013-01-18 00:39:06

What Chuck may be alluding to is the existence of this information on the site - in this case in Evolution (see above), hence surprise at the question.

Evolution gives the official numbers. As any sailor will know, though, official numbers for draught never survive the first loading of inventory: anchors, chain, pots & pans, alcohol, etc. Call it 4'9" to be on the safe side.

David Weatherston
Towser, Toronto
C&C 27 Mk IV

doogymon · 2013-01-18 12:43:20

Hi David and company.

Ok for the evolution page.

Great stuff.

Thanks very much.

Doog

bosco · 2013-01-19 00:15:41

I have read all of the good answers to the initial question but I HAVE to
add my own answer--- "about 1/8 inch or so, in calm water"

Clare Jordan. Aragorn

diva27 · 2013-01-19 03:43:58

C&C's design department drawings of the two hull versions of the 27 give the draft of the Mark 1 27 as 4 ft 3 in. and the Mk II (which in class association terms covers the Mk 3 and 4 versions) as 4 ft 5.5. inches. This is based on the "load waterline length." The drawings also indicate that the average flotation for the 27 is an inch and a half deeper than the draft based on LWL. The actual real-world draft as Dave notes depends on how much junk (I mean, irreplaceable gear) you have on board, although it would take an awful lot of stuff to immerse a boat of this size another inch or two.
Doug Hunter
Diva
C&C 27 Mk1
Midland Bay Sailing Club
www.douglashunter.ca

diva27 · 2013-01-19 04:06:29

Further this, I'm talking to a couple C&C design dept alumni about how much weight you have to toss in a 27 to make it float an inch deeper.. I'm informed by email: "The number you are looking for is "Lbs per inch immersion". This is the area of the water plane in sq.ft times .083' (1") times the density of water (62.4 Lb'cu.ft for FW). This is a standard item on the design data sheet for each boat, but unfortunately, I don't have any of those (I used to, but they have gone missing!)" This particular designer's pure guess is that for the 27 it would be 500 pounds for every inch, but I'll see if I can learn more. In particular, it would be great to have the design data sheet. I may be in the collection of the Marine Museum of the Great Lakes at Kingston.
Doug Hunter
Diva
C&C 27 Mk1
Midland Bay Sailing Club
www.douglashunter.ca

diva27 · 2013-01-19 06:56:48

Aaaand further to this, C&C design alumnus Rob Mazza says he'll have the answer for me Monday on how much crap you have to put aboard your 27 to sink it one inch.
Doug Hunter
Diva
C&C 27 Mk1
Midland Bay Sailing Club
www.douglashunter.ca

davidww1 · 2013-01-19 07:07:47

So, 500 lb per inch immersion means, leaving aside owner's and guests' junk, that 2.86 Standard North Americans (SNA @ 175 lb. ea. average) or 2.5 Standard North American Fatties (SNF @ 200 lb. ea. average) will immerse the vessel a further inch. However, since they'll all be sitting in a row in the cockpit like bumps on a log and there probably will be four of them, the poor 27 will be down 3-4 inches by the stern, up two in the bow. Not pretty and they'll all be wondering why they're not fast.

David Weatherston
Towser, Toronto
C&C 27 Mk IV

diva27 · 2013-01-19 07:22:29

Immagonna wait till Rob gets back to me with a definite result before drawing a firm conclusion on the fatty/immersion ratio. I frankly thought the number would be higher than 500 lbs for a full inch of immersion, bow to stern, but then that's almost 10 percent of design displacement.
FWIW Rob also said that C&C usually "painted" the waterline stripe about 2 inches above the LWL.
Doug Hunter
Diva
C&C 27 Mk1
Midland Bay Sailing Club
www.douglashunter.ca

davidww1 · 2013-01-19 07:57:09

Well they must have slopped the resin into Towser or the calculations weren't right because one of the first things I did was raise the waterline to the top of the stripe, which is probably 2 inches in vertical height.

David Weatherston
Towser, Toronto
C&C 27 Mk IV

diva27 · 2013-01-19 08:08:02

I'm not persuaded Diva's red waterline stripes are 1971 originals, but whoever did them seemed to get the rule of thumb right, as I show about 2 inches of bottom paint when she's floating level.
Doug Hunter
Diva
C&C 27 Mk1
Midland Bay Sailing Club
www.douglashunter.ca

diva27 · 2013-01-19 08:58:40

Just heard from Steve Killing. He checked his files and says the magic number for pounds per inch of immersion for the 27 is...

532.
Doug Hunter
Diva
C&C 27 Mk1
Midland Bay Sailing Club
www.douglashunter.ca

diva27 · 2013-01-20 23:15:35

I heard from Rob Ball on this as well. He helpfully points out that if the boat is already floating below the LWL (as the design dwgs indicate an average immersion of 1.5 inches deeper than LWL) then it would take more weight to immerse it an inch. (Because hull volume increases above the LWL, an inch of immersion equals more volume). Anyhow, Rob says a typical 27 would probably need about 560 pounds to immerse it one inch.
Doug Hunter
Diva
C&C 27 Mk1
Midland Bay Sailing Club
www.douglashunter.ca

clanning · 2013-01-21 04:01:19

David, you give me far too much credit.

I was in fact trying to be a smart a**.

All I know is that there is sometimes not enough water to float a 27 at the NSC harbour entrance in late summer. We're trying to address that!

Cheers and Happy Equinox.

(Harbour Master believes that Equinox is that point half way between lift-out and launch day. Willing to go with him on that, and we must be close...)

PS -- if anyone has experience with dredging permits and the like, please PM me. Thanks.
Chuck Lanning
NSC, Ottawa

davidww1 · 2013-01-22 00:12:03

Chuck, no one is going to give you a permit to dredge around Ottawa. Think of what might surface. Knowing where the bodies are buried is the prerogative of the Prime Minister's Office.

David Weatherston
Towser, Toronto
C&C 27 Mk IV

clanning · 2013-01-22 01:34:17

For the past few years, everything seems to be flowing through the PMO anyhow. Probably some dredging needs to happen there as well.

Cheers
Chuck Lanning
NSC, Ottawa

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#1 2013-01-17 00:09:00

Draft specs all over the map

#2 2013-01-17 23:07:15

Re: Draft specs all over the map

#3 2013-01-18 00:31:14

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#4 2013-01-18 00:39:06

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#6 2013-01-19 00:15:41

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