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Old 25-10-2014, 16:33   #1
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Stiffest Boat?

Can anyone tell which boat in this group would be the stiffest?

Niagara 31

NIAGARA 31 sailboat specifications and details on sailboatdata.com

Cal 31

CAL 31 sailboat specifications and details on sailboatdata.com

Morgan 323 SD

MORGAN 32 SD sailboat specifications and details on sailboatdata.com
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Old 25-10-2014, 19:13   #2
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Re: Stiffest Boat?

The Cal 31. The lower ratio is an indication of a stiffer boat. This is a simplified explanation.
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Old 26-10-2014, 07:24   #3
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Re: Stiffest Boat?

The flattest and beamiest one with the most ballast hanging the lowest.

As for structural stiffness: carbon. If GRP, avoid large flat panels. Etc.

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Old 26-10-2014, 07:48   #4
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Re: Stiffest Boat?

Quote:
Originally Posted by barnakiel View Post
The flattest and beamiest one with the most ballast hanging the lowest.

b.
Yep, that's why I was asking because the Cal 31 has a 10' beam, displaces 9170 lbs, and has a 5' longish fin keel. Bal/disp is 39.25%

The Morgan 32 with shoal draft has a beam of 11'6", displaces 11,000 lbs but the keel is only 4'
Bal/disp is 36.35%

The Morgan sure looks good going through the water. This one also has the shoal draft.

http://www.sailnet.com/forums/attach...tachmentid=105
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Old 26-10-2014, 08:08   #5
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Re: Stiffest Boat?

Not enough info to make any predictions, assuming you are talking about stiffness as in the ability to carry sail (as opposed to panel stiffness). Stiffness comes from 3 different places.
1/ Hull form, a hard turn to the bilge and a flatter bottom will give more form stability than a slack bilge hull form. There are no body plan drawings showing hull form.
2/ Ballast ratio, this can be deceiving as a keel/centerboard boat for example can have a high ballast ratio because it is in the bilge and not very effective.
3/ Location of said ballast, ie, 2000lbs in a bulb on a deep fin provides a more effective righting arm than the above example so can use less ballast for the same righting arm or the same ballast for a greater righting arm.
So as you can see, you cant draw much in the way of conclusions from the limited data on most of the online data sites, you need to dig deeper.
As an example I have an old Lindenberg 26 which has about a 50% ballast ratio but when you look at the data it does not reflect that the ballast is bolted to the bottom of a sump which is 27" deep at the trailing edge and 7" deep at the leading edge which effectively places the ballast 14" below the fairbody, so any calculations on that site and others that don't reflect this will give bogus results, garbage in, garbage out.

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Old 26-10-2014, 08:09   #6
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Re: Stiffest Boat?

Are you looking for hull stiffness, as in most resistant to flexing? Or stiffness as in Righting Moment (basically the ability to stand up to a breeze)? And of course it kind of begs the question, why's it important to you?
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Old 26-10-2014, 08:17   #7
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Re: Stiffest Boat?

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Originally Posted by UNCIVILIZED View Post
Are you looking for hull stiffness, as in most resistant to flexing? Or stiffness as in Righting Moment (basically the ability to stand up to a breeze)? And of course it kind of begs the question, why's it important to you?
Stiffness as in Righting Moment.

I tend to end up sailing in quite a bit of breeze and my Bristol 27 can handle it but we ride the rails so to speak. She is way over and you have to be somewhat of a gymnast to go below for important supplies like a beer now and then.

BRISTOL 27 sailboat specifications and details on sailboatdata.com
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Old 26-10-2014, 09:02   #8
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Re: Stiffest Boat?

cal has fin/spade set up below waterline, niagra has fin/skeg, as does morgan.
that would be only fail point i can see for deep water cruising.
would be nice to see pic of the morgan....
as for reputation, all 3 are decent
going by the pic in sailnet, i would go for the morgan, if i were into lower freeboard performance sailcruisers
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Old 26-10-2014, 09:36   #9
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Re: Stiffest Boat?

Why worry about it, mono hulls heel, deal with it. Yes some boats have less initial stiffness like the old full keel, slack bilge designs. What they lose in initital stiffness is more than made up for by easy motion in a seaway. Some flat bottomed boats with deep keels that have extreme initial stiffness reach a point of negative righting moment in a severe knockdown. Not something that you want in an offshore boat unless speed is more important than your life. If you want to sail upright, there are those training wheel boats but hope your wallet is gold plated for those. Other than that, try reefing. Cuts the heeling down right quick. People that brag about how stiff there boat is usually make me think their mast is too short or they aren't carrying enough sail for best performance.

None of the boats you are looking at are extreme and should all sail reasonably well. There are a lot of other things that will make the fit YOUR needs than a slight difference in initial stiffness. Buy the boat that you like the most for its features/layout/equipment.
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Old 26-10-2014, 09:48   #10
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Re: Stiffest Boat?

Define stiffness.

Initial stiffness, at low angles of heel, is due to form stability - which increases with increasing beam. Plenty of initial stiffness makes the boat comfortable to sail, especially for novices.

Stiffness at large angles of heel is due to the righting moment from the ballast in the keel, and the greater the heel the LESS the effect of form stability. In fact, at extreme angles, wide beams have a negative effect.

Finally, you could argue about whether it should be measured at a given SA/D. A boat with more sail area will feel less stiff, but reefed down to the same area would be a more sensible comparison.

A seaworthy boat has moderate beam, not extreme in the sense of not being too narrow OR wide, and plenty of ballast down low.
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Old 26-10-2014, 10:14   #11
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Re: Stiffest Boat?

I like the Morgan but was a bit worried about the short shoal draft keel at 4' as compared to the other two boats with 5' keels (but they are lighter in weight and more narrow)

1983 Morgan 323 Sail Boat For Sale - www.yachtworld.com

1982 Morgan 32 Sail Boat For Sale - www.yachtworld.com

1983 Niagara 31 Sail Boat For Sale - www.yachtworld.com

1980 CAL 31 Sail Boat For Sale - www.yachtworld.com
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Old 26-10-2014, 11:49   #12
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Re: Stiffest Boat?

Quote:
Originally Posted by roverhi View Post
Why worry about it, mono hulls heel, deal with it. Yes some boats have less initial stiffness like the old full keel, slack bilge designs. What they lose in initital stiffness is more than made up for by easy motion in a seaway. Some flat bottomed boats with deep keels that have extreme initial stiffness reach a point of negative righting moment in a severe knockdown. Not something that you want in an offshore boat unless speed is more important than your life. If you want to sail upright, there are those training wheel boats but hope your wallet is gold plated for those. Other than that, try reefing. Cuts the heeling down right quick. People that brag about how stiff there boat is usually make me think their mast is too short or they aren't carrying enough sail for best performance.

None of the boats you are looking at are extreme and should all sail reasonably well. There are a lot of other things that will make the fit YOUR needs than a slight difference in initial stiffness. Buy the boat that you like the most for its features/layout/equipment.
I didn't see anywhere where the OP was looking for a boat for offshore work, ( not every boat needs to be suitable for offshore whatever that is) but it seems that he is looking for something that doesn't sail on its ear like his current boat. I think he's right zeroing in on initial stability, unless of course he is planning on ocean crossing. Your right about rig size though, a few boats were available with tall rigs and some are tender because of it.


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Old 26-10-2014, 12:06   #13
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Re: Stiffest Boat?

One writer said "These boats (Bristol 27) were narrow with long overhangs, graceful low-slung sheerlines, and sweeping full keels that are cutaway in the forefoot. The narrow beam adds to seaworthiness but doesn’t do much for form stability, so they are quite tender initially. That’s not all bad as they were designed to lengthen their waterline when heeled."

The Bristol 27 Sailboat : Bluewaterboats.org
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Old 26-10-2014, 12:18   #14
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Re: Stiffest Boat?

How much effort retrofitting water ballast into your Bristol?

How much effort shifting the most important supplies to windward?

Sure, one crate would not do. I think a couple of kegs could help though. You could fill them with sea water once empty.

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Old 26-10-2014, 12:21   #15
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Re: Stiffest Boat?

Quote:
Originally Posted by thomm225 View Post
Initial stiffness or ultimate stiffness?

To really tell you will need to look at the righting moment graphs for these boats, anything else is a guess from first principles.
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