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08-10-2024, 16:02
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#1
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Registered User
Join Date: Sep 2024
Location: Eastham Massachusetts
Boat: Catalina 25 1983
Posts: 9
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Hull shape and performance
Hello,
You all seem to have a lot more experience than myself. This is just my second post.
My new to me used boat is a Catalina 25. I consider it a starter boat until I learn the ropes better and can get something bigger. So in the meantime I am trying to learn more.
As you can see the hull is extremely flat. How does that translate into speed and performance? From what I can find online that means it is relatively fast and can manuever well, but is not very stable in rough water?
What hull designs are blue water? I would imagine a full keel is the best and safest? Do blue water cruisers have more rounded hulls?
I have dreams of some longer voyages in the near future, say Massachusetts to the Bahamas? Just want to be prepared with the right tools(boat).
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08-10-2024, 19:40
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#2
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Registered User
Join Date: Jun 2018
Location: Seattle
Boat: Bavaria 35E
Posts: 270
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Re: Hull shape and performance
The more you read on these forums, the more you learn. But, I think you have the gist of it correct. Check out John Kretschmer's books. I particularly like "Sailing a Serious Ocean." As a delivery skipper for many years, he details his 15 best sailboats to consider and why in an index on most of the books. Interestingly, the modern cruisers have plumb bows which are nice for extended waterline speed and interior room, but likely to cause more hobby horsing in a rougher seaway.
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08-10-2024, 19:59
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#3
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Registered User
Join Date: Aug 2021
Location: PNW
Boat: 35 Ft. cutter, custom
Posts: 2,713
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Re: Hull shape and performance
Quote:
Originally Posted by Nauset
Do blue water cruisers have more rounded hulls?
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"Blue water" is a somewhat misleading term.
Plenty of boats with all kinds of shapes have made long ocean voyages.
However, the hull shape is very much part of what we call "seakindly" an old word that has little application in modern designs.
Here are a couple of pictures, the first I call "champagne glass", it's a pretty good example of most boats being built today.
They sail fast going downwind or on a reach but can beat the fillings out of your teeth going to weather, they are not seakindly.
The second picture is what I call a "wine glass" hull, it has more wetted surface, therefore more drag and is not as easily driven, but it "hangs on" the wind better while going to weather, and gives an easier ride, (more seakindly,) it's also more expensive to build.
__________________
Beginning to Prepare to Commence
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08-10-2024, 20:06
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#4
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Moderator
Join Date: Sep 2014
Location: Channel Islands, CA
Boat: 1962 Columbia 29 MK 1 #37
Posts: 14,964
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Re: Hull shape and performance
https://www.cruisersforum.com/forums...at-208582.html
This topic gets a good deal of discussion, and I always enjoy them! There are probably as many opinions on what makes a good "bluewater" design as there are sailors. Your boat makes an excellent starter boat, and there is probably someone somewhere who has sailed one across an ocean. In your explorations you'll see mention of seaworthiness and sea-kindliness... and you'll also see how different hulls perform upwind vs. off the wind. I have found a flatter hull uncomfortable going "uphill" if the hull is slamming the oncoming swells. Also a lighter, flatter hull, to my sensibilities, seems to respond on every axis to every little wave that comes by. I am sure folks get used to it, but it makes me queasy. But flatter hulls are good performers off the wind. A narrow and deeper, longer keel was considered the preferred design for offshore seaworthiness and seakindliness back in the day up to about 1963 or so. I would agree since that is the basic idea behind my little old boat, though I readily concede the hull gives up some speed and nimbleness with that longer keel, rudder attached and more wetted surface to drag through the water. An acquaintance has a Santa Cruz 50 (light and flat bottom) he wanted to sell. I thought, God what a great boat to go to Hawaii in, but it wouldn't be my first choice for a trip up the California coast. About my design, I find her comfortable once she is heeled over and scudding along. Her motion is limited to pitching mostly. I will concede that off the wind she can roll a bit, and sliding down a wave, to keep her from broaching she needs a lot of rudder, which, given that it is attached to the keel ends up acting as much as a speed brake sometimes. Every hull is a compromise, it all depends on what you'll be asking of the boat and what your own sensibilities are.
Anyway, when you get to the phase where you are actively hunting for an appropriate boat there are many folks here who can give you a lot of great tips.
These sites may help:
https://sailboat.guide/discover/blue-water-boats
https://atomvoyages.com/classic-smal...ers-list-html/
https://www.sailboat-cruising.com/
https://yachtdatabase.com/
My hull is more like a champagne flute.
Welcome aboard by the way.
__________________
DL
Pythagoras
1962 Columbia 29 MKI #37
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09-10-2024, 04:40
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#5
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registered user
Join Date: Dec 2012
Location: back in West Australia
Boat: plastic production boat, suitable for deep blue water ;)
Posts: 1,166
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Re: Hull shape and performance
Nice to compare wineglasses to boat shapes.
Here is an actual (local to me) boat in the shape of post #4: an old wooden boat, comfy sailing, but so slow, and quite tender, rolling in following seas. And hardly any room inside. To my knowledge, no new boats are built with that shape, for good reasons.
Sorry I cannot publish this pic the right way up, no matter how I rotate the original picture. The pic is not photoshopped and not made it look skinnier, it is a skinny boat with more draft than beam.
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09-10-2024, 07:46
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#6
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Registered User
Join Date: May 2013
Location: Potomac/Chesapeake
Boat: Hunter 36
Posts: 746
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Re: Hull shape and performance
The other big change in recent years is the shift from a hull that tapers aft to modern boats with very wide stern sections. It increases the living space considerably, adds stability, but probably not kindly in bad weather. On the other hand, if you sail faster, you are better equipped to escape bad weather. I do know my H36 has a wide butt and the downside when anchored is that when the wind and current are at odds, I constantly get water slamming against the hull which makes it very hard to sleep in the aft cabin.
Compare these two. I think the Benetau Sense line was the extreme version of this trend. They were so wide that they were nicknamed "monomarans".
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09-10-2024, 11:02
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#7
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Moderator
Join Date: Sep 2014
Location: Channel Islands, CA
Boat: 1962 Columbia 29 MK 1 #37
Posts: 14,964
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Re: Hull shape and performance
I will agree the older designs were/are a bit slower, but in my own case my 22.5' waterline still goes 7 knots pretty easily. And yes it is more tender than my neighbor's boat but once she is heeled over to between 15 and 20 degrees she is very stable and comfy. Certainly many folks don't find it comfortable to sail for days at a 15 or 20 degree angle, but before these designs become extinct, everyone should get a chance to sail a good one before putting headstones on them. The designers like Carl Alberg, Olin Stephens, Bill Tripp, Alfred Luders, and many more weren't stupid, and a lot of folks with experience have found their designs preferable for crossing oceans. All I am saying is don't be too quick to write them off.
Now, that said, many hulls were designed to fit the CCA rule for racing in the 50's and 60's and ended up with too much rocker and waterlines that were forced to be too short. Hence many of them suffer from "hobby horsing" which gave the long keels of the day a bad rep. I am lucky in that regard as my hull was designed to MORC rule and has less rocker/overhang and a longer waterline relative to length than similar boats of the day.
Ok sorry, can't resist, gotta show some pictures of Olin Stephens's beautiful sculpture, as an example of a good old hull... If you click on the shot on the right, it will orient itself correctly.
__________________
DL
Pythagoras
1962 Columbia 29 MKI #37
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09-10-2024, 11:20
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#8
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Moderator
Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 21,181
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Re: Hull shape and performance
Welcome to CruisersForum!
I would suggest updating your profile with your general location and your boat make & model or “Looking” in the "Boat" category. This info shows up under your UserName in every post in the web view. Many questions are boat and/or location dependent and having these tidbits under your UserName saves answering those questions repeatedly. If you need help setting up your profile then click on this link: https://www.cruisersforum.com/forums...ml#post3308797
I would happily help more if the link above is not enough.
__________________
Num Me Vexo?
For all of your celestial navigation questions: https://navlist.net/
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
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10-10-2024, 03:46
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#9
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Registered User
Join Date: May 2013
Location: Portland, ME
Boat: McCurdy & Rhodes 56
Posts: 243
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Re: Hull shape and performance
This question requires a long detailed discussion of performance - or intended use - tradeoffs. If you are really interested in a good discussion on this, I'd suggest subscribing to morganscloud.com where there is an excellent discussion on this along with other outstanding content not found anywhere else.
That said, here are some brief thoughts. I'll use two photos to help illustrate stark performance differences.
In the photo, the boat on the right reflects the latest in Class 40 design, optimized to a box rule - how fast can you make a boat within size & weight parameters. The hull shape is basically a surfboard, with max beam carried all the way aft and a bulb keel to maximize righting moment and carry as much sail as possible for as long as possible. This design does not consider comfort but is extremely fast as she planes off the wind (20+ knots). Comfort with wind aft of the beam is OK, upwind is brutal. No ability to carry stores, water or fuel that most cruisers need. However, this hull shape would be quite safe in gale conditions as long as she was keeping the wind aft and the autopilot & crew robust. Upwind would be a different story with shock loads requiring careful engineering and build strength.
The vessel on the left reflects a design from the '70's with relatively long overhangs and rounded bilge sections. This hull form has almost no "form stability", meaning she gets little righting moment from the hull shape as she starts to heel. Stability comes primarily from the keel weight and so she will heel over further than more modern designs as she goes upwind, and she will also have more tendency to roll dead down wind or in cross-seas. So heading up and gybing may be a tactic with this hull shape. She is a displacement design so will not plane. Speed is limited to effective waterline length. Will her long aft overhang, this is considerably longer than the design waterline. However her speed will not be affected much by adding stores, water & fuel. Her hull shape also allows large water & fuel tanks offshore cruisers desire. She does not have much volume in her ends, so she can tend to pitch or hobby-horse more than modern designs with more volume in the ends. On the other hand her motion will be quite soft and comfortable (no pounding) in most conditions, especially if the boat is larger.
While I understand that "gentlemen don't sail upwind", I believe an offshore boat should have the ability to sail upwind away from a lee shore as an important safety factor. Generally, more draft means an ability to get upwind. A fin providing lift and less leeway will go upwind much faster than a full keel or partial cutaway keel. Most full keel boats end up motoring upwind, but if the fuel filter get clogged and the engine stops, you need a backup.
Most modern designs reflect coastal cruising so offer lots of volume for a give length, good form stability offering good performance at low heel angles. The sacrifice is small tanks, lower performance with stores loading. Most of the modern designs do quite well at anchor or the dock where most of the time is spent, with sacrifices offshore or longer term living aboard.
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10-10-2024, 04:29
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#10
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Registered User
Join Date: Sep 2024
Location: Eastham Massachusetts
Boat: Catalina 25 1983
Posts: 9
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Re: Hull shape and performance
I would much rather go for comfort and liveability and stability over speed.
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10-10-2024, 05:18
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#11
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Registered User
Join Date: May 2013
Location: Portland, ME
Boat: McCurdy & Rhodes 56
Posts: 243
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Re: Hull shape and performance
Another discussion on modern designs:
TLDR: They don't go upwind in a comfortable manner.
But hey, no one goes upwind anymore so no big deal.
Oh, and twin rudders are hard to dock.
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10-10-2024, 05:27
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#12
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Registered User
Join Date: Aug 2011
Location: Lower Chesapeake Bay Area
Boat: Bristol 27
Posts: 10,914
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Re: Hull shape and performance
Quote:
Originally Posted by Nauset
I would much rather go for comfort and liveability and stability over speed.
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I have an old school Bristol 27 that for it's size has a very seakindly motion.
Cole Brauer though, the 5'2" 100 lb. 29 year old woman that recently finished second in a single handed Round the World Race, sailed a Class 40 Yacht which has the new style flat bottom and plumb bow.
Her boat was hitting speeds as high as 14 - 15 knots. (or more)
I definitely do miss sailing/racing at those type speeds, but the old Bristol 27 I have does quite well when the wind and waves get up. It's just slow and does not point well.
It's about the same speed as a Catalina 25 but handles rough weather better.
Best speed I have hit on my old boat was about 7.8 knots in big wind and strong favorable tide.
Her Class 40 is a rocket ship as compared to the old designs.
There is tons of video of her sailing in lots of conditions on youtube. She had Starlink and was in constant contact with her team and the public.
She had tons of nice equipment also even a forward looking camera.
Short video offshore:
https://www.youtube.com/shorts/3_KqowOr8zA
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10-10-2024, 06:59
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#13
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Registered User
Join Date: Jun 2011
Location: Caribbean
Boat: Hylas 46
Posts: 646
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Re: Hull shape and performance
Quote:
Originally Posted by Mal Reynolds
That said, here are some brief thoughts. I'll use two photos to help illustrate stark performance differences.
Attachment 295094
Attachment 295093
In the photo, the boat on the right reflects the latest in Class 40 design, optimized to a box rule - how fast can you make a boat within size & weight parameters. The hull shape is basically a surfboard, with max beam carried all the way aft and a bulb keel to maximize righting moment and carry as much sail as possible for as long as possible. This design does not consider comfort but is extremely fast as she planes off the wind (20+ knots). Comfort with wind aft of the beam is OK, upwind is brutal. No ability to carry stores, water or fuel that most cruisers need. However, this hull shape would be quite safe in gale conditions as long as she was keeping the wind aft and the autopilot & crew robust. Upwind would be a different story with shock loads requiring careful engineering and build strength.
The vessel on the left reflects a design from the '70's with relatively long overhangs and rounded bilge sections. This hull form has almost no "form stability", meaning she gets little righting moment from the hull shape as she starts to heel. Stability comes primarily from the keel weight and so she will heel over further than more modern designs as she goes upwind, and she will also have more tendency to roll dead down wind or in cross-seas. So heading up and gybing may be a tactic with this hull shape. She is a displacement design so will not plane. Speed is limited to effective waterline length. Will her long aft overhang, this is considerably longer than the design waterline. However her speed will not be affected much by adding stores, water & fuel. Her hull shape also allows large water & fuel tanks offshore cruisers desire. She does not have much volume in her ends, so she can tend to pitch or hobby-horse more than modern designs with more volume in the ends. On the other hand her motion will be quite soft and comfortable (no pounding) in most conditions, especially if the boat is larger.
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You say the boat on the left, with the shallow keel and no bulb, "has almost no "form stability"" and "Stability comes primarily from the keel weight." You don't specify as clearly for the boat on the right, but imply that it is different. Where does the boat on the right, with the really deep keel with bulb on the end, get its stability? If it isn't from the "keel weight," then one would have to wonder why the extreme keel with bulb...
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10-10-2024, 07:02
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#14
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Registered User
Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft 381 Catalina
Posts: 6,804
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Re: Hull shape and performance
Quote:
Originally Posted by Lee Jerry
You say the boat on the left, with the shallow keel and no bulb, "has almost no "form stability"" and "Stability comes primarily from the keel weight." You don't specify as clearly for the boat on the right, but imply that it is different. Where does the boat on the right, with the really deep keel with bulb on the end, get its stability? If it isn't from the "keel weight," then one would have to wonder why the extreme keel with bulb...
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The deep bulb keel still provides a lot of stability. But the hull form on that class 40 will provide more form stability at low angles of heel than the boat on the left in the example. If you put the same keel on both (and made both boats weigh the same), the class 40 would be stiffer at low angles of heel, although there would likely not be such a big difference in ultimate stability (and the class 40 might be at a disadvantage there with low freeboard, low deckhouse, etc.).
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10-10-2024, 07:17
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#15
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Registered User
Join Date: Jun 2011
Location: Caribbean
Boat: Hylas 46
Posts: 646
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Re: Hull shape and performance
Quote:
Originally Posted by rslifkin
The deep bulb keel still provides a lot of stability. But the hull form on that class 40 will provide more form stability at low angles of heel than the boat on the left in the example. If you put the same keel on both (and made both boats weigh the same), the class 40 would be stiffer at low angles of heel, although there would likely not be such a big difference in ultimate stability (and the class 40 might be at a disadvantage there with low freeboard, low deckhouse, etc.).
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If both boats weighed the same, the boat on the left couldn't look like that. (It has a lot more displaced volume.) But that's not the point...
Let me re-phrase the question: How does a "shallow" keel with no bulb and the VCG (of the keel) near mid-height provide more stability that a deep keel with bulb and much lower VCG (of keel/bulb)?
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