Length/seaworthiness

[BMP]

If I have an SOR for a cruising sailing vessel with a beam of ten feet or less (to fit on a trailer without major oversize requirements) and length from 30-60ft the goal being the most seaworthy vessel possible is a length of 30ft (3:1) or 60ft(6:1) better?

What would make you choose one or the other?

 

[HelmutSheina]

Your scenario is flawed because 30' is really pushing it for a trailer sailer, and 60' would need a huge road rig and waterside set up time, crane for the mast etc etc.

How about doing some reading? This bloke wrote several excellent books around sailing boats. Worth having your own copies if boats are a passion.
Seaworthiness : the forgotten factor : Marchaj, C. A. (Czesław Antony), 1918- : Free Download, Borrow, and Streaming : Internet Archive https://archive.org/details/seaworthinessfor0000marc_e3y2/mode/1up

 

[BMP]

True.
Great book btw (have it).
But the question is (once it is at the water) which would be more seaworthy or would it matter at all.
Would you rather cross an ocean in a (properly designed and built) 10'x 30' or 10'x 60' boat?
Would the 10x60 have a tendency to roll more than the 10x30 or less?
I've been told (by proa advocates) that the #1 dimension that determines seaworthiness is length.

 

[HelmutSheina]

Under your conditions, the longer boat should be more seaworthy. However keeping 60'x10' fairly upright under sail will require some consideration from both designer and crew.

 

[montero]

Yes. my best seaworthy idea is to go underwater.
What do the experts say?

 

[portacruise]

The longer one might be better if there is some way to keep the wind, waves, and current from hitting broadside? Will there be an amas or very deep keel to help with roll vulnerability?

I have had the same ideas as Montero, underwater might be the safest in the most severe weather, but it also introduces complexity and other possible hazards.

 

[gonzo]

Seaworthiness is the result of all the parts of the design. Length alone is not a dominant factor. 10 feet is a beam that can make for a roomy boat. Doubling the length, with all other dimensions the same, will double the stability. Seaworthy in itself is not a defined quantity. You need to first define the aspects that fulfill what seaworthiness means. I have cruised small boats in storms and survived. Others abandon boats and ask for rescue, largely due to the discomfort and misery of surviving bad weather. The weather conditions and area of operation also define seaworthiness to a large extent. Start a Statement of Requirements (SOR). This will drive the design. There are two main categories. First are the constraints, they are hard restrictions that can't be changed. For example, the 10 foot beam. The requirements are functions that need to be met. For example, able to sail to weather in a storm in the open ocean. The way requirements are met can be changed or modified within the constraints.

 

[Rumars]

Under your conditions, the longer boat should be more seaworthy. However keeping 60'x10' fairly upright under sail will require some consideration from both designer and crew.

Fortunately we do know how a 60'x10' boat sails, R. Perry has designed Francis Lee and if BMP's clients are also in the PNW they can go to Seattle and beg a ride.
Another boat that's of similar proportions is J. Spencer's Infidel (now Ragtime), slightly wider at 11ft wide.
We also know how the other end of the spectrum behaves, there are Hobie 33's still around.
The middle ground would be a 40'x10'ft boat, wich is probably the upper size of what can be made trailarable instead of transportable.

Final dimensions are going the be up to the client's other criteria like for example what they imagine under "trailarable" "Seaworhiness" isn't a problem, they will all cross oceans safely and handle more weather then the average sailor can handle.
The "will it roll more" highly depends on the underwater hull shape and ballast placement. You can always incorporate water ballast, that will keep the boat behaved but require more active management from the crew.

 

[Dolfiman]

For such issue, I first look at the mast height (/ waterline) versus the beam, and when this ratio is over 5, it acts like a warning for me, I dont want to be catch in a severe gale with a higher mast. So the question is : can we design a good 60 ft length / 10 ft beam with a mast height limited to 50 ft (meaning a priori an ULDB / sloop version) or with a ketch saiplan.

 

[Dolfiman]

A good illustration of my choice for this approach : the Swede 55, the masterpiece of Knud Reimers (in my opinion). Easy to sail and faster than a 30ft, seaworthy enough for an ocean crossing.
Swede 55 Boat Data https://swedesail.de/en/swede-55-boat-data/
Swede 55 Introduction https://swedesail.de/en/square-metre-boat-cruising-variant-swede-55-introduction/

 

[BMP]

Thanks so much.
Those are some beautiful boats!

 

[bajansailor]

Rumars beat me to it with his suggestion of Bob Perry's Francis Lee - if you want to eat up the miles to windward very comfortably, she would be a far better bet than a 30' x 10' yacht.
You just have to be prepared for much increased marina / mooring fees and maintenance costs.
Here is some info about Francis Lee
Robert H. Perry FRANCIS LEE - Classic Sailboats https://classicsailboats.org/robert-h-perry-francis-lee/

And there are many posts on Bob's Facebook page about her (him?).
https://www.facebook.com/groups/187149054996410

 

[skaraborgcraft]

If someone else is paying for berthing, I would prefer long over short.

holgerDanskeSoundings_Sail.jpg

 

[skaraborgcraft]

MacGregor 65.

MACGREGOR 65 - sailboatdata

 

[BMP]

Great examples.
Are there any similar boats with full keels or center boards for shallow draft?
Skerry cruisers are another set of stunning designs.