benefit of long overhang

[Weyalan]

Originally Posted by Southern Star

Weyalan, thanks for the informative post on the older IOR designs. Was the problem downwind with the prismatic coefficient of the hulls (they typically had fairly significant beam amidships , but as you say, very pinched ends)? Certainly there are a large number of boats with narrow beam throughout that have very good control in following seas.

Brad

The problem downwind was essentially because the IOR measurement system was based on some girth measurements taken at very specific points, so that designers could make the boat a specific shape at those points to "fool" the rule into giving their boat the rating of a heavier boat. I cannot explain it very well, so I'll let respected designer Ted Brewer say it for me (N.B. bold text is my own emphasis):

Originally Posted by Ted Brewer

The International Offshore Rule was adopted in 1970 to prevent yachts from having to be remeasured under another rating rule every time they sailed off to race in a foreign country. The early IOR had its faults, of course, and the rule was modified many, many times over the years. Basically, the IOR tried to estimate the displacement of a yacht by measuring beam and depth amidships. The theory was that all sailboats have prismatic coefficients in the .54 to .56 range so, by estimating the midship area you can estimate the displacement. In a very short time, designers were coming up with weird shapes with chines and/or great tumblehome in order to fool the rule into thinking that the midships was bigger and the boat was heavier than its true displacement.

Also, under the IOR the measured length (a major factor, of course) was based on the distance between girth stations, measurements taken at the hull ends. It took two pages in the rule book and a mess of diagrams just to explain how to establish these girth stations, and the whole rule took almost 60 pages to cover the calculations, with some 60 diagrams to explain how and where to measure this and that. Again, designers took advantage of the rule, using extremely pinched ends in order to move the girth stations toward midships and shorten the rated waterline.

The early IOR yachts were rather strange looking to my eyes, as the boats were fairly beamy but the ends, both bow and stern, were very pinched and the deck plan wound up looking like the ace of diamonds. If you see a yacht with a transom that resembles the letter V, then she's probably an early IOR boat!

I hope that gives you a better idea.

It should be emphasised that the IOR rule did go through numerous changes to try to close these loopholes and to encourage more seaworthy designs. The 80's boats (such as my own) had significantly less pinched sterns than the 70's boats and were, presumably as a result, slightly less of a handful off the breeze. I'm guessing that the catastrophic '79 Fastnet Race was an agent for change in the direction of more stable / seaworthy boats.

[Southern Star]

Thanks Weyalan, Ted Brewer is always a good source of information concerning yacht design and especially from that time period. So it seems that the entire hull shape of the ealier IOR designs was compromised in order to 'bend' the rules, keeping virtually indentical volume fore and aft (through pinched ends) and yet a relatively large beam overall.

When one considers many true cruising designs from the same period, for example Valiant 40's, Crealocks and the like, the beam overall was modest in relative terms and, although many have canoe sterns, the boats nevertheless carried more volume aft of center: no doubt all of this contributes to stability in following seas.

It would also tend to confirm that rear overhang and narrower (or no) transoms, are not what caused the downwind/following sea stability problems of some IOR designs.

Brad

[Aquah0lic]

OK, I'm going to try and post some pics of different stern styles. What I am wondering is how they each affect the sailing/cruising experience. #1 is the V stern, #2 is the U stern, #3 is almost squared off l_l

#4 is a Bristol. Why not just have the transom in the water? On most sailboats, the WL ends a little fwd of the transom and on the Bristol its alot fwd. What is the purpose of this?

[Resolute_ZS]

Epic thread revival here, but I was thinking about this after the Annapolis Boat Show and looking at some of the new(er) designs compared to old.

Aquaholic, in the post before mine, hits the nail on the head of what I am trying to figure out. I figured I'd just resurrect an old thread instead of starting a new one for the same information. Can someone post an answer based on the above pictures?

[Dexterbase]

Originally Posted by sandy daugherty

A Shields emerging from the early morning fog, moving silently at five knots with no more wake than a white swan in a garden pond is a thing of such beauty that you just thank the passing skipper for the vision.

Poetry. Beautiful.

[zeehag]

1903 built---


was for racing speed--longer waterline when heeled over on a tack.

[sabray]

Great shot zee. Course if they added 2 more people they could also get a longer water line.
I sailed a Marblehead skiff way back and you could nt do squat up wind without dead weight in the bow. She sailed best with a extended/ heeled water line and weight forward. Course it always had extended water line. Can we say tender. That's why I now am less irritating then I once was. I learned some patience. Learned to swim. Learned that even that small skiff would kick my ass if I neglected the relationship. I could have near the best fun ever get screwed and spend hours bailing out.

[SkiprJohn]

Squared off sterns provide much more storage in a boat designed to carry a lot. A raised or v stern provides a bit more seakindly motion when the wind is aft. If you haven't read many design books there are probably a bunch of them in your local library. Each author will give you a little bit different reason for each of their hull modifications and would not be possible to cover all in a thread.
kind regards,

[zeehag]

Originally Posted by sabray

Great shot zee. Course if they added 2 more people they could also get a longer water line.
I sailed a Marblehead skiff way back and you could nt do squat up wind without dead weight in the bow. She sailed best with a extended/ heeled water line and weight forward. Course it always had extended water line. Can we say tender. That's why I now am less irritating then I once was. I learned some patience. Learned to swim. Learned that even that small skiff would kick my ass if I neglected the relationship. I could have near the best fun ever get screwed and spend hours bailing out.

with our family, we only needed one more for longer water line--but she is a 1903 gaff rigged sloop designed for racing with a full keel and sweet fast lines.
definitely not the cruising kind of boat. (i am the smartass forward of mast with white scarf..)

my formosa has a sweet heart shaped transom allowing for ease in sliding down seas--is spozed to make boat act some like a double-ender in seas.

[Nicholson58]

Originally Posted by Weyalan

The problem downwind was essentially because the IOR measurement system was based on some girth measurements taken at very specific points, so that designers could make the boat a specific shape at those points to "fool" the rule into giving their boat the rating of a heavier boat. I cannot explain it very well, so I'll let respected designer Ted Brewer say it for me (N.B. bold text is my own emphasis):

The early IOR yachts were rather strange looking to my eyes, as the boats were fairly beamy but the ends, both bow and stern, were very pinched and the deck plan wound up looking like the ace of diamonds. If you see a yacht with a transom that resembles the letter V, then she's probably an early IOR boat!

Like this. I raced in the 70's & 80's on a Morgen Heritage One Ton. Beam is well aft with long tear-drop hull, nipped in stern with IOR bumps on each cheak, V-stern. 37'-9" LOA; 15,000 disp, high aspect ratio. THe boat pointed better than almost all other boats and was really stable. Trapezoid fin keel and very large spade rudder. On a reach and run it pulled a huge stern wave. Smaller boats often jumped on our wave and surfed with us. She gained 2.5 feet of unmeasured water line sailing on her lines. Note the other IOR hulls in the ripping start photo.

We now sail an 83 Camper & Nicholson 58 ketch with 45 LWL. LOVE the overhangs. It is a great ride in nasty weather. The Heritage is still being successfully raced but we selected the Camper for comfprtable cruising.

[GTom]

Originally Posted by Nicholson58

We now sail an 83 Camper & Nicholson 58 ketch with 45 LWL. LOVE the overhangs. It is a great ride in nasty weather. The Heritage is still being successfully raced but we selected the Camper for comfortable cruising.

Sorry for reviving an old thread, I recently looked at a smaller sibling of your '58, the Nicholson 43. I've run the sailboat calculator for its parameters and getting wonderful stability values but not-so-convincing Pounds per Inch Immersion.

How much cargo can a boat with long overhang carry? I am thinking on longer passages, if the Nic43 could support e.g. 4 crew on a Transpac.

[Copacabana]

Originally Posted by GTom

Sorry for reviving an old thread, I recently looked at a smaller sibling of your '58, the Nicholson 43. I've run the sailboat calculator for its parameters and getting wonderful stability values but not-so-convincing Pounds per Inch Immersion.

How much cargo can a boat with long overhang carry? I am thinking on longer passages, if the Nic43 could support e.g. 4 crew on a Transpac.

Well, one thing about those old boats with long overhangs is when you load them up for extended cruising (all the carp!) the waterline gets longer! They have a lot of reserve buoyancy as the boat sinks a bit on its lines and more and more of the hull comes into contact with the water. My boat (a Swedish 70's cruising design made by Vindö, much like a Hallberg Rassy) had overhangs (modest by the standard of its day) and has settled down nicely with all the weight- giving me about 12 more inches of waterline! To sink it another inch would take a lot of weight now.


I imagine you're looking at the Nic 43 on the under 30K thread. Nice boat, but you're really buying a 30 something footer with pointy overhangs. It's something to consider when evaluating the price. The cabin is the size of a much smaller boat. Also, the storage in the overhangs can be used, but not for heavy gear, so its utility is somewhat limited.

[GTom]

That's correct, the aft overhang would be great for cabins, unfortunately the 43 is simply not big enough for that. I really like the design, but at the end of the day, one has to check what he really wants to pay for. Available space is certainly a factor for me, but also skeg-protected ruder, encapsulated lead keel, bolted hull-deck joint and of course $$$... Decisions, decisions...

[NormanMartin]

A couple of observations about overhang. We have an Aphrodite 101. It was not designed to any rating rule.

The overhang forward does help keep the foredeck dry-ish. This is something for a boat with very little freeboard. We seldom have spray aft of the mast. The spray image is two reef motor sailing into a two foot chop on Nantucket Sound on a windy day.

Many older designs, such as the gaffer picture above, benefit from increased form stability when heeled. In many cases the prismatic coefficient increases with heel. Both help increase speed.

Hull form is always an interesting discussion.

Norm

[Cheechako]

Overhangs make for storage and aesthetics. The waterline is a good comparison of boats though. A 32 with a 29 ft waterline is comparable with a 36 with a 29ft waterline.