Heavy vs Light Displacement

[Cheechako]

Yea, I have gone over to the "light is right" camp over the years, (at least intellectually) the hard part is finding a lighter boat that you can have confidence in without breaking the bank..I dislike that "wallowing" a lot!

[sailorboy1]

I think we are getting displacement and weight confused. Weight is weight and has to do with a material density and it's strength as to use. Displacement is more about shape were the boat needs to displace more than it's total weight. And the dimensions for a cruiser are about living space and storage. There is nothing that says that a carbon fiber boat using the same dimensions is going to displace much less than a fiberglass one. Yes it is going to be a little less due to the overall weight of the hull, but probably not all that much. Then you would have to go back and adjust the sails/ballast etc to get the boat ride back to want you wanted. The reason carbon boats can weigh less is because it is stronger and can use less material so a thin hull can displace a lot and carry the needed extra ballast for it's sails before it breaks in half. But is this what a cruiser wants?

[sneuman]

Originally Posted by Paul L

Maybe so, but the the 'minimum amount of sail' on the medium weight modern design offshore boat is going to be a lot less sail than what is required for the heavy weight classic cruiser. Less sail is much more manageable by a small Mom and Pop crew. In addition, that classic is probably going to be wallowing or motoring in the light air while the modern boat is sailing along at 3 or 4 kts.

Paul L

True in many cases, but some heavy boats (such as my Tayana 37) still have generous SA/D (T37 = 17.3) ratios and/or easily driven hull shapes that therefore allow them to do acceptably well in light air.

I believe in planning for the worst, and while I realize that the majority of time offshore (at least along the Milk Run) is going to be spent in moderate-to-light air, I would rather take a knock on the lower side to gain more control and comfort on the other end of the scale: one extreme is inconvenient, the other could be life-threatening.

[andreavanduyn]

Look at design of modern lightweight cruising yachts in infusion method = straight sides and nose and wide with sexy stern meaning inside a lot of space /with

Now imagine the hull not flat for planing / racing but more cruising oriented

Still will make the boat fast and easy to handle with lots of space perhaps not below the waterline as much as the good oldies but certainly in locker space in cockpit area and such

Main point I learned from sailing carbon and infused lightweights is the sailing pleasureis back and the wife loves her galley and participation as all forces are minimal (mine even steers her into the docks)

[Joli]

You mean like our big old heavy cruiser working it's way upwind? Picture included.

Look, if you design a light hull with a high ballast to displacement keel you will most likely have a canoe body with U shaped sections. When working the boat upwind you must fall on the turn of the bilge or you will shake the boat pretty good or worse yet break the boat. I was told by our marina a race boat coming back from charter was driven to death by motoring it into 6 -8 footers. (ie total delam and busted ring frames). In other words the light easily driven carbon hull is now trash because it did not "fall" on the turn of the bilge but "fell" on the flat U section.

I love racing light high performance race boats but they are not boats I want to cruise on.

But you are right, pushing a heavy cruiser is more work then pushing a light race boat.

Originally Posted by Paul L

Maybe so, but the the 'minimum amount of sail' on the medium weight modern design offshore boat is going to be a lot less sail than what is required for the heavy weight classic cruiser. Less sail is much more manageable by a small Mom and Pop crew. In addition, that classic is probably going to be wallowing or motoring in the light air while the modern boat is sailing along at 3 or 4 kts.

Paul L

[andreavanduyn]

what boat is that measurement taken on Paul?
yours?

[Paul L]

Originally Posted by sneuman

True in many cases, but some heavy boats (such as my Tayana 37) still have generous SA/D (T37 = 17.3) ratios and/or easily driven hull shapes that therefore allow them to do acceptably well in light air.

I believe in planning for the worst, and while I realize that the majority of time offshore (at least along the Milk Run) is going to be spent in moderate-to-light air, I would rather take a knock on the lower side to gain more control and comfort on the other end of the scale: one extreme is inconvenient, the other could be life-threatening.

A Tayana 37 certainly can carry a fair more sail than a lot of the classic crowd. I suspect that is one of the reasons it is such popular cruising boat -- it can be sailed. It will be pushing 7 or 8,000 more pounds that than a newer design 37 footer. But so what. It's a nice, sailable cruising boat. I think when you get closer to the extreme ends of displacement is where you end up with boats that are not well suited to the typical cruiser. Add another 5-10,000 lbs and reduce the sail size on your Tayana and you'd have a pig. Go for an ultimate 7,000 lb carbon fiber sled with double the sail area, and you'd have something that is just out of the league of most cruisers to be able to manage or control. I sail a J/37 at 13,500 lbs and do not consider it a light weight boat. It is medium in its dimensions and displacements. Sails well and is easily controllable by a Mom & Pop crew. Turns out it displaces just about the same as my old Alberg 35, who many people look at and think it is classic design and much more 'offshore' capable.

Paul L

[Paul L]

Originally Posted by Joli

You mean like our big old heavy cruiser working it's way upwind? Picture included.

Look, if you design a light hull with a high ballast to displacement keel you will most likely have a canoe body with U shaped sections. When working the boat upwind you must fall on the turn of the bilge or you will shake the boat pretty good or worse yet break the boat. I was told by our marina a race boat coming back from charter was driven to death by motoring it into 6 -8 footers. (ie total delam and busted ring frames). In other words the light easily driven carbon hull is now trash because it did not "fall" on the turn of the bilge but "fell" on the flat U section.

I love racing light high performance race boats but they are not boats I want to cruise on.

But you are right, pushing a heavy cruiser is more work then pushing a light race boat.

Joli,
Have you ever compared those numbers on the B&G with the polars for your boat I wonder how 9+kts in 10kts of air compares.


Paul L

[sneuman]

Like Joli, I race too. I can appreciate a fast, lightweight boat. But (again, like Joli), racing and cruising are distinct and, to me, they require two substantially different kinds of boats.

[Joli]

Actually, the number shown is pretty accurate and is verified by GPS. 10 tws plus 9 bs is almost 20 over the deck.

Originally Posted by Paul L

Joli,
Have you ever compared those numbers on the B&G with the polars for your boat I wonder how 9+kts in 10kts of air compares.


Paul L

[Paul L]

Originally Posted by Joli

Actually, the number shown is pretty accurate and is verified by GPS. 10 tws plus 9 bs is almost 20 over the deck.

I don't know what your boat is. I assume it is a pretty long to get those numbers. My point was what you are showing 9+ kts in 10kts of true wind is probably a lot more than the polars for your boat would indicate, i.e. not a normal occurrence. Throw on enough sail, have enough water line and any boat can be made to reasonably fast. It's just a lot of work.

Paul L

[barnakiel]

What does the choice of material has to do with the design's displacement???

Impossible to build a Westsnail in carbon?

b.

[roger.waite]

FWIW, IMHO, etc

We need to recognise the demands of different types of cruising, and preferences.

For sprints between cruising grounds with sheltered anchorages, my lightweight works very well. While I am anchored to a workplace, I am happy to keep it. But it is not my preference for 7-27 day passages, in whatever the weather gods bring.

The boat might do it, but I would not. ;-)

Most people avoid designs with low length-weight ratios. But sailing boats, including cruisers, have lightened up considerably over the years. Boats that were considered light are now mediums. Light cruising skiffs are out there, and they don't break up unless trashed, crashed or poorly built. We know our boats and sail within our limits.

[Bloodhound]

To my mind, heavy displacement = comfortable and sea-firiendly, albeit slower than a racer in light air. Light displacement = faster in light air with less sail but very uncomfortable for anything longer than a few hours. In heavy air, equal LWL will have equal speed but heavy = comfortable. I like comfortable.

[roger.waite]

Nice summary Bloodhound.

If you go light, you might prefer shorter passages, lighter winds, better weather windows (esp. going to windward), and accessible secondary ports. In many places, and for most really long distance cruisers, that combination will not work very well.

Like your 'I like comfortable'. Sailors cave in well before well built boats!