Displacement and Vanishing Stability

[Tom Spohn]

Here is a site that has many of the calculations for 2000+ boats:
http://www.image-ination.com/sailcalc.html It also has an explanation for each of the ratios. Compare my Schock 35 with and Island Packet 35 for example, and even though they are both the same length, beam, etc. it is clear which one I want to race in Puget Sound and which one I would choose to sail in the Pacific to Mexico in.

[dcstrng]

Originally Posted by svHyLyte

There is an excellant article in this months edition of Good Old Boat written by Ted Brewer on this subject.... s/v HyLyte

Yep, that’s a great article from a designer with nearly impeccable credentials – although, I’d guess his commentary on some of the more avant-garde ware won’t please all…

[Cheechako]

It's like a lot of things, you really have to decide for yourself. There are good points for super heavy construction no doubt. I've had a few ( Hans Christian 38, Passport 47, Seawind 31) and sailed on and with a few Westsails of friends along the way. The Hans was a wonderful boat, but nearly impossible to go to weather in in a chop ...even motorsailing. One of my early boats was a Rawson 30. A full keel Garden design built up here in the NW for years. It was touted in the community as being a tough boat. I discovered when I outfitted mine that the hull was actually very thin. About 5/16 to maybe 3/8 max thick 2-3 ft from the keel. I sailed that boat down the west coast to mexico. I rarely got water in the cockpit. What a sweet little boat. It was properly built by a fishing boat builder who knew the sea. It didnt shudder and shake etc. Extremely light is probably bad and extremely heavy is probably bad also. Displacement is Displacement, it can either go into the stuff the boat is carrying or into the boat construction. At the end of the day a given hull shape with a given loaded weight will have a specific wetted area. My thinking has changed over the years for sure. They dont build airplanes with thick skins, they build them with thin skins and good supporting structure. But they are expensive!

[Cheechako]

wow! that is a great site! Compare Hans C 38 with an Island Packet 38 and you will see what I'm talking about. Very similar specs, but the IP is 6000 lbs lighter. That's 3 tons of liveaboard gear!
LWLIsland Packet 38 33.02Hans Christian 38 33BeamIsland Packet 38 12.73Hans Christian 38 12.25DisplacementIsland Packet 38 21532Hans Christian 38 27500

[Amgine]

If you purchase a relatively light boat and load it down with full liveaboard gear, extra luxuries and people, etc, sinking that designed waterline several inches, your boat will be much stiffer.

At first this seems great; you don't need to reef as early, the boat sails with less heel, everything is just more comfy... but you've increased the net forces on everything. So your rigging and fittings may now be somewhat undersized since it was spec'ed for a lower displacement, the cycles are higher load. You may end up breaking gear more often, and extreme weather is more dangerous to your boat even though the increased sea-kindliness of the boat makes that weather seem less scary to you so you're more likely to try to tough through it.

For this reason it's better to select a boat which is designed to suit the amount of gear you really plan on dragging around with you. Heavy displacement cruisers may cost more (though maybe not if you price them by the pound), but it's because they need different weight of rigging to do a different job.

[Weyalan]

My partner & I cruise a 40' monohull that weighs well under 20,000 pounds even with full tanks, fully laden with everything that we (don't) need. I would take that boat anywhere. One can get too focussed on trying to find the perfect boat when the perfect boat is, in fact, whatever boat you have.