weight factor and speed-seaworthyness

[sailormanbigd]

Just got off on a tangent on my previous post so I will post another topic. Why would more weight be better for a full keel cruising sailboat? I was always under the impression that lighter is always better/faster and that reducing wetted surface is the key. My Morgan 33oi was sitting (or setting) below waterline when i got her. Full of water saoked wood and junk. I have removed half the engine, all wood, spare tranny(rusted junk) ac equipt etc,etc. Now she sits at least a foot to 18" above waterline. I am rebuilding her soon and am always thinking about reducing weight on the rebuild.
There is this couple up north that are refitting their m33oi for an exstensive cruise 5 years or more and spent $100k on her so far. He states that he has info from Charlie Morgan that the "problem" with the 33oi is weight, and has added weight to her going from approx 14k lbs to 20k lbs. How can this help the performance . It must sit much lower in the water-probably adding to stability and depending on placement of weight/ballast righting ability, but she must have slowed down considerably? what are the experts thoughts on this? Even empty my boat barely moves when i step aboard.

 

[Benny]

It depends on the sailing waters. In a calm lake a boat with less wetted surface and reduced drag will accelerate better and have increased top speed than one with more wetted surface, all other conditions being the same. Out in the ocean things change and weight becomes perhaps more significant than drag. A light boat plowing against waves will find its speed reduced more than a heavier boat that can carry more momemtum through them. In a long voyage these small differences in lost boat speed can translate into hours of advantage for the heavier boat thus rendering a higher average speed. There is also comfort to be considered and in this area some boats will have better sea motion when they are weighted down. I guess performance is not just defined by speed.

 

[Stu Jackson]

You might want to read a full book or two

on the subject, like "Desirable and Undesirable Characteristics of Ocean Going Vessels", etc. Many more out there that include this discussion of weight, stability, length to beam, and all the characteristics that say, for instance, Ted Brewer uses in his comparisons of boats in Good Old Boat magazine.

 

[sailormanbigd]

thanks Benny, you have made the issue come to light in easy to understand terms-i get it now. I guess everything is a trade-off in boat design. I think I will go with strength and not be too concerned with weight when I rebuild. I was just at the boat and had a good thundersquall blow in. The boat strted to rock from the wind, i was in a protected canal so there were no waves. The motion was a bit surprising and uneasy at first-i was down below checking for "rain" leaks and found some. So I will go with the weight, of course the boat is completely empty, no water, and no fuel (I hope). For me i want a tough seaworthy boat with less motion. It was literally bobbing from side to side from the wind. No bimini, no sails on top, etc. Thanks. Patrick

 

[tsmwebb]

... Out in the ocean things change and weight becomes perhaps more significant than drag. A light boat plowing against waves will find its speed reduced more than a heavier boat that can carry more momemtum through them. In a long voyage these small differences in lost boat speed can translate into hours of advantage for the heavier boat thus rendering a higher average speed.

Hmmm... I take it you are arguing that on average heavier boats will be faster than light offshore. That goes against my experience both racing and cruising offshore. It is true that small differences in speed add up over time... It just turns out that this works against heavy boats much, much more often than not offhsore and near shore. Anyway, underweight voyaging boats are so rare (are there any?) that I don't think the OP needs to worry about that. Any weight saved in re-fitting will be used up in provisioning.

--Tom.

 

[Franklin]

I totally agree....the heavier plowing through theory doesn't add up in real world. Case in point, Regatta De Amigos with steep waves ranging from 10' to 14' for the first couple of days and then dropping to about 8' with the course a beat into them, the light racer boats did soooo much better. Take the J105 that blew my doors off which has about the same waterline as mine but much lighter.

I do agree that the more weight, the less motion it's going to have and that can be a blessing, but I think mainly the more weight is a result of a stronger built boat that most want to have when the nearest land is 2,000 miles away.

 

[tsmwebb]

... I think mainly the more weight is a result of a stronger built boat that most want to have when the nearest land is 2,000 miles away.

Just a quibble but weight <> strength. Light, strong and inexpensive are all desirable but you can only have two of them in the same structure.

--Tom.

 

[Franklin]

Just a quibble but weight <> strength. Light, strong and inexpensive are all desirable but you can only have two of them in the same structure.

--Tom.

true...but old habbits die hard and that's the way it used to be. Modern materials has changed the game but not everybody changes with it.

 

[Franklin]

My mistake....it was a J109, but still, it was 100 miles ahead of me after 2 days. The only boats in front of it was a J44 and a multihull (3) Farrier 35c, both very light racing boats. All kinds of boats behind like Catalina 470, Benny 42, Tanaya 37, and so on...Production boats and Bluewater boats and so on with much larger waterlines.

 

[Ross]

Depending on how the weight is distributed two boats of equal weight, length and beam can have very different sail carrying abilities. As they were discussing in the fuel tank thread weight can be useful or not depending upon where it is located.

 

[Don12364]

Default Re: weight factor and speed-seaworthiness

Uffa Fox, famous sailor and yacht designer of a few decades ago said "Weight is only useful in a steam roller".
Apart from the obvious, the designer of your boat had a displacement in mind to provide stability, easy motion at sea and achieve the intended waterline length to give the intended boat speed.
It could be that lighter is slower and more uncomfortable in your case.
On the other hand its like your waistline - to much is TOO MUCH.