Narrow Hull Sailing Yachts

[Karsten]

I was wandering why most shipyards are building wide hulls with heaps of freeboard? Clearly it is to maximise interior volume so you can squeeze in a few more passengers for charter operations. But what if you don’t want to play table tennis on the salon table but instead have a high performance boat that is easy to sail with a small crew and looks good?

A narrow boat would be fast at greater heeling angles and therefore the keel is more effective and lees people are needed on the rails to keep the boat upright. Also narrow boats should be lighter because less material is used for the hull. Because they are lighter and have less drag a smaller sail area is required to drive the boat. This in turn would be great for a smaller crew. Why are boats like this not build and designed more often?

I’m thinking about something that’s 12.5m long 2.75m wide with a 2.5m keel (Sydney Harbour is quite deep). The hull could be strip planked and the wood visible from the inside (safes also weight for the panelling). The whole boat should weigh about 3.5t and sail area would be approximately 60m2. I would also install some comfy accommodation so that weekend trips with my wife are possible. To race the boat in the very popular twilight races (they are sailed without spinnaker) you would only need a crew of 2 or 3 people to be competitive and it would also be great design to go sailing after work just with a friend.

What do you think about the idea? Any interest? I have started to bring something to paper to see what it would look like. Would be fun to sail circles around Sydney 38s and Farr 40s.

Karsten

[SailDesign]

A great deal of the "fat boat" syndrome will help to keep the boat upright. A boat that is twice as wide as yours will have 8 times the initial stability (yes, eight!). Obviously, at larger heel angles than 2 or 3 degrees, this will not be a big a multiplier.
A skinny hull will heel more (Steve Clark - paging Steve Clark ) when sailing, and because of the angle of the topsides forward when heeled, may well be wetter than a fat boat. Counter-intuitive, maybe, but think about it.
Steve

[MikeJohns]

You can have narrow boats that are very stiff and powerfull hulls (ability to carry canvas ) they are faster to windward in a seaway, and a darn site more comfortable, but the requirement is for a high ballast ratio, hence more displacement. The surfboards will allways outrun you and under our racing rating rules they outrate you.
Now if you were talking of a cruising yacht.............

[wafi]

The only advantage I see with a narrow boat is the angle of the waterline, which can be easier reduced to small angles than on a "fat" design. This will reduce the wave resistance. ..... BUT you need volume under water and so the shape of the boat will be much more curved in the aft than on a "fat" design. This will give you more resistance.
In the end, as written in the postings before, the narrow boat will have more deplacement, worst stability and ... as I believe more restistance under water than a "normal" design. With my 1/4 ton, 7.5m length and 3m width, I`m sailing circles arround narrow boats like H-boat or Folkeboat.

[jehardiman]

Karsten, also note that a large number of "wide" sailing hulls are actually "narrow" boats when sailing. Most of the "Open" class boats are designed to be sailed with a significant portion of the hull out of the water at a low angle of heel. An analysis of the immersed body will show that L/B ratios begin to approach 8 or 9 with the rest of the hull just being counterweight.

[dionysis]

Go for it Karsten. A narrow boat is initally very tender, so you need deep draft to pick up righting moment fast. Your ballast to displacement ratio needs to be half or more. You have to like sailing on your ear though.

One obvious way to go is a canting keel.

Just make sure your displacement to length is light - very light. You don't want to lose what you gain is less wetted surface, from a steep wave resistance hump.

Make sure your deck systems are ultra clean, and you have a very light mast. It is surprising how much righting moment you lose to mast self weight.

[Dutch Peter]

Originally Posted by Karsten

A narrow boat would be fast at greater heeling angles and therefore the keel is more effective and lees people are needed on the rails to keep the boat upright.

If your boat needs people on the rail to keep it upright, you should have an other look at it's stability curve. Life ballast can be a dangerous thing! You can't expect those people to stay there all the time! What happens then!