Centerboard Keels in Blue Water Vessels

[barnakiel]

I think IMOCA have up to three moving blades (now the new ones have 5 blades).


The center one is moving (side to side), the off center ones are daggerboard (up-down) style.


If they run in trouble, it is mainly when hitting stuff hard. But this is easy when going 20 knots night and day.


All OVNI boats have lifting keels too. These have sailed everywhere, including the Antarctic.


So this is my input. A centerboard as good as anything, just use it when there is a reason to have it (e.g. cruising shallow waters).


b.

[Manateeman]

Would I build a centerboard or lift keel boat for strenuous offshore sailing. No.
I like the French aluminum production boats. I like traditional wooden catboats.
Now I’ll tell you after building boats for 60 years I went with aluminum twin keels. Pure traditional centerboard boats do rely on form as they derived from fishing vessels which worked in shallow areas or great tides. The boards were relatively light and simple to repair as the boats were small. The advantages of centerline ballast placed low in the boat, evolved first into deep keel wood boats then gradually to fin keels with a lot of lead.
All the while, designers sought to please both markets. Go fast offshore, get skinny inshore. Centerboards gained weight, required more hull supporting structure and more powerful systems to lift what once was wood, now was ballast. There are a lot of wonderful centerboard / lift keel designs. The more weight which can be lowered, the stronger the internal support and the lifting mechanism must be. Internal support is weight above the waterline. Lift the keel and the stability curves move a lot. Failure to lift places the vessel in a potentially difficult position as it’s now full time deep draft. Stuck up and it’s tender because it’s form is not that of a catboat.
Twin keels are not perfect but neither is the centerboard nor the fin keel.
It has the advantage of let’s say half the draft and can self support on a sand bar. The weight remains low, not fin keel low. There are advantages in tracking in large seas. The interior remains open. There is no mechanism to fail. The disadvantage is a substantial increase in construction costs. For a commercial artic expedition vessel, initial costs are important and risks are balanced against these costs. In production boats, simple flat hull panels and centerboards are significantly less costly to build than foil twin keels.
Twin keels have a number of advantages and two significant issue which is why they are not as common in aluminum yachts. First, the keels are mirror images like your hands...a lot of care needed in the design and construction. Lastly, the cost of construction. As with all vessels, there is no perfect design, material nor method of construction.
Happy trails to you.
Mark and his happy manatees