deeper forefoot

dart dinghy

http://community.webshots.com/album/275766007BzDenS

 

Cool - it looks very weird, though, but I can see why something like that might work.

Thanks,

Andre

 

Sorry I am coming to this thread a bit late, another reason I believe that cruising boats should have some immersed forefoot is they tend to carry more weight in the bow (extra anchors, chain, windlass etc). This should be supported by extra underwater volume to stop excessive pitching and plunging (this also effects windward ability).

 

I really do think this is a nifty idea if designed properly.

A little thing though, assuming the forefoot acted as a keel, wouldn't the boat turn around that? (Edit: as when you're in a harbour, and instead of swinging around the keel/CB/fin, it will act as if it's longer, and it wil be hard to get the stem to "work" as in a normal boat?)

Also, I wonder if the forefoot is exaggerated, how will that affect "sailing" at anchor? Wouldn't a boat have a higher tendency of that, all things being equal?

 

Bhnautika:
Are you saying that the pitching and plunging effects the windward ability. So, a wave piercing (vs wave riding) bow is preferable for pointing to windward?

Danish Bagger:
As the center of lateral plane is move forward, I belive it will change the way the boat handles. The piviot point in a turn would move forward some. I believe the piviot of yawl motion is determined by center of buoyancy and center of lateral resitance. But I don't see this as a problem. Do you see a real problem in the way it would sail?

What do you mean regarding getting the stem to work as in a normal boat. What else are you looking for the stem to do besides break the waves and provide buoyancy?

 

Mcollins07 Yes pitching reduces speed, along with other things. Wave piecing bows are about shapes to pass through waves to flatten out the bumps but as wave-piecing hulls usually have a deep forefoot, it’s still about the distribution of volume to reduce pitching. Weight in the bows increases the longitudinal radius of gyration making the pitch period longer and deeper the extra volume both below and above the waterline helps to dampen the motions.

 

Not, not really, just thinking that the boat would need to have a much better balanced rudder, to make sure it wouldn't be hell controlling the stern in hard weather.

I just meant that in harbour manouvres, it would be seem harder, or at least demand another technique to get the bows pivot closer to the dock. Not a real problem, I guess, just another technique one would have to use. At least I would think one would have to use another technique.

 

Sketch of idea

Here is the direction I was thinking. Taking the line of thought of a cruising vessel, using the hull as much as possible to gain lateral plane.

From FreeShip, the longitudinal center of effort ( I believe is the Longitudinal center of lateral plane) Lcp = 39% from bow. This may make it difficult to place the sail plan's center of effort that far forward?

 

Broaching?

Just re-reading John Shuttleworths article on multihulls. http://www.john-shuttleworth.com/Articles/NESTalk.html
He suggested that too much forefoot might result in broaching.
So, is broaching in a following sea another reason to limit the forefoot in a monohull? How can a design counter this tendency to broach?

 

Mcollins07 as john shuttleworth comments the u shaped section help to prevent broaching in multihulls, the same could be said for mono’s. The volume this shape gives to the bow reduces the need for an excessive fore foot, the extra buoyancy enabling the bow to lift and reduce the tendance, like some of the deeper vee sections, to dig in .

 

Just reading Chris White's, the cruising multihull. In regard to the main hull of the trimaran, .... A very deep and narrow forefoot is nice beating to windward in a chop, but can make steering less sure when surfing downwind at speed. The shallow, wider forebody hull is great for surfing but tends to hobbyhorse when sailing to windward in sloppy waves.

Thanks for everyone's input.

 

I didn’t know about this interesting thread, thanks for resurrecting it! It may not have been there when the thread started but I found the coble in Wikipedia at http://en.wikipedia.org/wiki/Coble

I put an experimental sailing rig on my kayak which has very little resistance to leeway, mostly at the stem. The leeboard was mounted off the foredeck, so the center of lateral area was well forward. Apart from a tendency to fall off the wind before it got under way, because the sail was well forward of the CoG, it sailed and balanced OK for such a tiny sail area. However the low speed and long distance between rudder and forefoot made it slow to turn. Downwind it required constant correction to keep it on course. That kayak is hard work to keep straight when surfing downwind under paddle power.

All of which makes it difficult to understand the advantage of the coble in surf.

 

Many Dutch boats have exaggerated forefoots

(forefeet?) These boats have almost no lateral plane except for the forefoot, rudder and leeboards. The forefoot helps the boat hold her head up going to windward.

 

The Herrishoff cruiser rule of thumb was the draft should be 1/7 of the LWL, and the boat would point well.

FF