27' cat with 20' beam

[rob67]

Hi
Can anyone tell me whether this is a good design for a catamaran. Its being sold through www.harrisellis.com. the boat I am referring to is the
27' Dandee 8M Catamaran. It is 27' long and has a beam of 20'.

Just want to know about sail ability from sailors that have multihulls
ie handling in different weather conditions, mast and sail size

I have been on the boat and have seen it come in for docking not very maneuverable, it just looks very awkward to handle being that it is almost square.

not interested in how hard or expensive dockage fees would be
Not interested in buying

Thanks for the input
Rob

[Cheechako]

sounds to me like it will sail well upside down! The wider and shorter things get , the easier they turn over.... even in cars. I forget what that ratio is called in engineering terms.... Think of it this way... how stable would a skateboard be if it was 1 ft long and 1 ft wide?

[44'cruisingcat]

Originally Posted by Cheechako

sounds to me like it will sail well upside down! The wider and shorter things get , the easier they turn over.... even in cars. I forget what that ratio is called in engineering terms.... Think of it this way... how stable would a skateboard be if it was 1 ft long and 1 ft wide?

No, not really. A skateboard the same length as a "normal" skateboard, but much wider, will be just as hard to turn over end for end, but harder to turn over sideways.

As long as this cat has a rig/sails appropriate to it's length, it will in fact be more stable than if it was narrower.

[Cheechako]

Originally Posted by 44'cruisingcat

No, not really. A skateboard the same length as a "normal" skateboard, but much wider, will be just as hard to turn over end for end, but harder to turn over sideways.

As long as this cat has a rig/sails appropriate to it's length, it will in fact be more stable than if it was narrower.

I'm talking about directional stability.. not resistance to "rolling" if that makes sense. On a cat, maybe think of resistance to digging a front ama in and pitchpoling... in speedboats.. if they are too short per width they "skate" around and are hard to control. Another example is the Flying wing... the B2 has computers to keep it under control... without those it would likely be a boomerang!


“Directional stability is stability of a moving body or vehicle about an axis which is perpendicular to its direction of motion. Stability of a vehicle concerns itself with the tendency of a vehicle to return to its original direction in relation to the oncoming medium (water, air, road surface, etc.) when disturbed (rotated) away from that original direction. If a vehicle is directionally stable, a restoring moment is produced which is in a direction opposite to the rotational disturbance. This "pushes" the vehicle (in rotation) so as to return it to the original orientation, thus tending to keep the vehicle oriented in the original direction.
Directional stability is frequently called "weather vaning" because a directionally stable vehicle free to rotate about its center of mass is similar to a weather vane rotating about its (vertical) pivot.”
Think of it this way: What if the weathervane was as wide as it was long?
“With the exception of spacecraft, vehicles generally have a recognisable front and rear and are designed so that the front points more or less in the direction of motion. Without this stability, they may tumble end over end, spin or orient themselves at a high angle of attack, even broadside on to the direction of motion. At high angles of attack, dragforces may become excessive, the vehicle may be impossible to control, or may even experience structural failure. In general, land, sea, air and underwater vehicles are designed to have a natural tendency to point in the direction of motion.”

[44'cruisingcat]

Hmm, don't know if that really applies though. The hulls of this boat would still be long and narrow, with a rudder at the stern - so a very directionally stable shape.


Certainly if it were a mono at 27 x 20 (and similar waterline dimensions) it would be pretty hard to keep in a straight line, but the hulls on this cat are likely to be more like 10:1, LWL:BWL.


I mean, if it were a tri at 27 x 20, would anyone even be asking the question?


The real risk, when people make cats wide like this, is that they then fit much bigger rigs to them, and end up pitchpoling.

[blighhigh]

Seems as though you would be getting a square deal

[SearenitySail]

It is a Shuttleworth design. I would imagine if the builder didn't take liberties with the design it might have some merit.

I would research Shuttleworth designs, though, or even contact them.

[paxfish]

I've only got maybe 6 hour on the helm thus far, but our 28' by 20' seems to handle great upwind and reaching:

[Cadence]

My concern would be pitchpoling not docking. Sliding down a following sea and taking green water over hull bow, ama is for tris, might be a disaster.

[thinwater]

I've sailed performance cats with that ratio.

a. Keep the weight down and the bows will rise. This is NOT a boat where you fill the storage. No weight forward, no big anchors, no chain.

b. With hulls that fine it doesn't take a lot of sail to drive it. Reef before you have enough sail up to go end-over.

c. This is NOT an ocean boat. Shuttleworth will tell you that. It is a coastal/lake boat that will go over 2x any monohull the same size. It won't be out in big waves, because the ride would be awful.

d. Maneuvering was probably a skipper-factor. I've parked and own several 1-engine cats. The beam doesn't really figure in. Dagger boards and deep rudders will spin it.

----

Not every design needs to be for high latitudes. This is a good-fast have-fun boat. I would have liked it when I was younger, now not so much.

[valhalla360]

They need to share the mast height to get a real idea but
- if they put a mast of similar height to a typical 27' length cat (around 14' beam) it will be no more likely to pitchpole and less likely to capsize but it won't a better performer assuming all else is equal.
- if they put a mast of a similar height to a 20' beam cat (maybe 40' long) it will be more likely to pitchpole than a narrow beam 27' long cat.

The other issue is bridge deck clearance. The wider the beam the more clearance you need. Now if the whole boat is scaled up, you can get more clearance with little downside. On a smaller boat a wider beam quickly becomes a problem when taken to an extreme. Either you give up clearance, the boat becomes disproporionately tall or your bridge deck accomodations become very low or non-existent.

Judging by the pictures, there appears to be only around 1.0 to 1.5' of clearance and they gave up on bridge deck accomodations, so a double wammy.

Finally directional stability could be an issue though I've not heard the complaint from anyone. The downwind hull will be depressed further and have more drag than the upwind hull. That creates a moment on the boat trying to turn it downwind. The wider the beam the longer the turning arm. Racing multi's have been known to cartwheel from this effect but it's typically not until they start flying a hull and are really pushing hard. Typically bigger beams come with longer hulls which are harder to turn. I doubt it would be a concern her unless you try flying a hull and maybe not even then.

[Divevac]

I know and have examined this boat as it hails from my home club/town. It is not particularly pretty or well laid out as it was designed to be built in Taiwan and shipped worldwide in a 40' sea container.
As a Stiletto sailor (23\27), I agree that pitch pole is a major concern as is maneuverability. The wider the beam, the more the outside hull has to be dragged through the radius of a tack. I cannot imagine it is a stellar upwind boat.
Can't speak to value as I haven't checked out Harris-Ellis. As far as I know this prototype Dandee cat was the only one ever built-about 6 or 7 years ago.

[chiefcoxswain]

Would be ideal down here on the Great Barrier Reef off Queensland, Have seen many similar designs, easy driven hulls, small rig, just do not take them out to sea.