A Catamaran Question

[colemj]

Leaving out materials, design, weight, etc - think along the lines of passage making on a broad reach in 10-15kt winds.

How fast do you expect any boat to be in these conditions, and do you expect to average 15kts?

Similarly, make the scenario close reaching into 25-30kt winds and 8-10' seas. There are 40' boats that can reach 15kts in these conditions, but can you?

Both of these are common cruising conditions around the world.

Mark

[belizesailor]

Originally Posted by sy_gilana

Your mailbox is full, I cant answer you, 273201 is the answer....

Oops, thanks. Will clean it out.

.....now back to our orginally scheduled program. ;-)

[belizesailor]

Originally Posted by colemj

I thought is was 42???

Mark

Different universe. ;-)

[2Hulls]

Originally Posted by weavis

I understand length and fine entry is a help for attaining speed. I need to talk with Minaret and see if a 15 knot average is possible with a 40 footer built out of GRP, in a cruising configuration......

15 kt average? What was the average speed of the Gunboat on your sail?

For mortal cruisers, a 200nm day seems to be the arbitrary "goal" of passage making. Certianly there are very large and/or very expensive cruising boats - both mono and multis - that routinely can achieve this or better when the weather is right. Hell, some can do it motoring when the weather is not right. 200nm/day means an average of 8.33 knots.

As Mark alluded, this means some of the time you'll need to go substantially faster to make up for those equally frequent periods down around 5 kts.

We've had our share of 200+ days and I can tell you that it isn't all mangoes and rum drinks. Our best (that we kept close track of) was 438nm in 48 hours. That's an average of 9.13 kts. Sure, that's fun to brag about, but it wasn't all that pleasant. That took some wind and with it, the seas. You can't move around easily, you can't stand up for long, it's tough to cook, and you can't fish. At least when it's time to sleep you're plenty tired. It would be much more pleasant on much more larger boats.

And you want 15 kts average in a smaller boat?

2 Hulls Dave

[belizesailor]

I agree with the practical issues of attaining a 15 knot average too. To do that over a prolonged period on any boat, even a GunBoat, even in ideal conditions (land breeze, 20 knots true, sailing close to shore so minimal waves), you are sailing hard and must be very attentive all the time. I know from racing tris that **** happens fast at 20+ knots. Navigation is different too, you've got to work and react much faster at those speeds. Great fun if you are racing or day-sailing, but not very relaxing if cruising....especially on a longer run.

[weavis]

Originally Posted by 2Hulls

15 kt average? What was the average speed of the Gunboat on your sail?

For mortal cruisers, a 200nm day seems to be the arbitrary "goal" of passage making. Certianly there are very large and/or very expensive cruising boats - both mono and multis - that routinely can achieve this or better when the weather is right. Hell, some can do it motoring when the weather is not right. 200nm/day means an average of 8.33 knots.

As Mark alluded, this means some of the time you'll need to go substantially faster to make up for those equally frequent periods down around 5 kts.

We've had our share of 200+ days and I can tell you that it isn't all mangoes and rum drinks. Our best (that we kept close track of) was 438nm in 48 hours. That's an average of 9.13 kts. Sure, that's fun to brag about, but it wasn't all that pleasant. That took some wind and with it, the seas. You can't move around easily, you can't stand up for long, it's tough to cook, and you can't fish. At least when it's time to sleep you're plenty tired. It would be much more pleasant on much more larger boats.

And you want 15 kts average in a smaller boat?

2 Hulls Dave

Gunboat sets their daily average between 250 and 350 miles. In blows they can average 400 miles a day.

In the Westerly Centaur, Im happy if I average 4.something! The real average will be closer to 3.7 or less, sometimes 4 over a passage. Slow but stable for a coastal hopper.

I have the math for speed of a displacement hull as 1.34 x square root of the waterline length. Im trying to see what formula/weight/shape etc was used to suddenly produce a slew of fast Cats..... Gunboat, Outremer, Shuttleworth, etc... and I guess they all derive from the racing Cats, and modified for cruising. I read somewhere narrow hulls do not make a significant bow wave and therefore the hull can slide through the water without the negative effect of transverse waves. A hull to beam ratio of 10:1 will have a coefficient of 2.8 rather than 1.34 in Froudes law that will significantly increase the hull speed.

At this point, from comments made, I can see that length/size must play more of a role in the design than I figured.

what I can tell you is that I did like my time on a Gunboat and although impressed, it did not feel like we were smoking along, but we were. Its a different world once you part with $2.5 million.

[colemj]

Originally Posted by weavis

A hull to beam ratio of 10:1 will have a coefficient of 2.8 rather than 1.34 in Froudes law that will significantly increase the hull speed.

10:1 is considered slow still. Most of these boats will be well above 12:1.

Waterline is always the most important speed and comfort factor for any boat. For catamarans, weight comes second.

Mark

[weavis]

Originally Posted by colemj

10:1 is considered slow still. Most of these boats will be well above 12:1.

Waterline is always the most important speed and comfort factor for any boat.

Mark

You have all been very helpful. Thank you!

[category4jay]

I think to fully answer the question we would need to know exactly what size Gunboat you sailed on. The smallest Gunboat manufactured in the past has been 48' up until recently with their new 40' G4 which is probably not what you sailed on. They have also produced Cats up to 90' so you would have to expect dramatically different performance characteristics from different length Gunboats. That being said what "performance" criteria specifically are you hoping to emulate in a smaller cat?

As far as building a cat with presumably "high" performance characteristics similar to Gunboat check these designs out. Not cheap though.

The G-Force Series

[cwjohm]

The figures you quote for Gunboat are in racing mode where they rip a few ton off the boat. In cruising mode the numbers are much less.

I have seen a few GForce Schionnings come and go and the best I have been told is an average of around 12kn, but you need big bucks because realistically in 25-30kn and 3m swell if you maintain this pace things will surely break.

[colemj]

Originally Posted by cwjohm

but you need big bucks because realistically in 25-30kn and 3m swell if you maintain this pace things will surely break.

You are referring to big bucks AFTER you lay out the big bucks for the original purchase - correct?

So to be more precise, one would need big, big bucks…

Mark

[weavis]

Gunboat never mentioned it was racing configuration vessels achieving the big numbers for average cruising.
Fancy that.

It was a gunboat 60 that I was on.

"..........As we have learned many times, a lot of benefits occur at 60'. Smooth motion, incredible spaces and the potential for 300+ mile daily runs combine to make the Gunboat 60 exceptional."

[cwjohm]

I was quoted $1.7mill for a Schionning 45'.

All manufacturers take their new boats out with a top crew and no load and proclaim certain performance figures. It is a totally different story when you load them up.

I know of certain "performance" boats that could not get to 10kn no matter how hard they try, but they are loaded up with many tons of gear which makes the cruising experience worth having.

I also love the spin "potential for 300+ mile days".

[Jim Cate]

Originally Posted by cwjohm

I was quoted $1.7mill for a Schionning 45'.

All manufacturers take their new boats out with a top crew and no load and proclaim certain performance figures. It is a totally different story when you load them up.

I know of certain "performance" boats that could not get to 10kn no matter how hard they try, but they are loaded up with many tons of gear which makes the cruising experience worth having.

I also love the spin "potential for 300+ mile days".

Especially when you compare it with the claim of AVERAGING 400 mpd... racing format or not, I reckon this is BS.

I can't speak for GunBoat, but all too many folks designers and builders take their very best ever day's run, add 20% and claim that they could average this figure. To me, an average run is one that you can expect to maintain on a long passage where you encounter varied conditions. My observation is that damn few cruising boats of any size or configuration can really average even 10 knots when cruising, and not many can when racing. IIRC even Dashew when extolling the speed of his 80+ footer mentioned that when sailing speed dropped below 10 knots he fired up the engine... and then talked about averaging 300 + mpd. Different rules...

I imagine, without experience, that passage making on a 60 foot GunBoat would be a fantastic ride... lacking the 7 figure bank account, I will not be likely to gain that experience!

Cheers,

Jim

[D&D]

Originally Posted by Jim Cate

...all too many folks designers and builders take their very best ever day's run, add 20% and claim that they could average this figure. To me, an average run is one that you can expect to maintain on a long passage where you encounter varied conditions. My observation is that damn few cruising boats of any size or configuration can really average even 10 knots when cruising, and not many can when racing.

Well said Jim, as always...and we agree.