Real cruising multihull speeds

[BigCat]

Originally Posted by drewke07

Our cruising cat is a MVP/VLP designed Aikane 56. With a 52' waterline and a l/b ratio of almost 13. Fully loaded she weighs around 23,000lbs. We have had this boat for about 4 years now and have put over 10,000 sea miles on her.

While she has proven capable of speeds on many downwind runs in the high teens to mid twenties, We have found that she can reliably be counted upon to consistently turn out 180 to 220 mile days. However, the faster she travels, the less comfortable she becomes. Powered up in 20k of wind she will go upwind at 11k, but it is so much more comfortable at 9k. In any event, average speed is certainly a function of waterline and weight. Dut driving that function is comfort for a family.

Hi, Drewke07 - At that displacement, and a sail area of 1615 sq. ft., you would have a whopping sail area disp ratio of 31.4. With a DWL of 52', you would have a quite low D/L ratio of 73. Combine this with your hull L/B of almost 13, and you should have a very sweet ride indeed!

These statistics are very good indeed for a cruising cat, so if you average 200 miles a day in the long run, I'd say that's about as good as it is likely to get. That is 1.16 times the square root of the DWL. If the Aikane 56 gets that in the long run, it would be amazing if any other cat being cruised by a family or couple did any better.

The equivalent speed for my BigCat 65 would be 220 miles a day. Since I have a bit more hull beam proportionally, and a bit less sail area, that woud give me an estimated long term cruising average of maybe 210 miles a day for this design. So, the 2900 mile sailing distance from Seattle to Hawaii, for example, would take about 14 days. (The sailing route goes south from Cape Flattery to a point perhaps 150 NM offshore of San Francisco before taking the rhumb line to Hawii.)

Another sweet thing about the Aikane 56 is the lack of berth 'shelves.' So, I wouldn't think you'd get much wave thumping of the bridgedeck. What would you say your bridgedeck clearance is, and do you in fact get much thumping of it?

[Nordic cat]

Originally Posted by BigCat

I noted that you had a good rig, and what I have read about rotating rigs makes them sound very good indeed. Is your mast fairly airfoil shaped?

If you must have standing rigging, I like the idea of Spectra-less metal to fatigue. I have seen many a ss shroud and stay with broken strands where it enters the swedging.

Yes the mast is absolutely a symmetrical aifoil shape that can rotate about 60 degrees each way. Even hard on the wind, the full main sail area is working. As my mast chord is only 330 mms, I need to slightly overotate the mast in stronger winds, but this also helps to flatten the main.

My primary objective was to improve light wind performance, as in strong winds, comfort becomes one of the choices anyway. This has been achieved, so I'm happy

cheers

Alan

[BigCat]

On Chris White's website, he gives figures for his 55, and mentions 4 days of cruising speeds when delivering it. It has a DL ratio of 116 on its marks, a SA/Disp ratio of 24 with jib / 31 with jenny. They averaged about 216 miles a day over 4 days of sailing. That is an average speed of about 1.24 times the square root of the waterline length. Four days isn't a very large sample, of course.

[44'cruisingcat]

Originally Posted by rickm505

A lot of wind? Hell, I don't even hit my max hull speed unless it's blowing in the low 20's. Where exactly do you sail that 18 knots is a lot of wind??

David Adams wrote a book (Chasing liquid Mountains) about sailing in the solo round-the-world races. He recorded the windspeed for the entire trip, including Cape Horn, the Southern ocean etc. IIRC the average windspeed was just 5 knots. (I'll have to re-read the book, but I'm pretty sure that's what it was)

As you'd expect, he was very surprised by this, but built his next racing boat accordingly - so it would be well powered up in just 5 kts breeze.

[Eleven]

That does some it up for cruising - make the best of light winds, keep it safe as the winds rise. Much over eight knots seems to get progressively wearing, OK for a few hours dash to calmer waters but not cruising.
Does that mean a good genoa / spinnaker for lighter weather and small flat sails for windy days? So much to learn, but the house is under offer and we'll be off soon too.

[drewke07]

hi Bigcat,
the Aikane 56 is a sweet ride indeed. She has about 32 inches of underwing clearance and rarely if ever slams. All things considered if I were starting from scratch, about the only thing I would change is adding a few more inches in underwing clearance. She carries a powerful sailplan on a carbon stick and moves well in light air, but when the wind gets up she is a handfull.

[BigCat]

Originally Posted by 44'cruisingcat

David Adams wrote a book (Chasing liquid Mountains) about sailing in the solo round-the-world races. He recorded the windspeed for the entire trip, including Cape Horn, the Southern ocean etc. IIRC the average windspeed was just 5 knots. (I'll have to re-read the book, but I'm pretty sure that's what it was) Well, a boat that doesn't motor will

As you'd expect, he was very surprised by this, but built his next racing boat accordingly - so it would be well powered up in just 5 kts breeze.

Five knots seems low to me, for an average wind speed in the far S. Pacific and the two Atlantics, especially for a boat that sailed the roaring 40s, even if it did cross the equator twice.

National Data Buoy Center Historical Data Map Shows the locations for offshore weather buoys, and you can look up 'historical data' for a given buoy. One offshore from central Florida, of interest for those sailing to the Bahamas from the U.S., shows average winds varying from 10 knots in summer to 15 knots in winter. Some buoys give more summarized data than others do.

The site shows more than one U.S. government buoy system, and some are in, knots, some in meters per second, etc. For rough conversion, multiply m/s by 2 to get knots-you will overestimate knots by @ 3%.

[BigCat]

Originally Posted by drewke07

hi Bigcat,
the Aikane 56 is a sweet ride indeed. She has about 32 inches of underwing clearance and rarely if ever slams. All things considered if I were starting from scratch, about the only thing I would change is adding a few more inches in underwing clearance. She carries a powerful sailplan on a carbon stick and moves well in light air, but when the wind gets up she is a handfull.

Hi, Drewke07- I think the thread that is choosing ideal stock catamarans would do well to look at yours. I would have designed in a bit more freeboard, too-probably about 6" more. Still, if it rarely slams, we can't complain too much. In what way is it a handful when the wind pipes up? Hard to reef? Hard to steer?

[BigCat]

Originally Posted by Eleven

That does some it up for cruising - make the best of light winds, keep it safe as the winds rise. Much over eight knots seems to get progressively wearing, OK for a few hours dash to calmer waters but not cruising.
Does that mean a good genoa / spinnaker for lighter weather and small flat sails for windy days? So much to learn, but the house is under offer and we'll be off soon too.

Well, a high percentage of offshore long-distance cruising is in the trade winds, where it almost always blows more than eight knots. Wind pressure increases at a square of wind speed, so a little more speed = a lot more felt wind and wind power. Where are you going?

[Woods Designs]

to Eleven.

yes you summed it up neatly. Unless you want to motor a lot (and many people do) it is worth investing in at least a spinnaker. We used our masthead screecher/drifter to good effect crossing the Atlantic when the lightwinds coupled with ocean swells andd sailing under autopilot made the spinnaker collapse constantly. The drifter may have less drive but works all the time, just flapping away.

Most of my last 20,000 miles ocean cruising was in two 32ft catamarans (the rest was in monohulls down the west coast of the US from Alaska to Cabo St Lucas). So I was really talking about that size boat when I said 175 miles a day.

The fast sails I mentioned were in a 35ft Banshee catamaran racing back to the UK from the Azores, a 43ft Norseman in the Capetown to Rio race and a Swan 55 monohull racing from Antigua to Bermuda.

All these were when ocean sailing and I agree that on shorter trips (say up to 2 nights at sea) passages can be quicker. Also when racing and hand steering speeds will be at least 10% more.

On my 32ft Eclipse my fastest speed was 21 knots day sailing. Ocean cruising it was 16 knots the day we left the Canaries (so we were heavily loaded). Twice I sailed 65 miles in 7 hours anchor to anchor. Once along the coast of Puerto Rico and once along Cuba's north shore.

Racing in the UK Round the Island race (1800 starters, 50 multihulls, 50 miles approx) we beat the good Mumm30's to windward and finished 1 1/2 hours ahead of the next production cruising catamaran, which was a Belize 43.

You can scale up my day's runs for bigger boats. But as most have already said, to be comfortable few people sail over 220 miles a day.

I also agree that the world average windspeed is quite low. In the UK I think it is about 13 knots, 11 in France. I write this in BC Canada where the average windspeed is probably 5 or less. I've found that even when tradewind sailing the wind is rarely consistently high for 24 hours (unless I am sailing to windward) for high daily mileages.

In short, and from the comments others have made, it does seem that cruisers don't sail catamarans for their ultimate speed, but for their comfort under sail.

You can read about my cruising experiences on Eclipse on my website

Woods Designs Sailing Catamarans

Richard Woods of Woods Designs

[imagine2frolic]

drew,

Is it possible to post some pics of Aikane? I would love to see her in detail. What is the meaning of the name?

[ldrhawke]

Originally Posted by drewke07

hi Bigcat,
the Aikane 56 is a sweet ride indeed. She has about 32 inches of underwing clearance and rarely if ever slams. All things considered if I were starting from scratch, about the only thing I would change is adding a few more inches in underwing clearance. She carries a powerful sailplan on a carbon stick and moves well in light air, but when the wind gets up she is a handfull.

Clarify "handfull". How many Aikanes were built? I see an Aikane 56' is up for sale. Is that the one you discuss? Did I read somewhere that Catana has taken over Aikane?

[drewke07]

I guess my point is that even with a lightweight long waterline boat carrying lots of sail, you will rarely churn out high mile days unless you have a recing crew aboard. It is called Cruising for a reason.................

[imagine2frolic]

Pretty ship, but to my disappointment I was thinking of the CSK Aikane from the 50's....

[BigCat]

Originally Posted by drewke07

I guess my point is that even with a lightweight long waterline boat carrying lots of sail, you will rarely churn out high mile days unless you have a recing crew aboard. It is called Cruising for a reason.................

Well. of course, the problem with sailing fast in a catamaran is the danger of capsizing. You don't want to end up upside down with your wife and kids. It seems to me that the average speed of a cruising catamaran is about 20% faster than that of the average cruising monohull with the same waterline.

Aikane means friend or friendly, but it can mean gay (homosexual.)