Exceeding Hull Speed, Discussion?

[mr-canada]

This is more for interesting discussion than anything else.

I went out on my first cruise in my Columbia 26 Mk II beyond the harbour limits in Squamish where the boat is moored. The intent was to sail up to Powell River and back as I have family there, but we were held back nearly a week as the engine had troubles and there was nobody in the area who could service it.

On our way out we reached a solid speed of 7.5 - 7.8 kts. I had timed the currents and wind. We had a tailwind of 10-20 kts in a strong wind warning and the charts showed a 1 kn current on the ebb tide we were chasing.

Looking at the calculators and technical documentation, the hull speed of the Columbia 26 Mk 2 is 6.2 knots. The typical 5800 lb displacement was increased by 1000 lbs as we were carrying a whole boatload of gear, water, food, beer which added about 1200 pounds so on the way out fully loaded we were probably displacing about 7000 lbs.

When we were doing 7.8 kts you could deduct the 1 kn current for 6.8, still 0.6 above hull speed if you want to get fancy. For the sailors out there we were only flying a 150 genoa with the main down catching a great tailwind.

Waves were all cresting and were about 2-3 foot high in following seas. The speed was based on GPS COG speed. We were going slightly faster than the waves maybe about a half knot faster,

Anyone with a truly awesome understanding of boats, hull speed able to explain what was happening there and how we were exceeding hull speed and what was going on?

The trip is long over now and it was our first time going any real distance in the boat. I have only been sailing for about 3 months or so. I took two days worth of lessons and have done TONS of reading. I'm not an expert at all, far from it.

I am just curious as to how someone with a lot of experience and technical expertise in sailing would describe what was likely happening. It was a great sail!

[Navicula]

[Bash]

"Hull speed," is something of a misnomer, and the term often throws people. A better term would be "displacement speed." It's the speed you can't exceed while still in displacement mode.

Can a displacement hull, in select conditions, exceed displacement speed? Absolutely. While a boat like your Cal 2-26 may never actually achieve a full plane except for short burst of downhill surfing, it's possible to go into semi-displacement mode if conditions are right and enough power is applied.

The big question is whether you were throwing a rooster tail.

[Cruiser2B]

I have exceeded advertised hull speed several times on a broad reach, lots of fun.....I know on my Alberg I have been told that the hull speed increases a bit as the waterline length increases when the boat heels. Is this why???I have no idea but like you said its fun!

[micah719]

Hullspeed isn't an unbreachable limit, it is just the theoretical maximum beyond which going faster costs disproportionate energy. To go faster more economically, reduce the amount of resistance; by planing, hydrofoiling, or increasing waterline length, decreasing wetted area, etc. Or, get more energy by hoisting more sail.

[Bash]

Originally Posted by Cruiser2B

I know on my Alberg I have been told that the hull speed increases a bit as the waterline length increases when the boat heels. Is this why???I have no idea but like you said its fun!

It's a function of the sweep of bow and transom. When the boat heels, the waterline lengthens. However, on boats with plumb bows and sugar-scoop transoms that descend to the waterline, heeling doesn't make a significant difference.

On an older Alberg, you bet it makes a difference!

[djmarchand]

Hull speed, generally calculated at 1.34*sqrt(LWL) is just an engineering definition. That defintion is based on the theoretical speed of the bow wave. At hull speed the boat catches up and a trough forms. It takes a lot of horsepower to get out of that trough.

Any boat can exceed hull speed; all it takes is horsepower. But I would be surprised if a sailboat could exceed hull speed by 10% other than in ideal circumstances- ie 20 kts of wind on a beam reach.

David

[mr-canada]

No rooster tail behind the boat, I doubt we were planing, although it did feel like we were surfing on top of bubbles at times (sorry for the totally non technical description, but thats the only way to describe it) it was a very surreal feeling I havent felt the boat do before, even closehauled at 7.5 kts when I was doing a sailing lesson with my sailing instructor.

We were towing a dinghy too so it was hard to tell if we stopped laying wash behind us as we had the dinghy roped off nose high on the bar above the transom.

Wind was behind us and we were not heeling any measurable amount.

[Boracay]

My knowledge and understanding of currents is far from being "awesome" but I would expect that what you were experiencing would have been a forward eddy, a local effect or a misinterpreted chart representation.

If you check the tide tables for when you were out you may find an exceptional tide that could give a swifter current than anticipated. The numbers on the chart are only intended as a guide, and should be interpreted with local knowledge. Keep in mind that the information on many charts may be very old.

In addition you may have been experiencing a forward eddy. Currents are not constant across but have swirls and eddies. If you have a look at the chart there may not be straight banks but a series of bays and headlands.

If you were passing a headland this could also have contributed.

On a much larger scale we experienced an adverse current of almost 3 knots where the Australian East Coast Current tried to find it's way past one particular headland (from unreliable memory - Hat Head).

[mr-canada]

That is possible, we were moving out on an ebb tide that was set to fall about 10 feet.

The current in the channel should be somewhat predicatble for the charts as where we reached that top speed it was simply an inlet with a dead end where we started from in Squamish. If you look at a simple Google Map of Squamish, BC we were clocking those speeds prior to coming out adjacent to Anvil Island, once we entered the Howe Sound archipelago things slowed down about 1.5-2.5 kts until the wind completely died on us by Gambier Island. We made it from Squamish to Gambier in 1h 45m.

[S/V Alchemy]

Yes. My old Viking 33, which I keep minimally loaded because I like the performance bump, has a 26 foot LWL and a hull speed of 6.9 knots. I can, with a decent beam wind and not too much fetch, exceed that by half a knot, the key being 20 degrees of heel which extends the waterline.

On broad reaches in the low 20-knot true wind speed range, and carrying a No. 3 and a full main, I have hit 8.4 knots and have been clearly surfing (you feel it, then you hear it!) for 20-30 second stretches. Hitting 7.2-7.3 in no current SOG by GPS is possible for about a minute, but hit a wave wrong and we drop to the high sixes.

On a Newport 27, I've actually surfed and hit 10 knots SOG for a minute or better. The trouble is that the rudder isn't so effective while surfing and you can have a nasty broach in all that foam and spray. Fun, though.

[mr-canada]

Originally Posted by S/V Alchemy

I have hit 8.4 knots and have been clearly surfing (you feel it, then you hear it!) for 20-30 second stretches.

Yeah that was it exactly the feeling. It was a surreal feeling and then heard the "sound".

[Rakuflames]

Originally Posted by Bash

"Hull speed," is something of a misnomer, and the term often throws people. A better term would be "displacement speed." It's the speed you can't exceed while still in displacement mode.

Can a displacement hull, in select conditions, exceed displacement speed? Absolutely. While a boat like your Cal 2-26 may never actually achieve a full plane except for short burst of downhill surfing, it's possible to go into semi-displacement mode if conditions are right and enough power is applied.

The big question is whether you were throwing a rooster tail.

It's just a formula, and an imperfect one. My old boat supposedly had a hull speed of 6.11k, but I had no trouble getting it up to 6.5. There was no current. It's just how fast the boat could go.

Now I have a Hunter 31' (the old one, made in '83). Its hull speed is supposed to be 6.7k but I've seen it sail at 7.3 sustained by one friend. Another sailed it at a sustained 6.5k using only the headsail.

"Hull speed" is not terribly accurate. there are too many factors the formula doesn't take into account.

[highseas]

You say you had the ebb leaving Squamish,which would give you more speed not less.The river also adds some extra ebbing current for first few miles.

[SailtheWind]

Last Spetember while sailing from St Augustine FL to Charleston SC we were in the dark of the night (new moon) sailing in 26Kts wind on a broad reach (135% jib fully deployed and the main sail reefed as we always do at night) and our speed indicator showed 10.2kts which exceeds the hull spped of a Caliber 38 (7.81kts) the water was nearly over the side rail. This ride lasted about 10 minutes then we were back to 6.9 kts which we keep for a few hours.
I have to say it was both thrilling and worrisome to be going this fast in complete darkness. We were 54 miles offshore so not much to worry about other than the occasional freighter.
The fastest we have ever been on our boat is 12.9kts while me wife was at the helm she has reminded me that she holds the record speed for our boat.