Despite what the hull speed literature says, there are a number of tall tales among Hunter owners as to the most knots that someone has tweeked out of a Hunter 380, 340, 34, 32 or 31. We consistently have never been able to exceed hull speed other than for a few seconds where it is more likely equipment inaccuracy. Any comments or tall tales?
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Fastest Hull speed -world record???
When I was younger I had a sunfish. On many occasions I had the boat going at least 75 knots. This is a planing hull so it is not subject to the displacement formula.
When I was younger I had a sunfish. On many occasions I had the boat going at least 75 knots. This is a planing hull so it is not subject to the displacement formula.
David, David
That must have been a typo. 75 knots! Of course the water was perfectly flat. What kind of instruments did you use to record this miraculous feat. We're going to need all this information when we submit it to GUINNESS. Just kidding. Sean
That must have been a typo. 75 knots! Of course the water was perfectly flat. What kind of instruments did you use to record this miraculous feat. We're going to need all this information when we submit it to GUINNESS. Just kidding. Sean
cruise control
That's not so hard to believe, my old O'Day would do 75 kts. every weekend, on I-75 but never on the H2O.
That's not so hard to believe, my old O'Day would do 75 kts. every weekend, on I-75 but never on the H2O.
Sail or Swim
The Sunfish was atop the car when it did the 75, Right? Using similar reasoning, my H336 has hit sixty a time or two (while intransit on the trailer). More seriously, hull speed for a pure displacement hull is directly related to the squareroot of the waterline length. Exceeding hullspeed for such a hull means that you are surfing down the backside of a swell or the nose of the craft is being driven downward by the extra force on the sails. Continue with this over canvased condition should result with the bow digging and you do slow abruptly.
The Sunfish was atop the car when it did the 75, Right? Using similar reasoning, my H336 has hit sixty a time or two (while intransit on the trailer). More seriously, hull speed for a pure displacement hull is directly related to the squareroot of the waterline length. Exceeding hullspeed for such a hull means that you are surfing down the backside of a swell or the nose of the craft is being driven downward by the extra force on the sails. Continue with this over canvased condition should result with the bow digging and you do slow abruptly.
Fresh Water and Fixed Prop?
If you sail in fresh water you'll be handicapped over a boat that is in salt water due to bouyancy. Also, minimizing hull drag will be a factor and on of the big drag producers is a fixed prop. Shed the sea anchor and get a feathering prop then have a relatively clean bottom and your ability to sail faster will be greatly increased. The fresh water will still be holding you back, though. On our 35 we've been at 10 knots or better, in salt water, on several occasions, and it's a kick. One memorable trip was in a pouring rain but the wind was in the 25 to 30 knot range. We sailed from Bainbridge Island to Oak Harbor WA and were actually passing some trawlers!! They may have been going slower because of the seastate. My wife was down below where it was warm and dry, where she could say her prayers in peace. The water came off the gooseneck in about a 3 or 4 inch diameter waterfall! This went for a couple hours. Once at Oak Harbor Marina we were at the fuel dock (it was a minus tide) and had a Sea Ray 35 power boat broadside us and wipe out our pushpit and a few stantions - got caught in a crosswind goin slow. Another time we were north of Lasquetti Island in Georgia Strait, BC, trying to reach Comox before dark and were flying the spinnaker in 10 to 12 knots boat speed. The wind had been building and I said we should take the chute down. My wife, who was at the helm, said "But we're going so good - can't we continue?" (and I almost fell over!). We took it down and a short time later we were doing 10 knots again with just the main and a 110 jib! Another time, single handing up Johnstone Strait, I did 10+ knots nearly all day from Chatham Point to past Alert Bay and part of that time with just the main. The summer winds here can blow so hard that when an Alaska cruise ship goes by all you can see is the superstructure and a bit of the top of the hull. It's like they're floating on fog. You don't want to be out in that stuff. The above "tales" are for starters. It's exciting and memorable to sail in this speed range. The wake rises and the boat "sinks" to the point where the wake is as high as the deck! We have a Max Prop and haul the boat every year and paint with Pettit Trinidad, not a fast paint by any means, but the bottom is kept reasonably clean. By comparison, my motoring speed runs about 6.3 knots, faster when first painted, a little slower a year after painting. A clean bottom (minimum drag), lots of wind, a good sea condition, and other boat members that are willing to sail (or steer the boat) in that situation helps. Thanks, Scott, for the opportunity to reminisce! You probably saw those pictures of the 40 or 45 just posted in the photo forum - didn't they look good? .
If you sail in fresh water you'll be handicapped over a boat that is in salt water due to bouyancy. Also, minimizing hull drag will be a factor and on of the big drag producers is a fixed prop. Shed the sea anchor and get a feathering prop then have a relatively clean bottom and your ability to sail faster will be greatly increased. The fresh water will still be holding you back, though. On our 35 we've been at 10 knots or better, in salt water, on several occasions, and it's a kick. One memorable trip was in a pouring rain but the wind was in the 25 to 30 knot range. We sailed from Bainbridge Island to Oak Harbor WA and were actually passing some trawlers!! They may have been going slower because of the seastate. My wife was down below where it was warm and dry, where she could say her prayers in peace. The water came off the gooseneck in about a 3 or 4 inch diameter waterfall! This went for a couple hours. Once at Oak Harbor Marina we were at the fuel dock (it was a minus tide) and had a Sea Ray 35 power boat broadside us and wipe out our pushpit and a few stantions - got caught in a crosswind goin slow. Another time we were north of Lasquetti Island in Georgia Strait, BC, trying to reach Comox before dark and were flying the spinnaker in 10 to 12 knots boat speed. The wind had been building and I said we should take the chute down. My wife, who was at the helm, said "But we're going so good - can't we continue?" (and I almost fell over!). We took it down and a short time later we were doing 10 knots again with just the main and a 110 jib! Another time, single handing up Johnstone Strait, I did 10+ knots nearly all day from Chatham Point to past Alert Bay and part of that time with just the main. The summer winds here can blow so hard that when an Alaska cruise ship goes by all you can see is the superstructure and a bit of the top of the hull. It's like they're floating on fog. You don't want to be out in that stuff. The above "tales" are for starters. It's exciting and memorable to sail in this speed range. The wake rises and the boat "sinks" to the point where the wake is as high as the deck! We have a Max Prop and haul the boat every year and paint with Pettit Trinidad, not a fast paint by any means, but the bottom is kept reasonably clean. By comparison, my motoring speed runs about 6.3 knots, faster when first painted, a little slower a year after painting. A clean bottom (minimum drag), lots of wind, a good sea condition, and other boat members that are willing to sail (or steer the boat) in that situation helps. Thanks, Scott, for the opportunity to reminisce! You probably saw those pictures of the 40 or 45 just posted in the photo forum - didn't they look good? .
John
I beg to differ, Fresh or salt water, the hull speed is a function of the water. Crest to crest. The boat will produce a wake from bow to stern. This is crest to crest. Now getting to hull speed, friction and drag is another thing. David, I hope the new 11 footer is as fast. Good luck with the HIN. r.w.landau
I beg to differ, Fresh or salt water, the hull speed is a function of the water. Crest to crest. The boat will produce a wake from bow to stern. This is crest to crest. Now getting to hull speed, friction and drag is another thing. David, I hope the new 11 footer is as fast. Good luck with the HIN. r.w.landau
Speed instrument?
How do you measure speed? Is it with a knot meter, or do you measure by navigational techniques?
How do you measure speed? Is it with a knot meter, or do you measure by navigational techniques?
'81 H30: 7.5Kts; over an hour; by GPS; no current
Fresh stripped bottom; new hi-tech sails; feathering prop; smooth seas; big winds on the beam. But this is pretty rare. I've seen 8-8.2Kts for a few minutes, running with a long swell as I fell off the front. BTW, my knotmeter has read huge numbers that don't mean much. When you heel, you can lift the knotmeter impeller into turbulent, less dense water and get false readings. This is particularly true near hull speed since the middle of the boat starts to "dig in" as it creates its hull wave.
Fresh stripped bottom; new hi-tech sails; feathering prop; smooth seas; big winds on the beam. But this is pretty rare. I've seen 8-8.2Kts for a few minutes, running with a long swell as I fell off the front. BTW, my knotmeter has read huge numbers that don't mean much. When you heel, you can lift the knotmeter impeller into turbulent, less dense water and get false readings. This is particularly true near hull speed since the middle of the boat starts to "dig in" as it creates its hull wave.
Only on a plane
The only way I have been able to significantly exceed hull speed is by planing. Easy to do in a Laser or Hobie, more difficult (but possible) in a Soling, and highly doubtful in a 30 foot cruising boat. Once or twice I have slightly exceeded the theoretical maximum hull speed. When I have it is because I was just starting to get on a plane. The bow was pitched way up and the transom was dragging in the water. Anybody who has done a lot of planing knows the drop of the stern then the bow as you come off the plane - it's just that in a powerful speedboat you quickly get onto a plane and don't notice as much. I would have to see somebody significantly above hull speed without planing before I would believe it. Brian
The only way I have been able to significantly exceed hull speed is by planing. Easy to do in a Laser or Hobie, more difficult (but possible) in a Soling, and highly doubtful in a 30 foot cruising boat. Once or twice I have slightly exceeded the theoretical maximum hull speed. When I have it is because I was just starting to get on a plane. The bow was pitched way up and the transom was dragging in the water. Anybody who has done a lot of planing knows the drop of the stern then the bow as you come off the plane - it's just that in a powerful speedboat you quickly get onto a plane and don't notice as much. I would have to see somebody significantly above hull speed without planing before I would believe it. Brian
Water density
Hull speed should be marginally higher in fresh water due to the boat floating deeper in the water and slightly increasing the waterline length. Fresh water weighs slightly less than salt water so the boat must sink further to displace its own weight.
Hull speed should be marginally higher in fresh water due to the boat floating deeper in the water and slightly increasing the waterline length. Fresh water weighs slightly less than salt water so the boat must sink further to displace its own weight.
Sunfish at 20+ knots
Some years ago, I had my Sunfish out in the seaplane basin at Key West in a 45 knot gale with waves limited to around 3 feet by the size of the basin. The light boat was planing continuously on a reach with about 3-4 feet of the 14 foot hull in the water. Of course, I was hiked out all the way to keep her flat in that wind. After about 45 minutes of pure exhilaration, a wave front hit my body, and slowed the boat so fast that the aluminum mast sheered off at the deck. I pulled out the stub, set the broken end back in the stepping hole, and made it back to shore. The 20+ knot estimate comes from comparing the wake and ride of the boat to motor boats at similar speeds. In any case, it was a thrill well worth the lost mast. On the technical side, I understand a displacement hull to be limited to the familiar 1.34 times the square root of the waterline because the wake of the boat lengthens with increasing speed until it becomes a single wave from the bow to the stern. As you push harder (with sails or motor) the wave becomes deeper rather than longer and limits the speed. Actually, this might be called a "displacing hull." A "planing" hull beats this limit by moving on top of the water - like a speed boat. A 30-50 foot sailboat can become a "planing" hull if it is light enough, and develops enough power to lift out of its displacement wave. For most of us, this only happens when we get a gravity assist surfing down a wave front. Modern racing yachts maximise the ability to plane by decreasing displacement, and designing the hull to plane more easily.
Some years ago, I had my Sunfish out in the seaplane basin at Key West in a 45 knot gale with waves limited to around 3 feet by the size of the basin. The light boat was planing continuously on a reach with about 3-4 feet of the 14 foot hull in the water. Of course, I was hiked out all the way to keep her flat in that wind. After about 45 minutes of pure exhilaration, a wave front hit my body, and slowed the boat so fast that the aluminum mast sheered off at the deck. I pulled out the stub, set the broken end back in the stepping hole, and made it back to shore. The 20+ knot estimate comes from comparing the wake and ride of the boat to motor boats at similar speeds. In any case, it was a thrill well worth the lost mast. On the technical side, I understand a displacement hull to be limited to the familiar 1.34 times the square root of the waterline because the wake of the boat lengthens with increasing speed until it becomes a single wave from the bow to the stern. As you push harder (with sails or motor) the wave becomes deeper rather than longer and limits the speed. Actually, this might be called a "displacing hull." A "planing" hull beats this limit by moving on top of the water - like a speed boat. A 30-50 foot sailboat can become a "planing" hull if it is light enough, and develops enough power to lift out of its displacement wave. For most of us, this only happens when we get a gravity assist surfing down a wave front. Modern racing yachts maximise the ability to plane by decreasing displacement, and designing the hull to plane more easily.
75 Knots
Yes the sunfish was attached to its' trailer and the trailer was attached to my vehicle at the time. However, on a run with 20+ knots of wind on a lake with minimal waves I had it planing so fast a significant wake developed behind the boat, it was also quite thrilling to turn upwind when going say 10 - 15 knots to begin with and suddenly increasing the apparent wind while adding a huge heeling moment. Later in the day several sunfish were being towed in by the police boat because they became completely unmanageable. The period of the waves was such that the rudder would come out of the water and all control would be lost, impossible sailing conditions. Also in trying to run the bow would bury itself in the wave in front which were very large and steep, so that was impossible also
Yes the sunfish was attached to its' trailer and the trailer was attached to my vehicle at the time. However, on a run with 20+ knots of wind on a lake with minimal waves I had it planing so fast a significant wake developed behind the boat, it was also quite thrilling to turn upwind when going say 10 - 15 knots to begin with and suddenly increasing the apparent wind while adding a huge heeling moment. Later in the day several sunfish were being towed in by the police boat because they became completely unmanageable. The period of the waves was such that the rudder would come out of the water and all control would be lost, impossible sailing conditions. Also in trying to run the bow would bury itself in the wave in front which were very large and steep, so that was impossible also
Are There Exceptions to the Square Root Rule?
This is a debate that will probably never end. Is 1.34 times the square root of the LWL an absolute rule, with no exceptions? My understanding is that hull shape matters. A slender hull tends to be faster than a beamy hull. How, for example, do catamarans get such impressive speeds? Aren't they displacement hulls, albeit long & narrow ones? I have a Hunter 54. It's LWL is 43'6". If you've ever seen the 54, it has a very slender hull, only 11'4" at the beam. It also has a very light displacement, only 20,500 lbs. Having said all that, I believe I've gone faster than the formulaic hull speed on the 54, which computes to 8.8 kts. The top indicated speed on the knotmeter I've seen so far is 13.3 kts, under full power (3300 RPM's on the 80 hp turbo diesel). At that speed, the stern does settle down appreciably, and there is a noticeable stern wave that builds aft. BTW, I realize that the knotmeter isn't precise. When I've checked it against the GPS, it's usually 1-3 kts faster than SOG, but that's without adjusting for current, wave height, etc. Even if you knock 3 kts off the 13, that's 10 kts through the water, slightly better than that theoretical hull speed of 8.8. Eric Lorgus s/v Impulse 83H54
This is a debate that will probably never end. Is 1.34 times the square root of the LWL an absolute rule, with no exceptions? My understanding is that hull shape matters. A slender hull tends to be faster than a beamy hull. How, for example, do catamarans get such impressive speeds? Aren't they displacement hulls, albeit long & narrow ones? I have a Hunter 54. It's LWL is 43'6". If you've ever seen the 54, it has a very slender hull, only 11'4" at the beam. It also has a very light displacement, only 20,500 lbs. Having said all that, I believe I've gone faster than the formulaic hull speed on the 54, which computes to 8.8 kts. The top indicated speed on the knotmeter I've seen so far is 13.3 kts, under full power (3300 RPM's on the 80 hp turbo diesel). At that speed, the stern does settle down appreciably, and there is a noticeable stern wave that builds aft. BTW, I realize that the knotmeter isn't precise. When I've checked it against the GPS, it's usually 1-3 kts faster than SOG, but that's without adjusting for current, wave height, etc. Even if you knock 3 kts off the 13, that's 10 kts through the water, slightly better than that theoretical hull speed of 8.8. Eric Lorgus s/v Impulse 83H54
Not in the Chesapeake Bay
The "hull speed" formula comes from hydrodynamics; it relates the length and velocity of water waves. In theory a displacement hull will go at the same speed as a water wave with crest to crest length equal to the vessel LWL. However, the 1.34*sqrt(LWL) is an approximation valid only for deep water, i.e. when the depth is greater than 3*LWL. My Hunter 376 with 32 foot LWL needs 96 feet of water to achieve thke 7.6 knots "hull speed". I can't do this in my part of the Bay. In shallow water, defined as water depth less than LWL/11 for the purpose of the approximation formulas, the wave velocity formula becomes 3.4*sqrt(depth). So in less than 3 feet of water my 32 foot LWL boat has a hull speed of 5.9 knots. Lets forget the 5 foot draft for the moment. Anyway, hull speed for my boat is between 6 knots and 7.6 knots depending on water depth.
The "hull speed" formula comes from hydrodynamics; it relates the length and velocity of water waves. In theory a displacement hull will go at the same speed as a water wave with crest to crest length equal to the vessel LWL. However, the 1.34*sqrt(LWL) is an approximation valid only for deep water, i.e. when the depth is greater than 3*LWL. My Hunter 376 with 32 foot LWL needs 96 feet of water to achieve thke 7.6 knots "hull speed". I can't do this in my part of the Bay. In shallow water, defined as water depth less than LWL/11 for the purpose of the approximation formulas, the wave velocity formula becomes 3.4*sqrt(depth). So in less than 3 feet of water my 32 foot LWL boat has a hull speed of 5.9 knots. Lets forget the 5 foot draft for the moment. Anyway, hull speed for my boat is between 6 knots and 7.6 knots depending on water depth.
Eric
You answered your own question. The 1.34 x square root of lwl is theory. The extra power you applied has pushed it beyond hull speed. As you stated, current may play a role. The gulf stearm can add 2.5 knot or a incoming or out going tide can change the speed. My thought is that pushing your deisel to 3500 rpm has created a speed greater than the hull speed. I wouldn't make this a habit. It has not changed the hull speed. In my interpretation of hull speed is; "the speed that a hull can achieve under normal conditions. The maximum speed that is achieved by a continual increase of power at a steady rate. Once this speed is achieved, more speed can only be achieved by a disproportional amount of power." I am no expert, but this is the definition that I have compiled from the info I have consumed. r.w.landau
You answered your own question. The 1.34 x square root of lwl is theory. The extra power you applied has pushed it beyond hull speed. As you stated, current may play a role. The gulf stearm can add 2.5 knot or a incoming or out going tide can change the speed. My thought is that pushing your deisel to 3500 rpm has created a speed greater than the hull speed. I wouldn't make this a habit. It has not changed the hull speed. In my interpretation of hull speed is; "the speed that a hull can achieve under normal conditions. The maximum speed that is achieved by a continual increase of power at a steady rate. Once this speed is achieved, more speed can only be achieved by a disproportional amount of power." I am no expert, but this is the definition that I have compiled from the info I have consumed. r.w.landau
good wind
With sufficient energy, you can INEFFICIENTLY exceed hull speed.But, it ain't easy or often, other than planning. My 33 has a theoretical hull speed of 7 knots, but I once did two continuous hours above that, with bursts up to 9 knots (calibrated knotmeter) close to shore (flat water) in a roaring Santa Ana wind...you SoCal sailors will know what I mean. It was great fun. Every other time we were surfing. The 33 comes in at 10,400 pounds, give or take, with a LWL of 27 feet.
With sufficient energy, you can INEFFICIENTLY exceed hull speed.But, it ain't easy or often, other than planning. My 33 has a theoretical hull speed of 7 knots, but I once did two continuous hours above that, with bursts up to 9 knots (calibrated knotmeter) close to shore (flat water) in a roaring Santa Ana wind...you SoCal sailors will know what I mean. It was great fun. Every other time we were surfing. The 33 comes in at 10,400 pounds, give or take, with a LWL of 27 feet.
Which reminds me of the tugboat example
In discussing the theoretical hull speed issue with my sailing buddies, I've asked the following question: if you hooked a tugboat capable of 15 kts to a 10,000 lb displacement hull boat with a hull speed of 7 kts, what would happen? Would A) the displacement hull hold the tug back to a speed of 7 kts, or, B) the tug pull the 7 kt displacement hull at 15 kts, or, C) the 15 kt tug pull the deck cleats out of the 7 kt displacement hull? My vote is for B. I agree with Tim that with sufficient energy, you can INEFFICIENTLY exceed hull speed... the tugboat can pull the 7 kt displacement hull at 15 kts.
In discussing the theoretical hull speed issue with my sailing buddies, I've asked the following question: if you hooked a tugboat capable of 15 kts to a 10,000 lb displacement hull boat with a hull speed of 7 kts, what would happen? Would A) the displacement hull hold the tug back to a speed of 7 kts, or, B) the tug pull the 7 kt displacement hull at 15 kts, or, C) the 15 kt tug pull the deck cleats out of the 7 kt displacement hull? My vote is for B. I agree with Tim that with sufficient energy, you can INEFFICIENTLY exceed hull speed... the tugboat can pull the 7 kt displacement hull at 15 kts.
Don't know about that!
I would be inclined to think that the energy required to pull the barge at 15 knots would take more that the tug could put out, and that the result would be closer to the 7 knots. On the other hand, the barge would have to have a waterline of only 27 feet to have the slow a hull speed.....can a barge plane? (chuckling!)
I would be inclined to think that the energy required to pull the barge at 15 knots would take more that the tug could put out, and that the result would be closer to the 7 knots. On the other hand, the barge would have to have a waterline of only 27 feet to have the slow a hull speed.....can a barge plane? (chuckling!)
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