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Old 20-12-2017, 19:24   #76
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Re: International Micron 66

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Old 21-12-2017, 07:45   #77
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Re: International Micron 66

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-- hull speed is nothing other than a steepening of the curve which represents power versus speed. There is no one point on that curve -- like the sound barrier, for example -- where you just suddenly can't accelerate any more -- it just takes more and more power. So hull speed is not really a point, but could be better thought of as a band of speed during which power required to go faster increases disproportionately.

.
Actually, I've been through the sound barrier many times, (but only a few of them were in my Micron 66 equipped cruising sailboat...and I seem to have misplaced the video) and going through the sound barrier is different from exceeding hull speed because, while drag gradually increases as the airflow around parts of the plane become supersonic (similar to approaching hull speed), once the whole plane is supersonic, drag decreases and if you don't decrease power, you suddenly accelerate a little bit more before drag once more starts to build with increased speed. But with hull speed, the increase in drag doesn't abate once you get past a certain point, the curve just gets ever steeper. In an airplane, as you approach the speed of sound, you can feel the increasing resistance, but suddenly you feel the jet seem to slip ahead and you look down at your instruments and your speed is a bit over mach one and at that point you can pull your power back to maintain it. Also, on some jets your airspeed indicator becomes a bit unreliable during this regime so the best indicator of whether you're actually supersonic is that feeling of having slipped past a point of high resistance.

I've only exceeded hull speed a few times and that was for a few seconds at a time while surfing downhill on a really big wave. It wasn't a comfortable feeling at all because I didn't feel like I had full control of the steering and I could feel a vibration in the wheel. Not something I'd want to make a habit of doing! All of our sailboats have the potential for generating tremendous amounts of horsepower via sail, difficult to accurately quantify but WAY more than our auxiliary engines can put out, and if this power is properly harnessed it can push the boat right up against that very steep drag curve, and even climb it a little, but I question the wisdom of doing so on a boat that you plan to keep for awhile because the increase in forces involved on the whole boat, from the rig to the hull laminate, is logarithmic and is way beyond what it was designed to withstand on a regular basis. I guess it's one thing on a broad reach or a run, but sailing to weather, bashing into waves at 10+ knots over and over again isn't something I'd find comfortable, and I can't imagine that giving your boat a beating like that is doing it any good in a structural sense.

DH, I know you're working on it, but if you really want to sail that fast, I think you need to hurry up and get into your new boat that's built for it before your current production cruising boat falls apart from the pounding it's apparently taking!
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Old 21-12-2017, 07:57   #78
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Re: International Micron 66

Apparently, you'll need to install a "warp drive" on your Tayana displacement starship in order to go where very few (if any ) have gone before.
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Old 21-12-2017, 08:55   #79
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Re: International Micron 66

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Actually, I've been through the sound barrier many times, (but only a few of them were in my Micron 66 equipped cruising sailboat...and I seem to have misplaced the video) and going through the sound barrier is different from exceeding hull speed because, while drag gradually increases as the airflow around parts of the plane become supersonic (similar to approaching hull speed), once the whole plane is supersonic, drag decreases and if you don't decrease power, you suddenly accelerate a little bit more before drag once more starts to build with increased speed. But with hull speed, the increase in drag doesn't abate once you get past a certain point, the curve just gets ever steeper. In an airplane, as you approach the speed of sound, you can feel the increasing resistance, but suddenly you feel the jet seem to slip ahead and you look down at your instruments and your speed is a bit over mach one and at that point you can pull your power back to maintain it. Also, on some jets your airspeed indicator becomes a bit unreliable during this regime so the best indicator of whether you're actually supersonic is that feeling of having slipped past a point of high resistance.

I've only exceeded hull speed a few times and that was for a few seconds at a time while surfing downhill on a really big wave. It wasn't a comfortable feeling at all because I didn't feel like I had full control of the steering and I could feel a vibration in the wheel. Not something I'd want to make a habit of doing! All of our sailboats have the potential for generating tremendous amounts of horsepower via sail, difficult to accurately quantify but WAY more than our auxiliary engines can put out, and if this power is properly harnessed it can push the boat right up against that very steep drag curve, and even climb it a little, but I question the wisdom of doing so on a boat that you plan to keep for awhile because the increase in forces involved on the whole boat, from the rig to the hull laminate, is logarithmic and is way beyond what it was designed to withstand on a regular basis. I guess it's one thing on a broad reach or a run, but sailing to weather, bashing into waves at 10+ knots over and over again isn't something I'd find comfortable, and I can't imagine that giving your boat a beating like that is doing it any good in a structural sense.

DH, I know you're working on it, but if you really want to sail that fast, I think you need to hurry up and get into your new boat that's built for it before your current production cruising boat falls apart from the pounding it's apparently taking!
Ha, ha.

Well, I don't know if I've overstressed the airframe on this boat or not. I was quite eager and quite stupid the first few years, but she seems to be quite strong. One of the huge mistakes I made was not understanding that this more modern hull form doesn't like to heel. I started out assuming that if the rail was not in the water, I didn't have too much canvas up -- wrong!

But lighter boats (in terms of D/L) don't need huge forces to get up somewhat over theoretical hull speed. My previous boat (D/L -- 320) couldn't possibly do it, but this one (D/L -- 188) doesn't require a "pounding" to get up to about one knot over theoretical hull speed, just a really good wind on a favorable point of sail. I see 10 knots in this boat REGULARLY. But that's about it -- more than that does start to feel like a "pounding" unless surfing is involved, or it just becomes impossible.

Surfing requires the right sea conditions including, I think, not too much difference between the wave velocity and your own speed. That way the face of the wave catches you and holds you for some time, accelerating you, then you keep some of the momentum on until the next wave face catches you. If your speed coincides with this rhythm, you can really fly, riding the waves.

I do not have control issues when doing this -- I think because this boat has a very large, semi-balanced rudder -- not so good for efficiency, but very good for power. I have broached exactly one time, while getting knocked down once in the North Sea.
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Old 21-12-2017, 15:12   #80
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Re: International Micron 66

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Ha, ha.

Well, I don't know if I've overstressed the airframe on this boat or not. I was quite eager and quite stupid the first few years, but she seems to be quite strong. One of the huge mistakes I made was not understanding that this more modern hull form doesn't like to heel. I started out assuming that if the rail was not in the water, I didn't have too much canvas up -- wrong!

But lighter boats (in terms of D/L) don't need huge forces to get up somewhat over theoretical hull speed. My previous boat (D/L -- 320) couldn't possibly do it, but this one (D/L -- 188) doesn't require a "pounding" to get up to about one knot over theoretical hull speed, just a really good wind on a favorable point of sail. I see 10 knots in this boat REGULARLY. But that's about it -- more than that does start to feel like a "pounding" unless surfing is involved, or it just becomes impossible.

Surfing requires the right sea conditions including, I think, not too much difference between the wave velocity and your own speed. That way the face of the wave catches you and holds you for some time, accelerating you, then you keep some of the momentum on until the next wave face catches you. If your speed coincides with this rhythm, you can really fly, riding the waves.

I do not have control issues when doing this -- I think because this boat has a very large, semi-balanced rudder -- not so good for efficiency, but very good for power. I have broached exactly one time, while getting knocked down once in the North Sea.
Just for the record and following DH's example, our boat's fully loaded for cruising D:L ratio is around 140. I dunno if this will help Ken understand how we can achieve the "impossible" feat of exceeding hull speed on a fairly regular basis, but it should help... if he really cares to understand.

Jim
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Old 21-12-2017, 15:29   #81
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Re: International Micron 66

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Just for the record and following DH's example, our boat's fully loaded for cruising D:L ratio is around 140. I dunno if this will help Ken understand how we can achieve the "impossible" feat of exceeding hull speed on a fairly regular basis, but it should help... if he really cares to understand.



Jim


I posted a track that shows our tubby little boat (D/L of 403 in lightship config) exceeding hull speed for quite some time, with a large A-kite up. All it takes is power. In the right wind, the kite will generate way more power than the auxiliary engine could ever hope to do.
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Old 21-12-2017, 15:40   #82
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Re: International Micron 66

Whats this I see?
Theory beaten by reality?
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Old 21-12-2017, 15:48   #83
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Re: International Micron 66

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Whats this I see?
Theory beaten by reality?
No, you see evidence of wishfull thinking combined with a favorable current or tide.
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Old 21-12-2017, 15:55   #84
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Re: International Micron 66

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No. Wishfull thinking.


So youíre telling me that Iíve never exceeded hull speed on my lead mine with the kite up? Thatís incredible! And here I thought that with photographic proof there would be some relenting.
Ah well, maybe the evidence is just pointing toward your own inability to trim sails or push the boat.
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Old 21-12-2017, 15:59   #85
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Re: International Micron 66

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So you’re telling me that I’ve never exceeded hull speed on my lead mine with the kite up? That’s incredible! And here I thought that with photographic proof there would be some relenting.
Ah well, maybe the evidence is just pointing toward your own inability to trim sails or push the boat.
With a favorable current along with the kite, I’m sure it’s possible, we’ve even done it ourselves. Looks like you enjoyed a nice day of sailing. Congratulations!
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Old 21-12-2017, 16:05   #86
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Re: International Micron 66

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With a favorable current along with the kite, Iím sure itís possible, weíve even done it ourselves. Looks like you enjoyed a nice day of sailing. Congratulations!


I wish I had video of the STW....it was within a quarter knot of the SOG.....as it always is unless Iím in a current, like the Gulf Stream. There is no measurable current along that section of the gulf coast.
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Old 21-12-2017, 19:28   #87
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Re: International Micron 66

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No, you see evidence of wishfull thinking combined with a favorable current or tide.
Kenomac, you are wrong. Dockhead and Jim Cate have repeatedly and politely explained the truth to you.

In 1969, a Cal 36 with an empty DL of just over 250 averaged over hull speed for the entire Transpac. Here is the data on the boat:

CAL 36 sailboat specifications and details on sailboatdata.com

The elapsed time was 12:14:40:42, or 302.66 hours to cover 2225 nautical miles great circle route. The course sailed was much further, probably closer to 2400 nm. 2225/302.66 = 7.35 knots. Hull speed on 27 foot waterline: 6.96 knots. 3rd in class.

Same year and race, Esprit, an S&S 33 Spirit class boat, with a full length keel, DL of 238, waterline length of 28.5 feet did even better:

Sparkman & Stephens: Design 1557 - Spirit Class

Their elapsed time was 12:11:36:04, or 299.6 hours. 2225/299.6 = 7.46 knots. Hull speed on 28.5 waterline is 7.15 knots.

Or the ubiquitous Cal 40. LWL 30.33, DL is 248 -- substantially higher displacement ratio than Dockhead's 180 or so. Hull speed should be 7.38 knots. But in Transpac, we see:

1965 12:05 for 7.6 knots
1967 13:11 to 14:00 (below 7.4)
1969 11:16 to 12:07 for 7.95 knots to 7.54 knots,
1996 11:05:33 by Stan and Linsey Honey for Pacific Cup 2070nm for 7.68 knots.

In other words, DOZENS of boats making DOZENS of passages over several decades at average speeds over hull speed.

Nearly any powerboat exceeds hull speed, even if it can't plane. Fleming 55 has a 50 foot LWL, 230 DL, a 9.56 knots hull speed, yet is commonly cruised at 14 knots.

Hull speed is not a limit.
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Old 21-12-2017, 19:35   #88
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Re: International Micron 66

I sure wish there was a Forum function that ďtold me when the pissing match finishes.Ē

All I want to learn about is Micron 66.
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Old 21-12-2017, 21:22   #89
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Re: International Micron 66

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Kenomac, you are wrong. Dockhead and Jim Cate have repeatedly and politely explained the truth to you.

In 1969, a Cal 36 with an empty DL of just over 250 averaged over hull speed for the entire Transpac. Here is the data on the boat:

CAL 36 sailboat specifications and details on sailboatdata.com

The elapsed time was 12:14:40:42, or 302.66 hours to cover 2225 nautical miles great circle route. The course sailed was much further, probably closer to 2400 nm. 2225/302.66 = 7.35 knots. Hull speed on 27 foot waterline: 6.96 knots. 3rd in class.

Same year and race, Esprit, an S&S 33 Spirit class boat, with a full length keel, DL of 238, waterline length of 28.5 feet did even better:

Sparkman & Stephens: Design 1557 - Spirit Class

Their elapsed time was 12:11:36:04, or 299.6 hours. 2225/299.6 = 7.46 knots. Hull speed on 28.5 waterline is 7.15 knots.

Or the ubiquitous Cal 40. LWL 30.33, DL is 248 -- substantially higher displacement ratio than Dockhead's 180 or so. Hull speed should be 7.38 knots. But in Transpac, we see:

1965 12:05 for 7.6 knots
1967 13:11 to 14:00 (below 7.4)
1969 11:16 to 12:07 for 7.95 knots to 7.54 knots,
1996 11:05:33 by Stan and Linsey Honey for Pacific Cup 2070nm for 7.68 knots.

In other words, DOZENS of boats making DOZENS of passages over several decades at average speeds over hull speed.

Nearly any powerboat exceeds hull speed, even if it can't plane. Fleming 55 has a 50 foot LWL, 230 DL, a 9.56 knots hull speed, yet is commonly cruised at 14 knots.

Hull speed is not a limit.
I’m sure having a .2 knot following current didn’t hurt, but I don’t see any of them in full race mode beating hull speed by 3-4 knots as DH claims to do on a regular basis on his Moody 54 displacement cruising yacht.

Nice try.
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Old 21-12-2017, 21:55   #90
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Re: International Micron 66

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Iím sure having a .2 knot following current didnít hurt, but I donít see any of them in full race mode beating hull speed by 3-4 knots as DH claims to do on a regular basis on his Moody 54 displacement cruising yacht.

Nice try.
Probably because they are all considerably shorter in length.
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