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Old 12-28-2014, 04:20 PM   #21
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What eyeS so well points out yet again is that the SD hull types can be decent on fuel and also offer a speed option for use when you want. But good luck in trying to confuse the slow FD folks with facts.
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Old 12-28-2014, 05:58 PM   #22
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I enjoy moving at 6+ knots at less than two gph. No need for SD here. If the destination was the primary purpose, I'd likely drive, take a taxi, or a bus, or a train, or a plane. Regardless, I want a strong hull and keel-protected rudder and propeller.




But why would an SD owner feel defensive when he might have the best of two worlds?
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Old 12-28-2014, 07:38 PM   #23
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Bay,

We FD guys know what the facts are and it has little to do w fuel consumption.
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Old 12-28-2014, 08:30 PM   #24
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I have owned many boats the overwhelming cruising types were FD and I still spend on my present SD most of my underway time at or below hull speed as I was obligated by physics to do on my many FD boats. The only difference now is I can go faster if the need or desire is there. It is not necessarily or always a better way just one with added options and of course some price to pay for those options no free lunch. Far be it from me to be against FD. I still own a FD boat that tops out at 5.5 K under power.
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Old 12-29-2014, 12:32 AM   #25
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Long Distance Cruising

The major advantage of full displacement over semi displacement is the ability to carry weight without serious disadvantage. Semi displacement boats can not carry enough fuel and water for blue water cruising. If you were to burden them with sufficient fuel they would not plane and their hull shape at displacement speeds is not as efficient as a true FD hull. They are also not as seaworthy as a full displacement hull at displacement speeds. There are believe it or not times at which you cannot run your boat at 12 knots in the open ocean. For the 95% of us that don't make open ocean crossing, the semi displacement hull makes more sense. For one reason, you can actually go somewhere on a weekend.
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Old 12-29-2014, 01:41 AM   #26
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The major advantage of full displacement over semi displacement is the ability to carry weight without serious disadvantage. Semi displacement boats can not carry enough fuel and water for blue water cruising. If you were to burden them with sufficient fuel they would not plane and their hull shape at displacement speeds is not as efficient as a true FD hull. They are also not as seaworthy as a full displacement hull at displacement speeds. There are believe it or not times at which you cannot run your boat at 12 knots in the open ocean. For the 95% of us that don't make open ocean crossing, the semi displacement hull makes more sense. For one reason, you can actually go somewhere on a weekend.
I don't want to rain on your parade regarding SD and blue water use,but I think you might have to modify your opinion if you followed the world hopping( including northwest passage) of SD boats like the Flemings twin engines to boot. I think if you take a harder look you will find enough SD boats that do blue water both distance and comfort and safety wise. They may not be the best platform for live aboard pack rat types but they certainly carry what they need fuel-water-water maker-stabilization-refrigeration-food freezers etc etc....
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Old 12-29-2014, 01:58 AM   #27
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I don't want to rain on your parade regarding SD and blue water use,but I think you might have to modify your opinion if you followed the world hopping( including northwest passage) of SD boats like the Flemings twin engines to boot. I think if you take a harder look you will find enough SD boats that do blue water both distance and comfort and safety wise. They may not be the best platform for live aboard pack rat types but they certainly carry what they need fuel-water-water maker-stabilization-refrigeration-food freezers etc etc....
Outer Reef likewise. I especially like the 63 with Cat C9s for its long distance travel capability and CE rating.
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Old 12-29-2014, 07:46 PM   #28
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For whatever it's worth, my own personal experiences with a SD hull have been very positive, particularly with the new generation of common-rail engines.


Our 39 ft American Tug has a 480 hp Cummins (specially ordered over the stock 380 hp). At 8 kts FD speed, the engine is turning 1500 rpm, and fuel burn is 2 gal/hr, for 4 nmpg, which I think is roughly comparable to other FD 40 ft boats. 3000 rpms yields a fast cruise of 16-17 kts and fuel burn of 15-16 gal/hr, for about 1.1 nmpg (at max rpms of 3400 top speed is about 21 kts).


As always, speed costs. To double the speed takes a quadrupling of the fuel burn. But, it's been awfully nice to have the option of either cruising economically at FD speeds and essentially FD economy, or hustling along at SD (near planning) speeds when time is limited.


Also, with the Lynn Senour hull design, with its deep forefoot, plumb bow, and deep, full keel, at low SD speeds (11-13 kts) we have a totally smooth and pound-free ride in 6-8 ft seas, with no rolling at all (my wife has slept in the forward cabin several times while running in those conditions).


Like any SD design, it certainly doesn't have the range or capacities for blue-water ocean crossing. But, as much as I might dream and fantasize about it, that's just not going to happen in our lives, and the compromises of SD have been perfect for our coastal use.


I don't think there is any absolute 'right' or 'wrong' with FD or SD. It's whatever works for the use of the owner. Whatever floats your boat (no pun intended) is what's right for you.
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Old 12-29-2014, 08:19 PM   #29
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FD versus SD

It's been some time since I posted as we have been focused on the new house but this subject hit home from a slightly different perspective. While the argument of fuel burn is worth exploring especially if you are planning long distance trips (+2,000 miles non-stop) the one area of comparison that really caught us by surprise was the comfort levels between FD and SD. When we decided to exit the 6 knots FD boats and return to SD (still single engine) we looked forward to 9 -12 knots and getting someplace the same day. What we didn't expect was the very uncomfortable ride that 7 - 10 knots provided on the SD. Our mistake (I still believe) was thinking a 10 knot SD boat would be fast enough to compensate for the lack of stabilization. One trip outside into small 3' swells on the beam had the first mate signaling to return to port and to buy a different boat. The rest is history.

So what I took away from this experience is SD hulls are fine as long as the water is relatively calm, the boat gets up to 14 - 20 knots to help with stabilization and cut through the waves. Of course if it gets too rough you will have to slow down again of beat the boat and passengers to death and deal with the rolling.

Where does this leave us, well we have focused our sights on another bucket list boat - a Downeaster of some type and possibly a cold molded skiff to experience the build project. If we ever decide to travel far we would likely return the Turtle Speed FD boats with active fins.

Just my two cents.

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Old 12-29-2014, 08:19 PM   #30
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For whatever it's worth, my own personal experiences with a SD hull have been very positive, particularly with the new generation of common-rail engines.


Our 39 ft American Tug has a 480 hp Cummins (specially ordered over the stock 380 hp). At 8 kts FD speed, the engine is turning 1500 rpm, and fuel burn is 2 gal/hr, for 4 nmpg, which I think is roughly comparable to other FD 40 ft boats. 3000 rpms yields a fast cruise of 16-17 kts and fuel burn of 15-16 gal/hr, for about 1.1 nmpg (at max rpms of 3400 top speed is about 21 kts).


As always, speed costs. To double the speed takes a quadrupling of the fuel burn. But, it's been awfully nice to have the option of either cruising economically at FD speeds and essentially FD economy, or hustling along at SD (near planning) speeds when time is limited.


Also, with the Lynn Senour hull design, with its deep forefoot, plumb bow, and deep, full keel, at low SD speeds (11-13 kts) we have a totally smooth and pound-free ride in 6-8 ft seas, with no rolling at all (my wife has slept in the forward cabin several times while running in those conditions).


Like any SD design, it certainly doesn't have the range or capacities for blue-water ocean crossing. But, as much as I might dream and fantasize about it, that's just not going to happen in our lives, and the compromises of SD have been perfect for our coastal use.


I don't think there is any absolute 'right' or 'wrong' with FD or SD. It's whatever works for the use of the owner. Whatever floats your boat (no pun intended) is what's right for you.
Your experience is very similar to ours in our Nordic Tug 42. We have the 350 HP Lugger which gives us 2 gallons/hour at 8 knots and 8 gallons/hour at 12 knots.

Having good economy is great, and having the flexibility to vary our speed up to 12 knots allows us to accommodate various interesting sights along the way. A stop to enjoy the Orcas doesn't preclude hitting the next tidal pass at slack.
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Old 12-29-2014, 08:37 PM   #31
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JT, I think there is a wider range in SD hull designs than any other (FD or planning) form - there seem to be an almost infinite number of variations, with a resulting wide variation in the performance of the "SD" boat as a result. From "lobster boats", to penetrating hulls, to the Mediterranean Llaut design, to Lynn Senour's take on it, there seem to be a lot of ways to get to "SD" performance. The resulting boats also run the gamut from being near-FD, to near-FP (full planning), to splitting the difference. There are so many factors, the wetted area, the form presented to oncoming waves, center of gravity, it seems as much art as it is science.


With the American Tug (I've owned two, a 34 and current 39), we find that the hull form provides tremendous resistance to rolling - at SD speeds. We've been out in 6-8 ft seas (the worst we've been out in were 10 ft swells) on multiple occasions, and at 10-13 kts, the ride is like a train on rails. It just doesn't roll, or pound, at all.


Though, at higher speeds (14+ kts) in those same conditions, there is more both rolling, and a sense of impact (not pounding, but on the spectrum towards it) in short, steep chop. As speed increases on the Lynn Senour design, more of the hull raises out of the water, and it takes on some of the characteristics of a FP design. At FD speeds in those conditions there is no pounding, but there is rolling, as the hull form doesn't generate enough lateral stability at pure FD speed. For this hull, we've found the best sea-keeping abilities to be in the 10-13 kt "SD" range. The performance of a different "SD" design would likewise differ (as apparently did yours).


Conrad, it's not surprising that our experiences are very similar. Both the Nordic and American Tug hulls were designed by Lynn Senour. I suspect our hulls are extremely similar both below and above the waterline.


For us, having been working full-time until recently, the option for higher speed was necessary if we wanted to actually get someplace out of sight of our home marina in the limited time of a weekend....
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Old 12-29-2014, 09:27 PM   #32
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You can give accounts of time after time the SD types going to sea w good results.

But the seaworthyness, safety, range and lower fuel burn of a good FD hull is clearly supperior by a significant margin.

Also the higher speeds, greater space and better stability under many conditions not to exclude while tied to a float are very clear advantages of the SD type.

It should be easy to decide what's best for you. One's best for some and the other is best for most. Don't see any grounds for any kind of debate.
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Old 12-29-2014, 10:59 PM   #33
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I don't want to rain on your parade regarding SD and blue water use,but I think you might have to modify your opinion if you followed the world hopping( including northwest passage) of SD boats like the Flemings twin engines to boot. I think if you take a harder look you will find enough SD boats that do blue water both distance and comfort and safety wise. They may not be the best platform for live aboard pack rat types but they certainly carry what they need fuel-water-water maker-stabilization-refrigeration-food freezers etc etc....
I believe those Flemming's were 65', one belonging To Tony Flemming. Maybe a SD however the 78 has a bulbous bow. I don't know of any SD's doing the Northwest Passage. The Northwest passage was done in a Hobie 18 however. I know Captain Rains delivered a 52' Grand Banks to Hawaii from Cabo San Lucas , added bladders and boarded up the windows. Said it was one of the worst trips of his life. Leshman took a 40' Nordhavn around the world, Can you think of any 40' SD'S you'd do that in. People do all kinds of things in boats, doesn't mean they have the best tool in the box.
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Old 12-30-2014, 12:08 AM   #34
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I don't see the need to apologize having an SD hull. SDs are the vast majority of cruising MVs, so they must work for their owners. Regardless, I'm used to being a minority as in having a 6-knot FD boat. Works for me.
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Old 12-30-2014, 12:16 AM   #35
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Scary if we try to apply what is the best form for long distance blue water particularly in the sub 50 foot size I would agree that it is a FD boat. But I would not put forth a motor boat at all. Sail would be the answer overwhelmingly so. What I am pointing out is that SD can do it. Same as motor boats can do it. But probably a much larger group of blue water cruisers are in sail boats. You think its a FD power boat they think its a sail boat and personally I don't ever want to do blue water in any boat, but that's part of what makes life interesting.
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Old 12-30-2014, 05:40 AM   #36
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Like any SD design, it certainly doesn't have the range or capacities for blue-water ocean crossing. But, as much as I might dream and fantasize about it, that's just not going to happen in our lives, and the compromises of SD have been perfect for our coastal use.

Fully agree, there is no perfect boat/anchor etc that fits everyone. The overwhelming majority of boaters do not make open water passages which is where the full displacement boats shine. When we were based in Lake Michigan I saw few full displacement power boats and now in the Eastern Caribbean I see even fewer semi-displacement power boats. Basically boaters select their boats with some idea of the use they have in mind.
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Old 12-30-2014, 06:44 AM   #37
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Size matters...once large enough...the hull design is less critical I believe.

Didn't RickB post not only links to several good articles on on the subject but also rattled off a bunch of larger yachts that were semi displacement that traveled the world?
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Old 12-30-2014, 08:01 AM   #38
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Fully agree, there is no perfect boat/anchor etc that fits everyone. The overwhelming majority of boaters do not make open water passages which is where the full displacement boats shine. When we were based in Lake Michigan I saw few full displacement power boats and now in the Eastern Caribbean I see even fewer semi-displacement power boats. Basically boaters select their boats with some idea of the use they have in mind.
As far as I noticed, we are the only FD boat at our marina off Lake Michigan. The few others I have seen were loopers stopping off in Manistee. To a certain extent, people choose SD boats because that is what have been built. To retirees like us, FD is fine but if I were a working stiff limited to weekends and an occasional vacation, I would certainly want a much faster boat like a SeaRay or Regal. If you can work from home and do it on a boat, that is a real game changer and either FD or SD will do.
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Old 12-30-2014, 08:30 AM   #39
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Scary if we try to apply what is the best form for long distance blue water particularly in the sub 50 foot size I would agree that it is a FD boat. But I would not put forth a motor boat at all. Sail would be the answer overwhelmingly so. What I am pointing out is that SD can do it. Same as motor boats can do it. But probably a much larger group of blue water cruisers are in sail boats. You think its a FD power boat they think its a sail boat and personally I don't ever want to do blue water in any boat, but that's part of what makes life interesting.
Cruising sail boats might be the ultimate hybrid.
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Old 12-30-2014, 10:59 AM   #40
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As far as I noticed, we are the only FD boat at our marina off Lake Michigan.
I was cruising Yachtworld and noticed a Fu Hwa 38 double cabin with a listed maximum speed of 14 mph....semi-displacement territory. Did they make a variety of hull designs? Just curious...
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