Your hull type

Planing.


And it's extremely efficient at getting me to my chosen relaxation spot. When it runs low on fuel we fill it up. No worries because there's a smile in every gallon.

Semi-planing. I typically run it at 8-9 knots (slightly above theoretical hull speed) because it's relatively efficient there, the ride in 2-3 footers is typically best in that speed range, the 250 HP turbo engines like being on boost, and I can't stand poking along at 6-7 knots. It's not about the voyage for me as I'm typically single handing the boat on long legs. If it gets medium rough, I push it up to 12-13 knots and utilize the lift to hammer along the tops of waves. If it gets nasty rough, I slow to 6-7 knots and chug along like a FD. Handling and ride are good throughout that speed range. There's power available for 18 knots....installed power for 14-15 knots would be ideal. Obviously, SD hulls with twin Lehmans typically don't have the power available to fully utilize the flexibility of the design. SD hulls with power for much over 15 knots are ridiculous.

RickB said:

Does that mean the designers of freighters and tankers have been getting it wrong since the first cargo carrying hollow log?

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Maybe so, only their clients know for sure.You missed the whole point of the last several pages. The only right or wrong is what is right or wrong for you. That is why there are so many variations of hull designs. You pic the designs that suit you best.

In the oilfields in the Gulf of Mexico there are 3 main types of boats used. All of them carry personnel and cargo including water and fuel to the platforms and rigs.
Crew Boats - aluminum - typically between 95 to 135 ft. Pretty much a semi-planning or planning hull. Not very good at planing but they get up there a little. When at full speed, usually 18 to 25 kts they drink fuel. Efficient -NO. Comfortable - NO. Fast - YES. When they need parts, people and supplies, no one cares about cost. It's all about time. That shape hull is best for them.

Utility Boats - Steel Hull - semi displacement of sorts. Usually about 85 to 135 FT.
top speed is about 12 kts. Fuel Efficient - NO, Comfortable - Hell no!, Fast - Hell NO!. Underpowered - YES!. They are akin to a giant shoebox on the water. they carry a fair amount of cargo for their size and charter price is very reasonable. Used a lot for crew change and supplies including water and fuel when time and speed is not a factor. If we are unfortunate enough to have our crew change by Utility Boat we are pissed. On our day to go home we get 12 hours pay whether we fly an hour or spend all day on a utility boat - same pay.

Supply Boats - Usually well over 150 to 200 ft. Capable of very heavy loads like cement and mud in addition to water and other supplies. Longer deck makes them ideal for carrying drill pipe. Comfortable: so-so. Efficient - not too bad. Speed - I could swim faster. About 9-10 kts. on a good day. Best choice for large heavy loads considering they are the only style boats out there that can handle it.

So, the only right or wrong style is hiring the wrong boat for the intended job. So, maybe the freighters and tankers have been getting it wrong if the clients are not happy. Or maybe they are getting it right because there are a bunch of them out there.

Gotta go, I'm outta thorazine.

Ciao

thorazine ...... gotta get some of that stuff.

That'd be great. Take some meds and swim around in the fun zone with a whole lot of theories.

RickB said:

Does that mean the designers of freighters and tankers have been getting it wrong since the first cargo carrying hollow log?

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They must have gotten this one really wrong:

Wazat Mark?

Looks like it has anchoring spuds like a gold dredge.

manyboats said:

Wazat Mark?

Looks like it has anchoring spuds like a gold dredge.

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Ro-Ro. Roll on roll off. More specifically a PCC. Pure car carrier.

manyboats said:

Wazat Mark?

Looks like it has anchoring spuds like a gold dredge.

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It's a car-carrier, having left Benicia and presumably heading to Asia for another load. There are large hatches on the transom as well as on the beam, and with built-in ramps, the vehicles are driven off/on the ship.

manyboats said:

Yup .. I sure like them even if they are a light boat.

Semi-planing? That would be partly planing in my book and these photos of a NT26 in our yard show a bottom more capable of partly planing that many or even most on this forum. Owner says 10 knots w 55hp Yanmar.

Semi disp? Partly disp. Sounds like a hull closer to planing that has some tendency to perform fairly well at speeds that turn a planing hull into a dog.

I think the NT is not FD or planing and most use the term semi-disp. I'd like to see more rocker or/and a more convex aft buttock line ... the curve of the aft run. In other words semi disp but closer to FD.

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Definitely semi-something...

manyboats said:

Sail boats, canoes, kayaks and freighters are all FD types all for the same reason. They are the most efficient. So "When I keep my hard chine planing hull boats at or just under their mathematically calculated WLL hull speed the fuel efficiency is near or equal to FD, or SD, or SP hulls of similar WLL and weight" apparently just isn't true. When efficiency is really important FD boats are universally chosen.

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WOW!!

A wind driven type of midsized boat, two tinny tiny paddle type boats, and an enormous commercial ship... all four boat types related in one sentence as being very similar to one another and all FD for the same reason... i.e. sail boat, canoe, kayak, and freighter in the same breath!! And, all lumped onto one similar Displacement hull comparison as pertaining to and evidently in competition with planing hull design...

Again, WOW!!

Let's see now... A planing sail boat for wind drive with deep draught and heavy keel. A planing canoe for paddle or rowing propulsion. A planing kayak for small paddle use. A planing freighter with hull draft of 15' to 45' depth and umpteen tens of thousands hp, multi story tall, bunker fuel powered engines. Naw... planing hull design just doesn’t seem to fit into any of those boat categories!

But, then of course, then there is the category of pleasure-boat trawlers; for which, I believe, TF exists. These size and weight boats are light enough to accommodate nearly any shape hull design that can be use-friendly toward capabilities of single or twin engines that provide either low or high horsepower for slow or fast cruising.

Interesting thing is: Nearly any type hull design becomes quite efficient (regarding sipping fuel for increased nmpg) while “slipping” through the water at slow speeds... especially when low power, efficient engine or engines is used for propulsion. That includes D, SD/SP and P hulls!

Displacement Trawler hulls are great! Semi-Displacement/Semi-Planing Trawler Hulls are Great! Planing Trawler Hulls are Great!

I am in favor of any hull design that any boat captain may like to own and/or pilot...

I need say no more!

Interesting bottom...

Calafuria....canoe stern and flat planing surfaces aft...

Northern Spy said:

Definitely semi-something...

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Of course ........ Semi Displacement ...... in fact and in the vernacular. I'll stop talking semi planing as it just muddies the waters here. If one wanted to be vogue one could say crossover. I hate vogue.

In your broadside drawing of the 26 the rocker is a tad bit more noticeable but the photo I put up shows a very straight run aft ..... or set of buttock lines (if you prefer) and they are evident in the drawing. Looks to me like the NT26 is about 60% planing and 40% disp. But w the bow in the air and the stern down (at speed) the aft section assumes a position parallel w the horizon. This is a much more planing shape at that angle allowing near planing performance. And as NT says ..... "go fast go slow". If the NT32 had more rocker and considerably steeper buttock angle then I'd REALLY have to have one. And it would be powered by about 55hp. And be almost a knot faster than Willy.

Oh yes I remember the Cutter 28. It was marketed as a motor home/cruising boat. Like the flying car it didn't sell.

I would call that a sculpted stern on a planing hull. Definitely a planing hull ..... just like the Bartender .. and Sea Dory.

Art I accept your opinion as an alternative way of thinking.

manyboats said:

Art I accept your opinion as an alternative way of thinking.

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Thank you Eric - As I do accept your opinion too!

After all... we're really just a bunch of "old sats" having an internet powered banter fest on marine items. Main thing is to enjoy "Tawler Life", and, maybe even learn a bit o' new things too!

manyboats said:

I would call that a sculpted stern on a planing hull. Definitely a planing hull ..... just like the Bartender .. and Sea Dory.

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OK...but why would they go through the expense to "sculpt"....might it have a function at hull speed? Might this be the elusive FDP hull?

If a boat is light for it's length, it will be efficient in operation, no matter what the operating speed or hull form. Ray Hunt's earliest planing deep-vees were rather efficient, throughout the speed range, because they were very light. They had the hard chine above the at rest waterline, unfortunately this also meant they were tippy at rest, so he added a free flooding ballast tank that self-dumped under way. Their waterlines were very fine and the boats could slip along almost as efficiently as any displacement hull at "Hull speed". Not quite as efficiently, but the difference is so small it can only accurately be measured in a test tank with finely calibrated instruments.

No wide and heavy semi-displacement or planing hull would ever be considered efficient in operation, but it may well be very efficient in other ways. As the operating cost increases the market appeal decreases, thus the boat may become a better buy (more boat for the dollar). Especially if you are looking at something with 30 year old V8 or V12-71's....replace those with a nice pair of JD's and have a 12 knot cruiser at reasonable cost.

But that sound of twin water cooled DD 12-71 's sure gets my heart pounding.



WOW moments

Tad Roberts said:

No wide and heavy semi-displacement or planing hull would ever be considered efficient in operation, but it may well be very efficient in other ways. As the operating cost increases the market appeal decreases, thus the boat may become a better buy (more boat for the dollar). Especially if you are looking at something with 30 year old V8 or V12-71's....replace those with a nice pair of JD's and have a 12 knot cruiser at reasonable cost.

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Bingo! Some of the nicest trawler style boats around are those over-engined semi-displacement twins that came from the speed wars we've been discussing in the "3208 thread". The time is approaching when an owner will be able to recover the cost of investing in a repower for those hulls. Some of the mid to late 90's Grand Banks come to mind...also some Hatteras models (not exactly Trawler Forum fare, however). Might even be time for an enterprising soul to start thinking about designing retrofit kits for selected models.

markpierce said:

It's a car-carrier, having left Benicia and presumably heading to Asia for another load. There are large hatches on the transom as well as on the beam, and with built-in ramps, the vehicles are driven off/on the ship.

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Today's (took photo today) car-carrier at Benicia, here showing the transom ramp.

Take this

I hate to be left out and since everyone on TF is "mooning" each other with their bottoms...... take this!

Properly categorized in nautical terms, this hull type is generally referred to as bizarre.

Note: The barnacles are for ballast to reduce roll.

Tad Roberts said:

If a boat is light for it's length, it will be efficient in operation, no matter what the operating speed or hull form. Ray Hunt's earliest planing deep-vees were rather efficient, throughout the speed range, because they were very light. They had the hard chine above the at rest waterline, unfortunately this also meant they were tippy at rest, so he added a free flooding ballast tank that self-dumped under way. Their waterlines were very fine and the boats could slip along almost as efficiently as any displacement hull at "Hull speed". Not quite as efficiently, but the difference is so small it can only accurately be measured in a test tank with finely calibrated instruments.

No wide and heavy semi-displacement or planing hull would ever be considered efficient in operation, but it may well be very efficient in other ways. As the operating cost increases the market appeal decreases, thus the boat may become a better buy (more boat for the dollar). Especially if you are looking at something with 30 year old V8 or V12-71's....replace those with a nice pair of JD's and have a 12 knot cruiser at reasonable cost.

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Somewhat similar to the conclusions I was reaching,...that weight is a very important factor in ANY vessel that wants to plan off, or semi-plan. In some cases even more important than little subtities in hull shape.

It makes me wonder about the claims for much better performance by the Gerr hull shape, the SRD hull shape, the box-keel shapes etc. Are these more exagerated hull forms really that much more speed capable??

Passagemaker Magazine - May/June 2013

SRD is a better hull shape, fast, fuel efficient, stable

Capt Kangeroo said:

I hate to be left out and since everyone on TF is "mooning" each other with their bottoms...... take this!

Properly categorized in nautical terms, this hull type is generally referred to as bizarre.

Note: The barnacles are for ballast to reduce roll.

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Yo Capt K - What are the handling qualities on boat with that bottom... in various conditions? Sure is an unusual/interesting/unique bottom design for a fairly large boat... I like the entry profile and question closeness of the twin screw. I'd like to see reports from a test tank. Also, are the picts’ shapes at all altered compared to the view if seen by naked eye?

Art, Your quite right, it is a bit of an optical illusion. The hull actually flattens significantly as it tapers in and rises toward the transom. Essentially it has a beer belly, the widest, deepest point on the hull is approx midships. It would appear as slow as a slug but unbelievably it topped out at 19 knots during survey.

I have no idea yet how it will handle in rough seas but in 6ft of chop in the Gulf it had the stability of a cement dock, cut nicely and gave a dry ride. It does roll more than I'm used to, but not uncomfortably so.

Regarding the closeness of the screws, it may also be a bit of an illusion. While they may in fact be closer than normal it does not appear unusual when viewed from the stern.

Rough specs are 38 ton, 4'6" draft, 17'6" beam, 50ft, power 750hp

Capt Kangeroo said:

Art, Your quite right, it is a bit of an optical illusion. The hull actually flattens significantly as it tapers in and rises toward the transom. Essentially it has a beer belly, the widest, deepest point on the hull is approx midships. It would appear as slow as a slug but unbelievably it topped out at 19 knots during survey.

I have no idea yet how it will handle in rough seas but in 6ft of chop in the Gulf it had the stability of a cement dock, cut nicely and gave a dry ride. It does roll more than I'm used to, but not uncomfortably so.

Regarding the closeness of the screws, it may also be a bit of an illusion. While they may in fact be closer than normal it does not appear unusual when viewed from the stern.

Rough specs are 38 ton, 4'6" draft, 17'6" beam, 50ft, power 750hp

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Cool!! - Keep us up to date. TY, Art

Re Marks post 259 it can clearly be seen that the transom is completely out of the water.

brian eiland said:

Somewhat similar to the conclusions I was reaching,...that weight is a very important factor in ANY vessel that wants to plan off, or semi-plan. In some cases even more important than little subtities in hull shape.

It makes me wonder about the claims for much better performance by the Gerr hull shape, the SRD hull shape, the box-keel shapes etc. Are these more exagerated hull forms really that much more speed capable??

Passagemaker Magazine - May/June 2013

SRD is a better hull shape, fast, fuel efficient, stable

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Weight and length (waterline) are by far the most important factors in any hulls performance. Much smaller issues are the sectional shape, entry and exit shapes, CP and volume distribution, propulsion effectiveness, appendage drag, etc......

In general claimed superior performance is not real, or may only apply in very limited circumstances. Boatbuilders have been claiming technical advances in search of sales for ever.

I've already stated that the numbers in that Passagemaker article don't make any sense. Perhaps they did back in the time of wishful thinking before Summer Kyle was built. The original published numbers had her displacement at 16000 pounds and top speed 16 knots with 170 HP. In reality she comes in at 22,000 pounds and manages 11+ knots with 220 HP. But it will take more like 90 HP to achieve 11 knots, and not the 60HP that 3 gal/hr indicates. If she will get to 11 knots with 90HP and only tops out at 11.5 (with 220HP), I would suggest this hull would never reach 16 knots even with 500 HP.....Unhappy at speed.

Walter Schulz (SRD) is very cagy about giving out any hard and accurate numbers. He claims the SRD is "the most efficient powerboat on the market at speeds over 10 knots." but of course no numbers are available for comparison with other boats. I did some comparison years ago from numbers published in a magazine review of the SRD38. It was obvious there was no advantage to the form and I could see a standard round-bottom Lobster hull (semi-displacement) of the same length and weight would be as or more efficient.

I seem to recall an article in PMM about the SRD and was very taken by it all but never thought of it as being ultra efficient. Level riding, Low wake, probably a very nice ride punching through 3' waves and perhaps level riding at slower speeds too.
Of course it's so far out of my money range even if it did say something about efficiency I probably promptly forgot about it. Besides people that have enough money to buy something like that don't care about fuel burn.
I still think it's a very good design for a medium speed boat as very few venture into that speed range.
I do see it as something far superior to a lobsterboat w a huge following wake and the power lost making it.
Even a FD boat will benefit greatly from weight reduction. As in 25% weight loss = 25% power requirement reduction. So if you can get your GB to weigh half as much it will burn half as much fuel ... and probably be a much drier boat too. That would be nice to watch. A 36GB weighing 17Klbs making 15 knots riding high and proud.

The October, 2013 Power and Motoryacht has a short interview with Walter Schultz in regard to the new Shannon "Defiance 46". LOA 45'11'', weight @36,000. The magazine says there will be a complete test in an upcoming issue. The boat has a single Cummins @ 600 HP (or twin 330s) for high speed cruise...plus a 200 HP Cummins driving twin sail drives for low speed. Schultz says the hull is a combination of four hull shapes with reverse deadrise in the aftermost 10 feet. Cruise is advertised as 8-12 knots with top of 17.9.

Boatgm said:

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Those pontoons used as "ballast blow tanks" when the skipper decides to do some submarine action??

Kidding aside... What is the speed and fuel use stats on that monster and how does she handle with those pontoons in some really rough, conflicting seas? I mean 30 to 35 foot close duration seas with wind driven breakers atop... not just some 6 to 8 foot white cap chop atop lazy long duration rollers!