Shannon 46 with SRD hull fuel consumption

Anyone look at the performance numbers for the subject boat as listed in the May issue of PMY magazine? 6.9 NM/G @ 8.3 kt, 4.2 NM/G @ 12.2, 2.8 NM/G @ 15.9. 39,000 lb, 46 OAL. These numbers are for the single 600 HP Cummins. Another set for the second engine...a 220 HP Cummins powering hydraulically driven folding sail drives show even more remarkable numbers at very slow speeds. Data was taken by the testers and not given to them by Mr. Schultz.

Must be something to the SRD hull design. The trans-plane and slow plane numbers caught my eye.

Mighty skeptical of those burn rate numbers on a vessel that size and weight.

When I read the article could not believe the burn rate much too good to be true. I have become very skeptical of magazine fuel claims. Also remember in real life boats gain significant weight in first year after initial launching. If a boat is particularly light and has an efficient hull good burn #s are to be expected and I don't see that in this boat.The MJM is an example of a boat that gets good fuel burn based on light build. Some catamarans can also do well. There is no consumers union for marine products that will go and test this boat and give us an unbiased opinion.

Numbers are screwy.....you don't get 16 knots in a 46' boat using 110 HP (5.67gph). The max burn is only 20gph? That's around 400 HP......?

Tad Roberts said:

Numbers are screwy.....you don't get 16 knots in a 46' boat using 110 HP (5.67gph). The max burn is only 20gph? That's around 400 HP......?

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Yes, well, like I said "remarkable numbers". Some oddities between fuel flow between the big single and small twin prop numbers as well. The magazine says their data were taken using two way gps average and the Cummins instrumentation for fuel flow....

I think the reverse deadrise aft will deliver an efficiency advantage at a certain speed recouping some of the energy lost in the boat's following sea. The shape is wrong aft for FD speeds and for planing speeds but somewhere in the SD range there should be some benefit irregardless of whether these numbers are right or wrong. This certainly isn't the last word on the SRD Shannon.

Some (magazine test) numbers for the single 220 engine driving the hydraulic pump that drives the twin folding props (18x15) on the sail drives....


RPM KT GPH NM/G
1200 5.9 .6 9.8
1800 6.6 1.7 3.9
2200 7.2 2.8 2.6
2600 8.9 4.3 2.1
3000 9.8 6.4 1.5

By the way, the prop on the 600hp single is a 26x22.

Have not seen the article but at least part of the efficiency might be explained by the use of hydraulic drives. As I understand a hydraulic drive system, there is no transmission, the hydraulic motor turns the shaft directly and controls shaft RPM. The engine simply powers a hydraulic pump. Using an accumulator to even out engine/pump loads, along with the gains from no transmission friction, could lead to more efficient fuel usage numbers. That is before any effect the may come from the SRD hull shape.

The transmission losses in a hydraulic drive is greater than w gears. Pumping hydraulic fluid through the system of hoses, pumps and hydraulic slave motors takes more power than turning gears and bearings in a typical gear drive. There are many advantages to hydraulic drives but efficiency isn't one of them so it is usually not employed for a prime mover.

I am not overly impressed with the 220 motor at 3000 rpm and burning 6.4 gal/hr rule of thumb gets you about 120hp at that burn rate. My 34,000 lb boat with a 46 ft WL and twin 330 hp motors does 9.6K for 7 gal/hr. If I drop down to 9.2 K closer to hull speed the fuel burn is between 5-6 Gal/hr. While the 220 motors #s are good why go to the trouble of the second small motor with extra props and gear when a twin on a standard hull does almost the same. Also my total hp is similar to the big motor and the extra maneuverability of a twin is a plus. The whole concept of the three props seams overly complicated.

>As I understand a hydraulic drive system, there is no transmission, the hydraulic motor turns the shaft directly and controls shaft RPM.<

A std boat transmission is usually figured at a 3% power cost.(Twin Disc)

Hyd , depending on optimization will usually cost 15% to pump and another 15% , when used.

Some modern expensive setups claim to cut the losses in half , to only a 15% COST OVERALL.Aircraft priced.

For systems operation , windlass , bow thruster, cruise generator, boat hoist,, Hyd is the gold standard , but never for propulsion in std type boat.

When boat numbers are 10% better , I say great design,BRAVO!

when they are claimed 200% or 300% better , I think BS , physics is physics .

I went to the Shannon web site and looked up what numbers they advertise. At 10 knots they say 2 miles per gallon. at 15 knots they say 1.6 miles per gallon. Note miles per gallon, not knots. Given this maybe the magazine had some typos. These numbers are very good but more in the believable range for me.

I just sent PMY a note suggesting that they recheck their fuel burn data. Getting fuel burn numbers wrong on a boat whose claim to fame is efficiency should be cause for concern among the editorial staff.

eyschulman said:

The whole concept of the three props seams overly complicated.

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It is overly complicated, inefficient too. Mentioning hydraulic drive and efficiency is the same sentence is silly. Hydraulics are great for moving continuous power around the boat, but there are losses. Heat, noise, and vibration are some of the issues. The sail drives are high-maintenance and added drag that never goes away.

This kind of stuff is preying on the inexperienced, selling people complexity in the name of reliability and safety. It's neither of those things.

FF said:

>As I understand a hydraulic drive system, there is no transmission, the hydraulic motor turns the shaft directly and controls shaft RPM.<

A std boat transmission is usually figured at a 3% power cost.(Twin Disc)

Hyd , depending on optimization will usually cost 15% to pump and another 15% , when used.

Some modern expensive setups claim to cut the losses in half , to only a 15% COST OVERALL.Aircraft priced.

For systems operation , windlass , bow thruster, cruise generator, boat hoist,, Hyd is the gold standard , but never for propulsion in std type boat.

When boat numbers are 10% better , I say great design,BRAVO!

when they are claimed 200% or 300% better , I think BS , physics is physics .

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Agreed! - - > physics is physics!


To enable the nearly unfathomably bettered (increased) nmpg mentioned in OP of this thread would mean that the entire hull design to weight ratio of a boat, as well as energy use improvements via fantastic new propulsion system, would need to be hands down revolutionary as compared to previously available items. If those numbers [6.9 NM/G @ 8.3 kt, 4.2 NM/G @ 12.2, 2.8 NM/G @ 15.9. 39,000 lb, 46 OAL] are true... well then... there is a whole new sunrise about to dawn on the pleasure boating industry!

IMHO: Either - Something went askew in the tests / Misprint occurred / BIG ol’ FIB!

If those numbers are correct... I want one! If I like its build, design and handling capabilities that is!!

Happy Boating Daze! - Art

PS: Damn nice boats... Well worth watching videos!
http://www.shannonyachts.com/shannon_srd_videos.html

I visited Shannon Website - Nice Boats! Really good nmpg numbers that I highlighted below... probably accomplished before loaded with owners gear?? Sounds inviting. Enough improvement to set the boating industry on a BIG upswing? Well, SRD hull may help somewhat.

Quote:

"SRD Fuel Efficiency"

"Based on independent testing, the SRD hull, with a single engine or twin engines, is the most fuel efficient powerboat on the market at speeds over 10 knots/12 mph. While the SRD hull can easily reach speeds of 25 knots/30 mph or greater depending on engine horsepower, the hull provides exceptional fuel economy in the 10 knot /12 mph to 18 knot /20 mph speed range. At 10 knots, the SRD obtains almost 2 miles per gallon, or the same fuel burn found on a full displacement trawler at top speed. Traveling at 15 knots, the SRD provides over 1.6 miles per gallon, whereas a modified vee planing hull struggles to provide 1 mile to the gallon at the same speed. The fuel efficiency of the SRD hull translates into 60% less fuel burned, increased range and a significant reduction in pollution."

Tad-I would be interested in any comments you may have regarding the hydrodynamics of the "SRD" hullform. I pulled up the Patent application and it is quite interesting (if anyone wants to see it go tot he PTO website and do a quick search on "reverse deadrise"). The actual hullform as described is definitely different. A typical deep "V" entry (55-58 degrees)from bow to about 40% of WL length. Then the :twist to a reverse deadrise that actually creates a hollow area from 40% to about 70% of the WL length. This seems to almost create something like sponsons along the chine. The hollow is said to create water turbulence and substantially decrease wetted surface friction as well as directing flow to the aft 30% of the WL length. That aft 30% is virtually flat, with a small (about 10 degrees) reverse deadrise. Together, these two features supposedly produce the lift and result in the performance using less power and fuel.

Several things stand out to me:

1. The hull form would seem to have very little directional stability on its own, there is no keel to speak of and the reverse at the chines does not seem sharp enough to provide it.

2. Very little hull volume, these have to be "picninc" type boats, the 36' draws only 2'.

3. Although the boats tested apparently had almost traditional drives, the patent states that surface piercing drives would be the best option. That makes some sense as I am not sure what effect on props and efficiency the turbulence in the hollow are infront of the props would have.

4. The design seems to really operate in a vary narrow envelope as shown by the patent app and the test posted above. That is, from about 12 knots to about 16, maybe 18 knots. At displacement speeds there seems to be little gain and there is no discussion of its ability to run at true planning speeds, say 25 knots+.

Tad, if you can enlighten us any further, I would appreciate any comments.

For whatever it's worth, I seriously looked at the SRD38 a few years ago, the first SRD from Shannon (a smaller version of this boat).

I can't comment on the new 46, but THD, I noticed several of your observations. The boat was "small" for a 38, with a narrow beam and a sort of 'pinched' bottom design which resulted in a small cabin. It felt a lot like a 34-ish ft sailboat inside.

We ultimately sea trialed two different boats, one with twin engines, and one a single. Walter Shultz was very big on surface piercing drives for the boat, but both of the ones we sea trialed had conventional drives.

I personally loved the performance of the boat. It struck me as having some similar design elements and characteristics of powerboats of the 1930's - narrow beam, light weight, and as a result, more easily driven with less power. The combination of the deep forefoot and narrow beam gave them a very stable, smooth, wave-piercing ride, very different from any planning hull I've ever been on.

They both accelerated very quickly (one had twin 150 hp, the other a single 440). I can't comment on the total performance envelope, but each one seemed to comfortably cruise in the mid-high teens, and were completely unperturbed by waves and chop. It was almost uncanny, how this light and relatively small-ish boat was able to handle waves so well, and at speed. It was both a smoother and faster ride than lobster boats I've been on. That speed range ("semi-displacement", "semi-planning", whatever you like to call it) is where we like to be, so a cruise speed in the teens was perfect.

I found Walter Shultz to be delightful to talk with. He was (understandably) very passionate about and a big champion for his SRD design, I think deservedly so. He seemed very knowledgeable, and the boats showed a lot of attention to detail and seemed well-built. I can't comment on the performance specs in the magazine article, other than to say it wouldn't be the first time a magazine article had errors in some of the data they report and might later have to correct it. I seem to recall at the time the SRD38 getting about 2 nmpg at cruise speed, which struck me as about 50%+ better than either a conventional planning or a 'semi-displacement' hull. I would suspect the figures they quote on their website are the right ones.

In the end, we didn't buy one, mostly because a new SRD38 was just out of our budget. Despite the relatively tight interior, if it was less expensive, we probably would have bought one. The single engine boat we looked at was used and I thought a good value, but I moved too slowly and it sold before I could move on it.

I don't think Shannon made very many of the SRD38, maybe half a dozen? The boat is too different from what most buyers are looking for. It's not beamy with a spacious interior so it wouldn't be a good party barge or dockside condo, and the tight interior of the 38 also wouldn't lend itself to the long distance cruising many trawler owners do (it would have worked for us since most of our trips are short). I haven't seem a SRD46, but it seems like a smart move for Shannon, to make a bigger version to address one of the main design limitations of the previous 38, the tight interior.

The whole hydraulic drivetrain and second engine with saildrive seems overly complicated, unnecessary, and silly to me, for all the reasons previously discussed - the boat gets noticeably better fuel economy than others just with a conventional drivetrain, so why make it complicated? The price of the SRD46 is way out of our budget, but it would be on my short list (with conventional drive) if we ever win the lottery.

Yes Nick I agree that the advantages of the Shannon SRD are mostly in how they ride through the water. SD is always a hard nut to crack but retaining the soft and easy riding features of the FD hull fwd and controlling the tendency to squat is in combination is indeed IMO way ahead of the lobsterboat types even if the SRD didn't burn less fuel.

Also the fact that newer and advanced design features for SD hulls are rare IMO and the Shannon design should command a great deal of respect for that alone. PMM thought it was worth a full blown article w a cover pic included.

I don't think TAD is that thrilled w it and I question the SRD's following sea capabilities myself but it's definitely out of the box and I like and respect that.

I'm pretty much with Fred and Art, "Physics is physics".

The biggest factors, by a huge margin, in any boat's performance, are length on the waterline and displacement (weight). Next most important factor is getting the volume correctly distributed for the expected speed. (this is where most go wrong) Then come smaller factors like beam, depth, sectional shape, etc.

Build three boats, a Hunt style deep-vee, a round bottom Maine Lobster boat, and an SRD form. Identical length, beam, displacement, engine, gearbox, shaft strut, prop, and rudder. I guarantee performance (HP vs Speed) for all three will be within 5% of each other. And at that critical 10-15 knot speed range the Lobster hull will be best.

When the SRD38 first appeared I did some comparison with a typical lobster boat hull of the same length and weight. I could not find any huge performance gain, in fact I couldn't see any advantage at all.

If you go back a few years in Shannon Yachts history you find a boat called the Shoal Sailer. Graft a big square box with a concave bottom on the back of a Shoal Sailer and you have a SRD38. I really thought it was creative re-purposing of an existing tool.....

Manufacturers almost never (actually never) substantiate their comparison claims. "the SRD hull translates into 60% less fuel burned" really? Less than what? Which boat is it being compared to, what is that boat's weight and length, what speed are we talking about, and what are the load conditions of each test? And also are the numbers accurate?

I really don't get the surface drive idea for the SRD. I have done some high speed (like 65 + knots) surface drive boats and they make little sense at less than 25 knots. At 10 knots and lower they become (IMO) horrible.

Finally Endurance makes some comments about ride quality. That's a whole other conversation and one I can't address never having been aboard the SRD. Again from a technical viewpoint I would expect the SRD to have a quick motion, being light and shallow. Also the form will have great roll damping due to the large built-in convex damper back aft.

THD's questions.....

1. I think the drawing shows a central keel aft (ending a long way forward of the transom). But generally this boat will have minimal directional control with small keel fin and tiny rudders. But a small keel and tiny rudders reduce drag and thus fuel consumption, which sells boats. I'll guess a decent bow thruster will facilitate docking.

2. Small volume means light weight and efficiency. Having tried myself to sell small volume efficient boats I know it's pretty much not going to work.

3. See my note above, makes no sense.

4. Ideally all powerboats would be designed to operate within a very narrow envelope. That way the hull form, powerplant, and propulsion system could be really efficient at that one speed. Unfortunately that's not the way people work. For boatbuilders the investment in a hull tool is huge and they want to spread that investment as wide as possible. So they put different engines or deck or interiors on one hull, and it's less than ideal....sometimes a lot less.

If a boat is going to run over about 15 knots in any sea, it' better if it has some deadrise at the transom (IMO). I know there are big sportfishermen out there with zero deadrise at the transom, but I think a Bertram is more comfortable.

Tad-thanks for the comments.

I should add that in the Patent Application there was one humorous comment, although I am sure Schulz was not being funny. When discussing FD hulls, he noted the standard speed limit defined by waterline length and commented that adding power could not increase speed and that the hull, in his words, began to "sink" in the water, a reference I am sure to the notorious stern squat of FD hulls. But then he followed that by saying a FD hull would actually sink if driven too fast, it would drive itself right into its own hole in the water! I guess the moral for many of us is to beware overpowered FD boats!

I think one of the things one can learn from the Shannon 46 article is that stuff we read in magazines is not always accurate. When I read technical or scientific information in magazines or news print where the publishing entity is not known for scientific accuracy and the material is something I know about it is amazing how off base the published statements can be. My best guess is that the people assigned to write the articles may know something about writing but little about what they are writing about. The fuel burn anomaly figures published in a boating magazine regarding the Shannon 46 should have set off alarms for any knowledgeable boating person involved with boat performance testing. There should have been an attempt to substantiate before publishing and if proven true this should have been a front page breakthrough article. I personally find much of the boat magazine boat test articles to be free advertising with a very rosy tint,and In our present business culture truth in advertising is what ever you can get away with.

THD said:

I should add that in the Patent Application there was one humorous comment, although I am sure Schulz was not being funny. When discussing FD hulls, he noted the standard speed limit defined by waterline length and commented that adding power could not increase speed and that the hull, in his words, began to "sink" in the water, a reference I am sure to the notorious stern squat of FD hulls. But then he followed that by saying a FD hull would actually sink if driven too fast, it would drive itself right into its own hole in the water! I guess the moral for many of us is to beware overpowered FD boats!

Click to expand...

Apparently back in the days when the large ships were all sail driven, there were a number of cases where they didn't reduce sail in time and literally sailed right under water.

THD said:

I should add that in the Patent Application there was one humorous comment, although I am sure Schulz was not being funny. When discussing FD hulls, he noted the standard speed limit defined by waterline length and commented that adding power could not increase speed and that the hull, in his words, began to "sink" in the water, a reference I am sure to the notorious stern squat of FD hulls. But then he followed that by saying a FD hull would actually sink if driven too fast, it would drive itself right into its own hole in the water!

I guess the moral for many of us is to beware overpowered FD boats!

Click to expand...

And, the other moral of the story:

Own Really Well-Built / Well-Designed Planing Hull Boat!

Just Sayen!

Happy Boating Daze! - Art

eyeshulman,

Post #22

Spot on!

All the blither in the patent application was just to create a fog of difference in attempting to patent an old concept.

The Atkin folks used both reverse deadrise and box keels at the end of WWII.

These were published as plans in Rudder and Motor Boat in the 1950 era when folks might build a boat in their back yard.

The Seabright Skiff is known for efficiency (as well as being beachible) a gent named Rob White built an 18? ft version that got over 30mpg , at speed.

It was a version of the Rescue Minor .

The reverse deadrise does keep the boat level at slower speeds than pure plaining would.

Remember a boat really does not squat, it simply follows the water surface as it attempts to climb up and on top of its own bow wave.By pressurizing the stern to lift the boat stays level , so the boat begins to ride on the bow wave , and not climb it at a steep angle.

There is also some efficiency gained by the prop being parallel with the water , and recieving already accelerated water from the flow from the box keel aft.

The effect seems to peter out at over SL 2.6 or so and at SL 3 a genuine plaining hull is considered better.

With modern materials and todays light weight engines a more efficient cruiser that could go 12 --15K , burning 3 -6GPH GPH rather than 15GPH should not be hard to do. DL>100.

Perhaps tho the boat would have to be sold outfitted as the Huckins were , everything is aboard as sold , to prevent staggering weight increases by owners.

I looked into this as my first choice for a box boat , a cruiser to be shipped inside a Sealand container , at far less cost than actually motoring to the destination.

New England to down under , fly over , un box the boat and cruise away.

Yes the boat would be slender with about 7ft 6 in beam , but at 39 ft should be comfortable for a crew of 2 or 4 to explore new places ,even for months..

My concept is to have just the hull built , and install a used car engine to actually measure the performance.

If its crap, sell the hull to fish guys .

If works as well as Atkin claimed , the boat could go back in the box to have the interior and the rest installed.

The stability would be augmented with a center board style lowering , powered stabelizer.

Even cruising in the USA , where the USCG has given up the water to state and locals who install moorings in THEIR waters to rent , there is plenty of free space for a boat that doesnt mind a few hours aground during the visit.

The narrow hull would provide a superb seakindly ride , with a bow cockpit (Midnight Lace style ) the boat should be a very enjoyable cruiser.

FF said:

All the blither in the patent application was just to create a fog of difference in attempting to patent an old concept.

The Atkin folks used both reverse deadrise and box keels at the end of WWII.

These were published as plans in Rudder and Motor Boat in the 1950 era when folks might build a boat in their back yard.

The Seabright Skiff is known for efficiency (as well as being beachible) a gent named Rob White built an 18? ft version that got over 30mpg , at speed.

It was a version of the Rescue Minor .

The reverse deadrise does keep the boat level at slower speeds than pure plaining would.

Remember a boat really does not squat, it simply follows the water surface as it attempts to climb up and on top of its own bow wave.By pressurizing the stern to lift the boat stays level , so the boat begins to ride on the bow wave , and not climb it at a steep angle.

There is also some efficiency gained by the prop being parallel with the water , and recieving already accelerated water from the flow from the box keel aft.

The effect seems to peter out at over SL 2.6 or so and at SL 3 a genuine plaining hull is considered better.

With modern materials and todays light weight engines a more efficient cruiser that could go 12 --15K , burning 3 -6GPH GPH rather than 15GPH should not be hard to do. DL>100.

Perhaps tho the boat would have to be sold outfitted as the Huckins were , everything is aboard as sold , to prevent staggering weight increases by owners.

I looked into this as my first choice for a box boat , a cruiser to be shipped inside a Sealand container , at far less cost than actually motoring to the destination.

New England to down under , fly over , un box the boat and cruise away.

Yes the boat would be slender with about 7ft 6 in beam , but at 39 ft should be comfortable for a crew of 2 or 4 to explore new places ,even for months..

My concept is to have just the hull built , and install a used car engine to actually measure the performance.

If its crap, sell the hull to fish guys .

If works as well as Atkin claimed , the boat could go back in the box to have the interior and the rest installed.

The stability would be augmented with a center board style lowering , powered stabelizer.

Even cruising in the USA , where the USCG has given up the water to state and locals who install moorings in THEIR waters to rent , there is plenty of free space for a boat that doesnt mind a few hours aground during the visit.

The narrow hull would provide a superb seakindly ride , with a bow cockpit (Midnight Lace style ) the boat should be a very enjoyable cruiser.

Click to expand...

Fred - I hope you do that.

Your depiction of boat size, design, material, and greatly reduced fuel burn interestes me VERY much. If as you conjecture: "With modern materials and todays light weight engines a more efficient cruiser that could go 12 --15K , burning 3 -6GPH GPH rather than 15GPH should not be hard to do." And, I say, if that ratio could be held true for the 39' loa x 7'6" beam boat you mention... well... I feel you would have designed/created a "sales winner" in the pleasure boating market.

Good Luck! - Art

Art why did you need to quote that whole lengthy post? Seems totally unnecessary to me.

I think the lightness of the Atkins type box keel (actually called a "Seabright something") has more to do w it's perceived efficiency than the hull shape. The small prop and large wetted surface needs to be overcome w a feature that imparts a LARGE advantage in efficiency to overcome the small prop and large wetted surface.

Because of the fairly horizontal prop shaft and levelish running attitude some box keel designs may be more efficient that "some" other designs but I don't see it as a clear advantage to the type. Efficiency may not be an advantage of some heavier BK boats (for example those that resemble tugs) but the boat FF refers to (the Atkins River Belle I think) probably does have an efficiency advantage mostly because of her light weight and narrow beam.

I do like the River Belle and lots and lots of the Atkins designs. http://www.atkinboatplans.com/Cruisers/RiverBelle.html
I had a Sumner Craft boat that was a variation of the box keel concept. It was light also (composite) but had very soft chines and a rounded "box" kinda like a torpedo. A bit like a lobster boat powered by a torpedo bolted to the center of the bottom.

FF what is the status of your project or project to be. Sounds like it's still in the "to be considered" category. I thought about building "Tang" but I probably won't.

manyboats said:

Art why did you need to quote that whole lengthy post? Seems totally unnecessary to me.

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GEEEE - Sooo Sorrrrry Eric. Any other posting instructions for me?

Cheers! Art

Been waiting for somebody cool enough to jump on.

Thanks for being cool Art.