Reply
 
Thread Tools Display Modes
 
Old 05-17-2009, 06:01 PM   #1
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,723
Single v/s Twin

Expert opinion:
From a question/answer feature in Boat US (May) by Chuck Husic, Engineer, pilot and past president of Chris Craft says " I know no reason to assume that using two 100 hp engines will result in less thrust than a single 200 hp engine, other than the effects of prop selection and hull influences that may favor a single engine mounted low in the boat where the lesser prop shaft angle can improve efficiency ."

Eric Henning
__________________
Advertisement

Nomad Willy is offline   Reply With Quote
Old 05-17-2009, 09:33 PM   #2
Guru
 
City: Carefree, Arizona
Country: usa
Vessel Name: sunchaser V
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 6,376
RE: Single v/s Twin

Just who is buying all these high HP GB / Eastbay twin engine yachts? It would be interesting to see the real sale numbers for these new twin engine GBs, OAs, Offshores, Flemmings etc. Speed does have its followers, big entry $$ required of course. Saw a new Flemming 65 at the Anacortes PMM trawlerfest, a cool $3M.*

I'm about worn out on the single vs twin "debate." It really doesn't matter for 99% of us who will never do a true bluewater voyage and wnat to squeeze out the last 5% of gph/knots.*Even Dashew struggled with the FPB single vs twin decision. Lets do a twin vs triple IPS debate. Whew, on second thought ---
__________________

sunchaser is offline   Reply With Quote
Old 05-18-2009, 11:31 AM   #3
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,723
RE: Single v/s Twin

Tom,
** I only got into this as a result of some here telling newbies that single screw was something to look for in a trawler.* The old wives tale is deeply intrenched so Im not looking for converts (unless something really new comes up) and made the post yesterday only as a footnote. On a related issue I've read twice lately that the ideal WOT rpm would be 50 to 100 rpm OVER max hp rated rpm. I never thought over reving would be acceptable much less prefered. Makes one wonder whats real, whats fact and even whats objective as well.

*** Eric Henning
Nomad Willy is offline   Reply With Quote
Old 05-18-2009, 03:15 PM   #4
Scraping Paint
 
City: Fort Lauderdale
Vessel Model: CHB 48 Zodiac YL 4.2
Join Date: Oct 2007
Posts: 3,804
Single v/s Twin

Quote:
nomadwilly wrote:

On a related issue I've read twice lately that the ideal WOT rpm would be 50 to 100 rpm OVER max hp rated rpm.
*
*
That is kind of a strange thing for someone to suggest increase throttle to achieve a lower power output, even if you could do that with a fixed pitch propeller.
*Going back to that old truism about propeller matching, a properly matched propeller will absorb the maximum horsepower available at the rated output of the engine. The engine might be rated to produce (for the sake of discussion) 100 horsepower at 2000 rpm. Above this rpm horsepower will drop off because of (generally) gas flow and other characteristics which reduce available torque. This means (again for the sake of discussion) that increasing rpm to 2100 might only produce 95 horsepower.
*But this is where ideal WOT thing goes off the rails. *The propeller wont demand less power to turn faster, it will demand more and if the engine cant produce that power it cant turn the propeller any faster. All that will happen is the prop will load the engine to the point it cannot increase rpm and if throttle is available will simply*reach an overload condition*and start to smoke black.
*The engine should produce a higher rpm out of gear than it will in gear with a properly matched propeller as that is the function of a correctly operating governor. In gear the governor should reach its fuel stop (full load), out of gear it should reach its speed stop (high idle). Maybe that is what those people meant to say.


*


-- Edited by RickB on Monday 18th of May 2009 03:16:13 PM
RickB is offline   Reply With Quote
Old 05-18-2009, 06:06 PM   #5
Veteran Member
 
Phuket's Avatar
 
Join Date: Jan 2009
Posts: 77
RE: Single v/s Twin

Eric, I think you will find those recommending engine can achieve more than rated RPM are referring to high output diesels in planing craft. These engines are generally pushed to their limits and are very susceptible to damaging overheats.

This is like a built in safety factor to allow for accumulation of weight on the boat and or fouled bottom. Although they do recommend that trials to get props right are done in loaded condition.

I don't think there will be too many people applying the same advice to displacement craft that are generally run very conservatively due to hull speed limitations and fuel consumption reasons. Sailboats are also often over propped, even as delivered from production boat builders. Generally though this does not cause problems as very few people push their engines hard enough to overload them even though it is possible to do so due to being over propped.

Cheers, Leon.
Phuket is offline   Reply With Quote
Old 05-18-2009, 11:28 PM   #6
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,723
RE: Single v/s Twin

Rick,
*** Your'e right. My engine develops its max power at 3000 rpm and now that it's broken in I get 3100 rpm at WOT. True there is less power at 3100 but the difference is not noticeable*(only 1 or 2%) because the power curve is extreemly flat near max output.*At first I thought I'd need to re-pitch but I got to like it. When I run my engine hard (2700-2800) there is a lot more load on it if I'm proped for 2900. Proped at 3100 I feel I can run my engine at 2800 rpm all day. Ed Auck says in Sea magazine " If a broker or seller says you can't run at WOT because it's abusive or the engines are never run that way you should know that most pleasurecraft diesels allow WOT operation up to 10% of thier life." He also says " Ideally engines should be able to reach thier absolute maximum WOT rpm with the load that is on the boat." He's talking about a prepurchase sea trial. " In most cases this means you should be*using very little trim tab in the down*position, alowing the bow to lift and ultimately reduce extra hull friction with the water. Ideally, the engines will reach their recomended 2800 rpm as in the case of CAT 3208 (or even slightly*above). The biggest concern is if the engines are below the specs. his is when you need to start asking questions to find out if the engines have always been this way or if this is a new condition. When a diesel engine cannot make it's recomended WOT rpm this is called overloading and normally causes extra wear and tear on the engine. If the engine has no actual problems causing this, like a faulty turbo or an injector, this means the engine has been operating in an over loaded condition for a period of time or possibly always. Overloading causes high combustion tempetures and pressures and takes life from the engine. This is true throughout the rpm range as your WOT spec is your gauge."

Leon,
*** High speed craft are very sensitive to hull loading/engine loading at top speed so to guard against an over loaded enigne one should prop for*a normal heavy load and watch the tach when light. I have two under proped outboards. I keep them that way so I can take 3 or 4 people aboard and pop right up on plane to cruise at 20 to 25 mph w no chance of over*reving the engines. In a displacement boat the propeller keeps us from over reving** ..* w planing craft it's the helmsman's responsibility. All craft need to get to WOT rpm. Planing craft frequently need to be under proped to deal w a wide range of loads. A high speed guillnetter would be another good example. Going out he has only a light load but while comming home he hopes to have 10000lbs of fish aboard. Actually there are more variations for planing hulls so the WOT rule should apply more to trawlers and other displacement craft.
****
**** Rick,
**** I had to really think about that. With my 37 hp engine in an under proped condition (100rpm) lets say I make 36hp at 2900, 37hp at 3000 and 36 at 3100. When I'm at 3000 and I want to go to 3100*the prop*will demand more power*and thats fine because it's only consuming about 34hp at 3000. I go to WOT, gain 100rpm and*2hp. Notice, though, that under no circumstances can I consume or develop my maximum of 37hp. Thats OK w me though. Can't tell the difference*and you guys overproped hundreds of rpm can't even deliver 3/4 power. THAT, one can notice.

**** Eric Henning

*
Nomad Willy is offline   Reply With Quote
Old 05-19-2009, 09:00 AM   #7
Guru
 
Codger2's Avatar
 
City: San Diego
Country: US
Vessel Name: "Sandpiper"
Vessel Model: 2006 42' Ocean Alexander Sedan
Join Date: Oct 2007
Posts: 5,421
RE: Single v/s Twin

Although I drive a single engine, 8.5 kt. trawler, I have recently been aboard a 39' East Bay. At 30kts I don't recall what the fuel burn was because I was so enthralled with the ride! The boat was beautifully appointed and the ride was superb. Who will buy these boats? Probably the same people that buy Mercedes, Lexus, etc. Believe it or not, there is a rather large segment of the boating world that has the money and the desire to have a fast boat and I think that portion of the market will always be there.

Don't knock it if you haven't experienced it.
Codger2 is offline   Reply With Quote
Old 05-19-2009, 10:15 AM   #8
TF Site Team
 
Baker's Avatar
 
City: League City, Tx
Country: Texas
Vessel Model: Carver 356
Join Date: Oct 2007
Posts: 5,633
RE: Single v/s Twin

Sloby, who has pronounced the end of the large planing boat???? I don't think we are there yet and we may not get there any time soon. The appetite for diesel fuel in this country is growing. Have you noticed at your fuel dock that diesel is now significcantly cheaper than gasoline now....as it should be since it is less refined AND there is no road tax on it. But the spike in diesel fuel last years was caused by the conversion of all the refining facilities switching over to ultra low sulphur diesel. That conversion is complete. And the refineries are much more capable to produce diesel this year....not to mention our slow but steady shift to diesel powered cars in this country.

Now, I think Eric got it and others didn't. I was having problems with the terminology used in this thread until Eric's post. A prop that turns a higher RPM than the engine is rated is said to be UNDERpropped and UNDERloaded. I think there were references to the opposite above Eric's post or I misread.

I am not buying into the engine losing power above it's rated RPM. My boat is rated at 3100 continuous and 3300 max for one hour. Light and clean it will turn 3600....as confirmed by a laser RPM gizmo(I thought the tach might have been off). Would the boat not slow down as RPM increases if the power decreased as well??? It does not. The speed keeps increasing as RPM increases. This theory may be true in an NA boat but maybe the turbo just keeps huffin'! I have considered getting the prop tuned because it should help with speeds in the "normal" RPM range. Before my last bottom job, it maxed at 3400RPM....so fouling did that. Obviously I do not run the boat there for any length of time as I am sure overspeeding an engine is not healthy. But I do go up there for a short moment just to open things up on occassion.
Baker is offline   Reply With Quote
Old 05-19-2009, 12:00 PM   #9
TF Site Team
 
Baker's Avatar
 
City: League City, Tx
Country: Texas
Vessel Model: Carver 356
Join Date: Oct 2007
Posts: 5,633
RE: Single v/s Twin

I disagree. Is there a slow down? Sure. And Diesel fuel now is no more expensive now than it was 4 years ago...it is a non-issue. The market will likely rebound and there we will be. People will always want to go fast. ANd the market will meet that desire. I can't imagine a 10kt sportfish!!!!
Baker is offline   Reply With Quote
Old 05-19-2009, 12:01 PM   #10
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
RE: Single v/s Twin

I still see buying activity at the local GB dealer with regards to late 90s and 2000s boats, all of which are equipped with large engines. There was a 38' Eastbay for sale for a long, long time at this dealer but I don't think this was because people didn't want Eastbays' they wanted the larger models of Eastbay. The 38-footer finally sold; some of the payment consisted of the trade-in of a GB46, which in turn is now for sale.

GB itself has said recently that the US is no longer their primary market, it's Europe and the mid-east, and their current boats, the GB44 and the new GB41, are aimed squarely at that market.

There are still a lot of people out there with a lot of disposable income. The notion that the current recession/depression has hit everyone is not correct. In Xiamen, China where I spent two months this past winter there were several large, waterside condo/marina developments under construction and billboards for large, high-speed cruisers all over the place, and a lot of brand new boats in the new marinas. At the other end of the bridge to the mainland the Nordhavn plant had a number of boats, all the 60 and 70 foot models, under construction.

On our cruise to Desolation Sound last September we met several couples with new or almost-new Flemings. Our local boatyard is just about out of space to park boats. And almost all the recreational boats being worked on are large yachts, 50 to 70 feet long (the yard has a 150 ton Travelift so can accomdate these boats).

So I have not seen any reduction in the activity at the top end of the boating scale. The huge reduction I have seen, with fewer boats being used, many up for sale, etc. is in the "middle" of the market. The people with older boats, many of them twin-engine semi-planing or planing boats, seem to have curtailed their boating activities dramatically judging by the slowdown of activity in the marina and at the fuel dock across from our slip. But the big boats, including the big fast ones, are coming and going as usual.
Marin is offline   Reply With Quote
Old 05-19-2009, 04:17 PM   #11
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
Single v/s Twin

Quote:
sloboat wrote:
So, does anyone want to discuss drive line efficiency tradeoffs/concepts/options? I really was trying to spark a little techno discussion with a twist on the single vs twin theme (the subject of the thread).

Don't know about the technology, but there seem to be a ton of suggestions for how to repower with this engine or that one, use one engine to drive two props, diesel-electric power,*and so on.* They all cite higher efficiency as the benefit.

And I expect that if one could wave a wand and have the conversion installed*and running in their boat, there would be an efficiency increase, at least to some degree.

What I've not seen any of these armchair theories addres, however, is the true cost and true value of the conversion.* They say, "Just buy such-and-such*an engine from an industrial equipment junkyard, marinize it, mate it to such-and-such a transmission, rework the propshaft, bearings, etc., and there you*are."*

All of these proposals require modifications, in some cases very extensive, to the boat.* Engine stringers, engine mounts, shaft alleys, shaft supports, fuel systems, etc. are all candidates for alteration.* If all this is done by a professional installer, the labor cost will be astronomical.* If the mods and installation is done by the boat's owner, the time could stretch into months, years......, and the learning curve could be almost vertical, with lots of trial and error, hence more time and more expense.

One could probably power an existing trawler with a Coleman camp stove if one worked at it hard enough.* What I would want to know is, in the end, would the assumed increase in effeciency pay back the real money plus the value of the person's time, plus the time the boat was unusable?* Is anyone in the financial or age (retired) bracket required to undertake this sort of thing going to live long enough to see the benefit?

Versus simply continuing to use their boat complete with its less-than-ideal powertrain?

When we had the worn-out engine mounts on our FL120s changed a few years ago, the shop found that the correctly rated mounts would*put the engines a bit too high and they would hit the underside of the cabin sole.* The original mounts, installed by the factory, had been undersized for this very reason.* So the question we had to answer was---- 1) do we have new, custom-fabricated mount brackets made for each engine to provide the proper clearance, 2) do we have the engine stringers cut down to provice the proper clearance, or 3) do we simply install brand new undersized mounts identical to what the factory installed when they built the boat?

The estimated cost to do 1) or 2) was significantly over $10,000.* The cost to do 3) was $50 per mount plus two day's shop labor.* Theoretically, option 1)*or 2) was the most ideal solution.* But given that the eight*original undersize mounts had gone over 30 years before requiring replacement, we figured that spending a bit over $3,000 to have the same kind of mounts installed was the far more sensible solution (a decision supported by our diesel shop).* The boat was out of service for only two days, and by the time the mounts need replacing again, we'll proably be dead or close to it.* And we saved at least $7,000 that we could put toward something else, like fuel, maintenance, unexpected repairs, etc.

Repowering an existing boat with something totally different than what was put in it can seem like a good answer to the search for increased efficiency, but I wonder if it really is when all the actual costs and time value are added up at the end of the day.

-- Edited by Marin on Tuesday 19th of May 2009 04:26:30 PM
Marin is offline   Reply With Quote
Old 05-19-2009, 06:11 PM   #12
Guru
 
City: Carefree, Arizona
Country: usa
Vessel Name: sunchaser V
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 6,376
RE: Single v/s Twin

Philbrooks in Sidney BC is actively selling, installing*and promoting one diesel to replace two while using the existing twin shaft setup. On repowers it is an intriguing notion. There are lots of nice 20 - 30 year vesels out there that could benefit from this concept. Especially some old heavy Bertrams or Unilfites running 6-71s.*Google their website. On older twin DDs a nice "light" Cummins can save up to 30% fuel burn, cut weight by 1000s of lbs, cleanup ER and give a lot of space for extra??. Since most vessels*have 4 longitudinal stringers, the motor sets on the center two with shaft going to splitter box and then to gearsets. I'm not sure if you can forward/reverse separately so a bow thruster is likely required.

Yes, in the "old days" there were lots of drivers of MB, Lexus*and BMW buyers out there with leases - about 40% in fact - *cause they couldn't come up with cash. Same crowd as were*buying the new fast twin water toys. Think bankers and real estate mavens, now with less disposable income. The two boat shows I've attended this year show new boat down a lot with* discounting up to 30% to get buyers. A similar slowdown is occurring in China so I'm told.
sunchaser is offline   Reply With Quote
Old 05-19-2009, 07:49 PM   #13
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
Single v/s Twin

I know two people with GB46s. They have told me they typically cruise at 10 knots. One of them has a pair of 210hp Cat 3208NAs in it. I don't know what his fuel burn is. The other one has Cummins 370 hp engines and at 10 knots he says it burns 10-12 gph.

A GB46 with 375 hp 3208Ts is typically listed to have a max speed of 17.5 knots with a cruise speed of 12-14 knots. I'm guessing that at 10 knots the fuel burn will be similar to what my acquaintance with the Cummins-powered GB46 gets.

Grand Banks' own literature for an early-model GB46 with two Sabre-Lehman 135 hp diesels lists a cruise speed envelope of 9 to 14 knots with a top speed of 18 knots.


-- Edited by Marin on Wednesday 20th of May 2009 01:19:44 AM
Marin is offline   Reply With Quote
Old 05-20-2009, 04:39 AM   #14
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,534
RE: Single v/s Twin

, "Just buy such-and-such an engine from an industrial equipment junkyard, marinize it, mate it to such-and-such a transmission, rework the propshaft, bearings, etc., and there you are."

All of these proposals require modifications, in some cases very extensive, to the boat. Engine stringers, engine mounts, shaft alleys, shaft supports, fuel systems, etc. are all candidates for alteration. If all this is done by a professional installer, the labor cost will be astronomical.

Actually most times what is wanted IS A RELIABLE , Inexpensive replacement for a worn out or killed existing engine.

A small amount of smarts , replace an inline 6 with another inline 4 or 6 .

Look for height problems if yanking a V something and standing up an inline.

Since the power will be the same , the tranny can probably be reused , or up graded to marine commercial standards rather than fork lift take outs.


With similar power there will only be a prop shaft coupling to change COTS in any prop shop.

An upgrade to floating mounts and a vibration free Aqua Drive would add expenses for different more flexible fuel lines and perhaps a switch from mechanical engine controls.

Most of the measuring , parts hunt and assembly can be done by a knowledgable owner, the only use for a pro would be removing the stripped old block out and placing the replacement on the mounts.

A couple of hours with a crane , at an agreeable yard , no big deal.

ALL the dimensions on car truck and industrial engines are on line , so arm chair comparisons wont even get ones hands dirty.

Do it your way,
FF is offline   Reply With Quote
Old 05-20-2009, 11:36 AM   #15
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
RE: Single v/s Twin

Quote:
sloboat wrote:

But a big open question is whether anyone ever pushes the big engine configuration(s) beyond 10 knots...do they place any value at all on keeping a semi-planing capability?
*
Before fuel prices climbed steeply a couple of years ago, it was not uncommon to see the newer GB42s and 46s in our marina moving along at a pretty good clip.* The owners I know and the lead*broker at the large GB charter/dealer operation in our marina said they usually ran the boats at 14 to 16 knots to get to their*primary destination, say Desolation Sound.* Once there, they would cruise at much more economical speeds between*the local destinations.* Then they would make the long run*home at*the higher speed.*

They*all cited time as the reason.* Their business and vacation*schedules required that, in order to maximize the time spent*in their cruising area they had to get to and from it as fast as possible.** They all acknowledged the huge fuel burn increase---- from perhaps 9 or 10 gph at 9 knots to 23 gph*or more at 14 to 16 knots---- but this was far outweighed by the value of the time saved.

Today not so much.* The GB42 and 46 owners I know do not take advantage of the fact their boats can cruise some three to five knots faster than they run them.* When this has come up in conversation they say they still like the fact the boats are capable of the higher speeds (apparently in the hope that someday $1.50 a gallon diesel will come back) but at this point they are sticking to their 10 knot cruise speeds for all legs of a journey.

While it's true that in the overall scheme of things, fuel costs are not the signficant expense of running a boat, nevertheless with insurance, moorage, haul-out, etc. fees going up every year, plus the iffy status of the economy, people who a few years ago thought little of burning 23 gph for two or three days running seem to*think about it a lot now.

But I would hazard to guess that none of these people would willingly give up the ability to cruise at 14-16 knots even if they never do anymore.* Slowed down, these big-engined GBs are reasonably economical, so the fact they could be powered at the same lower cruising speeds with smaller, more efficient powerplants that were incapable of moving the boat at 14-16 knots would be of little interest to the owners I know.

But these are people who have experienced going fast in these boats.* To someone entering the market for the first time today, where economical operation is a bigger factor from the outset, the semi-planing speed capability of the GB42 or*GB46*may be of no interest to them as they never expect to use it.

None of what I've said is true of the few Fleming, GB52, Delta, and custom trawler owners I know or know of.* They still run these boats at a fast clip, 14-18 knots and the fuel burn be damned.
Marin is offline   Reply With Quote
Old 05-20-2009, 07:11 PM   #16
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,723
RE: Single v/s Twin

Sloboat,

Any big wide heavy slow boat with a straight run aft is going to burn lots of fuel. Need to think long narrow light w an upward curve in the bottom aft (or rocker in the aft section) to get to efficiency. Untill I found the Willard I was thinking of converting a sail boat to a trawler. Was looking for one w a high PC (full in the ends) and a keel that could be easily cut in half.

Eric Henning
Nomad Willy is offline   Reply With Quote
Old 05-20-2009, 11:54 PM   #17
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
Single v/s Twin

Quote:
sloboat wrote:
It does appear that older GB hulls achieve speed via brute force versus sophisticated hull design.
Not sure what you consider "older" but so far as I am aware, all GB hulls used the original, semi-planing configuration designed by Ken Smith in 1964 for the prototype GB36, "Spray." This basic hull configuration was used on all Grand Bands models until the introduction of the GB47 in 2005 (now called the GB44 as a result of adapting the ABYC measurement standard)) and the new Zeus-drive GB41.

But a GB46 built in the 2000s uses the same Ken Smith hull configuration as "Spray" did in 1962, or our own fiberglass GB36 has from 1973, etc.

So yes, you are correct in that the only way to drive Ken Smith's hull through the water at speeds significantly above hull speed is to apply brute force. Hence the trend starting in the 1990s to put 300-plus and 400-plus hp engines in the GB42, GB46, etc.

An interesting side note is that while American Marine (later Grand Banks Yachts) had recommended engines for every model, buyers or dealers could specify whatever engines they might want. So you got things like one of the GB52s in our marina being powered with a pair of 200-something hp engines at the orders of the original owner. This boat was new in 1998 and the light engines threw off the attitude of the boat on the water to the point where some of the deck drains had to be recut and relocated. The owner has it in the dealer's GB charter fleet where it has not been a popular boat because it is so underpowered by the standards of the people who can afford to rent the thing by the week.

*


-- Edited by Marin on Wednesday 20th of May 2009 11:55:33 PM
Marin is offline   Reply With Quote
Old 05-21-2009, 12:25 AM   #18
RED
Senior Member
 
RED's Avatar
 
Join Date: Jun 2008
Posts: 182
RE: Single v/s Twin

In my experience most semi displacement hulls are going to get 1 to 1.5 MPG (maybe as much as 2 MPG at slow cruise with an efficient power plant).

Some of my direct experiences

36 foot MMC (Monk 36) single Perkins 6.354; Fuel burn was about 3.5 gph at 7 mph slow cruise, or 2 mpg. At 90% throttle fuel burn dropped to under 1.5 mpg for less than 1 addidtional mph of speed.

48 Ocean alexander Classico. Twin Cat 3208TA's 435 HP each. Idle speed 6-7 mph. at 10 mph fuel burn was about 1 mpg. At full throttle, a thirsty devil doing 21 mph and burning 46 gph or 0.5 mph. Running offshore between Astoria and Tatoosh, for example, i didn't care what the fuel burn was, I wanted to make the passage quickly, and let the seas regulate our speed regardless of burn. We loved this boat, and gave it up only because of physical handicaps of my wife who couldn't negotiate all the levels of a pilothouse. If things were different, we'd still have the boat, and would run it the same way.

42 Ocean Alexander (trunk cabin, trawler style). Twin CAt 3208 NA 210 HP each. Amazing they got 435 hp out of the same engine, but I think the NA's will last longer. 8-9 mph with a fuel burn of 5 gph or 1.6 -1.7 mph. Fuel burn at 12 mph of 12 gph or 1 mph.

In the PNW there can be longer distances to get to cruising grounds (250-300 miles, say from Portland to San Juans/Canadian gulf islands). While this trip isn't cheap, it still represents a fraction of the cost of owning/maintaining/ mooring the boat.

Marin, for us the consideration wasn't fuel burn once we reached cruising grounds, it was and is comfort. When you're running at say 90% throttle, the boat is noisy, and you need to be "on" in terms of piloting the boat, looking for deadheads, etc. At the cruising grounds, the idea isn't getting from point A to B, but enoying the trip, at least for us.

Eric, I understand that long and narrow might be appealing for some, but not for us. I did 25 years in sailboats, and we were glad to "move up out of the basement". At our age, the comfor of a bigger, wider boat is key to us, and for the shorter time we have left for cruising, we don't mind the (somewhat) higher expense. Sailing (we did a lot and enjoyed it) is still more like tent camping/backpacking - great when you're young.

That's our experience - match the boat to your lifestyle/age/capability. Yes, you can see from our experience a modest improvement in fuel burn of a single over a twin; but I like the better handling at dock, and the ability to run when conditions like weather, seas would make us more comfortable.
Take your pick. Any time spent on the boat is good time.
RED is offline   Reply With Quote
Old 05-21-2009, 12:41 AM   #19
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
RE: Single v/s Twin

Quote:
RED wrote:


Marin, for us the consideration wasn't fuel burn once we reached cruising grounds, it was and is comfort.
You're right and if my earlier statement came across as saying that the folks who travel fast to their basic destination and then cruise slowly from place to place do so because of concerns about fuel burn, that's not what I meant to imply.* They cruise slowly in their destination area because they want to take their time to enjoy it.* In the case of Desolation Sound, the Broughtons, etc., the local destinations are not that far apart anyway.* So if you leave one anchorage for another one, chances are that even at 8 knots you're only going to be running the boat for an hour or two.* So booming along at 15 knots kind of goes against the whole idea of the cruise unless one simply likes to run a boat fast.

*
Marin is offline   Reply With Quote
Old 05-21-2009, 12:55 AM   #20
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
Single v/s Twin

Speaking of Grand Banks designs, American Marine introduced a very clean planing boat in the early 1970s called the Laguna. It was nothing like the Grand Banks trawler product line although from the photos I've seen the Laguna interiors were very similar in craftsmanship and materials to the trawlers.* Lagunas were 37 (or 38) feet long--- I don't know if they came in other lengths as well. * The Laguna was killed off by the 1973 fuel "crisis." But they come up for sale every now and then (the photo is from a broker ad). The company did not re-enter the planing boat market until the introduction of the Eastbay in the late 1990s.



-- Edited by Marin on Thursday 21st of May 2009 01:00:02 AM
Attached Thumbnails
Click image for larger version

Name:	thb879094127_1.jpg
Views:	97
Size:	50.5 KB
ID:	1092  
__________________

Marin is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
twin vs. single engine rages on.... Woodsong Power Systems 38 11-28-2011 06:12 PM
Running single on a twin to save fuel Nomad Willy Power Systems 61 06-21-2011 12:20 PM
Twin to Single conversion- Oh My! JohnP Power Systems 37 03-08-2011 09:46 PM
WANTED: Single 50 amp to single 30 amp adapter Woodsong Classifieds 8 10-25-2010 04:22 PM




All times are GMT -5. The time now is 02:53 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012