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Old 08-30-2012, 12:21 PM   #41
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ksanders,
"Lisas Way" .. Great little mini story.

In my own defense I need to admit I got the 1gph at 7 knots from a personal experience on the Willard forum. I have a lot of respect for both of the gentlemen involved in presenting those numbers. My own small Willard burns a gallon an hour and is much shorter and half the weight. So the numbers seem optimistic to me as well but the calculations were made on a very long ocean run and that itself eliminates a lot of variables. It may introduce variables too. Like how to measure distance and account for ocean currents. Was it speed over the earth or speed through the water .. the later being the only usable information re the question at hand.

I do recall and (perhaps someone could verify) that the W40 required 23hp to make 7 knots in the book "Voyaging Under Power" by Bebe. I can see the JD making 23hp for an hour given a gallon of fuel. That would seem to give the 1gph @ 7 knots credibility.

psneeld I know one way to convince you the FD hull is far superior for low resistance at low speeds. IF you can find 2 rowing boats. One a typical OB w a wide stern and submerged transom (easy to find) and a proper rowing boat w a fairly narrow stern and the transom clear of water. After rowing these 2 boats there will be no doubt about the resistance of the 2 hull types.
We have had this discussion before and we both still disagree...low resistance boats are long and thin closely or exceeding that 5:1 ratio as I explained...that has NOTHING to do with displacement. I rowed 2 years in college and have rowed many different designs...again at 6 knots there is verly little turbulence because my transom is only immersed about 4 inches.
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Old 08-30-2012, 12:29 PM   #42
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Interesting

My boat does not have a electronic anything engine.

We have a pair of 330 HP cummins 5.9BTA engines. Old fashioned mechanical fuel system.

I don't know when the engine came out but it was awhile ago.
Had a 210 HP 5.9BT (not after cooled) in my boat and have a 220 HP 5.9BT in my Dodge pickup. Wikipedia says "B" series started being produced in 1984. They are capable of 18+ HP per gallon of fuel consumed (at optimal efficiency).

Ted
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Old 08-30-2012, 12:42 PM   #43
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The Ford Lehan 135hp chart does...granted it claims it's gross hp not shp so I'm not sure exactly what that means but the other numbers match other peoples experience.
They can claim it, they certainly don't do it. Do you really think any scientific testing was done to produces those numbers back in the what 1960s when that literature was produced and diesel was pennies per gallon? The most fuel efficient electronic diesels are just over the 20HP per/gal mark. Do you really think the Lehmans are in the same neighborhood?

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Old 08-30-2012, 01:06 PM   #44
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Ok guys.
Based on the prop size stated in the boat specifications, I reckon that this boat was displacing full 17600 lbs. If the Perkins was the original version, he would deliver 135 HP @ 2800 RPM and the LWL of this boat would be in the neighborhood of 36.5’. Assuming all this from the yachtworld page I got to the following conclusion:
Speed 7 knots:
@ 7 knts engine burns 1.3 GPH = to 2375 miles with 10% safety reserve
Speed 6 knts
@ 6 knts engine burns 0.9 GPH = 2940 miles with 10% safety factor.
The calculations above had in consideration the 36.5’ LWL with a 17600 lbs displacement and the engine advertised in the site
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Old 08-30-2012, 01:16 PM   #45
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Ok guys.
Based on the prop size stated in the boat specifications, I reckon that this boat was displacing full 17600 lbs. If the Perkins was the original version, he would deliver 135 HP @ 2800 RPM and the LWL of this boat would be in the neighborhood of 36.5. Assuming all this from the yachtworld page I got to the following conclusion:
Speed 7 knots:
@ 7 knts engine burns 1.3 GPH = to 2375 miles with 10% safety reserve
Speed 6 knts
@ 6 knts engine burns 0.9 GPH = 2940 miles with 10% safety factor.
The calculations above had in consideration the 36.5 LWL with a 17600 lbs displacement and the engine advertised in the site
The calculations are wonderful estimates.

Here's a link to actual test measurements from the same boat, at the time of production

http://pacificmotorboat.com/willardb...rd40review.pdf
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Old 08-30-2012, 01:22 PM   #46
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Ok guys.
Based on the prop size stated in the boat specifications, I reckon that this boat was displacing full 17600 lbs. If the Perkins was the original version, he would deliver 135 HP @ 2800 RPM and the LWL of this boat would be in the neighborhood of 36.5. Assuming all this from the yachtworld page I got to the following conclusion:
Speed 7 knots:
@ 7 knts engine burns 1.3 GPH = to 2375 miles with 10% safety reserve
Speed 6 knts
@ 6 knts engine burns 0.9 GPH = 2940 miles with 10% safety factor.
The calculations above had in consideration the 36.5 LWL with a 17600 lbs displacement and the engine advertised in the site
People put far too much credence into generic hull speed formulas, HP requirement tables and fuel consumption calculations based on other formulas. They were only meant as very general guidelines and can be way off at the far ends of the scale (which is where we are here). What it is, what it will take and how much it will consume is ultimately best determined through trial and error.

BTW, Willard lists the displacement at 33,000 not 17,600.
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Old 08-30-2012, 02:01 PM   #47
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They can claim it, they certainly don't do it. Do you really think any scientific testing was done to produces those numbers back in the what 1960s when that literature was produced and diesel was pennies per gallon? The most fuel efficient electronic diesels are just over the 20HP per/gal mark. Do you really think the Lehmans are in the same neighborhood?

Ted
Whether it does or doesn't...I was discussing hull efficiency not engine efficiency so my though is elsewhere...t

The fuel numbers were very close on the Willard and my Albin based on my fuel curves and the ones from the Willard review....all I was saying that a Willard is no where's near 50-100 percent more efficient...whether they screwed up the drive train, underwater drag or bad engine I can't address...the numbers are a lot closer than some were trying to portray...so I rest my case..
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Old 08-30-2012, 02:19 PM   #48
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The fuel numbers were very close on the Willard and my Albin based on my fuel curves and the ones from the Willard review....all I was saying that a Willard is no where's near 50-100 percent more efficient...whether they screwed up the drive train, underwater drag or bad engine I can't address...the numbers are a lot closer than some were trying to portray...so I rest my case..
Just out of curiosity does your Albin have a single 135 Lehman or twins?
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Old 08-30-2012, 04:03 PM   #49
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O C

If 33000 lbs is the published displacement, then the published propeller for the, again published engine, is wrong or in the best case, inappropriate.

And then again, based on the apparent displacement, this is what we get as a guess value and a starting reference.
However, a boat that size with a 135 hp engine @ 2800 rpm, cannot have a 29 x 18 4 blade prop when displacing 33000 lbs.
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Old 08-30-2012, 04:08 PM   #50
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Just out of curiosity does your Albin have a single 135 Lehman or twins?
single
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Old 08-30-2012, 06:30 PM   #51
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O C

If 33000 lbs is the published displacement, then the published propeller for the, again published engine, is wrong or in the best case, inappropriate.

And then again, based on the apparent displacement, this is what we get as a guess value and a starting reference.
However, a boat that size with a 135 hp engine @ 2800 rpm, cannot have a 29 x 18 4 blade prop when displacing 33000 lbs.
Well I guess Willard better recall their 40s since they can't work.

What you are missing is the gear (transmission) ratio which is 2.91:1. In an ideal world the gear would be a 4:1 or taller, the prop wouldn't be quite so flat, the cruising rpm would be 2,000 +/- and the HP would be more like 80. Unfortunately, there aren't any 4:1 gears for small engines (that I'm aware of), so we use a bigger motor at lower rpm and a flatter wheel to make it work.

It may be in appropriate and the formula may say it doesn't work, but clearly it does. That's why you shouldn't treat the formulas as gospel.
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Old 08-30-2012, 06:41 PM   #52
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This has been an interesting discussion and is now far off of the original poster's topic. Oh, well, so what.

Let me offer some observations from published data. Bebe's book (as revised by Leishman) lists a number of true passagemaker trawlers and gives performance data. A good rule of thumb emerges: it takes 15 hp per 10,000 lbs of displacement to drive a full displacement hull to 1.34*Sqrt (LWL) which is the theoretical definintion of hull speed.

This rule of thumb holds up pretty good for boats from 30' to 70' long. An implied corrolary of this rule of thumb is that it takes less hp to drive a light long boat than a heavy short boat. Duh!!

So applying this rule of thumb to the Willard's 33,000 lbs displacement gives 50 hp. I don't know what the LWL is but the Pacific Motorboat article indicates that hull speed is 8 kts (on the axis of the third curve).

That article says that it takes about 4 gph (interpolating from the perfornance table or given in the text) to go 8 kts. My guess is that the Perkins makes about 15 hp per gph at the middle of its prop/fuel curve so that is 60 hp, which is in the ballpark with the rule of thumb.

In fact the article says that the hull shape is not a true round bottom (most of Bebe or rather Leishman's boats were round bottom) and has a very soft chine. Maybe that explains it being 20% over the rule of thumb, but realistically there are a lot of assumptions in this figure to account for this variation.

In any case it is a pretty slippery hull, much more than the typical semi-displacement GB, Mainship, etc. You can slow down to a 1.0 S/L ratio and go 6 kts at about 1 gph.

So enough of the technical BS. I like the boat a lot. It was built by the same yard that builds for the Navy and USCG. It is interesting to note that the list price in 1978 (when the PM article was published) was $110,000 with options and now a 1984 lists for $150,000. There aren't many other boats that retain their value that well.

David
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Old 08-30-2012, 07:30 PM   #53
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psneeld wrote:
"Whether it does or doesn't...I was discussing hull efficiency not engine efficiency so my though is elsewhere...t"
But you're using fuel burn as a yardstick to evaluate hull efficiency. So engine efficiency seems to be at the core of the argument. Can't blame you as engines that we usually talk about are all about the same. But it seems the new engines are 20 to 25% more efficient and perhaps more than that at certain engine speeds and loadings.

There was a discussion on this question about a year ago on BoatDesign.net and I've been trying to find it but haven't. If you can find it I'll go along w the essence of the conclusions. As I recall the difference was less than I thought it was but I think I thought the semi-planing hulls were 2 to 3 times as draggy. In reality there is probably greater differences from one SD hull to the next and much less difference in the drag of various FD trawler hulls. For example your SD hull w 4" of transom submerged and the usual w 6 to 10" submerged. So there's apples, oranges, grapefruit, plums and lots of other stuff involved. Anyway it made for a good discussion that nobody could win but I'm happy that it drew attention to whatever the difference is. But see if you can find the BD discussion.
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Old 08-30-2012, 08:51 PM   #54
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So far we have a brochure with numbers,real world fuel curves and a lot of opinions. The brochure and fuel curves have numbers that agree with a lot of other real world experiences by members and from posts I have gathered for years.

What am I gonna believe????

Geeez...tough one....
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Old 08-30-2012, 09:38 PM   #55
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march,
I like your comments.
So according to Bebe I'm supposed to be able to make hull speed w 22.5hp. I don't think I can attain hull speed at all and I've got about 40 hp.
I'm baffled by your comment about Bebe's boats having "true" round bottoms. Wazzat? My Willard is flat on the bottom amidships at 1/4 beam. The keel is a pinched wineglass section. And the chines are quite to very soft. It's more like a short canoe w a big keel. There's a fish boat here in Thorne Bay that is much fuller in cross section. I wonder if that's your round bottom.
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Old 08-31-2012, 06:49 AM   #56
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But you're using fuel burn as a yardstick to evaluate hull efficiency.

Before you guys get too upset about the apparent variations, keep in mind that the standards by which engine output was measured have changed a great deal over the years since the 1970s.

"Gross horsepower" was the brake horsepower produced at the flywheel and was measured on an engine without all the auxiliary bits that are installed when the engine is used in real life. Even then, the way that power was measured allowed for a 15 percent window. Your 135hp engine might deliver 150hp to the flywheel or it might only deliver 120hp. Depending on the transmission, water pumps, exhaust system, alternator, and shaft stuffing box the power at the prop could be far lower.

Trying to compare small horsepower boats and engines down to 10 or 15 percent can never be anything beyond an internet exercise since you probably don't know what numbers you are starting with.

Unless you put a torquemeter on the shaft and measure fuel efficiency by measuring exhaust constituents you can't possibly know what the real power and efficiency is.

All you can say is "my boat goes further on less fuel than yours does - or not."
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Old 08-31-2012, 05:28 PM   #57
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I found the thread on resistance on BD.
On the last page one of the senior members said
"At displacement speed, a semi-displacement or planing hull consume about twice the fuel as a displacement hull. Lots and lots of data support this figure."
But now I can't find the thread again.

Actually I think there's 2 or 3 threads on this.
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Old 08-31-2012, 07:49 PM   #58
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I found the thread on resistance on BD.
On the last page one of the senior members said
"At displacement speed, a semi-displacement or planing hull consume about twice the fuel as a displacement hull. Lots and lots of data support this figure."
But now I can't find the thread again.

Actually I think there's 2 or 3 threads on this.
And I supposed to believe him over the ACTUAL numbers Willard printed, my own/friends actual real world experiences and the numbers posted by dozens of other experience cruisers from numerous forums???

I think not...
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Old 09-01-2012, 02:28 AM   #59
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I agree ...

"I think not"
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Old 09-01-2012, 11:30 AM   #60
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However I have an interesting thought on the matter. There are three unquestionable truths on this issue. Nobody can dispute these facts.

1. At the start of a curve expressing drag for the two types of hull's at zero speed they are the same. This is obvious but it can reflect on the drag at very low speeds.

2. As speed starts to rise the FD hull's resistance rises at a slower rate. This continues as speed rises until at some point the difference in drag of the two hull types is the greatest. Probably at a SLR of .8 to 1.2. As speed rises further the FD hull's drag increases at a greater rate than the SD hull and at some point (probably in the vicinity of hull speed) they become the same.

3. As speed rises from The point where they are the same the FD hull never again has less drag than the SD hull.

So we have three unquestionable truths in a muddy situation where facts or unquestionable truths seem to not exist. And of course the the truth we want to know is what is the maximum difference and how great is it and at what speed does that occur. I think that the fact that SD hulls vary greatly in their drag at sub-disp speeds. psneeld's Albin w only 4" of submerged transom below the WL will have much less (at least less) drag at an SLR of 1 or 1.1 whereas a full planing hull would have much more drag at those speeds. A good low speed SD hull w only 2 to 3" of submerged transom may have only 25% more drag than FD and another SD hull w 6 to 12" of submerged transom may have 100% more drag. And of course the run aft on the bottom (quarter beam line) and it's angle as it rises to the transom also is a significant factor. Drag starts out the same and as speed rises becomes the same again. Below the speed that they are the same the FD hull has less drag and above that point the SD hull has less drag. But at least there are three unquestionable truths.
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