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Old 08-29-2012, 07:56 PM   #21
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Isn't the reason something like a carrier can go so fast is its hull length? If the formula for hull speed is based on, among other things, length, I would think that a WLL approaching 1,000 feet would have some influence on the hull speed. Yes, no, maybe so?
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Old 08-29-2012, 08:20 PM   #22
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Isn't the reason something like a carrier can go so fast is its hull length? If the formula for hull speed is based on, among other things, length, I would think that a WLL approaching 1,000 feet would have some influence on the hull speed. Yes, no, maybe so?
Yeah..I know big warships with unlimited power are all over the map as far as speeds go...but there is speculation that some of the big warship hulls are actually semi-displacement because they are flat enough on the bottom and some meet the supertanker rule (same as catamarans) where if the hull is 5 times longer than the beam....the 1.34 (or whatever) times the square root of the waterline length kinda goes out the window.

So....I just doubt that the Willard is THAT much better...better...but within reason based on what I have seen with other hulls such as the KK. Owners aren't always as honest as you are...
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Old 08-29-2012, 09:40 PM   #23
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Hull speed IS 1.34 X (the square root of the WLL) That's all there is to it. So if Marin's boat was 34'3" on the WL then the square root of 34'3" is 5.85. So 5.85 X 1.34 = 7.839. Marin's hull speed is (w that WLL) 7.839 knots. But GB may include the swim grid in the 36' measurement. At any rate his hull speed is very close to 8 knots.

Most ships have a much greater beam to length ratio that 5-1. That's more like a fat trawler.

Don't know what your'e talk'in about (1.34 out the window).

"flat on the bottom" length wise or cross ways???

At any rate if you want real efficiency flat submerged sterns don't cut it.

Yes the Krogens are about the best trawlers out there. Put flopper stoppers on them and go just about anywhere if you need to do that sort of thing. That's passage making and this is trawlering.
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Old 08-29-2012, 10:04 PM   #24
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According to the previous owner and under perfect conditions Voyager, at 1800 rpm, uses 1.8 gph at a speed of about 8 knots. That's 4.4 nmpg. This is a little better than the KK42 performance chart I have. I haven't taken delivery of the boat yet so I can't confirm the numbers. I'm looking forward to checking it out though.
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Old 08-29-2012, 10:12 PM   #25
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Found this in an article by Dolph McCranie called "Choosing a Passagemaker." Don't know who he is, don't know what the article appeared in, but he seemed to me to be knowledgeable about the subject.


"For a boat with a LWL [loaded waterline length] of 36 feet the square root is 6. Her speed at a hull speed ratio of 1.0 would be six knots. At a ratio of 1.2 it would be 1.2 * 6 or 7.2 knots. Her maximum theoretical hull speed would be 1.34 * 6 or 8.04 knots. She would be most economical between 6 and 7.2 knots (a ratio of 1.0 to 1.2). The boat could probably be driven to a hull speed ratio of 1.4 or about 8.5 knots but with a significant increase in fuel consumption."

The earlier GB36s like ours have an LWL of 34.'

I don't do math so have no idea what the theoretical hull speed would be. Nor do I really care. But GB says the hull speed of our boat is seven-something knots. Maybe they mean the true hull speed as opposed to the theoretical hull speed. I don't know. All I know that they and other people in the business have all said that for our boat, 8 knots is a wee bit over hull speed.

But it sounds to me like splitting gnat's eyebrows and so is more an armchair excersise than anything that's actually meaningful to how we run the boat.

So we will continue to run at 1650 and bust through the hull speed sound barrier to a whopping 8 knots and wish we were doing 30.
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Old 08-29-2012, 10:50 PM   #26
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Anyway, the Williard 40 is a great design. It was on our short list of monohulls along with the Hatt 42 LRC and Krogen Manatee when we were searching. My wife and I are gunk-hole crazy and do a lot of punching around in the shallows of Biscayne Bay and the Keys. We chose the KK Manatee cuz it's only 3'2" draft, but if there had been a nice W40 on the East Coast at the time, we'd have looked hard at it. It's hard to imagine a better combo than the W40 offers in that length of vessel.
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Old 08-30-2012, 12:47 AM   #27
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Marin writes "Maybe they mean the true hull speed as opposed to the theoretical hull speed." No such thing as theoretical or true hull speed. Just hull speed. Did you read my last post? This is really simple stuff. Hull speed = 1.34 X the square root of the water line length. 5.84 is the square root of 34. 5.84 X 1.34 = 7.8256. Your hull speed is 7.8256 knots. 8 knots for all practcal purposes.

John,
Most peoples fuel burn numbers are "optimistic" because they just use their hour meter for time but of course a lot of that time is'nt at cruising speed.
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Old 08-30-2012, 01:00 AM   #28
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" No such thing as theoretical or true hull speed. Just hull speed. ...Your hull speed is 7.8256 knots. 8 knots for all practcal purposes.
I dunno.... All these guys I've been reading since this topic came up talk about theoretical and true hull speeds. So who knows....?

Anyway, our boat will go (and has gone once) considerably faster than hull speed--- whatever it actually is--- even with the old Fords. Put a couple of 420 hp 6-cylinder Cats like what Carey has one of in his lobsterboat and the old GB would really get up and go. Now THAT would be cool.

Maybe someday........
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Old 08-30-2012, 02:03 AM   #29
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OK guys, so how about we look at some actual willard 40 data from when the boat was in production?

This will once and for all settle the range, and the NMPG issues.

Here's a link to a review of the Willard 40 from 1978. I think the fuel data is probably directly from the manufacturer.

http://pacificmotorboat.com/willardb...rd40review.pdf

It shows that at:

1000 RPM 4.8 knots 6.8 nmpg
1200 RPM 5.6 knots 6.0 nmpg
1400 rpm 6.3 knots 4.8 nmpg
1600 RPM 6.8 knots 3.8 nmpg
1800 RPM 7.4 knots 2.9 nmpg
2000 RPM 7.8 knots 2.4 nmpg

Thats not bad fuel economy, but I have to point out that my fuel inefficient 47' twin engine semi displacement boat gets only 25% worse fuel economy at the upper end of the scale.
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Old 08-30-2012, 07:13 AM   #30
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OK guys, so how about we look at some actual willard 40 data from when the boat was in production?

This will once and for all settle the range, and the NMPG issues.

Here's a link to a review of the Willard 40 from 1978. I think the fuel data is probably directly from the manufacturer.

http://pacificmotorboat.com/willardb...rd40review.pdf

It shows that at:

1000 RPM 4.8 knots 6.8 nmpg
1200 RPM 5.6 knots 6.0 nmpg
1400 rpm 6.3 knots 4.8 nmpg
1600 RPM 6.8 knots 3.8 nmpg
1800 RPM 7.4 knots 2.9 nmpg
2000 RPM 7.8 knots 2.4 nmpg

Thats not bad fuel economy, but I have to point out that my fuel inefficient 47' twin engine semi displacement boat gets only 25% worse fuel economy at the upper end of the scale.
Exactly my point...at the slower end, the "slipery" goes out the window and anyone that thinks that 1.34 is the only speed to length ratio definitely doesn't have a lot of hull design background and the 5:1 rule for length/beam ratio is why catamaran hulls like hobie cats (definitely not planing hulls) can scream.

25% for the Bayliner, and around 10% down in the 6 knot range for the Albin...no where's near 50-100% more efficient. Just cause Willards look slicker...looks don't mean that much at really slow speeds.

John H...those numbers are right in where I expected them to be.
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Old 08-30-2012, 07:32 AM   #31
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Originally Posted by ksanders View Post
OK guys, so how about we look at some actual willard 40 data from when the boat was in production?

This will once and for all settle the range, and the NMPG issues.

Here's a link to a review of the Willard 40 from 1978. I think the fuel data is probably directly from the manufacturer.

http://pacificmotorboat.com/willardb...rd40review.pdf

It shows that at:

1000 RPM 4.8 knots 6.8 nmpg
1200 RPM 5.6 knots 6.0 nmpg
1400 rpm 6.3 knots 4.8 nmpg
1600 RPM 6.8 knots 3.8 nmpg
1800 RPM 7.4 knots 2.9 nmpg
2000 RPM 7.8 knots 2.4 nmpg

Thats not bad fuel economy, but I have to point out that my fuel inefficient 47' twin engine semi displacement boat gets only 25% worse fuel economy at the upper end of the scale.
As mentioned earlier in this thread, those getting better fuel economy have repowered with modern diesels. The article you site was published in 1978 with a motor that was developed in the late 1950s and started being produced in 1960. Really doubt your boat would get the economy it does with engines from the 1960s.

Ted
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Old 08-30-2012, 07:36 AM   #32
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As mentioned earlier in this thread, those getting better fuel economy have repowered with modern diesels. The article you site was published in 1978 with a motor that was developed in the late 1950s and started being produced in 1960. Really doubt your boat would get the economy it does with engines from the 1960s.

Ted
At the power being derived either from an ancient diesel or a modern one...down in the 1.5-2.5 gallon per hour burn...I doubt there is enough efficiency difference to dramatically chane my point.

Even then...my boat has the same 70's vintage engine so the economies should be the same...I wasn't talking engine efficiency, just how slippery hulls are at slower speeds.
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Old 08-30-2012, 07:56 AM   #33
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At the power being derived either from an ancient diesel or a modern one...down in the 1.5-2.5 gallon per hour burn...I doubt there is enough efficiency difference to worry about.
To the contrary, modern diesels are far more efficient at the lower rpm range than their predecessors. Many Modern diesels develop their peak torque (become efficient) at around 1,400 rpm. Also, in that era, choice of engines was very limited. So they used an inefficient 130HP engine to produce around 20 to 25HP to push the boat at 7 knots.

Ted
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Old 08-30-2012, 09:24 AM   #34
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To the contrary, modern diesels are far more efficient at the lower rpm range than their predecessors. Many Modern diesels develop their peak torque (become efficient) at around 1,400 rpm. Also, in that era, choice of engines was very limited. So they used an inefficient 130HP engine to produce around 20 to 25HP to push the boat at 7 knots.

Ted
I don't know about that...this was a common repoiwer engine for awhile for small trawlers...If my boat takes 40 shp to go around 7 knots and burns a tad over 2 gal/hr...It looks like this more modern engine uses about the same at 2000 RPM....ant it tops at 80hp rather than 135hp...

Electronic engines are better for sure but how much better? I couldn't find the specs for an electronic 100-150hp diesel...have a link or fact sheet on one?
John Deere 4045DFM70

Fuel Consumption for Typical Propeller Curve
Engine Crank. Crank. Prop. Prop.
rpm Power Torque Absorption Fuel
hp (kW) lb-ft (N•m) hp (kW) gal/hr(L/hr)
2500 80 (60.0) 169 (229) 80 (60.0) 4.6 (17.5)
2400 80 (59.3) 173 (235) 71 (53.1) 4.0 (15.2)
2200 77 (57.2) 182 (247) 55 (40.9) 3.0 (11.5)
2000 74 (55.0) 194 (263) 41 (30.7) 2.3 (8.7)
1800 68 (51.0) 200 (271) 30 (22.4) 1.7 (6.6)
1600 63 (47.0) 207 (281) 21 (15.7) 1.3 (4.9)
1400 58 (43.0) 216 (293) 14 (10.5) 0.9 (3.5)
1200 50 (37.0) 217 (294) 9 (6.6) 0.6 (2.4)
1000 40 (30.0) 211 (286) 5 (3.8) 0.4 (1.5)
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Old 08-30-2012, 10:38 AM   #35
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I know the broker well, he normally only takes good vessels that will pass survey. I'd assume another $50K to get systems and vessel nicely updated and good for the long haul. That said, do you really want a 7 knot maximum speed (project??) boat that is 30 years old with hidden gremlins versus a much newer vessel. This is a buyers market and there are deals galore. There is more to it than theoretical MPG.

On a side note, Van Isle in Sidney BC is listing a drop dead gorgeous 1982 totally refurbished 34' CHB. Decks, windows varnish all redone. I've never seen anything like it in a 30 year old TT boat.
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Old 08-30-2012, 10:41 AM   #36
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As mentioned earlier in this thread, those getting better fuel economy have repowered with modern diesels. The article you site was published in 1978 with a motor that was developed in the late 1950s and started being produced in 1960. Really doubt your boat would get the economy it does with engines from the 1960s.

Ted
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.
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Old 08-30-2012, 10:54 AM   #37
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I know the broker well, he normally only takes good vessels that will pass survey. I'd assume another $50K to get systems and vessel nicely updated and good for the long haul. That said, do you really want a 7 knot maximum speed (project??) boat that is 30 years old with hidden gremlins versus a much newer vessel. This is a buyers market and there are deals galore. There is more to it than theoretical MPG.

On a side note, Van Isle in Sidney BC is listing a drop dead gorgeous 1982 totally refurbished 34' CHB. Decks, windows varnish all redone. I've never seen anything like it in a 30 year old TT boat.
Actually, in terms of a true passagemaker, with the range and the seakeeping ability to go anywhere in the world, the Willards are probably the most economical of that group. That boat seems to be a pretty good example.

I would agree that if a person were looking for a coastal cruiser there are much newer, roomier, etc... boats in the same price range, but not for a passagemaker.

The folks here on TF may not remember but when I was boat shopping last year I seriously considered that boat, and a Nordhavn 46 called Salvation II. My wife strongly favored the Bayliner 4788, and thats why we named the 4788 "Lisas Way".
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Old 08-30-2012, 11:57 AM   #38
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I don't know about that...this was a common repoiwer engine for awhile for small trawlers...If my boat takes 40 shp to go around 7 knots and burns a tad over 2 gal/hr...It looks like this more modern engine uses about the same at 2000 RPM....ant it tops at 80hp rather than 135hp...

Electronic engines are better for sure but how much better? I couldn't find the specs for an electronic 100-150hp diesel...have a link or fact sheet on one?
Think you are missing the point. Diesels generate between 15 and 20HP in their optimal efficiency range (full torque and above). Older diesels produce signicantly less HP per gallon when operated out of this range (below full torque).

Your boat might take only 30 shp to go 7 knots at 2 gal/hp and be generating 15 shp per gallon consumed. Where do you come up with the number 40 shp? There isn't a 10 year old diesel (less than 500 HP) that claims 20HP per gallon of diesel consumed.

There are non electronic diesels that get close to 20HP per gallon.

Ted
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Old 08-30-2012, 11:59 AM   #39
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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.
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Old 08-30-2012, 12:18 PM   #40
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Think you are missing the point. Diesels generate between 15 and 20HP in their optimal efficiency range (full torque and above). Older diesels produce signicantly less HP per gallon when operated out of this range (below full torque).

Your boat might take only 30 shp to go 7 knots at 2 gal/hp and be generating 15 shp per gallon consumed. Where do you come up with the number 40 shp? There isn't a 10 year old diesel (less than 500 HP) that claims 20HP per gallon of diesel consumed.

There are non electronic diesels that get close to 20HP per gallon.

Ted
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.
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