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Thread: A neat fuel efficient launch

  1. #71
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    Default Re: A neat fuel efficient launch

    Tom, I agree that Jan looks like she has a low righting moment at low angles of heel, but that is common with pretty much all high L/B hulls. I expect that she would gain righting moment quite quickly once past five or eight degrees of heel, and when in semi-planning mode she would settle back on her haunches and gain both form and dynamic stability, so would be quite comfortable at speed. But, that is just my opinion based on looking at a single picture on an internet forum...
    Hope for the best, but plan for the worst.

  2. #72
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    Default Re: A neat fuel efficient launch

    Quote Originally Posted by rbgarr View Post
    Except for noise of the diesel these would make good crew coach/umpire/judge/VIP launches.
    This is a good segue to the coaching launch designed by Edson Schock and described in Weston Farmer's book 'From My Old Boat Shop'. http://www.wolfeboats.com/design.php
    Farmer describes the basic features of this type of design that lead to good speed, low power and little wake.

    http://www.wolfeboats.com/downloads/...201.2%20mb.wmv
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  3. #73
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    Default Re: A neat fuel efficient launch

    I thought that the launches used at the London Olympics were pretty good. Sufficient speed, minimal wake, and very stable. They looked similar to this:

    Hope for the best, but plan for the worst.

  4. #74
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    Default Re: A neat fuel efficient launch

    Quote Originally Posted by Tom Lathrop View Post
    Also looks like she is easy to roll. Good thing she is not so tall.
    Jan has a remarkable low COG that helps her stability. Her length and overall design allows for all equipment like engine, fueltanks, fresh- and brownwatertanks, batteries etc. to be neatly placed under the floorboards amidships along the centerline. The fact that she has been built so light does make her sit a bit higher on the water; I bet if she would weigh the 1 ton heavier she would indeed respond different. She is equipped with a central placed 800L freshwatertank laminated into the structure of the hull right over and along the keel line. Having this absolutely helps her respond better to cross seas. Here’s a picture of Jan showing how her aft section sits in the water:

    B5B64976-E2FF-4BDC-ADB3-FC181E0C17DD.jpg

    Of the 14.5m design sofar only 2 have been built, both in The Netherlands; Jan and Stranger. I don’t have exact numbers but Stranger seems a bit heavier and is equipped with a bigger engine. Here is a clip of Stranger in cross seas:

    https://youtu.be/56bcFjYyNNY

    best regards,

    Hendrik
    Last edited by Haje74; 05-10-2018 at 02:26 AM.

  5. #75
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    Default Re: A neat fuel efficient launch

    I am surprised no one has mentioned the Panga. The Mexican ones where more beamy than the Central American built 25-28 footers with narrow beams of around 56. They used to run 25HP which where tax exempt and travel up to 100 miles offshore cruising speed was around 20 knots.

  6. #76
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    Default Re: A neat fuel efficient launch

    How about this for efficiency; one might think the Loxo 32 is too modern, ugly even but the numbers are promissing:

    https://www.powerboat-world.com/news...-cruising-boat

  7. #77
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    Default Re: A neat fuel efficient launch

    I am more interested in fuel consumption per hour. The two lung Deutz on Granuaile (LFH Marco Polo - 55' LOA x 10' B x 20 T disp) could push her along in flat water (sailboat, so windage a major factor if powering into the wind) at just shy of eight knots. At that pace she sipped 0.75 l/hr. If you pretend you're driving a car (or if you're marketing to auto drivers rather than sailors) then one could claim ten and two thirds miles per liter while giving the comfort of plenty of living capacity, albeit at a reduced speed.

    Light is always nice if the goal is speed and/or range for a given length. It's just that that's not quite my idea of how to measure a cruising yacht that should meed all weather carrying what her crew needs for basic comfort and sustinance.

  8. #78
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    Default Re: A neat fuel efficient launch

    Everything in boat design is a compromise. Want high efficiency? There is a price to pay for that. Want opulent accommodations? There is a price to pay for that. Want exceptional seakeeping ability? There's a price... Well, you get the idea. The point is, you - the boat owner - must clearly and level-headedly evaluate what is most important to you in a boat, and more importantly, what you are willing to give up to have that important feature or features, or else you will end up with a boat that doesn't satisfy your expectations of it.
    Hope for the best, but plan for the worst.

  9. #79
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    Default Re: A neat fuel efficient launch

    Quote Originally Posted by mmd View Post
    Tom, I agree that Jan looks like she has a low righting moment at low angles of heel, but that is common with pretty much all high L/B hulls. I expect that she would gain righting moment quite quickly once past five or eight degrees of heel, and when in semi-planning mode she would settle back on her haunches and gain both form and dynamic stability, so would be quite comfortable at speed. But, that is just my opinion based on looking at a single picture on an internet forum...
    Just so Michael and maybe I should have gone further with my statement. There is no magic to a boat like this and Weston Farmer's Coyote is probably the best design for the type. Regardless of having the CG low, its still a powerboat without a keel and there is just so much a designer can do as form stability is generally more a determinant of roll (initial stability) than CG. In Farmer's writing about Coyote, he says that it is best for the crew to have their hair parted in the middle to keep her on an even keel.

    At higher speed most boats will become more stable, up to a point where they can get cranky or dangerous. Deep V hulls are perhaps the best example of this behavior, tippy at the dock and much better when they get going. Greta, Jan or Loxo 32 and others of this type are not exceptions to the physical limitations although they do exploit the physics for a given goal.
    Tom L

  10. #80
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    Default Re: A neat fuel efficient launch

    Fuel efficient is a matter of word semantics. Unless you are comparing apples to apples in boats, weight, length, and layout, all this talk is just words. For example, if you compare that open launch to the cabin boat, you cannot come up with the like comparison. At the end of the day, [tired line for sure] to me its all about fuel burn per mile.

  11. #81
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    Default Re: A neat fuel efficient launch

    Tom. I wrote that bit that you quoted before I saw Hendrik's second photo showing a stern view of Jan. From that angle, her hull looks a great deal like the smaller Cape Island hulls of ten or twenty years ago, albeit with a bit finer entry. I don't think that stability would be an issue at all in the kinds of conditions that a pleasure boater would care to be out in. If she is significantly light to achieve propulsive efficiency, though, she might be prone to being blown about a bit in a cross-wind.
    Hope for the best, but plan for the worst.

  12. #82
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    Default Re: A neat fuel efficient launch

    For all reasons above, plus the difficulty of manouvering in close quarters the owner of Jan decided after the first season to install a small daggerboard just shy of amidships, halfway down the length of the hull. Fully extended it adds less than 1 square Yrd of lateral surface under the hull. This addition proved to give more stability against roll in strong cross seas and winds, and makes her turn on a dime when manouvering.
    Last edited by Haje74; 05-10-2018 at 02:26 PM.

  13. #83
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    Default Re: A neat fuel efficient launch

    Hendrik, some years ago I designed a high L/B aluminum motoryacht for a client that performed at or above expectations, but when at speed with the forefoot carried clear of the water surface tended to have the bow blown off-course in a crosswind. An additional 150mm x 3m flat bar on edge on the keel at 40% of LWL cured the problem. We considered a shorter and deeper appendage, but as it was to be fixed instead of retractable we felt that it would cause problems with haul-outs and groundings, so we opted for the long, shallow form.
    Hope for the best, but plan for the worst.

  14. #84
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    Default Re: A neat fuel efficient launch

    Quote Originally Posted by mmd View Post
    Hendrik, some years ago I designed a high L/B aluminum motoryacht for a client that performed at or above expectations, but when at speed with the forefoot carried clear of the water surface tended to have the bow blown off-course in a crosswind. An additional 150mm x 3m flat bar on edge on the keel at 40% of LWL cured the problem. We considered a shorter and deeper appendage, but as it was to be fixed instead of retractable we felt that it would cause problems with haul-outs and groundings, so we opted for the long, shallow form.
    I fully understand. If it is to be a fixed to the hull you want it to be as shallow as possible. The owner of Jan wanted retractable and as little drag as possible. In case of grounding the large lower part of the daggerboard is a functional crashbox, being constructed very light. We molded the part to be able to make an exact replica should it have to be replaced.

    Best regards,

    Hendrik

  15. #85
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    Default Re: A neat fuel efficient launch

    Quote Originally Posted by Ian McColgin View Post
    I am more interested in fuel consumption per hour. The two lung Deutz on Granuaile (LFH Marco Polo - 55' LOA x 10' B x 20 T disp) could push her along in flat water (sailboat, so windage a major factor if powering into the wind) at just shy of eight knots. At that pace she sipped 0.75 l/hr. If you pretend you're driving a car (or if you're marketing to auto drivers rather than sailors) then one could claim ten and two thirds miles per liter while giving the comfort of plenty of living capacity, albeit at a reduced speed.

    Light is always nice if the goal is speed and/or range for a given length. It's just that that's not quite my idea of how to measure a cruising yacht that should meed all weather carrying what her crew needs for basic comfort and sustinance.
    That sounds too good to be true.
    8kt, 55'. 10T, 0.75l/hr (0.198gal/hr)???
    You pushed a 10T 55' boat at 8kt with only 3.5hp? That's 40 Mpg (46 mi/gal) (5 liters/100km) (10.5M/l).

    http://www.boatingmag.com/calculating-fuel-consumption
    Efficient diesel should run 0.4 lb/hp-hr. Diesel weighs 7.2lb/gal
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  16. #86
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    Default Re: A neat fuel efficient launch

    Quote Originally Posted by MN Dave View Post
    That sounds too good to be true.
    8kt, 55'. 10T, 0.75l/hr (0.198gal/hr)???
    You pushed a 10T 55' boat at 8kt with only 3.5hp? That's 40 Mpg (46 mi/gal) (5 liters/100km) (10.5M/l).

    http://www.boatingmag.com/calculating-fuel-consumption
    Efficient diesel should run 0.4 lb/hp-hr. Diesel weighs 7.2lb/gal
    I smell a typo or brain fart.
    Tom L

  17. #87
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    Default Re: A neat fuel efficient launch

    I did hear of a 21ft boat with a 16hp Yanmar doing over 40mpg, as a displacement boat only at around 5 knots.

  18. #88
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    Default Re: A neat fuel efficient launch

    It's certainly the case that when an engine is verly lightly stressed, it's not using all of it's horsepower. But can this be real?

    I may be doing the math wrong but taking the average four stroke as requiring about 1/2 pound of fuel per hour per horsepower, diesel weighing in at about 7.2#/g, and getting 40 mpg at 5 knots, that's like the engine only actually utilizing 1/4 hp.

    I didn't know that a Yanmar 16 hp could even idle using that little.

  19. #89
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    Default Re: A neat fuel efficient launch

    Quote Originally Posted by Ian McColgin View Post
    It's certainly the case that when an engine is verly lightly stressed, it's not using all of it's horsepower. But can this be real?

    I may be doing the math wrong but taking the average four stroke as requiring about 1/2 pound of fuel per hour per horsepower, diesel weighing in at about 7.2#/g, and getting 40 mpg at 5 knots, that's like the engine only actually utilizing 1/4 hp.

    I didn't know that a Yanmar 16 hp could even idle using that little.
    I will try and track down the details, i think it was on Boatdesign.net. It was real world figures, not estimated.

  20. #90
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    Default Re: A neat fuel efficient launch

    I did calculate wrongly, doing it in my head. It's more like 1.8 hp used. That's not much but I can see it. I already gave Granna's ability to move along sipping a fifth an hour. I used to joke that I could sip that much scotch in an hour but, unlike the Deutz, after that hour I was done.

  21. #91
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    Default Re: A neat fuel efficient launch

    Post 111 on this thread, Tad quoted "Another small one is Pazapa, 20' by 8', designed, built, and sailed by Dave Jackman. He stated his needs were covered by a 6' cockpit, 6' saloon, and 6' bunk with 2' of overhang = 20'. He also stated that "a two ton diesel cruiser could comfortably make 120 miles per day on about 12 litres of fuel. A 20' sailboat has to work very hard to make 120 miles per day. " I'll attach four pages of an 8 page article.

    At the time of publication, he had about 135 hours underway in Pazapa, averaging 5 knots at 1500-1700 RPM. Top speed was stated as 7.1 knots. Average fuel consumption, including runs of 20+ miles into the wind, was .7 litres per hour. He obtained 45 mpg (imperial) at 5 knots by opening the rocker clearance somewhat."

    https://www.boatdesign.net/threads/p...r.34792/page-8

  22. #92
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    Default Re: A neat fuel efficient launch

    Quote Originally Posted by skaraborgcraft View Post
    Post 111 on this thread, Tad quoted "Another small one is Pazapa, 20' by 8', designed, built, and sailed by Dave Jackman. He stated his needs were covered by a 6' cockpit, 6' saloon, and 6' bunk with 2' of overhang = 20'. He also stated that "a two ton diesel cruiser could comfortably make 120 miles per day on about 12 litres of fuel. A 20' sailboat has to work very hard to make 120 miles per day. " I'll attach four pages of an 8 page article.

    At the time of publication, he had about 135 hours underway in Pazapa, averaging 5 knots at 1500-1700 RPM. Top speed was stated as 7.1 knots. Average fuel consumption, including runs of 20+ miles into the wind, was .7 litres per hour. He obtained 45 mpg (imperial) at 5 knots by opening the rocker clearance somewhat."

    https://www.boatdesign.net/threads/p...r.34792/page-8
    People are stuck on being restricted to going slow for maximum efficiency , for whatever that means to people, with the idea that you can only achieve this with a small engine. Well that's not always the case. There are hard chine boats that's designed to runs on plane that's quite effective in doing double duty. This is done with a 115 hp. Currently my hull when converted to a trawler style performance achieves around 1 gph and cruises between 7.3 to 7.5 mph and can transform itself into a high performance hull doing four times that at a similar efficiency, 27.3 at 5,000 rpm. burning just over 5 mph. This is also done in comfort with full amenities, frig included.

    .IMG_1982.jpg
    IMG_1984.jpg
    Last edited by erster; 05-12-2018 at 07:21 AM.

  23. #93
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    Default Re: A neat fuel efficient launch

    ^ That depends on how far you want/need to go. That Ozzy bloke had a range of 1800+ miles in a 20ft boat. Lightweight planing boats can be very practical and affordable for near shore use for most people.

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    Default Re: A neat fuel efficient launch

    Quote Originally Posted by skaraborgcraft View Post
    ^ That depends on how far you want/need to go. That Ozzy bloke had a range of 1800+ miles in a 20ft boat. Lightweight planing boats can be very practical and affordable for near shore use for most people.
    Well if you want efficiency coupled with long range passagemaker, use sails you know. But doing 1800 miles in a 20 foot boat is not really something that's high on the interest list in open water. But we are talking about efficiency. As I eluded to earlier, define efficiency, which varies across a wide range of desires and needs as it relates to boats.

    My last cabin cruiser, a similar style hull in 24 feet used a 40 hp four stroke outboard and I carried 2 six gallon tanks. At around 2,000 rpm I did 8 mph and burned less than 1/2 gph. I still had the ability to run just under 20 while burning just over 1.4 gph. But even with the 115 hp, I can carry 140 gallons of fuel without loosing storage. You surely don't need a displacement type hull, which restricts you to a maximum speed for sure when your desires are not to push the limits on smaller hulls, just because you know. Yes "depends" has a wide range of meanings, depending on who is doing the defining.

  25. #95
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    Default Re: A neat fuel efficient launch

    Absolutely, its different for everyone.Efficiency can be measured in time saving or perhaps mpg. Your boat at 8mph is only doing 16mpg, thats a lot worse figure than 40+mpg at 5 knots.......unless that extra speed/time is important to the user.
    I been becalmed for 3 days in the Atlantic in a sailboat, if i had an engine that could keep me moving with economy of 40mpg, i would use it without hesitation. There is also affordable efficiency, when some people here are pleased to get 20mpg from a car, most Europeans are shocked that your fuel burn is excessive, but you pay little for it, in comparison. I usually consider efficient as being able to get "more" from the same fuel load, but in my case, more would equal distance than speed, but as they say "your mileage may vary".....

  26. #96
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    Default Re: A neat fuel efficient launch

    Your boat at 8mph is only doing 16mpg
    That makes no sense. The visual speaks for itself. I am making 7.3 to 7.4 mph. while burning 1.1 or so at 8 mph. give or take. Go back and address what boat you are referring to, too. The link, IIRC said that the boat in question was burning 7 liters or so an hour at around 7 mph with the small hp. That's actually a bit more than I am doing with a larger engine.

  27. #97
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    Default Re: A neat fuel efficient launch

    Quote Originally Posted by erster View Post
    That makes no sense. The visual speaks for itself. I am making 7.3 to 7.4 mph. while burning 1.1 or so at 8 mph. give or take. Go back and address what boat you are referring to, too. The link, IIRC said that the boat in question was burning 7 liters or so an hour at around 7 mph with the small hp. That's actually a bit more than I am doing with a larger engine.
    I was not using your visual, i wrote what you had written in your post, which you have since edited. The top speed of the boat in the link was 7.1kt, with no fuel use given at that speed, but 41mpg @ 5kt and 59mpg @ 4 kt. A 4kt average is good for a 25ft sailboat, but put a headwind into the equation for a week and even 4kt direct upwind with that economy is a no brainer. I know someone who spent almost a month stuck in the Azores high, when a boat like the one in the link could run from Lisbon to Ponta Delgada in just over 9 days and use just over 15 gallons of diesel, thats better than a month at sea in a sail only boat.

  28. #98
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    Default Re: A neat fuel efficient launch

    Quote Originally Posted by skaraborgcraft View Post
    I was not using your visual, i wrote what you had written in your post, which you have since edited. The top speed of the boat in the link was 7.1kt, with no fuel use given at that speed, but 41mpg @ 5kt and 59mpg @ 4 kt. A 4kt average is good for a 25ft sailboat, but put a headwind into the equation for a week and even 4kt direct upwind with that economy is a no brainer. I know someone who spent almost a month stuck in the Azores high, when a boat like the one in the link could run from Lisbon to Ponta Delgada in just over 9 days and use just over 15 gallons of diesel, thats better than a month at sea in a sail only boat.
    I edited my post? The only edit that I did was 6 minutes after the post, 92. That post was about three hours before your post 95. My point stands, with a much larger hp engine and what is known as an efficient hull to most well known gas hogs, and the option to use it more than just a wallowing slug that will barely get out of its way will still be considered an efficient hull. My original point also stands. There is no real concrete meaning for a fuel efficient hull. And since when did a power boat not use any fuel while covering ground on the water? ;<}

  29. #99
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    Default Re: A neat fuel efficient launch

    And at 8 mph. and 16 mpg, that's 1/2 gph of running in any ones book.
    This is what I wrote, with no edit.

    At around 2,000 rpm I did 8 mph and burned less than 1/2 gph.

  30. #100
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    Default Re: A neat fuel efficient launch

    Your link specifically states as follows, 7 liters per hour. This converts to 1.84920437 U.S. gallons. I would not call that something extra special by comparison to either of my planning hulls. when I slow down comparing apples to apples as it relates to efficiency. And that's not even dealing with a putt putt engine. Now was that 7 liters or point 7 liters per hour? If so then that's a decent performance for sure. But we are still talking about barely getting out of their own way. And you want to talk about being stuck on a sailboat? in the wrong conditions, you are stuck with such little speed and safety can be a problem in open water. Thanks,


    At the time of publication, he had about 135 hours underway in Pazapa, averaging 5 knots at 1500-1700 RPM. Top speed was stated as 7.1 knots. Average fuel consumption, including runs of 20+ miles into the wind, was .7 litres per hour. He obtained 45 mpg (imperial) at 5 knots by opening the rocker clearance somewhat.
    Last edited by erster; 05-12-2018 at 03:08 PM.

  31. #101
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    Default Re: A neat fuel efficient launch

    Quote Originally Posted by erster View Post
    People are stuck on being restricted to going slow for maximum efficiency , for whatever that means to people, with the idea that you can only achieve this with a small engine. Well that's not always the case. There are hard chine boats that's designed to runs on plane that's quite effective in doing double duty.
    A nice example of an "efficient on-plane-runner" is B&B's Eco 18 Marissa.
    With a 25 hp outboard she burns 2.2 gal/hr at 21 knots.
    That's almost 11 mpg. At 15 knots she'll do 15 mpg.

    She's a small center console, without much comfort, but the economics are interesting to me:

    https://bandbyachtdesigns.com/marissa/

  32. #102
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    Default Re: A neat fuel efficient launch

    Quote Originally Posted by Ian McColgin View Post
    I did calculate wrongly, doing it in my head. It's more like 1.8 hp used. That's not much but I can see it. I already gave Granna's ability to move along sipping a fifth an hour. I used to joke that I could sip that much scotch in an hour but, unlike the Deutz, after that hour I was done.
    Quote Originally Posted by Ian McColgin View Post
    It's certainly the case that when an engine is verly lightly stressed, it's not using all of it's horsepower. But can this be real?

    I may be doing the math wrong but taking the average four stroke as requiring about 1/2 pound of fuel per hour per horsepower, diesel weighing in at about 7.2#/g, and getting 40 mpg at 5 knots, that's like the engine only actually utilizing 1/4 hp.

    I didn't know that a Yanmar 16 hp could even idle using that little.
    I said that 46mpg sounded too good to be true, but I didn't say it was wrong. I was hoping for a little more detail to back up the claim. I do know that had you sipped a fifth of scotch at the same time the boat sipped a fifth of diesel that any figures regarding the boat's performance would be suspect, and probably more entertaining.

    In the Power/fuel chapter in Farmer's book https://www.woodenboatstore.com/prod...oatshop/design, The 25 foot Edson Schock design did achieve that level of performance. For a Marco Polo to do the same with so much more wetted surface, albeit with a 50% higher hull speed (sqrt55/sqrt25=1.48) seems unlikely to me. I lack the expertise to pontificate further on skin friction than to say more surface causes more drag, so what I think and reality may be rather different. For the larger boat to get the same mpg as the smaller boat, skin friction must be a smaller part of the equation than I thought.

    The math as I see it is 0.75 l/hr x 0.264gal/l = 0.198 gal/hr. 0.198 gal/hr x 7.2 lb/gal (diesel) = 1.43 lb/hr. (1.43 lb/hr)/(0.5 lb/hp hr)= 2.85 hp. I used 0.4 lb/hp hr for diesel and got 3.57 hp before.
    EDIT:
    lb/gal kg/gal kg/l lb/hp hr gal/hp hr l/hp hr l/kw hr
    water 8.3 3.8 1.0 -- -- -- --
    diesel 7.2 3.3 0.9 0.4 0.056 0.21 0.28
    gasoline 6.1 2.8 0.7 0.5 0.082 0.31 0.42
    Last edited by MN Dave; 05-15-2018 at 12:23 PM.
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