Need fast, EFFICIENT, commuter boat

Discussion in 'Boat Design' started by MattM, Aug 26, 2004.

  1. MattM
    Joined: Aug 2004
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    MattM Junior Member

    I have reached a major goal in my life, I live on the water, 18 miles up the Willamette river from my job, which is on the water. I never have to get in a car again.

    I now commute to work on my Donzi 22, which takes about 10 gallons of fuel each day, or my waverunner, which takes about 5 gallons. The boat is great, but takes too much fuel, the wave runner is fine, but is cold in cold weather and I have to go too slow if there is any chop.

    Here's what I'd like; a 35 to 40 mph commuter boat that gets at least 10 mpg. I was thinking of some type of aluminum semi v boat, about 12 to 14 feet long, like a lightweight open fishing boat, then I'd put a deck and cannopy on it, sit right in the back. Add a 40-50 HP 4 stroke outboard. I know that they get almost 10 mpg on a little bigger boat at slower speed. This would be almost like an enclosed jet ski with a prop in the water that would tolerate skipping over waves better than a jet drive, and should be more efficient. Kinda like a miniature bass boat.

    Anybody know of a hull that I could use. Any other ideas? It's easy to go this fast, but not sure how to do it this efficiently. I've thought about tunnel boats, but they don't generate much lift until they are going much faster, also WIG boats.

    thanks for any ideas.
     
  2. Corpus Skipper
    Joined: Oct 2003
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    Corpus Skipper Hopeless Boataholic

    Small aluminum boat is probably the best way to go. You'll want the lightest hull you can lay your hands on. 10 mpg is a pretty lofty goal, but you may come close with the 4 stroke, but at 40 mph I doubt it. Don't know that I'd want to go 40 in a small aluminum boat. If you slow it down to maybe 25 you can probably achieve 10 mpg. Keep your top/enclosure short and narrow to reduce windage. I'd kill to have a 45 minute boat ride to work! Good luck.
     
  3. tspeer
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    tspeer Senior Member

    Here's an approach you may not have thought about: a rowing coaching catamaran. You can't beat slender displacment hulls for fuel efficiency. All you'd have to do is add a soft-top enclosure for bad weather, and you'd have a very comfortable, fast, efficient convertible for communting. The slender hulls will provide a far more comfortable ride in waves than anything that's planing.

    [​IMG]

    See:
    http://www.pocock.com/launches.htm
    http://plattdesign.net/_wsn/page2.html
    http://www.race1.com.au/lev2_cats.htm
    http://www.empacher.com/katamarane/t-60_ee.html

    Since you are interested in high speed, you might want to inquire about having one of these built with extra-long hulls.

    Or add a pilot house with very rounded corners to cut wind resistance. If the corner radius is greater than 10% of the width of the house, you can cut the aerodynamic drag by more than half. There's a reason why Airstream trailers look the way they do!
     
  4. Ilan Voyager
    Joined: May 2004
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    Ilan Voyager Senior Member

    Funny question...

    But very worth to think over it...

    I agree with Tom about long thin hulls for getting economy.
    Look at this link http://www.multihulldesigns.com/stock/28cat.html

    That may give you ideas. A part just the consumption you have to think about how long will last the engine(s).

    At high RPM outboards (and most of the engines) do not last long: 1000 hours a Yamaha 100 HP 2 stroke (data well stablished in commercial use on river) and 1200-1400 the 100 HP four stroke before rebuilding. The rebuilding gives a second life of about 600 hours for the 2 strokes and 800 hours for the four stroke. After the best thing to do is selling the outboard to your worst enemy.

    The better specific consumption is generally obtained at the max torque. So you need a boat giving you the speed without revving too high. The top speed must be of about 35-40 knots (you were good) to get a cruising speed of 26 knots.

    Lets assume you want to make the 18 milles in 40 minutes consuming 10 miles/gallon so 1.8 gallon or 6.816 liters of gas. It means 10.22 liters/hours.

    How many horses can you feed during an hour with 10.22 liters, that's the question. A good 4ST consumes 230 gr/hour per horse or 0.307 liter/hour. That gives you 10.22/0.307 = 33.29 horses... it's a too small cavalry.

    It's simply impossible, a part a very tiny hydroplane (a wet and dangerous but very funny thing) nothing in this sad world will be able to do that.

    Let us be realistic and let's make some crude calculations. To accomplish easily the goal of top speed with a small cat of 28 feet of about 850 kg full loaded (1875 pounds) you'll need 2 outboard 4ST of 50 HP each so 100 HP at total. A modest power, in fact the true speed will be a bit above 40 knots.

    To maintain a cruising speed of about 30 knots (and to get an average of 26 knots = 40 mn for 18 miles) you'll need to feed a cavalry of about 70 horses, consuming 21.5 liters/hour. The consumption will be of 14.35 liters each way of 18 miles or in imperial 3.791 gallons. That gives 4.75 milles per gallon.

    Kept at 70-75 % of the max power a 4ST will last a good time. The lone problem that is the skipper has to resist to the wish to push the throttle gas.

    This calculation is horribly crude and can be surely optimised. My nose is smelling that 5.5 to 6 milles per gallon is feasible while using a true boat which won't flip over a wave of 6 inches, or pushed by a gust of wind of 15 miles. Think also to your vertebrae, being pounded each day by a monohull planing boat...

    Air cushion cats are pretty dangerous, and have a tropism for flying. The problem they have not wings, nor tail...

    Better ciphers should be gotten with a akroplan or WIG but it's a lot of expensive engineering, prototypes and so on. Besides it seems that US authorities doesn't want to recognize them as boats.
     
  5. tspeer
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    tspeer Senior Member

    Good suggestion, and Kurt Hughes is an excellent designer.

    Given that MattM now uses either a Donzi 22 or a Waverunner, I think something a little smaller than Hughes' Powercat 28 is in order. It'll definitely do the job, but might be more boat than Matt had in mind:
    [​IMG]

    Hughes' 21' power cat is like the coach boats I posted previously:
    [​IMG]

    I could envisage the 21' with hulls stretched to maybe 25' for a little more speed, while keeping the same cross section. The center pod wouldn't need to be much bigger, but should be enclosed. Even though it would mean less maneuverability, it might be worth considering a single engine installation in the center - it's got to be more fuel efficient to operate one engine at higher power than two engines at low power. Although there's something to be said for the availability of two engines to make sure you do get to your destination.

    As always, a custom built boat is the most expensive option. If you can find a used coaching catamaran, that would be the best value for the money.
     
  6. tspeer
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    tspeer Senior Member

    FYI, my F-24 trimaran gets 10 nmi/US gallon. But that's with a 5.5 hp motor at 6 kt. Definitely not a commuter!

    The question is, what is the tradeoff you want to make between economy and speed? 18 mi @ 35 mph is a transit time of 31 minutes. If you drop down to 24 mph, you only add 15 minutes each way, but the difference in fuel economy would be significant - possibly by a factor of 2 - 3.

    So which is more important, 35 mph, or 10 mpg?
     
  7. Ilan Voyager
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    Ilan Voyager Senior Member

    You are perfectly right: in the states the gas is dirt cheap (that won't last), as european I prefer the economy of fuel.

    On cats a center engine may become a worry because it does not work in clean water, but in the middle of the waves generated by the hulls. I know well the 2 Yamahas and the 50 HP is simpler to maintain and as efficient as the 100 HP. ON a cat I would opt for the 2 engines.

    Another solution is a trimaran of 26-28 feet, one engine like the duratec 2.3L of 145 HP of the Ford Ranger. I'm making reliability trials with this very promising engine, only 150 kg complete with marine gearbox and closed cooling. Specific consumption is excellent. This engine is very well designed.
    With a surface propeller of 17 or 18" four blades...hummmm.
     
  8. Gilbert
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    Gilbert Senior Member

    Hi Matt,
    Wow, you sure got some responses quickly on this one.
    When I saw your post the first thing I thought of is the Seattle to Ketchikan races that were held back in the 1960's. The boats that rather quickly became the favorites of the competitors were outboard catamarans of the day and about 18 feet long with a couple (typically) 100 horse Mercs. These were 60 to 70 knot boats. I think one or two years when the weather was good the winners averaged about 60 miles per hour. I saw a couple boats going across the Straits of Georgia in 1960. I was impressed. This would be a low tech approach, but I think you could use a little smaller boat with somewhat narrower hulls because you would not need so much fuel capacity. Don't know what sort of fuel efficiency you might achieve but these modern motors are pretty good.
    Cheers,
    Gilbert
     
  9. MattM
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    MattM Junior Member

    Thanks for all the ideas. I am an engineer, although not a naval architect, and I love challenges. So this will be a good one.

    My wave runner gets about 8 mpg at 35 mph, it is a 2 stroke 650cc, and makes about 40 hp. The part that is not ideal is it is noisy, and when the water gets a little choppy I have to slow down because the jet comes out of the water. Also it's kind of chilly on cold days, but I'm going to rig up a fairing for that.

    But that is my data point and I'm thinking; if I go to a 4 stroke instead of 2 stroke, and a prop instead of jet, I should be able to pick up a good bit of efficiency. The four stroke will also be quieter. And an outboard will have the prop in the water longer so I could skip across the top of the waves better. All I would need is a short, light hull for it. I thought I could reinforce a 12' aluminum open fishing boat for 40 hp and put a canopy on it. Trouble is, all these boats I have found have flat bottoms, and I'm sure I would need a bit of a V to avoid beating myself and the boat to death at 35 plus.

    I found on the internet the other night the existence of a hydrofoil kit for a 1960s vintage grumman 14' boat. Anybody know anything about hydrofoils?
     
  10. MattM
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    MattM Junior Member

    Oh, also. I have to have 35 mph. Much slower and it gets too boring. I don't think any of these displacement hulls will go that fast?
     
  11. Willallison
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    Willallison Senior Member

    Matt, I think you're asking for a conflicting set of requirements. As the old saying goes - you can go fast or you can go far, but you can't go far fast. I know your journey isn't long, but the 'rule' stands true - if you want to travel at 35 mph, you will have to accept that there is an economy penalty to be paid. Which isn't to say that you can't travel at 35mph relatively efficiently, but to be able to do so in rough water in any degree of comfort you will need a longer and probably heavier boat.
    Why not take the Donzi when it's rough and the waverunner when it's calm?
    Cheapest of all of course - you could take the car! :eek:
     
  12. Greg Beers
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    Greg Beers Junior Member

    matt, i'd recommend a hydrofoil assisted cat. we are currently working on larger versions, but they will give you the speed and fuel savings you want. check out this site for examples. i can't vouch for the construction, but the theory is sound.

    http://www.hydrospeed.co.za/index2.html
     
  13. duluthboats
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    duluthboats Senior Dreamer

  14. Thunderhead19
    Joined: Sep 2003
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    Thunderhead19 Senior Member

    I just read all the posts, and mat buddy, I hate you.
    Just kidding. In all seriousness. Get a "Bathtub". http://www.bathtub.island.net/facts_buy.php
    It's your best bet. They're fast, light, and can handle some major water. What you power it with will determine your fuel consumption.

    I may just form a bit of a professional interest in bathtub racing. we'll see.
     

  15. YankeeBoater
    Joined: Oct 2005
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    YankeeBoater Junior Member

    This might do it

    Quintrex 140 Wide Body Dory - 14 ' long, nice sharp vee at bow to cut waves, carried aft to transom to track well and handle following waves, high freeboard all around and a convex deck at bow complete the dry mini-package. Can be had with a side or center console or tiller steered. You'll stay dry and save gas.

    MEASUREMENTS
    Length Overall: 14'0
    Beam: 6'2
    Depth 3'6

    MATERIAL THICKNESS
    Bottomsides: 0' 079
    Topsides: 0' 063
    Transom Shaft Length: L/S
    Weight (Boat only): 375 lbs

    HORSEPOWER RATINGS
    Recommended: 25HP
    Maximum: 40HP
    Max Transom Weight: 243 lbs

    [​IMG]

    [​IMG]


    They also make a spartan little 14' runabout based on the Dory called the 140 Estuary Angler that might be of interest. It's basically the 140 Wide Body Dory with a windshield on the deck, a panel to hold controls and wheel, and two seats mounted on the forward bench. Cheap and fuel efficient as well! :cool:
    MEASUREMENTS
    Length Overall: 14' 1
    Beam: 6' 2
    Depth 3' 6

    MATERIAL THICKNESS
    Bottomsides: 0' 078
    Topsides: 0' 063
    Transom Shaft Length: L/S
    Weight (Boat only): 496 lbs

    HORSEPOWER RATINGS
    Recommended: 30hp
    Maximum: 40hp
    Max Transom Weight: 209 lbs

    [​IMG]
     
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